tonytaylor

To state that the only limitations on the standard injector system is rpm is not really correct. The limiting factor is the injectors ability to supply enough fuel, that is, their maximium flow rate. If you provide the engine with more air then correspondingly more fuel is needed. Turbo or supercharging will provide more air than the standard injectors can flow without needing to raise rpm. It is true that raising rpm will increase the amount of air used by the engine per unit time and hence engines ability to do more work, ie hp.
The injectors are good for more rpm then a standard engine will run to, however it is equivicable as to whether they can flow enough fuel for non standard engines. All the data I have seen and discussions with various tuners, reading claims for packages from Cargraphic, Techart seems to point to the standard injectors limiting hp to around 300hp. It would also appear from the data here and from the dyno readings of 9Ms modified 964s with larger injectors, that 964s can produce more than 300hp at rpm below the standard rpm limit. This means that the standard injectors are the limiting factor in hp for non standard 964s and not the standard rpm limit.
The amount of fuel is soley dependant upon how long the injector is open for only until the injector is open all the time. Once the injector is fully open all the time it is flowing the maximium amount of fuel possible ( at standard fuel pressure)
Which would explain why modified engines are able to produce more hp with larger injectors than using the standard ones but this would only be true if the standard injectors were at their peak flow rate and limiting hp because of this fact.

YMMV

JasonAndreas

Does anyone have any pictures showing how to correctly tie-down a 964 on a dyno?

Red rooster

TonyTaylor has hit the nail on the head. Injector sizing is linked very directly to the power output the manufacturer wishes to get. With sequential injection there is always a compromise to make between proper control at idle combined with adequate fuel flow at max power.For this reason Porsche increased the injector size on the 993 by +20% to cover the 300bhp RS.
In an ideal situation the injector would be sized so that it was only ON during the inlet valve opening period.In practise this can lead to oversized injectors that make idle fuelling a problem.

I would say that a 964 at 300bhp is near the end of what the standard injectors will flow and I have been there many times!
My last serious Porsche mapping job was on a pair of 962s for the Historic Le Man . These wonder wagons have two injectors per cylinder so no problem with idle (one injector/cyl)or MASSIVE full power(2 injector/cyl).

Adrian

Dear Tony,
I think this is just going to go around and around in circles so we might was well stop it here.
I have seen the 964 engine deliver more than 300 HP at the flywheel (321 HP) using some of the originally installed fuel injectors and a couple of new ones that failed the spray pattern.
If you are saying this is not possible okay fine let us agree to disagree.
Ciao,
Adrian.

PS: Of course there is a limit to how much a fuel a particular size fuel injector can supply.
You are saying that ours are at their maximum limit already and I have seen we have plenty of room to move in with them.
It was like the guy who told me, swore black and blue that the 964 C4 transmission could not handle more than 300 HP. I then find 993TT engines with 500 HP coupled to them and they work fine and do not break.

tonytaylor

I thank you

You may care to know that my C2 is still running an AMD MAF, throttle body and chip fitted circa. Oct 2000 and with a catbypass and different exhaust was independantly dyno'd @298bhp/260ftlbs. A lot of track time with other 911s old and new confirms to me how hard it actually pulls.

I am not saying that it is not possible for 964s to make in excess of 300bhp with the standard injectors just relaying information from UK ECU experts, tuners with independantly verifiably practical experience and ex senior Bosch tecnical employees, again with a lot of practical experience of modified 964s, that suggests that the standard injectors will not flow enough fuel for much over 300hp in a 964. Since they have confirmed as much here on Rennlist I am not producing hearsay evidence or speaking on their behalf

YMMV

C4 transmission is a red herring. FWIW I know of several C4s putting out more power and torque than a stock 993tt.

BTW if you are using hp DIN or PS rather than bhp from the dyno you quote I would personaly find your figures more credible.

Lorenfb

"TonyTaylor has hit the nail on the head. Injector sizing is linked very directly to the power output the manufacturer wishes to get."

Not totally correct.

The factors which affect the amount of fuel:

1. fuel pressure
2. injector size
3. injector signal pulse width

At 6000 RPMs a six cylinder fires every 3.3 ms. As a result, each cylinder fires every 20 ms.
The typical no-load injection time is about 3-5 ms. Therefore, the needed fuel can be injected without
the limitation of injector size. Only when the RPMs get >>6000 does the fuel pressure &
injector size become critical & the limiting factors. Remember the key factors for fuel needs are;
engine size, max RPMs, type of intake (normally aspirated vs forced). Unless these are radically changed from the stock engine, DME re-mapping can achieve the results.


Bottomline: The re-mapping of the 964 DME can achieve the required modified fuel input
with most all engine mods. Changing the injector size is the "brute force"/no knowledge approach.
Furthermore, changing the injector size results in the engine being too rich at RPMs << max RPM,
without a fuel re-mapping.


