Engine/Transmission (1998.5 - 2002) Measuring Twin Turbo Boost

[Partyat33]

Wondering about measuring the boost between the turbos in the cold pipe. Is that an accurate representation of how much boost the big turbo is giving the little turbo. ???

 

[Jim Fulmer]

Yep, give you and idea if you are under or over working the bottom turbo!



Jim

 

[NoSeeUm]

I assume the optimum is 60%/40% at lower rpms and 50%/50% to 40%/60% at the upper rpm's?



Jim

 

[Partyat33]

Seems like the big turbo is not doing its job. Guess I have some wastegate adjusting to do.

 

[Jim Fulmer]

I don't know your turbo combination but your bottom turbo should be running in the 30-35 psi area.



Jim

 

[NoSeeUm]

I struggled trying to get my twins to work well. I kept thinking that I needed the bottom turbo to do more so I kept relaxing the wastegate on the top turbo. The s400 is non wastegated. My tuning was primarily for EGT and performance kept declining, so I went the other way.



I had to give up on my notion that I wanted the bottom turbo to do the work accept that it was the "system" that needed to be optimized vice just the bottom turbo. I am guessing that you are after maximum boost so my comments might not directly apply.



Jim

 

[GOT-Torque]

NoSeeUm, so your saying that optimun would be to have the little turbo provide more boost at lower rpm, than as boost comes up, it backs off some and lets the big turbo provide more of the boost?



I've done alot of messing around with my external wastegate (adjustable from inside the cab), trying to get max boost out of it (within its efficiency range) at full throttle. However, when I achieve that, it wants to build too much boost from it at lower rpms so I have to open the wastegate up again. How much boost is too much for a dodgezilla (for short periods of time, a second or two)



For the life of me, I can not pull my eyes off the track (when sled pulling) to look at my gauges long enough to read them I did it one time (my first pull) in a low gear (meaning a very long slow pull), however that was two sets of injectors ago.

 

[Partyat33]

Right now the HT3B is only making about 10 and HX 35 is making 40. Something has changed as I used to run 70 psi but now its low 50's. Hmmm.

 

[GOT-Torque]

external regulator I assume. Maybe it is stuck shut? The HT3B can't build any more boost because of the restriction (all air having to go thru the HX35). Careful so you don't overspin it.

 

[Partyat33]

Does not seem to be stuck. I am going to take the spring out completely.



Dennis

 

[NoSeeUm]

NoSeeUm, so your saying that optimun would be to have the little turbo provide more boost at lower rpm, than as boost comes up, it backs off some and lets the big turbo provide more of the boost?



I've done alot of messing around with my external wastegate (adjustable from inside the cab), trying to get max boost out of it (within its efficiency range) at full throttle. However, when I achieve that, it wants to build too much boost from it at lower rpms so I have to open the wastegate up again. How much boost is too much for a dodgezilla (for short periods of time, a second or two)



For the life of me, I can not pull my eyes off the track (when sled pulling) to look at my gauges long enough to read them I did it one time (my first pull) in a low gear (meaning a very long slow pull), however that was two sets of injectors ago.

That seems to be the way it works for me also. I crank down on the DZ waste gate and it builds boost faster. If I was in your shoes I might try a pressure switch / solenoid that bypasses the boost regulator. That would release the waste gate to fully open if it wants to and let the big dog down below eat its fill once your boost gets up around 30-40 psi. I am thinking that might help initial spool up, but protect the secondary from overspeed. I did something like this with my HX35. I also used an orifice type boost elbow to slow down the responsiveness a bit so that it would not bounce on the pressure switch.



Not sure how long a DZ can survive, but I don't intend to find out neither... .



I know that from talking with a friend that more boost does not make him run down the track any faster. If I remember correctly, he likes 60 psi and loses time with boost higher and lower than that. I don't have any friends that I can talk to that sledge pull. For myself, I focus mostly on EGT and maximum boost is a distant second in my application. .



Just about any way I can adjust my DZ waste gate I can come up against my pop offs, which are set for 55 psi give or take. I have all but disconnected the DZ waste gate and still made 55 psi easily, but during those times the EGT's rose to 1400F and unless I really stayed in it hard it stayed there. With the pop offs open I am likely doing nothing but pushing up my drive pressure.



From my testing of the DZ, the drive pressure ratio stays close to 1 up to around 25-30 psi AFAIR. This realy did not change when I put it in the twin set up. The DZ also makes its coolest boost (from map efficientcy chart) at around 26 psi for my altitude, but is more that capable of running at 35 psi non stop. At 40-45 psi boost from the twins is where I get the best EGT relief from the good ole SOP H-power meter. I have not fooled with the twins in some time because I am currently very pleased with the performance.



