Mods for trail riding

[0101]

What are the best mods for trail riding? I ride anything from fire roads to rocky and rutted trails.

My set up:
02 400ex
FMF Powercore 4 slip-on
K&N air filter w/air box lid on (the trails i ride have many water crossings too).
Pro-taper handle bars
DG bumper

everything else is stock... including the tires lol

I was thinking:
Sparks key
new tires when these go bald (recommendations?)
CNC steering stabilizer ($150.. worth it?)
Stage 2 Hotcam
450r carb
Drop 1 tooth up front

Should I widen it? Should I get 450r Shocks?

Any other ideas? Any input whatsoever will be greatly appreciated!

[Sanddraging28]

Originally posted by 0101
What are the best mods for trail riding? I ride anything from fire roads to rocky and rutted trails.

My set up:
02 400ex
FMF Powercore 4 slip-on
K&N air filter w/air box lid on (the trails i ride have many water crossings too).
Pro-taper handle bars
DG bumper

everything else is stock... including the tires lol

I was thinking:
Sparks key
new tires when these go bald (recommendations?)
CNC steering stabilizer ($150.. worth it?)
Stage 2 Hotcam
450r carb
Drop 1 tooth up front

Should I widen it? Should I get 450r Shocks?

Any other ideas? Any input whatsoever will be greatly appreciated!

i am not a big fan of the sparks key. some people love it.

i like the holeshot HD's. great tire and awesome traction

if you do a lot of high speed riding then the steering stabilizer is a great idea and well worth it

450r carb and a stage 2 cam will wake that bike way up. its a great upgrade. well worth the money and time

from the factory the 400ex suspension sucks....bad.... adding 450r shocks is a great upgrade, try ebay for a good deal

i always widen my front end for drag racing, it makes the bike stable at high speeds, but watch out in tight trails.


and there is nothing wrong with a little shot of nitrous :devil: :devil:

[BEAVER.989]

a stage 1 cam might be better suited for trails than a stage 2. for tires, i'm looking at the holeshot gncc series. you may want to look at these or razrs.

[jcs003]

suspension, handlebars and exhaust is good place to start.

[rob_990]

the list looks good but i wouldnt get a stage 2 unless you plan on doing motor work later on

[0101]

Originally posted by rob_990
the list looks good but i wouldnt get a stage 2 unless you plan on doing motor work later on Why do you say that about the cam?

What is a good cam for gains all the way around?

Also, how much does porting and polishing cost? Would I notice a difference in performance?

And from what I hear, the 450r shocks aren't the best for trail riding...Is that true? I don't really have the money to re-valve them :(

[Sanddraging28]

a stage 2 cam works a lot better with a higher compression piston, 11 to 1 is good. with a cam with larger lift and longer duration your compression will suffer a little. if at some point you are going to a higher compression piston then a stage 2 will be great. if not i would get a stage 1

as far as porting and polishing goes, its a good upgrade. your bike will perform better, the downside is the price. i have never seen a good P+P job for under $400. its one of those you get what you pay for kinda things.

[0101]

I think i edited my post while you were writing your reply.

What is your input on the 450r shocks for trail riding?

[Sanddraging28]

anything is better than the stock 400ex shocks. my brother has them on his 400ex and trail rides the piss out of it. he loves them. if ride a bike with elka's on it and then get on one with 450r shocks, you will see a big difference. but to upgrade to the 450r's i think you will be real happy

[0101]

And then how much would it cost to get the front 450r shocks revalved and resprung?

[Sanddraging28]

i have never had a set of 450r's re valved. it cant be that bad i have my elka's re valved for for $200 including shipping. so it should be cheaper than that

[0101]

What about revalved 450r shocks vs tripple rate elkas w/o reservoirs? ($485)

Heres the link to the elkas:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&_trksid=p3907.m29&_trkparms=algo%3DLVI%26its%3DI%26otn%3D2&item=270367449166&category=43974&viewitem=#ht_1662wt_953

It says that they are made to the riders specs (weight, riding style, type of a-arms ect.)

[Sanddraging28]

seems like a pretty good deal. with the price of 450r shocks and have them revalved and resprung you might be close to this....
plus elka's are a much better shock

[rob_990]

Originally posted by 0101
Why do you say that about the cam?

What is a good cam for gains all the way around?

Also, how much does porting and polishing cost? Would I notice a difference in performance?

