don527

If I can get people with head/cam packages to chime in, give some feedback on their h/c setup...

Who got their heads milled and upped the compression and by how much? Do you have any issues with knocking and/or pinging?
For those that upped the compression... would you be able to, for people still looking for daily streetability in a head/cam package, recommend doing it to others?

I've seen an article on compression ratios in a car mag and they tested and found that upping the compression is good for as much as a 4% increase in hp for every .5 in compression.

But my concern is, is it really a good idea to mill the heads in an LS6 and upp the compression from 10.5:1 to 11.0:1 for a car that will be a daily driver depending on varying qualities of pump gas? I know it can mean a 4% increase in hp but what about worries of knock and pinging even after tuning? I live in the east coast so I still have access to 93 octane but what about the west coast where people are posting about pinging issues on 92 octane... and that's with people with stock engines!

Don

oceanaire

Hi Don,

Mike Norris did my work with a set of Stage II heads. The compression went up to 10.8 to 1. Not sure how. I would give Mike a call and I'm sure he can give you the specifics. Mikes a real pro who is easy to speak with. There's a link in my sig to his website, or use the one at the right. He's one of our vendors.

No KR issues. And the car is very streetable. My only complaint is that I don't have enough traction with the street tires. :D

Eric :cheers:


[Modified by oceanaire, 12:07 PM 2/15/2002]

6Speeder

I have the MMS Stage IIx heads, which start on the 5.3 cores, for more compression on the 5.7 block. They were then milled, giving 11.3-11.4:1 compression. When tuning at sea level we saw 25 degrees of timing on 91 octane gas, with no knock problems. Higher compression = higher efficiency throughout the rpm and throttle opening ranges. Higher static compression ratios work well with longer duration cams, they tend to offset each other, giving better low and midrange without detonation problems. My cam is pretty mild and it still works VERY well. :cheers: Like oceanaire, my only problem is traction :crazy:


[Modified by 6Speeder, 2:51 PM 2/15/2002]

Steve02C5

I've got the MTI Stg.II heads w/ .030 milled (1/2 compression point) w/ no probs so far, however, they backed out ~3 degrees timing.

Morpheus

DRM milled my car's LS1 heads enough to increase compression by 0.5. I use 92 octane and haven't experienced any performance issues. I wish it was practical to increase it even more. :D

don527

Sounds very positive.

Sounds like modded cars could actually handle pump gas better due to the reprogramming of the pcm.

Don

Mako

My car first came out at about 12:1 on Pump 91 with 18 degrees of timing. The car was stong but I felt this was a bit much and it was a bit jumpy. I had the heads re-done for a CR of 11.2-.3:1, and 21 degrees. This change and a change to quieter, but more restrictive mufflers, resulted in a loss of about 8rwhp and 6rwtrq. The car seems to run a bit smoother, but it could be just my imagination. I run the MMS 229 cam.

It seems to me that any CR above about 11.2:1 has got to be tougher on the life of the engine.

Let us know what you decide!


[Modified by Mako, 2:46 AM 2/17/2002]

rwj383

i'd like to add to what 6Speeder is alluding to:
you can make higher compression work to your favor on pump gas with the right cam. the longer duration he speaks of, the overlap especially, is integral to bleeding cylinder pressures at rpm, thus, allowing the highest total timing possible on pump gas. i have heard of people building a 13:1 motor that runs strong on pump gas!! the above quoted 12:1 is the highest ive heard on an LS1, though. i personally plan to squeak out as much CR as possible, espcially with tuning tools such as LS1Edit available.

vette.se

I assume a 11.0:1 or higher compression ratio makes it impossible to use any kind of supercharger or turbo if not running on race gas. It may be something to concider then deciding about the ratio, maybe you want to add a supercharger later.

DRM normaly build their 427C5R to 11.0:1 but I ordered mine with 10.5:1 ratio to get a very reliable (no knocking and timing retard) engine. I loose about 20-25hp but I would loose even more because of timing retard on a 11.0:1 engine if I would get pinging on a hot day after many laps at the race track.

With a 10.5:1 ratio it's possible to add a ATI kit running on a low boost of 2.5lbs and raise the power from about 580hp to 700hp on a 427C5R.


:cheers:

Ram Air Tony

.030 milled and no probs ... but it does like all the octane she can get :yesnod:

very well mannered too :D

thanks

MattG

My LS1 heads are milled 0.030 which makes the CR around 10.8. I run 29 degrees timing on Sunoco Ultra94 and never have any detonation problems. I have also ran 91 and 92 octane many times as well and have had no detonation.

I think for a naturally aspirated heads/cam package some milling is a good idea. I don't think I would recommend going much past an 11.0 CR on a stock displacement LS1.