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opinions and perspectives wanted

8

89K5Blazer12

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hey all got a couple of quick questions. i recently bought an 89 k5 half ton blazer. it's got the tbi350/700r4/np241 combo. it's currently rolling on 33x12.5x15 tires. it's got 7 leaf rear springs (3/4 ton?) and naturally the trucks a dog in stock form. i've been tryin to find aftermarket speed parts for the factory 350 tbi but can't find anything other than a cam from i believe comp cams i believe.

what i'm wondering is whether or not i should try to build the 350 where i'm only getting 10-13 mpg now, or if a mildly built 454 is the way to go since they'd get similar mileage. i'm also thinkin of possibly droppin down to 31x10.5 tires. this is a truck that's a daily driver with a little trail riding and mudding thrown in from time to time.

any help and opinions would be greatly appreciated. thx
 
First gear it. It will make the biggest difference think at least 4.56s.

Then look harder, edlebrock makes, intakes and a cam, even a mpi intake. There are adapters to use other intakes and bolt on a tbi.

Still the gears will make more difference than any engine change.
 
GEAR it up to min of 4.56 or deeper . these things got 3.08 or 3.42 gears comon. with 700r4 overdrive helps with deeper gears .

and if going to beat it hard get bigger axles over wasting cash on 1/2 ton 10 bolts.

look for 3/4 or 1 ton axle pair used and basic bolt them in over gears/install kits / labor.
 
thx guys. how will that work for mileage? i know it's kinda stupid to ask bout that, but i'm in the army and looking at drivin from colorado back to the east coast sometime within the year for school then goin to my new duty station. so i'm tryin to find the best balance of basic offroad capability and on road performance with some towing thrown in. you can pretty much say i need an all round performer. 4.56 gears sounds doable for the towin and offroad. just not sure bout the long haul driving. how about 4.10s? would that be another choice or with this setup would the 4.56 be best? thx again guys
 
search here a bit. lots of guys with 33-35 inch tires and 700r4 with 4.10 -deeper gears .

think of it this way . you have a 1ft pry bar to use to move 1000lbs = stock gear setup .
or
you can have a 6ft prybar to move the same 1000lbs around = better gearing.

puts the motor in the sweet spot and not lug it down . also keeps the 700r4 alive as its not bogged down and or at highway speed hunting from 3rd - 4th to 3rd - 4th this will kill the overdrive section REAL FAST!

a long time friend had a 77 or 78 pontiac trans am bandit type car. ran good drove like a DOG . had 2.42 rear gears. highway was perfect. he swaped in a set of 3.42 gears and it made the car a whole new ANIMAL on the street. so much better in the end.

play with this to see your setup now on 1 side and other side to show possible setup . http://www.grimmjeeper.com/gears.html
 
Decide your tire size first, and how you are going to primary use the truck. Maybe find a set of 3/4 ton axles with 4.10s, with 33s that would be a decent gear. The 350 can benefit from a cam, a chip also. For an intake, i would recommend not even messing with a TBI only intake, i would buy a carb intake and use an adapter from transdapt for example. Remember though, the TBI can not use a wild cam, with lots of overlap. It needs a steady vacuum signal from the motor to tune itself correctly.
 
thx for the info. daily driver will be the primary use of the truck, occasional light duty offroading nothing serious, and towing a uhaul trailer when it's time to change duty stations where i'm in the army. not looking for anything hardcore for performance mods just something to liven up the 350 get it breathing a little bit and make some more power and torque.
 
full exaust on the tbi motor equiped stuff. thay were chocked big time.

headers back system will open you up a bit.

and shorty headers for 88-98 style seem to drop in with tiny mod to o2 sensor hole location and frame rail lip. then do a 2.5" custom y-pipe with somthing like this http://www.summitracing.com/search/...r-Scavenger-Series-Y-Collectors/?autoview=SKU to a single 3" muffler and cat if needed to pass emmisions .

this seems to be the best option out there. lots have done it and say it helps.
 
If this is a daily driver, I would suggest you get headers first (and a heated O2 sensor). You may not need much more than that. The TBI is a great engine. I get 20 mpg in town with a very light foot on the pedal. All I have is headers on stock tires (235's). It has plenty of power, and I tow trailers with ease. I run the stock exhaust out a 3" stock muffler. It's got a nice very deep grumble at idle and start-off, and otherwise is silent.

As soon as you get bigger tires you add additional mass that has to be overcome by the engine and transmission. The rotational mass of large tires and wide contact patch on the ground are two issues. Do that and you start to affect MPG.

If you really are daily driving this, consider two sets of tires. One set for everyday use, one for off-roading.

I run these Firestone Destinations for daily drivers and they are great. Quiet, good MPG, etc. They come up to 33" sizes. Do they look small? Yes, but if you're not worried about pecker jokes you should be fine. ;)

Then get your wild tires for weekends.

That's my $0.02.
 
good info guys thx. i'd like to potentially keep the 33x12.5x15 i got but not adverse to droppin down to 31x10.5x15. exhaust will probably work really well. right now emissions is not an issue for me but when i go to my next duty station it may be a necessary down the road. i think that once i get all this great info together i'm gonna have a great truck

thx everybody if anybody else thinks of something that might be useful feel free to hit me up with the recommendation.
 
