Is 300 hp possible from a tbi

[PlayingWithTBI]

Interesting - my 88 C1500 came with a 5.7L and a 10 bolt 3.42 open differential.

Edit - and a 700R4

 

[evilunclegrimace]

Interesting - my 88 C1500 came with a 5.7L and a 10 bolt 3.42 open differential.

Edit - and a 700R4

My truck was 8600 GVWR. That is why it had the THM 400. I think that some of the 7200 GVWR 2500's also got the THM400. There was a lower GVWR, I don't remember what it was off of the top of my head but it was what most of the C1500 trucks where equipped with, these trucks almost always came with 10 bolt rear differentials and 700R4 auto transmissions ( unless a manual was ordered)

 

[westsoundred]

VSSB - Not sure.

As far as the wiring for the harness though, I can give a little direction. Once again, download your factory service manual for the year of your truck from the thread I linked earlier. Find the pinouts for the PCM connectors, and the pinout for the 4L80E transmission wiring harness plug. Run all the wires for the pins in use at the transmission plug, and connect them to the appropriate pin at each plug.

Another thing to consider... This isn't the route I would go personally as I like having OD, but you could always swap in a TH400 and avoid all the electronics.

i did download the service manual, and found several youtubes on the rewire to trans, the VSSB trips me up.


The TH400 option is interesting, although since i drive the truck everyday I also prefer the OD. A 400 would render my truck to off-road /fun only truck, i fear, because of the drop in mpg

im running 3.42 gears fwiw

 

[evilunclegrimace]

i did download the service manual, and found several youtubes on the rewire to trans, the VSSB trips me up.


The TH400 option is interesting, although since i drive the truck everyday I also prefer the OD. A 400 would render my truck to off-road /fun only truck, i fear, because of the drop in mpg

im running 3.42 gears fwiw

The drop in MPG is not all that drastic depending on your out look. The THM 400 was standard equipment for years on trucks that where driven on the street, Relegating a truck to off road/fun status because it has a 3 speed transmission is a bit extreme. I drove my '88 K3500 5.7 THM 400 for 30 years and routinely pulled down 14-15mpg.

 

[L31MaxExpress]

The 87 G20 van I 6.0/4L80E swapped had a 305 TBI/TH400 with the TH350 output shaft and yoke and an 8.5" 10-bolt with 3.08s. It got about 15 mpg on the road turning 2,500 rpm @ 70.

 

[westsoundred]

well, maybe I'm shortsighted on the mpg drop.

 

[evilunclegrimace]

well, maybe I'm shortsighted on the mpg drop.

It all depends on how you plan on using the truck, if you are going to run the interstates then the OD is a welcome advantage. If you run around town most off the time then the OD is not really a plus.

 

[L31MaxExpress]

well, maybe I'm shortsighted on the mpg drop.

In my Express van with the 5.7 Vortec I saw less than 1 mpg difference running 70-80 mph in 3rd as I did in 4th when it had 3.73 gears. A big part of my decision to drop in 5.13 gears. I was able to get 2 mpg increase with lean cruise in the 0411. Went from 17-18 mpg down to 16-17 after the gears and up to 18-19 mpg with lean cruise and 5.13 gears with LT265/75R16s. 4L85E trans.

 

[C2500]

Was it with a 7.4L?

305

 

[C2500]

Was it with a 7.4L?

305