As I’m building out my Frankenstein 69 I’m going to add side pipes. Wondering if some of you smart guys could help me think this through.

It already has a custom exhaust, dual 3” pipes to a custom rear end.





I know I have to do some custom work already, just to get the noise level legal here in the PRC (People’s Republic of California). So I’m thinking to install some kind of a switch over, to switch between the two. I’m including a Progressive Ignition dizzy and Carb Cheater, both of which together will enable me to switch profiles programmatically, so I’ll be able to switch tuning when I switch pipes on the fly. The only trick I haven’t figured out is the hardware.

I imagine I’d tap into the 4” collectors, route to some kind of a valves and then to the rear pipes. Was also wondering if I should attempt a crossover while I’m at it, between the side collectors and before the valves. I’m replacing the P/S with a Borgeson so there will be room in front of the engine for a crossover. I think…

I tried finding some examples here but I must be using the wrong search terms. Could someone point me to some threads or links where someone has done this before?

BTW, I’ve done some looking into solving (ok, mitigating…) the noise issues and found plenty, though the most recent is a few years old. I got my hands on a set of Hooker 4” and it seems the best option is the STS spiral dampeners. Is there any newer solution that’s better? This is for a 383 stroker built for street performance (no expectation to race).

As always, thanks for your help!

 

Go read this thread on the subject.

https://www.corvetteforum.com/forums...r-exhaust.html

 

Thank you! Exactly what I was looking for!

 

I found a lot of kits for this, now that I know what they’re called! So a follow-up question:
Why use a valve at all? Would simply running it with both side and rear systems have any problems? Less noise? Affect performance?

 

Are you looking to do this with factory-style side pipes, or Doug’s/Hooker/OBX full header side pipes, where all the primaries come outside the car into 4” tubes?

 

The latter, 4 into one 4” hooker.

 

Then the configuration in Mr D’s linked thread isn’t going to work for you.
True, you could tap off the side of the 4” collector to connect your under-car exhaust, but you would need a shut off valve after that tap inside the 4” tube or collector. I don’t know if anyone that makes a valve for that, and it would require modding your 4” collector or tube.
Putting the valve in the under-car circuit won’t tone the sound down at all because the exhaust gases will take the path of least resistance, which would still be down the 4” tube.

 

Doh! Makes sense. Well, I guess I’ll just have to have bada$$$ all the time. I was hoping someone had already done it.

 

OK, so forgive the dumb question, but dad always said there’s no such thing.

What’s wrong with having both side and under-car pipes connected? I mean, if:
- adding a cross pipe between resonators balances standing waves between 4&8 and 5&7 cylinder pulses
- adding volume allows for sound suppression
- reducing back pressure increases horsepower
then adding a Y at the 4” collector to the under car mufflers should increase horse power and reduce noise.

I know there’s got to be a reason this isn’t done, I just can’t wrap my head around it. Please, help me understand.

 

The sidepipe headers put the collector over 1/2 way above the frame. So its be quite difficult to tap off it and go back under the car. You'd lose around clearance there too.

 

As Lionel said, your header choice just tanks the practicality and efficiency of your project. If you use shorty headers and a simple single tube sidepipe design. your project could be workable.
Your three "bullet" points make sense.

 

This thread just reinforces that I need to get off my butt and make the design idea I have happen for a dual-mode exhaust for Doug’s/Hooker/OBX sidepipes.

 

@wwiiavfan pm me if you’d like to collaborate.

 

OK, so let’s say I’m limited to the od of the primaries. That’s 1.75 I think. My under-car pipes are 3” so if I tapped off with two 1.75” pipes ( parallel ) into a custom collector that would solve my clearance problem. I imagine a 4” pipe, (a tee) that would insert between the collector and long pipe, with the two outbound pipes merging at the 3” under-car pipe. I’d have to cut either the collector or main pipe to account for the tee. So this would mean making a tee, custom routes pipes, and a final 3” collector.

 

are you.serious,?
​​​​

 

Yeah, refer back to Dad saying there’s no such thing as a dumb question. I’m trying to understand using a straw man. Draw it up, share it, no matter how crazy.

Not sure what you’re laughing at. The idea of the dual systems being always on? Or the idea of a separate tee vs cutting/welding straight into the collector? Seriously, I don’t know what I said that’s crazy.

Listen, there’s a ton of opinions out there on side pipes, performance and sound. Not once have I seen anything resembling engineering; e.g. charts comparing db or perfomance curves, any authoritative research. Closest I’ve seen is DV telling us all how everyone has it wrong and throwing out some formula without an explanation. Might be out there somewhere, I just haven’t found it. Yet.

I’m trying to understand how this stuff works, beyond just a bunch of “this worked for me, here’s a sound byte for you to listen to on your little phone”.

I think probably the most interesting I’ve seen in this forum so far is a few comments about how connecting a cross pipe between collectors somehow balances or buffers the pulses from cylinders 4/8 & 5/7. Also some about adding resonance pipes to deal with droning and/or leveling out power curve. I suspect both have to do with standing wave lengths, back pressure, and velocity, but I don’t know how.

OK, so I don’t care if anyone calls me crazy but I reserve the right to ask why. Why is the idea crazy?

 

Having a dual system is not crazy.

But, how you do it will affect how much work and misery you put yourself through.

I have tried in previous threads to offer up engineering options or methods regarding sidepipe noise and restrictions, but the favorite response too often seems to be "just wear earplugs".

I applaud you for understanding the main issue with sidepipe noise, the double exhaust pulse at the 8/4 and 5/7 cycles. Dealing with those pulses without just choking the system is the intelligent direction.

I look forward ti updates on your project.

 

@69427 Thanks, yes, I appreciate your posts, I’ve gleaned a lot from them.

So a few questions…
- does the cross pipe you’ve referenced provide an alternative path when the 4/8 & 5/7 pulses come out of phase with the other pulses? Is it done to scavenge or simply to relieve back pressure?
- my current under-car is dual pipes, independent. If I connect both types (side and under-car) as I proposed, do I still need to add a cross-connection? If so, would connecting just the under-car be enough? Ie if I have both side and under-car on each side, do I still need to connect them?
- my under-car is 3” straight through with straight through mufflers, and for the side I’m planning a Dougs glass pack muffler, which I believe is probably also about 3” id. Would that provide for balanced standing waves in both and allow good velocity?

 

@69427 Btw, no sleight intended re engineering content, just missed what you posted. Would really welcome any links or reading you send me to, will do my homework.

 

@69427 another question:
I just read your thread Exhaust System 4.0 and regarding the two 1.75” from the tee to a 3” collector, do you have any concerns over back pressure? I’m just guesstimating that the extra volume of the two (1.75 x 2 = 3.5) is enough. Or does the mismatch cause worse problems? Two 1.5”? One 3” flattened to 1.5” high (LOL!!!)?