I have an LT1 with stock compression and hotcam.

What does head cc mean. I mean I know its the combustion chamber volume...

but what is the significance of this..

What cc is best?

Is lower cc better for higher compression (assuming you wanted that)?

Should I try to match the cc of my current head (what is the cc of the '93 LT1 head?)

I do not know what cc head I should be looking for...

I think I want to go with AFR's or something that will yield a performance improvement....

I notice that some ported LT4 heads yield just as good or better flow numbers than AFRs.....

Does higher flow@ a given lift always translate into more power for that head, or are there other head factors...

ANy help would be appreciated.

 

Lets take a look at an example: AFR 190 Heads...68cc chambers.

Most heads are designated by their intake runner size. In the above case it would be 190cc (190 cubic centimeters)...and 68cc chambers (cumbustion chambers).

I can speak for the l98s, which had a 58cc chamber. So if you put the above mentioned AFR heads on a stock l98, the compression would be significantly lower. - you would want to have them mill them down to stock cc for you. Again not sure what the LT motors cc for the heads were stock.

For the flow you DO NOT just want to look at high lift numbers. A head that flows very little down low and TONs up top would be great for a LIGHT car, that is not run on the street. Ideally you want a head that flows super good down low, through mid range, and up top.

The best 23* heads, today, are Brodix M2 Track1s....but they are expensive, and probably are too large for you application. THey only come in 215cc ad 227cc intake runners.

The AFRs make great flowing heads, but I would try to buy them through JEGS or Summit - cause in the past they have had HUGE lead times and quality problems. Through one of these houses, you will be able to get better service I would imagine, and if close enough to one of them you can go look at them in person and inspect them, before buying.

A GREAT rule of thumb with buying heads is you want to definately error on the size of "small" with intake runner sizes. If you think that a 220cc head is going to be too large, get the 195cc. Its Always better to have a slightly smaller size than too big. Big intake ports kill velocity and that kills performance.

Heads are the #1 thing on a motor that makes power. You need air to make good power. More air, more power. The heads have to be VERY well matched to the other components to make good power.

Backing up to compression and calculations. The best calculator out there is smokemup.com. You have to register, but it calculates all the requirements for your specific engine.

For a street/strip application I would stick with around the stock compression- but again you HAVE to figure all this out with a new engine. How far in the hole the piston is, and all that stuff makes a world of difference. DON"T GUESS - it has to be EXACT.

Hope that helps.

 

If you have or will use stock pistons then to maintain the stock compression ratio you need to get a head that has the same chamber volume of around 55cc

Chamber volume is important, if you choose a head that is say 64cc then using the stock pistons your compression ratio would now be lowered by nearly a full point or more. This means you would loose power, but if the intention was to add a supercharger this would be a good thing because with a blower you need a lower static compression ratio.

Ported LT4 head will yield higher flow numbers than some AFR heads, but if you take their ported LT4 heads they have some heads that will far outflow any ported GM LT4 casting.

Larger flow numbers don't always result in bigger Hp numbers. There are other factors, first off your engines camshaft needs to be matched to the heads to take advantage of the higher flow numbers. Plus heads with big flow numbers often will not perform at the lower RPMs, heads with big flow numbers in the upper lift points are typically better suited for high RPM applications. If the engine designer was to add a blower this would offset the low RPM power issue because the low flow velocities that would tend to cause low torque and Hp at lower RPMs would be compensated by added boost pressure created by the blower.

Generally you are much better off trying to match the volume of your stock heads. Unless you are building a stroker, which in that case IMHO you are better off with a 64 to 70cc chamber. The reason I say this is because with an larger chamber, the valves are unshrouded more which promotes better air flow, you can also use a piston that is a flat top versus a dished piston, which IMHO promotes better flame propragation which reduces chances of detonation and makes more power

 

A little early for you, isn't it TJ?

BTW, good stuff so far...

Mike

 

Yah its real early for me.....couldn't sleep I think I got a load of bad chinese food last night

 

A little more :
When you go too large on the runner cc. Then you have to deal with offset rocker geometry, thus the pistons have to have different valve reliefs cut.

Then there's the tall runners which require a taller intake. This gives the air a straighter path to the valve. The straighter the path, the more power you can make at higher rpms. Example AFR 190 vs the 195.

 

If you really want to open a can of worms, try converting a set of regular 23 degree heads to reverse cooling specs ala LTx style heads. I have made that journey and let me tell you it isn't worth the headaches. I made this attempt to circumvent time because AFR has a 14 week delivery for LTx heads, and to save some $$$ as well. By the time these are done and its been a long time. The savings is lost.....