Does the aftermarket high compression heads put to much stress on China engine?

[SlugMan]

Hello,
I'm thinking about getting a high compression billet head for my Gumbee 66cc engine, but I'm conserned that it will cause the engine to prematurely fail... These engine are cheeply made... Thus, my thinking tells me not to upgrade to a higher compression, because it would put to much stress on the lower parts of the engine (connecting rod bearings, etc.)
I'm trying to build a bike that has a good reliability, and some performance upgrades. (I know, I should of bought a better engine ) But, I'm trying to work with what I have at the momment (First bike build).
What is your experience with this subject?
I have a new SNH 15.15 carb and Billet intake on order, plus a CDI / KX80 Coil to upgrade the timing.
Thanks for your help

 

[motorpsycho]

a Gumbee engine?
does that fit onto a Pokey bike?

 

[SlugMan]

It's the Grubee SkyHawk Silver 66/80cc. Sorry about the Gumbee thing Haha

 

[Ixlr8]

hi, its not necessarily the mechanical compression that is the main concern. Its the actual pounds that it creates. Most of my china engines run about 70-90 pounds. But I have one that has 210lbs. This was accomplished with a higher dome piston. milled cylinder and a billet radial head to get rid of the heat.

Higher compression does equal more heat. I know some may argue this point, but should know. Its rpm that kills. Unfortunately its also is what makes horsepower. By this I mean real horsepower. For the most part more compression will equal more lowend, midrange and top end, also increases throttle response and gas mileage

This is of course if there isn't detonation going on . detonation will kill it fast!..BTW I use a mixture of premium and small aircraft fuel.

 

[Skyliner70cc]

IxLr8, would love to hear about your 210 psi compression engine....please start another thread on that engine.

Slug, both of my current bikes have slant head engines with no issues. I wouldn't own anotehr HT engine unless it had a high compresssion head.

 

[Schwinn-Locura]

I would imagine it would put more pressure on the crank/bottem end. On my first engine the bearings in the crank failed. That's bound to be easier if there is more pressure on the bottem end I would imagine.

 

[Deleted member 12676]

Of course it puts more stress on the bearings but life without it is unbearable. I don't advocate "high" compression, just higher compression. You can bring it up to 135psi as I have with no problem. I have 1200 miles on mine. I've bought a new rod and bearings just in case but at the rate things are going I doubt I'll have to use them anytime soon.
It's essential that you buy a cheap compression tester.
Consider this also, its at high revs that most engine stress occurs and by ordering the CDI you'll be assuring there is much less stress. That is because it retards the ignition at high revs. The stock CDI just keeps on advancing the ignition at high revs, assuring maximum stress on the bearings. Maybe that's why my ported engine, which I rev to the moon, has 135 psi and no bearing problems (because I have the same CDI on mine).

 

[fall_down_stand_up]

Of course it puts more stress on the bearings but life without it is unbearable. I don't advocate "high" compression, just higher compression. You can bring it up to 135psi as I have with no problem. I have 1200 miles on mine. I've bought a new rod and bearings just in case but at the rate things are going I doubt I'll have to use them anytime soon.
It's essential that you buy a cheap compression tester.
Consider this also, its at high revs that most engine stress occurs and by ordering the CDI you'll be assuring there is much less stress. That is because it retards the ignition at high revs. The stock CDI just keeps on advancing the ignition at high revs, assuring maximum stress on the bearings. Maybe that's why my ported engine, which I rev to the moon, has 135 psi and no bearing problems (because I have the same CDI on mine).

Can you send me the link to the site that sells those CDIs?I had it awile back but lost it....
Thanks
John

 

[Ixlr8]

skyliner70cc sorry I missed and didnt read your post till now. I will be more then happy to start a new thread about this motor.

Although higher compression will indeed cut the life of an motor shorter, but then doing anything to raise the output or rpm will do the very same thing. I personally go with the theory and use this in my own motors. and most of the high end techs now think that the extra compression can actually cushion the piston and crank. Pretty much everything I own I make turbocharged and supercharged, and to me this would go to prove that this thinking may actually be true. Word is still out on it.

Its too complicated to get into an explanation at this time to explain why..but if you would like a google search will give you a few hits.

jaguar?? I noticed you put in a plug here for your custom cdi. dont really consider it kosher..you also put in few scare tactics there..but to help you out here I do run your cdi and it does for the most part. what you say it will do, mostly just a smoother running engine and it does make it capable of using a little more compression.. but that was kind of a misleading plug.More like you bought it then you made it. and of course you know and suggest the url. its your site...have to add that indeed you do know your stuff, I have kept most of your posts for reference. And I agree , the china motors timing is way too advanced. But some of the other things as much as I do respect your knowledge I do differ in some of what you say, but then again this is the spice of life, look forward to seeing more of your posts!

 

[Ixlr8]

I will post the high compression radial head tomorrow, I have too many ****ed off people today. I do think a effective compression of 135lbs is more in the lawn motor category then a true performance one. with husky we ran what would now sound crazy compression ratios. but high compression equals better mpg and raises the response and adds to the power curve thorough out its entire range..look at the high tech morini motors..they all have comps in the area of 14 to 1..the more compression the more power in response..BUT! not if you over rev the engine and if it starts to detonate that will destroy it as fast as an escaping wrist pin clip But one thing only does not make the motor..it a carfull mixture of all the modified part together in harmony so to speak ...with all this done you should have a decent running china