5speedsteve

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.

Under 2,000 RPM it is very stumbly and difficult to start from a stop with the manual trans. Half the time I look like I don’t know how to drive stick and have been doing it for 40yrs! I want drivability without losing to much power and feel it is something in my combination and need direction for where to look:

• 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?

Let me know what you think, the help would be greatly appreciated!

minytrker

iTrader: (13)

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.

5speedsteve

Thanks for the reply. Would the Terminator X give me the tuning capabilities needed? Or is there still something else that should be addressed?

minytrker

iTrader: (13)

Terminator x would everything you needed.

5speedsteve

Cam does not seem too aggressive?
Thoughts/experience from others? I would just like to get as much feedback as possible before I spend $1,000

TrendSetter

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.

revvlimited

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

5speedsteve

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?

revvlimited

you see how choppy the curve is and it keeps going up and down. Most of that should be tuned out. If the curve looks like that above 2500 then it prolly doing some of that below as well witch will cause weird things while launching and stuff.

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

5speedsteve

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.