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Discussion Starter #1
Hi there greetings from the UK.

Im having some issues with my Mkiv here in the UK and was wondering if anyone could advise me about the correct wastegate and manifold sizing.

I have a built 3.0 with 10:1 Compression
Precision 7685 Turbo
GSC2 Cams with supertech springs and a big valve head
Induction performance inlet manifold
Whifbitz exhaust manifold ( http://www.garagewhifbitz.co.uk/garage-whifbitz-687.html )
2 x Brand new genuine Turbosmart 40mm Comp gates on 14psi springs

When we are tuning the car on the dyno on pump fuel we cannot get the boost under control, at 3500rpm it has 0.7 bar, at 4500rpm it has 1.7 bar and at 5500rpm its reaching over 2.5 bar and the graphs are going up in 45 degree angles with no sign of tailing off.

We have tested all the lines and boost solonoid and done every test possable to see if it were a plumbing issue but everything is done correctly and working as it should be.

We have ran 30psi of compressed air through the wastegates to keep them open completly and the car is still overboosting.

I contacted Whifbitz in the UK who designed the exhaust manifold and they say that manifold with 40mm gates should flow that power no problem.

I phoned Sean at Titan who told me that set up should be ok for that turbo.

I contacted Induction Performance today who also said the same.

But every test we have conducted is indicating the wastegates are the problem.

Has anyone experianced a similar issue or can anyone advise what gate size i require for my car to flow correctly ?

The car will be getting used on the street and strip with both 99ron pump fuel and E85, Ideally I would love to make 1200 Horsepower.

Thanks for any input.

Biggie.:)
 

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Are they open dump or routed to the DP? If they're routed to the DP then there could be too much back pressure causing them to not be able to get the exhaust gas out.
 

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Have you removed the wastegates and tested them externally? You could be binding if the springs aren't set up correctly. I bound my greddy spring only half way through the adjustment. I know your gates are different but still best to test them outside the car so you can see the valves movong. Also are you certain your pressure lines are on the correct port on the wastegate? (Have to ask)
 

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Discussion Starter #5
Have you removed the wastegates and tested them externally? You could be binding if the springs aren't set up correctly. I bound my greddy spring only half way through the adjustment. I know your gates are different but still best to test them outside the car so you can see the valves movong. Also are you certain your pressure lines are on the correct port on the wastegate? (Have to ask)

We are planning to do this today if possible.
 
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