About a month ago I installed a metallic substrate high flow cat coverter to replace my stock cat. With the rest of the exhaust and intake wide open that resulted in solid boost creep.

I know that the best fix would be to port the turbo waste gate but, did not feel like taking out the turbo, after just installing it a few months ago. So, I decided to employ an old, tried method by installing a set of Supertrapp plates at the exit of the exhaust. These plates are mainly used on race cars for sound control but, they work for back pressure control, just as good. You basically put in as many plates as you can get away with for max flow. Reduce the number of plates for more back pressure.

Interestingly, back in 1995 when I raced my first FD with pretty much the same setup, except a midpipe instead of the metallic cat, I needed a maximum of 15 plates to prevent boost creep at 50F temperatures.

Today, at 52F, I started with 15 plates and my boost creep was gone, boost solid as a rock. So, I increased to 18 plates for more flow, boost still solid. Now, I have to order a 6-pack of more plates from Summit racing as it seems that the combination of metallic cat plus the Supertrapps will allow me to run more plates than I anticipated. According to Supertrapp 24 plates are pretty much equal to straight pipe flow performace.

I also welded the 3" supertrapp base plate to a 3" pipe which I then inserted into my Corksport 4.5" exit tube and mated it up with the 3" tubes in the muffler. I drilled 32, 3/16 holes, offset 90 degrees, in that added 3" pipe for additional silencing effect.

It worked, the car is really quiet now. At cruising speeds of 70 MPH, can not even hear any engine noise. Almost too quiet for me.

Total cost of Supertrapps is less than $100. If you try it, be sure to anticipate that in colder days, you may get boost creep with your max number of plates that you set up for a warm day. Keep an eye on your boost gauge!

 

Congrats on the fix, but I would probably opt for a restrictor plate in the exhaust line. The Supertrapp solution isn't the most attractive one.

 

I don't understand how that flows.

 

that's putting it nicely

 

Behind that solid plate there are 18 plates with a 3" diameter hole through the centers. The plates are held apart by built in spacers to provide an air gap for the exhaust to exit through. Thus, the more plates you put in, you multiply the size or the air gaps, increasing the flow through them.

As far as looks go, I can very well live with it, after using it for more than a decade on various race cars. I really did not like the "sewer pipe" look of an 4.5" exhaust too much. Now, at least it is interesting looking, making people look and wonder what the hell kind of an exhaust it is... Naturally all nuts will be in place once I figure the proper number of plates.

 

yea but wouldn't the solid plate block a significant amount of slow?

 

It sure gives that impression, does it not? That is why you get a lot of puzzled looks from people around you.

Like I said in my top post, according to Supertrapp specs, about 24, 5" diameter plates flow as good as a straight 3" pipe. The flow exit around the sides of the plates, not the back. These things have proven themselves in racing for a long time. The nice thing about them is that you can dial-in the EXACT amount of backpressure or sound controll, which ever you're after. I dynoed my race cars many times with various Supertrapp plate configurations and if you tune well, there is minimal power loss, even for race engines.

 

What he said. Get some stainless steel, get a 2.5 inch gasket, make the stainless steel look like the gasket. insert it into the exhaust track and your done.

My opinion is those other things looks like you are trying to see how far you can shoot a potato out of your exhaust.

 

lol..I had supertraps on my FC before and one time while I was driving and decided to go WOT the right muffler came apart from the pipe since it was only held by a clamp and not welded to the pipe...lol...it was a big explosion, thought I blew my motor...Everybody behind me suddenly slowed down....maybe they thought my car just blew up..

Took them off after that incident...lol...