[OCD_Performance]

Hello,

I have a 2001 Pontiac Grand Prix with a custom turbo set up. I am unable to regulate Boost.

Some back ground.

Ported heads, FI cam, Hand made exhaust manifolds, crossover and 3" down pipe.

69MM billet turbo with an 81 AR housing.

Evolution waste gate is reasonably central to the turbo in its location. It dumps into a 3" down pipe. I dont see an issue with plumbing at all.

However, it climbs to 14 psi, holds there for a a bit, then shoots up to 18 psi after 5500 rpm.

I had no problem regulating boost with the stock exhaust manifolds and a regular 72mm turbo with an 81 housing. It was laggy however. Wastegate bolted up to stock location of where the downpipe used to be before going turbo. The new manifolds flow much better, and the input to the waste gate is only 5" away from the turbo. This is the best we could get considering space limitations. In theroy, it really should work better, but it doesnt. I get 18 PSI with the red spring instead.



I think the pressure ratio is mucked up now. (?) Not enough back pressure?



Right now there is no vac to the top of the diaphragm. Only the bottom and its working fine.

[Robert]

Originally Posted by OCD_Performance

Hello,

I have a 2001 Pontiac Grand Prix with a custom turbo set up. I am unable to regulate Boost.

Some back ground.

Ported heads, FI cam, Hand made exhaust manifolds, crossover and 3" down pipe.

69MM billet turbo with an 81 AR housing.

Evolution waste gate is reasonably central to the turbo in its location. It dumps into a 3" down pipe. I dont see an issue with plumbing at all.

However, it climbs to 14 psi, holds there for a a bit, then shoots up to 18 psi after 5500 rpm.

I had no problem regulating boost with the stock exhaust manifolds and a regular 72mm turbo with an 81 housing. It was laggy however. Wastegate bolted up to stock location of where the downpipe used to be before going turbo. The new manifolds flow much better, and the input to the waste gate is only 5" away from the turbo. This is the best we could get considering space limitations. In theroy, it really should work better, but it doesnt. I get 18 PSI with the red spring instead.



I think the pressure ratio is mucked up now. (?) Not enough back pressure?



Right now there is no vac to the top of the diaphragm. Only the bottom and its working fine.

Do you have any pictures of the setup. Only two things I can see happening. The inlet on wastegate isn't optimal or the discharge on the wastegate has too much back pressure to function properly

Sent from my MB860 using Tapatalk

[OCD_Performance]

Hey,


I'll try and get some pics tomorrow. The wastegate vents into a very large downpipe. And the input is only inches away from the turbo inlet...

I put a 69 AR housing on it tonight. It spool far faster thats for sure, but still regulates out to 18 psi..

exhaust wheel is a 68..

[OCD_Performance]

Robert,

I havent been able to get a clear pics of the WG plumbing due to all the obstructions of pipes hoses etc.

I've run a few tests.

I put the blue spring in the WG and it regulates out to 12 psi. Still too high.

I just measured back pressure right at the turbo. Im only 3 PSI over boost!

Is it possible that they sent me a 65 ex wheel and I have it in a 68 housing???

There are no exhaust leaks. Not even small.

[Robert]

Originally Posted by OCD_Performance

Robert,

I havent been able to get a clear pics of the WG plumbing due to all the obstructions of pipes hoses etc.

I've run a few tests.

I put the blue spring in the WG and it regulates out to 12 psi. Still too high.

I just measured back pressure right at the turbo. Im only 3 PSI over boost!

Is it possible that they sent me a 65 ex wheel and I have it in a 68 housing???

There are no exhaust leaks. Not even small.

The issue isn't lkely backpressure at the turbine discharge but rather back pressure at the wastegate discharge. That's why I wanted to see some pictures of your set up. I'm most concerned about how the wastegate is dumped back into the exhaust stream. In fact looking at your set up more closely that Evolution wastegate (if its just a single one) is probably too small. I typically wouldn't recommend anything smaller than an RG-45 for a turbo of that size. But before we go there I'd like to validate the wastegate discharge is working as is. This issue has happned to me before. On my 350Z the initial design of the kit had the wastegate position for input in a position that lended it to this exact issue because of the inlet and outlet pressure differentials. When the kit was revised the wastegate had to be moved to resolve the isssue. Others were able to resolve it by going to a larger gate.

