EFI PSI?? More the better??

[Instigator]

I am converting a JohnRude to Mad EFI and the pump will peg a 100 psi gauge even though spec is 45psi.
If my lines will hold 100 psi (they will, I used hydraulic line) and the pump will keep up, isn't the higher the pressure better at atomizing the fuel??

Thanks Giys!

Gary

[BadHabit 21]

wouldn't blow the injector off its seat???

[TheRickster]

Fuel injectors are rated at a given pound per hour flow rate. Normally this is at a 39-42psi figure. Generally speaking the higher the fuel pressure on a given injector will result in a higher fuel flow rating which needs to be altered by a narrower pulse width..

Rick

[Stitch King]

What injectors do you have.

I have calculated fuel requirement for the cylinder volume you are using for both 14.7 and 12.5 AFR. If you get me the injector specs, I can calculate the pulse width needed at a given line pressure. I always try to use 43 PSI as that is the SAE test spec pressure that all injector flow ratings are done at.

Also what fuel controller are you using?

[rpm racing]

I would not run that kind of fuel psi. It is very hard on the drivers in your ecu to open the injectors with that king of pressure holding them back. Other than the new opti's and the direct injection motors I have never heard of any one running much over 60-65psi.

Your fuel map (injector pulse width) will have to be altered for any given psi that you want to run at, it is kind of like changing to a bigger injector but there is a point of diminishing return.

If you have not read the book "How to Tune and Modify Engine Management Systems" by Jeff Hartman you should it covers all this stuff and for anyone trying to build/run or understand how a EFI is working it is a MUST READ.

If your fuel system is pegging a 100psi there is a problem with it. The picture I saw it looked like you were running the stock merc Bosch gold regulator which is a 39lb reg, that is what it should be. I saw how you plumbed that set up and I know that Wayne was big on that idea, but I have never seen anyone not run a full loop with regulator after the last injector and return line back to the tank.

[1BadAction]

If your fuel system is pegging a 100psi there is a problem with it.
:iagree: it should hold the regulated PSI and no more. With any type of injector there shouldnt be an issue with atomization if you run at its designed pressure. even if there was, I don't think it would matter with the way a 2-stroke OBs induction path is.

if you need some extra flow, you can up the pressure a bit. :reddevil:

[gfinch]

"I saw how you plumbed that set up and I know that Wayne was big on that idea, but I have never seen anyone not run a full loop with regulator after the last injector and return line back to the tank."

A return less system is called a Dead Head system. This is how mine has been for a few years. I set mine up to return from the regulator thru the original fuel pick up, that way it doesn't areate the fuel and cause alot of vapor emissions. A lot or newer cars use the Dead Head system nowadays. Fuel pump, regulater, filter and leval sending unit in the tank in one assembly.

I now have a different regulator as that Bosch unit was maxed out at 45 or so psi.

[Instigator]

Thanks Guys!

RPM, great input. Thank You Sir. I will get and read that book and your comments on pressure all make sense and is what I was guessing.
Very interesting too on the return and I relplied to your earlier comment in the other thread and to be honest I was not sure how to do it.(the return plumbing in general)
I will study that issue.
Pump was only pegging gauge when regulator was removed. Interesting too that that is a Merc regulator as I get 40 PSI w/it maxed.
It has been a long exspensive/painful project to get to this point but one of the things I liked about the Mad is I felt like I could spend 6 more mnths playing mad scientist and really find out what the motor wants.

Rick, thanks. Thats what I was guessing.

StitchKing, it's the Simple Digital (Mad EFI) system and I'll check the injectors later today and thanks!

Jim, understand and was wondering if altering pressure would have an effect on tuning in a positive manner or is it something I need to set and leave.

Gary, interesting. Once I undertsood RPM's earlier comment about the aeration I planned to move the return to how yours is.

[BarryStrawn]

However you do the regulator, it has to be after the filter. Which I didn't see in your pictures, except for the inlet sock. And I think any gauge should up on the rail where it matters.