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6.2/6.5 performance thread, NEW question post #26

original balzer

original balzer

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Seams to me that while they are not the best diesel engines built, there would be more out there to make them better. Searching for info and modifications is teadious. Theres alot of the same info on differnt sites.

Maxpf's build seams to be the most involved build in this family of engines. I do recall one of the diesel mags that a 6.5 truck beat alot of other trucks in a compition. But I dont remember what mag it was. There are marine repower engines that claim 330hp and even 400hp. Being they are built for boats A guy would think they would have to be reliable. It would be kinda counter productive to put an unreliable engine in a boat.

While 400HP sounds great from a 6.2/6.5 nobody lists the tourque they put out. I mean the cummins 4BT is like 130hp but the TQ makes up for it being around 250-300 ftlbs. So would a 400HP 6.5 be close to 600ftlbs TQ?

I currently own 2 6.2's one is not so healthy but I have been told ALOT that I shouldnt consiter it blown up or junk just because it sounds bad. The other runs good but I dont know the history of the engine. It has been swapped into a 79 by a previous owner.

I have only owned 1 other 6.2 but it had well over 300k miles and still ran fine. The point im trying to get to is they seam to get alot of miles and are pretty economical, so why is it so hard to find performance parts and modifications. Is it mainly a popularity thing? Or are they realy that bad of a engine that nobody wants to do anything with them?

Anyway, this thread is where I will put any info I find on them as far as performance goes. Feel free to follow suit.
 
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i understood the fueling was one of the major limitations for the 6.2. There was a tractor puller guy that had a 6.2 in a vintage Massey Ferguson. it alledgedly put down about 500 hp, but he ran a stupid big Holset turbo and twin injection pumps. The injectors themselves had to be custom pieces too.

Indirect injection isn't known for making huge power. Direct injection diesels seem to be powerhouses able to make a ton of power without much effort.

Rene
 
The 6.2/6.5 has an unfair bad rap for several reasons:

1: The Olds diesels that predated the 6.2 were disasters, and many people think the 6.2/6.5 is either the same engine, a bored/stroked Olds, etc. In other words, ignorance

2: The 6.2/6.5, particularly the early years, had head gasket and glow plug issues. BEtter gaskets were developed, but just like with the Olds diesels, mechanics who had no diesel knowledge (and no knowledge to this specific engine) would replace the gasket and re-use the same torque-to-yield (non-reusable) head bolts. Then when the gasket blew again within a year, the engine was automatically condemned as a POS. Likewise, the unreliable glow controller would fail, and instead of pulsing 12V to the 6V glow plugs, it would keep them lit. They would swell and fail, causing poor cold starting and subsequently being a pain to remove.

3: These motors were hard on harmonic dampers (as are most diesels). When the damper failed, it would sound like a broken crank/rod/etc, and the engine was condemned as junk. If the owner ignored it and kept driving it, the crank would eventually fatigue and break due to a non-functioning damper, and the engine would be condemned as junk.

4: Any driveability issues meant a trip to the mechanic, who wasn't usually a diesel mechanic. Problems were misdiagnosed, with resulting expensive repairs that often didn't fix the underlying problem. Eventually, continuing problems caused the engine to be condemned as junk, and replaced with a 350. Also, the fact that these engines were used a lot more than others meant a lot more owners who treated them like gassers. When the such-treated engines developed problems, well, you know :doah:

5: By the late 80's everything was going smoother, but the 6.2 already had a bad rap. In 92 GM did a .080" punch and a .020" increase in stroke, added a turbo, and called it the 6.5 Turbo Diesel. Everything was fine until 94 when they went to the electronic Stanadyne pump. Then repeated problems with failing PMD's (pump mounted driver, also called the FSD or fuel solenoid driver), stuck turbo wastegates, and stupid overheating issues condemned the 6.5's as junk. Then, someone at GM decided that incorporating piston oil sprayers into the block would be a good idea. The motors already had fragile main webs (mainly due, IMO, to the too-short outer main bolts), and drilling holes in them for oil sprayers was the straw that broke the camel's back. Suddenly block failures went way up, but since GM was already close to releasing the DMax they didn't bother to solve the problem. It was left up to AMG and International to fix it when GM sold AMG the engine design and tooling. Personally, I would have no problem using a crack-free GM oil-spray block (97-2000) as long as I chamfered the spray holes and used main studs in place of bolts, and a girdle. Lots of guys have done this, and they work fine. But for the folks that have had a bottom end failure, well, you can imagine their opinion of the motor.


