I have a '87 GMC Jimmy with a 6.2L how can i get the most hp out of it and how much hp does a 6.2l have?

Ouch! That's a loaded question. I defer to the HP Gurus! I race gas engines, they're much much cheaper to replace!

Alright, this shouldn't be that hard:

You're going to need to convert it to a flatbed first.

Then install a large Pratt and Whitney jet engine. Be sure to get it pointed correctly (flames should shoot out the back).

:) Don't you love smart asses?

This is the Chev. data for my 1984 6.2L engine:
LH6 = 130 HP at 3600 RPM, 240 ft. lbs. torque at 2000 RPM
LL4 = 135 HP at 3600 RPM, 240 ft. lbs. torque at 2000 RPM

The LL4 was the heavy duty emmisions J engine. It didn't have the EGR and it had the heavy duty injection pump.

I think the last 6.2L's were rated at 145 HP, but I don't have the Chev. brochure.

Alright, this shouldn't be that hard:

You're going to need to convert it to a flatbed first.

Then install a large Pratt and Whitney jet engine. Be sure to get it pointed correctly (flames should shoot out the back).

:) Don't you love smart asses?
And if you want a jet that says together then you will want a GE one:D I can get you probably a good deal 1500 to 60,000 SHp from work, ain't real fuel efficient but lot of grunt.

Do you have access to Diesel Page Doc Lee over there has one of the hottest 6.2s I've seen out there & without a turbo. What you doing with your 6.2, running around or towing, for towing grunt you will need to move up to a turbo.



I have a '87 GMC Jimmy with a 6.2L how can i get the most hp out of it and how much hp does a 6.2l have?

Find another air filter housing, weld it to yours, use two filters, keep the large duct-hose to the front - lowers intake restriction, ducts cool frontal air to inlet.

More air = more power, free.

Plumb larger straighter exhaust piping runs, with long, large-radius bends - duals, of course.

Freer flowing = more power.

Turn the fuel pump up 1/4turn, just enough to get a little haze - more air + more fuel = more power, cheap.

Run 205deg t-stat, min 195deg - 180deg coolant is "desireable", but every btu you pull out into the coolant and into the atmosphere, is less btu useable to force the piston downward on the power stroke.

And, believe me - 6.2's don't run hot with 205deg t-stats, when the fan clutch works, that big radiator is clean, and proper anti-freeze\water coolant level is maintained.

'Nother words - maintaining the coolant system is just as important as dual exhausts, in your quest for power.

Synthetic engine oils offer less drag while providing increased lubrication at friction surfaces, increased engine heat-removal and quicker dissipation into the cooler.

Other than that, there were no mechanical changes to cam, pistons, porting - nothing.

Except - run the non-egr 'J' intake manifold - removes exhaust heat source from the intake system.

Add Cetane improver with lubricity additive to each tank.

Mo' Powah to ya, dude............

Thanks guy's thats helped out alot. I'm mainly just tryin to get more hp just to have. I don't really tow anything just drivin around and 4-wheelin. Any oher suggestions will be greatly apreciated

You also didn't mention your axle ratio's. Many 1/2 tons came with either 3.42 or 3.08 gears. These gears can make even a healthy engine feel weak. 3.73 or 4.10 with an overdrive trans are the ticket.
As for HP numbers, there are a lot of misprints out there. The 1982 J motor was rated at 145 hp and 280 torque. The C motor was 130 and 240. Main differences were fuel setting on injection pumps and intake manifold. When turboing a 6.2 the 1/2 ton injection pump will not flow enough fuel for a performance application. The fuel delivery valve needs to be changed to the J version or use a J version pump.
A while back Jim Allen from four wheeler magazine dynoed a stock 6.2 blazer, then replaced injection pump and injectors and installed a non egr intake and added stanadyne additive. Results were 130+ hp and 310+ torque at the rear wheels.
Every 6.2 I have ever owned would out perform a 350 chev hands down in the same opperating rpm range and deliver much better mileage. Add a turbo and now you are comparing to a 454. The biggest problem I have with how much to turn up the fuel is that since the sulfer has been removed from diesel it seems to take more fuel for the same btu's of heat. So the best way to judge how much to open the fuel valve is based on egt's.:cool2:

i really don't know the ratio's of my axle's. They're just stock axles i don't know much about my truck...thats why i'm askin u guy's.

Rear axle ratio should be on the RPO code list in the glovebox. if thats dissapeared, then jack up one tire off the ground and leave the other on the ground. Transmisson in neutral and count the driveshaft rotations for 2 turns of the tire.

3 driveshaft turns would be most likely a 3.08, 3 1/3 turns a 3.42, and 3 3/4 turns is a 3.73. yeah many came in 3.08 and 3.42, but there was stock 1/2tons with 3.73.

Got to get in that powerband.

Im also currently looking into improving airflow, its like my truck has asthma.

TFLundy, how happy with the gear setup you have are you? I am trying to decided between 3.73 and 4.10's with the 700R4 for my blazer.... What do you get on average for mileage?

