Turbo ? for Mr Bigley.

[Jason "Toby" Tobias]

Mr. Bigely,

I am a new member and recently read your turbocharger article. So, excuse me if this is a belated reply I did not check the date of the posted article. First off, I found the article extremely informational and it pumped me up (pardon the pun). However, I do have a few questions. First off, if you are talking about about pulling a load, doesn’t it make since to have your maximum increase in power due to the turbo occur at the point of maximum torque? So, why do you discuss the max increase in power occurring at 3000 rpm instead of 1800 rpm. To Answer my own question, is it because when you are pulling a load up, lets say I-70 in the Rockies were I live, that you will be operating at about 3000-4000 rpm? Also, for the turbocharger for everyone graph (i.e. the second to last graph), what turbocharger does that correspond to. I would definitely be interested in it.

Bottom line, do you have any suggestions for a better turbo. I am a lazy engineer and would rather have somebody tell me than do the number crunching myself.

Thanks

JT

[More Power]

JT,

Glad you read the article. It's only a couple months old, but was a long time in coming.

The somewhat low boost peak rpm and low torque peak rpm make the factory 6.5 a low rpm puller. Best towing rpm is in the 1800-2200 range. That's where the max torque is.

Generally, these diesel engines (6.5 & Duramax) produce max torque at an rpm where the turbocharger produces its maximum boost pressure. Boost pressure and torque are closely linked. According to the GM specs, both the 6.5 and the LB7 Duramax produce max torque and boost pressure at 1800-rpm.

If you move the boost pressure peak up by say 500-rpm, that'll also be real close to the new torque peak rpm - generally.

The horsepower curve will continuously climb as engine rpm increases, till reaching the governor setting. So, you'll have more HP at 3000-rpm than you will at 2500. A wider powerband makes a vehicle more driveable. If you want impressive 6.5 dyno horsepower, you've got to run to 3000+. If you want to maximize performance on a hill while pulling a trailer, a wider hp/tq curve will make the truck pull better over a wider speed range.

You can't run the factory GM turbo with the engine at 3000 rpm while towing heavy. The turbo chokes the engine, producing both high EGT and IAT.

The middle compressor map in the article is for a non-wastegated turbocharger sold by Peninsular a few years ago for the 6.5. It comes with the adapter to mate the manifold to the turbine housing. Like I mentioned in the article, those who use their 6.5 to pull love the Pen turbo. It produces 18-20 psi boost pressure at full song, so a low compression 6.5 would be a good match.

The final compressor map is for the prototype Schoolcraft has had in development. This one is wastegated, and has a little more flow capacity than Pen's. This one should be a good choice for a low-compression 6.5 that sees a mix of light and heavy hauling.

The factory Holset HX35, like that used on the mid 90's Dodge 12-valve Cummins should work well. These should be available for decent prices, but you'll have to fab a manifold adapter and downpipe. For a little more money, you could contact Peninsular. I know they were working on a couple different bolt-on turbo kits for the on-road 6.5 market, including a wastegated version.

Jim

[Robyn]

Just a side note here.

Running the 6.5 under a hard pull at around 1800 rpm may very well also be the point at which the issues of crank breakage and or block failures are occuring.
Having the peak power up in the 2500 range and running there as do most 3500 series rigs with 4.10 gears seems to have a positive effect on the life of these engines.

I would definately set up any tow rig to run in the upper ranges of the power band as this seems to be the area that sees the least amount of faliures.

This is a different subject but does play an important part when you are looking to make mods to the powerplant.

Best

Robyn

[Jason "Toby" Tobias]

Thanks for the info. It makes more since to me now. So, the schoolcraft is still a prototype? It is not being sold yet is that correct?

Take care

JT

[DennisG01]

Thanks for the info. It makes more since to me now. So, the schoolcraft is still a prototype? It is not being sold yet is that correct?

Take care

JT

Not yet, but Ron's getting close to being done with real world testing.