When going over 30 psi?

[imjoesnuffy]

Yes it was on purpose :tongue: .

Ran some Q16 this weekend, added some fuel through the chip and cranked the boost up. It was over 30 psi, my gauge only goes to the 30 psi. It hit 30 and I still had pedal left . Kept the timing conservative at 26 in 1/2 and 25 in 3rd. For some reason the powerlogger wasnt reading boost.

First question, with ARP head studs and stock gaskets how much psi will these cars handle before lifting the head?

Target AFR still around 11.0? I didnt let mine get above 10.6 Better safe than sorry, but hell I was pushing it pretty hard.

I know each turbo is different with efficiencies and turbo maps. I have never taken the time to really understand them. At what point does a turbo become ineffective with more psi with rising IATs? If so, what temp would that be? I have a powerstroke front mount intercooler.

Last one, and it may be a stupid one. Does your turbo sound different when pushing that hard? Mine is a little PT-51 but sounds totally different when going that hard. Has a whine to it like a supercharger instead of the whistle, but still seems to be pushing very hard.

I wanted to take it to the track and maybe get a 10 sec slip, but the family had some surprise plans for me.

 

[V6POWER]

What is your 60'? It may be easier to get into the 10's by improving 60' than running a whole lot of boost. JMO.

 

[WSLN 6]

Maybe give the info you have now (IAT temps,60ft,mph,rpm etc etc) and we can make some better guesses at your questions. I see about a 10 degree rise in temps in a quarter mile run with my powerstroke IC.

 

[imjoesnuffy]

What is your 60'? It may be easier to get into the 10's by improving 60' than running a whole lot of boost. JMO.

I agree my car makes enough power to get into the 10s as evidenced by the MPH in my sig. Didn't make it to the track though. Best 60' ever was a 1.60 I think I have narrowed down the problem with my 60 foots.

Just wondering about running the turbo that hard, thats all. I will get a 10 sec slip sooner or later .

 

[GNVYUS 1]

Not sure how you've adjusted boost but it's possible to hit max boost on less than 100% pedal, fuel pressure gauge could help you out with your total boost.

Tuning is a huge part of keeping the heads on the car and I'd bet stock headgaskets without any prior abuse can take 35psi no problem. Problem is, most GN stock headgaskets have had some prior abuse.

Backpressure is a huge key to pushing small turbo's. If you have any inlet or exhaust backpressure it's going to make the turbo work harder. I'd bet the Powerstroke does not have a great pressure drop across the core so twin alky would be a huge plus on a 51 turbo at 30+ psi. I know I gained 1psi with my preturbo injection so that would help also.

 

[imjoesnuffy]

Maybe give the info you have now (IAT temps,60ft,mph,rpm etc etc) and we can make some better guesses at your questions. I see about a 10 degree rise in temps in a quarter mile run with my powerstroke IC.

My logs show a rise of about 15-20 but I dont know the distance on the runs. What psi are you running in the 1/4?

Not sure how you've adjusted boost but it's possible to hit max boost on less than 100% pedal, fuel pressure gauge could help you out with your total boost.

Tuning is a huge part of keeping the heads on the car and I'd bet stock headgaskets without any prior abuse can take 35psi no problem. Problem is, most GN stock headgaskets have had some prior abuse.

Backpressure is a huge key to pushing small turbo's. If you have any inlet or exhaust backpressure it's going to make the turbo work harder. I'd bet the Powerstroke does not have a great pressure drop across the core so twin alky would be a huge plus on a 51 turbo at 30+ psi. I know I gained 1psi with my preturbo injection so that would help also.

Dont have the fuel pressure on the powerlogger, might have to look into getting it attached. Running the stock head gaskets as a safety valve type thing, better to blow a gasket than drive over the crank.

I like the wheels on the cold side of my turbo to much to try preturbo injection.

 

[RUQWKNF]

Here's a few things.