And from what I hear, the 450r shocks aren't the best for trail riding...Is that true? I don't really have the money to re-valve them :(

when you put in a cam it actually losses compression which is why most people run a high comp piston when they put in a cam.get a stage one if your keeping the rest stock.there good for low end power and will work better with a stock engine

[jcs003]

Originally posted by rob_990
when you put in a cam it actually losses compression which is why most people run a high comp piston when they put in a cam.get a stage one if your keeping the rest stock.there good for low end power and will work better with a stock engine

a cam has nothing to do with compression. a cam changes valve timing.

[Sanddraging28]

jcs003,(and anybody that doesn't know)
The more duration the intake valves have the more important it is to have a high(er) compression piston. This is because with lots of duration there is more opportunity for air to escape through the valves as the piston begins its compression stroke. Even on the stock cam, the intake valves are still open when the piston begins its compression stroke. With an aggressive cam some dynamic compression is lost through valves that stay open for a long time. This must be made up for with a higher compression piston. An aggressive cam with a stock compression piston may actually perform worse than the stock cam because too much compression is being lost through the valves being opened so much. I have personally seen this happen--dyno confirmed (although it wasn't a 400EX).

Here's a theoretical example to help in understanding this concept:

-bore: 85mm (stock)
-static compression ratio: 9.1:1 (stock)
-elevation: 1500ft
-intake valve closes: 40deg ABDC (After Bottom Dead Center) (stock at 1mm lift)

The resulting dynamic compression ratio is 8:1. Note that is a smaller figure than the static compression ratio we started with. Again, this is because the actual compression of the compression stroke doesn't really start until the intake valves close.

Now, if we increase the intake valve duration to 55deg ABDC and leave the static compression ratio at 9.1:1, we get a new dynamic compression ratio of 7.4:1! In order to get the dynamic compression ratio back to where we started (8:1) with the increased intake valve duration we would need a piston with almost 10:1 static compression. Just for the heck of it I looked at how 5500 ft of elevation changes things. At 5500ft with the 55deg ABDC spec you'd need a 10.8:1 static compression piston to yeild an 8:1 dynamic compression ratio.

Now, you might be thinking what's the point of adding a cam and a piston if doing both gets you the same dynamic compression ratio you started with?? Good question. The answer is that now you have the same dyanmic compression ratio you started with but also have the cam specs that will allow the engine to breath better. And in the real world, most piston choices are actually going to bump your dynamic compression beyond what it was stock even with the addition of a cam. A 10.5:1 piston with a cam (using the 55deg ABDC spec) would get you a dynamic compression ratio of 8.6:1--0.6 points higher than all stock.

I used a dynamic compression ratio calculator to get those figures. I guessed on certain required values because there's some information I don't have. So, the above numbers are not quantitatively exact. But the relationship between static compression, dynamic compression, and intake valve timing IS accurate.

not to tell you you dont know what you are talking about but building motors is my specialty!!!!

[0101]

Wow that's Some good info. Does anybody else have any input on anything? Anything else i should look for?

Personally I like the stage 1 hotcam better unless you are boring to a 416 or bigger. I feel there isnt enough bottom end grunt and I like the stage 1 better. I'm in higher RPM a lot racing which would make stage 2 a better choice but I need more bottom end for the turns. When I ride i'm usually in 3rd gear. Great gear you can still lug but it will pull good and has a good amount of speed. The problem is trying to break the tires free from low end of 3rd. 2nd gear will surely get it loose but runs out much to quick and is too slow. Thats why I want a stage 1 instead. I bought a 4 stroke because I typically dontcare for the 2 stroke powerband where most unless built are all about topend. I want a all around broad power type thing. On here seems misleading because stage 1 does infact add much more topend power too. I know I could gear down but that just mean more problems when top of 3rd is too low of a speed for jumping and 4th gear low end is not a good thing for hitting a jump and mid or upper 4th is just overshooting way to much. I like stock gearing best because I can ride 3rd for almost every situation, track or trail.

[jcs003]

Originally posted by Sanddraging28
jcs003,(and anybody that doesn't know)
The more duration the intake valves have the more important it is to have a high(er) compression piston. This is because with lots of duration there is more opportunity for air to escape through the valves as the piston begins its compression stroke. Even on the stock cam, the intake valves are still open when the piston begins its compression stroke. With an aggressive cam some dynamic compression is lost through valves that stay open for a long time. This must be made up for with a higher compression piston. An aggressive cam with a stock compression piston may actually perform worse than the stock cam because too much compression is being lost through the valves being opened so much. I have personally seen this happen--dyno confirmed (although it wasn't a 400EX).

