1989 5.7L 350TBI (fuel injected) power question
 

Hey All,
I was unable to locate a thread in regards to the powerplant for the 5.7L 350 and i have a few questions about the power. I have an 89 K5 fuel injected with brand new rebuilt heads (power is better than before i had them replaced) but for some reason the power does not seem to be at the pedal. The only performance modifications on the blazer is a magnaflow 3in cat and 3in piping to a single chamber flowmaster. I feel like there is no mid range power at all and top end power seems to be gone (i know its not a fast truck and heavy as well). It seems to have a slight lag in power on the bottom end and occassionally chokes if you jump on the gas too fast. When i drive to my work i go up a hill in which every once of my vehicles (98 ranger 3.0 6cyl and an 01 f150 4.6L) will down shift and accelerate up the hill (much faster than i need to go :icon_wink: ). My blazer on the other hand down shifts twice to barely keep me at 50 mph (as slow as the truckers). I do have 33in toyo tires with centerline wheels but they are not that heavy to really cause that much of a difference. I even have the top off so the its even lighter than usual. I am curious if anyone might have somewhat of a clue if the power i am seeing is correct or am i lacking power? Even on the freeway my blazer will shift in O/D but frequently down shifts as it cant hold the RPMs. Its killing me on gas!!! Please help if anyone can or would there be anything to look into for more efficiency/power? I was thinking a new intake manifold and possibly new fuel injectors...once i go up to 35's i will be re-gearing to help.

Please and thank you in advance for your help!

Going out on a limb here...

I'm going to say your Blazer came from the factory with 235/75/15's, which equate to roughly a 29" tire. Your Blazer more than likely came with 3.42 gears, or higher (as in lower number).

Now you are running 33's, which is quite a step up from the 235's. Being as your stock hp is 210 hp and tq is just a bit over 300 I can see why you think you have a lack of power.

What you have is a lack of gearing. You need to step up to lower gears, at a minimum of 4.10's. You will be amazed at the resurgance of "power".

I've seen some of the later K5's come with 3.08 gears which would be an ABSOLUTE DOG with 33's. 3.42's is bad enough. I have 3.73's in my '74 K5 with 33's. With a well loved 350 with a q-jet carb, headers, & 2.5" dual exhaust it doesn't do too bad cruising down the road.

I would try to figure out what gears you have first. If they're 3.42's or worse, 3.08's, get the gearing changed over to 3.73's (good if you're planning on staying with 33's) or 4.10's (better for 33-35" tires - any larger and you should look at getting 1-ton axles).

The gears shall be my main focus then! so if i plan on increasing tire size to 35's then definitely do 4.10? With lowering the gears to this, should i also see an increase in mpg or is it a slight change? Again i thank you both for your thoughts as i truly did not believe how much gears could change. That is the first thing on my list now to get done. :)

I would first figure out what you have in your truck. If no-one has changed anything, this can be determined by looking up the codes found on the SPI (service parts identification) label inside your glove box. Post up your Gxx codes (G followed by two numbers or a letter & number). If you need confirmation and haven't serviced the axles yet, pop off the diff covers and look for the numbers on the ring gear (xx-yy where xx is the number of teeth on the ring gear and yy is the number of teeth on the pinion gear).

If the largest tire you can see yourself putting on the truck is 35" and you don't see yourself doing any hardcore offroading, then upgrade the gears in the axles you have now to 4.10's and have fun with the truck! If you expect to go beyond 35" tires and/or do some heavy offroading, then upgrade the axles to Dana-60 in the front & Corp 14bolt - full floater in the rear (a 14BFF from the older 3/4ton pickups bolts right in to a 1/2 ton application - from a 1 ton, the spring perches will have to be moved).

I try and take the truck out as much as possible but times are tough financially (i know we can probably all agree) and being that im young i just dont have the money to do much at once...so i get to piece it together slowly! I love mudding and off-roading, but 98% of the time shes my daily commuter to work and i have to make sure she gets me from point A to point B safely. so i try not to go to extreme. i did hear from a close friend that 4.56's arnt too bad if i was going to jump to 35's or bigger...but would that still hurt me for the time being with 33's? Any thoughts?

You could use 4.56's with 33's, but it wouldn't really make for the best mileage. It would be snappy, that is for sure. If 35's is all you are going to go to, I would use 4.10's and leave it at that. Save the 4.56's for the 38" tires with a Dana-60/14BFF.

Example time (overdrive for the 700R4 is 0.74:1 ratio); for an actual ground speed of 65mph:As you can see, 4.11's will be closest to factory for both 33" & 35" tires and 4.56's will result in ~200rpm higher engine speeds in both cases. If mileage is a concern for you using this vehicle primarily for your daily driver, I would use 4.10's. You'll need to modify your DRAC module to correct the speedo with 33" tires.

I love the chart! Yea i bought the truck knowing mpg will be quite low but right now im pushing a solid 8-10mpg :( 4.10's will definitely be the way i go then. Yea my friend has a f250 diesel with 37's now and has 4.56's (was at 35's but thought it was time to go bigger) hes pushing around 22mpg freeway and 17mpg city (i could only dream for that). It might be a little bit before i can get my gears changed (not sure of the price but will be looking it up shortly). Again i thank you for your time!

No problem! Glad to help!