rrfpr vs. 303 bar fixed [Archive] - SaabCentral Forums

: rrfpr vs. 303 bar fixed


muff
10th May 2002, 01:23 AM
Has anybody tried Abbott Racing's 3.3 bar fuel pressure regulator? They claim it's better than a RRFPR but i don't know if their full of *** or not.

Johann F
10th May 2002, 05:01 AM
They don't seem to like RRFPR's do they ( possibly because they need setting up to suit an individual car and also reseting for the first few 100 miles - fixed FPR's are fit and forget)! Any way here are my ramblings on the topic; I reckon it depends on your cars fuel system - if you have a lambda feedback then changes in fuel pressure (up to a certain point) will be accomodated during normal driving and the extra presure from each unit will help under hard acceleration and WOT when the systems go to open loop and are relying on pre set fuel maps. If you have an early (or most Euro specs up to about 1990) non lambda car then the fixed rate may be a bit too rich under normal conditions. Having said that 900T's always run better with a slightly richer than stock mixture. My preference is for the RRFPR for one very good reason - it's adjustable - you can change the base setting to suit your needs and engine characteristics. However if you set it too high at idle you go very rich in early boost and it will cause a flat spot - you also raise the top end boost fuel pressure to a very high level this will put a strain on the fuel lines and seals etc but more importantly they can actualy reduce fuel delivery as the fuel pressure is preventing the injectors from opening properly - in theory.Many tuners have seen this on A/F dyno charts - early rich and leanout at the top. However this is when people are usualy trying to get the RRFPR to do all the work of supplying extra fuel for very high boost - if you regard, as I do , these devices as a simple way of pepping up the feel of the car by slight enrichment then you can't go wrong. Now if you are running a late Euro spec car with the lucas FI system then it's slightly different again..... but that's another story.

Alex
10th May 2002, 12:08 PM
The Abbott fuel reg is also horrendously over priced, at something over 100+vat!! Malpassi (people who make FSE) also do an adjustable reg with a 1:1 ratio. I bought one a while back and it was around the 50 ish mark.

Eric van Spelde
10th May 2002, 03:31 PM
GBP 160 + VAT IIRC... lots of money for an item which is just the same construction- and materialwise as all other Bosch FPR's that can be pulled from any junkjard, only with a higher rating. I think olny Porsche used it as OE. They never have given a solid reason as why having a fixed, but higher, rate fpr would be better than one that gives the same amount of fuel on idle and bumps fuel pressure up when you nail the throttle. 'd say it's a bit like putting bigger injectors on without any means to compensate the richness at al points in the engine load rpm 'map' apart from WOT, high rpm. Just seems a stupid way to do things. Burn more fuel all the time (and prolly wash your cylinder bores with excess fuel) because you need more at a well-defined area of the fuel map. In other words: why defeat all the development work in your ECU just because you want extra fuel at the few procent of time you are actually -using- more than stock max boost. Mostly, you'll have changed very little to the engine that would alter its fueling need at idle/light load/low rpm's, so the fuel maps in the stock ECU are still perfectly valid.

The top-end leanness many have seen in dyno charts is from the LH ECU changing from fuel delivery calculated out of AMM input to a 'fixed' map from 4.5 or 5K rpm upwards, not high fuel pressure working against injector opening (which wouldnt make sense to me because LH injectors are elcectromagnetic devices to which it theoretically would not matter **** how high the fuel pressure they see is - unlike K-jet injectors they're triggered by a PWM signal from the ECU, not fuel pressure). This is why an additional injector controller is a good idea - you can 'fill in' the leanness at the top end without making things over-rich in the middle rpm band. And any fuel distribution issues of a 5th injectro placed updtream of the intake manifold are rendered non-critical by the high air velocities when you actually use it, which is only at high rpm and WOT. And you can always set up a second fuel rail in the inlet manifold if that's not enough...

But then again, Abbott's expertise is mainly mechanical/suspension, not engine management... :wink:

Happy Saabing,
Eric