Cc check question?

[53003jason]

On a green plate motor I did a cc check on the motor it came out to 27.5 cc. Do you think I should try and get a little closer to the 26.5? There has been no machine work done to the head and it is .008 piston in the hole. Thanks Jason

 

[shoestring19]

Thats close. What head gasket thickness do you have? .009 is the thin gasket. 1cc is about the area of the spark plug hole. (Bottom of the threads to the top).

 

[older n dirt]

I get ours down to a close 27, leave some room for carbon build up.

 

[youngengines]

I have to say, one of my best engines left at 27.5cc..

 

[older n dirt]

I have to say, one of my best engines left at 27.5cc..

I would not disagree with that !

 

[PCMotorworks]

x3!

 

[Morton21]

I wouldn't push the issue. There is better places to gain HP in these engines. All it takes is a tech that doesn't quite understand how to do the CC check and you can be tossed if its to close.

 

[53003jason]

I wouldn't push the issue. There is better places to gain HP in these engines. All it takes is a tech that doesn't quite understand how to do the CC check and you can be tossed if its to close.

Where are the better places to find Hp in these engines?

 

[Morton21]

Cam and carb for starters.... can't give it all away. ;-)

 

[DynoDon]

Cam isn't as big of an issue as everyone makes it out to be. Unless you know how to tweek what is on the market. But carb and head are big issues. With the new shim rule you may be able to help the spring pressure on the one you have but, if you have a head that doesn't flow very well you may want to look in that direction. Also where is the engine timing? sometimes just moving the timing will aid in H,P. There are way to many variables for us to tell you what to do.

 

[alvin l nunley]

Where are the better places to find Hp in these engines?

Compression is the Holy Grail!!
More is always better. But it doesn’t take much carbon build up to get you under on the CCs.
You want other places, how about jetting. Going from a .039” to a .040” jet is more than a 5% change in area. If the air density changes 5%, that’s just what you need, but what about all the steps between, or over. And who has ever flow tested their jets? I’ve never heard of anybody doing that!
I was part of a team building a rocket engine for Bob Truax. We had 200 jets made and we flow tested them. Even thou they where made with high precision Swiss CNC laths, there was a big difference in flow. We tested every one of them and found a huge difference between them. Well, huge as far as rocket engines go.
It would be interesting to see flow tests done with these jets that are “drilled” out for use in karting.
Comments, compliments, criticisms and questions always welcome.

 

[Morton21]

Let me add to what i said... If you have your engine set at 27 cc so you know it will pass tech each and every time. Its not gonna hurt you as much as having a bad carb, bad head, piston rings not right, etc..

 

[53003jason]

Cam isn't as big of an issue as everyone makes it out to be. Unless you know how to tweek what is on the market. But carb and head are big issues. With the new shim rule you may be able to help the spring pressure on the one you have but, if you have a head that doesn't flow very well you may want to look in that direction. Also where is the engine timing? sometimes just moving the timing will aid in H,P. There are way to many variables for us to tell you what to do.

Don,
Where would I need to look for altering the cam? I dont think I can change the cam timing without turning the crank gear, which I dont know how to do. Also the ignition timing is set to 32 degrees I have a new ARC flywheel that has the 8 degrees built in. I am going to put a test light on it to confirm after break-in.
Thanks

 

[astrowrench]

I Think knowing where the timing IS NOW would be kinda Important; BEFORE break-in, Or even Starting the engine

 

[DCutshaw94]

Our best motors have between 26.9 - 27.3, compression definitely helps but only to a point, after some point you will only be adding heat but not making any more power, at least from my experience, everyone is right, there are plenty of other places to make more power

 

[alvin l nunley]

Our best motors have between 26.9 - 27.3, compression definitely helps but only to a point, after some point you will only be adding heat but not making any more power, at least from my experience, everyone is right, there are plenty of other places to make more power

It is true, too high a compression reading can hurt, but only because of the fuel. You can reach a point where even the highest octane gas will detonate, and it’s the detonation that kills the power.
The TT75 pumps right at 210lbs of compression and they run fine on the highest octane fuel.
Comments, compliments, criticisms and questions always welcome.

 

[jdg]

Compression is the Holy Grail!!
More is always better..
Comments, compliments, criticisms and questions always welcome.

Can we see your data that backs this up? How many of these engines have you built? Its easy to make blanket statements like this without providing data or anything to back up what your saying.

 

[Kart43]

Thats close. What head gasket thickness do you have? .009 is the thin gasket. 1cc is about the area of the spark plug hole. (Bottom of the threads to the top).

If your statement is intended to say the volume of the spark plug hole is 1cc, I think you will find it is closer to 3cc
(2.8cc)so if you are leaving a complete spark plug hole of volume you are leaving a lot of potential on the table. If you get to 27cc you will be plenty safe if you are using up .5cc of space for carbon, you need rings, valve guides or change the type of oil you are using.

 

[Kart43]

Can we see your data that backs this up? How many of these engines have you built? Its easy to make blanket statements like this without providing data or anything to back up what your saying.

I know you are quoting Al, but it is simple fact that an increase in compression in these engines does make an improvement. These come from the factory with a stated compression ratio of about 8.5:1 and that varies drastically from engine to engine. When the sanctioning body allows me to equalize and optimize my engine at about 8.39:1, I am not going to pass it up, neither will the other competitors who are serious about the game.

 

[DynoDon]

Don,
Where would I need to look for altering the cam? I dont think I can change the cam timing without turning the crank gear, which I dont know how to do. Also the ignition timing is set to 32 degrees I have a new ARC flywheel that has the 8 degrees built in. I am going to put a test light on it to confirm after break-in.
Thanks

You would need to set a degree wheel up and degree the cam. along with that you need previous knowledge of cam profiles to see if yours was or is tweeked.