Screamin' 6.2L vs 'the dog'

[dieselcrawler]

Hey all,
I have 2 trucks with 6.2L motors in them, a '84 K-30 CUCV 1028 that I have had for a year and a half. It runs great, winds out to what seems like alot for a diesel. I don't have a tach, so I don't know what it is for sure. I also have a '83 K-5 Blazer (Jimmy) with the 6.2L, and it's stock, 'C' code intake and all. It won't wind out near as far as the K-30 will, and has much less power. How much barring will the 'C' intake and stock exaust have on this? How much can I expect the performance to change if I swap the intake for a 'J' code one? I also have not changed the fuel filters on the K-5 yet, I will be doing that this weekend. How much would that be hurting performance? It runs smooth, just has low power, in comparison to the K-30.
Thanks for any input...
Greg

[john8662]

The J code intake won't hurt, I did this on 2 C code 6.2's i've had and it made a difference, mainly less black smoke. As far as revving up, the TH700R4 probably has a governor set to shift earlier than the way that the TH400 that you have in the M1028. I have never had a TH400 equipped truck until last week (got an M1008 for the axles - Dana 60/70, but it runs), so I will be comparing. Also (don't try this) but on another truck I have messed with that had a TH700 I adjusted the TV cable (looks like a kick down cable) and it make the transmission shift different and rev up more before a WOT shift. But messing with this cable WILL tear up the 700, because this cable is for shift linkage and regulates pressures in the trans. Maybe your cable needs adjusting, but this shouldn't be done just be the "feel" it has to be done with a pressure gauge (so I'm told).

On the J intake, keep an eye on ebay for an intake, you'll need the earlier J intake that has mounting provisions (horizontal thread) on the back of the intake for the secondary fuel filter since you'res is an 83. The 84 plus didn't have the secondary fuel filter mounted on the back of the intake, they used an all-in-one filter on the firewall.

[dieselcrawler]

John8662,

I already have a J intake, from a early '90's ton truck. I got the whole motor from my uncle, it's been sitting outside for a few years. He said it was missing a little when they took it out, but I am sure the intake will work. I plan to change the filter system to the newer type so I can use the same type of filter on both trucks.

As to the 700R4 limiting the engine rpms, even if you hold it in gear, you can't get it to wind out much, and at it's best, it still doesn't have near the power the K-30 does. There's no black smoke, so I'll expariment with turning up the fuel at some point, maybe when I change the intake and fuel filter system.

Where is the best place to get information on adjusting the 700R4? Spec's, tools needed, etc. I want to do the work myself, and I"m good at following directions, if only I have them.

Thanks for your time and input...

Greg

[john8662]

If you're changing out the fuel system then certainly go ahead and install the newer 90 model intake manifold. The 90 intake manifolds are a single plane intake, the older J intakes were Dual plane intakes (had a divider in the middle, but no EGR). Probably the same one on your M1028. It will bolt right up with no problems (I have a single plane intake on a project suburban). To tell if your blazer is revving up, you will want to go ahead and put a tach in, It might be winding up and just not sound like it. Also the C series injection pump is the same as the J series pump, just the fuel is metered down some. You can turn it up, detailed instructions are here on this forum somewhere.

[dieselcrawler]

I've got a copy of the instructions for how to turn up the IP, have yet to try. Hope to soon.
As to the intake, will dual plane vs single plane intake make much diffrence? Is one more disirable than the other? I will have access to both.

Greg

[john8662]

I can't say which is better, but my personal opinion is that the single plane intake is "wide-open" and it could flow more air. Only other problem you're gonna have with the 90+ intake is what to do with the CDR valve configuration. The later single plane intake only has one larger port on if for crankcase gasses to pass. The older dual plane intakes have two smaller ports on either side of the intake. To install my single plane intake I had to get a valve cover from a 6.5 with the CDR valve mounted to it to make it work with the newer intake. Or you could borrow the valve cover and cdr valve and hose off the doner engine and make it work on your engine.