Here's a theoretical example to help in understanding this concept:

-bore: 85mm (stock)
-static compression ratio: 9.1:1 (stock)
-elevation: 1500ft
-intake valve closes: 40deg ABDC (After Bottom Dead Center) (stock at 1mm lift)

The resulting dynamic compression ratio is 8:1. Note that is a smaller figure than the static compression ratio we started with. Again, this is because the actual compression of the compression stroke doesn't really start until the intake valves close.

Now, if we increase the intake valve duration to 55deg ABDC and leave the static compression ratio at 9.1:1, we get a new dynamic compression ratio of 7.4:1! In order to get the dynamic compression ratio back to where we started (8:1) with the increased intake valve duration we would need a piston with almost 10:1 static compression. Just for the heck of it I looked at how 5500 ft of elevation changes things. At 5500ft with the 55deg ABDC spec you'd need a 10.8:1 static compression piston to yeild an 8:1 dynamic compression ratio.

Now, you might be thinking what's the point of adding a cam and a piston if doing both gets you the same dynamic compression ratio you started with?? Good question. The answer is that now you have the same dyanmic compression ratio you started with but also have the cam specs that will allow the engine to breath better. And in the real world, most piston choices are actually going to bump your dynamic compression beyond what it was stock even with the addition of a cam. A 10.5:1 piston with a cam (using the 55deg ABDC spec) would get you a dynamic compression ratio of 8.6:1--0.6 points higher than all stock.

I used a dynamic compression ratio calculator to get those figures. I guessed on certain required values because there's some information I don't have. So, the above numbers are not quantitatively exact. But the relationship between static compression, dynamic compression, and intake valve timing IS accurate.

not to tell you you dont know what you are talking about but building motors is my specialty!!!!

that was the most pompous **** i have read in a long time. im a mechanical engineer my friend.

1. learn how compression is actually read.

2. know that those minor variations are just quasi-equiliberium.

3. if you were getting changes due to altitude it happens in your carb. you need to tune it!

4. to conclude, crankcase pressure is constantly changing and your final results is: change the valve timing. change the power delivery.

[Eviltanker]

Ok, while they are fighting listen, I run fast on trails. Here is my setup.(It's for Pa very rocky) I have full skids, Kenda Claw XCR rears(Hate them) IRAZR fronts(like them) on ITP Baja's 4:1, I'm running YFZ450 front shocks(better than stock) HMF slipon, Header welds ground, UNI airfilter in open aluminum airbox, Sparks timing key, Powemadd handguards w/the wrap, Sport nerfs.I have stock length a-arms since Pa has some real tight trails at spots. I am an old guy though, I am able to ride faster than alot of young guys because I'm in decent shape and I have more experience. Remember to be fast on trails You gotta be smooth. Power is not as fast as experience when it comes to trails.


Steering stabilizer is a good idea, Cam will do you good also. I am getting ready to drop a Sparks cam in mine.

[bigbad400]

2 pages and not a good mention of skid plates anyware. if you ride trails like i do youll want FULL skid plates, all the mods in the world wont help you if you smash a rock through your case, or break your chain, smash rear brake rotor, bend a arms...... and so on the list goes. if you ride trails you NEED skid plates. you also need better shocks, (so do i) the 450rs will be great for you, im getting some soon myself. def recomend the holeshot HDs or the gncc there both specificaly for trailing.

[0101]

Ive ruled out the 450r shocks. from what I hear, they are just too stiff for my type of riding. I could revalve them and such, but that would cost too much. So now im on the lookout for some used elkas.

[Eviltanker]

try the YFZ450 fronts. I like them, might work for you

[BEAVER.989]

Originally posted by Eviltanker
try the YFZ450 fronts. I like them, might work for you

Since this is far less common than the 450R swap, there's not a lot of readable info on the subject... Do these bolt right up, or are there any modifications that have to be made? Also, is the stock valving comfortable, or should they be revalved?

[Eviltanker]

Only thing you need to do is grind the top eyes alittle to fit. I'm 180lbs. and run stock a-arms. The shocks were not revalved but, ride like a cadillac compared to stockers. Havn't bottomed them out yet either.all around much better.

