Looking for advice on basic engine mods to boost performance.

[gldixon86]

35s and mountain roads? You need torque. I'd start with a cam, but that's not a "basic" engine mod. I'd go with an exhaust, cut out the restrictor in the air box, and a tune. If you get much above stock, you'll need to replace your fuel pump. The factory Vortec pump is a drop-in replacement that is a massive upgrade.

What restrictive part in the air box?? I want to know if I have one in mine an to take it off???

 

[Supercharged111]

What restrictive part in the air box?? I want to know if I have one in mine an to take it off???

TBI trucks have a pinched down section inside the airbox. It's an insert you can slide out by hand. Also make sure the heat riser isn't staying partially closed.

 

[Schurkey]

Heat riser? My '88 had no heat riser valve. The TBI manifold has a big coolant passage that warms the manifold.

Or are you talking about the temp-sensitive door in the air cleaner snorkel? GM used to use a vacuum-operated system, but the GMT400s seem to get a wax-pellet, self-contained door and thermostat.

 

[Supercharged111]

Heat riser? My '88 had no heat riser valve. The TBI manifold has a big coolant passage that warms the manifold.

Or are you talking about the temp-sensitive door in the air cleaner snorkel? GM used to use a vacuum-operated system, but the GMT400s seem to get a wax-pellet, self-contained door and thermostat.

Yes, the latter is what I was referring to. The wax pellet actuated deal.

 

[1989GMCSIERRA]

The best cheapest mod you can do is go and regear the truck to a 4;10 or 4;56 ratio. If it’s stock and haven’t been regeared you’re probably running a 3:08 or 3:55 ratio. With 35s you lost a ton of power. That would be my finest mod before anything else. My 89 was completely stock and I went from 3:08 to 4:56 gears and that woke the truck back up. It’s still running the stock engine with 396,000 miles.

If you wanna wake that engine up more bolt OBS a ren’t gonna do a huge amount of Hp for it until you get better heads and regear. Summit has aluminum heads that are made for TBI engines. Get heads and a cam take the TBI and have it bored out do headers and exhaust along with timing and a chip.
Anything else isn’t gonna do much.

 

[pgutier1]

The factory Vortec pump is a drop-in replacement that is a massive upgrade.

Erik, can you please explain more about this? My replaced Delphi pump just died after 10 years. Why is a Vortec pump a massive upgrade?

 

[Erik the Awful]

The stock TBI fuel pump can barely keep up with the TBI, and can't support more horsepower. The GM EP381 fuel pump from a Vortec-powered truck drops right in place of the TBI pump and can support significant upgrades. I'm running a Lunati cam with .515" lift at 240° duration, headers, and a Holley Sniper and the Vortec fuel pump is plenty.

More Information for GM GENUINE EP381

 

[Eargesplitten]

Timely question, I've been wondering something similar. I'm picking up a TBI 350 K1500 shortly here and live at a similar altitude. I was considering putting a junkyard M90 or something on once I finish my other project but can't find many examples of doing that with TBI and found some other concerning aspects.

The stock TBI fuel pump can barely keep up with the TBI, and can't support more horsepower. The GM EP381 fuel pump from a Vortec-powered truck drops right in place of the TBI pump and can support significant upgrades. I'm running a Lunati cam with .515" lift at 240° duration, headers, and a Holley Sniper and the Vortec fuel pump is plenty.

More Information for GM GENUINE EP381

Okay but what you're forgetting is it's starting with ~30% less horsepower, which with an ECU using closed-loop fueling based on o2 sensor feedback (which I assume TBI does?) means it's going to be adjusting down to less fuel. The fuel pump is a valid concern eventually but a lot of people don't realize how thoroughly elevation hamstrings engines. My rated 230 horsepower engine in my project car is 160 at the crank at this elevation. By the time I get up to Eisenhower Tunnel, let alone the higher passes, I'm at about 140.

5 psi boost at 9000 feet does nothing more than driving down the mountain to sea-level. If the engine can handle sea-level, it can handle 5 psi boost at altitude.

Ok, there's a couple of variables not accounted for: The air going through the radiator is also damned thin; and the supercharger is going to heat the air some; and draw some horsepower to do it. OTOH, both of those are also offset somewhat by the generally lower temperature at 9K altitude.

There's one more: a positive displacement supercharger pushes a fixed volume of air, since its rotation is based on the speed of the belt, whereas a turbo goes up to a certain PSI before the wastegate opens. That volume of air is going to similarly be at about 70% of sea level pressure, so your ratio of extra induction to parasitic loss from the belt is going to suffer. These people are a tuning shop on the front range of CO around 5000 feet that have a blog post about it. They suggest a smaller pulley, but I'm not sure what the practical ranges are on pulley size. https://www.5250performance.com/blog/lets-talk-about-supercharging-power-at-5000-altitude

 

[Erik the Awful]

The Eaton M90 is undersized for a 350, and for reliability reasons, I wouldn't try and overdrive it to make up for it. I have an M90 off a Jaguar sitting in my garage, and I wouldn't even attempt to install it on anything larger than 4 liters. If you can find an M122, that would be more reasonable, but you're looking for a needle in a haystack.

Okay but what you're forgetting is it's starting with ~30% less horsepower, which with an ECU using closed-loop fueling based on o2 sensor feedback (which I assume TBI does?) means it's going to be adjusting down to less fuel. The fuel pump is a valid concern eventually but a lot of people don't realize how thoroughly elevation hamstrings engines. My rated 230 horsepower engine in my project car is 160 at the crank at this elevation. By the time I get up to Eisenhower Tunnel, let alone the higher passes, I'm at about 140.

So, you're never going to drive down to sea level? A better fuel pump is needed, especially if you plan on forced induction.

 

[Eargesplitten]

I am definitely not taking a 30 year old truck on a 3000 mile road trip, no. The last time I drove down to sea level rather than flying was 2011. You make a good point about it still being something you would want to do for breathing room though. And who knows, maybe I find a unicorn car that needs towed across the country some day and decide to risk it.

When I was thinking of the M90 I mistakenly thought that the elevation would reduce the volume requirements of the supercharger to get some usable amount of boost, while now I realize that it's the opposite and you need a bigger one, an M90 might be too small for my 6 cylinder project car (which is a moot point because the engine bay barely has room for a hand, let alone a supercharger). I've made a whole thread about my indecisiveness to avoid hijacking this one though.