Andy Tang

iTrader: (3)

Have you tried your local dealer? I think they can supply 0.9 and 1.2mm but I could be wrong!

Andy

spider

iTrader: (1)

OK, I hold my hands up in total ignorance - what's this restrictor thing all about then? I presume it's something to do with airflow so it's MAF or turbo related?

There, I've asked the question that was on everyone's lips so you don't need to show your own ignorance and can say "I knew that all along!" Cheers,
Steve

Richard Curtis

Has anyone got or can anyone make a 1mm restrictor for fitting to my MY97?

There must be a huge market for probably the cheapest way to increase power.

If anyone has a access to a machine shop and could make a set of these things e.g. 0.9, 1 and 1.1mm for around £30 they'd be onto a winner (probably cost pennies to make).

Rich Curtis

Spider,

As far as I understand (which is not very much), the restrictor is a small brass rod about 4mm in diameter with a hole running through it which sits midway in one of the rubber hoses around by the actuator (you can actually find it by sqeezing the hose).

The diameter of the hole running through it relates to the maximum boost that the actuator allows before opening the wastegate (i'm just guessing here so please no flames ). The smaller the hole the higher the boost. Increasing the size of the hole is sometimes used to cure overboost caused by other mods.

For my UK MY97 i think the standard size is 1.2mm. I've been told that 1mm should be ok with a standard ecu without running into problems of fuel shutoff due to overboost.

It's a very cheap way of getting more power and is more insurance friendly than many other more obvious mods.

scoobystutoo

does that apply to a 94 WRX as well?
thanks STU..

Richard Curtis

I think the general principle still applies - what the restrictor size is on a WRX and where it's positioned I haven't a clue.

Do a search on this site - there should be loads of info.

All else fails post an enquiry in the drivetain section - plenty of expert advice there will probably know the details.

johnwiz

iTrader: (26)

Richard,you could email Stan Smith & ask him nicely about this mod--Stan.Chris@tesco.net apparently a P1 restrictor is 0.8 mm & a 97/98 UK one is 1.2mm.Part number for 0.8mm is 22326AA260 (orifice - 0.8) cost £2.68 incl VAT.
BE WARNED --Stan's car (UK 98 with PPP)hit 21psi with the 0.8 restricor drilled out to 1mm --very advisable to start big & proceed
slowly upwards.
Cheers,John

johnwiz

iTrader: (26)

Richard,forgot to mention Stan has now reverted to the standard restrictor until he gets both a knock sensor & boost gauge fitted.He felt the 1mm orifice was causing detonation.-John

farmer joe

have to admit but way back in my dim and distant past( about a year ago!) i'd heard a little bit of info. about this. apparantly i think earlier model turbos/wrx's (i.e pre- 96??) work dif. in that increasing the hole diam. increases boost. exact opposite than for 97 on. but i may be wrong( prob. get flamed for this) anyway, i totally removed the restrictor in my pre 96MY wrx and went for a spin.all i can say is it boosted way more than normal and i felt it biuld boost way quicker too. i'm not sure what the peak was but i caught sight of it over 1.1 bar ... so i quickly put the restrictor back where i found it.

Danny Fisher

Andy, I was getting boost cut at 21 psi. I think it relates to the restrictor your running.

Dan

Richard Curtis

Thanks John - I'll drop Stan a mail and try and order a few of the 0.8mm ones to have machined.

btw.
I was having a chat to a dealer mechanic about this a few weeks ago - on the QT he said to try reducing it until you get problems with fuel cut out (which I was told is usually a very repeatable limit to 0.1 bar)- can't remember what he said the actual boost limit the fuel cut was set at but i'm sure it was not nearly as high as 21PSI.

Maybe the PPP ecu changes this? I'll have a search and see what I find.
cheers

Andy Tang

iTrader: (3)

I thought the fuel cut out happened at 18psi!

DARREN

Would the 0.8mm restictor thats in a P1 fit my 1996 STi????????????????????

Cheers
Darren

john banks

I run a MY00 PPP with downpipe. The comments about earlier Scoobs behaving opposite to later ones is familiar.

I run 1.35mm and hit up to 18PSI and it holds at 16.5PSI. This is with PPP and downpipe. On the original 1.2mm restrictor it hits over 20PSI and does not get fuel cut out but then undershoots down to 14 and oscillates up and down when on boost. It drives craply. On MY00 PPP any peak higher than 18PSI and it never holds boost and wavers around all over the place and is slower overall. The best compromise is where you get a peak as near to 18PSI as possible with a small leeway for high octane/cold/damp etc which will give quicker spool ups. IIRC, the figure is supposed to be similar for non-PPP therefore allowing a higher peak-held difference without affecting smoothness.

These restrictors allow a decent peak boost which can be sustained for up to two seconds, but with my experiments they do not increase held boost from standard unless your restrictor is not allowing the boost to peak - ie it just meanders up to a held figure. For example if I put a 1.5mm restrictor in the peak and held boost is 14PSI. But however low I go, it never holds much more than 16.5-17PSI. If I remove the restrictor completely I get peak/held of 10PSI.

You can fill in the hole in the restrictor with solder and then drill it. Maplin sell drill kits with a range of drills in 0.1mm or smaller steps.

John Stevenson tried a brass screw off which he cut off the head and thread - try and get something that will fit the pipe nicely - take your restrictor's measurements first. Then make a set with a range of holes. It works well, but the change in boost for only a 0.1mm change in hole size can be great making it an imprecise art which requires upwards of 10-15 runs to know it is right! My current restrictor is an original filled in with solder and redrilled. I am awaiting a valve which will allow adjustments instead of using a restrictor.

At present, I get smooth boost in all gears except in 5th where the boost can hit 18 or so and hold for a few seconds which feels great and then for 1/2sec it drops to 14 before going up again to 18 and then falling towards the top end. This is at highly illegal speeds for the public road so doesn't bother me as I won't be flooring it in 5th at 3500rpm and holding until 4500rpm where there is the drop to 14PSI.

Also, you need to do a run for a reasonable few miles after a restrictor change to get the feel for the boost. For example, my latest restrictor when I first went out with a warm engine only went to 14 PSI but a few miles up the road was peaking to over 17PSI. Also the system can even be sensitive to the position of the restrictor in the pipe!

I would advise caution with trying to extract more, as a peak of boost could lead to detonation, especially if there is fuel cut off which would momentarily run things lean. Certainly don't go above 17-18PSI peaks if my experience on MY00 PPP is anything to go by, and unless your held boost is low I don't think you'll improve your performance that much - especially if the boost wavers around all over the place.

Edited to say - I only got into this to actually stop the overboosting, but in so doing the car is more driveable and the overall performance better as it holds a good health boost and is predicatable and repeatable.

[This message has been edited by john banks (edited 06 October 2001).]