Is it possible to seal the butterfly valves in the MEVI? I want to do this, because I think it will help cut down the turbulent air that gets caught up in the area right under the plates when in the closed position. And thus would help out the mid range loss.

Like I was saying I want to do this, but I'm unsure about how I'd go about doing it effectively. Does anyone have any suggestions?

 

That's an interesting question - when looking into TBs used as exhaust cutouts, there was mention of using a hi-temp red RTV to seal the butterfly completely. The thread is probably in All Motor, but not sure..

If you clean the bores around the butterflies with acetone and let dry a bit, then most any RTV / silicone adhesive would bond to the wall of the bore, I think. If high temps are not a concern, then a more conventional RTV could be used. I think if you put a little vaselene on the butterflies first, propped open the butterfly shaft all the way, washed the bores with acetone, applied a touch of RTV where the butterflies would touch the walls, then close the butterfly shaft and let set for 24 hours to cure, you might get a safe and tight seal.

Yes, I do have a MEVI, so I'm interested in what you find...

 

The turbulence is mainly because the butterflies are not flush with the runners.
With sealing them, I'd be worried about rtv comming loose over time and getting ingested.

 

The advantage of RTV is that it's soft and smooshy.... Using a very thin bead where the butterflies seat against the bore could work.

The only other choice I see is to remove the "closed" stop for the butterfly shaft, hand-lap each butterfly to match the bore it's in, hope they are all the same, and readjust the "closed" stop for a really tight fit.

Personally, I'd worry a lot more about all the turbulence caused by the runners opening downwards into the other main intake ports. That's a big problem you can't fix. There can't be much air movement up and down the runners when the butterflies are shut. That's a little problem that you probably could fix.

Personally, I don't have any loss of low-end power, and the top end keeps climbing until fuel-cut at 6550.

 

There is no low end loss. The loss is in the mid-range, and yes it is significant when compared to the USIM. This was first established circa 2002.

 

To the OP, i don't think this issue will ever be resolved until the valves are somehow lowered. Even if there is a good seal at the valves air is still being caught in that space, disrupting the flow.

 

I understand the turbulence being because of not being flush with the runners, however I think it also has to do with how much the air can move up and around the upper chamber. With the valves being sealed, there would still be turbulent air, however the section would be much more limited.

I've thought about the RTV a little bit but I too was concerned with it at some point breaking away and being sucked into the engine with the friction that would take place from the butterflies opening and closing.

I've also been thinking about perhaps some type of soft flexible gasket that could possibly be attached to the plate so when it closes the gasket would create a seal.

 

I don't mean to hijack but I had another idea to help out that air pocket the mevi has.
For some reason, GM decided to produce a TB plate like this:



Obviously, that particular plate is the wrong size and shape for a mevi but what if something similar could be made?
Have the wedge point downward, but not dramatically, round the edge that would be seeing inlet flow, all similar to the shape of the TB plate pictured.
A small difference like that may be enough to get the inlet air flowing a little better. The wedge will help develop flow better out of that right angle of a pocket. On the negative side, it will be pointing in the way of flow a little bit but the rounded off edge will help.
Without moving the pivot point, I think this could be enough to help the midrange loss.
But then theres the problem of how to go about mimicing that plate, and will a small change like that produce a noticeable gain in performance.
Agian, sorry to stray from the specific topic but I thought this was a good thread to bring this up in.