This thread had a question about the 964 DME units. They're all basically the same with
the exception of the EPROMs.

tonytaylor

To be pedantic, injector sizing is directly related to the power output the manufacturer wishes to get and hence the statement is totaly correct. However injector size is not the only factor which affect the amount of fuel the injection system can flow, as below;but surely 2) above, "injector size" contradicts what was written above?but the key words for "injection time" above are "no load". It would seem injection times are longer than this under load. At full load when max bhp is reached, which by definition will occurr 6000+rpm, then at standard fuel pressure, injector size does become relevant.
If the engine is not standard then injector size can be a limiting factor. Whether the changes from standard to reach the level where injector size is relevant are "radical changes" is semantics, but evidence that any 964 engines, whether NA or forced induction, that require enough fuel to produce over 300bhp are limited by injector size is compelling.
The key words here are "most engine mods". Would Loren not agree there is a level that the standard injectors at standard fuel pressure will no longer provide enough fuel?
I would be interested to know if Loren has any practical experience of re-chipping modified 964s running over 300bhp on standard injectors. ( I am aware of Lorens specialist expertise and the question should be taken at face value)
Perhaps Loren ought to investigate the nature of Red Roosters knowledge of the Bosch ECU before he claims a "no knowledge" approach because it doesn't look like a particularly clever statement from where I'm sitting.

Lorenfb

"but the key words for "injection time" above are "no load". It would seem injection times are longer than this under load"

Obviously that was implied in the statement about the max available injection time of 20ms.

Again, there's enough time available in the injection pulse width to supply adequate fuel without
changing the injectors for most mods, given RPMs <= 6000 & a 3.6L.

tonytaylor

Quite, but I'm not so sure it's that obvious. It would seem we agree that the injection times are longer under load. I'm sure you must know the injection times for standard injectors at max hp, perhaps you would like to share?Again, some of the key words here are; " most mods", but most basic mods will not cause a fuel requirement for more than 300bhp, " given RPMs<6000", which is lower than when peak load and hence peak flow requirement for the injectors occurs, and "3.6L", when 3.8L is a common upgrade ( not withstanding the fact that the fuel requirements for this upgrade are < 5% increase, which is less than other intake foremost, and exhaust secondly, mods )
Does Loren have any verifiable or not, practical experience of rechipping modified/non modified 964s to produce over 300bhp with the standard injectors?

Lorenfb

"I'm sure you must know the injection times for standard injectors at max hp, perhaps you would like to share?"

Actual injection pulse width values as measured from 964 DME (473) unit with stock chip;
1. no-load with head temp @ max ~ 4ms
2. full load with head temp @ max ~ 15ms (this is the max injection time)

Based on #2 of 15ms, the injection time can be theoretically increased another 5ms
to the max of 20ms (@ 6000 RPMs). This value is more than enough extra fuel
for most mods, e.g. 3.8L. A 3.8L mod is less than an 10% increase. Once the RPMs
exceed 7000 RPMs (17ms), the injectors or the fuel pressure would have to change.

tonytaylor

Thankyou for that information Loren. It's appreciated and stored for future reference

Do you think it is correct to assume that once injectors are at/near max 20ms opening their efficiency decreases since injector charge ought to correspond with optimal inlet valve opening? ( you quote 17ms@7000RPMs requiring fuel pressure or injectors requiring change)

Lorenfb

"injector charge ought to correspond with optimal inlet valve"

That's not that critical and has very little overall torque effect, i.e. more for emissions.
The 3.2, as do older EFI systems without sequential, provides two fuel pulses per
2 revolutions, e.g. like throttle body injection. Sequential allows for individual cylinder
shutdown for misfire problems (OBDII).

The 17ms is the max time for a injector pulse at 7000 RPMs for any engine no matter
the number of cylinders, i.e. that's one cylinder's 2 revolutions.

6000 RPMs = 100 RPS = 10ms per revolution or 20ms per 2 revolutions
for 7000 RPMs pulse time = 20 x 6/7 = 17ms

You are correct about modifying an engine to rev above 7000 & its'
requiring higher fuel pressure or different injectors. This assumes
that the unmodified engine required the full 15-17ms below 7000
for adequate charging.

High revving engines (>>10, 000 RPMs) use 2 injectors, e.g. motorcycles & F1 engines
because the desired pressure gets too high or injector design problems.

Red rooster

Well this subject has certainly been aired.To add to the observations, it is generally accepted that if an injector flow requirement is greater than 80% of the available time then the injector is undersized.I accept that this is an OE viewpoint but it has not done me any harm over the last 20 years with my involvement with Motronic calibration.
The 6000rpm/20ms point would lead to a max measured on time of 16ms before questioning injector size. I think the numbers quoted ,17ms , would support the view that the std injectors are near the edge.
This is why the 993 with 272/285/300 bhp engines run injectors with flow raised by 20%.

As another rule of thumb used by Porsche in the 964 days , motor and transmission should have a 100% safety margin.So you can double the power and torque without breaking stuff straight away!