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6.5 Na Max Potential?

S

scottm

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Location
the oven, Scottsdale AZ
Hi all, my first post. I apologize in advance for the length.. I come from the gas racing world, started drag racing a 327 Camaro in 1980, and since 2008 I have been racing a 1977 Chevy c10 class 8 desert race truck here in AZ. I have wanted to play with diesels for years now, plus I always like to do things a little different than the rest of the pack. Sooo my favorite bad idea right now is to build a max hp 6.5 na engine and put it in my desert truck just for the fun of it. The rules in class 8 don't allow forced induction, but besides that, I personally prefer to get the most out of an engine the old fashioned way - normally aspirated airflow and tuning.

I've been eavesdropping on the diesel forums for two years now, and I'm surprised that more people don't take the gas engine approach to diesels - porting and flow testing heads, trick intakes, cams, exhaust, etc, and a lot of dyno testing. I am most surprised at the lack of real headers for na diesels. The only reason a gas engine can make more than 1/2 hp per cubic inch is the exhaust, and the powerful suction or scavenging pulse that comes from a tuned header. Has anyone ever made a real header for the na 6.2/6.5 engine? (the military 'header' from the hummer is not a tuned header).

For a diesel making peak torque between 2000 -3000 rpm, I would say offhand the primary tubes should be about 1 1/2 inches diameter and at least 36 inches long. Combine headers with a strong short block, good flowing heads and a cam with a little overlap, and it should make more power than anyone would expect from a na diesel. I have access to a mandrel tubing bender, and I would love to fab up a set of stainless headers. BUT I need you guys to help me with the rest of the parts selection.

Torque comes from cylinder filling, and cylinder filling comes from air flow and exhaust tuning. Horsepower is torque x rpm, so the longer you can keep up the torque output (airflow), the more hp it will make. My engine build will start by extending the max safe rpm the engine can take, both so it can run strong into higher rpm, and so it can survive an over-rev from a broken driveline or a missed shift. What is the most rpm a stock 6.5 can physically survive? 3500? 4000? Whatever it is, I want to improve the bottom end and valve springs to extend the safe range as much as possible, within the reality of available parts.

From what I have read, the 92-93 6.5 blocks were the best for crack resistance. Is it possible to buy a AMG/GEP bare block?

What heads, factory or aftermarket, are best for crack resistance, airflow, and porting?

I will probably get the scat crank, and do a full race prep on a set of stock rods. Were any year rods known to be better than others?

Besides the Heath na cam, are any others available?

What would be the ideal compression ratio for this (relatively) high rpm engine? It must be easy starting in all weather.

What are my piston options? Lighter is better for higher rpm, and if they don't have it already, I will coat them with ceramic heat barrier and anti friction on the skirts.

What IP will be best for extended rpm and wide tuning adjustment?

I have access to a head flow bench, a chassis dyno and an engine dyno. The engine dyno is a Superflow water-brake type, and it does not work well at low rpm. The lowest it can absorb 400 ft-lbs is 3600 rpm. My plan right now is to find a cheap 6.5 td craigslist truck and take off the cab and bed. Then I can easily work on the engine and build headers, and just trailer it over to the chassis dyno shop for engine testing. No doubt people have known for 30+ years that this is all a bad idea, but even if it is, I will still have fun trying!
 
Going on a limb here but I don't think the same tuning principles on a n/a for a diesel that work for a gasser, due to how they work. I agree on porting, cam work. Some are messing with precup size's but those were for turbo engines. Headers, only a few vendors and most likely the only reason why is we are cheap, errrrrr frugal. I'll chat with my flowbench guy, he's got a boosted flow bench, used to build some serious bike engines back in the day.

I was recommend balancing, fluidamper and stud everythinng. I don't think you can buy a bare GEP block.

Best heads are GEP heads, thick and redesigned castings.
 
Scott welcome to The Truck Stop!

Please do keep us informed of your project as it goes along.
Scavenging does not work the same in diesel engines as a gasoline engine. Many have tried I've not heard of anyone succeeding, Myself included and I've done other small projects such as turn small block Chevy's into two strokes, and flip v-6's on top of each other to make them into x 12 cylinders into a quad delta crankshaft.
Everything else you're doing has potential. Strongly consider the use of propane if you're not going to use forced induction. Look through the posts on here- there's a couple places spoken about to buy used GEP engines. Those have the block, heads and rods do you want to use. Unless you have some serious numbers you are trying to reach, then get a p400. You also need to learn about multiple injector pumps.

Best of luck to you.
 
Looking foward to this.

If you think bigger valves would help then look for a set of 82 red block heads. Bad rep for cracking since they are so big.
 
tanman_2006 said:
Looking foward to this.

If you think bigger valves would help then look for a set of 82 red block heads. Bad rep for cracking since they are so big.
Click to expand...

Good idea, I forgot about those cause they were always on my "no" list. If you tore them down and refired them in a kiln to aneal them, along with the studs to hold them and cooling improvments, they should be ok.
 
Will L. said:
Good idea, I forgot about those cause they were always on my "no" list. If you tore them down and refired them in a kiln to aneal them, along with the studs to hold them and cooling improvments, they should be ok.
Click to expand...

That's the way I figured it too. Maybe even custom machine new valve seats to help prevent cracking. There is also a way to sleeve coolant passages.

Source Unknown
 
Most of the porting and other airflow work is cheaply overcome with a turbo. Most 6.5/6.2 owners are cheap. So this is why this path is not well traveled.

Going NA, well diesels are crippled without a turbo. So keeping this in mind...

Look at what GM did with the gutless Olds 5.7. They revved the engine up with a higher stall converter. Least the Cadillac I recently drove did. So I had an expensive high stall Yank converter built for my 1995 4L80E. Puts you in the power band quickly.

