Fuel starvation - Need advice on injector sizing...

[roadsleeper]

Help!

I'm looking at aftermarket fuel injectors because my engine isn't getting enough fuel towards the higher end of the rpm range. It is a 3.8l conversion and the Motec is set at an artificial rev limit of 6,000 rpm at the moment it because it runs lean anything above that (theoretical red line should be 7,200 rpm).

Need answers to the following:

1. Which aftermarket fuel injectors should I get? I am looking at RC Injectors at the moment

2. How do I calculate the size/flow rate of the injector needed?

3. Is there a standard sizing for fuel injectors (i.e., bulbs come in H4, H7, etc. sizes)

Thanks in advance!

[roadsleeper]

Bump...

[Tom W]

Try talking to Rich at Jerry Woods/Smart Racing 408-369-9607

[roadsleeper]

Thanks Tom, will shoot him an e-mail.

[Turbo Werks]

RC Engineering's web site has a simple inj. sizing formula.
do you have an adjustable fuel pressure regulator.
your press. should be about 55 psi.

[roadsleeper]

Originally Posted by Turbo Werks

RC Engineering's web site has a simple inj. sizing formula.
do you have an adjustable fuel pressure regulator.
your press. should be about 55 psi.

Thanks, I tried the sizing formula and came up with an injector output value of 388.28 cc / min. What I don't get though is that in order to get the output, you have to effectively guess your target hp, is that right?

Yes, I have an adjustable SARD Race fuel pressure regulator, need to check pressure.

I am not sure whether I need to get saturated or peak and hold type injectors though... I have a Motec so I assume I can get either?

[Cheyne76]

You can use low impedance peak and hold injectors with motec. Motec is able to maintain a great idle with even the largest of injectors. Remember that most if not all injectors flow rates are measured at 3 bar. anything over 85% duty would be considered too much. I run 780 cc injectors from Kinsler.

[Turbo Werks]

roadsleeper I don't know your eng. specs but my guess is that it should make between 350-375 hp so a 42# per/ hr should do. check your fuel press. very very important.

[roadsleeper]

Cheyne76 - Thanks for the input. Are you running a Turbo?

Turbo Werks - Yes, that's right, we're making 354.3 hp at the crank. According to their catalog, RC Engineering doesn't have a peak & hold injector size between 370 cc/min and 750 cc/min. Assuming my FPR is running at 55 psi, can I run a 750 cc/min injector or is that too big?

Also, does anyone know what the size of a stock injector from a 964 3.6l engine is?

EDIT: The FPR is running at 72.5 psi.

[Turbo Werks]

Hi roadsleeper I think the stock 964 inj. is about 22 lbs per/hr with the original f.p.reg. you can use the 944t inj. bosch # 0280-150-803 this are rated at 38 lbs with 43.5 psi rail pressure. so at 55psi or a 3.8 bar reg. this are good for 395 hp @ 80% duty cycle, they are low impidence . cool car you are building post more pictures thanks.

[roadsleeper]

Thanks Turbo Werks, very helpful!

I'm still comparing prices between all the injectors out there, but it's good to know that the 944T injectors are an option.

Here is why I need bigger injectors:

[Cheyne76]

Still a distributor? i guess not an m600. I have seen this build, very nice. i also have a c4

[roadsleeper]

Originally Posted by Cheyne76

Still a distributor? i guess not an m600. I have seen this build, very nice. i also have a c4

Yes and no.

We are running a M600, but it's still got a distributor for the sake of budget, mechanical simplicity and weight savings.

Also, PMS still fitted distributors to their period race cars, so we went with the "what's good enough for PMS, is good enough for us" mentality.

Perhaps when budget allows and the urge to splurge strikes me, I'll look into making the spark more efficient by having individual igniters for each plug. My engine guru started delving into this option but my wallet made a run for it and I couldn't stick around to hear him out...

[Cheyne76]

no doubt, Your build is awesome! i would go with at least a 550 cc injector.

[Raceboy]

Since youi have standalone, I'd suggest Siemens Deka 630cc injectors. They are bigger than you need at your current power level, but MUCH better than ancient ones that RC Engineering selles (which are actually Delphis). Difference is in fuel atomization and low pw linearity and faster opening/closing times.
Having converted some 993's and 964's to standalone EFI (one of them was TPC supercharged 993), I'd never use anything as old as Bosch EV1 style if you have newer available.

These Siemens ones look like this:


And are fully compatible with your new ones.

Set you fuel pressure to 3 bars (43.5 psi) with new injectors. Remember, on 6cyl engine, max hp supported by injectors equals roughly the injector capacity at 3bars (like on 630cc injector amx hp is around 600 hp).

And as for distributor, I'd get rid of it. You can get two Bosch 6cyl coil-packs for around 300usd total and have direct ignition (they require total of 6 IGBT inputs for twin-plug engine, if M600 doesn't have those, you'll need igniters also).

On 964 those coil-packs look like this:

[gring]

I'd run a Bosch EV6 36lb/hr injector at 5 bar to take advantage of the better atomization. For what you are doing, the distributor works great and there is no advantage of running a waste spark system as long as you are firing the distributor via CDI ignition.