Combustion chamber cc variance

[Caprimaniac]

G'evnin', folks.

Searched "combustion chamber" in tech- section and found no good matches on the 16 pages/ 132 hits.

For a 50cc Chamber set of V8 heads- what varaiance in cc would be acceptable? is 0.5 cc +/- OK?

Will be around 12.5 static, 9000 rpm dragrace motor.


I might have some litterature on the subject, but right now to lzy to look it up.

Ok to let out some FRUSTRATION as well? Using Google one some subjects I'd like to read up on, gives some links to HOTROD articles- which are OK to good reads, for the most. However: for me, over in europe, there are some legal rights that makes the website unreachable. Heck; you get redirected to something called "motortrend" where I find little value.

[MadBill]

You'll probably get some disagreement on this, but unless you're building to a class limit or racing in a very competitive one where no stone may remain unturned, I'd say that's more than close enough. It will likely result in less than 1/10 of a ratio variation and will be lost in the 'noise' of cylinder-to-cylinder SA needs, AFR, airflow variation, etc. For more info than you probably want, check out this vid: https://www.youtube.com/watch?v=rBZCnG1HwDM

[BOOT]

If one was larger than the other 7 would you enlarge the others to even them out? I mean in a perfect world everything would be equal but how many other slight variances throughout the engine cylinder to cylinder are there? I've always felt people get caught up in making all the chambers equal because it's easy, kinda like gasket matching. Of course if you can deck the head back to your desired CC but maybe now again one or more is now not the same CC because the chambers aren't consistent in shape or your didn't remove material in the same exact places. Plus some say over decking hurts flow?

[makin chips]

I found this one. Not sure how helpful it will be.

http://www.speedtalk.com/forum/viewtopic.php?t=32365

[Caprimaniac]

Good info there, chippers.

Fine- seems we all agree it’s close enough. 2% chamber variance will be less than 1% in compression.

Edelbrock casting. After pollishing the chambers showed 48-51,5 cc. Spent some time removing mass in the smaller chambers, did some testin, pollished and ended up 50,5- 51,5cc. They were supposed to be 47cc from the factory...

Some bad coreshift in the runners, so not surprised by the large spread in chamber cc.

[mag2555]

1/2 a CC is more then fine in my book, especially if you don't want to get into the crap of looking at how cylinder firing temps can effect the expansion rate of the valves and then in turn the CC volume!

You can never guarantee equal cylinder firing temps due to a normal unequal fuel to air ratio between all the cylinders, and that has a far greater effect on the ultimate cylinder firing pressure per cylinder then a 1/2 a CC difference in chamber volume!

Also I don't polish chambers any more it's a wates of time unless they are very ruff, or there are sharp edges left around the spark plug holes or around the valve seat incert I leave it as is.
Lightly ruff surfaces help break up wet flow globs of fuel just like we use in regards to the Intake runner surfaces!

A well built race motor should have no carbon build up to make for hot spots, and if you want to lock in more power you should get the chambers and piston tops coated to retain the heat in the chamber as a polish job really does not do that all that well.

[David Redszus]

You'll probably get some disagreement on this, but unless you're building to a class limit or racing in a very competitive one where no stone may remain unturned, I'd say that's more than close enough. It will likely result in less than 1/10 of a ratio variation and will be lost in the 'noise' of cylinder-to-cylinder SA needs, AFR, airflow variation, etc. For more info than you probably want, check out this vid: https://www.youtube.com/watch?v=rBZCnG1HwDM

Its nice to see that MadBill can do complicated calculations in his head.

For a typical 350 cuin, a change in chamber volume of 0.5cc would result in a static compression change of 0.09 ratio
(12.54-12.45), a TCR change of 0.06 ratio and a peak compression temperature change of 3.0F degs (821F-818F).

Accurate compression measurement will vary by far more than indicated above, due to variations in valve timing, induction flow, inlet temperature and sealing. Compression will even vary from stroke to stroke.

[makin chips]

G'evnin', folks...


Ok to let out some FRUSTRATION as well? Using Google one some subjects I'd like to read up on, gives some links to HOTROD articles- which are OK to good reads, for the most. However: for me, over in europe, there are some legal rights that makes the website unreachable. Heck; you get redirected to something called "motortrend" where I find little value.

Motor Trend owns HOTROD MAG. That's why it's all under the same banner. You'll find Roadkill, Hot Rod Garage, HotRod Magazine, and all sorts of stuff at Motor Trend.

[Caprimaniac]

OK- so when you follow the link, you get the motortrend page, and then you have to look up that article there? That’s very time consuming, if that’s the case. I’ll rather not follow that link and look elsewhere.... Too bad they get less hits, then