Dump Valve vs Recirc?

[pinnacle]

OK, so if that is true Yellowshed, how is it you know this ? B) If the race car ( presume GT car ) is running more HP, how much HP are you running where you feel the BOV is warranted ? C) are you guys running stock, or up-rated turbos where then I could see the need for the valves. Even guys running stock cars / turbos on the track might consider it as at higher boost pressures the blow back can be quite strong when quickly getting off the throttle for cornering, and in the long term have issues with their turbos. Any word if the M400 will be running BOV's on it's uprated engine ?

Also, what was done on the race car to add the BOV's ? Any further fuel management components too ?

[joust]

YellowShed said:

It appears to be a common misconception, but Lee has never fitted dump valves to his cars. The noise you all love is all that air coming back past the compressors. Thankfully, the turbos are small enough that they don't appear to suffer adversely.

Amazing fact Trevor!

How on earth do you occassionally get the "psst..pst..pst..pst..pst..pst..pst" when you let off that sounds like a "flap" chattering away.

I'm facinated now how that happens, and scratching my head like mad! Help me out please?

J

[goodlife]

pinnacle said:

OK, so if that is true Yellowshed, how is it you know this ?

pinnacle - Yellowshed created the engine management systems for Noble!!

[kentviking]

well blow me if this isn't interesting stuff...but it's got me a little concerned...

Do I take it that the GTO3 sounds completely different to the 2.5...it's only I have driven the 2.5 twice over a year ago...and the intoxicating noise was half the reason I fell so in love with the car...how many cars do you know where the sound of decelerating (or lifting off) gives as much a grin as the sound of the engine under hard acceleration?

My question is...will I need to move the filters on my forthcoming GTC to replicate the whooshing sound I so enjoyed on my test drives (previously thought to be going through dump valves, and now educated otherwise)

thanks, morten

[m12_nathan]

It is still there on the 3 but as the air filters are further away from you (next to the intercooler) you have to listen harder.

[LaurenceFrost]

joust said:

YellowShed said: It appears to be a common misconception, but Lee has never fitted dump valves to his cars. The noise you all love is all that air coming back past the compressors. Thankfully, the turbos are small enough that they don't appear to suffer adversely. Amazing fact Trevor! How on earth do you occassionally get the "psst..pst..pst..pst..pst..pst..pst" when you let off that sounds like a "flap" chattering away. I'm facinated now how that happens, and scratching my head like mad! Help me out please? J

I know - It's the compressor stalling.

When you lift off, the air pressure has nowhere to go except backwards (as air will always try to uncompress itself).

The turbos will still be spinning extremely fast (probably about 80,000 rpm), but the compressed air will move back through them the wrong way and slow them down. This would not happen under acceleration, but there is no longer any exhaust gas driving the turbos as the throttle pedal is lifted.

This air slipping through the impeller blades the wrong way and back out of the compressor housing is what causes the fluttering sound that is usually blamed on the wastegate, but apparently has nothing to do with it.

YellowSheds fact also explains why there are often two chuffs when lifting off under part load. Because the pipes from the filters to the turbos are of unequal lengths, so this causes the delay in between chuffs.

It's great having an expert like YellowShed around .

[pinnacle]

But here is the point, as Lee / Rousch increases the HP more with larger turbo chargers and mapping changes, does it not make more sense to be fitting BOV's to protect the turbos ................. against the blow back pressures ? ! Yellowshed, please chime in

[mr2turbo300]

Don’t pretend to be an expert on this , but wouldn’t the following have made for a much better set up without much additional cost as OEM.
Fit roller bearing based turbo’s (gt25’s I think) (to help reduce the lag ), added a dump valve to prevent compressor stall and all the associated ill effects, and add an external waste gate to prevent the boost peaks that yellowshed described on the 340BHP moded 2.5 L’s. Then just upped the boast to something more at the top end flow of the turbo’s (haven’t researched these turbo’s thoroughly enough to know how close they are already). Given however that they run on 95 Octane fuel without any detonation, and the boast is only half what I run on the MR2, gut feeling is there must be scope for these to run at a higher boast without the air temperatures reaching dangerous points (even if they lose some efficiency).
As for the recirc or atmospheric debate, assuming that the electronics are capable of handling both properly, is there not an advantage to be gained by an atmospheric valve as the heated air from the turbo is not sent back into the system for the intercooler to cool back down (allowing for higher boast levels) ?
(Please be gentle in the rebukes – only my second posting)
Rob.

[JimNoble]

The rollcenntre race car is actually detuned compared to the road cars, due to the power:weight ratio requirements of the class they run it.(It's about 270bhp IIRC)...

Jim