Changing fuel pressure

shaodome · Post by **shaodome** » Thu Sep 30, 2004 6:04 pm

Ok so with these ~310cc injectors I hit 85% duty cycle in order to maintain 7psi. My fuel pressure is a constant 45psi. Before I up my fuel pressure(~55psi?) and change my REQ_Fuel I would like to know if the VE table will need to be redone? I'm guessing a lot of things may have to change?

Peter Florance · Post by **Peter Florance** » Fri Oct 01, 2004 3:31 am

The fuel delivery will increase by square root of ratio of the pressures.

so sgrt(55/45) = sqrt(1.22) = ~ 1.11 or about 11% more making them 343 cc
injectors

always seems like you don't get all you should with increased pressure but
that's it.

Peter Florance
First Fives Dictator for Life
1981 Euro BMW 528i w/3.5L & Megasquirt Fuel Injection
1981 US BMW 528i "Repo Car"
http://www.firstfives.org
mailto:peter@firstfives.org

boost junkie · Post by **boost junkie** » Fri Oct 01, 2004 6:50 am

Even with an injector change, if tuned properly, the VE table should be really close. The VE table is just what it says... a volumetric effeciency table. Just changing the injectors or fuel pressure won't change the volumetric effeciency of the engine. Changing things like cams, head porting, intake manifold, turbochargers, etc would require some VE work.

shaodome · Post by **shaodome** » Fri Oct 01, 2004 7:55 am

So I"ll just change my REQ_FUEL value and thats it? I don't have to "scale the VE table?"

Post by **efahl** » Fri Oct 01, 2004 7:48 pm

shaodome wrote:

> So I"ll just change my REQ_FUEL value and thats it? I don't have to "scale the VE table?"

That is correct, change req_fuel, do not scale the VE table. You will
have to scale your acceleration enrichment values and cranking pulsewidths,
as those both are specified as injector pulse time values, which are not
affected by the req_fuel change.

--
Eric Fahlgren http://www.not2fast.com/

shaodome · Post by **shaodome** » Mon Oct 04, 2004 1:09 pm

good to know.....too bad really. I finally got my accel enrichments somewhat tuned....O well.

Post by **efahl** » Fri Oct 08, 2004 5:25 am

On Thu, October 7, 2004 10:01 pm, shaodome said:
> good to know.....too bad really. I finally got my accel enrichments
> somewhat tuned....O well.

Don't trash your good AE values yet, just scale them by the
difference in flow rates and they should be pretty close...

--
Eric Fahlgren http://www.not2fast.com/