a little more oomph from 6.2

[trailblazr81]

Hey guys, Ive been wanting to get into the diesel game and have found a 84 K5 with 6.2 for $2000 that looks to be in good shape for its age. Ive read that these motors make 130HP but what is the torque rating? Can I get the HP rating up to the gas motors power rating? Would just want a little more power for now then maybe think about a turbo later. Dunno yet, more interested in mileage, reliability, and not dumping alot of $$ in it. Just need it to tow a boat, and make the 300+ mile trip to visit my cousin. So I need to keep up with the truckers on the interstate with 3-4k pounds in tow. Also whats the stock gearing as I have some 3/4 ton axles with 4.10's, locker n 35's I would like to throw on but not sure how that would work with the diesel.

 

[stumblefoot]

I had the pump on my 6.2 turned up made a world of difference, also went from 3:08 gears to 4:10s, and a shift kit in the TH400, all in all its pretty peppy for a NA diesel, still get about 25mpg on the road.

 

[tRustyK5]

Good gearing really helps. A lot of the K5's and 1/2 tons got stupid gears which make the engine seem more sluggish than it really is. The K5 would have a 700R-4 so 4.10's would be great with 32's or 33's. With 35's I'd go as deep as 4.56's. Ideally you want to have your cruise rpm's at 65 mph in the 1800-2000 rpm range.

You can bump up the fuel rate a little, install good flowing exhaust etc but for real power gains a turbo is the way to go. I have seen the 'rated' numbers for the 6.2 and they don't do much to inspire awe. On the other hand I've seen chassis dyno numbers that seem to reflect my experiences with the 6.2. Torque on the chassis dyno in NA form and in good tune was about 340 ft/lbs at the rear wheels. This is considerably more than a SBC.

Both my 81 Jimmy (NV4500/203/205 and 4.56's with 39.5's) and my '83 1/2 ton (6.2, 700R-4 and 3.42's with 235-75-R15's) feel quite strong. 3 to 4K towing is well within range for a 6.2...

Rene

 

[35dp]

I always heard that you could swap a J code intake on them and get more power, if it doesnt already have one. can anyone confirm this?

Dustin

 

[Drey]

J codes only came on CUCVs and 1 tons I think. And yes they free up some power.

 

[trailblazr81]

Ya Ive run 35's on a 81 K5 with 3.08's and it was a dog. My 86 with 4.56's and 35's was good, and my current K20 with 4.10's and 35's does OK. Tho it has a 383 with high compression, big cam, aluminum heads, etc. But the mileage is pathetic. I would love to be getting around 20 MPG and have no worries other than oil changes. I just wasnt sure that with the diesel I would want different gearing than with gas motors.

 

[tRustyK5]

For the 6.2 you can pretty much gear it as if you had a small block. Just keep in mind that for fuel mileage, the ideal is about 1800-1900 rpm at 65 mph.

'J' code intakes help. They were available is anything but the 1/2 ton. Only the 1/2 tons got the 'C' code intake with the EGR deal. My Jimmy has the 'J' code intake and that one I port matched with a die grinder and a carbide burr. The casting was pretty poor IMO...I ended up opening the ports up by close to 25%. For a heavy truck it moves just fine IMO.

My '83 1/2 ton is bone stock and also get's out of it's own way but weighs less than 4000 lbs (versus 6000 lbs for my Jimmy)

rene

 

[MaxPF]

Hey guys, Ive been wanting to get into the diesel game and have found a 84 K5 with 6.2 for $2000 that looks to be in good shape for its age. Ive read that these motors make 130HP but what is the torque rating? Can I get the HP rating up to the gas motors power rating? Would just want a little more power for now then maybe think about a turbo later. Dunno yet, more interested in mileage, reliability, and not dumping alot of $$ in it. Just need it to tow a boat, and make the 300+ mile trip to visit my cousin. So I need to keep up with the truckers on the interstate with 3-4k pounds in tow. Also whats the stock gearing as I have some 3/4 ton axles with 4.10's, locker n 35's I would like to throw on but not sure how that would work with the diesel.

The earlier C code motors made 130HP. The J codes (different intake, heads, and IP settings) made 148HP. Some later motors made even more. For example, my 91 J code motor is rated at 165HP (RPO LMM - same RPO as the 2007 DMax ). The C code motors have slightly larger valves than the J codes, so in theory with the non-EGR intake, decent exhaust, and the pump turned up it should crank out 150HP or more. Without getting radical the only way to break the 170HP barrier is with a turbo. Of course, you can get radical: Lee Swanger over at The Diesel Page is supposedly getting around 200HP out of a NA 6.5.

 

[u2slow]

I had the pump on my 6.2 turned up made a world of difference, also went from 3:08 gears to 4:10s, and a shift kit in the TH400, all in all its pretty peppy for a NA diesel, still get about 25mpg on the road.

I don't get it. I got 12mpg with built pump, 4.10s, and a shift-kitted TH400. Now I can eake out 17mpg with tall gears (3.21) and manual trans (SM465) and have more power (seat-of-pants dyno).

 

[trailblazr81]

I think 150 HP with the 350+ lbs/ft torque would suffice. My 86 with 305 only made 160HP new and not that much torque. Thought I read somewhere theres a place that sells headers for 6.2's. Tho probly wont work if I add a turbo. I did the gear calculator and with 4.10's and 35's in OD its at 65 MPH at 1800 RPM. And theres only 2 hills I have to worry about when I visit my cousin, mostly flat Interstate 5 going to Nor Cal. And if it will just cruise between 1800-2000 I'll call it good and be done with it. I got another car to go fast in.


Tho I know sooner than later I will end up dumping my $$$ in it for mo' power!!

 

[colbystephens]

I don't get it. I got 12mpg with built pump, 4.10s, and a shift-kitted TH400. Now I can eake out 17mpg with tall gears (3.21) and manual trans (SM465) and have more power (seat-of-pants dyno).

did you change gear ratio/tire size and not account for it in making your calculations?

i rebuilt my 6.2, have an sm465 and 4.10's on 35's and it gets nearly 20mpg with absolutely terrible injectors that need replaced BAD. the fuel probably comes out like water from a hose! i bet i could break 20mpg if i had decent injectors not to mention power - tho i don't think i'm lacking in that dept. either.

 

[u2slow]

did you change gear ratio/tire size and not account for it in making your calculations?

Alll compensated for in my calcs.

Injectors and overall engine tiredness most likely play a part, but it doesn't explain why I get so much better economy going to taller gearing while everybody else seen to stay the same or improve going the other way.

 

[k204dr]

I can't get more than 15 or 16 out of mine, but the th400 sucks fuel. I got 17 out of my sm465 truck. I'm hoping the 4l80 we're working will bring it up to 18-19, but not holding my breath. turbo is definatley the way to get more power out of it. get yourself a cummins holset hx or hy35.