[0101]

Originally posted by BEAVER.989
Since this is far less common than the 450R swap, there's not a lot of readable info on the subject... Do these bolt right up, or are there any modifications that have to be made? Also, is the stock valving comfortable, or should they be revalved?
From what I hear, they are pretty stiff. If you do trail riding, you should have them revalved and resprung.

[0101]

What do you guys think about the Sparks Key?

[Eviltanker]

like mine so far

[sprayedgt]

Made a huge difference. No problems, extremely easy to install, and worth the $20 price tag.

[0101]

Did you guys need to buy a new gasket?

[Eviltanker]

I bought the side case and the starter cover. Didn't need them but put them on anyway.

[sprayedgt]

If you're careful you can get away with reusing the original gasket. I replaced the case gasket just to be safe. You do not need to pull the starter cover. It'll unbolt and slide the whole thing out. There is an o-ring seal that is reusable.

[crxjarred]

you could put some pool nudals in ur tires for runflat garintee lol its just like tire ballz but cheeper a lot cheeper im guna do it when i buy new tires

[0101]

^ lol i guess that could work...

[ae13291]

get a stage 1 cam for sure, my sparks key is great, it made the throttle response alot better. try the kfx450 shocks, you wont sacrifice any ground clearance, and i went 1 tooth down on my front and i got a new gold non o ring chain and it made a great improvement over stock, the stock skids arent that bad, but i have bent mine in a few times where the skid was rubbing on the rotor, but i just bent the skid back out.

[hoogiesngrinder]

I have kfx450 shocks on mine, but you need to make new shock mounts for the top. IIRC, stockers are 3/4" and the kfx's are 1 1/4". They are a much better shock though.

[0101]

Im thinking ill just pick up some used elkas.

And for the hotcam... How much of a difference should I expect to notice with a stage 1? Where will i notice the power?

[hoogiesngrinder]

Should be able to get 1-2 extra horsepower, peak power will come at a little higher rpm.

[ae13291]

Originally posted by 0101
Im thinking ill just pick up some used elkas.

And for the hotcam... How much of a difference should I expect to notice with a stage 1? Where will i notice the power?

i noticed my stage 1 right off the line to the midrange and a good amount on top, its a all around great cam,

[FarmerTed]

Originally posted by jcs003
that was the most pompous **** i have read in a long time. im a mechanical engineer my friend.

1. learn how compression is actually read.

2. know that those minor variations are just quasi-equiliberium.

3. if you were getting changes due to altitude it happens in your carb. you need to tune it!

4. to conclude, crankcase pressure is constantly changing and your final results is: change the valve timing. change the power delivery.

Not to be the n00b stepping into the middle here, but...Sanddraging28 is right. Changing the valve timing and/or duration does change the effective compression ratio. If you change the cam function without compensating then the end result won't match what you started with, in this case if you increase intake valve duration so that it closes later then you have reduced the effective compression ratio as well as the actual compression (obviously).

Don't take it from me, though. Read this if you still don't believe it to be true. It even shows you how to calculate the effective compression ratio based on all the data. Being a mechanical engineer you should know that if you change one variable in the equation then the result will be different.

http://victorylibrary.com/tech/cam-c.htm

As for altitude, that is part of the equation. Increased altitude results in lower atmospheric pressure as well as reduced air density. Tuning the carb doesn't change the air density or pressure, it leans the fuel to compensate for the reduced air. The reduced air AND fuel means reduced volume in the combustion chamber. If you make no other changes to the engine you will experience a lower dynamic compression ratio and reduced chamber pressures. In the end you're making less power because of all these factors; Less air, less fuel, and less pressure in the chamber.

[bigbad400]

what the guy said about your altitude being a factor and that it happens in your carb is a false statement, the altitude is a major factor in jetting your carb but carb is not under pressure, its under vacuum by the combustion chamber, the gas and air will not just flow into the motor it needs to be pulled in, there for if you have a change in altitude, your pull from the motor may increase or decrease, hence why we need to rejet. im not saying that the guy is wrong im saying that he was wrong about were the change happens, altitude affects the amount of air the motor needs, and the amount of gas, the carb just delivers it through vacuum pull.


now on a turbo charged motor. forget everything i said.

i am a product design engineer and i work on vacuums i know about that system and how it works, im graduating in 10 weeks, and my intership was for the company makes rainbow vacuum, the only vacuum in the world proven to suck up and kill anthrax virus. this is one of my specialties. look it up online the name of the company is rexair, its in cadillac michigan.


you are both right in a sence but even the most minor quasi-equilibrium changes will have big affect on the fuel delivery. and in turn will have an affect on the compression. if their is a demand for fuel and air to be increased then the compression will have already changed. in other words vacuum will have increased as well. hence why you need to rejet.

