The Beltless Boost Project is back up and running. Earlier this week I just ordered my McLeod twin street clutch and T-76 Ball bearing Q-trim turbocharger. Bonus money came through and its time to get the car going again.

The parts should be here in 3-4 weeks. Unfortunately my company might be sending me to Texas for a 6 week assignment starting in 2 weeks so the parts will be on hold.

I'm trying to finish up my ZF-6 conversion with my spare engine just so I can drive it down to Texas.

For those that don't know my 383 stroker with mildly ported stock heads pulled over 500hp and 530tq with 7psi on a conservative engine dyno last summer with a smaller turbo. We turned up the boost and the backpressure took out a chunk of the cometic headgasket and disformed some pistons. It made about 600hp around 12 psi not bad given that the builder said he has had people dyno slightly more rwhp then what his conservative dyno said.

 

I don't like the sound of that! Was the turbine to small for the amount of horsepower produced? I am new to turbocharging so this may be common knowledge.

 

I was using a P-trim turbine and it couldn't flow out enough of th exhaust. The other theory is that the cam exhaust duration is to small, but I'm not sure about that. I have a 224/218 cam.

 

Could it have been detonation rather than backpressure that damaged your engin?

 

It might have been, but we couldn't hold boost. It would peak up to 15psi and then take a linear drop down to about 10psi. I think there was so much back pressure that the wastegate was getting blown open.

 

Brian
Are you going to have the turbo up running for sure by Late Spring??? I want to see some # with the new Q trim turbo.

 

it all depends on where they send me for my job. It will be up and running this summer for sure, I'm working toward the sooner rather than the later though.

 

I would guess the turbo couldn't supply enough CFM to hold peak boost at high RPM. If the wastegate was getting blown open it would have never made peak boost. The chunk of headgasket is from detonation, their is no way back pressure from a turbo exhuast housing blow off a chunk of headgasket and disformed the piston. It may have indirectly caused it through heat, but I would bet it was the detonation that did the damage.

 

I believe it was the lack of evacuation of the cylender causing a spike in cylender pressure. I'm sure detonation was in there somewhere though. I'm planning on pulling back some of the timing.

The reason it made peak boost at 4000 rpm is because it could handle the flow of air and as the rpm increased(ie airflow) it could not keep up, which would show why the turbo was slowing down.

Cubic Inches * boost ratio * rpm * X = cfm of exhaust Where X is the combustion ratio of intake to exhaust gases with thermal expansion taken into account. As RPM goes up so does the exhaust flow.

 

You do realize on most turbo's the exhaust manifold back pressure is 2 to 3 times the intake boost pressure (only on race vehicle spinning high rpm can that get dow to 1:1 ratio.) Their is no evacation of the cylinder from the exhaust manifold in turbo motor, this one reason why you don't want a lot of cam overlap becuase the exhuast will end up in the intake.

The more back pressure, the faster the turbo would spin.

 

Yes I do

This is not true. What happens when you put a single T3 turbo on a 454 big block. That comparison might be a little overboard, but the exhaust pretty much just kills the engine. The turbine is too small to flow out enough air so the back pressure picks up and then the wastegate blows.

It goes with the same theory that if you have a bigger a/r on your exhaust turbine that you will have a higher peak HP number. Imagine the old turbo being a very small a/r number.

My guess is that the back pressure to intake pressure was quite high.

 

Brian,

is there any particular reason for going with the smaller Q-trim? The S-trim flows alot better and is much more efficient. my T74 GTS has a smallish physical size turbine housing so I think you could find the right size that still fit your setup. I think Precision is who makes the T76GTS in the smaller sized T4 housings. just a thought!

Chris

 

I don't agree ...

No way the turbo is slowing down at higher engine RPM!

If you have enough exhaust pressure to blow the wastegate open from that, then you have enough pressure to spin the turbo to extreme RPM's ... it will not slow down.

That is beacuse at the same rpm on the turbo (same boost) you will have less exhaust pressure and the engine will breathe better.

