View Single Post
911st 911st is offline
Registered User
Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
I am jealous, white in my favorite Porsche color and the 930 is my fav Porsche.

Are you willing to change out the Inter-cooler? You can still get a good power without doing so but that is about the best way to make Hp right after a muffler change.

Think increasses in effecency, not how do I carry 1 bar to red line. If a motor flows well, it will swallow as much air at .8 bar as another less effecent motor at 1 bar.

My opinion and others will disagree: K27-7200 turbo, .9 bar boost spring, sport muffler, inter-cooler (C2Turbo, Koklen IC, Andial, or? in order of choice.), 3% CO at idle, ports and SC cams when the motor comes out for something else.

I will get push back for this but I would avoid the HF or K29. They do "start to" come in sooner (bigger compressor pushes more air for earlier boost onset) and make more HP up top. However, They they build to full boost slower and make the car more like a big V8. The are also prone to over boost at upper rpms because of the small hot side and they increase pressure in the exhaust manfold lowering VE a little. Further, they need a fueling strategy to support the last 1000 or so rpm's of power. The 7200 comes in much harder, starts just a little later, and works very well up to .9bar. Full boost by 3000 rpm is still very possible. Then get it on a dyno to dial in the AFR and ignition with someone that knows these cars.

There is a lot of extra in the detials.

Note that your AFR will change from hot to cold session so setting it up during the hot time of the year is best. It will run a little leaner during the cold weather and that is ok because of the cooler charge temps.

I am assuming a well maintained car. Valves adjusted, injectors cleaned and checked. Injector / head flow balance checked, good plugs, wires, clean air filter...

An AFR gage on the dash is good insurance on a turbo but not required. The stock air cleaner is a good unit. No reasion to change it except it can make it easyer to change the air filter. Some add holes to the pre filter secton or cut it off. May not add much more than sound though. When clutch time comes, somthing you can slip a little with out burning up is nice. A lower ring & pinion is well worth the effort and price. Use the money saved on fancy fueling stuff and a custom turbo here.

A couple of exoteric tricks.

Replace the black plastic Bosche BOV that comes with most aftermarket IC's with an adjustable piston style BOV. Reverse its normal direction of install so the boost wants to push it open. Vacunm and air flow in the intercooler section will keep it open during non acceleration so the turbo will be spinning faster and in reserve. This will get you less exaust back pressure on the freeway during cruse and quicker boost with acceleration when you need it. (I used to get instant .5 bar boost from freeway curse). You may have to play with the spring tension so it closes as soon as you blip the throtle. Just put put somthing on the BOV and listen to it as you blip the throtle and you should hear is close. Under acceleration boost pressure building up against the much larger surface area of the piston in the upper chamber will ensure the valve slams shut with boost and stays fully closed under boost.

Find someone that can modify the WUR to be boost sensing. This may be hard. the 76/77 3.o Turbo WUR worked this way. This will not just give you boost enrichmen but will gain you acceleration enrichment and alow you to run a little leaner at idle and curse. You will get added fuel instantly with acceleration instead at .5 bar boost and it will also help the metering plate to open faster. If done righ this all helps reduce lag.

The comb of low back pressure muffler, fast spool K27-7200, vac open / accel closed BOV, and a vac sensing WUR makes a big, big differance in lag and how fast bost comes on. You can also play with cam timming and ignition some for further improvement. All this addes up to a huge amount of amost instant mid range power with this combonation and no loss of boost between shifts. Please note a vac sensing mod is not a good fit with a K29 or HF that needs more fuel up top with out other accomidations.

This is a little different than the direction that most are curently taking but trust me, it works very very well once dialed in.
Old 03-16-2009, 05:45 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)