I have a 90 Formula with TBI and have read several posts on the swap. What I'd like to know is what kind of performance should I expect after everything is up and running. It's a stock 305 TBI engine just to put that out there and the TPI will be pretty much the same except for an airfoil and K&N. I know that the TBI cars have a small cam and the heads aren't the best so what can I look forward to from the car afterwards in regards to driveability,performance,etc?
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Another reason I'm asking is that I'm considering selling it and would like to know if it would be worth the effort to swap. And there's a 350 somwhere down the road..................somewhere................out there.

 

 

I can't really say what you would expect, but I can tell you what I got from my TPI swap.

I have an L69 (5.0 H.O.) Monte Carlo SS that I just got done swapping in a MAF style TPI system. (This is a 9.5:1 compression motor) The engine has 105K miles on her and ran out great with the Carb. The engine was completely stock when I began the swap. I added the TPI, Longtube Flowtechs, true dual 3" exhaust with 3" Spintech Mufflers, cool air intake, upper plenum and lower intake were ported and only the EGR valve is functional.

My gains were phenominal!! The car definitely has a power band now that it never had with the Carb. Now the cam is stock for an 86 L69, which is a hydraulic non-roller style that was used in the 85 IROC's and Z28 TPI cars. In that year the engine was rated at 215bhp. With the mods that I stated and a Desktop Dyno 2000, I am in the neigborhood of about 250 to 260bhp.

 

Do a search for posts on this topic by myself and my dad Dyno Don. We swapped from TBI to TPI on his former 92 RS, and gained 17 HP and 70 TQ at the wheels, as well as 2+ miles per gallon.

 

Thanks for the info from your swap on the MCSS. What I'm looking for Kevin is how did the car feel once the swap was done and you drove it. More specifically how was driveability and seat of the pants feel affected? I'd read in a post that due to the TBI heads and cam that this swap would result in a strong increase in torque but that performance would take a nosedive above 4000 rpm. I would think this would be perfect for a street driven car but as is often the case most people want to talk horsepower when we drive torque. Any further input would be appreciated.

 

4000? You can give it a few more 100rpm. More like 4400-4600. But you are right, that is all the rpm you need in town. You will love it.

Do it, do it.

 

Thanks for the input. I had put this up for sale but I'm about to talk myself into keeping it since I've only had a few replies and no money has shown up.
Anyone else?

 

my tpi 305 car ran a 15.39 @ 88 mph with only a hypertech chip/160 thermostat and a flowmaster catback. it actually ran better than i thought it did.

that was with a cracked distrubutor and no tune up. the plugs, wires, cap and rotor probably hadnt been replaced since the mid 90's.

 

This is my chart from my TBI to Sequentially injected TPI swap (Vortec 305 Van PCM) Red is TPI, blue is TBI.



https://www.thirdgen.org/forums/tbi/...03-update.html

I gained 1.5 MPG city and lost 1 MPG highway.

 

My dad said it was the best thing he'd ever done to the car. Because of the small TBI cam, any engine will die off around 4000 rpms, regardless of the intake up top.
I was waiting for Fast355 to show up.

 

LOL.

I will further add that in my experience 1.6:1 roller rockers when used with a stock TBI cam will extend the powerband another 300-500 RPM. Retarding the cam 4* will give you around 250 RPM more. That will move peak HP from around 4,000 on the dyno to 4,600-4,800. PS, this is after intake mods and a full exhaust.

 

Thanks again for all the inputs. Kevin, did your dad do any tuning on the chip after the swap? I'll be running an OE PROM with a Moates adapter from TPIParts.net with the following changes: AIR,rev and speed limiters disabled and calibrations to run properly with 22# injectors.

 

See also this thread + discussion.

https://www.thirdgen.org/forums/tbi/...ml#post2976055

The intake manifold debate of TBI vs TPI is a torque bubble under the wallpaper: push and the bubble moves to a new location. TBI has it's torque spread more evenly, TPI has it concentrated.

The debate on heads lives elsewhere in many threads, and there too the difference between the "good" heads and the "bad" heads has been greatly exaggerated by the TGO masses.

 

Yes, I did tune it for optimum output with the 19# injectors.
I installed a LT1 cam and 1.6 rockers on the intake and it produced a 14.94 @93.xx mph (still with stock exhaust manifolds) Also if not noted before, this car was a 5spd. w/3.45's.

PS. All this on a stock L03 (starting out) with 235k on the clock.

 

Here is a dyno graph of mine b4 and after. When you can add headers and a ypipe it will really wake up the car. Just from the tpi swap i got about 10rwhp 40 rwtq. I didnt lose any power threw the power band. You will feel the torque in the seat of the pants.

http://bitchincamaro.no-ip.com/files/dynotbivstpi.JPG

 

So with mine already having the TPI type headers and 3" exhaust I could stand to see a little bit better performance than if I were doing the swap on a stock setup. I had been thinking of doing rockers but wasn't sure if 1.6 or 1.52 would be the better choice.

