When adding ported heads or milling them you effectively increase the compression. This should mean that you are sucking more air into the combustion chamber and thus more air (with the correct amount of fuel) is more power. However, if you go too high with the compression you get detonation, KR.
My question is, is this correct so far?

If so, wouldn't the 5.3L heads, ported with an appropriate cam be the most economical H/C setup one could go with?
What is the max compression, on pump 92-93 gas that a stock 346 CID motor, such as ours, be allowed to manage? Thanks.

[ February 04, 2002: Message edited by: NastyC5 ]</p>

 

I will defer to the experts on this board to tell you how high you can go. However, one thing that is going to affect how high you can go is cam selection - the bigger and more overlap, the higher you can likely go (that static versus dynamic pressure thing).

 

You aren't sucking more air in - you are just taking the air/fuel charge and compressing it into a smaller package. this results in a faster burn and a greater pressure delta - so you make more power.

compression is always good -generally you want as much as you can get without getting into abnormal spark conditions - but since situations always change sometimes it's better to play it a little safe.

Chris

 

[quote]Originally posted by ChrisB:
<strong>You aren't sucking more air in - you are just taking the air/fuel charge and compressing it into a smaller package. this results in a faster burn and a greater pressure delta - so you make more power.
Chris</strong><hr></blockquote>

Thanks for the clarification. I'm leaning toward 5.3L heads becuase they are cheap to get and can be made to flow VERY well and up your compression quite a bit!

I'm just trying to gauge the most compression as this is my daily driver and I don't "random misfire codes", having to let the car warm up for 10 minutes before it will run properly, replace springs every year and a half, etc.
I want around 400+ RWHP with H/C/I/Und Pulley.
Just researching so I come to an educated decision. Thanks again, Chris.

 

[quote]Originally posted by NastyC5:
<strong>

Thanks for the clarification. I'm leaning toward 5.3L heads becuase they are cheap to get and can be made to flow VERY well and up your compression quite a bit!

I'm just trying to gauge the most compression as this is my daily driver and I don't "random misfire codes", having to let the car warm up for 10 minutes before it will run properly, replace springs every year and a half, etc.
I want around 400+ RWHP with H/C/I/Und Pulley.
Just researching so I come to an educated decision. Thanks again, Chris.</strong><hr></blockquote>

In simpler terms, same air and fuel but a smaller space. About the safest max compression for an LS1 head is 10.7:1 which with the right cam, exhaust, tuning, etc. etc. can get you over 400 RWHP.

- Mitch

 

Thanks, MitchR. <img src="graemlins/gr_cheers.gif" border="0" alt="[cheers]" />

 

You can't really specify a static compression that is "safe max" except with one specific setup. What really matters is your dynamic compression - which is going to be greatly effected by camshaft choice. A larger duration on the intake is going to bleed off more compression. A wider LSA will also bleed off more compression, a narrower lsa will increase dynamic compression. You also have charge quality, and increased overlap will dilute this charge, causing you to not get as high of a pressure/temp delta out of the combustion.

It's all going to be relative, but with a smaller cam (say 216-220) I would probably be looking for right at or under 11:1, and as you get larger you can probably add in more compression. Some of the bigger grinds (226/234, 114) etc. would probably be perfectly happy with 11.5:1

Chris

 

My car is having other issues, but I am running 11.4:1 with my T1 cam. So far no KR. I switched to TR6's and put water wetter in to avoid any detonation..

 

I know of a combination that was 11.7:1 229/229 combination and made GREAT power on pump gas. Safely I would go 11.3 to 11.5 for cams 222/222 or better. Cylinder head efficiency plays a large factor in what is safe. An old cast iron chevy head with a poor spark plug location and very little swirl/tumble will be very inefficient and thus prone to detonation. There tends to be hot spots in the chamber etc. With a highly efficient design such as the LS1, with excellent motion in the chamber, you can safely run higher compression ratios. Many people don't realize this but the compression ratio is very important for cam selection. Larger cams need the compression to run good because they bleed off so much pressure.

Generally a point in compression increase (alone) is good for about 2-3% more power. And fuel economy is also increase!

 

Thanks Scott.. So far the T1 is holding its own with 221.. If I go bigger cam I will up the compression.. <img src="gr_stretch.gif" border="0">