The NA manifolds are not as bad as the turbo manifolds. Always room there. :hihi:

Precups in addition to your other ideas can not be stressed enough. All NA precups are for economy. The military precups are for more power without emissions concerns. You trade power for economy with precups. You can only put so much fuel and air through the precup hole. You know you are at your limit when it is rolling coal. You could experiment with 6.5 turbo precups and see how much fuel you can throw at it. Head studs would allow quick comparisons between precups. Bigger the precup the less MPG you get.

Gapless rings will keep your oil visibly cleaner and give you an edge for power.

See if you can get the prechambers ceramic coated. Keep the heat in the engine not in the cooling system.

Timing is a major factor with diesels and power. IMO more so than a gas engine.

Last, with all engines: Compression makes power. Lower compression diesels are made up for by insane boost numbers. Compression from the factory nowdays is lowered for NOx emissions. If anything you might look at slightly higher compression.
 
X2 on higher compression. Deck the block, use stock head gaskets and hold on. Use a delta cam. Use marine injectors with raised pop pressure. Take advantage of ceramic coatings if rules allow.
 
You're on the right track for NA.

Air in, air out. The more efficient the better.

Turbocharged engines respond to the same principles, but slightly differently. You will see greater benefits on a NA as opposed to a forced engine with porting.

Bill Heath reportedly spins his 6.2 Twin turbo to 5,000 RPM on a salt run.

Now, power expectations?

Will be low. I'd guess somewhere around 110-120 at the rear wheels, Tq figures somewhere in 250-300 range.

The HMMVW's were rated at 165/330 crank IIRC.

There's not much more potential without huffing them and wicking up the fuel.

I would suggest a standard trans to minimize drivetrain losses and a mechanical pump for simple ruggedness. You'll run out of air before you run out of fuel with a DB2 pump.

Good news is the 6.X is one of the lighter diesels out there and will do a bit better in a desert runner. It's a smidge heavier than a BB chev.

The 599 casting is widely considered the strongest OEM block, but I've scattered one before. I am turbo and turned up though. NA should be fine.

If you want a Navistar block and heads(best of the breed), they're not sold bare. No way, no how. The Franklin plant doesn't let them out without being fully dressed for the party. Best bet is to source a military take out from Ted's trucks or similar. Count on paying around 2 grand for one.

The Optimizer P400 casting would be complete overkill in a NA application. Lots of money for little gain over a regular Optimizer. But it would set you up for a good Turbocharged build in the future, should you want to eventually go there...
 
I think with a lot of head work and custom intake and high rpm, you could get a decent power rating. I would easily speculate 150-160 at the rear wheels. With torque around 300-320ft lbs. ported heads, larger valves, custom intake, wild cam, high compression, coated precups, DB2 pump, optimizer block, military NA precups, Harland rockers, main girdle, and head studs, SCAT crank and a set up for 4500rpm would easily put you there, maybe even more horsepower than that. That may even get you up to around 170rwhp at that rpm. On the right track with tuned headers. Maybe look at a SM465 with 4.10's. my 4.10's will take me to around 100mph at 3500rpm. Maybe with a 4000-4500rpm setup and some 4.10's or even 4.56's would allow quick revving ad getting up to speed fast while allowing a decent top speed too. It would help the fact it was naturally aspirated. Treat it like a small block haha
 
Great, thanks guys! I read about the Heath Bonneville racer and how it uses the larger 1982 6.2 valves. Interesting that it revs to 5k, since he used reworked stock rods and a Scat crank. If it can maintain decent torque up to 4000, it will make good power. Iirc, hp = torque x rpm / 5250. If so, then 300 ft-lb at 4k would be 228 hp at the crank.

How much of the cracking problem is really caused by poor cooling? If the cooling system is in perfect health, will the heads sometimes crack anyway?

The first thing I buy will be a set of heads, since I could start flow testing and experimenting right away. Is there a brand or a source of heads you can recommend? There's a lot of stuff on ebay, but I suspect most is Chinese junk.
 
Yup. High flow water pump and all aluminum radiator as well, and if possible I would recommend the dual thermostats, and a stock oil pump ought to meet all your needs for lubricating. At that high an rpm it will do just fine.
 
Navistar heads (Well, GEP heads really) eliminated cracking by redesigning the heads internally and changing the metallurgy during the casting process.

There have been many theories floated as to why they crack. My personal opinion is the IDI design retains too much heat in the castings combined with the compression ratios these see.

Guys advancing them for more power doesn't help either....cylinder pressure rise and hammering the heck out of them and whatnot.

Pretty sure Bill switched to a NA oil pump when running the salt as the Higher volume pumps put so much into the upper end with high RPM that it couldn't drain back fast enough. You'll have to research that one out though as my remembery isn't as good as it used to be....:lol:
 
Don't forget that the redline of 6.2 engines is 3600 RPM. Precup engines hate to be spun faster than their rating. You will have to work hard to bump the redline up. I recall that one of the salt flat racers bent every rod in the engine. But that is racing - pushing the limit for a short run and not being surprised if it doesn't even live that long.
 
War, the factory rating of 3600 is no doubt conservative, plus they won't breath or fuel above that anyway. I am really encouraged by the Heath Bonneville racer, because they used a scat crank, stock rods, and 6.2 pistons and ran it to 5000. I'll be happy if my engine still makes power at 4000, with a nice rpm factor of safety in case of a momentary over rev.

Is Ted's trucks the only place to get a rebuildable optimizer engine core? I don't want to pay $3k for a healthy engine, I would rather get one needing rebuilding.

http://www.dieselpowermag.com/featu..._diesel_race_engine/bosch_injection_pump.html
 
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