SPS 62 in twins. Drive pressure reduction?

[JasonCzerak]

There is definately more than one way to skin a cat. Like I wrote in the other thread, pick a power level and build for it.



Chris, 15 psi off the primary could yeild up to 45 psi off the secondary, but definately not more than that.

Tho, not to burst anyone bubble heres. From the guys I grew up with, the guys make big numbers with singles on 2 liter 4 bangers (900hp, 12,000rpm, blah blah blah). Their big agrument was not PSI totaly, PSI was more for bragging rights. It's was more so CFM... . The more CFM flow to put more air cylinder with less driving pressure the more power you got.



The more CFM on a N/A motor could use the better. This has to be the same with turbo motors.



Velosity is also important, as to how much when you're dealing with boost I'm not sure.



How do you get the biggest straw to push air though? With these stock intake manafolds, is is possible to get enough? I mean Comp and sbentz for example don't use the stockers for a reason right?



If everthing in the intake and exahust piping was increase say . 25" in diamater, same turbos same fueling. The head ported that little bit more to compasate would there be much of a benifit vs. money spent elseware?

 

[paulb]

You are pretty much on the right line--I don't recall the exact multplication factor that the smaller turbo compresses the air to, but I've always heard it's more than two times--but of course that was when twins were being first put on and guys were shooting numbers out like if you had 15lbs of boost from the big turbo you will end up with 70 lbs of boost--those aren't correct numbers just an example---finally some guys started putting guages on the cold pipe to see what the big turbo was making, but this isn't done by many, so we will have to wait and hear some better specifics from guys who have the guages set up to monitor this--chris

The way mine is set right now, at 15psi on the bottom turbo, I have 37psi total. This is with a fuel level that produces ~370hp (comp box off), and EGT's are at ~950. At ~480hp (comp box on 3x5), the bottom turbo is at 27 psi and 50psi total, and EGT's are ~1150. I'm not sure yet what happens on 5x5, because the gauge I have on the bottom turbo on goes to 30psi... That will be changed in the near future.



Paul

 

[Diesel Freak]

Tho, not to burst anyone bubble heres. From the guys I grew up with, the guys make big numbers with singles on 2 liter 4 bangers (900hp, 12,000rpm, blah blah blah). Their big agrument was not PSI totaly, PSI was more for bragging rights. It's was more so CFM... . The more CFM flow to put more air cylinder with less driving pressure the more power you got.



The more CFM on a N/A motor could use the better. This has to be the same with turbo motors.



Velosity is also important, as to how much when you're dealing with boost I'm not sure.



How do you get the biggest straw to push air though? With these stock intake manafolds, is is possible to get enough? I mean Comp and sbentz for example don't use the stockers for a reason right?



If everthing in the intake and exahust piping was increase say . 25" in diamater, same turbos same fueling. The head ported that little bit more to compasate would there be much of a benifit vs. money spent elseware?

No bubble to burst!!



I agree completely!!!



It goes a little beyond CFM. A good engineered turbo system will optimize density ratio at the inlet plenum.



Ask some of the Diesel Turbo shops what this means... I will bet that they do not even know how to calculate DR.

 

[Diesel Freak]

The way mine is set right now, at 15psi on the bottom turbo, I have 37psi total. Paul

looks perfect!!



remember that at that flow, there is about a 6 psi drop across the intercooler.

 

[JasonCzerak]

No bubble to burst!!



I agree completely!!!



It goes a little beyond CFM. A good engineered turbo system will optimize density ratio at the inlet plenum.



Ask some of the Diesel Turbo shops what this means... I will bet that they do not even know how to calculate DR.

And people wonder why the Banks Hi-Ram and that ATS intake thing doesn't do much more then look shinny under the hood.

 

[paulb]

looks perfect!!



remember that at that flow, there is about a 6 psi drop across the intercooler.

Actually 4 psi... It was less then I expected, but the twins are not heating the air as much as I expected.



Paul

 

[Diesel Freak]

hmm I may need to clean mine

 

[Jim Fulmer]

Mine is 4 psi drop across at 60 psi, but dropped the intake temp 55 degrees.



Jason, it just like a Jet engine, it gets more efficient when being force fed. Jet's have to perform at optimal or close to it at all temps and pressure altitudes to a point. That top turbo's map is kind of thrown out of the window when it being pressurized beyond 14. 7 psi(standard day air pressure)



I like Cliff's approach, pick a power and build to it... ... ... I'm still trying to pick that power and keep it a street truck.



Jim

 

[RonA]

I went out and checked a few points on mine. Takes 7lbs of drive to move the boost gauge off the peg. 2lbs primary,10lbs manifold,15lbs drive. 6lbs primary, 20lbs manifold, 22lbs drive. 10lbs primary, 30lbs manifold, 32lbs drive. 15lbs primary,40lbs manifold, 47lbs drive. Drive pressure goes up fast from this point.

 

[Idaho CTD]

I went out and checked a few points on mine. Takes 7lbs of drive to move the boost gauge off the peg. 2lbs primary,10lbs manifold,15lbs drive. 6lbs primary, 20lbs manifold, 22lbs drive. 10lbs primary, 30lbs manifold, 32lbs drive. 15lbs primary,40lbs manifold, 47lbs drive. Drive pressure goes up fast from this point.

Loosen your top wastegate 1-1 1/2 turns and try it again.

 

[Idaho CTD]

Actually 4 psi... It was less then I expected, but the twins are not heating the air as much as I expected.



Paul

At 75psi and 100*+ ambient I was losing 10psi across the intercooler. At 50* ambient it was closer to 4psi for me.

 

[AK RAM]

If your goal is to relieve as much drive pressure as possible without slowing down the top turbo, thinking internal wastegate only here, would it be better to use a bigger exhaust wheel on the top turbo or clip the existing wheel?