[SPDSNYPR]

Originally posted by jcs003
that was the most pompous **** i have read in a long time. im a mechanical engineer my friend.

1. learn how compression is actually read.

2. know that those minor variations are just quasi-equiliberium.

3. if you were getting changes due to altitude it happens in your carb. you need to tune it!

4. to conclude, crankcase pressure is constantly changing and your final results is: change the valve timing. change the power delivery.

Someone is being pompous, alright.


I pretty much just ride trails, and think the first two additions should be better swingarm skids and nerfs.

[Sanddraging28]

i sent him a PM and asked him to explain himself a little better and he has yet to return it.

[FarmerTed]

Originally posted by bigbad400
what the guy said about your altitude being a factor and that it happens in your carb is a false statement, the altitude is a major factor in jetting your carb but carb is not under pressure, its under vacuum by the combustion chamber, the gas and air will not just flow into the motor it needs to be pulled in, there for if you have a change in altitude, your pull from the motor may increase or decrease, hence why we need to rejet. im not saying that the guy is wrong im saying that he was wrong about were the change happens, altitude affects the amount of air the motor needs, and the amount of gas, the carb just delivers it through vacuum pull.


Just to be clear, I never said the carb was under pressure. :) That said, altitude affects the amount of vacuum the engine pulls. For every 1000ft of elevation you lose approx 1in of vacuum. The other references I was making to pressure were cylinder pressures, not atmospheric, and I stand by what I said in my post. Hopefully this clears up the confusion.

Also, altitude doesn't affect how much air the engine needs, it actually affects how much air the engine gets due to density and volume. An engine jetted for sea level runs rich at 5000ft because there is too much fuel for the volume of air that is able to be sucked in. You have to lean out the AFR and, as I said, the result of reduced air, fuel, and cylinder pressures results in reduced power output.

[pods_BMOC]

I had my Port and Polish done by a professional that used to build race eninges,.. only cost me $100.

[jcs003]

Originally posted by FarmerTed
Not to be the n00b stepping into the middle here, but...Sanddraging28 is right. Changing the valve timing and/or duration does change the effective compression ratio. If you change the cam function without compensating then the end result won't match what you started with, in this case if you increase intake valve duration so that it closes later then you have reduced the effective compression ratio as well as the actual compression (obviously).

Don't take it from me, though. Read this if you still don't believe it to be true. It even shows you how to calculate the effective compression ratio based on all the data. Being a mechanical engineer you should know that if you change one variable in the equation then the result will be different.

http://victorylibrary.com/tech/cam-c.htm

As for altitude, that is part of the equation. Increased altitude results in lower atmospheric pressure as well as reduced air density. Tuning the carb doesn't change the air density or pressure, it leans the fuel to compensate for the reduced air. The reduced air AND fuel means reduced volume in the combustion chamber. If you make no other changes to the engine you will experience a lower dynamic compression ratio and reduced chamber pressures. In the end you're making less power because of all these factors; Less air, less fuel, and less pressure in the chamber.

i will make this simple. DCR can be understood to be the amount of 'work' an engine is doing. i.e. has the potential kinetic energy to do work. eventually to rear wheels.

the cam controls how the work is delivered. i,e. lift and duration ratios. at whatever RPM moter is at its highest potential.

the carb, using the Venturi principle atomizes fuel/air to create a combustable mass at a specific volume.

now, the DCR is the true measure of an engines compression when under a load. when motor is running through its 4 cycles.

altitude has very little affect on what a motor can do. this is what the carb and its many jets control.

does an aftermarket cam design affect an engines compression? no, it changes where an engine is at its peak and will lower a compression reading on a static compression test.

this is why race engines may show a low compression ratio. i.e. torbo/superchargers etc.

this is why you do the correction and discover a nominal compression ratio after correction.

i may of left out a few details but you get the point.

[jcs003]

Originally posted by Sanddraging28
i sent him a PM and asked him to explain himself a little better and he has yet to return it.

sorry i did not try and be insulting. seems i mistook your resonse.

you just made that more complicated than necessary and left somethings incomplete.

