CamB

I have an engine being tuned on the dyno.

It is a 3.2 short stroke (98mm p&c) with 10.3:1 c/r, S cams, SSIs, 40mm throttle bodies and early MoTeC EFI.

It is maxing out the duty cycle at about 250hp at 6000rpm.

Other issues:

- 2.7 CIS fuel pump is at or beyond limit too
- injectors test fine - 230cc/m
- fuel filter dirty and will be replaced

Any opinions on whether the injectors will be up to the job with a better fuel pump? I have an adjustable fuel pressure regulator too.

Steve Weiner-Rennsport Systems

Hi Cam:

Make sure that fuel pump will deliver 1 litre/minute of fuel volume.

You need bigger injectors, period. If you are at 80% duty cycle, then the injector drivers are pulling max current and you should step up to bigger ones. Adjust the FPR to 3 bar when you do and finalize fueling on the map.

That should be dandy.

Roland Kunz

Hello

Rule over the thump is that you have some 10-15% reserves.

CIS Fuelpump with a Motronic ?

If you rise the pressure from the fuelsystem your injectors have to work "harder" and fail sooner.

grüsse

CamB

Thanks guys.

I am changing the pump to one which exceeds Steve's recommendation, and am right now crying into my coffee at the cost of 944 Turbo injectors.

I think 10 people just got un-invited to my wedding

Oh well. Do it once, do it right? At least I get credited for the cost of the injectors and pump I have.

CamB

Just to follow up - the engine is now mostly mapped with the new injectors and fuel pump.

It is at 235 hub horsepower at 6300rpm (on a Dynapack) and may climb a little. This is in the region of 260hp. I am pleased

Cam

Bill Verburg

Anyone happen to know the speced flow rates and pressure for the CIS and Motronic fuel pumps. I just continued to use my CIS pump when the Motronic was dropped in. Any potential issues?

Steve Weiner-Rennsport Systems

[quote]Originally posted by Bill Verburg:
<strong>Anyone happen to know the speced flow rates and pressure for the CIS and Motronic fuel pumps. I just continued to use my CIS pump when the Motronic was dropped in. Any potential issues?</strong><hr></blockquote>

Hi Bill:

Heres some stuff to look at:

CIS: 1000cc min in 30 sec at 4.7-4.9 bar

Motronic: 850cc in 30 sec at 3.8 bar

As you can see, both pumps have adequate volume but the operating pressures do vary significantly.

An adjustable FPR would do the trick and permit you to close the gap on operating pressures.

Bill Verburg

Thanks Steve, I vaguely remember some talk about a f/p regulator, I'll have to go look to see if it was installed. I thought the excess fuel would just bleed back to the fuel tank?

ken louie

hey Camb go over to the 944 turbo board. I know that you can get a set of used injector cheap. I believe that 944 turbo injectors are good for 290-320 wrhp. good luck ken

Roland Kunz

Hello

The "problem" with some CIS pumps is that they run open end ( unrestrictet ).
Under normal conditions they make over 7 bar peak pressure but if **** happens they can exceed that.
Now the CIS and the DME fuelsystem are designed to work with 5 bar full duty and have reserves for 10+bar pressure dutys.

But most people are adopting the DME to the existing CIS fuelines wich is mostly done by "straight forward simple solutions".

Thats just playing with chances to get stranded or even worser.
( Normaly you loose some fuel, time & money but if things went bad you loose much more )

The DME enginefuelrails intermediate rubber fuelines are known for geting cracks after 6-8 years duty ( And thats with "softer" german fuel ).

Injectors get shot due overpressure tending to either run open fuel quantity or sometimes they stop working. ( Both will lead to massive problems on that cylinder, if you are lucky it´s cyl 3 with the NTC or you are sensetive ).

If you shop a 928 DME fuelpump you will have more volume then the CIS.

Suiting injectors are aviable from Bosch or Pierburg. You will find bigger units in other Porsche or BMW´. Also Pierburg has a adujstable FPR ( think for BMW ) that allows you to change the base and the peak pressure level but not the curve from the throttle underpressure/to fuelpressure. The FPR is important for throttle response and enrichment during engine spool up.
If you hit the rich side the engine hangs better on the throttle but unburnt gas can start problems. If the curve from the FPR is to lean you will win nothing.

If you use a lambda sensor setup you are not risking to run to rich or to lean on normal driving.

Said that there are just to much parameters involved to perfect tune a upgraded engine and without technical background and hardware sources you are on the ineffective try & error path.

Grüsse

Bill Leonard

Steve,
Do you have a source for finding the flow rates of the injectors used on the 3.2L and '90 3.6L engines?

CamB

My first set of injectors were 3.2 ones, and the measured at 230cc at 3 bar (slightly above spec of about 214cc).

I understand that the 964 ones have the same spec (at 214cc), although this seems borderline to support their power output.

As pretty much everything I know is on this page, take my knowledge with a grain of salt.

The fuel pump I got was quoted to me as a Bosch rated at "3.2 litres per minute", and was about US$180 or so.

By the way, my final RWHP was about 245 - about 270 flywheel. Not bad at all for a "small" exhaust.

Cam

Steve Weiner-Rennsport Systems

[quote]Originally posted by Bill Leonard:
<strong>Steve,
Do you have a source for finding the flow rates of the injectors used on the 3.2L and '90 3.6L engines?</strong><hr></blockquote>

Hi Bill:

I have a FI database that is not complete as Bosch is stingy with that information but I believe the 3.2 Carrera injectors are close to 23.1 lb/hr.

I do not have any flow information on the 3.6 injectors but I think they are less than 33 lb/hr, perhaps 26 lb/hr. On the dyno, it would be easy to extrapolate that based on pulse width and lambda, based on the programing in the chip.

Bill Verburg

There is some good injector flow rate info here;

<a href="http://www.autospeed.com/A_0102/page1.html" target="_blank">Injector flow rates</a>