Thinking of removing bailey Dump valve

[The Baron]

Hi,

May sound like a daft question but i cant seem to get a 100% answer online so i thought i would ask the experts.

Will removing the dump valve have any impact on the set up? Scoff has very kindly set this up a few times (WIth the dump valve on) and i am very happy with how the car is running but the dump valve sound is starting to p1ss me off. I would happinly just remove this but want to make sure that it;

a) Wont cause any issues with set up - I can't see why it would just wanted confirmation
b) Wont cause the turbo any issues?

Thanks in advance

Dan

[Trevhib]

If you take it off you'll be back to the way Renault sold the car.

It won't affect your set-up.

Whether it has an affect on the turbo has been the root cause for many an argument and disagreement on this site in years past. The side that generally won were those that said it had no affect.

If you no longer like the sound, ditch it. It's one less thing to go wrong, and if it's a piston valve type, it should have never been on the car in the first place.

[R5MJH]

block it off matey if you got a air filter not box you will get a bit of compressor surge that sounds better than the dump valve anywayz

[Ian S]

Manufacturers used to, or do, fit them for longevity. When Renault rallied the 5GTT they had to change the turbo every day or so. Higher boost, harsher usage, just like users of 'boosted' 5's give (gave) them.

The dump valve allows the turbo to slow a bit more gradually than a sudden stall when the throttle is closed at full boost. Probably avoiding a pressure peak.

I had a close loop one originally for the quietness. Then a double piston because they're the best as they keep some pressure instead of venting it all, faster throttle response and spool up from low or off boost.

I use the noise to bring my presence to the attention of slow moving cars I wanted to overtake. Hiss it a few times; they tended to get the message.

Renault originally supplied a low boost engine, 10psi or so before the carb. At 24 psi (manifold) of boost, which I had, a dump valve may be helping the turbo last longer.

If you have the rubbish diaphragm type, or single piston, you might find the car a bit more lively without it.

As far as Scoffs set up, you might have some low boost pressure without it at 'off boost' where you have none with a diaphragm or single piston, so that may mean a little bit more gas flow for the throttle position.

[Trevhib]

It should be noted that when rallying Renault weren't changing the turbo every day due to a lack of a dump valve and if they'd fitted one they'd have still been changing the turbo every day. Lol.

Modern manufacturers fit recirculating dump valves for efficiency as much as anything.

[R5 WRM]

I took mine off a long time ago and my turbo is still in great condition.

It still makes the same kind of noise without it, only better in my opinion! I am on standard turbo with 14 psi and running the cup mod. I also have forge front mount, the turbo is very vocal 😆

[scratcher]

I love this topic!

A turbo won't stall. They spin at thousands of RPM.
The chatter sound is the fins cutting the air, like if you blow into a fan, not the turbo stalling.
Look up some videos on YouTube

[Alex]

You'll have no issues if you remove it and won't notice ahy performace difference. I've done many track days on a very old T2/T25 turbo running at least 15psi @ the manifold and it's still going strong.

[Ian S]

A turbo won't stall. They spin at thousands of RPM.

Up to 200,000. When the throttle plate is shut suddenly this causes a pressure peak and apparently a supersonic pressure front that bashes back and forth between throttle plate and compressor.

The chatter sound is the fins cutting the air, like if you blow into a fan, not the turbo stalling.

Do you mean cavitation due to the pressure differential across the compressor fins?

On my carb, we cut away one side of the throttle plate securing shaft, so as to increase the cross sectional area through it and therefore reduce restriction by something like a third. Over a couple of years the remaining part of the shaft bent and jammed more and more into the carb. I can only presume it was the pressure peak that was doing that as there's very little resistance offered by the injection pump.

I was on 24psi with a big T28 compressor and shaft which has a fair bit more inertia than a T2.

[Ian S]

If I've done the numbers correctly,

The area of the throttle spindle is about 800 sq mm.

1 sq inch is about 650 sq mm.

So 24psi (manifold) of boost is exerting about 30lbs of force on the throttle plate and it's supporting shaft when the throttle is suddenly shut.

I had a double piston dump valve and it still bent; if this pressure was the cause and not something else.

The compressor is only making that sound after the throttle is shut and the pressure is having to push back past the still spinning compressor. That 24lbs of pressure in the boost hose is having to go somewhere, so yes it's going to have a braking effect on the spinning compressor. I don't have any data on it but I expect the exhaust manifold might briefly go into vacuum depending of the inertia and rate of pressure loss from the exhaust manifold.

Never mind you tube, these are the laws of physics.

I would say that if it's a single piston or diaphragm dump valve that you remove, you may well notice an improved performance difference at slow speed with off boost get up and go and spool up time. If it's a double piston then less so or not so. I did with diaphragm to double piston, but I was very perceptive to small changes and I know some people are not.

Also, with my first DV, the single whatever re-circulator, it did keep the boost up during rapid gear changes, where it would drop a bit without it. The exhaust was not all that free flowing I think, and maybe the turbo a bit clogged. When they were put right and I had to remove it as the boost hose split, that effect was there anyway, ie, it wasn't dropping for that moment.

[Trevhib]

Interesting thoughts.

From a strictly performance perspective, if you have a non-recirc DV (of whichever type, double or otherwise), you're letting that pressure out every time you close the throttle. Meaning (I assume), that pressure has to be built up again when the throttle is reopened (taking a small amount of time). If you don't have a DV, that pressure remains in the boost circuit, so when you reopen the throttle you're not losing that time I guess. So it seems a DV allows a quicker turbo spool after a gear change but coming on-boost is then subject to some delay due to a loss of pressure. Is that right? How significant is this, on balance?

[Ian S]

Personally I didn't like that slight decrease in spool up. The car was more eager 'off boost' with no DV. The turbo might always be spinning a bit, even at idle. So 'off boost' is really on low boost and making a worthwhile improvement to what is otherwise a very under torqued low compression engine.

IIRC, and it's a long time now, the double piston, that very soon replaced the single piston, kept maybe 6psi in the boost hose that had been being vented by the diaphragm (or single piston) type. The double only dumped from above 6psi, or so.


Reading my above post again, I realised two errors:
One is that the boost in not manifold, 24psi there would be at least 26 before the carb, in fact at one point my two boost gauges showed a 7 psi drop across the carb. So that would be more then 30psi on the throttle plate.
And then there is the moving column of air, at 70 litres per second or minute (can't remember! ), that has mass and inertia of it's own, which adds further 'weight' onto the throttle plate until it's been stopped. Maybe that's where the wave front comes from; the air column squashes up hard against the throttle plate then, once the momentum is stopped, expands back with a 'bang'.