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post #1 of 6 (permalink) Old 01-27-04, 12:57 AM Thread Starter
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Varying boost on turbo'd 4L

After recently rebuilding my motor, i have been driving my car around for a couple of weeks without a boost gauge on, i had noticed that i had losed a little bit of power in first gear, but second and third felt the same.

Today i stuck the boost gauge on a went for a drive, i have 9psi in first gear, and 13psi in second, now previously i was running 13psi all gears and not changing.

Anybody got any idea why?

My thought was that i did have the turbo off and had changed the angle of the outlet slightly and also therefore varying the wastegate position, i have a rather bad designed dump pipe, whereby the wastegate doesn't flow properly into the pipe, and i think that when i have altered the position i have lowered the wastegate pressure, and the dump pipe is causing this inconsistent boost pressure, could this be it?

The turbo is a IHI RHB6 VJ23 with internal wastegate, it is factory high flowed and flows 450hp.

I pulled the car right out in the revs to 6500RPM, and it doesn't back off from 13psi, and the minute i nail it in second it has 13psi.

Thanks

Matt
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post #2 of 6 (permalink) Old 01-27-04, 02:17 AM
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Re: Varying boost on turbo'd 4L

Cant help ya with the problem, but I'd be ok with a little less boost in first gear, makes takes off a little easier - you are less likely to sit there in a plume of tyre smoke!

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post #3 of 6 (permalink) Old 01-27-04, 03:05 AM
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Re: Varying boost on turbo'd 4L

Ahh generally the way turbo's work.The more load you put on them the more boost they make[this doesn't happen with superchargers].So bassically in 1st its like its free reving almost.. Btw does it make any boost just reving it in park? It shouldn't...

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post #4 of 6 (permalink) Old 01-28-04, 12:03 AM Thread Starter
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Re: Varying boost on turbo'd 4L

If i was to sit there in park, and from idle give it one almighty rev to 6500rpm, the boost gauge will go to about 1psi just. would a boost controller put more control on this? The haltech ig5 i have on the car has a boost controller function which i was thinking of getting happening on the car in order to lift boost in first gear.

My problem is that will second gear the car hammers, in first it feels to me rather slow. And previously it wasnt like this.

So changing my wastegate setup wont fix it, i have been playing around with the wastegate a bit and even tried winding it all the way in so that it opens really early, and now i have a slowly climbing boost in first gear, ie: 2000rpm- 4psi, 3000- 6psi - 4000rpm - 8psi - and finally finishing off at 10psi after 5000rpm, in first, yet second still gets up at around 12psi from word go.

i was also thinking that maybe i should look at moving the wastegate pressure pipe to the intake manifold? Would this make much difference, i thought it might be able to give better boost control there.
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post #5 of 6 (permalink) Old 01-28-04, 01:00 AM
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Re: Varying boost on turbo'd 4L

a mate has this happening to his vs 5litre with a powerdyne s/charger, id also say its because its in first gear and not much load is on it. maybe test it towing a trailer lol.

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post #6 of 6 (permalink) Old 01-28-04, 03:23 AM Thread Starter
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Re: Varying boost on turbo'd 4L

I worked it out, adjusted wastegate to 10psi, richened up the mixtures a tad, problem fixed.

now i have 10 psi all gears, right through the rev range, it was just because it was running a tad lean.

I really need to get it dyno'd but have been putting it off until intercooler is on and all finished.

Thanks for your help
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