anyone know if the heads from a 6.2 could work on a 6.5 if need be? Is there a difference in quality between them?
thanks,
paul

should be interchangeable...IIRC

The injectors are on a bit less of an angle on the 6.5 engines to help clearance issues with the turbocharger exhaust manifold.

i know the prechambers are a little different, but how do the compression chambers compare? if you wanted to turbo up a 6.2 and drop compression, would 6.5 heads make any difference?

The 6.5 compression is lower than the 6.2, this is to handle the turbo that the 6.5s were designed for. I personally don't believe that you should interchange them. IMHO

I am by no means an expert, but I'm pretty sure that the differences in compression come by way of the selection of PISTON, and have nothing to do with the heads, as they are essentially the same in the "combustion chamber" department(FLAT). IIRC, the major changes between the two are injector angle, some of the cooling passages, and the size of the pre cup openings, not the volume of the pre cups themselves.
To answer the question(s) YES they are interchangeable. NO they will not lower the compression on the 6.2 engine. The 6.5 heads will give you the necessary clearance to use the factory turbo setup without issues. But you still wont want to run boost above 10psi on the 6.2, or risk hurting things.
If I've given any erroneous info, I'm sure someone here will correct me.

Yachtcare has pretty much hit the nail on the head.

The only thing I will add is that it is possible to use the injector lines from a 6.2 on a 6.5 without too much bending. It is very tough if not impossible to put 6.5 injector lines onto the 6.2 heads. The firing order, general shape and installation is close with the two head designs. The 6.5 lines are physically shorter than the 6.2 lines. You can bend the 6.2 lines back a bit to fit the 6.5 heads, you will have a tough time stretching and bending the 6.5 lines enough to reach the 6.2 lines.

The precups are different also between them, from when I asked, the difference is neglible.

Yes, the piston affects the compression ratio, not the head.

I am by no means an expert, but I'm pretty sure that the differences in compression come by way of the selection of PISTON, and have nothing to do with the heads, as they are essentially the same in the "combustion chamber" department(FLAT). IIRC, the major changes between the two are injector angle, some of the cooling passages, and the size of the pre cup openings, not the volume of the pre cups themselves.
To answer the question(s) YES they are interchangeable. NO they will not lower the compression on the 6.2 engine. The 6.5 heads will give you the necessary clearance to use the factory turbo setup without issues. But you still wont want to run boost above 10psi on the 6.2, or risk hurting things.
If I've given any erroneous info, I'm sure someone here will correct me.
Hey - your response here begs the question - what if some material was removed from the pre combustion chamber? Think of it as porting the cups - similar to porting the intake or exhaust... If you add a few cc's to the normal head volume, you can change the compression ratio of the engine - maybe not a huge amount, but maybe enough to run a few more psi of turbo. It would be much cheaper than upgrading to the low compression pistons. Combine that with an intercooler and you may be able to take the power output a little higher without pushing the heads through the hoodl

Anybody have any thoughts on this?

I have always been too chicken to modify the pre cups and here is my reason. When you look at a pre cup and how its shape mates up to the small combustion chamber and swirl marks machined into the top of the piston you realize that its shape has a direct effect on the combustion flame direction of travel. I have heard of guys porting and/or polishing them to promote heat reflection and to modify the combustion process. I have not heard of anybody saying that they ruined an engine by modifying them. I am too chicken to try it myself, and I am very experienced at flowing, porting and polishing cylinder head ports. I hesitate to do anything unless I have seen concrete proof on a benifit or am able to prove a benifit myself.

So if we choose not to modify the flame hole that leaves the material in the head itself or the upper side of the pre cup to grind on. The chance of you porting a pre-cup enough to substantially lower the compression ratio is unlikely. I can not offer any concrete numbers on this opinion though. I would have to measure the volume of the precombustion chamber and do some math to do so. Adding a .010" thicker head gasket reduces the compression ratio on 6.2/6.5 less than a single point. Using that as a baseline the volume of grinding in the precombustion chamber would have to be pretty substantial to get a measurable effect.

