[Diy_efi] injector placement

[William Shurvinton]

Hi John,

'perceived wisdom' is that port injection is best for economy when using
readily available stuff. Direct injection is better, but you run into other
issues. I've looked at a couple (but only a couple) of bikes with EFI and
the OEM location seems pretty good. If you want more power at 8-10K RPM then
moving the injectors further out can help, although I know someone with a
car engine who fitted them and peak HP was not effected, but the power band
was nicely flattened. He doesn't know why, but is very happy with the
performance increase.

Carbs can produce really good atomisation but (and I am very willing to be
shown wrong here) I haven't seen one that produces more power AND better
economy from the same setup. I know the bike racing community are very fond
of ditching EFI and fitting slide throttle carbs, which is great for me, as
those bike TBs are really good for the sort of EFI I play with, but I
suspect there reasons are more due to  the facts that there are very few
bike friendly programmable ECUs out there and that they understand the
carbs.

With batch EFI the fuel isn't puddling but vapourises quite nicely on the
hot valve whilst waiting to be slurped in. Not perfect, but works.

Bill
----- Original Message -----
From: john smith
To: diy_efi at diy-efi.org
Sent: Friday, June 21, 2002 6:14 AM
Subject: RE: [Diy_efi] injector placement


 Been thinking about fuel economy. Perhaps doing something to aid
atomization or keeping fuel in suspension rather than sitting on the
manifold wall waiting to be sucked into the cylinder. I am looking at
motorcycle engines and from what I have seen carbs can be more economical
and put out more power. The main reason for FI seems to be drivability and
emission control. If you think about it fuel drawn from a carb jet is in a
moving airstream all the time whereas the injected fuel is often squirted in
when the valve is closed and probably turns back to liquid while it is
waiting. Although I have read part of a SAE paper which said the fuel
atomization and mixing doesnt take place until the last phase of the
compression stroke. Anyway, just wondering if anyone has seen different
effects from different placements.
Thanks



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