bought some injectors

Alan Pritchard apritchard at
Thu Mar 11 05:42:19 EST 2004

Ok, heres my reference data I used to size the injectors. Its taken from a
pdf file published by autospeed.
500cc per minute is approximately equal to 49 lbs per hour, which is equal
to approximately 100hp
lbs/hour=cc per min /10.2
lbs per hour = hp/2.04
cc per min = hpx5

ok, what I did not realise was that this is based on 100% duty cycle
24 x 2.04 = 48.96 hp per injector
48.96 x 5 = 244.8 @100% duty (held open)
safe limit on a road car approx. 80%
244.8 / 100 * 80 = 195.84
ok, so not ideal, close to your maths......
 extra half bar fuel rail pressure will bring that safe working limit to
215hp... still not ideal.... DOH!!!!!
Read the small print before buying stuff!!!!!!! May see if they have been
sent, and get some bigger ones...

Best Regards,

Alan Pritchard,
Mechanical design engineer,
Network administrator.

Seaeye Marine LTD.
+44 (0)1329 289000

 -----Original Message-----
From: 	Cody [mailto:Cody at] 
Sent:	10 March 2004 16:24
To:	Quattro List (E-mail); Alan Pritchard
Subject:	Re: bought some injectors

Um, only one issue with that. 5 24lb injectors at 80% duty cycle will only
support a 5cyl up to 180hp. You can use those for now, but you'll be running
them past the recomended 80%, but you will be running the injectors hot and
thier expected lifespan will shorten greatly. On an otherwise stock car just
removing the airflow plate and tuning the EFI properly should put you beyond
that 180hp mark. I'd say you should look for some 33lb injectors which
should keep you flowing for 240hp (about what you should expect @ .8bar

Maybe though I'm wrong on your application, it is a turbo 5 right? I've been
so busy recently I barely remember that MY car is a 5cyl lol.

Heres the formula just in case.
To get injector size if you know the hp:
HP divided by # of Cyl divided by 0.8 times 0.55 = Flow rate
(300hp / 5cyl / .8 x .55 = 41.25lb/hr injector for a 300hp 5cyl car)
If you know your injector size but want max hp use:
lb/hr times # of cyl divided by .55 times .8
(24lb/hr x 5 / .55 x .8 = 174hp)

-Cody Forbes
'86 5ktq
'87 5ktq EFI/k27
'88 80 4cyl
'88 90 4cyl

---------- Original Message ----------------------------------
From: Alan Pritchard <apritchard at>
Date: Wed, 10 Mar 2004 15:57:30 -0000

>>From 5o motorsport in the us.
>Set of 6 24lb 5L (I think) jeep injectors.
>All up - 214$ to the uk.
>Not bad at all, I don't think....
>Bring on my Megasquirt!!!!	
>Best Regards,
>Alan Pritchard,
>Mechanical design engineer,
>Network administrator.
>Seaeye Marine LTD.
>+44 (0)1329 289000
>quattro mailing list
>quattro at

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