Compound drive pressure

blackdiesel

blackdiesel

New member
Joined
Feb 8, 2009
Messages
243
I have a 351 over a s472 with a 1.10 on it and my drive pressures are out of control. Motor was originally built for towing, marine pistons, 5x.012 injectors, stock 215 inj pump with plate removed and 4k gsk.

When I built this engine I gasket matched everything on the hot side, but I did not externally gate my 351cw. I did drill out the internal gate but looking back I should've just went with a different charger.

When truck is tuned properly for max power and no smoke on boost, my secondary drive pressure will be 120 psi plus (and climbing) while my boost will be in the 70 range. My primary is nearly always 1:1. Truck runs awesome but as you can imagine my egts rise quickly.

To combat this I have been driving it recently with the set screw backed way out of my boost elbow and have de-tuned my afc big time. Now I stay around 55-60 boost and 70 drive. However it doesn't run anything like it should.

Will a spring gate or larger wastegate actuator help me any? Or am I down to an external gate or a different secondary?
 
Wheel Dimensions:
Compressor: 71.4 mm inducer, 100.8mm exducer
Turbine: 83.5 inducer, 74mm exducer
 
That is your problem. That 72 is far to small to be ran in a compound setup.

If you want drive pressure to be in check, you'd need to step it up to the 96mm turbine and T6 1.32 housing for the best results.

Properly matched set of chargers will make all the difference.
 
My 72/88 compounds seem to compliment each other rather well. The 72 is a 72/87/1.0, the 88 is 88/112/1.23...I am making a hair over 1000hp with 70 psi of drive pressure with no gate.
 
uh no^. many run that primary in towing compounds.

what does the he351 make by itself for boost pressure? sounds like the gate might be too tight
 
jlbayes said:
uh no^. many run that primary in towing compounds.

what does the he351 make by itself for boost pressure? sounds like the gate might be too tight
Click to expand...

Agreed ^^

The 351 is the drive pressure issue long before the 72 will be.
 
I remember way back ronA claimed a super B special over the 3x3 s400 was the best driving compound setup he had run.

From experience that 72 shouldn't really come on full tilt until around 3k rpm on a 5.9 12v. In theory that would be perfect for towing compounds, to the op I would put an external gate on the manifold and vent around the chargers to the exhaust pipe
 
If I back the boost elbow set screw nearly all the way out my secondary pressures are 1:1. max boost suffers greatly along with my egts. The sweet spot on the current configuration is primary 30 @ 1:1 and secondary60 boost & 70-75 drive. Egts will still get out of hand though.
 
Naturally I'd like to try the easiest things first. An External gate will require me to pull the cab back off my Ford. Will a spring gate or a bigger actuator be worth the time?
 
not sure how the manifold is set up but I don't see how or why you'd need to pull the cab to put in an external gate. it sounds like the gate port is not flowing enough to meet your needs. a spring gate or larger actuator will not help with your issue.
 
Uh oh I was just thinking of doing a similar setup with around the same mods. I have ran into the problem of the gate not flowing enough before, I ended up with a external gate.
 
I'd never run anything less than a 96mm/1.32 turbine in the primary charger period. On the hot side compounding is in reverse. The secondary turbine is compounding the drive pressure it sees from primary turbine.
 
Joesixpack said:
I'd never run anything less than a 96mm/1.32 turbine in the primary charger period. On the hot side compounding is in reverse. The secondary turbine is compounding the drive pressure it sees from primary turbine.
Click to expand...

Can you clear this up for me please?

How is the secondary turbine compounding the drive pressure it sees from the primary, when the secondarys turbine gets drive pressure from the engine exhaust manifold?
 
A fairly easy concept is back pressure after the turbine in the case of a single charger can be a huge detriment to power. This is the same case in what the secondary turbine is seeing as back pressure or primary inlet pressure.
 
I agree with that.
So moving up to a bigger turbine wheel and housing on a primary, will help more than moving up in size of turbine wheel on the secondary?
If I was the OP, I would change to a bigger primary, and gate around the small secondary. (Keeping the quick bottom end spooling for towing/street manners.)

Which is what I'm probably going to do with mine.
 
Make sure the gate is working right on your 351. I run a 351/480 setup. At around 60lbs of boost I have around 80psi of drive pressure when the gate is open. My S480 has an 87 turbine with .90 T4 exhaust housing. I used a 1 inch bit to make the gate bigger on the 351. It will almost stop the drive pressure gauge in its tracks when it opens.
 
If I was to external gate it, I assume you guys will insist on a steed speed? Or a little witchcraft and nickel rod? Like an idiot I didn't put a spacer in for a future gate. I don't have much experience welding cast, and I sure don't want it cracking out later
 
Joesixpack said:
I'd never run anything less than a 96mm/1.32 turbine in the primary charger period. On the hot side compounding is in reverse. The secondary turbine is compounding the drive pressure it sees from primary turbine.
Click to expand...

I run a super b over a 75/83 on westons recommendation and my drive pressure is near 1:1 until 3500 rpm at full fuel. They also light at virtually the same time with the interstage gauge showing about 1/2 the boost of the overall.

Sent from my SM-G900V using Tapatalk
 
blackdiesel said:
I have a 351 over a s472 with a 1.10 on it and my drive pressures are out of control. Motor was originally built for towing, marine pistons, 5x.012 injectors, stock 215 inj pump with plate removed and 4k gsk.

When I built this engine I gasket matched everything on the hot side, but I did not externally gate my 351cw. I did drill out the internal gate but looking back I should've just went with a different charger.

When truck is tuned properly for max power and no smoke on boost, my secondary drive pressure will be 120 psi plus (and climbing) while my boost will be in the 70 range. My primary is nearly always 1:1. Truck runs awesome but as you can imagine my egts rise quickly.

To combat this I have been driving it recently with the set screw backed way out of my boost elbow and have de-tuned my afc big time. Now I stay around 55-60 boost and 70 drive. However it doesn't run anything like it should.

Will a spring gate or larger wastegate actuator help me any? Or am I down to an external gate or a different secondary?
Click to expand...

I had the same issue. Added bigger injectors that drove the big charger harder and still stayed about the same ratio but boost went from 60psi to 70-75psi.
 
You must log in or register to reply here.
Back
Top