Jack up the rear end. Make marks on both tires and on the drive shaft coming from the transfer case to the rear diff. With the tranny in neutral, get someone to help you spin the rear wheels -- one person on each wheel. Working together, you spin the wheels one revolution (going a quater turn at a time helps syncronize the process). In one revolution of the wheels, count the number of revolutions of the driveshaft. This is your ratio. For instance: 4.1 driveshaft revolutions = 4.10 gears. You need a helper otherwise just spining one wheel makes the other spin in the opposite direction due to the differential gears.

On edit: I guess the above method is easier

Both methods work, but like you said, the one is easier, especially if you are by yourself. As long as you get the correct number, its all good and the same! if done it to three trucks, one being mine(with ratio already known) and 2 unknowns. Seems to work good. 1st truck, a c20 came up 3.42 and the 2nd truck, a c2500 crew cab came up 4.10.

mangus, I like my 3.73 gear ratio. thats what i set out to look for as well. Good for everyday driving and light duty things, but still puts good amount of power to the wheels when hauling. Been hauling full bed(long bed) of oak firewood on and off last 2 weeks, and never cursed the 3.73. Also, I like the 700R4 because of the overdrive, and the low first gear. Some say not so strong of a tranny, but you can rebuild them stronger then oem. Though Ive seen a standard oem 700R4 do crazy things for years. Remember, if you change your rear gears you will have to change your front to match.

MPG..differs. Average 20mpg, been close to 22 a few times. few times 18. cant beat that with a fullsize K20 pickup, you know? depends on grade of fuel, temperature, and your driving habits for that cycle..and honestly, how the truck feels that day.
Hope it helps. comes down to what you like and what how you plan to use the truck.

I was figureing that 3.73's would be about perfect. I posted on another subject about it as well...... I have 4.10's in 3/4 ton axles... trying to decide if I want to use those or buy 3.73's (3/4 axles need ball joints and such so the $$ is about a wash).

My daughter's jimmy is an 86 and it had 3.73 gears. Easy way to find gear ratio:

Jack up one rear tire, block front wheels, place trans in nuetral and e-brake off. With a piece of chalk or black marker, place a mark on the pinion flange and also on the housing next to it. Make another mark on the brake drum of the wheel in the air and the backing plate. Turn the wheel 2 complete revolutions and count the number of times the driveshaft turns based on your marks. You have roughly 3 choices. About 3, 3.5, 3.75 . Works like a charm!:grd:

i really don't know the ratio's of my axle's. They're just stock axles i don't know much about my truck...thats why i'm askin u guy's.
Easiest way is to check your RPO code list in the glovebox sticker, in FAQ RPO code list I think stuff I listed should cover both 6.2 & 6.5 RPO lis though assumes you still have factory equipment, & nobody has been in the diff yet

Of all the n/a 6.2's I have owned, I liked the 4.10's with the 700r4 the best. When run with 235/85r/16 tires this set up would produce consistant 20 mpg with good towing power and with the lower gears there is less strain on the 700r4 so tranny life is better than with higher gears.:eek:

Would you say the same thing if you never planned to tow with it? I am still up in arms with 4.10's vs 3.73's.... of course there will be a point where I just :grd: hehe

For me the big consideration is the transmission. Th 400 = 3.73 no overdrive, best comprimise. 700r4, 4.10 over drive brings final drive to about 3.0. This is assuming 31 inch tires. I recently put 4.10's in my daughters blazer and it runs real good with 235/85/16 tires, step up to the 35/12.5/16.5 and it is a little doggy in overdrive, but looks cool.:cool2:

I suggest that you find out what your gear ratio is right now so you have a good comparision point. You would feel kind of silly if you had 3.73's already):h

So even in her blazer you like the 4:10's better? I am running 31's so from the sounds of it, I guess that settles it. Wonder where I can get 15" 8 lug rims... :)

I was in the same boat last year looking for 15 inch 8 lug wheels. If memory serves me US Wheel still makes them and they are reasonable. Some of the other off road wheel makers also offer them but they are spendy. Do a search for U.S. Wheel and see if you find a discount store that has them. 15x8 white spokes were about 40.00 each.

If you decide to use your 3/4 ton running gear, use your knuckles with ball joints from your current front end to save yourself some money and trouble. You might even want to use axles and spindles too.:grd:

My guess is, by removing the knuckles and ball joints, that I will end up destroying the ball joint seats. If I have to replace them, i think I will use Military surplus as they should be GM parts I would think. Not the junk after market that I put in the old 3/4 ton 3 times in less than 10 years!! and $40 each sounds about normal for white spokes.

Summit has the rims...$30 each for 15 x 8's $42 for 15 x 10's... Wonder if I can get US Wheel to do me some custom "Army Green" ones... ;)

If you want good ball joints buy spicer, they are the oem and they out last all others. I have had good luck taking knuckles apart to reuse ball joints, not that I am cheap, but when you have a bunch of axles laying around and one needs ball joints.......

It works faily well as long as you use some penetrating oil on the upper sleeve and carefully use a pickle fork on the lower after hitting the top loosened nut with a big soft hammer. Spicer ball joints can be had for about 40.00 a pair. contact a company like drivetrain warehouse or 4wp.;)