Cant decide...11:1 or 10:1

[grassman]

Im getting a 88mm piston... I cant decide what compression to get... I have a stage 1 hot cam thats going with it. I ride mostly trails but alot of wide open trails.( full rabbit). Im wondering about heat and life of it. I know you get more power out of higher compression. Any words of wisdom would help. Thanks

[slightlybent47]

Reliability will be the same as a lower compression. I’ve been running 12.5 to 1 for years with no issues at all. I’d go with 11.5 if I were you. you can still run 93 with no problem on that compression.

[sneaky11]

it's really depends on the cam choice... if you go too high c/r with a stg1 you'll build too much dynamic compression on a 88mm bore, and be more close to pre-detonate... so keep that in mind
i'll go 10:1 if you don't wanna change cam or get a better cam to go with this application.

[IMSROLL450R]

11:1 for sure. Even with the Stage 1 you are ok. The reliability difference is non existant....

[DragonGunner]

Originally posted by IMSROLL450R
11:1 for sure. Even with the Stage 1 you are ok. The reliability difference is non existant....

This^^^ I ran 11:1 on a 88mm bore with Web cam.

[400man]

Originally posted by sneaky11
it's really depends on the cam choice... if you go too high c/r with a stg1 you'll build too much dynamic compression on a 88mm bore, and be more close to pre-detonate... so keep that in mind
i'll go 10:1 if you don't wanna change cam or get a better cam to go with this application.

so your saying that you would need to run a higher octane gas (like around 100 or so) if you ran a high compression with a lowend-midrange cam? and I guess the power would be nice and torquey feeling with the power in the lower end of the rpms.

[CJM]

11:1 is nice, no real issues there besides heat for some. Use a spal fan or get an extra or larger oil cooler (can use an automotive trans cooler). Downside-wanna run the sparks key you cant-way to much heat and possible detonation without at least 100 octane-even then not a good idea.. Also may need heavy duty head studs

10:1 Same as above, less heat of course. Can run sparks key or +3 custom key forum member wheelie makes.

I wish I had a 10:1 sometimes so I could use the +3 key.

[sneaky11]

11:1 in 88 bore will generate some good btu's and with a tinner sleeve, heat disipation is more tricky... so combine that with a cam that give you not a big amount of velocity to expel the heat fast generated by the explosion and you have a motor that gonna become hotter during the day and may start to pre-det after... 30min... 1h...3h... maybe on hotter days that can show up pretty quick.

I suggest you to uprgade your cooling system if you run stage 1 with 11:1.

Keep in mind that alot of factor can influence that... maybe you'll be good and never have any problems...

[tri5ron]

although you do Some "full rabbit"
Trail riding often is at a slower pace with limited airflow for cooling.

My opinion of the perfect trail bike build, that will never let you down is ...
Stock piston, or up to 416, at 10:1, or 10.5:1 (MAX.),
foam air filter,
muffler, (slip-on), of your choice,
ground welds on stock headpipe, (full header systems are not cost effective)
stage 1 (or 2) hotcam, or equivalent,
04-05 450r carb properly jetted to your elevation/temps
Sparks +6, (or Wheelies +3) ignition timing advance key.

upgraded front shocks of your choice,
steering stabilizer of your choice,
XR's Only Oil temp gauge (just to keep an eye on it),
Spal fan, or larger cooler if you need it,
gearing stock or 1 tooth down on the front


It will run on pump gas, be a stump pulling torque monster, never overheat (even in the slow and rough terrain), will produce about 34 hp, (over the stock 24-26 hp), still be just as reliable as a bone stock machine, and always bring you back home.

(jmho). that, and a $5 bill will get you a gallon of gas.

[grassman]

Thank you guys for the info. I love that you can still count on some good knowledgeable opinions on this forum. I think Im gonna go with the 10:1 to play it safe. If I had the stage 2 cam I would go with the 11:1. Thanks Ron for your set up opinion.. I do, do alot of "full rabbit" trails, but I also mix some "1/4 turtle" trails in for fun so I like your ideas of reliability. Ill post some pics up once I get this thing going... Again thanks Sneaky, CJM, 400man, Ron, IMS, Dragon and slightly... I appreciate it.

