I have a 305 tbi motor but im planning to add a tpi. I noticed that the tpi 305 motor is rated at like 60hp more than the tbi 305. besides the injection was there any internal differences that account for that difference? that's a pretty big hp gain. my motor is a 91 if that makes a difference.

 

Heads and cam are the main differences. Possibly the pistons too.

RBob.

 

The TPI itself makes up some of that power gain. My 91 Formula (TPI) had the engine replaced with a GM crate engine back on the early 2000's and since you could not buy the LB9 it was an LO3 long block. The original owner I got it from said she couldn't tell the difference. Indeed with the 3.42 LSD and T5 it's still pretty quick. The TPI engines had a lot of torque due to the long, small diameter runners. But they lacked top end. You will see a big gain in torque off the line.

GD

 

Heads, exhaust and possibly cam,( depending).

 

what are the differences in the heads? now that I think about it I have heard people use the term tpi heads but I never thought about it. the cam grind for the tbi and tpi are different as well?

 

The main difference besides the fuel injection is the cam. TBI got a very wimpy cam compared to the TPI engines. TPI heads were not the swirl port type like on TBI and thus were better especially on the intake side. 081 305 TPI heads weren't a bad factory casting.

 

Just for a reference, my first thirdgen was a 1992 Camaro RS with TBI. When I got my 91 Z28, my dad took over the 92. It dynoed stock at 150 RWHP and 220 RWTQ. He converted it to TPI using the same cam and heads, and it made 167 RWHP and 290 RWTQ.

 

And for further reference - my slightly modded (full exhaust and headers, 1.6 rockers, and EBL tune) '86 LB9 (305 TPI with the peanut cam) made 189 RWHP and 295 RWTQ on my DynoJet. That's through a 700R4 with 3500 stall, and 3.70 gears.

So yeah - about what you would figure. You're going to lose 20-30 HP with a TBI bottom end, heads, and peanut cam.

GD

 

Makes me wonder what kind of drop in HP/TQ I will have on my stock L98 running TBI?

 

If it has a good chip tune, nothing in the HP department and maybe 10% at peak torque. The TBI will actually make power to a higher rpm than a stock TPI.

 

mine is a driver. I don't care about peak hp. I want torque. lots and lots of tire squealing throw you back in the seat torque.

 

I've done exactly what you are proposing: LO3 TBI to TPI. You will gain a significant amount of low rpm torque. You will not achieve "lots and lots of tire squealing throw you back in the seat" torque.

 

I'm not looking for huge power by any means. My L03 is starting to smoke a lil and that's not cool at carshows full of nice cars. Instead of spending any $ at all on a 305 I picked up a good running L98 and freshened it up to drop in along with a modded TBI and intake and chip tune from Brian. Stock #049 cam, probably HO manifolds and magnaflow y. In a few months we will see how much power TBI loses to TPI but at the end of the day I will be fine with a pretty much stock 350 which is light years better than the lil L03. I will give the L03 credit though its been a great running lil engine and I plan to maybe find an older pickup to drop it in with maybe an L98 cam +headers.

 

I understand the tpi alone will not create the torque im looking for. its just one of the ingredients im also going to do heads and a cam and rear gears. .

 

Gears, an S10 torque converter, posi, and a shift kit alone will really make it 100x more fun to drive in itself. Even with my weak 170 hp engine I can tear out smoking tires and smoke second gear in mine. I'm running 3.73s but 3.42s would be better suited for these cars really.

 

something I havent heard mentioned is about the 305 TPI auto and the 305 TPI with 5 speed.. the 5 speed did not have the peanut cam that the standard 305 TPI auto came with. what was the cam in the 5 speed tpi? maybe that would be a good addition?

 

5 spd cars had the 350 cam.The 91-92 cars even in automatics shared the same cam as the 350 cars. Before that ive heard auto cars had the peanut cam. I can tell you my 91 auto car would flat out move for a 305 car. Pretty much stock except for a chip, 3in exhaust and cat delete it ran 14.7s..

 

Thanks for that. I did not know this. my 88 would really move and I knew it had a more aggressive cam than the auto. I didnt know it was from the 350. Appreciate the info!