I had a pickup, carbed though, a long time ago, a 350/700/208. Very similar to your build. We put a body lift on it and ran 33in BFG All Terrains. The motor was a stock 350, headers with full exhaust, intake, carb, with a shift kit. We put 4.10s in the 10blts and it was a great truck for a long time. I would always recommend the 3/4ton swap, as in the long run its cheaper than regearing and the brakes are much better as well. I was always satisfied with the way the truck performed as it sat, it wasnt a tire melting, building scaling monster, but it would do a burn out, and haul a 20ft bass boat no prob. Worst comes to worst, you can install a cam later if your not happy and always squeeze a little more out of it, but like I said, i was happy forever with that pickup, until i seen 40in boggers in person, and I was forever ruined.:rolleyes:
 
What gears do you currently have???

My first recommendation, as always, throw away those junk half ton axles. Find a set of 3/4 ton axles. They are a direct bolt in. The only thing needed is new u-bolts, and a conversion u-joint. Can be done in a day. To keep your 15" tires, you would need to buy a set of 8 lug, 15" wheels, and grind your front calipers, but that is also not a big deal.

Martin
 
Just a side note, 10-13MPG freeway, or city, or combined?

If that's freeway mileage, something is wrong with the truck.

My experience has been that in town, big block or small block, mileage is going to be equally horrendous. But on the freeway, the big block will suck considerably more gasoline. Pure freeway 12MPG is good for a BBC, 17 is good for a small block.

Of course, that BBC mileage assumes a fairly heavy truck and proper gearing, not freeway gears in a "light" truck.
 
I have a 383/700/208 and 33s with 4.10s and I should have went 4.56s. I don't think the mpg would really be affected that much. Mine tends too lug too much in OD. Also if you are expecting mpgs better than the teens you need a 6.2 diesel or a different vehicle.
 
first off the gears in it now are factory gears. not sure exactly what they are haven't dug that far into the truck yet. workin on squaring away the interior first. second of all that 10-13 is all city. i haven't had it on the highway yet. not looking for mpg better than the teens just trying to get a little higher into the teens like mid teens. definitely hafta consider the 3/4 ton axle swap.

thx again all for the helpful information
 
I'd be willing to bet those are 3.73's. Look for the codes starting with "G" (As in G80, the gov-lock) on the sticker in the glove box, then decode them anywhere online.

10-13 all city is pretty good. A 454 all city I can't see getting any better than 9MPG.

I've never seen anywhere near mid-teens in anything other than freeway driving, and my truck is about as "efficient" as can be without getting real technological. I get a solid 10MPG crawling up and down hill on logging roads.
 
The 20 mpg I get is city driving. Of course, I drive with a VERY light foot on the pedal.
 
My 88 runs pretty well and used to be basically the same truck you appear to be starting with so here's what I've done and my thoughts on it:

Engine
350, tri-Y full length headers, heated O2 sensor, CFM-tech fuel regulator, spacer plate, and injector spacer. Also has the 'Ultimated TBI mods' done (google it). Comp Cams 4x4 cam (242 I think but I'd have to check), MSD 6A ignition box, true dual exhaust with flowmaster super44s. I never got a chip because the MSD box works well with the cam, which has a range of idle-3500 rpm. The bottom end torque is a great improvement over stock. MPG unknown. I regeared but haven't (in 8 years) fixed the speedo gear yet, so my odometer rolls faster than it should.

Axles
I agree with the others. Get bigger axles. I blew 2 10 bolts and re-geared them twice before I wised up and went bigger. BTW, once was with 31s and one was with 33s. I now have 35s with 4.10s. This is a good gear to me, but If I ever have to re-gear it, I'll probably go 4.56s solely because it will downshift on some pretty mediocre hills on the interstate. Otherwise, I dig em.

Welcome to the cult.


.
 
I have an 88 K5, new GM goodwrench 350, stock exhaust manifolds, high-flow cat, 70 series flowmaster, k&n air cleaner element, 10 bolts, 4.88 gears, 16" wheels 315/75r16 tires (34+"). I get 10 mpg average on highway or city. My foot is white, but it isn't light. The 4.88 gears really helped. 65mph is 2300-2400 rpm, but it can go up a hill in overdrive. My trans(700r4) just lost overdrive, so it needs some work. I might get better mileage with a good trans, but I doubt it will change that much. The 350 is pretty anemic, but I towed a small trailer with the original engine and got the job done. I am also used to a carbed 406sbc capable of 525 tq. at 3500rpm and 420hp, so it is a bad comparison. The only other truck I drive is my mom's 2005 silverado with a 5.3. It would spank the K5. My K5 does beat the hell out of my grandfather's 2005 4 cylinder, 5 speed Toyota pickup.

If you might have to smog it later, consider smog legal upgrades to the 350tbi and possibly smaller tires. It will help your mileage as well. 35" mud tires on aluminum wheels are damn heavy and hard to stop. I bought my k5 as a weekend vehicle, but now it shares DD status with my 79 C20 pickup. The pickup with the 406 also gets 10mpg with a heavy foot, but sits on a 4.10 14bff and 33" all terrains, and spins at 2200-2300 rpm at 65mph, in overdrive (th400+gearvendors 0.78:1 ratio).
 
Jessie James said:
The 20 mpg I get is city driving. Of course, I drive with a VERY light foot on the pedal.
Click to expand...

First, let me state that I know the EPA estimates are now achieved by gorillas who were taken out of the jungle and strapped in the drivers seat. I exceed the EPA freeway estimates on my car by ~20%, and city by over 40%, so it's not like I don't know how to drive to get economy.

20MPG in the city in one of these trucks? How? That's a 50% increase over the rated city MPG when new! That's what the 6.2 was rated on the highway in the same vehicle.
 
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