The 6.2/6.5 is an adequate design that suffered from a lot of stupid little problems. As far as power goes, it has some limitations. One oft-cited limitation is the indirect-injection design, but this isn't really a limitation from a physics standpoint. The main problem is that you will end up burning up the precups. IP's for large HP output is another problem - some have solved it by running two IP's in parallel. The nodular iron crank isn't the best setup for really high output, and since the block was designed to be lightweight it doesn't have the strength to tolerate really high cylinder pressures. The AMG blocks are beefed up, but the current Peninsular engines are probably the limit of what the engine is capable of while still having a reasonable lifespan. I think the 6.2/6,5 is a good motor, but it is what it is. It isn't a DMax - heck, the Dmax, PS, and even the Cummins are far from bulletproof when you start exceeding their design limits.

Anyway, I suppose my opinion is that if you want more power than a single IP can provide (around 250HP or so, depending on the pump and how it is built) and still have good durability then your best bet is to use a DMax or a Cummins. Then again, I would say the same thing to someone who wants more than 400HP from one of those diesels. They will do it, but not continuously for long periods. Put a 500HP Cummins 6BT on a dyno, load it up to full power, and see how long it runs. A lot of folks would be surprised. There is a reason Cummins, Cat, and others make their 500HP engines much larger and stronger than the 6BT.
 
Edit: I should add that if you get an AMG long block or a well-girdled and ARP-studded GM block I don't see a problem with 300-350HP as long as you don't try something stupid like towing with no EGT gauge. The IP to make this power is very expensive, but it can be had. Personally, I would settle for less power in trade for longer engine life, but to each their own. :D
 
What are you expecting with your build Max? As far as HP and more importantly TQ numbers.

It seams your build will better than anything anyone else has done.

Expence? Is this a 10k build or consiterably less?
 
original balzer said:
What are you expecting with your build Max? As far as HP and more importantly TQ numbers.

It seams your build will better than anything anyone else has done.

Expence? Is this a 10k build or consiterably less?
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It should make around 200-220HP and 400-450lb-ft without smoke. There are a lot of variables, so I can't give a specific figure. My target is HP similar to my current TBI 350. The 350 isn't a rocket, but it moves the truck around quite well. The diesel will have considerably more low end torque, so it should actually work better getting the big pig moving. My main thing is to have better fuel economy vs. the 10MPG I get from the small block :(

The reason for my build being elaborate is to try to get the utmost reliability from the engine, not necessarily to be able to make huge power numbers. It's really not much more elaborate than a lot of other 6.2/6.5 builds you see. Yeah, I built my own girdle, but so have a lot of other folks. Most use ARP studs, at least on the outer main holes. The use of the gear drive is pretty comon. Roller rockers aren't usually done, nor are heavier valve springs and such, but I figured since I would have done it on a gasser, why not on the diesel :D Besides, the stock shaft setup has been known to have issues, albeit rare.

Cost? Probably 5 grand by the time it is all said and done. Figure another grand for all the stuff I will need to actually put it in the truck, since the truck currently has a TBI gasser.

