recirculation dump valve advice needed.

**Waynesworld** · 28-04-2011, 06:02 PM

Ok even though I love the sound my dump valve makes Ive decided after doing abit of research to go for a recirculation type instead.
The reasons being my car shows the classic signs of the dump valve destroying my engine!!
How I here you say well I will try and explain if you dont already know.
A dump valve or blow off valve vents unused boost preasure to atmoshere this in turn makes your MAF sensor think that the air has been sent into the engine which inturn ups the mixture accordingly to compensate. But because the air isnt there your mixture runs lean and the unburnt fuel goes into your exhaust system and thats why you may here the odd pop and bang. Which Ive always heard since I bought the car.
Thank the heavens I have a good solid sti forged engine or my car engine would be scap metal by now.
So my question is do I go for a standard valve or is there a more performance alternative.

**colin41** · 28-04-2011, 06:21 PM

Originally Posted by Waynesworld

Ok even though I love the sound my dump valve makes Ive decided after doing abit of research to go for a recirculation type instead.
The reasons being my car shows the classic signs of the dump valve destroying my engine!!
How I here you say well I will try and explain if you dont already know.
A dump valve or blow off valve vents unused boost preasure to atmoshere this in turn makes your MAF sensor think that the air has been sent into the engine which inturn ups the mixture accordingly to compensate. But because the air isnt there your mixture runs lean and the unburnt fuel goes into your exhaust system and thats why you may here the odd pop and bang. Which Ive always heard since I bought the car.
Thank the heavens I have a good solid sti forged engine or my car engine would be scap metal by now.
So my question is do I go for a standard valve or is there a more performance alternative.

if the car ups the fueling and the air isnt there the car will run rich but your o2 sensor should pick that up and lean the mixture off again.

**Big Red T** · 28-04-2011, 06:40 PM

The pops and bangs are not caused by the dump valve alone. The exhaust you have on and decat and the air intake and front mount and the jap ecu are all contributing to the pops. As Colin said if your running rich the o2sensor should be backing this off a bit to compensate. Some believe that the dump helps to stop the turbo stalling a bit and may cause a slight hesitant gearchange but I'm sure it's unlikely to kill your engine. As for you r good solid forged sti engine , it'll not matter a bit how strong if it's not fuelling correctly . As I said in a previous thread you need to get them on the rollers or datalogged on the move to see how their fuelling properly and if any knock present. But yes I agree you've seen the light on removing the chav valve lol.

**octanejunky** · 28-04-2011, 07:04 PM

Hahahaha! Who did the forged build for ya? Dont beleive everything ya read on tinternet then!

**Shambles** · 28-04-2011, 07:25 PM

Standard Subaru IMO - prob developed far more than any aftermarket item.

**Waynesworld** · 28-04-2011, 08:54 PM

Originally Posted by Shambles

Standard Subaru IMO - prob developed far more than any aftermarket item.

That's it and it's very true. It us a forged engine in an Sti. I thought that was comon knowledge. The only thing is you can get better forged internals from after Market manufacturers. Well I must say in previous threads I have said things that I am constantly learning that I'm not correct lol. But I'm not sure about the O2 sensor correcting the fueling but I do believe the bov type valve doesn't help and you are using more fuel and wasting boost preasure. So any ideas what to go for? Standard or aftermarket ??

**Gambit** · 28-04-2011, 08:59 PM

STI only has forged pistons everything else is same as WRX

you cant run a std recirc as you have a FMIC though

**scoobyride** · 28-04-2011, 09:03 PM

The standard dv will always do a better job wayne but you cant fit that now with the fmic. Also chum the early sti engine has no forged internals whatsoever. Any sign of that never came into sti7 on etc

**Shambles** · 28-04-2011, 09:05 PM

Don't think the narrowband 02 responds quickly enough to make up for overfuelling with a bov

**Stu** · 28-04-2011, 09:12 PM

Ok you can run a recirc Valve on a FMIC as im doing it as is Nath and a few others, its just a bit more plumbing.

The sti Engines have forged pistons from 94 onwards, the 97 wrx also runs forged pistons dependant on the engine code.

Waynes car is running an original V1 sti closed deck block, forged pistons and handbuilt at STI and blueprinted.

However no forged piston can withstand prolonged lean mixture they melt, or if the engine is detting that can also destroy a piston.

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**scoobyride** · 28-04-2011, 09:22 PM

I stand corrected

Wayne you must have had all these problems before the fmic was added or did u have the engine out on the sly

**octanejunky** · 28-04-2011, 09:44 PM

If standard pistons r forged, how come there so s h i t then? Different metal? Surely the rod is the week point anyhow!? Stain!

**Stu** · 28-04-2011, 09:57 PM

They are not that bad, the problem arises when people run JDM cars on the wrong fuel

Yes there will be different grades and various mixes of silicone within the metals used.

Classic rods are weak newage rods can take more due to better design, the cars get better as they evolve, however they seriously ****** up with the 2.5 engine lol. Piston design is flawed hence so many failures and they are alot more prone to head gasket failure than a 2.0 engine.

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**octanejunky** · 28-04-2011, 10:10 PM

O rite nice1 m8! R they not aluminium or something? Dont know y i think that like haha any1 for waffles?

**Stu** · 28-04-2011, 10:24 PM

Yes different grades of alloy Paul

Wayne, ive done it and others have done it and got away with it ie bolt on some choice mods, i got away with it as have others and the car didnt show any signs of running bad.

Its time for you to get the car looked at as has been said, a session with detcans and a wideband will highlight any fueling issues. OMA are only up the road from you and Michael has the gear to do it, whether he has the time is a different matter. If your still stuck at the end of the month JGM is over and he will be able to run AFR and Det check.

In the meantime i would check and double check what you have done and look for errors, compare the pipework against another car to ensure it mirrors. It could be the case you have fitted something incorrectly on reassembly.

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