[FarmerTed]

Originally posted by jcs003
i will make this simple. DCR can be understood to be the amount of 'work' an engine is doing. i.e. has the potential kinetic energy to do work. eventually to rear wheels.

the cam controls how the work is delivered. i,e. lift and duration ratios. at whatever RPM moter is at its highest potential.

the carb, using the Venturi principle atomizes fuel/air to create a combustable mass at a specific volume.

now, the DCR is the true measure of an engines compression when under a load. when motor is running through its 4 cycles.


Doesn't matter if it's under a load or not, DCR or ECR is the corrected compression ratio after taking valve timing and/or duration into account. To say an aftermarket cam doesn't change an engine's DCR/ECR is preposterous. It absolutely does change the compression and DCR if the intake valve stays open later. DCR is based on when the intake valve closes, among other things.



altitude has very little affect on what a motor can do. this is what the carb and its many jets control.


Altitude plays a very large part with an engine's potential power output. I'm not sure where you get your facts.

Under "ideal" conditions (60F, 29.92in/Hg, 0% humidity) an engine on an SAE J1349 certified dyno will show the engine is making about 104-105% of the "corrected" HP, so if it's putting out 50HP at the wheels the corrected HP is 47.75. I'm sure we all know this correction factor is to make sure, regardless of operating conditions, the corrected dyno numbers should be nearly identical.

Let's take the same vehicle, same dyno, same temp...and take them to 5000ft elevation. Atmospheric pressure has now gone from 29.92 to roughly 25.8. Hop on the dyno and the same engine will only make 88% of the power it made before, from 50HP down to barely over 40HP. That doesn't seem like "very little" effect to me. Jetting for high altitude will put the engine in tune for the conditions, it will NOT restore the power you have at lower elevations. Period.



does an aftermarket cam design affect an engines compression? no, it changes where an engine is at its peak and will lower a compression reading on a static compression test.


It absolutely will affect an engine's compression and DCR if it changes the point at which the intake valve closes. It's that simple. Hell, even a stock cam will change the compression and DCR if you change the cam timing.



this is why race engines may show a low compression ratio. i.e. torbo/superchargers etc.


They may show it because the compression IS lowered for forced induction. Why? Forced induction increases the cylinder compression, if you don't reduce the compression ratio you're likely to blow the motor. Not only that, the higher compression increases the potential for detonation and requires higher octane fuel. The increased power from forced induction isn't from the increased cylinder pressure from the FI but from the increased volume of air and fuel. You reduce the SCR to compensate and maintain the DCR. You know the saying "There's no replacement for displacement", well FI is a replacement for increasing N/A displacement.



this is why you do the correction and discover a nominal compression ratio after correction.

i may of left out a few details but you get the point.

No offense, but you left out a lot of important details and added a bit of misinformation.

[jcs003]

first, i didn't say advance cam timing. i said the "cam" controls valve timing.

altitude has nothing to do with the engines potential output. the carb must be tuned to compensate for the altitude. you set the jetting to meet the engines specific fuel/air needs.

also, dyno's do not similate real world scenarios. like traction, air turbulance , air moisture and etc. so leave the dyno info for the big number seekers.

and when i said "load" i was explaining an actual running motor.

it is safe to say your no engineer if you are likely to pull out info you obviously got off of google to suite your argument. i could do the same but, with real experience this is not necessary.

When preparing and engine for high performance output, selection of the optimum compression ratio (CR) is one of the important factors in the process. However, CR by itself is somewhat meaningless. What we are really interested in is compression pressure, because that is what the engine sees. High compression pressure increases the tendency towards detonation, while low compression pressure reduces performance and economy. Maximizing cylinder pressure benefits power, and one sure way of increasing cylinder pressure is to increase the compression ratio. The cam selection and intake system can also have a major affect. In my opinion, the most important factors in selecting the optimum CR is the deck height, the cam timing, the shape and finish of the combustion chamber and pistons, the operating rpm range, and of course, the fuel available. All of these factors can be controlled to some extent, especially during initial build and assembly of an engine.

CR and what it really means. "Static" or "rated" CR is a ratio of the fixed volume of space above the piston top in the cylinder at Top Dead Center (TDC), to the volume of space displaced by the piston when moving from bottom dead center (BDC) to top dead center. When we look at actual cam timing specs, we find that the intake valve does not close until sometime after BDC. There can be no compression until the intake valve closes, so actual CR will be less then the static. How much less will be determined by the closing point of the intake valve. This actual CR will be referred to as the "dynamic" CR. These two different CR values are predictable and calculable. There is a third type of CR which represents the total cylinder pressure, and is the result of many more variables, but this value is unpredictable and for all practical purposes, unmeasurable.

if anything a hotter cam will raise compression by increasing cylinder pressure with more valve overlap.