Finally, there are always a lot of folks who say "Why not put in a Cummins instead". It has certainly been done. Here's my thing: The 6.2/6.5 is literally a drop-in. The 4BT fits OK, but it is noisy, sounds like a Case backhoe, and shakes and rattles way too much for my liking. The 6BT is also noisy, is really too heavy for a K5 or 1/2 ton truck, and needs to be shoehorned into the engine bay. The 6.x is lighter, fits better, quieter, and runs smoother. If I wanted big diesel power I would use a DMax - it's lighter (although not as light as a 6.x), fits better (well, it still needs to be stuffed in there), quieter (no doubt) and runs smoother (than a Cummins, about the same as a 6.x). Of course, plan on 10k plus for the engine and swap :doah:
 
400-450 ftlbs sounds nice I would like to get that. Im not even sure what the 6.2 im useing realy is other than it is the orange colored block like the one in my 83. But as far as HP and TQ I have no idea what its rated for. I do know niether has a J-code intake.

Funny you should mention the 4bt being noisy and sounding like a tractor. Thats the factor that I would get a kick out of, sounding like a tractor would be cool lol.

I may just run my 6.2 the way it is until it dies then swap in a 4bt or 6bt. Then again it may last a good long time, as I mentioned my 84 K5 with a 6.2 had well over 300k on the ticker.

I just dont know if or how much money I want to throw at the 6.2. I will probably get a new dampner for it just to be on the safe side and look for a bargan on a turbo.

Is a turbo a good mod to an otherwise stock 6.2? Would I be safe to add a turbo new balancer a stud girdle and turn the pump up a bit?

I should have payed more attention in the diesel class of my high school auto shop.:haha:
 
original balzer said:
400-450 ftlbs sounds nice I would like to get that. Im not even sure what the 6.2 im useing realy is other than it is the orange colored block like the one in my 83. But as far as HP and TQ I have no idea what its rated for. I do know niether has a J-code intake.
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C-code motors are typically 130HP and 240lb-ft TQ, IIRC. Early J-codes were 148HP and something like 260-265 lb-ft. Later J-code motors like mine breathed a tad better and had the pumps turned up a bit more from the factory, and gave 165HP and around 300lb-ft TQ. In it's final version the turbo 6.5 was around 190HP and 385lb-ft. There are 6.5's that made 215HP and 440lb-ft TQ, but I don't think GM ever put those in a truck.

Funny you should mention the 4bt being noisy and sounding like a tractor. Thats the factor that I would get a kick out of, sounding like a tractor would be cool lol.
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It's been done and it works. Most 4BT's that I have come across had rotary pumps which limit how much power you can get from the engine, but there are 4BT's out there with inline pumps. I understand those motors can do 300+ HP. If you like the sound and the shake, go for it.

I may just run my 6.2 the way it is until it dies then swap in a 4bt or 6bt. Then again it may last a good long time, as I mentioned my 84 K5 with a 6.2 had well over 300k on the ticker.

I just dont know if or how much money I want to throw at the 6.2. I will probably get a new dampner for it just to be on the safe side and look for a bargan on a turbo.
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If your goals are really big power numbers I wouldn't throw money at a 6.2/6.5 or a 4BT. go with a 6BT or DMax. If modest power with good reliability is your goal and you want a drop in solution, then the 6.2/6.5 is good way to spend your money, IMO. Of course, since you like the noise and shake you might want to find a 4BT. Since your rig is running you don't have to do the swap right now, so you have time to prepare and collect parts.

Is a turbo a good mod to an otherwise stock 6.2? Would I be safe to add a turbo new balancer a stud girdle and turn the pump up a bit?
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Something like a Banks kit is a good power mod to an otherwise healthy 6.2, but I wouldn't feel good about putting it on a motor with 300K on the stock head gaskets and TTY head bolts.

I should have payed more attention in the diesel class of my high school auto shop.:haha:
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I dunno.. I doubt they had "How to bomb a diesel 101" :dunno: :D
 
This truck I have never run on the road I assume when its done it should do better than my old K5 I had years ago. It was literaly a snail on the highway. When I owned that 84 K5 it had a auto and 10b's I swapped in d44 14bff and a sm465/205 and it was like night and day. I figure 1: the direct power the manual trans gave, and 2: the lower gear axles, that helped so much. but about 60-65mph with 33" tires was all I dared go. It was then just a fast snail.

