is this turbo too big

[zexystang2]

Ok well i dont want to put any companys name out there yet as im not sure its the turbo. But i called and turbo company and told them that i have a 3v mustang with forged internals at 9 to 1 compression with port and polished heads with stock valves and told them i wanted between 900 to 1000 rwhp and they suggested a 7879 ball bearing turbo. so i put it on and i only made 455 rwhp at 14 llbs of boost. So i call the turbo company and they suggest it must be a boost leak or either the wastegate is bad. So i reversed the lines on the wastegate coming from the m.b.c so that it would keep the wastegate shut no matter what and the car still only made 14 llbs of boost and it took all the way to 6200 rpm to make it. So i call the turbo company tech guy back and now hes saying that the turbo might be making too much cfm for my motor to take and is acting like a exhaust brake because the shaft speed is too slow. Has anyone heard of a 7879 turbo being too big for our motors?

 

[weather man]

I think the turbo you made power with in your sig answers the question.

 

[gray1622]

Is it a T-4 or T-5? What # spring do you have in the wastegate, what size wastegate do you have? Where are you getting your boost reading from? What intercooler are you running?From my understanding of a waste gate you have.

Presssure filling the diaphragm + Pressure from exhaust gas on piston = Spring.

With a boost controller you can have

Presssure filling the diaphragm + Pressure from exhaust gas on piston = Spring + Pressure coming in from top of wastegate.

A way to see if you have wastegate problem would be simple unhook vacuum line too it and see if you can make more than 14 psi. But be ready to let out of it. This may be a bad idea.

I would be looking for leak on cold side. The thing that's really weird is I would of thought you would of madee more HP than that on 14 psi even if you have a boost leak. I seen a car on this form with T-5 turbo work just fine but I can't seem to find a thread.

If you can rule out cold side leak and wastegate it only leaves the turbo.

 

[zexystang2]

I think the turbo you made power with in your sig answers the question.

No not really. Thats all the power that turbo would make and i wanted around 1000 rwhp so i had to go bigger.

 

[zexystang2]

And its a t4 turbo with a .96 a/r. and i tryed the unhooking the vacuum line to it and it still wouldnt boost over 14 llbs so it must not be the wastegate then. But I know turbopete on this forum runs a 78 precision turbo and some others as well. So i just wanted to know if anyone had heard of this size turbo being to big for our motors.

 

[gray1622]

If you reading boost from turbo instead of intake. A leak on cold side would make sense since you are only making 450 HP.

You could have the valve seal in wrong.

 

[CPRsm]

Dragging too much ass for a good answer tonight just got home. Tagging the thread for tmrw. Too big of a turbo lol. What a crock of shit. This turbo replaced the 67/66 I'm guessing. I know the company and can about guarantee it's the turbo.
How any more info? Whose kit, intercooler size, headers, mufflers, tubing size, etc

 

[weather man]

No not really. Thats all the power that turbo would make and i wanted around 1000 rwhp so i had to go bigger.

Dragging too much ass for a good answer tonight just got home. Tagging the thread for tmrw. Too big of a turbo lol. What a crock of shit. This turbo replaced the 67/66 I'm guessing. I know the company and can about guarantee it's the turbo.
How any more info? Whose kit, intercooler size, headers, mufflers, tubing size, etc

The totality of the car has to be able to take advantage of the bigger unit or, what CPRsm said.

 

[TurboX]

PTE 7675 would have got you there, but to answer your question the motor isnt too small and the Turbo isnt too big. You got problems somewhere else, Ive 4.6s make 30psi on much bigger Turbos.

Spill the beans , Who is feeding you this stuff ?

 

[s8v4o]

What is it with turbo manufacturers NOT giving compressor maps or even relevant information like lbs/min????? Does anybody know the specs for this turbo?

 

[psfracer]

The turbo is not too big, the fastest car on this board runs a single 88 on a 3V.

 

[Sactown]

My 76mm precision turbo is fine, I don't see why/how a 78mm would be to big.

 

[LAllison20]

Im having a hard time understanding why you only hit 455hp on 14lbs. Where are you measuring boost, and what did your tuner say?

 

[CPRsm]

So i call the turbo company and they suggest it must be a boost leak or either the wastegate is bad.

A boost leak or bad wastegate will not effect peak power. It can sloow spool and show a loss under the curve. But if you still hit peak boost, the power will be the same.

So i reversed the lines on the wastegate coming from the m.b.c so that it would keep the wastegate shut no matter what and the car still only made 14 llbs of boost and it took all the way to 6200 rpm to make it.

That's a damn good indication of a back pressure issue.

So i call the turbo company tech guy back and now hes saying that the turbo might be making too much cfm for my motor to take and is acting like a exhaust brake because the shaft speed is too slow. Has anyone heard of a 7879 turbo being too big for our motors?

The only way a turbo can be too big and cause a real power loss is to surge. But the turbo would have to provide too much cfm down low by spooling too fast. At 14psi by 6200, seriously doubt that's a problem. If you were way off the map or the compressor was blowing hot air it could cause it but your tuner should have scene that immediately.

The exhaust acting like a brake is exactly how the turbos make boost. The turbo creates more cfm than the engine can handle.
If you take that turbo off you'll more than likely find your problem. The inducer is only 78mm which is a touch large for that turbine. But if you take the cover off the exducer from them is always huge. When you have a large compressor aggressively trying to move air you need a large turbine so it can apply enough leverage on the compressor to keep back pressure from sky rocketing. On the turbine you'll see a 100 trim cut wheel. Instead of having say an 85mm inducer(then neck down to 79) which would create the leverage I was talking about, it will also be 79mm. If you look at other turbines you'll see a step down in the turbine as it exits the housing. So now you have a 79mm turbine trying create leverage and turn a compressor wheel which is probably 130-145mm. If I knew nothing else about the car I'd say the exh was too small. If you replaced the 67/66 which this and can't come close to the power the answer is pretty simple. That turbo isn't going to work for you. I used a 74/82 from them and it started to slow down about 750rwhp.
You're kinda stuck because they don't offer a larger turbine in that size frame. You could go up in AR but that won't solve a leverage problem. Someone on hear ran smaller turbo from them and came up short on HP. I explained my thoughts, but not sure if they believed me.

 

[gray1622]

Is it a TRIPLEX CERAMIC Bearing turbo?

 

[Bobby]

I might be wrong but I don't think he is talking about comp

 

[gray1622]

I am still interested to know where are you reading your boost from?

 

[toorbeenee]

Never too big LOL

 

[zexystang2]

I read my boost from the intake and i also put a gauge on the compressor cover to check both. And Im running the on3performance hot side piping. I changed the cold side to 3 inch. the intercooler size is 31x11.75x4inch thick. I also run a exhause cut out before the mufflers

 

[zexystang2]

The company wants me to send the turbo back and they said they will resize it for free