Precision 6765 Over-boost

[Jeff Rand]

Has anyone had issues with this turbo over-boosting using a 3" downpipe and a 1.300" puck. The hole was opened up to 1.100" and a new actuator installed with a 18 lb spring. Even with the actuator out of the loop and the puck wired open, the boost still goes (slowly) over 20 psi. The exhaust housing is a .63.
Thanks,
Jeff

 

[GNVYUS 1]

RJC is working on a 1.65 puck, might wanna call them.

 

[Jeff Rand]

RJC is working on a 1.65 puck, might wanna call them.

Thanks, I will give Jason a call tomorrow.
Jeff

 

[Quik Six]

Has anyone had issues with this turbo over-boosting using a 3" downpipe and a 1.300" puck. The hole was opened up to 1.100" and a new actuator installed with a 18 lb spring. Even with the actuator out of the loop and the puck wired open, the boost still goes (slowly) over 20 psi. The exhaust housing is a .63.
Thanks,
Jeff

I'd talk to Cal about it and see what he has to say.

Jason does have a 1 5/8th's puck. I've got one of these but haven't used it yet since we would have to cut so much out of the DP wall. We cut some material out the wall to give some more room for the air to flow around the puck and that helped a lot.

You may want to look up some of Bison's posts in turbo section, he's talked about this several times and you may want to see what he has to say before you start making a bigger hole.

My 6265 has been quite a challenge in this area and the 6765 seems to be a bigger problem that many have solved with external wastegate. I'm sure you didn't want to read that but I've found that it is almost impossible to change just ONE part on these cars without having to change some other things.

 

[slimtastic]

your turbo is too efficient for all that high velocity exhaust gas to make that harsh 90 degree turn through a stock style wastegate hole. this was proven when you wired the puck open. youll need to go external witha nice and soft exit angle.....or stepping up to a larger housing might help(a little) but dont bet the farm on it

 

[GNVYUS 1]

His current WG hole is 1.1, so have others that have opened it to around 1.4 having issues? That appears to be about a 50% increase from the stock castings WG hole.

 

[bison]

What is your target boost?

 

[toomanymodz]

Subscribed. I just ordered a 6765 and I really would rather not have to sell my 3" THDP.

 

[TurboBob]

when you ported the hole, did you radius the inside edge closest to the header flange?

Bob

 

[Jeff Rand]

when you ported the hole, did you radius the inside edge closest to the header flange?

Yes, I did radius the inside. I spoke with Precision today and they suggested going to a .81 exhaust housing ($229). I was thinking of adding a Deltagate at the crossover pipe.
My target for the street is 18-20 psi. running with a Razor kit. (I built this engine and I want it to live for the owner. It came to me with a blown head gasket and that makes me nervous).
Jeff

 

[slimtastic]

do this

 

[bison]

You should have went with a smaller turbo if you wanted to have the boost that low. There is no power there running that turbo at low boost on that engine at that low of a boost pressure over a 62 trim or an old p trim. You just made it hard to get boost control.

 

[L8TRH8R]

FWIW My Deltagate couldnt hold back the power the 6765 was making with my combo. Would hold for a split second then bury the boost gauge. Bit the bullet & bought the new Precision pw46. Now boost pressure is rock steady.

 

[Jeff Rand]

You should have went with a smaller turbo if you wanted to have the boost that low. There is no power there running that turbo at low boost on that engine at that low of a boost pressure over a 62 trim or an old p trim. You just made it hard to get boost control.

This is not my car and I am trying to make what was given to me work. I would not consider 18 lbs to 20 lbs of boost low. RJC is making a 1.6" puck so I will try it and report back.
Jeff

 

[GNVYUS 1]

Jeff, definitely report back and fill us in on the hole size.

Slimtastic, I like it, curious what did you do to close off the turbo housing wastegate hole? I've seen other vehicles weld it shut and some welded the puck to it.

 

[bison]

This is not my car and I am trying to make what was given to me work. I would not consider 18 lbs to 20 lbs of boost low. RJC is making a 1.6" puck so I will try it and report back.
Jeff

The turbo will support over 700hp easily. You're not going to get anywhere near that with the small ci engine and boost that low. It would have been a better choice for the owner to choose something that will support the power he's looking for. Spoolup would be greatly improved and boost control would be a lot easier to deal with. But since these parts were given to you to work with I'd just spend the $ and go with a different wastegate setup.

 

[Otto J]

I set a 6765 on the last car i did, I used a 3.5 GN1 externaldownpipe.
I had to open the wastegate hole to tthe diameter of hte gate pipe to get th boost to 20-21 #s.

I am setting up a 6265 on a aluminum headed stroker now with a swing valve,i am doubting it will control the boost down to the low 20s

 

[jasjamz]

http://www.turbobuick.com/forums/ge.../309163-billet-wheel-turbo-boost-control.html

I have the big RJC Puck in an ATR 3" downpipe. This has been out for a while. I'm surprised its not used buy more of the billet Turbo guys.

 

[slimtastic]

Slimtastic, I like it, curious what did you do to close off the turbo housing wastegate hole? I've seen other vehicles weld it shut and some welded the puck to it.

i use a rjc internal wastegate delete flange. it mounts between the downpipe and the turbo....doubt that its 100% sealed but it seems to work good for me

besides im really good at cracking cast iron with a welder lol

 

[John Wilde]

I set a 6765 on the last car i did, I used a 3.5 GN1 externaldownpipe.
I had to open the wastegate hole to tthe diameter of hte gate pipe to get th boost to 20-21 #s.

I am setting up a 6265 on a aluminum headed stroker now with a swing valve,i am doubting it will control the boost down to the low 20s

Wow, please keep us updated on the 6265.