The Stovebolt Site Forums The Shop Area The HiPo Shop TPI vs LT-1

I've been working in putting together a TPI system for my 327. My brother called me tonight and told me that he found a late model LT1 complete with the harness, computer & transmission for $900. He needs a tranny for his '68 and wanted to know if I wanted to split the cost. That would be a complete engine, harness & computer for $450! Now I have to decide whether to keep working on the 327 or scrap those plans for the LT-1. I'm sure that I could sell my engine & TPI setup and make a profit, the question is do I really want to. I'm thinking that the late model stuff might be the way to go.

If you were closer, I would take the LT1 off your hands.

Scott

Look in my photobucket pics. There are pics of my lt1. I think the lt1 really gives the engine compartment a clean look.

I think I personally would run the TPI. I like the low end response of the TPI and I think the LS motors are oriented more for high end performance.

But then I guess it depends on what you really want performance wise.

If you move ahead with the LS PM me.

They're both good engines. In 350 form, I believe the TPI, even mildly built up with better heads and cam, would be stronger in the low rpm and midrange than an LT1. But in 327 form, there is enough deficit in cubic inch-derived torque to make the LT1 probably about the same torque-wise. So the difference there would be more of a wash.

Where the LT1 shines is its capability to make power above the rpm of a TPI, and its reverse-cooling set up. The heads have a perfect heart-shaped combustion chamber design for excellent swirl, and the cooling system cools the heads first, and then the block. I would have to check, but I think the LT1 runs on pump gas with something like 11.5:1 compression, and I know it has a hydraulic roller cam. Peak RPM is about 6500, compared to 4400 to 5200 on the TPI, depending on how you cam it and the quality of the heads.

I have had an opportunity to compare a 350 TPI, nicely cammed, to a 350 LT1, first-hand. In a 350, my TPI made so much torque that even at a mile in altitude, you could burn rubber easily and "drift" for about a city block. It was much more powerful up to around 4500 rpm than the LT1 was. But then above 4500 rpm, the LT1 pulled a lot better and made up the difference, about when the TPI was flattening out.

I also had a 327 and a 350 in the same car, and the torque difference between those two engines is substantial. So I predict that the difference between the torque of a TPI 327 and an LT1 350 is negligible. Although I'm more of a TPI fan, myself, I think the LT1 is an unbeatable deal and you should jump on it. Then I might suggest you finish the 327 and then compare the two, see what you would like better. But I feel in this case the LT1 350 would be the stronger engine.

Kept the TPI.

I think I'd have made the same choice. My stock TPI 'vette will fry the tires pretty much anytime I ask. It does flatten out somewhere above 4000, but I rarely use that part of the range, and in a truck I doubt I'd ever use that high end.

I doubt if I'll ever run it that hard. Updated photos in my webshots. Are you running speed density or MAF?

I agree you probably wont run that truck hard enough to get the full benefit out of an LT1 but I would choose the LT1 anyway.
Truly an incredible motor, with the roller cam and reverse cooling , I will vouch for the top end power as I have one in my 95 Impala SS. Ive had her over 100 mph and it just kept pulling like I was soon gonna reach 150 but chickened out at 120 and let off. However I think it has neck snapping low end range as well. Sorry I'm getting carried away.
All I'm saying is the LT1 is SUCH a sweet motor.

Yes, the LT1 in my son's '95 Trans Am is a very good motor. It's a lot more powerful down in San Diego than it is here in Taos at 7000 feet. I can believe the neck-snapping torque at a lower altitude. But then again, the TPI 350 I had in my IROC was definitely quite a bit stronger than the LT1 in the low and midrange.

It's a trade off, but a pretty good one.

My TPI had an MAF...to answer your question. The MAF is supposed to do a better job at determining the instantaneous fuel requirement, but like a lightbulb, it will burn out periodically and is a couple hundred bucks to buy a new one.
Also, it restricts the flow down to around 500 cfm, unless you cut out the screens, and then you'll get 710 cfm...at the cost of longevity.

My TPI is MAF. Fantastic low end response where it matters, running around locally. Nearly instant passing speed on the freeway.

But I'd hide rather than race an LS powered Corvette.

Oh I don't know. If it's an LS-1 from a C5 Corvette, I've seen them run mostly low-14 second quarters at Bandemere in Colorado. My TPI admittedly was warmed-over, but was capable of at least half second quicker quarters when installed in my IROC-Z. So it probably comes down to who's got the most mods on their engine, and how well the driver can drive their cars.

Now in a truck...I tend to agree with you. Unless my TPI motor has a couple of turbos strapped on, I don't know if I would try racing a new Vette either.

I'm too old and stiff to work my manual transmission fast enough to have any business racing anything, regardless what it is.

North of 100,000 and zero mods I think mine should really be kept to cruising. Or smoking the tires.

I do think the LS platform is a better place to start if you are modifying for acceleration or top speed. A buddy of mine and I bench-race prepped my 'vette for Bonniville and settled on an LS-7 as the right power plant. It will never actually be built that way.

But to tow it out there I'd prefer something built for torque and personally am much more likely to build that tow rig around a torquey TPI motor than ever build the top end runner or drag car.

Well said. My thoughts exactly. That's why I kept my TPI when I got rid of the IROC, so that I could put it on the truck's 350.

But you gotta admit, with 4.56 gears and a TPI 350's torque, it sure would be fun to bewilder some of these proud Porsche SUV folks at a traffic light driving a half-century old truck.

I'm not sure what the gear ratio is in mine. It came from a Chevy II. Do you think 3:73 would be a good mix with this combo?

Depends on your combo. I've got an SM420 Muncie 4 speed with a supergranny first with around a 7:1 ratio. Final drive is a 1:1. I have an SM465 Muncie 4 speed, also with a supergranny first, that will readily adapt to a transfer case for 4WD that I'd really like to use.

Although I'd really like to get a 3.50 differential ratio, (Dana 60), a 3.73 WOULD work too. 3.73 x 7.0 = 26:1 ratio. You can jog faster than top speed in first gear. And 75 mph would be around 3100 rpm with my tires. 3.50 is a little more useful, with 2900 rpm at 75 mph. But either would work with me.

Your combo depends on what you've got, but for most combos, yes, 3.73 would work well.

Forgot to mention it's a 700r4.