white 944 turbo

First I want to thank rage and the rest of you who helped me with the SDS questions I had. I will likely go with a stand alone system but still am unsure of which one. Next topic is fuel injectors. I see alot of people using very big injectors. From what I know, and I am no expert, there is a formula to calculate the size of the injector needed for the horse power goal. If you take the HP and take half then divide that number by the number of cylinders you have you should have a rough answer. For example if you have 944 turbo and have 400 HP. Take half of that and then you get 200. At this point you divide by the number of cylinders in this case 4 and you get 50. So shouldnt a 400 HP 944 turbo use around 50# injectors? Also, with oversized injectors isnt there concern of the cylinders being washed out and causing engine damage? Lastly, are there alot of problems with getting the car to idol right? Even with the flexibility of a stand alone or mapped chips you can only adjust so much.

Danno

"So shouldnt a 400 HP 944 turbo use around 50# injectors? "

Nope, that will be good for about 300hp @ 80% duty-cycle. You don't ever want to drive injectors to their full 100% static-flow capacity because that'll over heat them and the driver-transistor in the ECU. To do 400hp you need at minimum 72-75lb/hr. To be comfortable, 83-lb/hr.

"Also, with oversized injectors isnt there concern of the cylinders being washed out and causing engine damage? Lastly, are there alot of problems with getting the car to idol right? Even with the flexibility of a stand alone or mapped chips you can only adjust so much. "

That's just a matter of dialing in the correct fuel-maps on whatever system is controlling our car. Even the stock DME can idle correctly and pass emissions testing with large injectors if it's programmed properly; meaning it's getting a real and true air-flow signal and points to the correct location on the 3D internal fuel-map.

Danno

Here's a good site with injector calculations (calculate BSFC first using known variables from stock car before doing 'what-ifs', i.e. 217bhp, 50psi fuel-pressure @ 12psi boost, etc.):

<a href="http://www.rceng.com/technical.htm#WORKSHEET" target="_blank">http://www.rceng.com/technical.htm#WORKSHEET</a>

Also some past threads on 400hp injector requirements:

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=18&t=001996" target="_blank">WTK- Injector requirements for 400rwhp </a>
<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=18&t=002422" target="_blank">What size injectors for 400HP? </a>

Alan C.

I know 3 people, myself included, that use 83 lb. injectors on 951's with around 370 rwhp.

Alan

Pannan

AlanC,

What´s the serial-nr. and make on the 83 lb/hr injectors? Price?

//Johan

Alan C.

The injectors are from Siemens. I purchased them from Marren Motor Sports for about $350 - $400. Don't remember the exact price.

From the test sheet:

Type: P&H 2.8 ohm Test Pressure: 43 psi
Injector Part No. 3105 Test Pulse: 6.0 ms
Gravity Weight 0.75

Flows at noted parameters:
1=283.1, 2=280.3, 3=285.7, 4=282.3

That's all folks

Alan