Getting more HP from an 87 Porsche Carrera

[stlrj]

Originally Posted by stlrj

I' still on the stock chip but went to the GM multec 5 hole injectors on my 87 Carrera and also have a beast of an engine. What a joy just driving around town!


Cheers,

Joe
87 Carrera

It runs so cool, the front oil cooler never gets close to being used. I'd say that's a good thing for the engine.


Joe

[KTL]

What's the scoop on the GM Multec injectors? I thought some of those were troublesome. I believe the early Multecs shorted out and caused all sorts of problems? I see the C4 Corvette crowd craps all over the Multecs like crazy

[scarceller]

You really should not just drop in any injector, especially a hi-impedance (hi-ohm) injectors. This is because the injector on/off times are considerably longer than the stock (lo-imp) injectors. The chip program has injector on/off time compensation baked into the program and not setting this correctly will cause AFR mixture to vary considerably based on engine load.

Not saying these injectors won't work, just pointing out that you may get them to work correctly at idle a and part throttle loads (low-load) but they will likely cause lean conditions at hi-loads like WOT.

Originally Posted by KTL

What's the scoop on the GM Multec injectors? I thought some of those were troublesome. I believe the early Multecs shorted out and caused all sorts of problems? I see the C4 Corvette crowd craps all over the Multecs like crazy

[stlrj]

Originally Posted by scarceller

You really should not just drop in any injector, especially a hi-impedance (hi-ohm) injectors. This is because the injector on/off times are considerably longer than the stock (lo-imp) injectors. The chip program has injector on/off time compensation baked into the program and not setting this correctly will cause AFR mixture to vary considerably based on engine load.

Not saying these injectors won't work, just pointing out that you may get them to work correctly at idle a and part throttle loads (low-load) but they will likely cause lean conditions at hi-loads like WOT.

Good advice Sal, but after 10 years of dropping dozens of hi-impedance injectors in my Carrera, I have yet to run into any problems but good advice for any non factory modification to keep in mind.

Also, I might add, that I rarely drive my Carrera at wot since these multi hole injectors give me so much low end torque I rarely feel the need to go above 3500 rpm. Even at wot, as rare as that may be, I have not noticed any problems either.

Interesting to note that the biggest issue I had with high impedance injectors was that they tended to run too rich at high rpms and the major challenge I had was to adjust the air flow meter to lean it out. So lean at wot was never a problem.


Cheers,

Joe

[Tippy]

Originally Posted by stlrj

Good advice Sal, but after 10 years of dropping dozens of hi-impedance injectors in my Carrera, I have yet to run into any problems but good advice for any non factory modification to keep in mind.


Cheers,

Joe

That's interesting you've had no problems.

[scarceller]

If you want to really understand the importance of injector modeling I suggest this book:
https://www.amazon.com/Engine-Management-Advanced-Greg-Banish/dp/1932494421
It's a wealth of information on EFI in easy to understand style of writing.

[scarceller]

If you rarely go WOT and you set AFR for idle a PT you may be OK but you still have no factual data about AFR at WOT! Get the book and read, you'll think twice about just dropping injectors into a given setup!

Greg Banish is a wealth of information on EFI tuning and his books are the very best I've seen! He was a mentor while I designed my MAF.

Originally Posted by Tippy

That's interesting you've had no problems.

[stlrj]

Originally Posted by Tippy

That's interesting you've had no problems.

Not true, not the type of problems Sal describes. I had lots of problems, but most of wich were due to running too rich at mid and wot. Had to resort to much lower flow rate new style injectors for optimum performance.


Joe

[RarlyL8]

Hey Sal I've got my active exhaust system for Carrera ready if you'd like to play with it and make a chip. We've used your injector/chip tune on a Carrera in our shop and it rocks! Took a little time to set it up correctly but well worth the effort. Feels like we added 50hp to an otherwise stock engine.

[Tippy]

Sal, does the ECU still manage peak and hold when trying to trigger a high-Z injector?

[stlrj]

Originally Posted by scarceller

Not saying these injectors won't work, just pointing out that you may get them to work correctly at idle a and part throttle loads (low-load) but they will likely cause lean conditions at hi-loads like WOT.

Sal, you got me wondering why I found the opposite results at hi-loads with the high impedance injectors. Perhaps the longer response times of these injectors compared to low impedance injectors causes them to stay open longer (and deliver more fuel) with the same pulse width. Seems to be the most logical explanation that makes sense.

Cheers,

Joe

[Raceboy]

Most injectors nowadays are high impedance and the open-close times have become fast. You rarely see a new late technology low impedance injector these days..

[Canada Kev]

Originally Posted by RarlyL8

Hey Sal I've got my active exhaust system for Carrera ready if you'd like to play with it and make a chip.

Brian, now my curiosity is piqued. What's this active exhaust?

[douglas bray]

Sal, ask anyone that has been anywhere near my car how the 715's perform And they will scream OMFG!!! Flawless at idle, power down low, and screaming all the way to 7,000+. Bisimoto was impressed with the Multi-board before the 715's went in......now it beyond. But ya.... interesting indeed.

[J-Mac]

Originally Posted by RarlyL8

Hey Sal I've got my active exhaust system for Carrera ready if you'd like to play with it and make a chip. We've used your injector/chip tune on a Carrera in our shop and it rocks! Took a little time to set it up correctly but well worth the effort. Feels like we added 50hp to an otherwise stock engine.

More information required on this. ^^^^^^^^^^^^^^^ Please.