John

[dieselcrawler]

I have the whole motor, so I can take all the parts off of it I need to make the intake, etc work for my older 6.2L. If I'm not mistaken, I think this newer motor also has the rectangle type ('84-newer) fuel filter mounted to the intake? I should be able to use it, right? I haven't looked at the donor motor for close to a year, it's been tarped and covered out back since then, I"ll look at it later today and see what parts I have to work with.

Greg

[john8662]

Hmm, fuel filter mounted on the back of the intake, sure this 90 model engine didn't come from a panel van or van in general. Either way you may have scored a fuel filter assembly, as long as its the square type filter.

[dieselcrawler]

I'm a slacker... I've been too busy to stop out at the ol' man's to look at the motor. However, I do know that it came out of a '90 or '91 GMC 1 ton tow truck that my uncle had... he swaped it out for a 454 and gave me the 6.2L. I'm not sure it has the filter on the back of the intake, but that's what I seem to remember. I'll look closer when I have the time, hopefully by this weekend.

Greg

[ropinfool]

I'm sure you probably realize this but the military truck probably has a gear ratio of somewhere around 5.42/1 and the blazer could have a ratio of 3.42/1. Also the t-400 is lower geared than the 700r4. This is going to make a huge difference. You may think you are comparing trucks, but I think it may be more like apples to oranges, but what do I know??? Just my opinion. Good luck. John

[dieselcrawler]

Ropin':

I've swaped things around a bit... The K-5 was stock when I got it, and it was a dog. Had 3.08 gears, stock tires. Swaped the axles that came from the CUCV K-30 into it, with 4.56 gears, and 39.5" boggers... performance is about the same.
The TH700R4 has a lower 1st gear than the th400, and I can tell the diffrence there, at crawling speeds... compaired to the K-30, when it had the same axles and tires under it. It just won't wind out at all. Tromp the go pedal, and it falls on it's face.

Greg

[dieselcrawler]

Hey all,
Finaly got a chance to look at the 'parts' motor out at my dad's. It does have the fuel filter mounted on the back of the intake, and it is the single plane intake. Man, it's wide open! Looks like you could sit a bowling ball inside that thing! I will try swaping it on to the K-5 as soon as I can. Are there gaskets between the intake and heads, or can I use high temp RTV silicone? I remember reading somewhere on this BB that something didn't take gaskets, but maybe it's the exaust manifolds?

Greg

[john8662]

Yes, there are gaskets, just go to the parts store and get the felpro intake manifold gasketes for a HD 6.2, no RTV here! You're right about the exhaust manifolds though, they don't have gaskets.

[NH2112]

Originally posted by ropinfool:
I'm sure you probably realize this but the military truck probably has a gear ratio of somewhere around 5.42/1 and the blazer could have a ratio of 3.42/1. Also the t-400 is lower geared than the 700r4. This is going to make a huge difference. You may think you are comparing trucks, but I think it may be more like apples to oranges, but what do I know??? Just my opinion. Good luck. John The M1028 CUCV's gearing is 4.56:1, and a 700R4 actually has a lower 1st gear than the TH400 does (3.06:1 vs 2.48:1.) The differences in gearing alone are enough to account for the 1 truck running at a much higher RPM than the other. M1028s are basically a 65MPH truck and you'll be right on the governor then. Like John says, the Blazer most likely has tall gearing, but more likely 3.08:1 or even 2.73:1. Add in the emissions crap that the CUCV won't have, and the higher HP rating of the CUCV, and they may explain why the Blazer's a dog.

[dieselcrawler]

As I said earlier, I've swaped things around a bit... the CUCV's stock axle w/4.56 gears and 39.5" tires are now under the K-5. When the CUCV had thoes gears and tires, it was slow, but did ok. The K-5, with the same gears and tires, and the advantage of the lower 1st gear in the 700R4 trans, and it will not turn near the RPM's that the CUCV would going up some of the same hills. Just plain slow. I'll tinker with it, if the only diffrence is in the intakes and emmision control crap, I should be able to get it to run rather well. I have another J code intake to put on the K-5, That should help.

Greg

[NH2112]

It could be any number of things. I believe the K5's engine would have been rated at 130HP and the 1028's at 150-160, so that alone would make a difference. Maybe the engine's just getting tired. There's also the possibility of a slipping converter or that it's not locking up, weak springs or low pressures in the tranny, etc. If you know the stall speed rating of the converter in the K5 then a stall test would provide a lot of information.

