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Garage Queen Club
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2,818 Posts
Discussion Starter #1
Here is my scenario, although NOT a supra, almost close.

46mm Tial on #1 runner (4g63 engine), 3" o2 housing, 3" downpipe, 3.5" catback. The system flows too good. I get boost creep even with this wastegate. from 6krpm + it shoots from 14psi to 22!

How do you supra guys control boost with a single and 4" exhaust? Is there something I'm missing here? I know of 1 T61 running 8psi boost with no creep, and he runs a titanium 4" exhaust.
 

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Garage Queen Club
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2,818 Posts
Discussion Starter #4
Ok.

I removed the WG, with a bike pump, I pumped air to the bottom section. The valve started opening at 14psi. At 20psi, the valve was fully opened and wouldnot open any more. It would 'leak' out the air in 2 second. I kept trying and the WG seemed to be moving out?. What would be indications of a bad diaphram?
 

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Super Moderator!!ON PATROL ALL OVER!!
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check your pm !
 

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Super Moderator, Piss me off. I dare you.
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12,619 Posts
I will answer this one!

I was the sales manager for Hahn Racecraft...;)

The main reason why DSM's have boost creep issues is the size and style of turbo being used. Generally, most stock and modded DSM's use a small 6cm, 7cm, or sometimes an 8cm exhaust housing. Most aftermarket "big" 16G's and "Frank" turbos use a larger compressor wheel and/or housing, and bolt it to the same small exhaust housing. DUMB!! You have just created a HUGE boost creep scenario! Regardless of how much you port the wastegate housing or clip the turbine wheel, the wastegate port can't handle the amount of air being produced by the compressor. The exhaust has nowhere to go but back through the exhaust turbine, and skyrocket your boost.

Now, in your case, you have an external wastegate mounted on the first runner. Not a bad idea, but think about it. Due to the location of the wastegate, the other 3 cylinder runners are still spooling the turbo. There may be enough exhaust getting past the wastegate to cause a boost creep problem.

The main reason a large single turbo Supra does not have a boost creep issue is due to the large exhaust housing. The fact that the wastegate is mounted so ALL cylinders can be vented properly is another reason.

My advice: If I were you, I would sell your manifold/wastegate/turbo setup. Seriously! You can get some good money for those items. Not a cheap plug, but I really, HIGHLY recommend an HRC setup like this:

HRC Super 16G w/10cm (yes) exhaust housing
HRC cast manifold (Turbonetics)
HRC 3" downpipe

You will not have ANY boost creep problems, no porting is required, no external wastegate is needed, and you will make BIG power. The turbo lags as much as a ported and clipped small 16G! The secret is the exhaust housing. The HRC/Ayala Turbo Neon has run 9.80's with a Super 20G turbo, 27psi, no boost creep, and an INTERNAL wastegate...
 
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