restoman45

iTrader: (2)

I was just curious because from everything ive read, it seems like the highest that i see is mid 11 to 1. During the old school muscle car days, the factory dished out some 12.5 to one cars so that got me wondering...why dont i hear of ls1's having compression that high??? Thanks
Yosh

<img src="graemlins/camaro.gif" border="0" alt="[Chevrolet]" />

LS1derfull

I think Ls1 has less to gain going after that kind of compression because flame speed and efficiency is so much greater than old style comb. chambers. The only scenario where 12.5 to 1 would be needed is with large duration cams(big)
or on really big Cubic inch LS1's that dont have enough cylinder head to reach targeted rpms.

RyanJ

Colonel runs more than 12 and SAM runs more than 13.

LS1derfull

I am not saying it hurts too have this much, but it doesnt pay off like it would in older design motors. And dont both of those applications fit my examples about C.I. or large cams?

RyanJ

[quote]Originally posted by LS1derfull:
<strong>I am not saying it hurts too have this much, but it doesnt pay off like it would in older design motors. And dont both of those applications fit my examples about C.I. or large cams?</strong><hr></blockquote>

oh yeah...i wasnt disagreeing or anything...he asked and i told 2 people that have about 12:1.

Colonel

Yep, 12.2:1 here. And it'll still run on pump gas too! <img src="gr_images/icons/cool.gif" border="0">

Hydra

Really... Very Impressive Colonel! What exactly have you done to make your motor so detonation resistant?

JimmyKash

a steady diet of 104 <img src="gr_stretch.gif" border="0">

Hydra

If you'll notice he said that it runs on pump gas

LS1derfull

Cylinder pressure is controlled by the throttle, cam,static comp.,and rpm determine how high that pressure can be. Im sure that motors with 12+ to 1 can be driven without detonation, but full throttle at hi rpms is risky on pump gas, you could break motor and not even have heard the detonation until its too late.I wouldnt try it on a good motor, drive it on pump, race it on C12.

Pro Stock John

iTrader: (34)

SAM car is 12.8:1.

PaiN is also more than 12:1.

I think that Tom the Roofer is too.

I'm 11.25:1.

RyanJ

i think SAM's website is wrong. i remember Eric or Pat saying Judson runs more than 13.5.

Colonel

[quote]Originally posted by Hydra:
<strong>Really... Very Impressive Colonel! What exactly have you done to make your motor so detonation resistant?</strong><hr></blockquote>

Glad you asked! <img src="gr_stretch.gif" border="0">

Several factors are helping me...

Maybe the biggest is the fact that we have aluminum cylinder heads and block. Aluminum dissipates heat more rapidly than iron.

Flat top pistons. My extra compression is gotten from my shaved LS6 heads and my thin metal head gaskets.

Quench area. My quench area is very small for the same reasons that my C/R is high. This creates some major turbulence in the combustion chamber which is condusive to having a more even fuel/air mixture throughout the combustion chamber (less chance for a lean spot.)

A camshaft with lots of overlap makes for less dynamic compression at rpms when you are "off the cam." 244/244 112 makes for some pretty good overlap.

160 degree thermostat.

The ability to lower the timing advance and enrichen the fuel mixture by cranking up the MAFT. Running the mixture rich helps to prevent detonation. I can also lower my timing advance through use of a resistor plugged into the IAT sensor. A 5.2K ohm resistor gives the ECM a reading of 92 degrees, for example. The ECM uses a less aggressive timing scale for hot weather.

Practically no backpressure in the exhaust system. This one has been debated but testing at MTI has shown that having cats installed on a car makes for more detonation.

Pro Stock John

iTrader: (34)

Judson told me himself on the fone a month ago that the SAM SS is running 12.8:1 compression. 13.5:1 was planned.