6.5 into a 90 suburban (has 454)

[coxfmly]

We would like to intstall a new 6.5 into a 90 suburban. The sub currently has a 454 and a 4 spd auto. The Sub is in great shape but unfortunately only gets 10-12 mpg. The engine has 140K on it.
The 6.5 is currently installed in his 85 sub. This engine has less than 10K, runs great and gets 20+ mpg. We want to combine the 2 because the 85 is trashed subject to the engine. We thought about a body swap but the engine seemed like a better deal.
Since we have both suburbans, how tough will this swap be? We know our way around engines but would like to know if a land mine is waiting for us.

Both are 3/4T, with 4 spd trans. The 85 has no options while the 90 is fully equiped.

Thanks

[john8662]

Wishin you'd bought the burb to hold him hostage for the 6.5 eh?

The swap is doable, with some minor details that I can see right off.

What transmission is involved?

You mention 4 speed (overdrive) automatics in both 3/4 tons. Out of that selection that leaves the TH700 for the '85, but am unsure about the '90. In 91 The 4L80E started showing up in 3/4 ton trucks and burbs, so it's possible that the 90 is actually a 91. The usual suspect in a 3/4 is a TH400 3 speed (which you have).

The swap shouldn't be hard at all since all the hardware is there from the donor vehicle.

He will have to swap nearly everything, radiator, all the accessories (from the diesel) will work in the '90. Which brake system does the 454 burb use? I'm thinking it's hydroboost brakes (if so, thats great news), if not, that gets swapped too.

As far as the transmission, you'll leave whats in the 90 in the 90, just swap torque converters (if both TH700's) or purchase a diesel converter for the 4L80E if it turns out to be.

The throttle cable will need to come from the '85. Now, the hard part... I don't know about the engine harness compatibility with the 90 and the 85, it could possibly just plug into the firewall, maybe not. Perhaps purchasing the diesel harness for the '90 would be the best move. A person could test the '85 engine harness on the 90 firewall connector and see what happens w/o installing the engine. Otherwise, you can modify the gas harness to work for you needs. The transmission controls are USUALLY separate from the main engine harness anyways..

Does this help?

J

[coxfmly]

John,
You have definately helped out. The 85 was picked up for $500 with a new GM crate 6.5 (never started). The gentleman who had it couldn't start it, he was using starter fluid ! My brother has driven it for the last year and loves it. He has never had any issues with it so he would like to keep it.
Yes, I was dreaming of getting that engine because the rest of the truck is so trashed and then came the 90:(

The 85 has a 700r4. I'm not sure about the 90. It doesn't look like the 700r4. It is a 4 spd and aluminum. It has gussets on the sides like the ford's.
If we use the 90 trans we would have to bring over the 85 flex plate and torque converter right? Would it be better to pick up a converter for a 90 diesel?

Thanks for the help, Paul

[john8662]

Have to identify what transmission it has.

The flexplate is specific to the transmission being used. The TH400 and 4L80E share the same flexplate IIRC.

You couldn't swap the torque converter from the 85 if it had a 700R4 into a 4L80E transmission.

To identify the tranny, look for a round (pretty large) connector located on the drivers side of the vehicle on the transmission, it will have ~15 wires. If you have this plug, it's a 4L80E.

[Craig M]

You did not mention if the 6.5 was NA or turboed. If it has a turbo you will have a problem with the heater box and controls. If natural it will drop right in with no major issues. Fuel return line, and glow plug controler or manual switch will be two "new" items for the 90 suburban.

[Craig M]

On your transmission issue, why not stay with the 700R4 that the 85 has. The overdrive on the 700R4 is great, and it is a non electronic trans. It will bolt right in. The 90 transmission may well be an electronic. The 4L80E does have a better reputation than the 700R4. A diesel converter would be required for the 90 gas transmission. If you do not plan on towing with the "new" 90, than the 700R4 should be fine. Dr Lee had 2 articles on the 700R4 a few months ago. You might review those for thoughts.

[coxfmly]

John and Craig,
I have not had the chance to look closer at the trans but I will get under there in the next day or so. The 6.5 is N/A so it seems it will be an easier swap.
If we keep the 700r4 which is mated to the 6.5 in the 90, will the 90's trans fit into my 84? I currently have a T400 and desperately need a 4th gear.
The 90 will never tow a think. I will tow a 4-5 K trailer for summer vacations. For the most part the rigs are used as daily drivers.

Thanks again for all of the information.
Paul

[Craig M]

Hi Paul

Yes the 90 transmission should bolt up to your 84 engine. You will still require a diesel converter for this gas transmission, and if the transmission is electronic you will have those issues to deal with.

[4348rd]

if it a 4L80 going into the 84 you will also need a computor i've done been their done that and it ain't no picnic

[Craig M]

More Power did the 4L80E install with a non electronic engine on the 6.5 Power Project . Used a Jet Performance "mini" computer to control the automatic transmission. Article on the install is in the archives. Took some work, was is a doable option. For a daily driver with not much towing, the 700R4 would be easier and probably work just fine.