Exhaust system idea

[scubasteve231]

This exhaust system is for a 77 GMC truck with a ~450HP 383 small block. The goal is to have a simple and lightweight exhaust that flows extremely well, but still routes the exhaust gasses out from under the body. I have read quite a bit here about termination boxes and I would like to try them out since there is plenty of room underneath the truck for them. The Y pipe will be Flowmaster # Y300400 unless someone knows of a better Y pipe. Muffler will be a Hooker Maximum Flow 4". I have used this muffler before with good results. The exhaust will exit in front of the drivers side rear tire. The frame of the truck angles up behind the cab, so there's plenty of room to pass the exhaust to the other side of the frame without decreasing ground clearance.

The only thing I'm not so sure of is that the David Vizard articles show an H pipe, placed up by the header collectors or on the termination boxes. I omitted it from my design because mine comes together as a single exhaust and it seemed redundant.

The drawing isn't to any kind of scale, just a rough sketch to get the general point across. Does anyone see any issues with this design or areas to improve on?

[mag2555]

That should work well especially if your able to get the muffler mounted way after the rear axle, but if that's doable I would then perfere even one 2.5" muffler for each bank at the rear of the truck.
Even Oval type mufflers can be hung vertical/ parallel to the gas tank with tons of ground clearance on a pick up truck!

[dwilliams]

I had a similar exhaust on my old F100. It exited under the passenger side step. It was *way* quieter than the old system exiting out the back; I'd guess the pipes themselves transfer a lot of noise to the vehicle, and by making them shorter there's less to transfer.

The short pipes didn't have the drone or rattle-back-up-the-pipe noises various out-the-back systems I've had exhibited. If the pipes on my current truck ever need replaced, I'd be likely to go the shorty route again.

[ptuomov]

A couple of comments. These aren't informed by much practice, but I've been thinking about the problem for a little while. So take these for what they're worth.

I think the proposed setup has a lot going for it. It combines the pulses and reduces the cross-sectional area a little bit at the tail pipe. That makes sense.

Here's how I would chance the proposed system.

First, I would definitely add a cross-over upstream of the first set of cans. An X-pipe would be ideal, but if there's no convenient room, then 2.5" or larger H pipe would be ok, too. Pipemax might give you some idea about location, but I think it's more important to have any cross-over than an optimally placed cross-over. There may or may not be lower rpm torque benefits from the cross-over, but mostly I'd do it just to knock out 1-2 dB by combining the pulses upstream without creating any restriction. The second cross-over at the tail-pipe muffler would then again combine the pulses, and it would do that after unequal pipe lengths. This would lead to further phase shift and would quiet the system further. So better or equal performance with less need for muffler. My system will have two cross-overs and unequal pipe length in between, and although it hasn't been proven yet I'm confident that it'll work well in terms of sound.

Second, I'd use mufflers instead of empty boxes in the place of exhaust termination boxes. The cross-over upstream will take care of most of the tuning needs. Also, I think that muffler technology has advanced since the times of Walker Super Turbos and termination boxes. I would use largest Borla or Magnaflow mufflers that fit in those spaces, instead of constructing termination boxes. Acoustically and in pulse tuning sense, I believe that the large-case Borla and Magnaflow mufflers behave largely like a termination box with a cone-shaped diffuser entry.

[MadBill]

I concur with most of the above, except that I don't think the Borla or Magnaflow mufflers are "empty enough" to act as really effective terminator boxes. I'd go with Spintech or the less-than-universally loved Flowmasters. Something like the latter's 40 Series is practically empty anyway and the modest baffling acts more as a support structure and anti-oil canning feature but with still some useful sound reduction capability.

[englertracing]

Looks good scuba, but I think you should use a big ole taper going into the termination box, and a big ole bell mouth going out.

[ptuomov]

I concur with most of the above, except that I don't think the Borla or Magnaflow mufflers are "empty enough" to act as really effective terminator boxes. I'd go with Spintech or the less-than-universally loved Flowmasters. Something like the latter's 40 Series is practically empty anyway and the modest baffling acts more as a support structure and anti-oil canning feature but with still some useful sound reduction capability.

