Debate, please. Twins versus big single for towing ?

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me2

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I'm building a tow pig engine based on a Cummins 6.7. I'm looking for advice on which turbo setup to use.

I'm looking for as much safe, efficient, cool, smokeless power I can get with a basically stock fuel system for towing large trailers in the mountains. If I had 400 RWHP all day long, I'd be pretty happy. More would be a bonus.

My engine will run 1650 RPM in OD and a bit more than 2000 RPM in the next gear down. I'll be towing 15K in mountainous terrain. I have no interest in racing.

Starting from a stock 6.7, my present mod list is

- full deletes
- EFI Live tuning
- dual remote fuel filters
- gauge package including 2 boost gauges and drive pressure
- H11 headstuds
- BHAF or something similar

To make the power I want, I figure I need 35+ PSI of cool boost at 1650 RPM (40 pounds per minute, 0.32 kg/sec) and 40+ PSI at 3000 RPM (80 pounds per minute, 0.6 kg/sec ).

I have a number of options for turbos.

1) - an S475 over HE351VE twin setup. I'll implement interstage cooling if it becomes necessary.

2) a 64mm HE451VE

3) Just about any big single turbo

Which would you use and why ?

Thanks !

Here are some pertinent turbo maps.

Various BD turbo setups.
BDdieselcompressormap.jpg


HE351VE map
he351_map.jpg


S475 map
S475%2520map.jpeg
 
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I don't think you can beat a 351 over an S400 for a set of towing twins. I know the 6.7 can spool chargers like crazy but I would still go with a set of twins over a big single for towing.
 
DDually said:
I don't think you can beat a 351 over an S400 for a set of towing twins. I know the 6.7 can spool chargers like crazy but I would still go with a set of twins over a big single for towing.
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Agreed
 
Thanks guys.

DDually... wanna tell us about your air to water intercooler and give me some hints about inter stage cooling ?

Any other mods I should think about doing to this engine ? Tap and port the coolant plugs under the valve cover ? Bottom end girdle ?
 
me2 said:
Thanks guys.

DDually... wanna tell us about your air to water intercooler and give me some hints about inter stage cooling ?

Any other mods I should think about doing to this engine ? Tap and port the coolant plugs under the valve cover ? Bottom end girdle ?
Click to expand...

Thought about a lift pump and a slightly larger injector?
 
also, inter-stage cooling on a mild twin setup is, in my opinion, not worth the hassle.
 
Hurley said:
also, inter-stage cooling on a mild twin setup is, in my opinion, not worth the hassle.
Click to expand...

An S475 can over supply an HE351 volume wise if the inter charge temp is high. Interstage cooling removes that problem. The other solution is to replace the HE351 with a larger charger, but that starts getting expensive and defeats the purpose of having a small charger, ie good spooling and good boost down low without surging.
 
The s475 will always oversupply the HE351. If it didn't, you'd have a vacuum in the interstage pipe, instead of positive pressure. You won't be seeing more than 25-30 psi in the interstage, and the compressor sizes aren't vastly different, I think intercooling would be low on the cost:benefit ratio.
 
Tate said:
The s475 will always oversupply the HE351. If it didn't, you'd have a vacuum in the interstage pipe, instead of positive pressure. You won't be seeing more than 25-30 psi in the interstage, and the compressor sizes aren't vastly different, I think intercooling would be low on the cost:benefit ratio.
Click to expand...

By oversupply, I meant push the VE351 outside its compressor map.

I'll start without interstage cooling and report back.

Interstage cooling doesn't have to be expensive. The Cummins 6.7 has an unused water port on the water pump for the EGR cooler when deletes are done. You can get a good quality water/air cooler for less than $200. Some places charge that much for a cold pipe.

The biggest worry I have with interstage cooling is the cooler cracking and flooding the next turbo and the engine intake with water.

The Ford 6.7 uses a water/air charge cooler. It must be good !
 
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it's not an argument against liquid/air cooling, it's an argument of cost:benefit with the particular setup in question. (cars have radiators!)
 
Just run the 351 and the 475 or gt42. Will be plenty. Interstage cooling benefits mostly when the turbos are greatly different in size or youre trying to get the most out of them by spinning them hard and creating heat. Otherwise a 60/75 setup will support a cool 650.
 
You could water/meth between stages. That would also artificially increase the 351's individual compressor map by creating a larger surface area along the blades when the water hits them
a small amount (small nozzle, high pressure, fine atomization) in this situation will go a long way. No real need for meth, just filtered water
 
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If you want to stepup to a better tow setup do a he351 over a gt4202wg.
 
Bponci said:
If you want to stepup to a better tow setup do a he351 over a gt4202wg.
Click to expand...

The gt4202 is smaller than the S475. About 95 pounds per minute versus 105. And its twice the price. I paid $650 for my S475.

garrett-gt4202-twinscroll-turbo-content-1.jpg
 
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me2 said:
By oversupply, I meant push the VE351 outside its compressor map.

I'll start without interstage cooling and report back.

Interstage cooling doesn't have to be expensive. The Cummins 6.7 has an unused water port on the water pump for the EGR cooler when deletes are done. You can get a good quality water/air cooler for less than $200. Some places charge that much for a cold pipe.

The biggest worry I have with interstage cooling is the cooler cracking and flooding the next turbo and the engine intake with water.

The Ford 6.7 uses a water/air charge cooler. It must be good !
Click to expand...

Using engine coolant for interstage cooling is a horrible idea. How hot do you think the 475's discharge air temp will be when you're cruising along on the freeway with 1-2 psi boost between stages? I can tell you it's much less than 180-200* you'll raise it to using coolant.

The only time the discharge temp will be above engine coolant temp is when you're on a long grade pushing 20+ psi between turbo stages.


Oh and the 475 is not too big for an He351 compressor wheel, there are trucks out there running anything from a 71mm to 95mm turbo feeding an He351, so with a 475, you're at the lower end of the spectrum.
 
Not the ball bearing unit. Gta4202 journal bearing, 1.15 w/g housing found on detroits. If you want a superior towing turbo you want this turbo. Plain and simple. 171702's are outdated for this application.
 
Big Blue24 said:
Using engine coolant for interstage cooling is a horrible idea. How hot do you think the 475's discharge air temp will be when you're cruising along on the freeway with 1-2 psi boost between stages? I can tell you it's much less than 180-200* you'll raise it to using coolant.

The only time the discharge temp will be above engine coolant temp is when you're on a long grade pushing 20+ psi between turbo stages.


Oh and the 475 is not too big for an He351 compressor wheel, there are trucks out there running anything from a 71mm to 95mm turbo feeding an He351, so with a 475, you're at the lower end of the spectrum.
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The turbine wheel is the topic here.
 
Very interesting discussion.

AHall said:
Not the ball bearing unit. Gta4202 journal bearing, 1.15 w/g housing found on detroits.

If you want a superior towing turbo you want this turbo. Plain and simple. 171702's are outdated for this application.
Click to expand...

Do you have a compressor map for it ? How big is the compressor wheel ? What makes it better than an S475 ? Just trying to learn here...
 
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