Boost vs backpressure

Extended Power said:
Ok, I'm confused...
You were able to get 80psi out of a 75mm compressor, with 30-40psi drive pressure on a 88mm turbine....as a single?
E
How is it that I can throw 50psi drive to a 80-84mm compressor, with the same turbine wheel and housing as you, and only get 30-35psi boost out of it in a compound setup?

Wouldn't/shouldn't the pressure out of the primary be higher than 30-35psi?
Doesn't the secondary act as a restriction in the airflow, which would cause the pressure to rise? (Boost pressure is restriction pressure, right?)
Click to expand...

Yes 80 psi from a single 75, 96/88 turbine 1.32 housing. Your pressure (restriction) is coming from your manifold turbine. Are you measuring drive pressure as total or between turbines?
 
Leiffi said:
What kind of changes were made to the engine ? If rpm is the same then 475 should make more power.
Click to expand...

I modified the pistons, and went from a single feed 5/22 145* to triple feed 5/25 from scheid.

I had a better average power across the board with the 75 but the mid to peak with the s588 is much stronger now.
 
Joesixpack said:
The funny part is most think that's the case but it's not.
Think of it this way, what would you expect the boost to be for the same mass flow on a 5.9L engine vs a 12L.
Click to expand...

I would think that if you have the same volume of air, the pressure would be less.

DieselheaD said:
Yes 80 psi from a single 75, 96/88 turbine 1.32 housing. Your pressure (restriction) is coming from your manifold turbine. Are you measuring drive pressure as total or between turbines?
Click to expand...

Measured between the turbines.
 
Exactly. So how does the secondary compressor become more of a restriction than your base engine when the secondary has doubled or better the mass flow?
 
I need to go hook up my drive pressure gauge and see what kind of back pressure I am getting from my 72/87/1.0, 88/112/1.23 compounds. I dynoed 875hp at 52 psi boost. On the track I see about 55 psi overall and 24 psi from the big charger.

I don't even have my gate hooked up trying to drive the secondary as hard as possible. Wondering if going down to a .90ar turbine housing on the secondary would benefit me more over the 1.0ar??
 
DieselheaD said:
Believe it or not I've had the best luck with a standard s475. 96/88 t6 1.32, drive at 30-40 was half of boost 70-80 across the board. Never staged and launched at the track but it was a rocket ship out of the hole leaving at 25lbs.

With the s588 boost is at 80 lbs peak with drive around 60-80 , still tuning and trying different things but its an animal. I believe due to the difference of a .85 a/r on the s5 compared to the 1.32 s4 is why drive rises faster and ends up higher, so far egts are in check with this s500.
Click to expand...

I asked a question about the S400 a while back and this is what I was told by BW. Made me think when you mentioned the .85 exhaust housing on the S500.

Hi Cody, The largest S400 turbine wheel is the 96mm while the most commonly used S500 turbine wheel is the 110mm. We bridge the gap in between with the different turbine housing sizes. The 96mm turbine wheel in the 1.32 A/R turbine housing will flow more volume of exhaust than the 110mm turbine wheel in the 0.85 A/R turbine housing.
 
SmokinCAT said:
I asked a question about the S400 a while back and this is what I was told by BW. Made me think when you mentioned the .85 exhaust housing on the S500.

Hi Cody, The largest S400 turbine wheel is the 96mm while the most commonly used S500 turbine wheel is the 110mm. We bridge the gap in between with the different turbine housing sizes. The 96mm turbine wheel in the 1.32 A/R turbine housing will flow more volume of exhaust than the 110mm turbine wheel in the 0.85 A/R turbine housing.
Click to expand...

The 110/99 in the .85 open T6 is acting like like it does flow less than the 96/88 1.32. I'd be much happier right now with a divided 1.15 or the open 1.0. I hate trying to make a wastegate work, it's a headache to say the least...
 
We saw 4psi more drive on the dyno with the S500 0.85AR vs the S400 1.32AR.
 
Last edited:
Smokem said:
We saw 4psi more drive on the dyno with the S500 0.85AR vs the S400 1.32AR.
Click to expand...

If you were to ask me I'd say you would see more than 4 psi difference between the two. It is what it is, different applications is apples to oranges. What were the peak boost and drive pressures of said tested s4 and s5 chargers if you don't mind?
 
With sampling data down to a hundredth of a psi every 100RPM I would say the information I have is accurate.
 
Smokem said:
With sampling data down to a hundredth of a psi every 100RPM I would say the information I have is accurate.
Click to expand...


I'm not saying your information is inaccurate. I'm saying that I think it would be a greater difference than 4psi, considering the differences I've seen myself.
 
DieselheaD said:
I'm not saying your information is inaccurate. I'm saying that I think it would be a greater difference than 4psi, considering the differences I've seen myself.
Click to expand...

I don't think your drive pressure for s400 is right. No way it was half boost.
 
mike diesel said:
I need to go hook up my drive pressure gauge and see what kind of back pressure I am getting from my 72/87/1.0, 88/112/1.23 compounds. I dynoed 875hp at 52 psi boost. On the track I see about 55 psi overall and 24 psi from the big charger.

I don't even have my gate hooked up trying to drive the secondary as hard as possible. Wondering if going down to a .90ar turbine housing on the secondary would benefit me more over the 1.0ar??
Click to expand...

I would say that if you went tighter on the secondary housing, your just going to create more back pressure and restrict the power potential of the setup.

Unless you run the gate, and dump the excess drive into the hot pipe to drive the primary harder...but then you may need a bigger turbine housing on the primary to prevent corking up the whole exhaust path through both turbines....or run a gate to control the drive pressure to the primary as well.
 
How about this for a question...
What are people seeing for drive/boost numbers off their primary's?

In all the twin sets I have ran on my truck, I always seem to have pressure like:
50psi drive, 30-35psi boost.
So I have no idea how some can get a 1:1 ratio, or even a 1:2 ratio of drive to boost. (If all exhaust is running through the turbine...not gated.)

What I'm saying or asking is, if it takes 50psi to make 30-35psi in my setup off the primary, how are others making more with less?
 
Last edited:
You can't compare your primary vs the same charger in a single position. Your primary is seeing a great flowing huge displacement. As a single it's seeing the ****ty diesel head flow most of us are stuck with.

Those are pretty much the same numbers I had with a s480 in the primary position, boost near half drive, a good indication it's on its knees.
As a single boost was higher than drive at the exact same power level. As a single it was able to cram the same mass flow only at a much higher pressure ratio.
 
Joesixpack said:
Maybe in unicorn land. Brad has a blower pushing his charger and boost still isn't double drive.
Click to expand...

I have been thinking the same thing. Those boost to drive ratios seem crazy. I wonder if the line to his Drive sensor was plugged with soot and gave him a false reading? This is in reference to the s475 not brads.
 
My former working truck had bp 0,5 bar lower than boost through rpm range, max boost 3,1 bar, no smoke. HX 60 80/92/32 . Many tractor pullers have much better ratio.
 
It's not plugged, it works fine. I'll replace it just to be sure. I don't have anything to gain from my results, it is what it is.
 
You must log in or register to reply here.
Back
Top