This truck is getting a NV4500, that should help on the highway. I also want to gear the axles to be happier on the highway, as I am trying to buy a doubler transfer case from one of the members here. That will cover the low gears for off road.

My ideal set up would be about 200-250hp or 400-450ftlbs. The NV4500 and the doubler and gears to make it happy in the axles. 65mph and still being able to pass, so up to 75ishmph would make me happy. Im trying to build a good all around off roader with enough highway manners to drive wherever I want to wheel. (Moab is a 3 hour drive from my house)

I would like to run between 38" and 42" tires but most likely will go with 38's just because cost is a factor. That being said any axle gear sugestions would be very helpful.
 
Max, dunno if you've ever seen these chassis dyno numbers or not. Progressive dyno pulls starting with a poor running 6.2, and finishing with a Banks turbo'd 6.2 in good tune/condition.

129_52095z+chevrolet_blazer+specs.jpg


K5 had a 700R-4 and 4.56 gears on 35's. It casts a fair bit of doubt on the factory numbers IMO.

Rene
 
theres 2 factors you have to consiter with that dyno

#1 thats rear wheel HP factory HP numbers would come from the flywheel and be much higher

#2 banks is notoriously low to keep reliability

That being said the TQ numbers are what I look for and that end result is still 451ftlbs. Thats respectable for a daily driver. Sure its not gunna win drag races but it would cruise the highway.
 
114 hp at the wheels without the turbo is also higher than i expected with a stock 'C' code at the rear wheels. You have to consider about 20-25% loss through the tranny.

Stock rating was 130 hp, and about 265 lbs of tq at the flywheel

Chassis dyno numbers before the turbo was added was 114 hp and 329 lbs of tq. OK the dyno sheet even says gearing helps the numbers out a bit. You'd think the parasitic losses through the drivetrain would cancel out the gains made by gearing. I see the factory rated numbers as complete crap to be honest.

I can remember chassis dyno numbers for a TBI 350 in a 2WD 89 GM pick-up back when they were new. hp was right around 150 to the rear wheels with a 700r-4, torque was about 245 lbs or so. I wish I had kept all my old mags...

Rene
 
I havent ever delt with an actualy chassis dyno. Automatics are claimed to loose some HP as its gets sucked up with the TQ converter. Then other places you read the TQ converter is a TQ multipler. So I dont know. I would like to see one with a manual trans though.

How does it work? Say I have a manual trans and I strap my truck onto the dyno. Ok now what? Do I go through the gears like in a drag race? or just smoothly till in direct? or go to overdrive?

I dunno I would think axle gears and trans gears tire size ect. would affect your results.

Its like my very first truck. It was a weak 6 cyl at first then I put 4.11 gears in it and it was alot more powerful. Then I dropped a 350 in and had LOTS of power
 
I think the factory numbers are probably accurate. Chassis dynos are good for showing relative power gains (or loss) when modifying or tuning an engine, provided the same dyno is used. Put the same vehicle on 2 different dynos and you will get 2 different figures. The loss through the drivetrain is also highly variable - RPM, rear gear ratio, transmission gear, is the TC locked or unlocked, temperature of the tranny and gear lube, etc. The TC is the worst culprit. It has the effect of a variable gear reduction, which can skew the torque readings.

The numbers on that chart are good for showing the relative power difference of each mod, but only an engine dyno will give you the actual torque and HP the engine is making.
 
I did see an article in 4WOR where the chassis dyno'd a Ford with 3.54's, changed nothing but the gears (went to 4.56's) and re-dyno'd it. They gained about 20 lbs of tq and 15 hp roughly. It was enough that you'd notice, but not as much as you would think.

My understanding is it's a part throttle accel into 1:1 (regardless of what tranny it is) and then Hammer down in 1:1 gear til redline. The 700R-4 will not stay in OD at WOT (unless it's a Vette or F-body version). The convertor will not be locked up though.