The last time I did check primary pressure, it was very low until about 10-15 psi of boost then worked its way up to 20-25 psi at 50 psi of boost. This was before I made some more tuning changes. At any rate these days it is a struggle for me to reach 1300F and then the EGT comes down. In my case the twins can push EGT down and because about that time I run out of of any more mph to accelerate too. I can get to 1250 towing only if I decide to test capabilities by towing in 5th gear at around 1700 rpm.



Jim Fulmer (or RonA) is the real expert here and I was just trying to fish an answer from him for myself. Which he has answered. Rookie here, so please take what he says for gospel and what I say for a grain of salt... .



Jim

 

[Partyat33]

My waste gate was pretty gunked up. I cleaned and lubed it and it moves much more freely. Still only making 10 to 12 on the big turbo. Gonna try a weaker spring.



Dennis

 

[NoSeeUm]

My waste gate was pretty gunked up. I cleaned and lubed it and it moves much more freely. Still only making 10 to 12 on the big turbo. Gonna try a weaker spring.



Dennis

When I was trying to tune my twins, initially I would just remove the actuator and adjust the link rod in or out. I did it so much that I cut slots in the actuator bracket to make it very easy.



In my case, adjustments made there did not really effect primary pressure significantly. The adjustments did effect EGT's a great deal.



Guessing you have an external gate? You could try testing it with shop air.



Jim

 

[Partyat33]

Just for fun I took the spring out completely. Truck was lucky to make two pounds of boost. I put in a weaker spring make 46 psi with big turbo still only making 10 psi. Gonna try another spring tonight. I am not sure I can get the whole assembly off to try the shop air idea. It bolts to the hot pipe and I suspect those little screws are stuck.

 

[NoSeeUm]

Just for fun I took the spring out completely. Truck was lucky to make two pounds of boost. I put in a weaker spring make 46 psi with big turbo still only making 10 psi. Gonna try another spring tonight. I am not sure I can get the whole assembly off to try the shop air idea. It bolts to the hot pipe and I suspect those little screws are stuck.

It's best if you think of it like this: Twins amplify the power capacity of the smallest turbo while keeping close to the same drivabilty/spool up as the small turbo.

This is probably the best advice that I have read for the twin turbo neophyte. I take that to mean that you have to optimize your secondary and let the primary act as a multiplier for the secondary.



You think maybe your problem is with your bottom turbo?



Two reasons:

1) You are making 40 psi secondary and your primary is not spooling.

2) Secondary WG wide open and your primary is still not spooling.



I don't know for sure, but from my experience there is only so much you can do with a secondary WG. Like I said, my primary would spool to about the same pressure and I would make about the same boost just about any way I messed with the secondary WG. But, in my case I just came up against the pop offs. What changed for me was the rpm that I got maximum boost and the rpm I got EGT relief.



You might try reading through this thread. There is just allot of turbo goob contained.



Here are other good quotes after some argument in the thread.

they (twins) don't spool up as fast... you can make them spool SOONER by going smaller on the turbine, but the boost needle doesn't swing as FAST as it does on a single turbo... due to intake and exhaust restriction...

Agreed, funny how my truck makes max power now 400 RPM sooner.



Jim

Jim

 

[GOT-Torque]

Is it as simple as a boost leak in the line feeding your gauge for the primary turbo?



If it worked before and made 70 psi, and now it only makes 50. I wouldn't think a spring change would be necessary.



Exhaust leak in hotpipe?

 

[Partyat33]

I was thinking the same thing. I don't think its a leak to the intermediate guage as the SPA would still be reading 70 or so. My EGT's are through the roof as well. I have not completely ruled out a problem with the HT3B, but all signs still lead me back to the wastegate. I'll do some more experimenting tonight. I will try to look at an exhaust pipe leak, will take two people. Don't see any soot though. Keep up the suggestions, I need them all.

 

[GOT-Torque]

Maybe you sucked a small bird or mouse into the HT3B and its partially plugged up the compressor housing?



Never rule anything out until you've checked...

 

[NoSeeUm]

Maybe you sucked a small bird or mouse into the HT3B and its partially plugged up the compressor housing?



Never rule anything out until you've checked...

Man, that would have to hurt and probalby leave a mark... .



Jim

 

[Partyat33]

You got that right. I am a trying to avoid taking it all apart. I will check to see if it seems to spin right.