trophy

Over the past few weeks I have been toying about a number of upgrades I would like to do to my car, while still keeping in mind I don’t want to do it all in one hit but would also like to consider making incremental improvements on the way to my final goal.

So when issues arise or things need replacing I would like to replace them with appropriate items that will not restrict my end goal, and would provide incremental improvement as I move towards my goal. And realistically I don’t want to do things more than once.

This leads me to thinking about fuel injectors. I keep thinking that the injectors in our cars are getting old (mine are almost 15 years old) and during this time there have been a number of improvements in FI technology, and wonder if our cars would benefit from an upgrade even with the stock ecu.

After reading a number of posts about duty cycle, flow, impedance etc I am getting just a little confused but have come to the conclusion that for many of us, our injectors may be holding us back with regards to the improvements we are making to our cars. So for a point of reference here are the specs of the injectors in our cars (first table) the specs come from the following site. (http://users.erols.com/srweiss/tableifc.htm#ITABLE):

After putting the stock 993 figures in the calculators here (http://www.injector.com/injectorselection.php) the calculated HP figures are in the second table.

Based on the calculated HP figures, and with a maximum recommended duty cycle for bosch fuel injectors being 85% then the max power our injectors will support safely is 282 hp (coincidence?). By safely I mean without running the risk of damaging the fuel injectors due to overheating or adding stress on the ECU.

So, I see claims of HP increases by exhaust manufactures (lets leave the validity to other threads), chip makers, intake manufacturers etc and think, even a claim of 10hp increase is going to put our fuel injectors above the 85% duty cycle and therefore run the associated risks.

My point and my question?

• Is my thinking valid?
• Is there a benefit for changing our fuel injectors to higher rated aftermarket ones?
• Is the change going to yield a performance gain and longevity
• or am I smoking some really good stuff…..

Many ‘tuners’ of other vehicle manufacturers (BMW, VW, GM etc) all recommend changing the fuel injectors when making other improvements to realize the full gains, why should our cars be different?

Your thoughts Ideas and comments are welcome

KBell

I am definately interested in any advice.
Particularly since my engine bay is in pieces.
Last pic I think is of gas line and fuel injector.
Excellent topic Steve

Kevin

Tango635

trophy

Great time while you have access.....

blitz928

I just did fuel injectors on my 928, I highly recommend http://www.fiveomotorsport.com/fuel-...s/porsche/911/ if you're looking for injectors, they have everything and prices that are hard to beat. Great service to boot.

Stealth 993

The only bad part about changing injectors is you NEED to change the chip to match, or play with the fuel pressure to get the proper flow.

Bigger injectors will have a rough idle, & can bog the engine on WOT. Unless you are maxing out your injector DC, putting in bigger ones is a waste of time. Do we have high or low impedance ones?

What size are the RS ones? You will no get any power gains from going bigger injectors unless yours are maxed out.

black ice

My opinion is that it's a useless upgrade, assuming your injectors flow well. I have no knowledge about how often injectors are clogged or last otherwise.

I looked around and all of the factory 3.8 power kit upgrades I saw online do not come with injectors (implying you keep the stockers).

dave

trophy

Our injectors are high impedance.

What about the efficiency of the new injectors vs ours?

bart1

Names that come to my mind are Steve Weiner, Goeffrey Ring and Colin Belton. Maybe one of them will weigh in. Locally to me, I would talk to www.patwilliamsracing.com

trophy

Over here on Pelican they have posted (Post 38 by Noah) some details about the differences, and they list Larger Fuel Injectors.

Maybe Bill V has some additional info as he has been collecting RS info for many years.....

NP993

IIRC, Colin at 9M has recommended bigger injectors as part of a mid-level upgrade that includes valves, cams, exhaust, and engine management.

matt777

I would think that basic theory would say that bigger injectors won't help unless you are moving more air and need to up the fuel delivery to keep the proper AFR. However, I wonder if there are gains to be had by improving the timing on the fuel delivery and by getting better atomization. Perhaps a new computer would be required anyway. I'll let you do the legwork here Steven and ride your coat tail one day.

trophy

Colin's system is probably what got me started on this.....

I agree that the atomization improvement could be an improvement, I am also thinking the intake and exhaust mods most of us do allow more air to move hence the requirement for more fuel. If our injectors are being maxed out then it is only logical that larger injectors would improve performance.

black ice

Steven, I wonder if there would be any improvement given same injector placement, same fuel pressure, etc. i know you said this was not the forum for discussing efficacy of intake/exhaust mods - but it's hard to ignore - how much additional CFM can flow with a new filter or muffler? At what RPM (full throttle at high RPM is the only place you'd glean any benefit from additional injector if your theory is correct).

Totally OT. My first Porsche was an 82 931 as well! It was white and very low to the ground. We called it Casper. To my college girlfriend's great chagrin, I rebuilt that engine in the bedroom in my apartment...

dave

bobesser

I would think that at mild states of tune - intake and exhaust, there would be little performance increase in terms of HP. You might see a bit better mpg with improved fuel atomization.

But, in terms of reliability, if, as you say, the nominal max HP at 85% duty cycle is 282 HP, we are there. If you have a car with mods that makes more HP, you would be overdriving the injectors. So, then, you may consider replacing the injectors with slightly more flow. The trade off of more flow is that you will have a harder time fine tuning the low range where you start flowing too much per duty cycle increment.

Bob