Alright, I'm in need of a good Chevy small-block expert to answer a few questions I have regarding TBI and TPI equipped engines! It's mainly regarding engine interals/differences between the 305 TBI and TPI, and the 350 TBI/TPI. I've noticed that the TPI engines are factory rated at significantly more power than their TBI counterparts, and I'm wondering if the TPI system alone really makes that much more power, or if the TBI engines have different heads/cams too?

Also, do the TPI engines use different wiring harnesses/sensors than the TBI engines, or are some parts interchangable here? The main reason I'm curious is because the long term goal w/my car is a mild-moderate 350 TPI set-up under the hood. However, this won't be happening for awhile, and 350 TPI engines seem to be getting harder to come by in salvage yards and from craigslist. (at least around here)

Thanks!

 

TBI and TPI heads and cam are different. Applies to both 305's and 350's.

TBI and TPI have different harnesses and sensors, although some of the sensors can be used on either, and you can re-pin one harness to make the other. Usually best to get a complete system.

 

What all sensors are interchangable with one another? or is the list too long to get into here?

I guess I'm mainly curious, because the 350 TPI's seem to be getting harder to come by, and whenever I do see any TPI stuff pop up for sale on CL, it's usually the TPI system, and/or intake manifold by itself, or a 305 TPI for sale. Another possible route I had in mind was to snag a 350 TBI up (I see them for sale more often, and cheaper), and convert it to TPI. Or is the TBI even really that bad if it's the heads/cam that make most of the difference?

 

Sensors that work on either are pretty limited. Like the knock sensor. Maybe the coolant temp sensor.

What you could do:
- 350 TBI engine from truck or passenger car.
- Trash the heads
- Get this heads/base kit http://sdparts.com/details/scoggin-d...er/sd8060ratpi
- Buy a CL TPI set-up (only differences between 305 & 350 are injectors and tuning)
- Get a decent roller cam
- Computer tune

All new exhaust would be required.

You may need to rebuild the shortblock (best to assume it will have to be rebuilt).

A similar head kit is available for TBI. The main issue with TBI is the lack of aftermarket performance support. Some people get decent performance out of the system, though.

 

So would that heads/base kit you posted be a smog legal set-up? (I live in WA). And are there any relatively inexpensive, but decent options available for aluminum heads? Also, will I need the wiring harness with the TPI system for the easiest conversion?

Lastly, is an LT4 hotcam a good option? Thanks!

 

You will need to plumb the EGR externally like the Vette TPI did.

You won't find aluminum heads that will outperform those Vortecs for less money.

Getting the TPI harness would be the only way I would buy a TPI set-up.

Scoogin-Dickey used the LT4 Hot Cam in their Vortec TPI crate engine.

 

Once you upgrade/replace the rubbish factory TBI ECM with EBL flash http://dynamicefi.com/, TBI is performance friendly.

All sorts of intake manifolds, TB sizes and Injectors are available.

 

Hey guys. Bringing this thread back a year later, lol.

So based on my own research I've done, it appears I'm making another change in direction w/regards to engine stuff w/this car, and I think I'm gonna run TBI instead of TPI, for the following reasons.

1. Lack of (local) TPI part availability - Not alot of scrapyards or individual sellers around seem to have TPI setups for sale. And those that do often only have parts of the set-up, or at best, the set-up minus the wiring harness for sale. Piecing together a complete TPI set-up, along w/the cost of aftermarket go-fast goodies for them, seems to be a fast track to getting nickled and dimed, lol. TBI parts seem to be a dime a dozen in comparison.

2. I already have the TBI - Self explanatory. Not to mention, they're simple and easy to work with.

3. EBL Flash - Seems to solve a lot of the limitations of tuning the TBI.

4. The long-tube runner debate - As pretty as the TPI looks, it's my understanding the long tube runner design is great for torque, but by nature will choke the engine at upper RPMS. Since TBI doesn't have this, shouldn't it provide more "even" flow and powerband characteristics, given it's properly tuned? Is there a major driveability difference between the two? (I've never driven a TPI car).

Lastly, should I go through w/TBI, is there anything else I need to consider to put it to good use on a 350 besides the following...?

- Bigger injectors
- 350 knock sensor
- 350 ESC
- Upgraded fuel pump
- EBL Flash

Also, what about Holley units, or (as I've also heard of being used) the 454 TBI unit? How much power will the stock TBI w/350 sized injectors be good for?

 

ebl flash is the best mod i've done to this point . headers obx 3" catback an a tune an i'm up 50 + hp !
my injecters go 100 % at 3725 rpms just so ya know !

 

And yet, more good things I keep hearing about the EBL! . That, combined w/how awful others have emphasized the factory exhaust manifolds are, is definitely leaning me towards giving the TBI a chance.

50 horses w/your mods sure says alot about the limitations of the factory ECU/manifolds/exhaust when stock. Especially w/a 305.

 

i still have a lt1 cam to put in an a aluminum 4 barrel intake with adapter plate . but i have to buy a new fuel pump first .i also have a 14 " open element air cleaner 3" thick by k&n on the car right now . i'm guesing 50 hp because of where my injecters go 100 % . i can't say enough how great the ebl flash is ! i need suspension work now cus just bumping the throttle around a turn an the azz end slides way to easy now .lol

 

I prefer to reply here, so everyone can chime in.

Using EBL works wery well and is easy to use, thakes some learning but not much, it is available for TPI and TBI.

Stock L31 produces 250 fwhp ? An LO5 with a LT1 cam will produce about the same. In this situation I would go with the LT1 cammed LO5, so I could reuse basically every part of the LO3 TBI system except injectors and FPR spring (or evetually use a VRFPR).

Though for a cammed L31 it would make sense to spend the money and buy the GMPP vortec intake. There is a fantastic sticky in the TBI forum, documenting this swap.

As for TPI or TBI, both are fine for 250 fwhp.

The stock thirdgen LO3 TBI, including the intake are ok for 280 fwhp, not sure were the TPI starts to be restricting.