What injectors to use on 88TBI 350 for best mileage?

[Rockhounder]

Hi there,

I am thinking about replacing the original injectors on my 88 suburban 350 TBI. The originals now have close to a quarter million miles on them, and better to replace at leisure father than 100 miles from nowhere in the desert....

I want to alter the motor (which is currently bone stock) to get the best possible mileage while at moderate speed and low throttle position (45 - 55 mph, highway style driving). Are there any injectors that are known to give better mileage? I also know that I should swap the intake manifold with a better breathing one, I'm guessing?

Driving behind semis, trying to draft, I can get just about 13 mpg on long freeway trips. Combined I get around 11 mpg. I have 33 tires, and about 600-700 pounds of extras always on the truck like the extra batteries, solar panels on roof, freezer fridge, big bumper, etc.

Anybody have any tips and suggestions?

 

[1stDeuce]

Ugh. 13 is not very good in general, but for an '88 suburban on 33's with crap on the roof, not too bad. Stock replacement injectors are your best bet, and if yours have 250k on them, you'll probably see a little better mileage from the swap. Undersizing the injectors will cause the engine to start hard, and run like crap until it learns all the fuel trim values back up to compensate, and then you'll only end up starving it at higher throttle settings, which will do far more damage than good.

If it's geared like so many trucks in the 80's, the gearing is too tall. Most likely you have 3.07 axles, which means you may well get slightly better mileage at 55-60 in 3rd gear vs. OD. If you have 3.42's, it's a little better, but still geared too high. 3.73's would be ok-ish at best for 55-60 in OD with 33's, but very few trucks came with 3.73's back then.

Normally with such tall gearing, a mild "RV" cam would be the best bang for the buck, but the factory cam in an '88 350 was a fairly low end oriented anyway, so even that's not much help.

Good luck!
Chris

 

[Rockhounder]

Thanks,

I have the 3.42's and I actually got better gas mileage by a little when I went with the 33's. If I am at 55mph, and coasting along, I am able to keep the rpm's in overdrive, which ends up feeling like it's spinning at 1500 rpms... Once, on a trip, I was ableto keep most in that range and got 14 mpg

 

[cyclic]

Stock injectors, with "ultimate" TBI mods will help. Between the TBI mods and a good exhaust, it will do better. Once past that you will be looking at programming of one form or another. I went with Dynamic EFI, it upgrades the factory computer and makes it user adjustable and even has a self learn cycle. I'm eventually going with a complete 96-00 Vortec 350 and tune it. But for now, the TBI mods and exhaust are my next things. I'm right in the middle of a 2004 disk axle swap and some home improvements.

 

[Bojak]

A quick sorce for your question is cfm technologies, and tbi chips. Google both those and they sell matched injectors and more. I am about buy a cfm tech whole new throttle body with matched injectors and bump up the fuel pressure myself. Ive heard stay away from the holley replacement.