[400exrider707]

I ran an 11:1 with a cometic thin head gasket (thinner than the XR400 gasket) with a stage 1 hotcam for 2 seasons of MX racing and ice racing and ran 87 octane with it and never had a single issue. I would do it the same way again if I did it over. I loved that combo on the 400, really woke the bottom end right up.

[IMSROLL450R]

Originally posted by 400exrider707
I ran an 11:1 with a cometic thin head gasket (thinner than the XR400 gasket) with a stage 1 hotcam for 2 seasons of MX racing and ice racing and ran 87 octane with it and never had a single issue. I would do it the same way again if I did it over. I loved that combo on the 400, really woke the bottom end right up.

Experience at its best right there fellas. Mike is one smart dude.

Once again 11:1 for the win.

[sneaky11]

Originally posted by 400exrider707
I ran an 11:1 with a cometic thin head gasket (thinner than the XR400 gasket) with a stage 1 hotcam for 2 seasons of MX racing and ice racing and ran 87 octane with it and never had a single issue. I would do it the same way again if I did it over. I loved that combo on the 400, really woke the bottom end right up.

what is the bore size?

[tri5ron]

Originally posted by 400exrider707
I ran an 11:1 with a cometic thin head gasket (thinner than the XR400 gasket) with a stage 1 hotcam for 2 seasons of MX racing and ice racing and ran 87 octane with it and never had a single issue. I would do it the same way again if I did it over. I loved that combo on the 400, really woke the bottom end right up. wow, that's something I don't think I would have ever tried. 11:1 w/87 octane. I'd have surely bet that it would have a Pre-det issue.
it's gotta be very close.
apparently the squish band is not what I would have assumed for these engines. That could be a good thing, in reguards to how much ignition timing we could push, but it does raise many interesting questions..
But if you got it to work, then thats great !


to the OP,
here's just one of hundreds of interesting articles on the subject, that may help you decide.

http://www.popularhotrodding.com/tech/0311_phr_compression_ratio_tech/index.html

(yeah, I realize it's from Hotrodder Mag., and not everything necessarily applies,... but the principles are the same)
Just google "compression ratio vs octane" and you can read till the end of time about the subject.
Subscribed to see how this develops. Hell, I might learn somethimg here !

[400exrider707]

Well 400ex pistons are made for XR400's. You might think they'd be the same right? Well the piston itself is, but if you've ever had a 400ex head off you might have scratched your head when looking at the piston to deck clearance when at TDC. At TDC with a stock piston, it's .040" down in the hole. An advertised 11:1 wiseco is 11:1 on an XR400, but NOT on a 400ex. Most guys would also run NO base gasket (to gain even more squish up top) and use a thin line of RTV maker, then use the XR400 head gasket or the even thinner Cometic unit. Which can be had from C&D racing. I think it was like $20 when I got it a few years back. I used the thin cometic, but left the stock base gasket.

I ran 93 initially, then after doing my research and just wanting to see how far I could go, I started running 87. I probably wouldn't do it on a stock cam, but with an aftermarket cam in there it was fine the way I ran it. I'd imagine even easier with a stage 2 or 3. I'm not saying 87 is the way to go, and for the cost 93 probably would be fine, but I ran 87, checked my plug often and ran it hard. Never had an issue.

This was on a stock bore machine though.

Why are you wanting to go to 88mm anyways?





Originally posted by IMSROLL450R
Experience at its best right there fellas. Mike is one smart dude.

Once again 11:1 for the win.

Thanks dude! Glad to see you're back on the boards. I need to get another quad ASAP.

[NacsMXer]

Originally posted by IMSROLL450R
Experience at its best right there fellas. Mike is one smart dude.

Once again 11:1 for the win.