[OCD_Performance]

Robert,

Thanks for the reply, muchly apprciated

I have attached a photo of the WG plumbing. Under the rubber hoses at the top of the pix is the WG. It is upside down. The input end of the WG pipe is only about 5" away from the turbo inlet flange on the cross over.

Where the WG dumps into the DP, the pressure there is only 1 psi under full boost.

Yet at 9 PSI of intake manifold pressure, I am only seeing 11-12 PSI of BP at the turbo. It was my understanding that the pressure ratio had to be 1.5 to 2.0 to get decent regulation. Meaning at 9 PSI of boost, I should have seen 13.5 to 18 PSI of BP.

And we have done other build very very close to this layout, yet we have never seen this low of BP before. Or a problem of regulation for that matter. The only thing that is really different, is the HPC69.

Im still very interested in your opinion for sure. However Im going to pull the turbo tonight and check the ex wheel. With this motor and a standard T72BB / 68 ex and a 69 AR housing, BP is close to 2:1.

Say, off topic, you would happen to have a compressor map for the HPC 69 would you? Or a reasonable faxsimilie.

Regards

[OCD_Performance]

Originally Posted by Robert

The issue isn't lkely backpressure at the turbine discharge but rather back pressure at the wastegate discharge. That's why I wanted to see some pictures of your set up. I'm most concerned about how the wastegate is dumped back into the exhaust stream. In fact looking at your set up more closely that Evolution wastegate (if its just a single one) is probably too small. I typically wouldn't recommend anything smaller than an RG-45 for a turbo of that size. But before we go there I'd like to validate the wastegate discharge is working as is. This issue has happned to me before. On my 350Z the initial design of the kit had the wastegate position for input in a position that lended it to this exact issue because of the inlet and outlet pressure differentials. When the kit was revised the wastegate had to be moved to resolve the isssue. Others were able to resolve it by going to a larger gate.

The pressure value of 1-2 PSI over boost is not turbo discharge pressure. It is pressure Pre Turbo. Measure right at the square flange just before entering the turbine wheel.

Meaning its close to running 1:1.

[Robert]

Originally Posted by OCD_Performance

The pressure value of 1-2 PSI over boost is not turbo discharge pressure. It is pressure Pre Turbo. Measure right at the square flange just before entering the turbine wheel.

Meaning its close to running 1:1.

I guess my base point is the exhaust gas is going to go path of least resistance. If path of least resistance is through the turbine wheel up until the elevated pressure ratio you are seeing you are going to over boost. The gate needs to be path of least resistance in order for it to work properly. One thing I would test (if its possible) is to dump the wastegate to atmosphere. Is there any way in this set up (I can't tell by just that one pic) to dump the wastegate discharge straight down out the bottom of the car and see if it still overboosts?

[OCD_Performance]

An open air test of the WG yeilded no improvements.

However, I reinstalled my T72 with a 68 ex wheel and a 69 A/R and regulation got better, but not perfect.

My pressure ratio with the HPC 69 was 1.25:1 and the T72 produced 1.35:1.

So my course of action is to install a 40mm WG. I was surprised to learn the Evolution unit was only 32mm.

And a change of turbo.

So do I go with a HPC 69 and a 62 ex wheel or an HPC 64 and a 65 mm ex wheel....

Thats the question. Suggestions?

[Robert]

Originally Posted by OCD_Performance

An open air test of the WG yeilded no improvements.

However, I reinstalled my T72 with a 68 ex wheel and a 69 A/R and regulation got better, but not perfect.

My pressure ratio with the HPC 69 was 1.25:1 and the T72 produced 1.35:1.

So my course of action is to install a 40mm WG. I was surprised to learn the Evolution unit was only 32mm.

And a change of turbo.

So do I go with a HPC 69 and a 62 ex wheel or an HPC 64 and a 65 mm ex wheel....

Thats the question. Suggestions?

That's kind of what I was thinking. The Evolution is a 35mm gate but that's a little too small for the power range you are looking for. The RG-45 (45mm gate) is more in line with what you should be running for the amount of power you are making. Personally I wouldn't switch out the turbo until you test the new gate.