• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Different cylinder heads, rockers & bump sticks for use on the 6.5

F

FellowTraveler

Well-Known Member
Messages
4,757
Reaction score
6,155
Location
Nature Coast
Not to jack other threads I figured lets talk about available heads and maybe get a better idea of what is available.

Cooling has haunted the GM 6.2/6.5 platform which is related because that is what mostly causes head and block failures, however that is a much different topic. Any cooling mods on this platform should include waterless coolant to eliminate steaming and cavitation.

Let's leave complex and labor intense porting out of this conversation as we already have a string for that keep it simple.

Generally, the IDI diesel is not a high RPM design so in order to increase volumetric efficiency (VE) blowers or turbos are used.

The 1982 6.2 "J" cylinder head has the biggest valves and is billed as great flowing for OEM. Valve sizes are 1.96" & 1.63". Heath uses these sized valves in his performance build.

The 6.5 applications go with 1.81" & 1.53".

I posted the question as to what sizes are the P400's valves and it appears no on one knows.

Constructive input is welcomed.
 
A few have confirmed the P400 has the same valve size as earlier 6.5's
1.81" & 1.53" Thanks.

So the question is "can the bigger J head valves be installed into the P400 head w/o cutting into water galley, or?"

What bump stick grinds are available that don't interfere w/pistons?

If cutting pistons to clear a higher lift cam is a good idea?

Different rocker ratio's available, or?
 
Last edited:
My 2cents by old valuation, not counting for inflation:

On the cam, there are bigger lift cam, but same lift can be achieved by the 1.6 roller rockers, which reduces drag by going roller- so that's the better gain. Unless you get into piston alteration which IMO is not worth cost on this engine for the tiny gain it adds.

The overlap of duration has repeatedly shown a loss in Idi diesel- in fact Idi MB guys learned a better cam that eliminated some of the overlap do better. More turbo, less cam theory.

Scavenging is not as helpful in a precuped overhead design, and if not for positive pressure of turbo- 6.5 hot rodders would learn quickly of reversion. Ask me how I know.

Because you're doing in the differential between vacuum and pressure, it is 2.03 inches of mercury vacuum :1 PSI. The greatest vacuum achievable in theory is 3". So if you 6.09 lbs of boost you negate magical (almost impossible) scavenging. If we had a Uniflow design-different story but alas...

There has only been a couple aftermarket cams cut that I know of, with conflicting reports on them. Big can of worms there. There are several thread about it, here and other places. I have yet to see numbers on stand alone cam testing that impressed me enough to spend an extra $50.
 
Something I thought about on this- has anyone here done a custom grind extending duration by the 6-8 percent tolerance?
Also what about a sharper ramp on the cam to maximize it?

The other things I haven't seen or played much with is solid roller lifters and altered valve springs?

Has anyone ever heard of a 6.2/6.5 floating the valves? Probably some improvement for power/mpg there if someone is willing to out a set of springs every 100k miles. Ive checked spring tension on sets with over 300,000 miles still in great condition. That tells me they are heavier than needed. Especially if you stick with the hydraulic lifted taking the ramp slap.

I hope my previous post didn't come out negative sounding, I never want to discourage anyone from playing the game.

On the psyco side of ideas, I made a 350 sbc into a reed valved 2 stroke. It would sure be interesting to see reeds on a 4 stroke diesel.
 
Will L. said:
Has anyone ever heard of a 6.2/6.5 floating the valves? Probably some improvement for power/mpg there if someone is willing to out a set of springs every 100k miles. Ive checked spring tension on sets with over 300,000 miles still in great condition. That tells me they are heavier than needed. Especially if you stick with the hydraulic lifted taking the ramp slap.
Click to expand...
Bobby Martin I think have a floating valve issue.
 
How about OEM grinds for the 6.2/6.5 N/A & turbo anyone know of a difference in these cams or?

So far Heath has shown stock J cylinder heads flow under boost enough for 475/500 hp on IDI but not street-able.

Bigger J valves in the 6.5 cylinder has some promise for now.
 
Why are stock J heads not street-able at 475 HP ?
 
I kinda wondered that too. Back I the 90's I DD my 69 Camaro when it popped high 8s, so ya -a touch over 475 ponies- haha. Not so fuel efficient, but 1st to the drive thru. Proposed to my wife in that chev.
 
Last edited:
Will L. said:
I kinda wondered that too. Back I the 90's I DD my 69 Camaro when it popped high 8s, so ya -a touch over 475 ponies- haha. Not so fuel efficient, but 1st to the drive thru. Proposed to my wife in that chev.
Click to expand...
Apples and oranges IMHO the 6.2/6.5 IDI are different animals from rat and mouse motors. So far the only IDI I've found that held up at those levels in any DD are Mercedes 4 valve IDI diesels.

The GM IDI needs boosted 850+ cfm to produce 450+- HP @ 3k rpm's & 2.5 VE your 69 Camaro did it N/A @ much higher rpm's and perhaps 1.2 VE.
 
Last edited:
Ok, agreed different animal. I was saying that power level is very streetable.
But I don't get what about those heads couldn't be ran on the street. If the block was a dry concreted block I could understand say it's not good for DD. But the heads?
 
I'd guess the question about using larger valves is long-term head durability/cracking btwn the valves?

Wasn't that GM's logic? Started with larger valves in less stressed, N/A 6.2 application. With turbocharged, 6.5 application valves got smaller leaving more material in the head btwn valves.

Heath's lsr probably didn't have 200k miles durability as a design criteria.

Not saying it couldn't work now if newer head castings (P400 or other) have better metallurgy?
 
His lsr to 200,000 miles? No. Not what it's built for, I agree. Neither are his tires for the street. But his rims could be. My point is the heads themselves, unless he has them cut so thin that his plan is a new set every year should be able to withstand DD.

On the p400 heads cutting the higher heat treated valve areas would probably take longer, and you might have to retreat them to get back the strength the treatment done in the first place. I agree I would like to know how much help the metallurgy would help.

Gm reasoning we only speculate. My speculation is they were still focused on a mpg engine, but demand for more power and turbo was proved the answer to them by the Banks sidewinder. Dropping valve size saved mpg, and helps on the lower end. There is not one place in the engine that was designed to maximize power or longevity.
 
[QUOTE On the p400 heads cutting the higher heat treated valve areas would probably take longer, and you might have to retreat them to get back the strength the treatment done in the first place.[/QUOTE]

The heads that come on the truck model P400 are NOT heat treated in the seat area like what we are use to seeing, so hardness isn't a concern. The thin area as seen in pics I have posted in the past could still be there, until I get one of these heads donated to cut apart we still don't know...

The shop that will be doing my valve work refused to cut them for larger valves and sited how thin it is now (he saw the pics also) and just how much thinner it would be after .. so mine isn't getting bigger valves..
 
if the valves are bigger in a 6.2 head can they be used in a 6.5 block? Or would that just be not a good plan? Also I noticed when I was putzing around the other day there is a block off plate on the back of the heads for coolant. Could one be made, or is there a cross over pipe that would bolt to them and help with coolant flow? Take my questions with a grain of salt, I'm no engineer. Just throwing questions out there.
 
What does air flow thru the intake and exhaust ports have to due with IDI precups ?
 
You must log in or register to reply here.
Back
Top