MPG with 3.5 FPR vs. Stock FPR

[Robin-535im]

I've been comparing my actual MPG (Dividing the miles travelled by the gallons used) to the OBC calculation, and it's been between 0% - 4% off... much closer than I expected since I've got a 3.5 bar FPR and I assumed the computer would be calculating less consumption due to the shorter pulse length.

Anyone looked at this before with their car? I had assumed that the OBC MPG was 10% - 20% optimistic.. but it looks very close considering the likely measurement error. I've only done this for 4 tanks now, but 0%, 1.6%, 2.3% and 4.2% were my calculated differences...

[willobmw]

On a recent trip in the 535i, I averaged (80mph) 23.5 mpg on the OBC and 24.5 mpg actual or a little more than 4%. Sounds like you're doing pretty good. What kind of MPGs are you getting? Don't you have 19.4 lb injectors also? The M30 may be a dinosaur, But it can be pretty efficient also.
Willobmw

[Robin-535im]

On a recent trip in the 535i, I averaged (80mph) 23.5 mpg on the OBC and 24.5 mpg actual or a little more than 4%. Sounds like you're doing pretty good. What kind of MPGs are you getting? Don't you have 19.4 lb injectors also? The M30 may be a dinosaur, But it can be pretty efficient also.
Willobmw

I've got the mustang 19 lb injectors and a 3.5 bar FPR off a Porche 944.

I'll get 25 mpg if I baby it or 19 if I goose it... so I usually average around 18 or so :) .

What's your setup? 24.5 is pretty good at that speed.

[Bill R.]

stock injectors combined with the 3.5 press regulator , you might be back to the same flow as stock, which would explain why your mileage hasn't changed much.




I've been comparing my actual MPG (Dividing the miles travelled by the gallons used) to the OBC calculation, and it's been between 0% - 4% off... much closer than I expected since I've got a 3.5 bar FPR and I assumed the computer would be calculating less consumption due to the shorter pulse length.

Anyone looked at this before with their car? I had assumed that the OBC MPG was 10% - 20% optimistic.. but it looks very close considering the likely measurement error. I've only done this for 4 tanks now, but 0%, 1.6%, 2.3% and 4.2% were my calculated differences...

[willobmw]

Injectors stock. I am running a E.A.T. chip, ITB foam filter in the box and Eisenmann exhaust. I'm considering the Mustang Injectors at replacement time.
Willobmw

[DeefMan]

Is 3.5 Bar fuel pressure regulator a bit much with 19lb mustang injectors, I thought mustang injectors are rated 200cc/min vs. stock 535i injectors at 185cc/min??

So are the fuel mileage improvements by others possibly from just using newer injectors & fpr, vs. the older worn out ones??

Of course the computer can adjust to the higher flow of the bigger injectors and higher fpr, but at wide open throttle, will it create an overly rich condition with too much fuel?

Pricewise a replacement stock 3.0 bar FPR is actually cheaper than a 3.5 Bar FPR at autohausaz.. So should I go with a 3.0 Bar or 3.5 Bar FPR to go with 19lb Mustang Injectors for my 535i?

[Robin-535im]

Is 3.5 Bar fuel pressure regulator a bit much with 19lb mustang injectors, I thought mustang injectors are rated 200cc/min vs. stock 535i injectors at 185cc/min??
I don't know, but IIRC Genphreak was looking into injectors quite a bit a while back, search the archives and you might find some interesting info...


So are the fuel mileage improvements by others possibly from just using newer injectors & fpr, vs. the older worn out ones??
Don't know. Newer should flow better / more balanced than older ones in theory, but I don't think BMW has a chronic problem with them in general.



Of course the computer can adjust to the higher flow of the bigger injectors and higher fpr, but at wide open throttle, will it create an overly rich condition with too much fuel? I don't think so, as long as it's linear (or similarly non-linear as the stock ones) the WOT map should scale the same.