X2

We can speculate on setups all we like but nothing is better than first hand experience with the parts in question. To top it off, his setup was using the thinner XR400 gasket, and low octane 87 fuel (that combo makes it have more compression/more susceptible to detonation).

So if you don't run the thinner gasket, and run higher octane 93 or even splash in some 110 with it on the really hot days, you are that much safer in avoiding motor-ruining detonation.

I'm all for the 11:1, you will have very nice low end torque especially coupling it with a stage 1 cam. I think it's a good match. I would go with a 87mm (416) piston though. Only time the stage 1 wouldn't be appropriate is if he was going to 12:1 and higher compression. As long as the motor is put together properly with the correct jetting and good fuel you won't have problems with reliability.

If you go with the 10:1, don't be surprised if you don't notice too much of an improvement in performance. I used to run a 10:1 Wiseco 440 setup with a midrange Webcam and it was ok, but nothing compared to the 12.5:1 setup I have now. It pulled harder than stock but was nothing too crazy in terms of an "upgrade".

[grassman]

Man.... I thought I was confused before... All you guys make great points. Ive always heard you get the power from compression. The reason Im going with a 88mm is that I already have the cylinder ready. My buddy is a mechanic at a local honda (powersports) shop. He had the cylinder ready to go with a 88mm wiseco and the guy decided to go with a 440. So Im gonna use that cylinder and keep mine as a stock back up. I still need to order the 89mm gasket.. should I get one for a xr400 or just get the cometic 89mm gasket?

[CJM]

Originally posted by 400exrider707

This was on a stock bore machine though.


Thats why it probably worked so well. Less overall heat than any other bore size.

I like my 11:1 416, Im using cometic EST gaskets. Not sure the thickness but they are the best gaskets you can run basically. All are multi layer steel and seal (or are supposed to) better than others.

I have no heat issues, yes I can feel it get hotter when its hot outside-but nothing out of the ordinary.

[400exrider707]

Originally posted by NacsMXer
To top it off, his setup was using the thinner XR400 gasket,

It was actually even thinner than the XR gasket, it's special made by Cometic.

Also, go with GOOD gaskets. I went through several of the gaskets from Rocky Mountain (I forget what brand, maybe it was Tusk?), they were crap. Blew them within an hour of riding every time. Went to Cometic, no problems!


Originally posted by grassman
Man.... I thought I was confused before... All you guys make great points. Ive always heard you get the power from compression. The reason Im going with a 88mm is that I already have the cylinder ready. My buddy is a mechanic at a local honda (powersports) shop. He had the cylinder ready to go with a 88mm wiseco and the guy decided to go with a 440. So Im gonna use that cylinder and keep mine as a stock back up. I still need to order the 89mm gasket.. should I get one for a xr400 or just get the cometic 89mm gasket?

The 426 bore has some extra inherent heat built in because the cylinder walls are pretty thin at that point. I don't think I'd ever do a 426 simply because I could do a 416, or just resleeve and go to 440. However, since you've already got the parts, just go for it. Run the 11:1, thin gasket and just use 93. Make sure jetting is on, and keep checking the plug!


Originally posted by CJM
Thats why it probably worked so well. Less overall heat than any other bore size.


Agreed, which is why I pointed it out. Ideally you want to run the lowest octane fuel that doesn't detonate or have pre-ignition issues. If you're running a 50/50 mix of pump and race, but it doesn't have issues on just 100% 93octane, you're wasting money. Maybe it's just for peace of mind, but myself I like seeing what actually works. I got down to 87 octane without a single issue and the motor never felt hot. Again, elevation, climate, riding style, it's all going to effect this. I would just run 93 if you have any worries.





Lastly, this forum desperately needs a multi-quote feature... this is a lot of unnecessary work this way! :scary:

[IMSROLL450R]

If you already have the cylinder ready get the 11:1 and call it a day. Put it together and ride....

[Thumpin]

With my 416ex I was looking for something that rocks for trails and tried many combos with my 11:1 compression engine, and my favorite is the stock ground out header with a free flowin slip on and the stage 2 Hot Cam.