[dieselcrawler]

Finaly got the J intake off the parts motor. Hope to swap them this weekend. I will have to use the CDR valve w/only one port, as was said earlier, there is only one on the pass. side of the intake. Otherwise, it looks like it will be an easy swap. Picked up some gaskets the other day also, just need the time to do it now...

Greg

[kreider]

Hey Greg,
I'm in need of a "j" head for my 91' crewcab, my valve train broke and I ate a piston and the head, the other side is fine though, I originally bought the rig and the other side had a valvetrain rupture and ate a piston! so one side is fine and rebuilt but the other is hammered now....

anyway, just caught your posting and thought i'd drop a line and see if ur interested, i'd be willing 2 buy both or whatever....

i have a classified listing looking for one as well on this site...

I'ts a beater truck/garbage hauler but it sure is nice to have around as a backup....

Thanx for a reply, Irv smile.gif kreider@gci.net

[dieselcrawler]

As of right now, I'd like to keep this motor compleat as a long block. I'll post parts as I get them, I may have another one in a few weeks/month or so...

I was under the hood of the K-5 the other day, found a wire at the injection pump that needed spliced back together. It went to what I'm guessing is the throttle position sensor, has 3 or 4 wires going to it... My K-30 w/ TH400 has vac lines going to this area on the IP. I spliced the wire back together, perhaps this might have something to do with my full-throttle upshifts not happening from 1st to 2nd? I will have the ol' beast out this weekend, goin' 'wheelin' with some friends. I'll see if it runs better. I know it's starting alot better, put in a set of Kennedy's glow plugs and a manual switch... wow, what a diffrence. Fires right up.

Greg

[kreider]

Let me know if u decide 2 part it out...or find another j head somewhere!

thanx, Irv kreider@gci.net

[dieselcrawler]

Here's some new info on the subject... I was out 4-wheeling this past weekend, and the day went on, the K-5 just kept running worse and worse. No power, would idle fine, but would not rev up. I suspected that I might need to change the fuel filters, as I hadn't done that since I got the truck, it's been about 3 months now. I had the filter with me, so I pulled the old one off, and filled up the new one, spun it on, cracked the air bleeder, cranked the engine. No fuel. Crank some more, alot more. No fuel. Had a buddy crank it while I held my finger over the bleeder, no air. I have come to the conclution that the fuel pump has failed. I put a new one on last night, but need to charge the batteries before I try to crank it again.
So, my question is this: Can a failing lift/fuel pump cause the problems I have decribed in the past posts? I would think so, and hope that a new pump solves the problems. I just hope I don't run into more problems, haveing to bleed the injectors them selves, I may have gotten air in the system. I didn't have the wire pulled off the IP one of the times I tryed cranking it over... Guess I'll find out tonight.

Greg

[Keith Richards]

sounds to me like a failing fuel pump can cause poor power/power loss.By the way I checked out your rigs on that photo page,pretty cool.I have always liked those military chevys and finally got one,only catch is its a gas motor.It was actually a forest service truck,with the same specs,dana 60 ,14 bolt 4.56 gears,th 400,brush guard etc.All I need is a dieselmotor.

[dieselcrawler]

Here's the latest... While I had the K-5 in the garage, I went ahead and pulled off the intake maifold, and put on the J-code one I had, as well as changed the fuel filter to the newer, box type filter. Cranked the motor over, primed the filter, cracked the injector lines to bleed them, hit the glow plugs, and after a few seconds, it fired right up. Took it for a test drive, it runs great. Nearly as good as my K-30 does. So, I dont' know how much of it was the fuel pump, the filters, or the intake, but it rev's up great now, has quite a bit more power. Still won't shift out of 1st gear with out letting off the trottle a little bit though. Not sure why that is. Other wise, I'm very happy with the results. Can't wait to take it out on the trails again...

I hope to post some more new pictures from this past weekend soon... there was one truck out there with 2.5 ton rockwell axles and tractor tires... screamin' big block under the hood, was just eatin' up the mud holes.

Greg