Saabscene Saab Forum - Saab Technical Information Resource banner

1 - 12 of 12 Posts

·
Registered
Joined
·
191 Posts
Discussion Starter #1
Hi All,

Next Saturday, some tuning will be done to my Classic 900 T16v
. One of the parts is a RRFPR from speedparts. This is needed to get the extra fuel in the engine, so I am told. An other option was to 'modify' the excisting FPR to deliver 3bar pressure.
Now I have been looking to the specs of my car and it has a Lucas Fuel Injection system, so the FPR I got at this moment already produces 3 bar pressure. Do I really need the RRFPR ?

Thing is, I have read that having a RRFPR combined with standard injectors, the very same injectors might get damaged.

any opinions / facts to share?
Thanx,

Tijn
[spelling ]
 

·
Registered
Joined
·
14,305 Posts
There are various points of view about RRFPRs and their effectiveness with adaptive/intelligent fuelling systems. Some say they make it hard for the ECU to adapt and fuel properly, as the fuel pressure is not linearly varying with manifold pressure. This might not apply however to the C900 which relies on an AMM.

I don't see any reason why one should damage your injectors. You may be better though opting for an adjustable fixed pressure regulator so you can optimise the performance.

Some folk have found that the RRPFRs base pressure drifts over time and needs re-adjusting, and thus opt to fit a pressure gauge with it so idle pressure can be checked.

HTH
 

·
Registered
Joined
·
161 Posts
I started with an FSE RRFPR, on ex LPT Aero, my unit was fitted and setup by a well known saab tuning house in Notts who like to use them.

Even with a IC and a tweaked wastegate actuator i didnt notice a difference. I did notice an annoying squeeling (especially when cold), and idle problems. Im since told the only way to get those jobs to seat correctly is to give them a smack with a mallet, uhm?

Anyhow, on puting my car and cheque book through an intensive grilling by Abbott the item was replaced with a Bosch fixed 3.3 Bar FPR! Which matched the remapped fuel ECU nicely- no problems.

Thats my knowledge on the matter anyhow. Im also told, you cant run a RRFPR with an remapped fuel ECU, I did for a bit before i did the full upgrades and cant say i had any probles other than those associated with the afforementioned problems.

Also, as a tuning tip. I found one of the most succesful sole upgrade was the remapped/upgrade fuel ECU coupled with wastegate! Obviously you need some sort of IC but on a T16S you should have all this, yet having said that you have an APC so i guess you wont appreciate the full gain as it will be governed on those parameters.
But if you had an LPT car, then its a great tune-up
 

·
Registered
Joined
·
54 Posts
I really don't like RRFPR's. Even using some of the better makes you can still run into problems especialy on some later jap cars (obviously not applicable here).

The FSE unit (available under lots of names) is pretty dire, they don't tend to hold a base pressure and fixings vibrate loose and they begin to leak fuel amongst other things.

A fixed unit along with a remapped fuel ECU or signal modifier between the AMM and ECU is a much better way of doing things.

Cheers
Matt
 

·
Registered
Joined
·
191 Posts
Discussion Starter #5
Too late ! It is already fitted. Oh well we will eventually find out what it does. So far I do have got a big grin on my face, having 0.9 / 1.1 bar turbo pressure and 4 bar Fuel pressure.

Thanx for the advice

If anything odd happens regarding the RRFPR I will post it here.

Tijn
 

·
Registered
Joined
·
4,215 Posts
my rrfpr on my t16 lasted a couple of thousand miles until the "petrol in " connector fractured


I would watch it like a hawk and do not overtighten !!
 

·
Registered
Joined
·
661 Posts
I ran one for a few thousand miles but recently took it off and sold it!!,
Apart from a minor fuel leak from the diaphram and a couple of occasions when fuel pressure creeped up it wasnt too bad however its always in the back of your mind when driving the car hard is it going to fail

Now running a 3 bar reg.....

Pete.
 

·
Registered
Joined
·
191 Posts
Discussion Starter #8
Hmmm....so it might be failing me after a couple of thousand miles? I have got a standard FPR on it as well. Delivering 3 bar. Now I am told that is not sufficient for a 1 bar-ish boost. So that is why I purchased this RRFPR. Now I am confused.. .
 

·
Registered
Joined
·
1,676 Posts
Pete is running bigger injector's so he's sorted on the WOT front. This means, however, that at idle and light loads he's running a bit too rich because the bigger injectors will not only provide more fuel when on full boost, but all across the board. This needs to be offset by inserting a resistor in the air mass meter output wire but I think that will only work for CO at idle.

Therefore I'd say in principle an RRFPR is a desirable thing when running a standard ECU and bigger injectors, though, as the 'rising' rate of 1.7:1 does work the other way, too - i.e. if you have a fixed 3.0 bar regulator then fuel pressure will be about 2.4 bar at idle (when the manifold depression is ca. -0.6 bar on a healthy engine), and 4.0 bar under full boost. If you have a rising rate fuel pressure regulator with a 1.7:1 rate set at 3.0 bar you will have 3.0 - (1.7 x 0.6) = ~2.0 bar at idle, and 3.0 + (1.7 x 1) bar = 4,7 bar fuel pressure at 1.0 bar boost.

So then at vacuum (idle/low load) the 'rising'rate will actually a 'falling' rate which to an extent counteracts the higher flow of the big injectors so the actual fuel delivery at idle will be closer to what it should be than with a fixed rate fpr.

In prectice however - yes, rrfpr's do tend to have some quirks. Base pressure tends to wander (mine settled down after a month or so), I did have a fuel leak on re-install after a rebuild because the bolts were loose and -worse- I suspect the rise and fall in rate is not dependable and repeatable anymore. I'll have to investigate this further before casting a verdict.

All I know Felix's Trent/FSE rrfpr had the same fuel leak problem at one point, and wandered off to show a base prssure of 1.2 bar at another because it had not been re-checked a couple of hundred miles after install, which the instructions call for. It was rock solid between re-setting it at 3.2 bar and checking it a year later, though.
 
1 - 12 of 12 Posts
Top