I think I may have stumbled into something that may raise a few eyebrows. Last mounth I installed a X pipe on Little Red. It was a Magnaflow and it seem's to work well, however today I was looking at the stock H pipe we cut off and decided to do a little snooping. First I scribed a line on the H pipe just in case we want to weld it back togather. Got the ole hacksaw out and cut the connector pipe in half. Now you need to relase this is a 2.5 inch pipe. Well Sir I got it cut off and took a look at the hole the factory put in the header pipe. Guess what, the hole the factory put in it is only 12/16. I damn near laughed myself to death. You would assume they would have put at least a 1.75 or a 2 inch hole in the pipe to balance the pulce of gas out. This explains the popping and the jinglebell sounds not to mention a drop in hourse power. Some time it really makes you sit and wonder.
What I plan to do now is get the ole hole saw's out a cut a 1.75 hole in both header pipes, re weld it up and re-install it on the car for a little evaluation. I have a very strange feeling some noises will be gone and a noticable horse power gain will appear. I'll keep you guy's updated and we'll see what happens.. :cool:

 

Cool, let us know your results. Although I have to figure the pipe is that way for a reason, whatever it is.

 

Yeah the small holes in the stock H-pipes are pretty well known around here. I don't get why they did it!

 

Ok guy's here's what we have. The small hole in the header pipe is 12/16 which is RCH larger than a dime. A dime will fall in the hole but it's snug. Now what happens is hot gas pulsing through this hole under pressure at idel which will cause a bell sound as it pulses and strikes the opposite header pipe. If you hold the pipe and tap it it will have a ringing sound like a bell. Now by enlarging these holes to 1.75 or 2 inches you will lessen the pulse pressure and the noise to say nothing of creating a more efficient scavange effect.
Some one out there with a M.E. and works on gas flow and pressure waves please jump in....

 

No offense meant, but I wouldn't count on a larger diameter pipe increasing the power. Once the exhausts are connected, they're connected and the pressure is balanced (that's the point of the exercise). That's why it's more correctly called a balance pipe.

What you may well find instead is that you've incurred a resonance point somewhere between 1500-3000rpm. There's probably a good reason for the diameter chosen. Good luck, though.

 

All very interesting. I will be :lurk:

 

Good point RWD. I won't be increasing the pipe size, only the hole size in each pipe. All the pipes will remain a constant. Remember back in the ole hot rod days, we would inatall a balance tube appx. 18 inches down stream of the header flanges. Back then we used it to mellow out the sound and eliminate the cracking sound or sound wave pulse. This will have the same basic effect plus create a more balanced gas flow from one header pipe to the other.
Thanks for the feedback...

 

I believe rwd was talking about enlarging the cross-over hole: there have been reports that increasing the hole size results in low frequency resonance (probably worse than the jingle as it happens during load, and can be quite loud).

Instead of enlarging the hole (as a bigger circle), you might try making it oblong: use a grinder to cut forward (toward the engine) to a smaller rounded point. Or see an NACA low drag inlet and perhaps match the shape somewhat. This is an intuitive guess; I'm not aware of anyone trying this.

Creating an X-pipe with a NACA low drag inlet cross section (instead of elliptical) might have some beneficial properties. I wouldn’t be surprised if there were more optimal shapes for crossover holes and X-pipe cross sections.

 

:iagree: It is more of a sound tune than anything. See my post http://forums.corvetteforum.com/zerothread?id=694344

:seeya

 

Hay Guy's, thanks a million for all the response. That's what makes this fourm so great. If you have an idea, problem or just want to talk about something you need an answer too just fire up the ole kyeboard and bang away. The great thing is we have lots of talent and professional help out there and all that needed is the question.
Once again guy's thanks, it was great talking to you all. PS when I get the 'H' pipe modded and reinstalled I'll let you'll know what happens... :chevy

 

Don't know for sure but when this first came up several years ago it was mentioned that the H Pipes in the early 97s had a much larger diameter hole and it was reduced to the current size as a running change during the 97 model year.
Bill

 

I think the technology used here is similar to what Corsa does to eliminate resonance. GM used the crossover pipe to harmonically cancel the 1500-1800rpm noise. If you change the hole diameter, you change the frequency. The small hole and large pipe is there for a reason. I wouldn't doubt if the early C5s with the larger hole had resonance problems. What would probably work to eliminate the resonance and eliminate the jingle would be to put 2 or more crossover pipes with stepped harmonics in series. But this is expensive and time-consuming to install.

The easy solution is to just install an x-pipe with a Corsa exhaust. :)

 

This ME ain't jumping in! It's where angels fear to tread! :blueangel: :blueangel: :blueangel: :D