will lower FP on larger injector=same as stock?

[blownintegra]

If a rising rate regulator works by adding more fuel, is there a way to lower fuel pressure to a point that a larger injector will inject the correct amount of fuel while still being able to atomize correctly?

Like if you have a 240 cc injector and raise pressure from 45 idle psi to 70 psi you get 25% more fuel. (I don't really know what it adds, I'm just trying to explain), so if you take a 310 injector which is 25 percent larger and you lower the idle pressure 25% to like 34 psi, will you still get the same amount of fuel? Then you could take a FPR to compensate for the lower idle pressure to adjust the fuel curve so that you get more fuel at 50 than you would with 240 cc's at 70 psi?

I'm trying to make something work on a car that doesn't have computer tunability, so that's why I'm asking....

Please respond with any ideas,
Thanks,

Mike

[img]biggrin.gif[/img]

[Holden]

SQRT(new_pressure/old_pressure) * old_flow_rate = new_flow_rate

Throw that in a spreadsheet and play with the numbers.

A quick answer is that increasing injector size x amount can allow a reduction in fuel pressure of y.

[5 Liter Eater]

It's very possible, a lot of us do it but you'll find that the larger injectors are harder to tune throughout vacuum and boost. You can see by Holden's formula that the relationship is not linear so you need to change your rise rate. That much you already know, what you have yet to have fun with is trying to find the right combination of vacuum, static on FPR, static on FMU and max on FMU fuel pressures that makes the car as drivable as it was with stock injectors. It's something I have been dealing with for a while and am still not happy with the results.

[JRCivic]

Yes, it can be done successfully as long as you do NOT get your idle pressures under 26 psi. This is about as low as you can go without having poor atomization... and thus, a cranky idle.

[blownintegra]

Okay,

How would I go about lowering my idle pressure to 26 without making a hole so big in my stock FPR that I am not able to get FP high enough when I need the higher pressures.

Actually what I am doing is trying to get a low boost 4-5 psi turbo, that I am building from used parts, etc for my 87 CRX that does not seem to benefit from any computerized fuel and timing management support. That's why I am trying this method.

Unless someone has better ideas.......

[Holden]

Open your wallet and buy an AEM FPR. They offer complete adjustability for any fuel pump. I'm very happy with mine.

With a little searching, you should be able to get one for <$160.

[blownintegra]

You are not referring to the little AEM thing that you cut your factory regulator and put the adjustable piece on, are you?

26 psi, cool.....

[5 Liter Eater]

<BLOCKQUOTE><font size=2 face="Verdana, Helvetica, sans-serif">quote:</font><table border="0" width="90%" bgcolor="#333333" cellspacing="1" cellpadding="0"><tr><td width="100%"><table border="0" width="100%" cellspacing="0" cellpadding="2" bgcolor="#FF9900"><tr><td width="100%" bgcolor="#DDDDDD"><font size=2 face="Verdana, Helvetica, sans-serif">Originally posted by blownintegra:
You are not referring to the little AEM thing that you cut your factory regulator and put the adjustable piece on, are you?
</font></td></tr></table></td></tr></table></BLOCKQUOTE>

No, those are the B&M and Vortech units. The AEM is a total replacement for the stock FPR and comes with different disks to be able to achieve pretty much any idle/static pressure you want. It also rises the fuel pressure 1 PSI per PSI of boost whereas the stock FPR stops at atmospheric pressure so take that into account when dialing in the FMU's rise rate.