Pricewise a replacement stock 3.0 bar FPR is actually cheaper than a 3.5 Bar FPR at autohausaz.. So should I go with a 3.0 Bar or 3.5 Bar FPR to go with 19lb Mustang Injectors for my 535i?
Up to you - I got the 3.5 just for extra capacity... didn't see any increase in top end per se, but others have noticed a faster throttle off idle perhaps.

[DeefMan]

Up to you - I got the 3.5 just for extra capacity... didn't see any increase in top end per se, but others have noticed a faster throttle off idle perhaps.
Searching thru the archives it seemed that most people went with the 3.5 bar FPR just cuz it was both bolt-on and cheaper than a stock replacement..

But.. at autohausaz, the stock replacement is cheaper than 3.5 bar fpr.. so I'm wondering if just replacing my almost 200k fpr with another stock 3.0 bar should be fine...

3bar vs. 3.5 bar is only about 7psi of pressure difference.. so it's probably not that big of a deal, either way..

[mholbrook]

Originally, a couple of years ago, I think I was one of the first to try the 3.5 bar FPR from the 944S with the #19 injectors. As Bill R correctly pointed out, at idle the #19 injectors do not flow as much as the stock injectors. This cause a stumble just off idle with the 3.0 FPR and #19 injectors. The 3.5 bar FPR corrected this stumble and allowed a 7psi boost in FPR.

In California you have to pass a visual inspection at smog. An adjustable FPR just won't pass a visual unless you have a hidden mounting.

In my opinion, I felt there was a seat of the pants increase in power with the #19 injectors and the 3.5bar FPR. I bought my injectors used for about $20 and I think the FPR was about $75 at BMA. I guess to me it was worth a C-note to play around and experiment with it.

I don't recall there being any difference in fuel mileage. With regard to my previous 535i, the three things that made the biggest difference were in this order:

1. 3:64 LSD over 3:46 open differential
2. Conforti Chip
3. #19 injectors with 3.5 bar 944S FPR
4. No, I did not have a K&N filter, I believe in the stock filters.

Your mileage may differ.

[genphreak]

Now that is very interesting... I have Type III 19lb injectors, stock FPR and cam, a more open exhaust. With stock chip I get a stumble at the lights unless I go very smooth on the gas. Also, sometimes the motor doesn't start perfectly in high heat 2-10 minutes after shutdown. (ie takes a hard-start), but that could be the ICV. Everything else is new and it runs just great.

Here's the chart I compiled (http://secure.picturesystems.com/images/535/M30InjectorsR1.0.pdf) on other comparable injectors (as Robin mentioned earlier) a while ago.... I had trouble posting it at the time, so the original link may be dead by now.

:) Nick

[DeefMan]

OK, based on that chart, stock e34 M30 injectors are 20.35lb injectors, so 19lb mustang injectors flow less than stock injectors... unless the lb ratings aren't all with a standard psi pressure rate...

Previously I was only able to find comparisons of flow rates for e28 m30 injectors vs. 19lb mustang injectors..

Based on some googling.. supposedly the lb rating is supposed to be rated with standard 3 bar or 43.5 psi.. so a mustang 19lb injector running at 3.5 bar will produce 20.52 lb/hr (sqrt 50.75psi (3.5bar) / sqrt 43.5psi (3bar) * 19.00), which yields 215.46 cc/min (20.52 lb/hr x 10.5)

stock setup of 20.35lb injectors at 3bar yields 213.67 cc/min (20.35lb x 10.5)

but.. using 19lb stock injectors with stock 3bar fpr yields 199.5cc/min (19x10.5), which is a bit less fuel.

so based on these calcs (assuming that mustang injectors are rated exactly 19lbs and not 19.4lb as type 3 might be) 19lb + 3.5 bar yields just a little more fuel flow than stock setup, but 19lb + 3 bar yields quite a bit less..

Are these numbers and calculations correct? did I get anything wrong?

[genphreak]

That's seems like what I worked out before... (without checking your figures against my formulae) but with my Megasquirt I'll be able to 'cycle them up' just a tad.

I think the moral of this effort is to stick with stock fellows... I think my ICV is working fine, so the occasional stumble off the line might well be these injectors. :) Nick