In a message dated 6/1/00 2:59:00 PM Pacific Daylight Time,
midlman@... writes:
I have an adjustable FPR on order and it needs to be
adjusted/optimized after installation. Is there another way to do
this (without A/F meter) or is this a necessity. I assume the car
will run OK after installing the FPR??? You have the adjustable FPR
on you GT right?? Did you optimize it yet?
I wonder if there is a place where this can be rented?? Maybe the
dyno
shops.???
Hi Tom,
Yes It needs to be set/optimized. You will need a fuel pressure gauge to set
it to the correct (stock) pressure to start with. The instructions that come
with the FPR say to never adjust it without having a gauge connected so you
can see what the pressure is while adjusting. You won't need to adjust it
very far off of the stock setting so it is mostly a fine tuning of the
pressure. With my adjustable FPR, I did the best I could by using a mixture
meter, the JC Whitney one that recently broke. After I put on the Dastek
Piggy back computer, I set the A/F ratio (for max power) with that so I set
the adjustable FPR back to the stock setting and left it.
How to do the optimization? I think the best way would be on a dyno since max
power is the result you are after in the end anyway. An A/F gauge is the next
best way and you would set the mixture for about half way between center and
full rich. From what I have seen, the stock setting errors on the rich side
of max power. Expect that you will need to reduce pressure to lean it a
little from stock. There are formulas which will give you the percentage
change in fuel flow vs pressure change. I can try to dig out the formulas if
you want. The way you would set it on the dyno would be to start at the stock
setting and make about 3 runs to get an average. Then richen the mixture
about 2 or 3 percent using the formula to figure what that pressure change
would be. Make 3 more runs and see what the result is. If power goes down,
then you know you were too rich to start with so then reduce fuel flow by a
couple percent from the stock pressure and try again. You keep doing this
until you can't get any more gain. It's like changing jets on a carb and
checking power. It takes some analysis of the dyno runs and jotting down the
effects of each pressure change so it will be easier and you will use less
dyno time if you have a helper. You always start by going rich so if it
happened to be lean you won't go even leaner and maybe damage something. If
you have made some mods like a different exhaust, don't expect that you will
find a pressure setting that will give the max power throughout the rpm
range. It will be a compromise, and if you have to leave it too rich at some
rpms to get max power at some other rpm, leave it rich at the top end.
When setting the mixture with the Dastek piggy back computer, I had to make
the mixture richer at the bottom, leave it alone in the middle, and lean it
at the top to get best power across the whole range.
I recently put my car back to stock exhaust and stock chip to take baseline
stock hp/tq readings. I was on the dyno Wednesday and noted on my mixture
meter that it was pretty rich all across the rpm range. I had the FPR set for
stock pressure, and I may have picked up a few hp by reducing pressure.
I have my mix meter and fuel pressure gauge permanently mounted in the car or
you could borrow them. Maybe someone else has a set you could use. I'll have
a look at my old mixture meter. Maybe the reason it quit wasn't too drastic
and you could use that one.
Louie