Are you running the stock MAP sensor?
If so, doesn't the power logger use it to read boost? If so, the factory MAP will not read 30psi, due to it being only a 2 bar sensor. You'd need a 3 bar or 5 bar map sensor to read more than 30psi. I would check with Mike at Full Throttle to be 100% sure about this.

The thing to remember about our head gaskets on stock blocks is, we are limited to 4 bolts per cylinder. Under extreme conditions (yes 30+psi is extreme but common when people start pushing the limits) this excessive pressure tends to lift the head off the block. Which leads to gasket failure obviously. ARP heads studs dramatically helps, but is not the perfect cure. The other thing to remember, just a small amount of detonation, can loosen up a head gasket. Enough detonation can break the fire ring away from the graphite material of the gasket and lead to failure even quicker. The tune has to be almost perfect with no detonation to make OEM GM or Victor style graphite gaskets survive 30+psi enviroments. C-16 is the fuel of choice for this tune. Also, you might hear of people who have run high boost on low mileage motors and never a failure. This is because the factory Victor style gaskets have over the years glued the heads to the block. If you've ever changed gaskets on a low mileage motor that has never been abused you'll know what I'm talking about. The age and heat cycles help to glue the heads to the block. This is also why when people replace blown head gaskets with the same stock style on a tune that regularly see's 30+psi, won't live long. The gaskets don't have enough time to fully heat cycle and seal.

With regards to at what pressure the turbo is done at, this can only be determined using a Back Pressure gauge/back pressure reading. The common rule of thumb is, when you back pressure surpases 2:1 ratio (2psi of back pressure for every 1 psi of boost, EX: 60psi of back pressure and 30psi of boost at the intake, and you're done) the wheel is done. Anymore than this, and you run the risk of over speeding the rotating assembly, or super heating the charge temps. Back pressure is typically measured just before the inlet of the turbine housing.

If you can datalog charge temps before the intercooler, this would dramatically help in determining at what point the compressor wheel starts to become inefficient.

Example: If say your discharge temps at 25psi are let's say 295*, and at 30psi, the discharge temps jump up dramatically to 475*. This would be an indicator that the wheel is starting to become inefficient. Note, this is just a example, not real world results for the PT51.

On a PT51, we didn't recommend pushing it much past 28psi. Not to say that there hasn't been anyone have done it with good results. Just that it's not recommended. Yes, the sound of the turbo will change slightly with higher pressures. (IE: a higher pitched whistle/whine) And honestly there have never been any real world test results of the PT51, with regards to discharge temps at what psi. I would concentrate on making the combination more efficient, than to keep cramming more boost in. This means, ported heads or aluminum heads along with a better cam. Which I see you already have done with your combo. This way, you wouldn't have to run the pressure so high to make the power. You don't want to over speed the rotating assembly, that leads to destruction. Once you reach the limits of the rotating assembly with regards to back pressure and discharge temps, on an optimized combo, it's time to stepup the rotating assembly. In your case, I would recommend either a HP6262 or a PT6765 from Precision.
Hope some of this helps.

Patrick

 

[imjoesnuffy]

Thanks for your response Patrick. I am running a 3 Bar MAP sensor, for some reason it didnt show up on the powerlogger. I have always tried to remain on the conservative side when it comes to tuning my car and it has worked well for me so far.

Whenever I am running a race fuel I always tune for no knock. Making very small changes, 1 at a time and seeing how the car responds. I have been fortunate enough to have very little knock when pushing this car for more.

I read every one say just flog the motor after you get it re installed and no need for a break in period with a roller cam. Reading what you said about the stock gaskets, makes me glad I put 500 miles on it before I really started to hammer on it. Maybe that has helped???

Any ideas on how to measure back pressure? Or is it something that I should even worry about. I realize it is a more definitive way to see if the turbo is no longer efficient with more boost. but is there a practical way that a regular guy on the street can measure it?

You also bring up a good point about turbo discharge temps. Is there a reference range that could be used to determine efficiency verses rich/lean conditions pre intercooler? No idea on how to rig something like that up either. EGT gauge in the pipe going to the intercooler??

You have definitely given me some things to think about. Thanks!