View Full Version : Heads for Dummies


USMC5811
08-13-2012, 08:11 PM
Could someone break down the specs on a set of heads? I'm not sure what the 59cc refers to or the 250cc refers to in a set of heads. or the ange degree 13, 16 etc. Or the flow charts listed under a particular set of heads. Just want to know what i'm looking at when shopping! thanks for the info!

djfury05
08-13-2012, 08:26 PM
59cc refers to the amount of volume the combustion chamber can hold.

This is the combustion chamber.
http://image.carcraft.com/f/techarticles/9168001++w750+ar1/116_0412_08_z+gen_III_head+ls1_combustion_chamber. jpg

250cc refers to the intake port runners measured in the same fashion. Filled up and measured with the valves closed. Exhaust ports same way.

Intake Runner.
http://image.gmhightechperformance.com/f/8989789/0607htp_04_z+ls1_heads+intake_runners.jpg

Exhaust Port.
http://www.ls1howto.com/howto/fbody/heads.cam.pulley/pics/exhaustport.jpg

As for the valve angle I believe it is measured in reference to the piston at TDC but I'm not certain on that. Different valve angles account for better flow and different characteristics of how the combustion process happens.

Flow numbers don't mean shit. Go by real world testing when looking for heads. A lot of companies skew the numbers and use pipes on the flow fixtures to inflate numbers. I had a set of 243s and they didn't flow over 300cfm on the intake side yet I ran 125 mph in the 1/4 and made more power than most LS1's with larger heads.

Did any of this help at all lol?

garygnu
08-13-2012, 09:53 PM
valve angle refers to how many degrees the valve stem is off from perpendicular with the block deck.the fewer degrees the better flowing in most heads.

USMC5811
08-14-2012, 07:33 AM
DJFURY- your the man! thats exactly what i needed lol but now i have a few follow up questions....

does the bigger the combustion chamber always mean better?
same for the intake runner/exahust?

conan
08-14-2012, 08:01 AM
No, the bigger the combustion chamber the less your compression ratio is.

I run the 317 casted head witch has a 72cc cumbustion chamber, this droped my compression down about 1/2 point. So now I'm around 9.4:1 from 10:1 compression. Stick a 59cc head on your moter and you'll start to bump the compression up to the 11:1 mark. This is all with a (stockish style) flat top piston.

Big combustion chamers = lower compression ratio, good for forced induction bad for a N/A motor.

For a N/A app you would want to bump up the compression, just watch the smaller cc combustion chambers heads can cause you piston to valve clearance problems depending on how big your cam is.

USMC5811
08-14-2012, 12:46 PM
what should be a good goal Compression for an NA car....

also, im okay with a smaller cc chamber as long as my pistons have some valve relief in them for the cam correct?

conan
08-14-2012, 03:08 PM
10.5:1 - 11:1 would make for nice throttle responce on the street (93/94 octane). If your pistons have valve relief in them that will give you some extra PTV clearance.

Do you have heads/cam yet or are you going to be ordering a package soon ?

djfury05
08-14-2012, 03:52 PM
Valve reliefs in the piston will also decrease the static compression ratio

garygnu
08-14-2012, 06:52 PM
pick the cam last .you need a certain static compression to work with cam to create a certain dynamic compression,which dictates what gas you use.

USMC5811
08-14-2012, 06:55 PM
10.5:1 - 11:1 would make for nice throttle responce on the street (93/94 octane). If your pistons have valve relief in them that will give you some extra PTV clearance.

Do you have heads/cam yet or are you going to be ordering a package soon ?

im ordering the 408 assembly this week and while its being assembled to my new 6.0 iron block i'm going to order the heads/cam

USMC5811
08-14-2012, 06:57 PM
pick the cam last .you need a certain static compression to work with cam to create a certain dynamic compression,which dictates what gas you use.

yea i'm going to have Pat G custom grind me one once i get everything else in place.

garygnu
08-14-2012, 07:56 PM
you can get stock unported l92 heads SDPC for $375 each.ported l92 from TSP look like a good deal.big block power from 408 ls motor ,cool.