cold engine driveability, fuel pressure

[Franc Buxton]

Carter Shore wrote:
> 
> 
> I have literature that describes the injector flow
> rate increase as proportional to the square root of
> pressure increase, ie, to double the flow, use four
> times the pressure. In your example this gives:
> 
> 1.8/1.4 = 1.28 -- displacement increase ratio
> (1.28) * (1.28) = 1.65 -- fuel pressure increase ratio
> 3.2 bar * 1.65 = 5.28 bar -- fuel pressure in bar
> 
> Of course, this number does not match what you
> obtained for proper operation, so much for theory!
>
	I think you're right, and I stand corrected!
Actually, the car does feel as if it could use more
fuel sometimes, but I didn't dare turn it up any more...
I have access to an injector flow test rig and lots of
different injectors, so I'll do some flow tests when I
have time and maybe use higher rate injectors instead.
Maybe I can test the square root idea, too...

> I'm looking at a similar situation, running a 1.5L
> motor with EFI calibrated for 1.9L. In my case, I plan
> to select smaller flow injectors, then diddle the fuel
> pressure if needed to fine tune. Once running, I will
> hack the spark and fuel tables.
> 
> BTW, what method did you use to adjust the fuel
> pressure?
> 
	I put an aftermarket adjustable fuel pressure
regulator which just happened to be to hand in series
with the existing one on the fuel rail, because the adjustable
didn't fit (having hose connectors not 'O' ring fitting)
and I was desperate! I checked the pressure with a decent
gauge.

> Thanks,
> 
> Carter Shore

	Thanks to _you_ for the education! Must remember not
to be quite so authoritative when I don't have backup theory! ;>)

	Regards,
		Franc.
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