5abivt

I'm about to choose a new cylinder head. Question is what effect does chamber volume have in the cylinder head when altering piston domes to keep the CR the same. that kinda sounds confusing but what i'm asking is does having a larger chamber volume help airflow around the valves?

I'm choosing a new head and getting ready to order custom pistons anyways so I was wondering which i could alter for the desired CR if it makes any impact on performance etc.

cardo0

The tighter/smaller the head chamber volume shoud be the better. Better combustion/performance with as much of the volume as practical in the piston/cyl rather than the head chamber - BTW an advantage of wedge type heads compared to hemispherical head chambers when using high compression. And the step dish piston promotes better combustion than regular dish (if there is a regular dish) or flat top or dome.

Hope this helps ya',
cardo0

5abivt

It does help. thanks for the reply ! Reason I'm asking is because the new 210cc AFR eliminator heads only come in 65 cc. the Stock LT4 heads I am using are 53 or so. I have heard larger cc heads will help flow #s on a flowbench. So I was wondering if that is helpful to use larger cc heads on a motor and have the piston make up the compression lost with a dome or whatever.

427Hotrod

It's not just the cc's. It's the shape. You can easily have a head that is much more open around the intake valve, yet is tighter on the quench and plug sides of chamber to keep CC's low. The more modern designs are that way.

You generally want as much room around intake valve as possible.

If you get real serious you can have custom pistons made to exactly conform to heads. You ship heads to them, they trace them and cut piston to exactly match chamber. It's done all the time with flat tops and dome pistons. There are even shelf pistons already designed for particular heads.


You can always angle mill heads to reduce cc's...but you need to have them re-flowed afterwards. Usually angle milling helps airflow..but sometimes it hurts...you never know until you test them.

It all depends on how much compression you're shooting for. You can get quite a bit with a real tight quench and the proper pistons.


JIM

cardo0

I recall it aids volumetric effeciency - the tigher head chambers. Something to do with a larger head chamber leaves more spent gases inside than a tighter chamber given that more volume is cleared by the piston stoke and less volume to trap spent gasses.
Now for positive pressure engines (turbo, supercharged) the larger head chambers provides greater a volumetric effeciency due to the larger static volume availible for fill and spent gases are forced out by the positive pressure. Yes interesting the positive pressure relationship is opposite than for natural asperated motors and the larger head chambers are the better.
Now to confuse u even more at the high compression ratios (natural asperated c.r. >13:1) will reduce the volumeteric eff, but this is due to the smaller volume to fill with A/F mixture for a given displacement. Something like the higher c.r. has less fill vol availible for same displacement even though the higher c.r. increases the eff of A/F mix itself.

And yes its true you want to unshroud the vlvs as much as reasonable but just look at phase 6 bowtie - or what ever they call them now - race only heads from GM performance parts. NASCAR/SB2 heads have 45-48cc chambers and there's some 15* heads with only 35-37cc chambers from the General.

Well i guess to have to use what best fits your application.

Good luck,
cardo0