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spuggy spuggy is offline
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Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 2,841
Don't bother changing the spring. You can achieve the same result with a manual boost controller that costs about $50, without having to dismantle the wastegate or buy a spring. You can also change the boost level back down (e.g. on hot days) without needing to dismantle the wastegate.

An MBC can also prevent premature wastegate opening at low boost levels - e.g. before the "correct" setting - because the wastegate doesn't "see" any boost until the MBC opens and lets it through.

I was told that each .1 bar is worth about 12-20 HP, but also that there are better ways to get the same power with less stress on the motor - e.g. a better turbo and intercooler is worth about 100HP at factory boost level, but intake charge temperatures will be lower, due to better cooling (intercooler) and less heat imparted (better compressor maps).

You might want to bear in mind that US readers are used to octane ratings calculated as (MON+RON)/2, sometimes known as the "Road Octane Number". Don't confuse this with the RON used in the formula above, this is the "Research Octane Number" - which UK filling stations post on the pump.

With a 930, you should pretty much always use the highest-octane rating you can buy. Especially if you're going to increase the effective compression ratio by increasing boost. This was well illustrated by the most useful graph someone (else) posted here recently:

'77 S with '78 930 power and a few other things.
Old 05-25-2008, 03:26 PM
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