6.2's or 6.5's

[Steve K]

I am building a 6.5 turbo and have available a set of 6.2 and 6.5 heads. Since the 6.2's have larger intake valves, logic would say the 6.2's would be the better choice. Any thoughts?

 

[ak diesel driver]

since the 6.2s had bigger valves they were more prone to cracking between the valves. what are your plans for the engine?

 

[Husker6.5]

Are you sure you have the early 6.2 heads with the larger valves and not the later 6.2 heads with the same valves as the 6.5? Also, if you do have the early 6.2 heads with the long injectors, you will have clearance issues with the passenger side turbo exhaust manifold. Then there is the issue of the precombustion chambers on a 6.2 vs 6.5. Best bet, stay with late model (2001+) 6.5 heads.

 

[WarWagon]

The real difference is injector angle making the turbo manifold a tight fit on the passenger side with 6.2 heads and the precup difference is very important. The 6.2 precups are smoky with the factory restrictive turbo and even smokier with bigger turbos. I forget, but, it was pointed out on here the 6.5 and 6.2 precups may be a different diameter in the heads. Up to you to measure this.

I ran the military emission exempt 6.2 NA precups: they smoke like a freight train with a bigger turbo. Also run the NA 6.5 precups now on patch. Both hurt my ability to burn lots of fuel cleanly. Neither matter with factory fuel and turbo. More fuel and factory turbo it isn't that noticeable - ran this before I went to bigger turbos. Note I am talking about 14 PSI or less on a GM3 and visible smoke at sustained WOT. I have failed emissions so badly cars on the rollers in the next bay ALSO failed. With non 6.5 turbo precups getting through emissions with the smoke meter is a challenge.

None of my 6.2 heads had bigger valves. IMO this was a 1982 thing.

On the left is a head with Military precups on a 1986 6.2, 3 bars. The cups sitting on the head are 1995 turbo precups, round dot. The head on the left is 1995 NA 6.5 precups, square mark.

 

[Steve K]

going in a 3/4 tn pick-up

Are you sure you have the early 6.2 heads with the larger valves and not the later 6.2 heads with the same valves as the 6.5? Also, if you do have the early 6.2 heads with the long injectors, you will have clearance issues with the passenger side turbo exhaust manifold. Then there is the issue of the precombustion chambers on a 6.2 vs 6.5. Best bet, stay with late model (2001+) 6.5 heads.

I know the 6.2 heads I have are 82's. Ran into the clearance issue on another engine. Had to fabricate a 1/4" spacer for the rt manifold for clearance. Will check pre chamber dia.

 

[Will L.]

What turbo?
How are you using the truck- grocery getter most of the time, or towing a big 3 axle trailer?

 

[Husker6.5]

It's not just the pre-chamber diameter, it is also the internal configuration and the throat parameters that make stock 6.2 heads a poor choice for using in a 6.5TD conversion. Pay attention to what @WarWagon said of his experiences turbo charging 6.2's or using unmodified 6.2 heads on a 6.5TD. The man has more experience with 6.2/6.5 heads, motors, blowing them up and what combos work and which don't than anybody else I can think of on here. Using stock 6.2NA heads in an attempt to make a hybrid 6.5TD just doesn't work for the reasons WW outlines above PLUS, you will not see ANY appreciable difference between the early and late intake valves as far as performance, fuel mileage, etc. goes. Been tried many times before, reality proved theory to not be valid.

 

[Steve K]

It's not just the pre-chamber diameter, it is also the internal configuration and the throat parameters that make stock 6.2 heads a poor choice for using in a 6.5TD conversion. Pay attention to what @WarWagon said of his experiences turbo charging 6.2's or using unmodified 6.2 heads on a 6.5TD. The man has more experience with 6.2/6.5 heads, motors, blowing them up and what combos work and which don't than anybody else I can think of on here. Using stock 6.2NA heads in an attempt to make a hybrid 6.5TD just doesn't work for the reasons WW outlines above PLUS, you will not see ANY appreciable difference between the early and late intake valves as far as performance, fuel mileage, etc. goes. Been tried many times before, reality proved theory to not be valid.

Looks like ak diesel driver called it. Die-checked both 6.2 heads and found a crack between valve seats on #8 cyl. Guess I'll be using the 6.5's. Not sure what year they are, 96 I think.

 

[Steve K]

What turbo?
How are you using the truck- grocery getter most of the time, or towing a big 3 axle trailer?

Not a tri-axle but a tandem enclosed 24 ft car hauler. Also have a dump trlr that has hauled 12k and a 24 ft gooseneck that has hauled 16k. So yea, it's gonna work a little.

 

[Will L.]

Ok, What turbo?

The reason i ask is: your thinking better flow with less restriction is a good thing. Correct. However on a turbo diesel, the biggest impact is the turbo, not the valves. Your focusing on a natural aspersted gas engine line of thinking.

If you are wanting decent towing power, with better air flow, better mpg :remove the gm turbo and throw it out the window at the next car tailgating you.
GM built these turbos as something to get by on, not something to perform properly.

 

[Husker6.5]

Think HX35, HX40 HX35/40 Hybrid, ATT or 200 series BorgWarner.

 

[Efjay]

I am building a 6.5 turbo and have available a set of 6.2 and 6.5 heads. Since the 6.2's have larger intake valves, logic would say the 6.2's would be the better choice. Any thoughts?

Before investing anything in a 6.5 I would make sure the block was an updated casting. Not GM / Detroit Diesel



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[Will L.]

Before investing anything in a 6.5 I would make sure the block was an updated casting. Not GM / Detroit Diesel



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While no one will disagree an optimizer or p400 is superior, GM blocks are ok, as long as you inspect for cracks in the main webs, keep good harmonic balancer on it, use the balanced flow waterpump, and never run it north of 210f: they can be good to go for couple hundred thousand. At risk for failure, yea but manageable.