dynamic compression

[honda400ex2003]

So, this has not been talked about for quite some time and I was curious to see what some opinions were on the subject based on mods and such like cams and how to choose them. Maybe ron or someone will chime in and have some ideas since they have read and calculated most of this stuff at one time or another. I think this could help some of the newer guys also by introducing them to the concept of choosing parts wisely. I am hoping you may be able to help me out a bit and my apologizes for asking questions such as these as i am sure you get this quite often. I noticed you have not been on exriders too much so i am not even sure if you are still doing anything with the 400ex. I am wondering if you can help me out or what your thoughts are on this at least. i am curious on your opinion on how different the hotcam stages actually are on these 400s. After doing some testing today, it has me wondering about how much different my machine would run with the stage 1 compared to the stage 2 i ran it with. Although, I wonder since the dynamic compression would be higher with the 1 in it than the stage 2. It is not a huge difference by the looks of it, only around .3:1 per stage and 1.1:1 drop from the actual static compression of the engine. so my 10:1 wiseco is actually around 9.5:1 with ex gaskets, then go into the stage 1 and 2 which would take off 1.1 and 1.4 from the current ratio which is 8.4:1 and 8.1:1 dynamic compression for stage 1 and 2. as i have compared to your 11:1 example in one of the past threads with a comparison of cams by GPracer2500. this difference is not much but is it actually noticable on a dyno with the same f/a ratio when testing? This leads to my next question on how much does the f/a ratio change with just changing the cam? I know in the past we mostly say that it doesnt make much difference but is this the truth and has this been tested? I dynoed 34.1 hp today with 13:1 a/f ratio with my stage 2, t-4 slip on, sparks key, monster coil, p&p a bit, 10:1 416 in my sig. I think that even if i swapped back to my stage 1 it would still be right around the same peak since there is not that big of a difference in dynamic compression. I think it would just change the peak hp from around 7000 rpms to somewhere around 5500 rpms. The torque would probably be what changed the most with more torque going to the stage 1 but more peak hp going to the stage 2. What is your opinion on this?

heres my dyno chart and f/a ratio on the bottom. I dont have the torque sheet since it did not measure that today. I hope it works.

http://img33.imageshack.us/img33/7978/dynorun416ex.th.jpg

heres the link in case it does not work.
http://img33.imageshack.us/img33/7978/dynorun416ex.jpg

Thanks and i appreciate it,
Steve

[Ryan'07400ex]

Sorry , I can't answer but I wanted to thank you for asking this because I'd like to know more to. I've been dragging my feet about get a Hotcam stage 1 or 2 for several months now.

[honda400ex2003]

i hope john doesnt mind me posting his pm about the subject for a bit of help to some. steve

There will not be any noticable hp gain, on a dyno maybe 1 or 2 hp.

it changes the air flow in and out of the motor by making the valves open and close slower or faster, and at different height's.

bigger bores need bigger cams, strokers need a stage 3, piped and jetted use stage 1 and everything else use's stage 2.

the longer the valves are open the lower compression will be, not by alot but enough to lower compression.

you could essentially lower or raise compresion slightly, just by adjusting your valves.

Anyway, H.P. wont be effected much by a cam but performance will, if you had a 416 11:1 with a stage 2, sure it would lower your compression to 8 or 9:1, but that only changes what type of fuel you run and your timing....whole other subject.

if I had true 13:1 compression, stage 2, jetted with the right gas...and you had the same quad with 9:1, jeted with the right fuel, we would have roughly Within 1-2 hp range of each other but I could fly past you from start to finish in a race.

A 660 raptor has 10 more cc's the a ninja 650....but the ninja has several pistons, cams, carbs that move alot more air threw the motor....a 660 raptor is essentially a lawnmower engine compared to a ninja 650.

The 650 makes 70hp....get the 660 to make 70hp and it stil wont come close to the 650 ninja.....cam and air flow example.

long subject...thats as short as I can make it.

[honda400ex2003]

my response question to him again. steve
Thanks for that info. Do you know how much the actual dynamic ratio would be for a 10:1 with either cam. I dont think that it would be but a couple of tenths different. I am not sure if it would make more hp with the stage 1 or 2 in it. I dont even think it would be more or less than 34 hp with either cam. I could theoretically be at around 35-36 hp with the stage 1, that is what i am wondering for. This would make it sound much closer to a 450 at 38 hp and make it a much better performing . I am not really concerned about it but am more curious than anything. I think it would be cool to run again to see how much different it actually is. It would just change the rpms of the peak hp i think with the different stages. the duration of the cams being larger makes for a bigger breather and makes for a better high rpm engine. This would make for an assumption that the peak power would be with the stage 2 but the more torque would go to the 1. this is def the case as i have experienced riding it all along. If the match would be better with the stage 1 it would thoretically make more hp since it would have a bit higher dynamic compression than the stage 2. I am not sure if i make sense anymore but I hope i am. I wish i could afford to take my machine back to the dyno just for my own satifaction and to find out how much of a difference there actually is. Do you have any side by side comparisons on a dyno with each of these cams by chance? thanks again, steve

[honda400ex2003]

heres a thoretical example of what i am talking about with the different ratios with different duration cams and such. I based my estimates on this example since the comparisons are correct. this thread is found at http://www.exriders.com/vbb/showthread.php?s=&threadid=237131

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.

steve

[Ryan'07400ex]

Ok so basically are you saying that it will not benefit much to do just a piston by itself or just a cam by itself? You should do both?

I'm confused why the compression dropping is a good thing.

