S vs. RS MFI inj. pump in 2.7RS engine - Page 3

69911e · 06-11-2004, 05:14 AM

This is all theory because I have no knowledge or much experience with adjusting these pumps.
Henry's statement that the govenor stops doing anything above 4K got me thinking. Any pump could be adjusted to work as good as any other pump at full throttle and above 4K, and the AFR canl be optimized at 2 RPM points above 4K. The pump will run rich once the torque curve drops off below the second optimized AFR point.
The E and S torque curves are very similar below 4K, therfore at full throttle they should be similar at all RPMs. The problem will probably be at part throttle (including idle), because I imagine the engines are very different in this respect at all RPMs.

(This graph is from Mike Piera's page)

AndreasLanghoff · 06-11-2004, 07:00 AM

My pump specialist confirms that the 2.4S and 2.7RS do have completely different delivery levels and are not similar.
On the other hand the old 2.0S and the 2.7RS pumps are similar in calibration characteristics he remembers.
By the way, for racing purposes it is always easy to have the pump deliver enough fuel for whatever hp needed just by adjusting the main rack.

Andreas

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally posted by Jim Richards
I'm planning a 2.7RS upgrade on my E motor in a few months and I have questions about the injection pump. Is it necssary to use the RS space cam in the MFI injection pump or can an S-spec pump do the job? What's the downside of using an S-spec pump? Thanks for your help.

Does anyone remember the original posts?
Jim asked will the 2.4 "S" pump work.
I'm saying that it will work. I've done it many times and it works well.
Not theory, not conjecture.
Our experience is that you will have a hard time seeing the difference on a dyno. We tried and it's hard to see the difference. You see as much difference between like pumps ( two RS pumps) as you will see between properly tuned 2.4 "S" and a 2.7RS pumps.

BTW If you want to spend the money we have 2.7 space cams and I will be happy to install it in your 2.4'"S" pump. It's only money !!

Jandrews · 06-11-2004, 06:18 PM

Henry,

What kind of variation were you seeing on the dyno on the 2.4S vs 2.7RS pumps, and between similar 2.7RS pumps?

JA

AndreasLanghoff · 06-12-2004, 01:10 AM

John,
on the dyno you are measuring full throttle HP between 4000 and 7000 rpm. This is the easiest part to adjust on an MFI pump. Just adjust the fuel mixture correcty (look at the plugs) and power output will be the same. The difference lies in town driving at closed throttle. Then a fine tuned MFI will avoid you hick-ups, edginess etc. of the engine.

Andreas

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally posted by AndreasLanghoff
John,
on the dyno you are measuring full throttle HP between 4000 and 7000 rpm........

Andreas

Funny thing about a good chassis dyno
set you can set your perimeters. But your point is well taken. I guess next time we try to compare engine modifications we'll have to drive the car too.

Oh wait a minute , that's right we did.
Same result, can't tell the difference on the big dyno, America's hiways.

thor · thor's Garage

well nice posts !!!!
then for a 2.0S and 2.2 S pump I think they are very similar , no ?
do you know the value of injected fuel at idle and full throttle or may be the curves ? I would like to compare the two pumps in terms of injected fuel or flow curves VS RPM .

thor · thor's Garage

nobody knows the value for theses pumps , only for 2.7 ?

NevenM · 06-21-2004, 10:08 PM

Henry

Can you tell me if the rack position to fuel output relationship is linear? and if so what is the ratio. The reason I ask is that I'm considering developing an eMFI system, using a megasquirt to control a servo driving the rackof an MFI pump (it would make all that space cam stuff redundant). I think it will require a wideband O2 sensor as well, as you'd want to operate them slight richer than stoic. The software changes are minor basically involves changing the injector pulse to a positioning pulse (output every 10mS or so) The Positioning pulse is between 1 and 2 mS (This is the std for Futaba Servos)

Also what is the rack range of movement, I'm hoping its about 20mm so it can be driven by http://www.emsjomar.com/linear.aspx

Thanks

Neven

AndreasLanghoff · 07-20-2004, 06:02 AM

Hi Chuck,

as suggested I replaced my 2.4S distributor with a new 2.7RS distributor 0231 184 004.
My engine is a 2.4S converted to 2.7RS with correct space cam, all freshly rebuild several weeks ago.
The difference is really tiny if not neglectable at all. Beeing really picky one could say that the engine is running slightly smoother at low rpm.
I have to admit that I did not do a long comparison. The engine was running excellent with the 2.4 distributor, I put in the new one , set timing at 35degrees @ 6000 rpm , and the engine is running also fine.
So, there is no hurry in updating the distributor to 2.7rs.

Andreas

KobaltBlau · 07-20-2004, 08:24 AM

...As Henry said.

911SCfanatic · 911SCfanatic's Garage

This wasn't addressed so far in this thread. I think Henry established that the S and RS pumps are so similar that for practical purposes they're the same. What about a T pump? I will be sending my heads, t/b's, stacks and pump off to Henry in about a month or so to work his magic so I wanted to bring up this thread again.

Clearly, the T pump can be richened to deliver the desired amount of fuel to my 2.7 high compression engine based upon Henry's 2.5mpg story above. But, I would have to believe that it would be a noticeable improvement to run the 2.7 space cam instead of my 2.4T cam. Sure it may not be necessary functionally, but if it didn't make a noticeable difference, why would Porsche even use a different space cam? Henry, what say you?

(Henry, BTW, I was starting to box my stuff up today, and my 71S stacks are actually 69S stacks--can't use them with my 73 t/b's. Maybe I could swap these stacks for a 70/71 set you have?)