Can i run a LT4 at 10:8:5 compression?
11-08-2001, 12:21 PM
#2
Safety Car
Member Since: Jun 1999
Location: Austin, Singapore, Kuala Lumpur, Houston, Dallas, Hong Kong, Elgin, etc.. Texas
Posts: 3,570
Likes: 0
Received 3 Likes
on
2 Posts
Re: Can i run a LT4 at 10:8:5 compression? (Impala SS Z06)
Yes. The knock sensors may pull out some timing.
11-08-2001, 12:57 PM
#3
Safety Car
Re: Can i run a LT4 at 10:8:5 compression? (Impala SS Z06)
Depending on cam, gas, etc. easily!!! With a healthy cam, we have run them up to 12.4:1 on pump gas with NO knock. :)
11-08-2001, 01:06 PM
#4
Melting Slicks
Member Since: Dec 1999
Location: Austin, TX
Posts: 2,813
Likes: 0
Received 0 Likes
on
0 Posts
Re: Can i run a LT4 at 10:8:5 compression? (Impala SS Z06)
You mean 10.85:1 compression, right? The biggest thing is going to be setting up the program to work most effiently with that high of compression. Like Mez said, the knock sensor will trigger the ECM to pull out timing. The only problem is it will probably pull out too much and you won't make max power.
I'd work with one of the ECM tuning experts with your car sitting on a dyno to get the program optimized.
Also, be safe and go with some quality aftermarket forged pistons and good rings.
I'd work with one of the ECM tuning experts with your car sitting on a dyno to get the program optimized.
Also, be safe and go with some quality aftermarket forged pistons and good rings.
11-08-2001, 02:45 PM
#6
Melting Slicks
Re: Can i run a LT4 at 10:8:5 compression? (ncChris)
I agree, stock LT4 compression is 10.8:1 from the factory, I did much research on compression when i was doing my motor, like crushed head gasket thickness and safe deck amount to retain combustion chamber efficency. my motor is effectively running at a little over 11:1 and tuned for 10.5:1 and iu get knock retard unless i use high octane race gas. I am going to have it tuned to run properly on pump gas in the next few weeks. good luck!
Chris :smash:
Chris :smash:
11-08-2001, 06:05 PM
#7
Racer
Thread Starter
Member Since: Nov 2001
Location: Houston TX
Posts: 474
Likes: 0
Received 0 Likes
on
0 Posts
Re: Can i run a LT4 at 10:8:5 compression? (lcvette)
Well here is the story i had a 409 built for my 96 impala SS. They missed the compression bad! It would only not ping on race gas! So they are raising the cc's on the head to lower compression. They cannot take any more outta the head so they can get the motor to 10:85:1. So they are gonna put it back together next week.I have the Lt1 edit how much timing can i run with this compression???? Ed Wright had it at 31 deg at WOT and it pinged bad.
11-09-2001, 01:00 PM
#9
Safety Car
Re: Can i run a LT4 at 10:8:5 compression? (Impala SS Z06)
The stock LT-4 compression is indeed 10.8:1 you should not have any problems with it. My suggestion to tune properly would be to get on a dyno with a wideband O2 and your LT-1 edit and tune accordingly, every car will be a little different.
Mike
Mike
11-09-2001, 02:01 PM
#10
Melting Slicks
Re: Can i run a LT4 at 10:8:5 compression? (MVR 155)
I'm running 11.5:1 compression in mine and i get some timing retard from knock, but i also found while i was at the dyno that Ed had programmed my computer on the lean side, at WOT i was getting 13.8-14.0 AFR which is way lean. 12.5 is about the best you'll get for safety and p[erformance, i would put her on a dyno and see what your AFR is, i spoke with fastchips today and they told me to send back the computer with the dyno graph and my datamaster log files from the dyno. so maybe after you dyno it you will find why your getting knock. a lean condition in a high compression motor will most certainly cause detonation!
chris
chris