Porting 6.2 Heads

[Chevypoor]

Well as alot of you know I am re-ringing a 6.2 for the 95 K2500 GMC. I have ordered all the parts and most are in. Called to check on the rings and gasket package and they are delayed. Well I have been wanting to port a set of these heads for awhile now so as I was taking the heads apart I could not resist any longer. Took me about an hour to blend the bowls on one head.

 

[scottm]

Any progress on your build? That porting looks great, but you can do more around the guides. I blend them into a teardrop shape, right down to the liners. The last set of sbc heads I did flowed 280cfm on the intakes with 2.05" valves.

 

[Chevypoor]

Any progress on your build? That porting looks great, but you can do more around the guides. I blend them into a teardrop shape, right down to the liners. The last set of sbc heads I did flowed 280cfm on the intakes with 2.05" valves.

Looks real good.That 280cfm is a nice number. Are those GM castings?

Thanks. This is only the second set of heads I have officially (actually installed) ported. I have gasket matched a set but no bowl work and I have about 3 sets I used to practice on. The other set are small block RHS 170cc runner castings with 1.94intake and 1.5exhaust. I got [email protected] lift, [email protected] lift, and [email protected] & .600 lift. The valves were backcut PBM race valves and those numbers were obtained with a 4" bore.

I have only done bowl work to date as my understanding is that is were the most gains are to be had. I am hoping that the next set of 6.2/ 6.5 heads I port I will have time for the valve guides and I am planning on gasket matching the intake and exhaust.

The 6.2/ 6.5 screamed port me because there was so little needed to clean up the bowls. I was surprised how quickly it went and I am curious to see if I can feel a difference once they are on the truck.

 

[scottm]

The heads in the picture are World Products S/R torquers, flow not measured. The 280 cfm number was from AFR 200 cc aluminum heads I built, which made 520 hp on pump gas in a 372ci smallblock, the engine that is in my offroad race truck now. A lot of internet experts say there is no gain to be had from porting the heads on these 6.2/6.5 diesel dog motors, but I don't believe it. I expect well over 200 hp from my naturally aspirated 6.5, by combining normal hot rodding stuff like bigger valves, head porting, custom cam, headers, even a custom intake if it needs it. In fact, a mere 300 ft-lb of torque at 4,000 rpm is 240 hp. I could be wrong, but I think it will be easy.

 

[Chevypoor]

I too believe the power potential is underrated in these motors. They have a very favorable rod stroke ratio ( same as a 350 chevy ) and they are under square motors. In my opinion that is probably why they like to rev. I think the bowl blend is probably worth 10-15hp on a NA motor and maybe a bit more on a turbo motor. I think with a full port job, headers, bigger IP, bigger pre cups ( get ready for lots of low speed smoke ), a cam change you could probably touch 210-240 on a NA motor. You may surprise yourself and do a little better. I do know diesels seem not to follow the traditional torque equals horsepower formula but maybe that is because the turn such low rpms. I believe Heath is turning 5grand in his race truck so they do have some rpm potential. Good luck and keep us posted on the build. I will let you guys know if the truck seems to run better with the ported heads.

 

[Mike K3500]

I would think for build / porting a set of heads for a 6.2 / 6.5 would and should net some power gains while reducing drive pressures on the Turbo motors..

Best bet would probably to bowl blend, gasket match a set of GEP International castings, install the largest of 6.2 valves "J" code intakes of 1.968" and "C" code exhaust of 1.653"

Stock turbo 6.5 valves are measily 1.811" intake and 1.535" exhaust.... HUGE difference, between these and the biggest N/A 6.2 valves.


I would also consider some Harland Sharp rockers (bushed pivot, roller tip) in at least 1.6 if not 1.7's



.

 

[Chevypoor]

I think people ignore the heads on these trucks because hey I can stuff a bigger turbo in there and get 50hp. However that certainly leaves power on the table. With a good port job that same turbo might make 70hp and ported heads ( in my experience ) seem to drive easier, better part throttle response if they are done right.

I have looked at the Harland Sharp rockers and they are nice. I believe a couple of guys have used them.

I have also thought about the bigger valves but my understanding is they went smaller because of cracking in the "bridge" between the valves. Now putting these valves in a newer heavier casting would be a thought.

 

[sshewins]

If you're worried about cracking, do a pre emptive strike. I forget which side (intake or exhaust) there are 4 little (1/4") freeze plugs type plugs.pull them out, have a shop ream out the bore, and press in what looks like a valve guide. This is how the cracks are repaired after they crack, and they almost always crack.

I know, I know, some will say just chuck em and get new ones. But with all that porting work, it would be a shame to t them. I talked with Bill Heath a few years ago and he (at that time - not sure if he's changed his opinion) seemed to think this repair process was promoted from the factory.

 

[Chevypoor]

Bill would be correct. It is TB-1238. I know if I ever use the 6.5 heads I have from gerties motor I am going to try it on the couple of cracks they have.

Sent from my DROID RAZR using Tapatalk

 

[scottm]

Can you explain the crack repair method a little more? Are you talking about cracks between the valve seats?

 

[Chevypoor]

Here is what I have form the 6.5l Turbo Diesel Volume III:

TB-1238 - Came out during the fall of 95. Cracks between the valve seats on the end combustion chambers (1&7, 2&8) on 6.2L and 6.5L GM diesel cylinder heads occur all to frequently. There is a drilled coolant passageway that runs between each set of valve seats. This passageway is plugged with a soft plug on the intake manifold side of the head. Remove the small diameter soft plug over the passageway you want to repair, then ream out the passageway with a .404" valve guide reamer. Ensure that the pilot for the reamer is no longer than .500". Prepare a .375" x 2.5" x .030" bronze valve guide liner. Remove all metal chips and other debris from the newly drilled hole, then coat the passageway with a suitable sealer such as Loctite valve guide liner seatlant. The bronze valve guide liner should be driven in with the slit facing away from the valve seat side of the head until the end of the liner is approximately 2.25" from the bore opening. To ensure that the liner does not interfere with with the normal coolant flow through the affected area, do not drive it in too far or too little, because an incorrectly positioned liner will restrict coolant flow. Since the hole was enlarged slightly with the .404" drill, you will need to tap and install a 1/4" pipe plug to finish the repair. Pressure test the head and return to service.

 

[sshewins]

Yeah, what he said