Resonance

[TedC]

I like the product videos CC!!! You can see that the left exhaust tip has a built in restriction.

 

[Jeb]

Problem solved. Well almost, it's now almost quiet inside the car. Thanks to one of the posts in this thread, I simply blocked off the inside exhaust tips... The reduction in resonance is truly amazing. My technique (two tennis balls and duct tape) could not be viewed as elegant, but it worked! Next step will be to find a less obvious and more permanent solution.
ps Idle revs down maybe 75 or 100 too.

Inspired by tennis balls and duct tape, I had my muffler guy block off the inside pipes on my 87 and..................VIOLA! It's as quiet as a mouse! No resonance at all, a little higher pitch (which is good) and a nice clear sound. I lost about 50 RPM which I believe the computer will adjust to but if it doesn't I can handle that. In gear and stopped at idle, I get only about 20# oil pressure and I don't like that. Current in gear idle is about 500 RPM. I am a happy dude. Thanks!!!!

Edit: 1/2 Qt of Mobil 1 took care of the oil pressure issue. I am now a happier dude.

UpDate: The in gear idle is back to normal (550-600) and the idle oil pressure is no longer a concern. This thing is quiet as a mouse inside and I can't tell any difference in performance. Wish I had done this a few years ao.

Just in case anyone is wondering, I have the stock front Y pipe and cats hooked to Ecklers Pt #31034 rear Y pipe with the crossover tube, Eckler part #38869 mufflers and Corvette Central Pt #323201 exhaust tips which do extend a tad past the end of the bumper.

 

[jonszr1]

here is a low cost way to get quiet yet maximum performance from your c4, allthough my car is a zr1 i believe the same gains could be had by you . i ran my car with a corsa that was on it when i bought it @fontana it ran 12.64@114+ mph i then on awhim took an old zr1 exhaust which is 23/4 in all the way back just like the 92 up c4s . put in a 21/2 in x pipe and dyno max 3 in super turbo muffler with dual 21/4 exits and it nice and quiet. and on the plus side it ran 12.23@117= mph. i am going to try 21/2 in super turbos with 2 in exits to further quiet it down .from what i have read the size of the mufflers isnt as important when they are at the end of the system . the 23/4 in piping can support up to 500 hp . if one goes to 3 in on a fairly stk car you will lose low end hp from the big pipe .plus the big pipe makes more noise .jmho

 

[boomdriver]

here is a low cost way to get quiet yet maximum performance from your c4, allthough my car is a zr1 i believe the same gains could be had by you . i ran my car with a corsa that was on it when i bought it @fontana it ran 12.64@114+ mph i then on awhim took an old zr1 exhaust which is 23/4 in all the way back just like the 92 up c4s . put in a 21/2 in x pipe and dyno max 3 in super turbo muffler with dual 21/4 exits and it nice and quiet. and on the plus side it ran 12.23@117= mph. i am going to try 21/2 in super turbos with 2 in exits to further quiet it down .from what i have read the size of the mufflers isnt as important when they are at the end of the system . the 23/4 in piping can support up to 500 hp . if one goes to 3 in on a fairly stk car you will lose low end hp from the big pipe .plus the big pipe makes more noise .jmho

I agree.
I was very surprized at how much low end pulling power was lost by going to a bigger exhaust with almost zero restriction. The key is where you apply some restriction. There were several combos of TB, intake duct and exhaust that were tried before an acceptable low end was found with a faster rev. You can make an L-98 rev up instantly BUT, you'll loose lots of low end if you;re not careful.

 

[CharlesBrown]

At last I've solved this problem. At least in my estimation. As I said when I started this thread that the tennis ball trick works. However, it looks a bit dorkey. My muffler man said that he could weld one side shut. That would do the trick ($80.00) but what if there was a problem or if you wanted to sell these expensive mufflers. Who would want them with one pipe emasculated? Right! So I found a set of 2-1/2" silicone rubber plugs good for 600F (Google them...easy to find). Stuffed them in place (see attached photo) and held them with a piece of old hack saw blade. Spring steel would be ideal but Home Depot doesn't carry spring steel. Final cost $18.00 inc. S&H. And its reversible! Side note, the resonance in the 10 to 14k is still there but the 14 to 21...Quiet!

 

[6 Shooter]

WOW - Looks great...

:ugh​

otfl​

 

[DaveH_RRTX]

I think I just threw up in my mouth a little bit.

 

[6 Shooter]

YEP - I agree!

I think I just threw up in my mouth a little bit.

otfl otfl otfl otfl​

 

[XLR8]

CB... I see that you provided a closeup photo to show details of your "fix" and in that photo it is easily noticed. How does it look from a greater distance - invisible or still obvious?

Jane Ann

 

[catbert]

Increasing back pressure cures or deceases resonance - that's a well known concept. My friends at GHL have proven that many times. The trick is to cure resonance without going back up to factory back pressure. That takes hundreds of hours of engineering, testing and a little luck.

 

[Jeb]

Increasing back pressure cures or deceases resonance - that's a well known concept. My friends at GHL have proven that many times. The trick is to cure resonance without going back up to factory back pressure. That takes hundreds of hours of engineering, testing and a little luck.

What's wrong with "factory back pressure"?

 

[catbert]

What's wrong with "factory back pressure"?

It's about volumetric efficiency...kind of like a pump.

 

[93Rubie]

Ah yes, volumetric efficiency...in a nut shell an engine is an air pump, the faster you get air in and out, the more power you make. Higher RPMS=More Power, if you can move the air...More Air=More Power

In comparison the TPI setup has poor volumetric efficiency to a LSX motor. Then again TPI 250HP, LSX 400+HP.

 

[Jeb]

Again...What's wrong with "factory back pressure"?

 

[93Rubie]

Nothing wrong with factory back pressure if you keep you engine factory. If your interested in at all improving performance, factory back pressure is a problem. Back pressure in of itself is not a bad thing, some is what you want for better torque, but too much is very bad. There is a reason LT1 cars came with true dual exhaust. If an engine can breath it can make power and torque.