If your boost drops as the engine RPM rises, then the compressor side of the turbo is too small.

If the exhaust pressure rises too much then the turbine is too small and you loose power, but you should still make full boost.

 

Joby, I believe when you get to that point of maxing out the compressor the turbo will spin faster to compensate.

Now that I sit down and think about it I wonder if I am maxing out my 2.5" intake piping and intercooler. But then agian I'm not sure about any of it.

Here's some fairly concrete evidence that the turbine is too small. I have three runs, the first is a normal 15psi run pre spooled. The second is a high rpm only 15 psi run. With the turbo not pre spooled look at the horsepower gains from the lack of back pressure. Oh and the third run is just a 7 psi run. Notice the peak hp rpm between the 15psi and 7psi runs.


PSI - its a few pounds high according to my map sensor.



3600 15.2___ 0.0___ 7.6
3700 15.2___ 0.0___ 7.6
3800 15.3___ 0.0___ 7.6
3900 15.6___ 0.0___ 7.6
4000 15.8___ 0.0___ 7.6
4100 15.8___ 11.5___ 7.7
4200 15.7___ 11.7___ 7.8
4300 15.8___ 12.3___ 7.7
4400 15.6___ 12.9___ 7.8
4500 15.6___ 13.4___ 7.8
4600 15.4___ 14.1___ 7.9
4700 15.3___ 14.4___ 8.0
4800 15.1___ 14.7___ 7.9
4900 14.9___ 14.6___ 7.9
5000 14.7___ 14.6___ 8.0
5100 14.5___ 14.4___ 7.9
5200 14.2___ 14.4___ 8.0
5300 14.0___ 14.2___ 8.0
5400 13.9___ 14.1___ 8.0
5500 14.0___ 14.0___ 7.9
5600 13.5___ 13.7___ 7.9
5700 13.3___ 13.5___ 7.8
5800 13.3___ 13.4___ 7.9
5900 13.4___ 13.5___ 8.0
6000 13.1___ 13.5___ 8.0
6100 13.0___ 13.6___ 8.0
6200 13.1___ 13.2___ 8.2



Horsepower

EngSpd 17 STPPwr 15 STPPwr 13 STPPwr
RPM CHp CHp CHp
3600 441.4___ 0.0___ 339.9
3700 454.4___ 0.0___ 343.7
3800 465.3___ 0.0___ 356.7
3900 482.4___0.0___ 368.4
4000 505.7___ 0.0___ 380.3
4100 514.0___ 452.6___ 396.6
4200 525.0___ 466.6___ 406.7
4300 536.7___ 491.0___ 420.2
4400 553.5___ 508.0 ___429.1
4500 559.5___ 533.1___ 446.8
4600 563.2___ 550.8___ 455.4
4700 566.8___ 563.7___ 464.4
4800 564.6___ 575.3___ 466.9
4900 566.9___ 584.0___ 474.9
5000 569.8*___585.8___482.1
5100 568.4___ 588.7___ 489.4
5200 562.5___ 590.8*___495.6
5300 558.5___ 586.8___ 500.5
5400 557.6___ 588.0___ 500.1
5500 559.0___ 579.9___ 501.9
5600 549.7___ 575.3___ 503.0*
5700 542.0___ 567.5___ 500.6
5800 539.7___ 570.8___ 492.0
5900 524.6___ 557.3___ 489.2
6000 506.3___ 548.8___ 489.4
6100 494.8___ 539.2___ 478.8
6200 495.8___ 525.9___ 478.4