[honda400ex2003]

yes when done together it makes the best combination. The best combination is the trick and what i am trying to find out. lol. losing compression is not a good thing per say but it can be a worth while thing to have happen if the machine is set up correctly for it. I hope i helped you out, steve

[Ryan'07400ex]

Originally posted by honda400ex2003
yes when done together it makes the best combination. The best combination is the trick and what i am trying to find out. lol. losing compression is not a good thing per say but it can be a worth while thing to have happen if the machine is set up correctly for it. I hope i helped you out, steve

This makes since. So can you answer this. Is an aftermarket cam a waste by itself on a stock bore, specifically the 400ex?

[honda400ex2003]

Well there are mixed opinions on this. lol. I feel that a stage 1 would be alright for it but nothing else. the dynamic ratio would be quite low with a stage 2 as shown in the example. I even feel that in some cases, such as a stock carb on 10:1 comp the stage 2 will be a bit too much. I am still having mixed opinions on it myself, this is why i am wondering how much difference there is in overall hp using both cams. If there is not a difference in hp then the dynamic compression differences are not that great and would not effect overall performance of the engine. This then would enable us to run either the stage 1 or 2 without sacrificing alot of hp. It would just determine how you want the power delivery as hotcams suggests by designing their cams for a certain area or type. stage 1 is for low end mainly and mid, 2 mid mainly and top, 3 top and mid but mainly top. I have been experimenting with each of them and have found this to be the case actually myself. i feel like i am contradicting myself now and really i am. I am tossed between how it actually is and the numbers behind it. The only number i have is the 34 hp with my stage 2 from a few days ago. My original question was if the stage 1 has the same peak hp, with just a different placement rpm wise. lol. Does anyone have info? Steve

[Thumpin440ex]

While the dynam ratio does come into play, a cam shaft that is matched to say a head that has had work, flows better over a stock head, is where the gain will be the best.. IMO the hp you pick up from the more aggressive grind, will over come the slight loss in power from the loss of compression.. It will be a matter of where the power of a said cam will come in, how flat the tq curve will be.. Hp is good on the top end(as you know) while tq is what pulls you there. As we all or most of us know the flatter the tq curve is the better and harder a bike will pull through out the rpms.. I would like to see some info on what a stock untouched head is capible of flowing. If it can't keep up to what a stge 3 cam can move then it is pissing in the wind. The more air you can move in and out and do it the most efficiently is where its at..

John

[honda400ex2003]

Nice thanks alot for the info thumpin. Do you know any numbers of what each of these cams would run at all by chance to show any sort of comparison with out of curiousity? thanks again, steve

[honda400ex2003]

Also does anyone have any answers to my exact questions throughout the thread? steve

[m0t0xk1d]

im sorry for posting as i do not have an answer to your thread but 34hp out of your 400 with those mods? is your motor worn? tht just seems kind of odd to me as i got my 300ex dynoed the other day and it was 36hp. i mean i have the bike fully modded out but i was told the 400ex with make alot more power. especially where you are 116cc more then me and you know the saying " there's no replacement for displacement".

[honda400ex2003]

mine has over two years and probably 2000 miles on it so it is a bit more tired than a fresh rebuild. it is not real tired though imo, it will keep up with 11:1 comp 416s and other machines. a stock 450r will dyno 38 hp on the same dyno. steve

[Thumpin440ex]

Originally posted by m0t0xk1d
im sorry for posting as i do not have an answer to your thread but 34hp out of your 400 with those mods? is your motor worn? tht just seems kind of odd to me as i got my 300ex dynoed the other day and it was 36hp. i mean i have the bike fully modded out but i was told the 400ex with make alot more power. especially where you are 116cc more then me and you know the saying " there's no replacement for displacement".

What kind of compression are you running in your bike, what kind of fuel are you using?? Thats alot of hp from a bike, that is 300 cc, unless it is stroked or bored.. Lets have some specs on it :) also a dyno can be made to make diff amounts of HP, it is more of a tuning tool rather then a bragging tool... 2 diff kinds of dynos will dyno the same vehicle and give diff hp /tq readings.

Compression is def a good hp upper, but only when it comes into the full points of comp, not 050 or .5 of a point... To the OP, I do not have any data on what a stock cam can flow nor what a stock head flows.. It is give and take game when it comes to cams.. A cam with a higher duration and lift will make the power up higher in the rpm range, be more peaky on a bike with a stock rev box.. However if it can or is able to pull that high, then it will make a nice hp curve, but up higher.. I do not know if they make cams for atvs like they do auto engines, dual pattern cams, split, reverse patt cams.. If they do, I want to know, it would be awsome if they did, each one of them designs do diff things in diff areas of the rpm band :)

John

[m0t0xk1d]

Originally posted by Thumpin440ex
What kind of compression are you running in your bike, what kind of fuel are you using?? Thats alot of hp from a bike, that is 300 cc, unless it is stroked or bored.. Lets have some specs on it :) also a dyno can be made to make diff amounts of HP, it is more of a tuning tool rather then a bragging tool... 2 diff kinds of dynos will dyno the same vehicle and give diff hp /tq readings.
It Has a 14:1 high comp piston runnning vp c12 race fuel. i have the sparks X25 cam with hardened rockers/big valve springs. it is ported with a 37 mm fcr carb on it with the x4 sparks pipe. thats about it for the engine. its a 76mm piston so it is a true 300cc. but its not any more than 300cc

[Thumpin440ex]

LOL yah that is one bad *** 300 with a 14-1 slug in it.. When you jump points in comp it is well worth it.. Along with aftermarket bigger valves.. The power with that bike is prob instant, just from the comp alone... :)


John