350 Tbi engine, transmission and cluster swap

[jpnc]

I have a 1988 GMC Sierra 1500 long bed pickup. It has a 305 Tbi with a turbo 400 and 3.42 rear end

I have a 1993 350 Tbi engine and I want to install it with a 700R4 transmission.

I will have to get a different PROM (chip) for it.

I have a 3 speed cluster in it now. Will I have to change the cluster?...The 700R4 is a 4 speed

What all do I have to change for the engine and transmission to fit? ( drive shaft, and etc)

I have a 1991 GMC Sierra 1500 5.0L engine, 700r4 transmission for a donor truck

Will I have to change the wiring harness?

[Jsdirt]

Probably have to shorten ... or lengthen the driveshaft a bit. 700R4 is 30-3/4" long (shorter if Corvette trans.) - TH400 is roughly 28' -37", all depending on what tailshaft is used.

 

No need to change the cluster - just count your shifts. One down from park is Reverse, 2 neutral, 3 drive, etc ... No need for a chip either. Those were only used for a performance increase (and that's debatable, IMO).

 

With the 700r4, the most important thing is getting that TV cable hooked up correctly, and with the correct geometry - you can burn that SOB up in 25' adjusted wrong. Sunnax, if I remember right, sells a TV corrector for Edelbrock carbs to get the geometry right - you might not need one for other carbs, or TBI ... not sure there.

 

Engine should drop right in - block between 305 / 5.0, & 350 is identical. Only electrical connection for the tranny would be for converter lockup - if it came with a TH400, then you'd have to wire one up & run it manually via toggle switch - flip it on whenever your going over 50 unloaded.

 

If it were me, I'd pitch the TBI and go carb .. but I seem to be a rare breed these days ...

[jpnc]

Thank you Jsdirt for your time and information....I may just swap engines. Take the 305 out and drop the 350 in it. I found out yesterday that the rear end is a 2.73

 

How do you think the 350 would run with a 2.73 gear?

 

I wanted more low end power. It's going to be a lot of work to change the engine, transmission and rear end.

 

You got any ideas of what I should do?

[Jsdirt]

It won't set any records, but I think you'll be happy with the pull it should have over the 305. Could always throw a mild cam in there (would have to carb it to maximize that, however) to boost low end a bit more. You'll get excellent highway mileage with that gearing, though. With the 700r4, I bet that thing will turn UNDER 2,400 RPM at 75. With that overdrive, your effective final drive is 1.91 - Bonneville gearing.

 

I'd get the biggest transmission cooler you can find - TWO of them - & plumb them in series from the return of the OEM radiator tranny cooler. Torque converter is going to do alot of slipping getting everything moving with that gearing, and you can never be too cool with transmissions, IMO. The deep 1st gear of the 700 will help ALOT with off-the-line power, though.

 

I would run it a while and see how it is before modifying anything. You might end up satisfied with how it is.