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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
I am not an expert but there are couple of ways to go so identifying your goals up front can save you money.

Irregardless, the best opertunity is fixing the restriction after the turbo. Get the lowest restriction muffler you can handle. This will make for faster turbo spool, increase effecency, and deliver more HP. My favorit is a bit SS glass pack that exits on the left side.

I belive the stock heat exchangers are a solid set up and do not have the potental to crack that the after market shorties may have.

I also suspect most the of the reduction in lag attribuited to the high dollar systems is in the muffler not the short tube length.

The added power attribuited from the shortie systems I suspect is really from the ineffecent wast gate circut that tricks the WG into delivering more boost.

Next is the Turbo. This is where you should decide what your goals are.

A larger turbo like a K27HF has a biger compressor wheel and can make monster HP, will run a bit more effecent at higher rpms, and will have a softer and latter boost onset.

A K27-7200 from the factory 91-94 C2 Turbos is great turbo up to around 375HP and it but comes in with less lag and much harder boost onset. More fun in the street I would say but no bragging rights.

A better intercooler is expensive but is free HP. I also alows you to run more boost for even more HP. Just adding an intercooler can be good for 20-30hp with out adding any boost.

With the lower restriction muffler, K27-7200, a .9 bar spring and a better IC you can have a very nice running car that works will with the stock cam, ports and compression.

Note that changing cams helps the motor breath better as dose larger intake ports. However, this is not totally reqired for big HP.

The 930 has small ports to work with the CIS fuel injection. CIS squirts fuel at all time and the fuel just sits in the port untill the intake valve opens and the air starts rushing by. Porsche had to make a small port in increas the volicity of the air flow to get the air and fuel mix properly for better emmissions.

As to the cam. The 930 cam is a low rpm torque cam. Going to an SC or C2 cam can help breathing but actually lowers the effective compression ratio for a small reduction in pre boost torque. Many have make a lot of HP with small ports and stock cams.

Playing with the WUR and ignition has some potental.

The WUR from a 76/7 turbo reduced Control Pressure with a loss of manifold vac as soon as the throtle was cracked. The 78-94 WUR required .5 bar of boost before it reduces CP. The differance can be felt in throtle response as lowering the CP sooner alows the metering plate to move easyer and the car to come up on boost quicker.

Your WUR can be modified to act this way.

On the ignition side a programable ignition would be the best. Or on can to a MSD system that has the built in boost retard function and have the distribuitor modified and recurved to work with it. The side benifit to an MSD system is 930 ofter will be run a bit rich and with the low compression it is more difficult to lite the mix. The muliple spark of the MSD can help with this.

If you need to go through your motor, making it biger seems to have a double pay back with better lower end an more HP.

May have found that gears can transform a 930 as the wide gear spacing can take you out of you power band quite a bit of the time.

Good luck.
Old 07-31-2008, 10:41 AM
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