76 GTQ has lag to it?

[Reggie West]

And here is why. The turbo housing is 2.75 inches now and the downpipe is 2.50 inches. This creates a lot of turbulence and it explains why this turbo seems to have some lag to it when spooling up. If you notice in the pictures we could not simply cut the flange and make it bigger. The pipe is not centered on the hole so it wont work. I wish it did.

The solution for this is a new and bigger flange. RJC makes the 3 bolt flange with the correct size hole for a GTQ turbo. So we can cut the old flange off of the downpipe and weld on the new one. We will be taking the exhaust housing to the fab guy so he can center the pipe on the turbo housing and then cut the hole for the wastegate.

It should be interesting to see what the turbo spools like once this is done. It should be a little more responsive.

Just for info this turbo is on a stroker stock block, forged rods and pistons, GN1 heads, classic FAST and SMC alky kit.

Just thought this might get a few of you thinking......

 

[GNVYUS 1]

Well that's not an ideal solution since the ID at the turbine wheel is still too small. Have you ever seen what a T6 75mm turbo's exhaust housing looks like, 5". Even if you can stick a 5" DP on that PTE housing it's still choked off at the outlet of the turbine wheel creating backpressure where it matters most.

I'd look to see if PTE makes a true 3" V Band for that turbo or even bigger. The 3 bolt is probably the true reason it's so small and you're sort of stuck.

 

[Reggie West]

You may be right about the pipe but I am trying to find a solution given what i have to work with. I am sure there plenty of guys out there putting bigger turbos on the car and not looking at possible restrictions to flow at the turbo or the headers (port matching).

I have a 4 bolt 70 turbo sitting on the shelf but was waiting for this one to go out before making the switch to that.

Really the 76 is overkill for a street car that might see some track runs every now and then. We are using what we have and tuning accordingly.

 

[bison]

Some flanges are better than others. I typically only need to remove metal around the top of the flange. It's worth some power if you are in the 700+whp range or higher but won't do much for spool up unfortunately. The t4 tang housing will take care of this and has a 3.5" v band flange. Precision part # TH8180A. This is the housing that would work best on a 800+whp application with a fairly stout engine. Spoolup won't be any better than the 3 bolt. The .96 version would spool even slower. For a car that is rarely raced I'd get the .68 housing. It will flow a lot more than the 3 bolt .85.

 

[RUQWKNF]

Some flanges are better than others. I typically only need to remove metal around the top of the flange. It's worth some power if you are in the 700+whp range or higher but won't do much for spool up unfortunately. The t4 tang housing will take care of this and has a 3.5" v band flange. Precision part # TH8180A. This is the housing that would work best on a 800+whp application with a fairly stout engine. Spoolup won't be any better than the 3 bolt. The .96 version would spool even slower. For a car that is rarely raced I'd get the .68 housing. It will flow a lot more than the 3 bolt .85.

I completely agree. Only problem is, the TH8180A part number is no longer available and none in stock.
I have also seen people grind the flange to as sharp an edge as possible, when port matching the downpipe flange to GTQ and HPQ turbine housings. That is a must do on applications wanting to make over 700 hp as previously mentioned.

Patrick