[Diy_efi] Fuel rail sizing

[Dave Dahlgren]

The point for me was everything matters. If the list of things that don't matter
get too long then inevitably things that do matter get on that list as well. On
batch fire systems I have run into this problem as well. The rails worked fine
on sequential but on a batch system the end cylinders did not run right. Plugs
looked wrong as well as EGT readings wrong/different. You can say it can't
happen or it does not matter but it does. I have the pistons or lack of to prove
it. This is not a problem for most street cars as there time at WOT is minimal
at best. Try it on a 1/2 mile straight at WOT or Bonneville with 5 miles of WOT
or a powerboat at WOT for an hour and it will start to matter to everyone. What
I have found if in doubt make the fuel rail larger. It does add in the heat soak
to the fuel if they get way huge but I have found at least for 6 injectors at
100 lbs an hour that 3/4 works fine as it does with 4 injectors at 160 lbs/hr.
Yes i understand this also has nothing to do with a street car with 30 lb/hr
injectors. The original question was ' Does it matter' answer 'yes it does'.

BTW we do use fuel radiators in some cars as well as fuel temperature
compensation that follows the change in specific gravity. As the fuel gets
lighter add more as the engine needs fuel in lbs/hr and the injector delivers it
in cc/minute. A while back Honda was heating fuel so it would be at the same
temperature at all times as well as vaporize better, for what little that is
worth to this discussion.

Dave Dahlgren

Bruce wrote:
> 
> There comes a point of being practical.
> You want to get to nanosecond timing, sure go ahead, but for the rest of use
> not running GTPs there is a point of practical limitations.
> And what effect does high DCs have with other injectors closing as some are
> opening?.
> And what's the response time of vac referenced fuel Pressure regulators to
> manifold vac changes?.
> And I guess we could work out a correction for actual fuel temp., since it's
> viscousity is gonna change.
> You can carry about anything to the extreme, but there comes a point of
> where some folks just bite the bullet, and say this is close enough.
> Bruce
> 
> ----- Original Message -----
> From: "Dave Dahlgren" <ddahlgren at snet.net>
> To: <diy_efi at diy-efi.org>
> Sent: Wednesday, September 04, 2002 5:29 AM
> Subject: Re: [Diy_efi] Fuel rail sizing
> 
> > Are you suggesting that if there are 6 injectors in a line and they all
> open at
> > once the one furthest away from the supply will have exactly the same
> pressure
> > as the one closest? What piece of physics would you base that on? Do you
> have a
> > part# for the pump and regulator that will accomplish this working in the
> > microsecond range for response times?
> > Dave
> > Phil Lamovie wrote:
> > >
> > > At 90% duty cycle it doesn't make s spit of difference
> > >
> > > phil
> > >
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