I used to think the same, but I ended up revising my opinion this year after reading everything I could get my hands on about mufflers. That is not to say that I'm right, just that I've changed my mind. I was either wrong earlier, wrong now, or both!

I think that the case volume and diameter make a huge difference here. If it's an old-school glasspack that has a diameter maybe an inch larger than the inner pipe, then it doesn't act like an empty large box. If it's an modern large case muffler packed with ss and rock wool, it'll behave not too differently from just an empty box with a perforated tube from the pulse reflection perspective. The perforated tube itself doesn't behave too differently from a a diffuser entry to an empty box. So now I'm thinking that a big case Magnaflow will look about the same to the pulses as an empty box of the same size with a gentle diffusing cone inlet inside the box. The reason why I think this is that the flow resistivity and porosity of the packing material isn't going to change the game much in terms of the pulse reflections. The case volume is the key, in my opinion.

[1989TransAm]

That is almost identical to what I put on my TransAm. Except I had 2 3/4" pipes out of the header and 3 1/2" after the wye going into the muffler. Worked out quite well. I made my own termination boxes out of oval tubing.

[scubasteve231]

I had a similar exhaust on my old F100. It exited under the passenger side step. It was *way* quieter than the old system exiting out the back; I'd guess the pipes themselves transfer a lot of noise to the vehicle, and by making them shorter there's less to transfer.

The short pipes didn't have the drone or rattle-back-up-the-pipe noises various out-the-back systems I've had exhibited. If the pipes on my current truck ever need replaced, I'd be likely to go the shorty route again.

Good to see that someone has done a “shorty single” exhaust with good things to say about it. My truck has had dual 2.5 pipes all the way out to the bumper most of the time I’ve had it. It just seems wasteful to have so much pipe/weight underneath the truck.

[scubasteve231]

A couple of comments. These aren't informed by much practice, but I've been thinking about the problem for a little while. So take these for what they're worth.

I think the proposed setup has a lot going for it. It combines the pulses and reduces the cross-sectional area a little bit at the tail pipe. That makes sense.

Here's how I would chance the proposed system.

First, I would definitely add a cross-over upstream of the first set of cans. An X-pipe would be ideal, but if there's no convenient room, then 2.5" or larger H pipe would be ok, too. Pipemax might give you some idea about location, but I think it's more important to have any cross-over than an optimally placed cross-over. There may or may not be lower rpm torque benefits from the cross-over, but mostly I'd do it just to knock out 1-2 dB by combining the pulses upstream without creating any restriction. The second cross-over at the tail-pipe muffler would then again combine the pulses, and it would do that after unequal pipe lengths. This would lead to further phase shift and would quiet the system further. So better or equal performance with less need for muffler. My system will have two cross-overs and unequal pipe length in between, and although it hasn't been proven yet I'm confident that it'll work well in terms of sound.

Second, I'd use mufflers instead of empty boxes in the place of exhaust termination boxes. The cross-over upstream will take care of most of the tuning needs. Also, I think that muffler technology has advanced since the times of Walker Super Turbos and termination boxes. I would use largest Borla or Magnaflow mufflers that fit in those spaces, instead of constructing termination boxes. Acoustically and in pulse tuning sense, I believe that the large-case Borla and Magnaflow mufflers behave largely like a termination box with a cone-shaped diffuser entry.

If this system did get an H pipe, it would end up underneath the torque converter dust shield or run below the transmission pan. So it would be a little more time and effort to get it to work. It seemed redundant to me, but with what you said and the fact that the 2 to 1 Y merge is so far back in the system, I can see where the H would still be effective if it were placed in collectors before the terminator boxes. I will definitely use an H if I can.

I have thought about using mufflers for the termination boxes. The big issue with terminator boxes seem to be that when the pulse enters the chamber, the expansion of the pulse seems to carry a lot of energy all at once. Much like smacking a piece of metal with a hammer. A lot of peoples accounts of terminator boxes seemed to mention the boxes blowing completely apart at their welds, or having a ringing resonance. Mufflers will either have welded baffles or sound absorbing packing to combat these problems which makes them a natural choice.

