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1990 350 motor

1990k5fan

1990k5fan

1/2 ton status
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Jul 7, 2006
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Location
Gilroy, CA
Well as I'm sure most of you who have driven the 1990 blazer know that the 350 motor it came with is a dog. It gets bad gas mileage and has no power.

I'm wondering what are some good mods that I can do to increase my power.
I've put in 4:10 gears in the back which have helped but I'm looking for more. Everything else is stock. I live in California so mods need to be CARB approved.
 
My '90 k5 runs pretty good for stock, and gets 16+ mpg, but the motor is fairly fresh with a rebuilt TBI and has 4.10 gears and 35 inch tires!!!
 
"Bad" gas mileage? If you are getting something other than 15MPG freeway, + or - a couple, then you've got a problem that needs addressed.

You won't get good mileage in these things if you consider 38MPG good.
 
I get 15 but I want more power. It seems so slow to accelerate. My mom's 2001 ford triton runs circles around it. I'm just looking for some bolt on stuff that I can add to give it some more power.

I read that in the early 90's they bogged the motor down a lot because of smog crap.
 
Actually the late 80's and 90's are the exact opposite. Compression went up, and so did power, immensely compared to the late 70's and early-mid 80's.
 
http://www.cfm-tech.com/index.htm

Check this link out. If you want some bolt on stuff to give it a litte more, then they have a few things that you will like. There is a tech article on there about fuel pressure for the TBI system that is helpful. I went from 9 psi. to 13.5 psi. of fuel pressure and it made a world of difference. I have yet to install my adjustable fuel pressure regulator, too busy trying to get the winch and the cage in the truck, but I am hoping to run around 15 psi. when I'm done. I can roll my 40's over on dry pavement with just a few bolt ons.
 
My motor has about 120k miles on it. Will it damage anything or hurt the tpi if I start boosting up the fuel pressure? Also, is it smog legal?
 
Um, thats a pretty well respected motor. I have one with 160k on it in my 94, same motor. Does fine. 15 highway mpg, 18-19 on long trips, no complaints.

What gears/tires are you running? crappy gears would make it perform like crap.
 
I have one with 200K and I have gotten as good as 20 with it. Replace the fuel filte if it has been over 15K also bump the timing to 8 btdc and make sure it has a clean air cleaner. Make sure it has a good tune up including cap rotor plugs and wires. Then if you need more power you can worry about fuel pressure and porting the tb. Mine runs HARD for stock internally.
 
I'm not so sure about you guys claiming 15mpg out of your rigs. Unless the rig is bone stock i don't see that happening. I have an 89 blazer with 234K on the clock and it still runs strong but i'm only getting 9mpg on the freeway and it is properly tuned and well kept. I think most people here are probably judging mileage off a speedo that wasn't recalibrated after a gear and or tire size swap. I've had my speedo recalibrated so my mileage is accurate. Don't get me wrong, when my blazer was stock i got 15-17 easily on the freeway but it now has 8" lift, 35's and 4.56 gears. There is no way the mileage will ever be what it was stock.
 
definately change out the fuel and air filter, with 120k on it, if the fuel pump hasn't been changed before, it may be starting to run low on pressure, that's how mine started out anyways until it just started bucking and spitting, stalling and all the fun stuff :crazy:

Yeah, fuel mileage drops big time when you lift, with big tires, and change out gearing, the Burb with the TBI 350/700r4/10b with 3.42's used to get about that 15-17 area, now with the 35" tires, 4" lift and 4.11 gears, i am lucky to get 10-12 out of it on the highway. Funny thing is it seems to do better on the surface streets. Guess it also has something to do with forcing something with the aerodynamics of a brick to do 70+mph.:doah:
 
Bow-Tie-Boy said:
http://www.cfm-tech.com/index.htm

Check this link out. If you want some bolt on stuff to give it a litte more, then they have a few things that you will like. There is a tech article on there about fuel pressure for the TBI system that is helpful. I went from 9 psi. to 13.5 psi. of fuel pressure and it made a world of difference. I have yet to install my adjustable fuel pressure regulator, too busy trying to get the winch and the cage in the truck, but I am hoping to run around 15 psi. when I'm done. I can roll my 40's over on dry pavement with just a few bolt ons.
Click to expand...

So how exactly did you increase your fuel pressure if you haven't installed the adjustable fuel regulator?
 
I have gotten 14 MPG on the highway with my 1990 TBI motor, 40" tires, and 4.56's (with an sm465). The motor has aprox. 180K on it.

I attribute that to running at a REASONABLE and consistant speed (65MPH)....and no high winds :haha:

This was calculated using a GPS unit running down to Albuquerque and back.
 
I'm more concerned with making more power as i don't do much driving except back and forth to school and my girlfriends house.

What bolt-ons give the best bang for the buck?
 
The only way to get a significant power increase on that motor is heads , intake and cam plus a good exhaust but with that goes tuning. It all gets very expensive. Things like inj. housing spacers, TB spacers and aircleaner risers all MAY add a little, so may upping the FP a tad but I bet you'd be hard pushed to notice the difference. What size tires are those? If they're bigger than 35s you under geared really.
 
I put a Flowmaster muffler on mine for sound. I couldn't believe how much more torque it made. Do that first.
And I used to get 15 MPG on the highway. Now with 40"s and 5.38s, I don't want to think about it. I love trailers.
 
ut a high volume pump on it from summit. The stock pump with somewhere in the neighborhood of 150,000 on it, had a whopping 9 psi., just the pump change bumped it up to 13.5 psi..
Click to expand...

I've got news for you, just installing a higher pressure pump DOES NOT make your fuel pressure higher. The fuel pressure regulator is what determines fuel pressure. If in fact your new higher pressure pump did increase your fuel pressure then you have a defective pressure regulator.
 
1990k5fan said:
Well as I'm sure most of you who have driven the 1990 blazer know that the 350 motor it came with is a dog. It gets bad gas mileage and has no power.

I'm wondering what are some good mods that I can do to increase my power.
I've put in 4:10 gears in the back which have helped but I'm looking for more. Everything else is stock. I live in California so mods need to be CARB approved.
Click to expand...

I have a '90 K5 w/ TBI 350 and I would definitely disagree that "it gets bad gas mileage and has no power". If you keep your foot out of it the gas mileage, in my opinion, is not bad at all for a full size 4wd. Sure, its bad if you compare it to a honda civic................ . I would also say that the power is pretty good. Maybe not compared to an aftermarket build, but for the day it was built the power was pretty good. I can tow my 28 ft. camper at 65 mph all day long. Hills slow me down, but I don't push it too hard either. In my opinion the best characteristic of the engine is its reliability. Man those things will run forever and rarely give trouble. At least mine didn't.

Would I go back with it? No. I didn't. In fact last summer at 256,000 miles I decided to replace it. I'm going back with a MPFI 383 w/ Vortec heads. I'm like everyone else, I want more power, but b/c I can have more doesn't necessarily mean that what I had was "bad".
 
4X4HIGH said:
I've got news for you, just installing a higher pressure pump DOES NOT make your fuel pressure higher. The fuel pressure regulator is what determines fuel pressure. If in fact your new higher pressure pump did increase your fuel pressure then you have a defective pressure regulator.
Click to expand...

Well then I have news for you. If your old stock pump can't put out what the stock pressure regulator is "set" for, then yes, putting a new pump on would up your pressure. It wasn't the regulator that was limiting my pressure, it was my crappy old pump that had it limited. I would probably have the same pressure with a new OE pump as I do now. But as soon as I do install the new adj. regulator, I will be able to up the pressure a tad bit more.
 
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