[hoogiesngrinder]

Originally posted by jcs003

altitude has nothing to do with the engines potential output. the carb must be tuned to compensate for the altitude. you set the jetting to meet the engines specific fuel/air needs.


Sorry, you're wrong. Jetting lower is to compensate for thinner air. Potential output is roughly 3 percent lower for every 1000ft you get above sea level.

Ask any pilot :)

[FarmerTed]

Originally posted by jcs003
first, i didn't say advance cam timing. i said the "cam" controls valve timing.


And valve timing can and does affect compression and DCR. Whether or not you install an aftermarket cam or change the timing of the stock cam, if you change when the valves close you change the DCR. Did you forget you said this?

"a cam has nothing to do with compression. a cam changes valve timing."

Change valve timing and you change compression. The whole argument here was started when you made that false statement.



altitude has nothing to do with the engines potential output. the carb must be tuned to compensate for the altitude. you set the jetting to meet the engines specific fuel/air needs.


So let's just make this clear, are you trying to say you can get the same power output at 5000ft that you can at sea level just by tuning the carb and making NO other changes? Simple yes or no question.



also, dyno's do not similate real world scenarios. like traction, air turbulance , air moisture and etc. so leave the dyno info for the big number seekers.


What in the world...dynos are the perfect tool to validate changes made to an engine. The fact that dynos DO take into account humidity, atmospheric pressure, and temperature make them PERFECT for showing the differences cams and carb tuning make. The "SOTP" dyno is not a valid way to measure anything. To be honest, I'm shocked someone would basically say a dyno is useless when it comes to this very discussion.



and when i said "load" i was explaining an actual running motor.


So next time say running engine, load is an actual load put in an engine, such as a dyno brake connected to an engine's output shaft or drums being turned by the wheels. An engine doing zero work has zero load.



it is safe to say your no engineer if you are likely to pull out info you obviously got off of google to suite your argument. i could do the same but, with real experience this is not necessary.


Sorry, but you're no engineer if your "real" experience is being proven wrong repeatedly.



When preparing and engine for high performance output, selection of the optimum compression ratio (CR) is one of the important factors in the process. However, CR by itself is somewhat meaningless. What we are really interested in is compression pressure, because that is what the engine sees. High compression pressure increases the tendency towards detonation, while low compression pressure reduces performance and economy. Maximizing cylinder pressure benefits power, and one sure way of increasing cylinder pressure is to increase the compression ratio. The cam selection and intake system can also have a major affect. In my opinion, the most important factors in selecting the optimum CR is the deck height, the cam timing, the shape and finish of the combustion chamber and pistons, the operating rpm range, and of course, the fuel available. All of these factors can be controlled to some extent, especially during initial build and assembly of an engine.


So, you do admit cams can change compression. ;) I already mentioned high vs. low compression, detonation, and fuel. You brought up forced-induction, I explained why lower a lower SCR is needed to compensate. I don't think we need to keep repeating ourselves, do we?



CR and what it really means. "Static" or "rated" CR is a ratio of the fixed volume of space above the piston top in the cylinder at Top Dead Center (TDC), to the volume of space displaced by the piston when moving from bottom dead center (BDC) to top dead center. When we look at actual cam timing specs, we find that the intake valve does not close until sometime after BDC. There can be no compression until the intake valve closes, so actual CR will be less then the static. How much less will be determined by the closing point of the intake valve. This actual CR will be referred to as the "dynamic" CR. These two different CR values are predictable and calculable. There is a third type of CR which represents the total cylinder pressure, and is the result of many more variables, but this value is unpredictable and for all practical purposes, unmeasurable.


You know where your credibility just went? Right out the window.

http://www.boyleworks.com/ta400/psp/compression.html

Wow, pasted word for word, including the section above it.

Before you claim someone else got all their information off the internet I'd suggest you stop doing it yourself.

Some engineer... :rolleyes:

[jcs003]

Originally posted by FarmerTed
And valve timing can and does affect compression and DCR. Whether or not you install an aftermarket cam or change the timing of the stock cam, if you change when the valves close you change the DCR. Did you forget you said this?

"a cam has nothing to do with compression. a cam changes valve timing."

