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JohnJL's Avatar
 
Join Date: Jan 2005
Location: Toronto, Ontario
Posts: 4,728
Fuel injector sizing

I'd appreciate a check on my calcs before placing an order...

I am assembling my first go at a turbocharged engine and have done the calcs to estimate a need for 50-55 lb/hr injectors based on fuel pressure of 45psi and a target flywheel HP of 475 hp/475 ft-lbs.

Thats seems intuitively corrrect also since the last EFI 911 engine I built gave ~240 hp on 26lb injectors and managable idle and duty cycles.

This engine is going in my race car so need to keep in mind duty cycles will be high.

Displacement is 3.2 on new perfectbore cylinders and coated 8:1 JE pistons. SC or DR20 cams.

Thanks all
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2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 11-02-2007, 03:31 PM
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TimT's Avatar
 
Join Date: Mar 2002
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I get 60# injectors are needed, based on calcs with 80% duty cycle, and 0.6 BSFC @43.5 PSI

what specs did you use to calculate your injector needs? 55# injector should be fine though.. just might work above the 80% threshold more..
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Old 11-03-2007, 12:23 AM
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BTW: get some real cams if its going to be a race car.... DC20 or SC or SC sports are to tame
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who are those guys? <<< ( Butch Cassidy and the Sundance Kid)
Rent a GT3RS from us!! Call or e-mail.
Transportation and Track support
Rudtners Racing

'69 911 GT-5
'75 914 GT-3
Authorised Haltech seller and installer
Authorised Unichip installer
BBS wheels
Fikse wheels
Redline motors oils
Swepco
1500 hp chassis dyno
Old 11-03-2007, 12:24 AM
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DonE's Avatar
 
Join Date: Mar 2004
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I don't know your build, but as a matter of reference, I use 60lb Siemens in my 525hp motor. Max duty cycle so far is about 72% or so, at 12.2:1 AFR.
Old 11-03-2007, 12:14 PM
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Don, why don't you run 12.0 AFR?

TIA buddy.
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Old 11-03-2007, 12:59 PM
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Any lower caused the plugs to really darken. Around 12.5, they quickly started to lighten and I don't want to grenade another motor.
Old 11-03-2007, 04:29 PM
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Thanks guys.

60s it is then.
I mentioned the SC and DR20 cams because I've got those already. I plan on talking to JD before settling but of course suggestions are welcome.
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2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 11-04-2007, 01:01 AM
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Just another data point.

I am running 55 lb injectors. I think with my boost turned up a little they are close to maxed out. At 13 lbs of boost on a DynoDynamic dyno I got 352 RWHP. Now I am running about 17 lbs of boost.

So I would go bigger that 55's also.

Dean
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911 SC turbo, 3.0L 930 motor, G50, 930 brakes, DTA EFI, 352 RWHP DynoDynamic dyno,
Old 11-04-2007, 01:37 PM
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