Overrun valve on flapper system

[deetes]

Just a small question. Does this valve serve any vital purpose? The reason I ask is that I converted my 390 to Megasquirt thus doing away with the AFM. I also took the oportunity to repostion the air filter to the back of the engine compartment, ala SEAC(well some of them)as this gives a straight run to the plenum. On overun, even when just revving the engine, there's a loud moan coming from the inlet. This stops as soon as the throttle is cracked open. Could this be caused by the overrun valve fluctuating and could I get rid of the valve without causing any major problems?

Picture of the current inlet deal.
Any ideas?

Edited by deetes on Wednesday 25th July 10:27

[adam quantrill]

I wonder if that pipe is just the right length to set up some sort of resonance. With the throttle closed it would be about 2 foot long? Resonating at about 200Hz (half wave). Try different length pipes to see if the pitch changes.

What's that thingamyjig just behind the filter - a temp sensor?

You coming to BBWF (or any others with MegaSquirt?) - I'd like to take a look at this.

Edited by adam quantrill on Wednesday 25th July 12:37

[GreenV8S]

I think it improves emissions by stopping the engine from developing excessive manifold depression on overrun. Obviously you'll have to keep it, just think of the millions of children who'll die due to global warming if you don't.

[deetes]

adam quantrill said:

I wonder if that pipe is just the right length to set up some sort of resonance. With the throttle closed it would be about 2 foot long? Resonating at about 200Hz (half wave). Try different length pipes to see if the pitch changes.

What's that thingamyjig just behind the filter - a temp sensor?

You coming to BBWF (or any others with MegaSquirt?) - I'd like to take a look at this.

Edited by adam quantrill on Wednesday 25th July 12:37

Had a shorter inlet hose on before this and it still did it.

Yep that's the air temp sensor.

Afraid I can't make the BBWF. Enjoy yourselves though. Not too much beer.

[deetes]

GreenV8S said:

I think it improves emissions by stopping the engine from developing excessive manifold depression on overrun. Obviously you'll have to keep it, just think of the millions of children who'll die due to global warming if you don't.

Yeh, wouldn't want the Eco Nazi's adding Wedges to their list of taboo posessions, large 4x4's and patio heaters to name but a few.

[350zwelgje]

That valve is adjustable. You can find a description in the wedge bible how to set it up best. This could minimise the noise or even eliminate it (don't have much of that noise on my standard 350i).
I would not ditch it, as it should help the RV8 to lower the revs more quickly. Eliminating it, could perhaps make the engine take for 'ages' to go back to lower revs/idle... Think it also helps to have better engine braking, but this probably is linked to losing revs as well.

Rob

[TVRleigh]

hi Deetes,

So you finaly installed the MS.

How do you find it. also did you use new injectors or keep the old low voltage resistor pack ones.

[tempus]

Hi,does it do it when the engine is warm or just when its cold?iwould suspect a bit of muck in theoverun valve have you gone onto jag inj. or still on rover?Tempus

[deetes]

Thanks for all the replys.

Didn`t realise this valve was adjustable. I`ll have to have a bash at that.

The MS was quite easy to instal and it fired up on the first turn of the key. Setting it up was a bit of hassle, as I could never get a hold of the guy I bought it from to bounce ideas off him. I ended up taking it to a rolling road to get a half decent map for the fuel. There`s still a couple of places where it hesitates on and off the throttle but I,m going to go back to the rolling road to sort that out.

Most of the fueling issues could probably have been sorted out easily if I`d gone for a wide band Lambda sensor, unfortunately I went for a narrow band one, ah well!

This winter I hope to convert to wasted spark ignition and let the MS run that as well. Then it`s goodbye dizzy. Need a plug for the dizzy that will still drive the oil pump.

Regarding the injectors. They`re as per standard, including the resistor pack.

[TVRleigh]

Sounds an iteresting system, could you not change the style of oil pump, that don't run off the dizy. as the currect set-up has allways been a week point.

How does the BHP compare to the old EFI.

Could MS work ok in a RV8 race car.

[GreenV8S]

deetes said:

Need a plug for the dizzy that will still drive the oil pump.

It's possible to cut the top off a dizzy, but rather a lot of work for no real gain. You might just as well take the cap and rotor arm off and either leave the dust shield exposed, or jam a suitable plastic container over it to hide it. Changing from pre-serp to intermediate/serp front end will take a lot of time and money.