Gentlemen, i'm going to be rebuilding the LB9 in my '91 Trans Am. It is a daily driver with a focus on fuel mileage and reliability. The car has 2.73 gears and a T5 (.73 OD). This car is not raced and ultra performance is not an issue. I'm looking for great torque and efficiency for good mileage. The car is currently my daily driver but has a wristpin noise. I don't want it to be down for a long time, so I'm looking to build a new long block and just swap it in. I have all the pieces to build a new shortblock, but I dont have heads yet. I know where a set of '92 L03 heads are and I've thought of using them but wasn't sure. I did some searches earlier and it appears that below 4000rpm, the swirl ports make more power and torque than 416s or 081s, which is ideal for me. This engine will rarely see over 4000rpm, and I'll be shifting at 5000 at redline. I'll either use the stock '91 LB9 cam (which is the L98 cam) or I'll be using a stock LT1 cam. So, are stock swirl ports a good idea with a stock LB9? Has anyone done it and what were the results?

10:1 350 running 187 swirl ports and a Production GM LT4 cam. Stock TPI top-end and Thorley Tri-Y headers.

Fast355 (Chris, right?) you were one of the guys I was hoping would respond. I've read many of your posts on this along with JPervost, ShiftyCapone, Kdrolt?, and many others I'm forgetting right now. You guys have posted flow numbers as well as dyno comparisons, and that is what initially intrigued me. Fast, I didnt realize you were running TPI on your van, for some reason I was thinking it was TBI. Anyway, this looks to be a good idea? Again the car is just a relaxed daily driver, and i'm looking for great torque and great mileage with a 'stick and 2.73 gears, I'll likely run the stock LT1 cam to get the extra lift.

It started with a CCC Q-Jet. I went to TBI. Then switched to TPI. So you are right it was TBI.

I think the TPI cars should have come with TBI heads to begin with. The TPI runners/Small cam run in the TPI cars did not fully utilize the extra intake flow of the 081/083 castings. The 187s make more torque and burn fuel more efficiently at part throttle. This is the reason the TBI 305s run so well on the highway with their 2.73 gears. My van has 3.08 gears, 29" tall tires, and had a stock stalled 700r4 in it when that video was made. Definately ran very well for no more than it was. I was able to get 17 mpg around town in 50% residential 50% highway driving and up to 21 mpg on the highway. It had the torque to pull almost any hill in OD with the TCC locked, which is no small feat considering it weighs 5,500 lbs and has the slug highway gearing. I had my WOT shift-points right at 5,200 rpm and it would pull well to that RPM.

L03 TPI with LT4 cam



I am now running a TPI 350 with heavily reworked vortecs and an aftermarket cam.

I am working on swapping to an OBDII PCM as we speak...


I think with the right prom tuning you will LOVE the TBI heads for your application.

I recomeended a set of TBI heads a while back for a motorhome running a 350, TH400, and 4.56 gears. He goes by user name avst03. His motorhome cruises around 3,200 rpm @ 60 mph in that rig. Even running in the higher rpms, his 10,000 lbs rig ran alot better than with the crappy slow burning 624 casting carb heads.

A quick quote he posted on FSC

This is something I'd like advice on as well. In my skimming earlier today I saw that the SP heads don't want as much timing. Would it be a good idea to just copy the whole spark table from a TBI .bin?

Also, how about fueling?

Im just subscribing guys.. I'm also planning to build my LB9 soon, hoping to gain efficiency and maybe a few horses. Keep us posted MeanZ.

BTW you have an awesome IROC.

Anybody else got any info on what to change in the tune for the swirl port heads? I've heard less timing, but anything else?