Seems if you use a bigger exhaust wheel, in addition to helping drive pressures, the turbo slows down, which will effect overall airflow from it at the same wastegate settings. Verses clipping the existing wheel will relieve some drive pressure, and while spool up will slow, once it gets going it shouldn’t affect overall shaft speed, correct? With my compressor wheel being as small as it is to begin with, I worry about slowing it down in my quest to relieve some drive pressure.



Also, in regard to the tiny compressor housing that compliments the 57mm wheel, how much is the smaller housing hurting intake temps due to compression you think with a B2 feeding it? I like the setup, but wonder how much a step up in compressor housing size would help and if it is worth it. If you go up in housing size do you necessarily have to go up in wheel size also? I seem to get enough air from it now, but I sometimes wonder just how much better it could be, more and cooler, with minimal upgrade cost.

 

[Idaho CTD]

If your goal is to relieve as much drive pressure as possible without slowing down the top turbo, thinking internal wastegate only here, would it be better to use a bigger exhaust wheel on the top turbo or clip the existing wheel?



Seems if you use a bigger exhaust wheel, in addition to helping drive pressures, the turbo slows down, which will effect overall airflow from it at the same wastegate settings. Verses clipping the existing wheel will relieve some drive pressure, and while spool up will slow, once it gets going it shouldn’t affect overall shaft speed, correct? With my compressor wheel being as small as it is to begin with, I worry about slowing it down in my quest to relieve some drive pressure.



Also, in regard to the tiny compressor housing that compliments the 57mm wheel, how much is the smaller housing hurting intake temps due to compression you think with a B2 feeding it? I like the setup, but wonder how much a step up in compressor housing size would help and if it is worth it. If you go up in housing size do you necessarily have to go up in wheel size also? I seem to get enough air from it now, but I sometimes wonder just how much better it could be, more and cooler, with minimal upgrade cost.

Adding a larger wheel will slow the turbo down but relieve some back pressure. Clipping will increase flow and affect the spool slightly. Clipping reduces weight too so it wont change the spool up nearly as much unless it's done excessively.



Remember the wastegate works on back pressure. If you relieve back pressure it will open later. Once the top turbo get's things rolling it takes a break and the big turbo does the rest of the work. So once you get past the wastegate setting the top turbo adds very little additional boost. It just sits there and compounds the air. This is all dependant upon wether or not the wastegate can keep up though.



If your worried about spool up then clipping will be the thing that effects spool up the least. If it was me I'd go up to a 60 or 62mm wheel and a larger compressor housing.

 

[paulb]

Loosen your top wastegate 1-1 1/2 turns and try it again.

I was going to say 1 turn...



Another couple questions Ron...



Are you using an adjustable boost elbow, or are you adjusting the wastegate rod to adjust the boost? I think I remember in another thread you said you had the wastegate actuator set to 24psi. At what psi is the wastegate full open?



Paul

 

[paulb]

At 75psi and 100*+ ambient I was losing 10psi across the intercooler. At 50* ambient it was closer to 4psi for me.

It was about 45* when I tested mine, so the 4psi sounds like it's right in line. Thanks!



Paul

 

[BradyWilliams]

D. F. that VP44 is probably getting pretty thin. Call me if it stops I'll send AAA. 188,000 miles is very impressive. Wait till you see the hp number that we will be making. I think it should be good. Thanks, Brady

 

[RonA]

AK RAM.

I went back and forth between this turbo and my Bell WSB which has the small (57mm) comp wheel and the small outlet housing. The bell spooled up the 3B easier on the bottom. With the K31 on the bottom it would run 40 psi going up a slight grade. Power level never felt any better, just higher boost numbers. The larger wheel and housing cut down a bit right on the bottom, but does better in the midrange. I imagine the top end would be better also. I can't really verify the top end just yet. Brown truck brought a couple of small air regulators to me yesterday. I will install the external gate by the weekend. That will probably solve two problems. Drive pressure, and low boost off primary. I think I am just pushing a bit too much exhaust gas through this . 7 housing. The drive pressure is going up, and there is not enough gas going through the housing to drive the primary any higher. If it doesn't work, I'll only be out a few hours time and a 20 dollar regulator.

 

[AK RAM]

I kind of like the 57mm wheel so far. If I settle on clipping the current exhaust wheel then I'll definitely keep it as I get plenty out of it already. Just seems like a lot to ask for a B2 to be pushing through that tiny compressor housing. Would going up in compressor housing size but maintaining the current wheel be feasible or do they kind of have to match in size?

 

[Diesel Freak]

D. F. that VP44 is probably getting pretty thin. Call me if it stops I'll send AAA. 188,000 miles is very impressive. Wait till you see the hp number that we will be making. I think it should be good. Thanks, Brady

Thanks for the offer, but I think I will stick with new unit from Cummins.



That is unless you intend on cutting me one sweeeeeeeeeeeeeeeet deal on a VP44. My parts guy at Cummins is VERY helpfull!!



oh, and for everyone that has hot start problems with a VP44, AND it checks out electricly, replace your bypass relief!!!!!!!!!!!!!!!!!!!!!!!!!!!!



It could be allowing too much air back into the pump via the return line which also may have a small leak allowing air in.

 

[paulb]

Thanks for the offer, but I think I will stick with new unit from Cummins.



That is unless you intend on cutting me one sweeeeeeeeeeeeeeeet deal on a VP44. My parts guy at Cummins is VERY helpfull!!



oh, and for everyone that has hot start problems with a VP44, AND it checks out electricly, replace your bypass relief!!!!!!!!!!!!!!!!!!!!!!!!!!!!



It could be allowing too much air back into the pump via the return line which also may have a small leak allowing air in.

Would this be the bypass relief valve that you modified?