Ls conversion drivability
Thread Starter
Teching In
Joined: Jul 2013
Posts: 31
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From: NW suburbs Chicago
Ls conversion drivability I’m looking for advice for the causes of a drivability problem. My setup as follows:
- LS conversion is a 68 Pontiac Lemans
- ENGINE: Stock LS2 bottom-end, L92 Square port heads with spring/trunnion upgrade, Corvette intake, Edelbrook DBC 90mm TB, Texas Speed Stage 1 cam (duration at .050" intake225deg/exhaust230deg, intake.629"/exhaust.615" lift @1.7 rocker ratio, LSA=112deg, Intake CL 110deg), shorty headers
- TRANS: Tremec TKO600 5-speed (1=2.87, 2=1.89, 3=1.28, 4=1, 5=.64)
- REAR: 12-bolt GM, 4.11 gears
- FUEL: Stock LS2 injectors Holley in-tank pump, 255LPH
- COMPUTER: MSD Atomic LS EFI. This is the one you usually see in red and fuel rails are part of the computer. It was discontinued a few years ago. 3 set points for tuning (idle/part throttle/WOT). Other than that self-learning I guess.
- SITUATION: 90% street including HRPT, 5% track. Current best time, 12:60@112mph on slicks.
- Is the Cam too aggressive?
- Could a computer with more tuning capabilities (Like a Holley Terminator X) help?
- Is there something with my gearing combination?
- Other things?
Your going to need a better EFI system that can actually be tuned, All the the atomic learns is your fueling. It has a few set premade tunes and picks the rest of the parameters based on what you select when you build the tune. If your combo isnt really close to one of the pre-made tunes then it will have drivability issues.
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Joined: Dec 2004
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From: Florida
ls2 with ls3/l92 heads can be pretty finicky at low rpm. they can work fine, it just may take a little extra work sometimes, and having a ecu that you can tune will help a lot. id suggest the terminator x as well.
Teching In
Joined: Jun 2014
Posts: 13
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From: Chicago area
I 3rd you really need to tune especially when your upgrading things.
The cam isn’t to aggressive but I bet it’s shifting the power curve out to the top a good bit witch means your going to have to dial in the fueling at the bottom and top especially.
I use hp tuners a lot on stock ecu stuff and the terminator is pretty much the go to these days
The cam isn’t to aggressive but I bet it’s shifting the power curve out to the top a good bit witch means your going to have to dial in the fueling at the bottom and top especially.
I use hp tuners a lot on stock ecu stuff and the terminator is pretty much the go to these days
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Thread Starter
Teching In
Joined: Jul 2013
Posts: 31
Likes: 0
From: NW suburbs Chicago
Well, computer will be the first place I go. The motor actually started as an L76 from a 2008 Pontiac G8GT; LS2 bottom end with the L92 heads. Had not thought about the heads being too big for the CI since GM supplied it that way, but maybe combined with the cam it does start to cause problems. The cam for sure pushed up the power band, but I don't think to a point that it would cause drivability problems. Attached is a chassis dyno run. Its only from 2500rpm so not really showing the range I need for drivability, but can you draw anything from it? Can you tell if the power curve pushed up enough that it is causing some of the issues also?
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Verdad Gallardo Teching In
Joined: Jun 2014
Posts: 13
Likes: 0
From: Chicago area
Well, computer will be the first place I go. The motor actually started as an L76 from a 2008 Pontiac G8GT; LS2 bottom end with the L92 heads. Had not thought about the heads being too big for the CI since GM supplied it that way, but maybe combined with the cam it does start to cause problems. The cam for sure pushed up the power band, but I don't think to a point that it would cause drivability problems. Attached is a chassis dyno run. Its only from 2500rpm so not really showing the range I need for drivability, but can you draw anything from it? Can you tell if the power curve pushed up enough that it is causing some of the issues also?
I watched a couple of Richard Holdeners head tests on YouTube the other day and notIced when he used heads that flowed more than the motor could use it did hurt low end torque and the bigger throttle body did slightly as well
Thread Starter
Teching In
Joined: Jul 2013
Posts: 31
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From: NW suburbs Chicago
Revvlimited, Minytrker, Trendsetter, thanks for the feedback! I guess I know what to ask for from Santa this year. Once done I will post back to let everyone know how it goes. I got the MSD as cheap EBay score, I guess you get what you pay for.
The car L76 TB was also 90mm factory DBW. I got the DBC because the MSD computer would did not support DBW. I knew nothing about the car L76 when I bought it and just stumbled onto it. Once I did a little research I realized I had nice platform to start with; 6L, 10.4:1 compression, L92 heads, Corvette style intake and 90mm TB. All it needed was to dump the DOD and give it a real cam. It went from factory rated 355HP/384TQ to high 400s based on the chassis numbers. I was super happy.
Anyways, thanks again and if anyone else feels the need to sound-in the feedback would be welcomed.
The car L76 TB was also 90mm factory DBW. I got the DBC because the MSD computer would did not support DBW. I knew nothing about the car L76 when I bought it and just stumbled onto it. Once I did a little research I realized I had nice platform to start with; 6L, 10.4:1 compression, L92 heads, Corvette style intake and 90mm TB. All it needed was to dump the DOD and give it a real cam. It went from factory rated 355HP/384TQ to high 400s based on the chassis numbers. I was super happy.
Anyways, thanks again and if anyone else feels the need to sound-in the feedback would be welcomed.