Ben's 914 TURBO Official World Premier, 'cuz it didn't blowd up. Options

[airsix]

Ok, so it isn't as cool as Chapman's 914-6 Turbo 3.0, but it's a turbo 914 all the same. Ladys and Gentlemen, at about 10:00 PST I got boost and there was much rejoicing. I took the car out, filled it with premium, tuned it with the laptop a little to make sure it got plenty of fuel under boost, and the mission was a sucess. Boost starts to come on at ~2,700rpm and is going full-steam by 3,500rpm.

I stand (ok, sit) here before you my brothers to declare that yes indeed, you can turbo a 914. (IMG:style_emoticons/default/clap56.gif)

Details:

Engine: '73 1.7, stock internals
EFI ECU: Perfect Power MIC3 (Cost ~$500 to get on the car and running 3 years ago)
Misc EFI stuff: Subaru 1.8T injectors, Holly throttle body off a 3.0 Chrysler, BMW 5xx fuel pump, foam motorcycle aircleaner (temporary)
Turbo: IHI off 1.8L Subaru (including wastegate)
Misc Turbo stuff: Bosch blow-off valve (for a Saab I think). Cheap. Plastic. Works great.
Total cost to add turbo: $175 (EFI was already on the car. Use Megasquirt+turbo and you can do this for <$400 easy)

I tried to modify my fuel pressure regulator with a boost-reference port like the in the dune-buggy.com article but I broke off a wire guage drill bit about 1.5" deep into the bolt. Dang. Only had about a quarter-inch to go too. So I just bolted it back on the car and set the fuel pressure at the 30psi I have the ECU turned for. I tried to crank up the injector pulse width under boost to compensate, but they hit 100% duty cycle at 5,000rpm because at that point they only have 20psi effective pressure (because there's 10lb of boost by that point). So I'm keeping it under 5k rpm until I get a rising-rate pressure regulator. The wideband O2 says mixtures are just fine below that point. I estimate I'm getting 110hp (That's not a WAG. I really did the math) which doesn't sound like much but is sure better than the 80hp I had before. I would still like to add an intercooler which could put it in the neighborhood of 130hp without getting too boost-happy. Even as it is now I would say it's 100% more fun to drive. I'm really happy about it. I'll get the pressure regulator issue squared away so I can run it up to 6k and I think it'll keep me happy for quite a while.

Rick said "This thread is worthless without pictures" so here's the best I could do. If you missed the earlier thread I'll throw in one of the earlier pics too. I tried to make a video but all you hear is wind noice and the blow-off valve between shifts.

[lapuwali]

It's not really the compression ratio that's the problem, it's maximum cylinder pressure, which, all else equal, is higher with a higher CR. Add boost, and you're raising the peak pressure, since the starting pressure is higher. Ultimately, the limit is detonation/spark knock. Lowering the CR lowers the peak pressure on-boost to keep the engine below the detonation limit. The disadvantage to that approach is you also kill power and efficiency off-boost, which is where a street engine spends most of its time, anyway.

Older OEM turbo engines often had low CR as a conservative safety measure. It allowed an idiot owner to put regular gas in the car and not kill the engine completely, just cause enough knock to remind them not to do that again. It also allowed the car to be run at very high ambient temps with the AC on while driving up a steep grade, the worst possible combination. With modern engine controls, spark timing can be retarded and boost regulated more effectively to keep cylinder pressures down while still having a high CR. This kind of thing was hard to do in the 80s, and pretty much impossible in the 70s, so early turbo cars just ran low CR. With a knock sensor, you can control knock pretty well and keep CR and boost relatively high, and still allow an idiot owner to put in a tank of regular on a 100 degree day while getting ready to drive west out of Denver and keep the engine safe by just disabling most of the boost. It's the advent of these electronics that are allowing turbos to reappear in OEM apps after they nearly vanished for awhile. Modern systems are now so good that turbo lag is nearly gone completely, and it's often hard to tell the turbo is there at all.

Ben did absolutely the right thing in getting a programmable engine management system on the car first, and getting used to working with it, before attempting a turbo. He can get fuel and spark set perfectly and responsive to boost w/o too much worry of melting things.