350 TBI build

[L31MaxExpress]

I put headers n Y-pipe on mine, got rid of cat with 3" pipe, then already had a cat back, but that made a HUGE difference in torque, like swapped a big block in...

I had a stock 1-ton 8.75:1 compression TBI 350 crate engine years ago. First I swapped to an edelbrock performer rpm intake manifold with a GM 2" marine TBI and the matching marine TBI adapter. Then used a 454 air cleaner with a built in powerbowl. I already had thorley tri-y headers into a factory G30 van catless 2.5" dual exhaust. I used a X-pipe up front and custom made pipes to connect the headers to the factory duals. Then I tuned my own chip without the EGR. It made stock vortec horsepower at the tires (about 210 rwhp) and way more torque (308 rwtq). I then swapped the stock TBI cam for a 96 LT4 roller cam and 1.6 rockers using "Z/28" valve springs. Well exceeded the power numbers of a stock Vortec while keeping the torque and fuel mileage. With the stock heads and 18cc dished pistons it was making 250 hp at the tires and about 310 tq at the tires.

The factory TBI cam degreed about 194/203 @ .050. Lift was .390/.410. The LT4 cam was 203/210 @ .050 and .47x lift. The roller obviously had more lift and duration across the whole lobe as well. With the breathing modifications the cam change was enough to make about 50 hp more at the crank without sacrificing torque, idle quality or fuel mileage. That is a big win. If I were doing the same build in 2020, it would be a bigger cam around 220/220 @ 0.050 on a 108 LSA and Rhoads V-Max lifters hot lashed with a 0.020" feeler gauge between the rocker arm and valve tip. The more I play with Rhoads lifters the more I like them. Gives a person the ability to have two cam grinds in the same cam which broadens the torque curve and keeps the manners of a much smaller cam. Not uncommon to see 3-5 in/hg more vacuum with the Rhoads lifters.

 

[Rico387]

Here's info on Vortec vs TBI differences.
https://www.gmt400.com/threads/how-to-put-a-vortec-motor-in-a-tbi-truck.49463/

Here's a video on porting TBI heads. I used this as a guide for porting my TBI heads, but I didn't open up the chamber - when I practiced on a garbage head I kept gouging too deep into the head. I did all the rest of the mods he shows. I'd tell you how it runs, but my motor's still in work.

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I watched the entire series and I was fascinated. That’s the most anyone ever spent refining the very under appreciated tbi heads. I’d like to see before/after torque numbers on a dyno.

 

[Schurkey]

If you use the cash-wrench...

Thanks for that. Clever and appropriate. Somehow, I missed it the first time through.

As the Wise Man* said, "Never underestimate the power of the Greenie to make problems disappear."




*Smokey Yunick

 

[Marcus W]

What’s the best way to convert the tbi to efi? I saw a truck trend article about an edlebrock system they put on a ‘95 Tahoe that gave decent power gains, however the article was from 2004 and I can’t find anything similiar to the system they used

 

[884x4310ci]

Edelbrock had a kit( I think it's discounted) that converted a tbi truck to mpfi. It reused the throttle body with out the injector pod. New intake injectors fuel rail was all included.
but I think they had trouble tuning it. And that lead to it being discontinued.

 

[Erik the Awful]

What’s the best way to convert the tbi to efi?

A Vortec fuel pump fits right into the stock TBI sending unit. Then Holley Sniper. If the truck runs before you start, you can get the swap done in about four hours.

You will need:
Vortec fuel pump
Square-bore manifold
Basic Holley Sniper kit - no need for the "Master Kit"
TBI adapter fittings - I adapted to AN and used braided line.
TV/throttle cable bracket (Summit G1514)

...and probably some other stuff I've forgotten.

 

[Marcus W]

A Vortec fuel pump fits right into the stock TBI sending unit. Then Holley Sniper. If the truck runs before you start, you can get the swap done in about four hours.

You will need:
Vortec fuel pump
Square-bore manifold
Basic Holley Sniper kit - no need for the "Master Kit"
TBI adapter fittings - I adapted to AN and used braided line.
TV/throttle cable bracket (Summit G1514)

...and probably some other stuff I've forgotten.

Will this kit control the transmission? Or do I have to worry about transmission control at all?

 

[Schurkey]

What’s the best way to convert the tbi to efi?

TBI IS EFI. No "conversion" needed.

 

[Erik the Awful]

Will this kit control the transmission? Or do I have to worry about transmission control at all?

If you have a 700R4, the TV/throttle cable bracket lets the transmission work. I left my computer hooked up to the TCC, but I haven't driven it enough to see if it's really working. There are ways to control it electrically without the computer.

If you have the 4L60E, you'll need a way to control the transmission.

Schurkey does have a good point, better expressed as "Why does the factory TBI EFI not meet your needs?" It's fairly reliable. I went with a Sniper because my cam is too big for the TBI without a lot of tuning and modification.

 

[Marcus W]

If you have a 700R4, the TV/throttle cable bracket lets the transmission work. I left my computer hooked up to the TCC, but I haven't driven it enough to see if it's really working. There are ways to control it electrically without the computer.

If you have the 4L60E, you'll need a way to control the transmission.

Schurkey does have a good point, better expressed as "Why does the factory TBI EFI not meet your needs?" It's fairly reliable. I went with a Sniper because my cam is too big for the TBI without a lot of tuning and modification.

I’m looking to go to a different injection system for more efficient fuel delivery, and I have the 4L60 transmission.