Terminator Box Option 1:
My original plan was to order a stick of 6” diameter exhaust tubing from Walker/Dynomax and use that as the main body of the terminator box. I would have to fabricate ends for them. These would have the largest overall volume, but they could have a ringing resonance and would not offer any noise reduction at all.

Terminator Box Option 2:
There are some race series Flowmasters that have really large case volumes and are quite empty inside (unlike the street versions), and I believe the internal passages where they do neck down are the same diameter as the inlet/outlet. David Vizard says to use a Flowmaster with an inlet/outlet much larger than the collector pipe and then using reducers/adapters to plumb it together. He doesn’t make any recommendations for specific part numbers. I looked at Flowmaster part #854040-10 it has 4” inlet/outlet and it has one of the largest case volumes that Flowmaster offers. I’m not so sure that I have room between the transmission and frame rail for these since the case is 10” wide. They are $166 each which is on the spendy side. I feel these will take the edge off the open header sound, but that’s probably about it. The potential for a ringing resonance or droning is there since there is no packing.




https://www.summitracing.com/parts/flo-854040-10

Terminator Box Option 3:
Another option is really large inlet/outlet straight through diesel performance muffler. There are several 5” inlet/outlet mufflers available with a 24” long case and an overall length with stubs of about 32”. They have plenty of volume just from the perforated core alone, not counting the case volume where there is packing. I feel like these would be especially well suited to terminator box duty, just because the packing is really going to deaden the energy from the pulses expanding. I do not think there is any potential for ringing or droning, just because the packing will naturally deaden it. Once candidate is MBRP GP290022 with a 7” round case. Another candidate is Flo-Pro M12772 with an 8” round case. These mufflers cost around $80-$100 each.




http://www.ebay.com/itm/Flo-Pro-Max-5-S ... 2515539465

Since these have a high potential to quiet the exhaust system, I may not even need the 4" muffler at the end of the system, but it could be added later if needed. That would save additional weight and cost if that were the case. These could very well be the best candidate since they offer so many advantages and have a relatively low price.

[scubasteve231]

That is almost identical to what I put on my TransAm. Except I had 2 3/4" pipes out of the header and 3 1/2" after the wye going into the muffler. Worked out quite well. I made my own termination boxes out of oval tubing.

I believe I've seen the ones you made back when I doing a lot of reading on terminator boxes. Did you have any issues with ringing/resonance? It looks like you were able to get away with not having any internal supports/baffles ?

[1989TransAm]

That is almost identical to what I put on my TransAm. Except I had 2 3/4" pipes out of the header and 3 1/2" after the wye going into the muffler. Worked out quite well. I made my own termination boxes out of oval tubing.

I believe I've seen the ones you made back when I doing a lot of reading on terminator boxes. Did you have any issues with ringing/resonance? It looks like you were able to get away with not having any internal supports/baffles ?

Yes. That is why I went with the oval tubing. Hardly any ringing/resonance. I just sold my TransAm today as a guy made me an offer I could not refuse. While I was looking around for items for the car I found the termination boxes. I had taken them off to pass smog. If you were in SoCal I would let you have them. I used the formulas to make them. The motor in the car is 369 cubes and has 420rwhp. That should be well past 500 at the flywheel for comparison to what you are working with.

MadBill had made his square and that did not work out so well in the long run. I used his experience to design mine.

[jsgarage]

Some or most of the 'ringing resonance' in an exhaust system may come from the flat sides of ANY exhaust component. People underestimate the energy involved in hundreds of thousands of hot exhaust pulses. I suggest using round/oval components if there's space, or if you must, reinforce the outsides of any flat surfaces with welded or brazed ribs, to keep resonance/flex- then metal fatigue/cracking, away. No need to reinforce the insides; its usually more convenient to not cut a component open.

[77cruiser]

Any thought about changing to 2 1/2 inch collectors? Might pick up some torque along the way.

[1989TransAm]

Any thought about changing to 2 1/2 inch collectors? Might pick up some torque along the way.

I used Pipemax for my design and 2 3/4" was the best fit and that is why I went that route.