CR80 compression

[BenchRacer]

Hello i'm running an AR-4 chassis with a honda cr80 set up. I'm just trying to find a good base line on what the compression should be. I dont want to pull it apart if i dont have to it seems to work good but it also seems like other 80's are hitting harder motor wise ? Anyone know what the stock compression is on these engines. I have heard anything over 125 psi and your safe. And from my other posts the tag worked great i had no issues with the chain and gears. Thanks in advance for any info.

[Marc Miller]

Hey Bench,

Stock compression ratio on the CR80 is about 8.4:1.

Not sure what they equates to, but I know companies like Swedetech o-ring the heads to run more compression safely in the 125's.. not sure about the 80's.

[Noah Stark]

This is a touchy subject, especially coming from someone who has tested over and over again different compressions and porting layouts. Anyways, I dont really like testing compression with a PSI gauge. You must have the motor hot and spin it over extremely fast for a good read. The only real way to know what you have is to cc the head. All of my best motors run better with lower compression. 80cc, 125cc, or 250cc regardless. More compression does make big and easy power gains, but presents alot of new issues.... many of which you dont want. If you need more power, dont look to more compression, but focus more on the tuning of the pipe, carb, reeds and ignition to what you have. This will ultimately make more power and it will last longer and cost you alot less $$$ both initially and over the long run.

FWIW: Michael and I's stock hondas both went low 2:17s at Daytona. Both right at the stock 11.4:1 compression ratio. Both of us won and set fast times. I also had a full mod customer run at the front and set a fast time of his class also at a low 2:17. His motor is set at a tad under 13:1 compression. How is it that us with motors making 10 less horsepower than the mods can run just as fast or faster than them? Its all in the tuning and maximizing the package. I have built numerous motors in the 17-18:1 compression ratio area that did make more power on the dyno, however the useable power and tuning range makes them pretty much junk and much slower. Compression(engine) braking is also a big factor even though it doesnt seem like it.

I do have a customer that runs at Circleville with a pretty much all stock cr80 and runs just as fast or faster than some of the guys with 3x more money in their package. Point is more power isnt always better. The guy with the most usable power will always win. Ever wonder how ICC's are faster than cr125s? They are all suprisingly low compression....

[BenchRacer]

All good info thanks. yea i'm getting 188 to 190 for the psi from dead cold and i just spun the engine by hand with the throttle wide open. I'll gauge it again at the track when it's hot. I'm not going for a full mod moto i just wanna catch it beofre i chew up the cylinder. I have no clue what has been done to the engine i bought it used and i guess for now if it aint broken i'm not going to fix it. I'm also hearing honda doesnt rate these engines in terms of hours they say something like 1500 miles on there stock motos.

[Noah Stark]

Feel free to shoot me a email or give me a call and I'll help you as much as I can. 180-190psi cold sounds pretty good and high, so I dont think theres anything wrong or worn up top. Just might need some more tuning or just doesnt quite have the porting and properly matched components like the other racers. Where abouts are you located?

If the motor is stock, i can see 10-15hrs on a piston and ring before you start to see a noticeable loss. If its full mod, about 2hrs before you see a loss and it will be a big drop off. Stock bottom ends will get 35-50hrs and mod 10-12.

412-335-6671
nsewracingengines@hotmail.com

[BenchRacer]

I'm in socal Nearest track is perris Apexraceway. And oh yea i put more than 2 hours on it last time out so it's most likely stock. It's been the most trouble free kart for me yet so i just wanna keep it alive. Forsure when i rip it apart i'll get in touch for know i'm just going to put another 2 or three hours on it see what happens. And i'll get a read hot at the track see what hits on the compression

[Noah Stark]

Sounds good. Again compression via psi isnt my favorite way of checking. If you just have different stiffness reeds, it will give a different reading. Does changing your reeds change your compression, no... but it will give a different reading. Anyways, do this. Pull the pipe off and use a flashlight and look in the exhaust port at the piston. You can easily see the side of the piston. Look for blowby directly under the ring. That will tell you the most about the age and condition of the top end without tearing anything apart.

[BenchRacer]

I pulled the pipe theres is a fairly even line just under the ring all the way around maybe about 1/8inch. Nothing comming down the skirt. There no build up on top of the piston and all i use is caster.

[Noah Stark]

The ring is just starting to let go. You will see the power start to drop off gradually now little by little. Castor is the best oil to make top ends last longer. Synthetic oil will make a tad more power and protect the bottom end more, but the piston and ring will show signs of wear faster.