Manual tranny numbers I'd love to see...a lot less variables going on. No convertor slip%, no tranny fluid temp variations, no parasitic losses driving the pump either.

Max, I may be beating a dead horse in your mind, but there must be some calibration involved with a Chassis dyno. They don't assign random numbers to the forces generated. Every chassis dyno pull I've seen has shown numbers lower than flywheel numbers. This is one of those without exception things. It would literally be impossible to generate higher numbers on a chassis dyno, than an engine dyno.

In this particular dyno pull the hp looks about right. I can't accept that number as being 'about' right and throw the tq numbers out the window. Figuring parasitic loss through the drivetrain 171 hp at the rear wheels is roughly 200-205 hp at the flywheel. That is completely believable. The tq numbers used to generate the hp number had to have been reasonably close...or the hp numbers would be absurdly high. tq is measured, hp is calculated.

If Chassis numbers were so unreliable and so variable why do i never see any of the 6BT dyno junkies complaining? A lot of them have run multiple dyno's, and keep getting similar numbers that are realistic for the mods they've done. The Mustang Chassis dyno has a good name and I cannot see it measuring and recording numbers 35-40% above factory flywheel numbers even if it was horribly out of calibration. The hp numbers would have to be just as 'unbelievable'.

Rene
 
I would think it would be pretty easy to overcome most of the gearing and tire size issues by simply measuring the engine rpm vs. tire rpm and including both of those into a calculation. I don't know exactly how they work, but there has to be something like that going on otherwise the torque readings would be way off just from the rear axle gearing (4.10 gears would mean the measured torque would be 4.1 times the engine output).

For the torque converter, it will only have a limited effect in regards to torque multiplication on a dyno pull. You have the above comment, since any torque multiplication in the converter is effectively the same as gearing, because at the higher speeds the converter will have the smallest amount of "slippage" (i.e. torque multiplication). While the common multiplication people use for a TC is around 2:1, this maximum number is only seen right at that instance the vehicle goes from stationary to forward, with the multiplication decreasing rapidly as the vehicle accelerates.
 
tRustyK5 said:
I may be beating a dead horse in your mind, but there must be some calibration involved with a Chassis dyno. They don't assign random numbers to the forces generated.....

.....If Chassis numbers were so unreliable and so variable why do i never see any of the 6BT dyno junkies complaining? A lot of them have run multiple dyno's, and keep getting similar numbers that are realistic for the mods they've done. The Mustang Chassis dyno has a good name and I cannot see it measuring and recording numbers 35-40% above factory flywheel numbers even if it was horribly out of calibration. The hp numbers would have to be just as 'unbelievable'.

Rene
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There was a story about the development of the dynojet in Hot Rod last year. It was in the mid eighties, and was done primarily using motorcycles. It seems they were having problems getting numbers that matched calculated and real world experience numbers, so they introduced a fudge factor into the algorithms. It isn't that repeatability was a problem, the difficulty is that there wasn't a way to account for all the variables. An engine dyno can accurately measure the torque applied to the crankshaft, the chassis dyno measures how fast the tires can accelerate a roller of known mass. Think "how much power" vs "how much power to the road". The correlation between the two is vehicle specific. To further complicate matters, a Mustang dyno also uses simulated road forces, which is one reason a dynojet typically shows higher numbers.

Regardless, a chassis dyno is a very good tool to document changes. With a skilled operator, repeatability using the same brand and correction factors is quite good. Compare between them at your own risk.
 
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I don't think chassis dynos are unreliable. They just have the limitation of having to measure the engine output after it has gone through a drivetrain. This makes the results very dependant on said drivetrain. Remember, chassis dynos measure torque and RPM at the roller and use those values to calculate HP. However, the torque figure they give is corrected for drivetrain gearing. Put a slipping TC in there and it will artificially inflate the torque figure.
 
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