vendetta

hey guys, not to sure if this is where i should post this or not but here it goes

im looking at buying a third gen and found a 88 iroc with TBI, i would prefer TPI

how hard is it to go from tbi to tpi, what would u need?

im just not able to find and TPI's that are brutally priced

thnx -erick

Fast355

iTrader: (2)

You could swap in a nice Vortec 350 and tune it running TBI for what it would cost to switch your TBI 305 to TPI. I should know, its just not cost effective.

vendetta

i figured as much

i just A) like the look under the hood better and the name of it lol

B) just seems all around a bit of a better set up?

anyone wanna give me some pros and cons for tpi and tbi? jw

-erick

90c350

how much power are you looking to make?? What type of use is the care going to be used for? Tpi has the advantage of being mpfi and will not suffer from a wet manifolds minor quircks. But it will cost more to run and repair as well as to convert to. You will run out of manifold if you plan on producing larger power numbers and the aftermarket manifolds and runners are not cheap. Tbi can be tuned to run very well and you can use any manifold that you wish,Dual plane/single plane etc etc. Just need an adapter. Alot cheaper because you already have the system. Im sure that Fast355 has been into the 400+hp range with a tbi unit. You will need to get into chip/ecm tuning with either system, so that cost will be equall. If I was to go to mpfi i would go with one of the converted single plan manifolds and injectors from holley/weiand/Accell etc. Then just use your gutted tbi for the Throttle body and get DynamicEfi's Flash ebl to run it. Easy conversion and fairly cheap. Just my 2c's

Fast355

iTrader: (2)

IMO, it IS the best looking small block factory injection setup.

TPI
A.)Higher Cost (Initial and for upgrades)
B.)"Tuned" means just that, peak torque under 3,500 rpm, and peak HP by 4,500, restricts breathing above 5,000 rpm
C.)More complicated and more parts to fail
D.)Better Mid-Range torque and slightly better throttle response
E.)Potential for better fuel mileage

TBI
A.)Lower cost (upgrades easier/cheaper)
B.)Works on ANY carb manifold including single plane, so its not bound by resonance in RPM range
C.)Less complicated and fewer parts
D.)Better low-end torque on a dual plane manifold or more HP with a single plane than TPI
E.)Still gets GREAT mileage when dialed in properly.


I have had both on the same engine, in the same vehicle, with the same gearing, and same transmission. Both were tuned properly by me. The TPI feels quicker, because it has more HP, but the TBI would roll right around it and keep pulling. Higher RPM means more HP and more torque to the wheels for a longer period of time (higher shift points). The TPI has a better fun factor, but that fun doesn't last long, when you are spinning the tires and not going anywhere once it hooks up. TBI was easier on the tires and FLEW up top.

vendetta

thnks alot for your tthoughts

theres a red 88 iroc tbi auto for sale for like 4500, think i mite pick it up

would like to sell my 78 nova firs tho,....single car garage

Kevin91Z

iTrader: (1)

There are tons of TPI cars in the 12's and faster.

There are very few TBI cars that make it to the 13's. Most are stuck in the 14's or slower. Simple as that.

Fast355 is the only person I know on these boards that has converted from TBI to TPI and wasnt happy. Every other person who has done it has been very happy and recommends it. Do a on TBI to TPI and you'll see. Its a very common topic.

nimrod_sixty9

Dont know if this directed cirectly at you but may help:

https://www.thirdgen.org/tbitotpi

oaksinspace

I have decided to do this. A mechanic friend is helping me, but i need to do the research, some of the planning and get the parts. He lives in Finland and does not know so much about f-body, but made to of these conversions earlier, but long time ago. I also have to pay for he hours, but he wont overcharge and will get me a really good deal, it is his garage. I am a student, so this is a low budget project, but I want to get it as good as it gets. I don't want to waste on bying not good enough parts and in the end it is going to be fast, but also possible to drive a bit economic. It must have 300+ hp and useable fuel economy when done.

I have some questions that might seem obvious, but still.

• Can i use a 350 tpi on a 305 or does i have to be from a 305?
• If so,can I use one from a vette? Is there any point?
• Can I get the VATS working some how, my last car got stolen?
• Is there any years that are better or is it the same?
• Does it have to be automatic if I have automatic? I want a 6-speed later anyhow, but now I don't have money.
• Porting the heads is decided to do, but is there any difference from the tbi to the tbi?
• The manifold/intake is probably getting changed to a bit higher peak since it is going to get freeflowing from headers and on. Any recommendations?
• I am getting some used headers later, but then a bottleneck might be from there to my 3" flowmaster singlecat catback. Suggestions that will fit the specs?
• I have decided not to mod the block, therefore I want peak hp under 6000. Is this nessesary?
• witch tpi is easyest and best (most important) for my conversion? I have all winter to find cheap parts.
• Is there any mod to the tpi that is a lot for the money later?

----------------------------------------------------
91 305 tbi automatic. Not yet fitted flowmaster 3" singelcat catback. Ported heads later. Have some ground effects, but not complete yet. Getting ram air hood. Upgrading to ws6 or something later, the brakes are to soggy already.

Kevin91Z

iTrader: (1)

Yes you can use a 305 or a 350 TPI intake manifold. The are the exact same. The only difference is the injectors, 19lbs for a 305 and 22lbs for a 350.
No, the Corvette intake manifold is slightly different. It only bolts up to older heads with the perimeter bolt valve cover system.
Yes as long as you get an '89-'92 system that includes VATS.
Its my preference the '90-'92 speed density system is better, and its what your TBI car already has, so the conversion will be slightly easier.
The engines are the exact same for automatics and sticks, the only difference is the flywheel or flexplate that goes with the tranny.
Yes the heads are different. TPI heads are slightly better but not worth the cost and expense of changing. Get aftermarket heads if you're going to change them.
Get an Edelbrock TPI intake manfold. They sell it for the least expensive price.
Either Hooker 1 5/8" headers part number 2055, or contact board member Dyno Don for his 1 3/4" headers. Or you can try to find some used SLP 1 5/8" or 1 3/4" headers.
I dont know what you mean by "mod the block" but 6000 rpm is the limit on a stock engine.
As I said above, the '90-'92 speed density TPI computer is more popular and is a better system, in my opinion.
Yes, get the Edelbrock TPI intake manifold now, as I said. Its easier to change it now than it is to change it later.

oaksinspace

Thanks a lot for the answer! If I buy an older TPI that is cheaper, will it do the sme job as a 90-92 with a new harness and ECM? It would broaden local availability and eliminate the risk of electronic problems.

oaksinspace

Is it possible to use a custom speed density 90-92 harness http://tpiparts.net/inc/sdetail/1052 on a 88 tpi system and change the chip in the ECM? Will the rest of the stuff then work as a 90-92 speed density system?

oaksinspace

I found a guide here http://sethirdgen.org/tpi1.htm and will go for the 90-92 system. Anybody got one, let me know