 

i was waiting for some one to have a stock lo3 baseline run then tpi swap run

as i will be doing a tpi swap soon aswell

 

The link I posted was from a stock tbi car and all I swapped was the intake. The car was dynoed agian after headers and 3 inch cat back. The link below has all the dyno graphs.
http://bitchincamaro.no-ip.com/dyno.html

All of these are done with the stock tbi heads and cam.

 

After doing the math it appears that the 205 hp TPI engines found in the ,I'll call them common TPI cars ,may have the same engine as the TBI cars did. The difference between the rated 170/205hp is roughly the same 20% as the dyno numbers 152/188hp at the rear wheels. Maybe?

 

I think they have the same cam but different heads.

 

With those crap TBI heads, your looking at 300+ flywheel tq and about the same horsepower.

 

Hmmnn, Kevin and his father have posted results, probably the best comparison you'll ever see.

Fuggit about the HP, look at the torque achieved.

Now, before you go all hog wild on doing a stock TPI swap, you may want to do some searching on different intake setups that compliment the EFI..no use doing it twice/3 times

 

Unfortunately mods to the TPI itself will have to wait, funds being low and I still have to round up the last few parts. I did want to ask how much of an improvement would I see from a set of siamese runners and an Edelbrock base? Who else still makes a base for these cars?

 

what parts where you still missing?

on a another note so if the lo3 heads make the same hp but make more torque dose that mean there the better head for running tpi?

i also have a set of 083 heads but ill end up makeing less power over all i wont use them

did they swap to speed density tpi or maf
i well be useing a sd type or all all tbi conversions sp tpis?

 

A fuel pump and some sensors. Works been short lately and other things have priority.

 

well, tbi heads will make lots of torque with tbi, but if you ever want to make power about 3k rpm, switching to an L98 head, or even an LB9 head would be beneficial. 416 casting heads can be found pretty cheap and would be better than those junk tbi heads.

 

doing a cam, headers and some other bolt-ons on teh TBI motor can result in some impressive performance.
My friend did an LT1 cam, Carb intake with TBI Spacer, shorty headers, 3" catback, K&N Filter and filter cover, 3.42 gears, and ended up getting the car to run a 14.7@93mph. Not too shabby I think.

I did a carbed LG4 to TPI with cam and many bolt ons on my 86 Trans Am and got it to run a 14.1@100. with the carb it ran 14.94@92mph.

 

I don't plan to get too involved with many more mods on the 305 once the TPI is up and running other than a Racetronix fuel pump kit during the swap. After that I'll just enjoy the car until the anticipated 350 makes it's appearance.

 

The power crossover is a lot higher than 3k rpm.... and the choice isn't as clear cut as you make it seem.

Dewey316 had stock TBI swirl port heads on his car when he dynoed it. 205 rwhp @ 4700 rpm with cam/exhaust/PROM as the major mods. He ported a set of 416s, put them on (using the same cam/exhaust and retuned the PROM) and got 225 fwhp @ 5200 rpm. His before/after dyno plot appears halfway into page 3 of the thread.

The good news is that the ported 416s were worth +20 rwhp.... but the bad news is that the stock junk SP 305 heads outpowered the 416s until 4200 rpm. The further bad news is that the air:fuel ratio on the ported 416 pull was nearly optimum at or under 13:1... and on the stock heads it was down to 12:1 at 4600 and then increased to 13.5:1 by 5500..... so the stock pull still had something left. And all that extra torque under 4200 rpm is useable on a car whose purpose is primarily street-driving.

So the optimum gain of the ported 416s (which flow on-the-order of 220/160 cfm when ported) is less than 20 rwhp over stock unported 187 casting 305 heads (which only flow in the 165/140 cfm range). The stock heads 187 also need less than 30 deg max ignition advance, while the ported 416s need more than 34 degs... which means the swirl port heads are more efficient as fuel burners.

So even though the stock 187 SP heads flow poorly in stock form, they were better as fuel burners to the point that they made more power than ported 416s up to 4200 rpm. Ported 416s outflow stock 187s by over 30% aggregate (average of the intake and exhaust) but they make less power up to 4200 rpm than the stock unported 187s... at least as shown by Dewey's tests. And the peak power gain was only a 10% increase (205 increased to 225 rwhp), even though the head flow gain was +30%. That's why the answer isn't so clear cut as you made it.

That should not be a reason to rush out, buy, and port a set of 416s. But it might be a reason to port the 187s.