Wanting to buy a GMT400, how old is too old, and years to avoid? (discussion)

[pgutier1]

Based on your description, are you trying to restore or have a daily driver?

GMT400s (both pickups and SUVs) have a VERY MILD collectors market. 88-94 GMT400s are becoming mild collectors pieces if restored to showroom condition. 88-94 has the "old" style interior and the TBI fuel injection. While the TBI injection is archaic by today's standards of fuel injection, it was revolutionary for its time. People love TBI bc of the simplicity of it, but a lot of people hate it for its lack of fuel efficiency and lack of power that it has compared to the Vortecs.

1995 is the worst year for the GMT400. The "new" interior came out, but the TBI still remained. 95 is an oddball year with wiring being proprietary to the year and still being OBDI.

96-99 Classic had the Vortec heads and injectors. People like Vortec fuel injection bc it's better than TBI in both power and fuel economy and really made the old school gen 1 small block relevant in the modern era. Vortec GMT400s are also hated for the poor design and location of the injectors too. The injectors are located below the intake manifold and will likely need replacing if they haven't had them replaced already and it can be a huge PITA. Vortec heads are also the most free flowing stock heads out there too. A common budget upgrade to a SBC is to use Vortec heads bc of the free flowing nature of them and they're so cheap and plentiful everywhere. 1996 also saw OBDII and 1997 saw the addition of the passenger side air bag on 1500s. The 2500/3500 didn't come with an airbag, so you just get a hole on the passenger side of the truck/suv instead.

If I were you, I'd get a 96-99 Classic 2500 with 8 lugs and a 4L80E. 4L80Es were standard on 2500/3500 trucks and are virtually bulletproof out of the box. 8 lug rear axles are full floating IIRC so they're far more durable than any semi floating rear axle out there. You can get either a 5.7 V8, 7.4 V8, or a 6.5 Diesel. I'd recommend either the 5.7 or 7.4 over the 6.5 bc the 6.5 isn't very good in terms of diesels. The 7.4 will have huge towing power, but terrible gas mileage. The 5.7 isn't great on gas either, but will be better than the 7.4 and will be more common parts wise to find. Towing won't be as good either, but it's no slouch. My friend has a 1998 Chevrolet K1500 with the 5.7 and towed a SkiDoo trailer with 2 riding lawnmowers, 2 push mowers, and a weedeater with no issues. He used to run his own landscaping business.

I can put '96-'99 Vortec heads on my '92 TBI and it will increase my MPG an get better performance? Am I hearing this right?

 

[Boots97]

I can put '96-'99 Vortec heads on my '92 TBI and it will increase my MPG an get better performance? Am I hearing this right?

Yes you can IF you buy a new lower intake. The Vortec lower intake is proprietary and older SBC lower intakes will not bolt up to Vortec heads. Thankfully there are aftermarket lower intakes that bolt up to Vortec heads and allow people to use carbs. IIRC TBI is more or less a computer controlled carb, someone more knowledgeable than myself should verify.

 

[Schurkey]

Yes you can IF you buy a new lower intake.

And screw with the EGR, various brackets, find a way to secure the EST module/MAP sensor, and EGR Solenoid bracket, jack-up the fuel pressure (or re-tune the computer which would be a better plan.)

The Vortec lower intake is proprietary and older SBC lower intakes will not bolt up to Vortec heads. Thankfully there are aftermarket lower intakes that bolt up to Vortec heads and allow people to use carbs.

...and a carb-to-TBI adapter plate.

Or buy the insanely-expensive Genuine GM Vortec-to-TBI intake manifold.

IIRC TBI is more or less a computer controlled carb, someone more knowledgeable than myself should verify.

I'd say the TBI is "more" than just a computer-controlled carb. We dealt with "real" computer-controlled carbs starting in 1980, and ending about the time TBI got popular.

But both carbs and TBI provide a "wet" intake manifold, and relies on the intake manifold to achieve decent cylinder-to-cylinder mixture distribution.

 

[sneakingfart]

Without reading the entire thread, these trucks are at least 24 years old now. No matter what, you're going to dump money into them if you want a reliable driver. I'm about 10k in a free to me, non running (broken rear end) 1999 Suburban. And I'm still finding problems. I could probably half that price if I was willing to live with doors that don't lock, handles that don't work, no AC, sluggish power windows, and some other technically non essential things. And half the work I did myself.

Edit: mechanical stuff is fixable, but above all, make sure there is no rust. Surface rust on the frame is fine, but significant frame corrosion, rust on body panels, etc, run away.