LS2, New Heads, lost power? Ideas anyone?
Teching In
Joined: Dec 2005
Posts: 27
Likes: 0
when was the first dyno done from the last setup to this setup? that makes a big difference. humidity, temp, every dyno is different at reading numbers. dynos are a tunning tool and thats all i would use it as who cares what the hp is, thats just for bragging rights. run it down the track and see if it made a difference or not then.
Also my car doesn't run on the track.. It's been on the track once and that was when it was pretty much stock..
Anyone else have any ideas??
I really can't base how "strong the car feels" because I was gone for almost 3 months.. You tend to forget what your car feels like after being stuck on a ship for so long..
Launching!
Joined: Aug 2008
Posts: 206
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From: a place
well what intake are you running a stock ls2 intake is junk, the intake wont flow enough air for the heads. and what injectors are you running?
if you cant afford a fast buy a ls6 and have it ported. either one will shine over the ls2
if you cant afford a fast buy a ls6 and have it ported. either one will shine over the ls2
Launching!
Joined: Aug 2008
Posts: 206
Likes: 0
From: a place
well if your flooding the motor with your injectors at wide open and not pulsing then your putting to much fuel in it, happened to me. and that intake dosnt flow worth crap with a good heads.
my afr was right but my duty cycle was well over 100%
my afr was right but my duty cycle was well over 100%
I am sorry that This thread seems to have slipped past me. I kept on waiting for it to pop back up but it never did until today on my search, so I apologize for the late response.
I guess one thing that I am looking for that I still haven't seen answered (or maybe I missed it) was in regards to the pushrods. How much pre-load is on them? My biggest concern is it's very rare for a stage 3 head to use the same length pushrod as a stock head. Also what procedure did you use when adjusting the rockers? I assume these are the bolt down non-adjustable type correct?
Also another problem that I would view is the oil. If there is oil in one bank (when it was on the dyno) it could be effecting the power. Now you said that the tests were done at sepereate times. Did you have these oil issues when it was dyno'd the first time? I know you said the plugs were clean this time, but there obviously was/is a problem causing the oil to appear at times.
I guess one thing that I am looking for that I still haven't seen answered (or maybe I missed it) was in regards to the pushrods. How much pre-load is on them? My biggest concern is it's very rare for a stage 3 head to use the same length pushrod as a stock head. Also what procedure did you use when adjusting the rockers? I assume these are the bolt down non-adjustable type correct?
Also another problem that I would view is the oil. If there is oil in one bank (when it was on the dyno) it could be effecting the power. Now you said that the tests were done at sepereate times. Did you have these oil issues when it was dyno'd the first time? I know you said the plugs were clean this time, but there obviously was/is a problem causing the oil to appear at times.
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Verdad Gallardo Teching In
Joined: Dec 2005
Posts: 27
Likes: 0
We will check the pre-load with the directions you gave me and get back to you on that.. It seems that the oil burnt residue on the plugs was from the intake sitting on it's side for 3 months.. We have since cleaned everything out and have checked the plugs 3x since then and they have always looked the same as the last pictures that were posted up..
The rockers are the non-adjustable just tighten down type.. Yella Terra..
I will get back with you about the preload tho..
The rockers are the non-adjustable just tighten down type.. Yella Terra..
I will get back with you about the preload tho..
Staging Lane
Joined: Nov 2001
Posts: 69
Likes: 0
From: Ft. Lauderdale, FL
Sure is nice to see Livernois posting up here and helping out. I'm planning to get a set of stage 2's through my shop Horsepower Sales in Pompano as soon as I save my nickels. My buddy Clevite Kid just got a set.
TECH Apprentice
Joined: Jan 2008
Posts: 366
Likes: 0
From: Gladstone, Queensland, Australia
I recently had a preload issue. I had over 100thou on LS7 lifters and torque was dropping off quickly above 4000rpm with an erratic line on the graph, was losing cylinder pressure. My heads were milled 20thou and the ls7 lifters are 60thou longer in piston length. So I went to 50 thou shorter pushrods problem solved, the engine now responds to timing and fuel changes in the topend. good luck
Teching In
Joined: Dec 2005
Posts: 27
Likes: 0
Now I only want to ask this question since I'm new to all this but if it's got preload then doesn't it mean it isn't sealing all the way or does it mean that it's not opening up all the way?
Wouldn't preload have been evident on the leakdown test we did?
Wouldn't preload have been evident on the leakdown test we did?
Only if there was so much preload that the valve never closed. However it could have alot of preload and only hang the valve open based off of RPM.
Basically here's the way it works... Not enough preload and you could potentially not open the valve all the way, but usually it would just have very noisy lifters and could run therisk of the pushrod dislocating itself. Now if it were too much preload you could see a power loss.
I always recommend 1 full turn, to 1 1/2 turns of preload, but 1 1/4 is perfect from what I have seen...
Basically here's the way it works... Not enough preload and you could potentially not open the valve all the way, but usually it would just have very noisy lifters and could run therisk of the pushrod dislocating itself. Now if it were too much preload you could see a power loss.
I always recommend 1 full turn, to 1 1/2 turns of preload, but 1 1/4 is perfect from what I have seen...
TECH Regular
Joined: Sep 2006
Posts: 447
Likes: 0
From: Houston
I recently had a preload issue. I had over 100thou on LS7 lifters and torque was dropping off quickly above 4000rpm with an erratic line on the graph, was losing cylinder pressure. My heads were milled 20thou and the ls7 lifters are 60thou longer in piston length. So I went to 50 thou shorter pushrods problem solved, the engine now responds to timing and fuel changes in the topend. good luck
Teching In
Joined: Dec 2005
Posts: 27
Likes: 0
Honestly no I haven't and didn't think that would be needed.. he's pretty well known amongst the corvette board and GTO board.. He may even be on here but I'm not sure.. Still working on getting the preload for livernois.. Might get a chance today..
Thread Starter
Staging Lane
Joined: Oct 2006
Posts: 59
Likes: 0
We'll check preload as soon as we can, and will post up.
Regarding stock intake, you wouldn't have a power loss on the heads, worst-case scenario it would have to be something not the intake and you would simply not gain. Plus there's plenty of LS2 gto's with significant gains using a stock intake and aftermarket bolt-on heads. It could quite possibly be pre-load, let's hope it's simple like that.
I concur that the dyno was probably skewed with that oil, and should be done again. Will check pre-load first. We're very thankful Livernois is on the thread and is being constructive and very helpful, and we look forward to posting up our results either way.
Regarding stock intake, you wouldn't have a power loss on the heads, worst-case scenario it would have to be something not the intake and you would simply not gain. Plus there's plenty of LS2 gto's with significant gains using a stock intake and aftermarket bolt-on heads. It could quite possibly be pre-load, let's hope it's simple like that.
I concur that the dyno was probably skewed with that oil, and should be done again. Will check pre-load first. We're very thankful Livernois is on the thread and is being constructive and very helpful, and we look forward to posting up our results either way.