Change valve timing and you change compression. The whole argument here was started when you made that false statement.



So let's just make this clear, are you trying to say you can get the same power output at 5000ft that you can at sea level just by tuning the carb and making NO other changes? Simple yes or no question.



What in the world...dynos are the perfect tool to validate changes made to an engine. The fact that dynos DO take into account humidity, atmospheric pressure, and temperature make them PERFECT for showing the differences cams and carb tuning make. The "SOTP" dyno is not a valid way to measure anything. To be honest, I'm shocked someone would basically say a dyno is useless when it comes to this very discussion.



So next time say running engine, load is an actual load put in an engine, such as a dyno brake connected to an engine's output shaft or drums being turned by the wheels. An engine doing zero work has zero load.



Sorry, but you're no engineer if your "real" experience is being proven wrong repeatedly.



So, you do admit cams can change compression. ;) I already mentioned high vs. low compression, detonation, and fuel. You brought up forced-induction, I explained why lower a lower SCR is needed to compensate. I don't think we need to keep repeating ourselves, do we?



You know where your credibility just went? Right out the window.

http://www.boyleworks.com/ta400/psp/compression.html

Wow, pasted word for word, including the section above it.

Before you claim someone else got all their information off the internet I'd suggest you stop doing it yourself.

Some engineer... :rolleyes:

that was my point. i can go on the net too.

either way the point i was trying to convey was way over your head. stick to farming.

my credibility is my B.S. Mechanical Engineering. Carnegie Mellon University; 2005.

[jcs003]

FarmerTed, you have an interesting way of twisting thing to benefit your argument. i espically like the way yoiu multi-quote to do this. it seems you got your info from an internet source, seeing how you know where i found mine.lol nice how things were twisted in my benefit for a change.

[FarmerTed]

Originally posted by jcs003
that was my point. i can go on the net too.

either way the point i was trying to convey was way over your head. stick to farming.

my credibility is my B.S. Mechanical Engineering. Carnegie Mellon University; 2005.

Indeed you can go on the net, what you pasted proves your other statements were wrong. You made a false statement and won't or can't admit it. Cams do affect compression. Altitude does affect power output. You said otherwise.

Are you ready to admit you misspoke yet? :)

[jcs003]

Originally posted by FarmerTed
Indeed you can go on the net, what you pasted proves your other statements were wrong. You made a false statement and won't or can't admit it. Cams do affect compression. Altitude does affect power output. You said otherwise.

Are you ready to admit you misspoke yet? :)

it's apparent you cannot grasp the full aspect of my argument. there is more in my explanation than you are getting.

i do admit i am not thorough with every aspect of my argument but i thought most would follow. apparently i was wrong.

[FarmerTed]

Originally posted by jcs003
FarmerTed, you have an interesting way of twisting thing to benefit your argument. i espically like the way yoiu multi-quote to do this. it seems you got your info from an internet source, seeing how you know where i found mine.lol nice how things were twisted in my benefit for a change.

Do you deflect often? I multi-quote because I prefer to respond to specific section of a post. Any normal person would do the same, it doesn't make sense to throw multiple, different points onto the end of a quote, does it? No.

My info comes from understanding how engines function and what makes them function, I did not quote a single thing from an internet source as I don't need to.

Twist your words? No, I simply am following your own twisted path, the path where you keep changing the subject or making irrelevant points. A dyno is useless...what the hell...

I'm not a farmer, but thanks for making that assumption. Being an engineer you should base everything on fact, assumptions don't belong anywhere in engineering. ;)

[FarmerTed]

Originally posted by jcs003
it's apparent you cannot grasp the full aspect of my argument. there is more in my explanation than you are getting.

i do admit i am not thorough with every aspect of my argument but i thought most would follow. apparently i was wrong.

I'm done with the thread and I'm done arguing with a monkey that can type.

You've been proven wrong multiple times, if you insist on embarrassing yourself some more then someone else will have to step in. Or perhaps the mods should just close the thread since it's so far off topic at this point.


Have a nice day. :)

[hoogiesngrinder]

Agreed, a moderator should shut off the lights and close the door to this thread.

[250R-Dee]

Too many of you guys are giving too much value to your own OPINIONS. This thread has strayed too far from the original topic because of PETTY bickering so it is no longer useful.

In the future, STAY ON TOPIC or create your own topic so that you can argue, misinterpret, and/or try force your point of view/opinion on other people.

CLOSED!!