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Hello exhaust enthusiasts

I'm not finding much info online for my particular problem.. maybe you can help?

Virtually all motorcycle exhaust systems have a header/manifold.. a collector.. a somewhat short midpipe... and a slip on silencer.. ...then they cut off, and the exhaust exits at the tail end of the muffler.. simple-light-effective..

On my BEC, I think I want to run a 'full' exhaust from the front of the car (MC engine location) to a tailpipe sticking out of the back of the car.. So it will go: engine/header(s) @4-2-1/short midpipe/MC silencer/then about 8 or 9 feet of traditional, car-like exhaust exiting out of the back of the car..

My question is this: What diameter exhaust pipe should I use to link the silencer (which is near the engine) to the exhaust exit out at the back of the car?

===============

---Of issue/concern---

**TMI- Engine; 2000 Honda VFR800/ 12K Redline/ aprox 100 hp/ car will weigh about 900 lbs / will run a 'Dynojet PCIII fuel controller

**I'm not able to position the silencer out at the back of the car due to space constraints.. the MC silencer must live up near the engine..

**Running the exhaust all the way out the back of the car is a preference; I could just cut it off after the silencer (MC style), but that will have it dump out under the car up near the engine/under-hood area, and I'd like to get the smoke and noise out behind the driver and to the rear of the car..

**Finally, this exhaust will have a vanity 'open' dump valve at the header collector (purple in the pic)- when desired, you can flip a switch and have a truly open exhaust, a move that always gets all the chicks.. When not showing off and getting all of the chicks, I want the exhaust to be a bit more user/driver friendly

**In conclusion and most finally, when I settle on my exhausts diameter (which is the basis of my question/problem), I need to go as small as I can, as space to route this exhaust is super, super tight.. could I get away with 1.25" ID?? Maybe 1.5" ID?? truly, every 1/8" matters as I try to find space to do this..

..as always- thank you for your thoughts and input. much valued and appreciated

--ccrunner

*pic below is my groovy 1st attempt to use the latest 2D/3D paint.. new skill!

_________________
Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=16309

1959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397

"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com

Option number 743
Run two small exhaust pipes and muffles in parallel. If possible even out exhaust pulses per system.
Davew

For ground clearance, I would use 14ga rectangular tube in 3/4 or 1 inch thickness as wide as needed to have slightly more area (l x w) than the round pipe (3.14 x radius squared). I'd fit the rhs to the belly first with bends if needed to possibly kick up at the rear. Bolt it to the belly with 1/4 or 5/16 bolts, large washer, belly, large thick rubber washer (2x1/4ish?), flange welded to rhs, another washer, metal washer, and double nut. Fit header tubing to wrap around and go between the end of the rhs and the header, then make a slip fit or add flanges at the header. Spread one side of the rhs to accept the header tube and weld so the system is easily removable with two, opposite sides and ends rubber mounts and the flange bolts.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Yeah, it’s a little “outside the box”. So if the head pipe is 1.5” od, 3.14 x .75 squared is an area of 1.76625 square inches. The closest larger and commonly available square section in either .75 or one inch is 1x2 rhs for 2 square inches or .75x2.5 rhs for 1.875 sq”. You can have as much flow as you want without reducing ground clearance by going wider. You could also make slots in the rhs at 45 degrees to the flow to fit 1/8 plates to weld from one side for an integral muffler similar to a flowmaster design. It would also be easy to fab an exhaust tip from stainless sheet that resembles a diffuser.

Downside is it weighs more than the same area round tube but ground clearance is more important. Enough back pressure and heat could oval the rhs but you should have very little if the rhs is wide enough and the wall heavy enough. If you are going to add weight to a car, it can’t get any lower and would lower the cg of the car. You were talking about nine feet of round so I assume it would taking an indirect path with a few extra bend where this is maybe six feet of straight rhs. A nine foot tube will have more back pressure than a six of the same area not to mention having more bends even if they are mandrel bends.

I forget who came up with it here, but you can make the exhaust grommets with a hole saw on the sidewall of an old tire.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

How about twin side pipes, i.e. through a cut out at the rear of the front fender along the rocker panel " Cobra style". Way less heat in the cabin area. Davew

On the Lotus Elan (first version) the round exhaust tube was partially flattened for more ground clearance under the car. Easy to do a little at a time in a press.

_________________
When you're racing, it's life. Anything that happens before or after is just waiting -- Steve McQueen from LeMans

My build log viewtopic.php?f=36&t=10658&start=0 NOW NAMED =The Wycked 7

My other build log viewtopic.php?f=18&t=15162 The Skayt'R6

The '54 Maserati A6GCS had duals down one side.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Make the 9' section larger than all the others. That way you can treat it as more or less the exhaust on the bike where it terminates after the muffler

_________________
mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.

Thanks guys for your thoughts so far.. This is exhaust is still in the planning stages, so nothing is off the table, and I still get to work in preferences until the brick walls in design set in..

-I didn't think of side pipes.. certainly an option, but I'd like the exhaust to be stealthy if I can pull it off..

-The idea of rectangle tubing could work too, but this car has a smooth, enclosed lower pan that I'd like to not have the exhaust hang below if I can help it..

I guess what I'm looking for is an exhaust volume calculator to learn the smallest diameter tubing I can use after the MC silencer (the online calculators I'm finding won't give be an answer at my 50ci (800cc) .. I simply don't know how much volume I need to flow, and more directly, what's the smallest tubing I can use to get the job done and not hurt performance..

***If you're wondering, I'm trying to see if I can fish/snake/route the exhaust through, in, and around the car's frame and internal structure, and simply have it exit out the back, all while keeping the exhaust system up above the lower pan... A bit unconventional, but it would be cool if I can pull it off..

thanks-

ccrunner

_________________
Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=16309

1959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397

"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com

If all we are talking about is tubing without tricks for improved scavenging that are impractical, adding any tubing hurts performance (adds back pressure over the oem design parameters). You can minimize the loss by using larger tubing, fewer bends, and required bends are minimal in degree and mandrel bent. IMHO, the system you are suggesting in terms of tube size, length, and number of bends would provide a very noticeable loss of performance but so what? This is not a race.

One good thing about longer pipes is they reduce reversion and provide a little sound dampening so the oem silencer could be modified for less restriction to comp for the longer pipe.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

From the flow calculation charts I've seen, it might be possible to go as low as 1-3/4, but with that length my WAG is you'd be starting to lose top end with that. I'd go with 2.0" to be on the safe side.

A heat source without enough ventilation is an oven. Keep that in mind as you figure out where to route it.

Out of curiosity, if you're not adding a cat or another muffler in the downstream exhaust, what about just dumping it out the side of the car right next to the muffler outlet You could even have symmetric dump holes on either side of the car, one for muffled and the other for straight piped. With a little black high-temp paint, and some natural carbon buildup, it might even be relatively subtle.

_________________
-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

.. good points guys.. I was afraid if I made the run too long I'd hurt top end- keeping in mind this mighty 800cc lump spins at 12k up on the edge.. *aside; also, 2.0" tubing is simply too large to coax through my tiny available area..

I like the idea of just dumping out early on the side(s) of the car.. In this pic that I borrowed from the net, I've marked in yellow where might be a place to have a little exhaust tip (or two) peeking out.. would help me achieve the look I'm after, and somewhat get the noise/smoke away from the driver.. Also keeps the exhaust system relatively short, helping to keep the weight of those 'extra' few feet of tubing out of the build

Thanks guys.. always helpful

--ccrunner

_________________
Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=16309

1959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397

"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com