upcoming dyno day for my twin turbo 12v cummins

1

12vtwin

diesel enthusiast
Hey guys, new to the forum. I bought a '98 12 valve cummins with manual trans, 4x4, and 3:55 axles a few months ago with only 150k miles on it, in great shape so it is now my project truck. Modifications so far are as folllows: Valair dual disc clutch, injector pump bench flowed, full cut delivery valves, 150hp injectors, no fuel plate, timing advanced to *22, 4k gsk kit, coolant bypass system, BD R700 twin turbo setup with boost at 75psi (wastegate almost completely closed) Banks twin ram upper intake manifold, hamilton pushrods, 60# valve springs, arp headstuds, 3 piece exhaust manifold.
I was fightng a boost leak and had blown a freeze plug, but everything is good now and I am headed to the dyno this Friday. First time on a dyno and i wanted to ask if anyone had any helpful tips or suggested quick mods/changes between runs. Also what horsepower/torque range should i be able to expect from this setup. I want to be able to tell if something is way off. Thanks a lot!
 
I think you're going to get past 500. Hold the brakes in 3rd gear locked, get it spooling low, and then let off the brakes and give her the berries! Make sure you line up 2000rpm (standard) when getting on the rollers to get the best results. If you're at 2200 when they set it for 2000, it'll come up short (and vice versa).


What size is the R700 again?
 
Yes use 4th gear for you dyno pull, and clean a spot on your balancer for a piece of tape. I have always had trouble keeping the tach pickup tape on the balancer if I did not clean a spot for it.

The R700 kit should be a super B 57/65/12cm over a s471/83/1.25 T4.
 
Great, thanks a lot guys. Is there any point in trying to adjust my p-pump at all between runs? And right now my wastegate just barely cracks open at 75psi, would it be better to just tighten it up and close it all the way? I've heard that all the way closed is better for tq but worse for hp and slightly open vice versa, not sure if this is true.
 
just the secondary. it's BD's R700 setup 57mm s300 secondary and 71mm s400 primary. only the s300 is wastegated.
 
12vtwin said:
Great, thanks a lot guys. Is there any point in trying to adjust my p-pump at all between runs? And right now my wastegate just barely cracks open at 75psi, would it be better to just tighten it up and close it all the way? I've heard that all the way closed is better for tq but worse for hp and slightly open vice versa, not sure if this is true.
Click to expand...

I made 30hp more with the wastegate open even though the boost was lower, and the drive pressure was way less scary (68psi vs 99psi!)
 
JQmile said:
I made 30hp more with the wastegate open even though the boost was lower, and the drive pressure was way less scary (68psi vs 99psi!)
Click to expand...

agreed with this!

I would start with the secondary gate opening at 30 PSI. while on the dyno try 35 or 40 see what your truck likes the best.
 
Pretty clean engine bay you got there. Should make some pretty decent power. How good do you like that twin setup? Had a buddy kinda tossin around the idea of somethin similar
 
Hdhorton said:
Pretty clean engine bay you got there. Should make some pretty decent power. How good do you like that twin setup? Had a buddy kinda tossin around the idea of somethin similar
Click to expand...

Thanks man, I hope I hit a nice number. I love the setup, spools very fast (16-1800rpm starts to get boost and has full boost (75psi) by about 2800rpm. Lots of power, I have 3:55 gears and it will smoke the tires in 3rd gear if I stomp on it at 35-40mph. I have about 1000miles on the turbos and I don't have any complaints.

94 12valve said:
agreed with this!

I would start with the secondary gate opening at 30 PSI. while on the dyno try 35 or 40 see what your truck likes the best.
Click to expand...

Why 30psi? Right now I am hitting 75psi...
 
12vtwin said:
Thanks man, I hope I hit a nice number. I love the setup, spools very fast (16-1800rpm starts to get boost and has full boost (75psi) by about 2800rpm. Lots of power, I have 3:55 gears and it will smoke the tires in 3rd gear if I stomp on it at 35-40mph. I have about 1000miles on the turbos and I don't have any complaints.



Why 30psi? Right now I am hitting 75psi...
Click to expand...

Opening the gate will help drive the primary harder while dropping your drive pressure. There is some good reading about tuning twins here if you do a search.
 
Ok, thanks, I'm looking at some of those threads now. I'm planning on making 3 runs, maybe do a low, medium and high pressure run? 30psi, 50psi, 75psi maybe?
 
That would be interesting. My results were: Wastegate closed: 65psi boost 99psi drive, 401rwhp. Open: 57psi boost 62psi drive, 432rwhp. Boost was 8psi lower, but because the drive was 37psi less, it made more power. That was with very small injectors. With a timing bump, fuel system, and 5x18's, I later did 601rwhp with the same 57/71mm setup.

Edit: Boost is now 70psi with the big injectors and 28 degrees of timing.
 
Last edited:
I dont currently have a drive pressure gauge, but my primary is fully lit and making 75psi at about 2500rpm and i can hear my wastegate opening. It stays open with boost staying at 75 as long as I hold wot.
 
You must log in or register to reply here.
Back
Top