Combustion chamber size of various heads?

[Eric Fischer]

I searched the forum but didn't come up with the answers.

I need to know the cc's of the combustion chambers for:

1) Stock Sy/Ty heads
2) Vortec heads

and for completeness might as well throw these in:

3) L35's

Feel free to add others to the list if you know them...

Thanks,
Eric

 

[jwaller]

68 or 67 on stock and L35 and 62 or 63 depending on valves size for vortec's

 

[Lynn D. Brown]

CC cc

CC cc

John & Eric,

So, does that mean that the Compression Ratio will be higher w the Vortecs ?

 

[jwaller]

YES unless you do something to account for it. ie flycut the pistons or order a larger dish.

 

[Lynn D. Brown]

CC cc

CC cc

I will have 8.5/1 pistons in my rebuild. Assuming that all of the cylinder volume is in the combustion chamber, then the Vortec Heads would raise the CR to ~ 9.3.

I guess this brings up the old arguement - Do we want more CR and less Boost, or more Boost at lower CR ? The bottom line is Cylinder Pressure as far as making Power - U get this by adding Boost P on top of the already existing static pressure. So, the question is - how much of each ?

The main advantage of higher CR is that the engine is more powerful and more efficient @ higher pressures, and a gradual rise in the CR has been the ongoing goal thruout the history of automotive engine design. This has been made gradually possible due to evolutionary improvements in engine design, machining accuracy, metallurgy and materials technology and gasoline quality (octane, etc.)

So, any car runs better at higher cylinder pressures. Some of the prices to achieve this are the need for higher Octane fuel, higher combustion temperatures and increased tendencies for destructive detonation. More Power means more Fuel and more Heat.

One advantage to achieving the pressure with more Boost is that the additional heat generated can be partially removed by the additional cooling that can be made available by Intercooling with ambient air. Whereas with higher CR's, the volume of water and the capacity of the cooling system are unchanged and therefore can be no increases in cooling capacity.

The main advantage in higher CR's is that the naturally aspirated engine (w/o boost) is more powerful and efficient. So the part throttle and spoolup performance should be better along with normal road performance. U have higher Octane needs but then most of us use Premium anyway because of the boost. So, U will make better use of the Premium gasoline that we pay more for.

I guess there R 2 schools of thought on which way to go. For instance, Kenny Dutweiler likes lower CR's and Lawrence Conley tends to like higher ones. For racing, I think most engine builders like lower CR's. However, I am street 1st, so I tend to like higher CR's.

 

[leroy]

My primitive concept is we need to prevent detonation.

The vortec heads have a much better design. The better design alone would probably allow a higher compression ratio.

While rebuilding, try to get quench between .035 and .040. This will also help prevent detonation.

After that, it's time to do some calculations for compression ratio. Combustion chamber volume, bore, deck height, compressed gasket thickness, and the volume of the piston dish need to be accounted for. Different head gaskets and pistons are available to achieve the desired compression ratio.

I'm sure John Waller or others could elaborate.

Jim

 

[Eric Fischer]

Re: CC cc

Re: CC cc

I will have 8.5/1 pistons in my rebuild. Assuming that all of the cylinder volume is in the combustion chamber, then the Vortec Heads would raise the CR to ~ 9.3.

Not sure where you are getting these figures from but by my calcs, a decrease in combuster chamber volume from 67 to 62 would only increase your CR by 0.4

I guess this brings up the old arguement - Do we want more CR and less Boost, or more Boost at lower CR ? The bottom line is Cylinder Pressure as far as making Power - U get this by adding Boost P on top of the already existing static pressure. So, the question is - how much of each ?

Well, I have been struggling with this too that's why I asked the question about the combustion chamber size. However, in my case, my CR may wind up to be around 9.1:1 (for a variety of reasons). I know with the stock heads, that would be a no-no, but with the Vortec's I am not sure....

 

[Eric Fischer]

While rebuilding, try to get quench between .035 and .040. This will also help prevent detonation.

Jim

This is difficult to do on Chevy blocks since most piston designs leave the piston in the hole by 0.025". Of course you could deck the block by that much, but that could introduce some alignment problems with the intake. Another option would be custom pistons but that gets expensive. Unless I am missing something here. Are there aftermarket pistons that provide near zero deck height??

 

[leroy]

While rebuilding, try to get quench between .035 and .040. This will also help prevent detonation.

Jim

This is difficult to do on Chevy blocks since most piston designs leave the piston in the hole by 0.025". Of course you could deck the block by that much, but that could introduce some alignment problems with the intake. Another option would be custom pistons but that gets expensive. Unless I am missing something here. Are there aftermarket pistons that provide near zero deck height??

The block should be decked. There seems to be a lot of variation between deck heights on stock engines (even between cylinders on the same engine!) I've not seen any additional problems with intake alignment. The vortec intakes have to be somewhat customized anyway.

Jim

 

[Stuka]

Vortec, 65CC all.

 

[nightdiver]

Pontiacs 68-69cc (just did the water thing)