It wont run on 91 octane at 2000' without pinging, but on E85 it is a cool running, torque monster, that has been reliable as any 400ex should be.

[grassman]

Pulled the trigger today and bought the 11:1.. I figured if I dont get the power I want I would rather change the cam than the piston... So after months of debate and saving spare change and selling old stuff on craigslist & ebay (more fun and rewarding than just using the paycheck)... Ive got every thing I need to rebuild the 400... piston, cam, gaskets, timing chain and clutches. Only thing left is to save a few bucks to give to my buddy for labor and tuning. Im psyched!!!

[Thumpin]

Thats great on your piston choice you wont be sorry! Are you running the stg2 hotcam? I havent paid attention what your can is?

The full exhaust made a bigger differance on power band range in my quad than the cam did with my setup. And that Stg2 HC gave me more lowend and strong midrange with good topend over rev, compared with the CT full exhaust with poor lowend and killer mid thru topend pull. I prefer the low to mid snappy torque in the EX for trails.

If I wanna go fast like a dragster I'll jump on my Can-AM DS450X. Good luck with your build up!

[BenHonda400ex]

So I have a question, what's the biggest piston you can but if you have a stock bore? Or what's the stock piston?

[grassman]

85mm stock
86mm 406cc
87mm 416cc
88mm 426cc
89mm 440cc... requires resleeving

88mm is the biggest bore you can go with stock sleeve...

[400exrider707]

Good choice, you'll be happy with the 11:1. I think with a 10:1 you wouldn't notice much difference.

[vinson581]

i dont mean to highjack this i picked up an ex with a bad head gasket, upon pulling the cylinder the walls look absolutlly perfect with no ware on the piston or cylinder walls, can still see the cross hatching...do you think its even worth me putting in my 11:1 416 (already had it from years ago), or just save the bore for when the engine wears out and throw in a stg 1 hotcam for the meanwhile? i feel like i have the motor apart and i want to do it but at the same time, the engine is perfect so why tear up 2 bore sizes by going to a 416...

[grassman]

I always said I wasnt gonna mess with my engine until it started smoking... that was 3 yrs ago and still no smoke. So I said f-it and decided to just do it. Its really up to you if you want more power... then go and make it a 416. From what I hear and read a 416 is just as reliable as stock. I would if I were you since you already have the piston... $.02

[DragonGunner]

Originally posted by vinson581
i dont mean to highjack this i picked up an ex with a bad head gasket, upon pulling the cylinder the walls look absolutlly perfect with no ware on the piston or cylinder walls, can still see the cross hatching...do you think its even worth me putting in my 11:1 416 (already had it from years ago), or just save the bore for when the engine wears out and throw in a stg 1 hotcam for the meanwhile? i feel like i have the motor apart and i want to do it but at the same time, the engine is perfect so why tear up 2 bore sizes by going to a 416...

If you do regular oil changes, your going to be waiting many years waiting for the stocker to go south...either bored it for your 416 piston....OR, buy a 11:1 stock 85mm piston an put in it.

[vinson581]

looks like i will go for putting my piston in! its basically free power, while i had the head apart i just changed the valve seals (to be safe) i dont really need more power lol, ive got a fully built motor in my yfz450r thats my speed bike, i just figured ey why not, its such a nice piston to sit in a box :macho, so just to re-cap no head studs are needed with the 11:1 416, going with cometic gaskets, and a stg 1 hotcam, still have to sort a pipe out most likely will be a sparks x6 as thats what i used to run on my 400 and loved it.

[CJM]

You will be much happier with a stage 2 hotcam in a 416, stage 1 tends to trail off to much. in a more power engine.

headstuds arent needed but arent a bad idea either.

[vinson581]

hmm i appriciate the imput! doesnt the stage 2 hotcam require changing the springs? not a big deal as i can change them myself in under 15 mins but figured i should know the correct answer before i swipe my card lol

[CJM]

Nope, you can run it stock.

