964 injector upgrade?

[Moriartyhlms]

Hello. I'm wrapping up the rebuild of my 964 engine and am wondering if it's worth upgrading my fuel injectors. I've read elsewhere on this forum that they're a limiting factor in the performance of these engines. Does anybody have any experience or recommendations on this?

If it makes any difference; my engine is a 3.8 with a Varioram intake, 993 OBD1 DME, Webcam Suspersport cams, and a Billyboat Exhaust.

Thanks,
Sam

[michael lang]

Why not just have the ones you have sent out to be serviced and rebuilt? Makes them like brand new.

[turbobrat930]

I would think, unless you are putting on a supercharger or turbo, then you really wont need a bigger injector. Stock injectors have enough head room to cope with minor perfromance mods, before they run out. What duty cycle are you seeing at WOT?

Mike is right, send them out to get serviced and rebuilt...

[Raceboy]

Stock injectors are in fact at their upper limit already with stock hp and they are too small for anything over 270-275 hp. But you cannot upgrading the injectors without either reprogramming stock ECU or going some sort of standalone engine management system.

[Bill Verburg]

Part of the problem w/ the '84-98 Motronic cars is that w/ 10% Ethanol the injector needs to be open longer than w/ pure gas(which is what they were designed to use), the closer to the edge of the duty cycle the poorer the results. Especially so if the injector duty cycle is at or near 100%

You need a new chip anyway, tuning w/ better flowing injectors should add power at minimal cost

[Moriartyhlms]

Thanks all for the replies. Definitely agree having injectors serviced by Witchhunter is a great idea. That said, from what I've read from 9M and others, I'm expecting no more than ~310HP with my current set-up. That being injector-limited (again, just based on what I've read here and Rennlist). I'm running a Steve Wong-chipped 993 RoW DME. And (again, based on forum 'research'), I've seen optimistic reports of being able to achieve 360HP with that DME and the right set of mods. So, anecdotally, the injectors are my missing link. Thoughts?

(And please feel free to dump on my conjectured HP figures)

[Steve@Rennsport]

Originally Posted by Moriartyhlms

Thanks all for the replies. Definitely agree having injectors serviced by Witchhunter is a great idea. That said, from what I've read from 9M and others, I'm expecting no more than ~310HP with my current set-up. That being injector-limited (again, just based on what I've read here and Rennlist). I'm running a Steve Wong-chipped 993 RoW DME. And (again, based on forum 'research'), I've seen optimistic reports of being able to achieve 360HP with that DME and the right set of mods. So, anecdotally, the injectors are my missing link. Thoughts?

(And please feel free to dump on my conjectured HP figures)

Hi,

I can tell you without any doubt that 360 BHP isn't possible without a completely different intake system, exhaust system, higher-compression pistons, some headwork, and camshafts.

310-325 BHP is quite possible in your case with a different exhaust and custom software.

[Moriartyhlms]

Thank you Steve, I completely agree with you. To return to the original question though;

- Does anybody recommend a specific injector as an upgrade to normally aspirated M64 (964/993) eninges?

And, on a related note, does anybody have an idea what sort of power figures a chipped 993 Motronic DME/ECU can support (assuming optimal supporting mods to the rest of engine)?

Thanks again
-Sam

[preston_brown]

On my 3.9L race motor I just subbed in these injectors:

Bosch 0 280 155 831
Flow: 300cc/min @3 bar



That is about 30% more than the stock 993 injectors, which are a little bit more than the 964 injectors.

I believe they are originally a Volvo app. They are drop-in replacements, and feature a more modern 4-hole spray design. Gives a good deal more headroom.

Of course, I have a custom ECU and the tuning required to deal with these larger injectors. And I'm running 5 bar on the fuel rail...

[Steve@Rennsport]

Originally Posted by Moriartyhlms

Thank you Steve, I completely agree with you. To return to the original question though;

- Does anybody recommend a specific injector as an upgrade to normally aspirated M64 (964/993) eninges?

And, on a related note, does anybody have an idea what sort of power figures a chipped 993 Motronic DME/ECU can support (assuming optimal supporting mods to the rest of engine)?

Thanks again
-Sam

Sam,

We use the stock injectors on 964 & 993 engines with the Motronic ECU's up to 325 BHP. If you substitute another injector, you may need custom software to prevent overfueling.

The only time we use different injectors is with Motec-equipped engines, however that's a totally different subject.

[Moriartyhlms]

Thanks to all for the input. Consensus seems to be that 964 injectors will be at their limit at about 310hp, but that my engine spec will be hitting other limits at that point anyways. However, also sounds like that will correspond with 100% duty cycle on stock injectors. Vendor suggested these injectors to me today: Bosch 0280155767, 375 cc/min at 3 bar, or 36 lbs/hr at 43.5 psi. Going to have live tune once engine is broken in, will make decision before then. Taking engine out again tomorrow...