Check around in the 6.5 section for some pictures of the lower compression pistons, they have alot of material removed from the top to reduce the compression ratio to 18:1.

Chances are pretty good that I will try some polishing soon on my pre cups on a upcoming 6.5 build up. I suppose I could cc the chamber while I am at it for all the time it would take but it will be a couple of months down the road.

Chances are pretty good that I will try some polishing soon on my pre cups on a upcoming 6.5 build up. I suppose I could cc the chamber while I am at it for all the time it would take but it will be a couple of months down the road.


I don't see why we wouldn't consider a coating of some sort in there, on the chamber and piston top. I bet that could yield some killer results.

Agreed.

Mahle and Speed Pro pistons for the 6.5TD have had a black ceramic coating on their replacement pistons for several years now. Infortunately they do not coat much more than the center 80% of the piston. There is no reason not to coat the piston right down to the top compression ring.

I was hoping to remove the coating on my 6.5 pistons and replace it with a full cover. I had also planned on a dry film lubrication coating for the piston skirts and there is a coating that you can put on the bottom of the piston that actually promotes heat transfer that I want to use. That would help transfer heat from the bottom of the piston as the oil from the squirters wash them.

I think that John Kennedy's website has pictures of some ceramic coated head surfaces. That is where I started to dream about the space age coatings. I may even consider a coating inside the exhaust ports to help reflect heat back towards the exhaust stream and out of the head casting and coolant.

The only bad thing about coatings is the cost. I can get the pistons and dry film for the skirts done here locally, maybe even do it myself. If my schedule and pocket book allows it I will go all out with the coatings.

When I built my Dodge turbo Caravan, I had the pistons tri coated, bearings done, turbine housing and exhaust manifold coated with high temp stuff. Can't say any differene in power but I did it to help with engine life and reduce underhood heat. I found an article in Hot Rod or Car Craft that found coatings were worth very little in HP per dollar spent.

I had mine done at performance coatings in Seattle.

i recently purchased a 94 chev with a 6.5 diesel.it appeared to smoking excessively.i thought it was the injectors ,so i changed them ,,then i found excessive oil on the exhaust side of the turbo so i changed it.still smoking.by accident i found that if i loosened the radiator cap the smoking stops.then i found out that the engine was an earlier model 6.2l non -turbo and they just put the turbo and all off the 6.5 on it.is this a possible problem or do i have blown head gasket?

i recently purchased a 94 chev with a 6.5 diesel.it appeared to smoking excessively.i thought it was the injectors ,so i changed them ,,then i found excessive oil on the exhaust side of the turbo so i changed it.still smoking.by accident i found that if i loosened the radiator cap the smoking stops.then i found out that the engine was an earlier model 6.2l non -turbo and they just put the turbo and all off the 6.5 on it.is this a possible problem or do i have blown head gasket?


The 6.2's compression is higher so I bet the head gaskets are gone.

so i change head gaskets...then how do i fix my problem without changing engine ..or can i?

You should be able to just change the head gaskets and be ok. Check the heads for cracks when you have them off, that is really just common sense. You need to monitor the turbocharger boost level on your engine when you get it back together. Too much boost will screw up the head gaskets, that is what might have happened on your truck Kieth.

so i change head gaskets...then how do i fix my problem without changing engine ..or can i?

To do it properly, you need to change the pistons to run lower compression, if not, the advice given is good.

My truck has a 6.2 block, 6.5 heads and injector setup. I was told this was the best of the both worlds for power and fuel saving ability of the older chevy diesel.

ARP head studs would be an excellent investment, I personally wouldn't run a 6.2 turbo without them, limiting the boost to 10-12 PSI would help a lot too, otherwise you'll need the cooling upgrades & lower compression pistons of the 6.5=$$$!