Torque
EngSpd 17 STPTrq 15 STPTrq 13 STPTrq
RPM Clb-ft Clb-ft Clb-ft
3600 643.9___ 0.0___ 496.0
3700 645.0___ 0.0___ 487.9
3800 643.1___ 0.0___ 493.1
3900 649.7___ 0.0___ 496.1
4000 664.0___0.0___ 499.3
4100 658.4___ 579.8___ 508.0
4200 656.5___ 583.5___ 508.6
4300 655.5___ 599.8___ 513.2
4400 660.7*___606.4___512.2
4500 653.0___ 622.2___ 521.4*
4600 643.0___ 628.9___ 519.9
4700 633.4___ 630.0___ 519.0
4800 617.7___ 629.5___ 510.9
4900 607.6___ 626.0___ 509.0
5000 598.5___ 615.4___ 506.4
5100 585.3___ 606.3___ 504.0
5200 568.1___ 596.7___ 500.5
5300 553.4___ 581.5___ 496.0
5400 542.4___ 571.9___ 486.4
5500 533.8___ 553.7___ 479.3
5600 515.5___ 539.6___ 471.7
5700 499.4___ 522.9___ 461.2
5800 488.7___ 516.8___ 445.5
5900 467.0___ 496.1___ 435.5
6000 443.2___ 480.4___ 428.4
6100 426.0___ 464.3___ 412.3
6200 420.0___ 445.5___ 405.3



these numbers definately show the turbine should be bigger. The fact that they do have the same "drop off" of boost could indicate something else too. Perhaps the compressor, perhaps the intercooler.


The way that I have the turbo kit designed I'm very limited on the intake side. I can't get a bigger turbo or intercooler because of the way things are set up. I am limited to my 2.5" piping without some major rework and what not. The only opion I had left was to increase the turbine side. But from the compressor map I would have to be moving 80 lb/min of air to max out the compressor at 15 psi, I'm not sure that would be the case here given the numbers. I never did actually check the size of the compressor and I bought it off ebay so I may not have gotten exactly what they said it was.


But if it was the intake piping I would think that the max hp would have hit more of a wall when you got the max cfm through the system. But I could be wrong on that one.


Compressor map:
http://www.turboneticsinc.com/cm_t76.htm

 

How are you controlling boost? Is it an external Wastegate?

 

To me it sort of look like the boost is set for a 13psi and the boost over shooting that number. Too small of a wastegate (or exhuast housing if that is where the wastgate resides) would cause that problem. The higher the boost teh worse the control would be. What does you boost look like on the highway when the motor downshift (or did you have a 6 speed already by this time)

 

Boost is controlled by a Turbonetics Racegate. I've never heard of them having a problem controlling boost. I tried using a boost conroller at one point and got the same results another time I just tightened down the top spring and the same thing happened. I really don't think a boost spike would take 2000 rpm to compensate though.

By the way the numbers on boost are one or two psi high. At the end of the runs the boost was around 11.

The engine isn't in the car. Its sitting on an engine stand in my garage. I'm hoping to get it in soon though, once I get the new clutch and turbo and have some time.

 

I did a graph of the data.

 

Joby, thanks for posting a graph of this. I've got one in excel but didn't know how to post it.


Besides the hp difference in the two 15 psi runs(thick yellow and blue), here's something else interesting I noticed. Lets compare the HP and TQ curves of the Yellow(15psi) and the Red(8psi) lines. They start out with almost exactly the same slope with the yellow being 100-125hp higher. This works until about 4600 rpm where the Yellow planes off and the Red keeps climing. The Yellow starts going down even before the Red has hit its peak hp. This can easily be explained by the decreasing boost causing the Yellow line to change. But when we look at the very end of the runs there is still a 5psi difference, but only about 15 hp and tq greater.

I guess what I'm saying is that the ratio of HP should be roughly 1.3:1 from high boost to low boost or (14.7 + 15psi) / (14.7 + 8 psi) = 1.31

And this seems to hold true until about 4100 rpm and then it stars to deviate from that. Kind of interesting to see theory and practice work together. I'm sure things like extra heat being generated have some thing to do with it, but its about a 20% deviation in the end. Thats alot of horsepower, like loosing a cylender.

 

If you only have 15hp/15ft lbs of torque from an additional 5psi your ECM is most likely taking all kind of timing from detonation. What does your Intake/Manifold air temps look like.