Its a much better setup for a bigger bore engine b/c like I said earlier the stage 1 is more for low to midrange power and trails off when your really goosing the throttle. Stage 2 (least for me) gave all around power and then some.

[vinson581]

well it looks like stage II it is then!

mods are as followed

Sparks full exhaust
Uni filter, no lid
416 11:1 piston
Hotcam Stage II - per your reccomendation
Clean up port on the head
(i have an fcr, dont know if it will go on or not)

[CJM]

Pretty much what I have done minus full exhaust-I got a slip on and this sucker hauls compared to a stock EX and hangs with the 450s pretty easy.

[vinson581]

yea i would assume so, and to tell you the truth i believe you when i used to race motocross, i had a 400ex with full suspension, tires.beadlocks, and just a sparks slip on, and uni, 42 pilot 155 main, and used to holeshot 450s that were fully built back when they came out in 04, and to prove this theory, one of my buddies jumped on my ex, on pavement and raced a ported, cammed full exhaust yfz450, and pulled him till the middle of 3rd, pretty impressive for that air cooled 28 hp honda!

^ that right there is what made my buy another 400ex, i ride a built yfz450r right now, it makes 53hp on the dyno, but honestly i have more fun on a 400ex any day of the week, plus i can put 1000000 hours on it and not have to touch the engine ever. one of the best bikes ever built imho!

heres my old one :( wish i never sold her..

http://i20.photobucket.com/albums/b206/vinson581/P9210031.jpg

[CJM]

Very nice!

Im not sure what it is about the EX I like so much. Maybe its the fact it doesnt need to rev out to make some good power like so many of the 450s do, maybe its cause its simple, maybe its the fact you can do so much to them..idk.

Back when I got mine used 450s were still 5-7k for a good decent used one and 400s were 3k and up. I scored mine all beat up for 1500 bucks and it needed minor junk.

[vinson581]

not bad at all, i just picked up this for 1000$

http://i20.photobucket.com/albums/b206/vinson581/2011-03-15_17-51-16_238.jpg

it needed axle bearings, other then that its super low hours, the paint isnt even worn off the cases!

i already had full skid plates from my other bike so those went on, along with a billet bearing carrier i had from east coast atv, i plan on putting my shocks, a-arms and axle on from the old bike as well. so all in all i have a setup bike for around 1000$ i got lucky and saved all my old parts from my old ex, i knew someday i would be building another one!

[CJM]

Very nice, thats a steal for a g note!

[grassman]

It was driving me nuts about having a stage 1hc with the 11:1 piston so I went ahead and bought a stage 2 hc last night...Now hopefully I will really get the power Im looking for... next will be the 450r carb ( just bought a adapter from zrpilot) and some head work. Im sure after that there will be something else... there always is:rolleyes: a.a.d.s is a very addictive and expensive disease...

[jstalnaker]

it never stops :D :D :D

[CJM]

^ Indeed.

Even when you think your done-you find something else you want to buy or do. But its fun!

[tri5ron]

Originally posted by CJM
^ Indeed.

Even when you think your done-you find something else you want to buy or do. But its fun! Haha,.... So did you order that puck yet ??? :D :D :D

[grassman]

GOT IT!!! Now I just have to schedule a time with my mech to put it all together...

[whc]

i have a 416 with a stage one hot cam 11 to 1 comp and have to run 100 octane to eliminate all pinging when riding hard.

[CJM]

Originally posted by tri5ron
Haha,.... So did you order that puck yet ??? :D :D :D

With what money Ron? I did nab a CFM oil tank that should be coming soon-couldnt pass up 50 bucks vs 100-120.

Summer comes and I get a job its puck stabilizer and shocks among other stuff lol

[sneaky11]

Originally posted by whc
i have a 416 with a stage one hot cam 11 to 1 comp and have to run 100 octane to eliminate all pinging when riding hard.

That's what I thought too!! thanks for sharing

[CJM]

Not sure why you guys need 100, if anything its not properly jetted.

I run 93 all day long with no issues at all.