Topic: Performance Exhaust - 4to4 or 4to1?

[CrazyRocketMan]

So gentleman..

CB750K5 here. Lightened crank, fully ported and polished, forged aluminum rods - you get the idea.

I have not found any topics on exhaust system types and performance in this forum.

So here begins the debate.

I am told that the back pressure provided by a 4to1 enhances performance, All of the modern world class race bikes have it, and all of the stock bikes come with it.

However, an engine is basically an air pump as I understand it.  The more (and faster) you can get air in and out the more power it develops. So a 4to4 makes sense from that standpoint. Plus you can tune back pressure for each cylinder.

Anyone care to voice their experience / opinion followed by their logic behind it?

Humbly,

 - George

[Retro Rocket]

I have not found any topics on exhaust system types and performance in this forum.

There have been lots of threads on pipes on the forum, not so much on the actual performance side by side but there are plenty of threads about pipes.... I prefer the older Yoshi style 4 into 1 pipes, there are at least 4 companies making these....   Most 4 into 4's i have seen have been ridiculously expensive...

[SOHC Digger]

Drag Racer magazine just had an excellent article on exhaust header design.  It explains in great detail all the advantages of using a header that combines your exhaust into a common collector.

The primary advantage of 4 into 1's is that they produce the scavenging effect, whereby the low pressure area behind and exhaust "slug" from one cylinder will actually pull the slug from the next cylinder out.

Here's the cover if anybody wants to look for it:

[CrazyRocketMan]

Thanks, I'm actively looking for that issue now! looks to be a good read..

 - G

[turboguzzi]

if truth needs to be told, then most modern high performance systems are 4-2-1, not plain 4-1, with quite a lot of importance given to primary vs. secondary length, it helps with mid range torque, an area that 4-1 are not good at. There's a guy in germany doing them for cb750's.

Legend has it that Pops always thought that single pipes were the best for all out power but if you really tune their lengths for max power you will get extreme "megafonitis" , i.e.  big hole in torque  bellow the power band. Indeed, honda GP racers from that period where amazingly peaky, not sure you'd want that in a street bike. 4-1 where able to give a much better compromise of max power and torque.



 

[mec]

There's a guy in germany doing them for cb750's.

see: http://www.schuele-maschinenbau.de/pages/klassik.htm

what i like most, is the weight advantage of a 4in1

mec

[Gearheadgreg]

Same thoughts a motor is just a compressor, being the owner of supercharged and turbo motors, lots to think about, any World record holder of TOP fuel will run individual single Zoomy type exhaust...Pump it and Dump it out as fast as you can! on the flip side road coarse and street competition will not be WOT their whole life, Naturally aspirated motors are very sensitive to head-pipe diameter and length, also firing order is important for a 4-1 collector to create scavenge to clear out the last cylinder to reduce back-pressure. i have had 2 sets custom headers made, one on my Supercharged Valkyrie and my V-Drive circle race boat by Basset racing exhaust. $$$$

[turboguzzi]

Well CRM.... as you see there's lot of info on the subject... so seems like we all forgot to ask you the most important question first:

what type of racing/riding you do?

fast street riding / road racing / drag racing / LSR have all very different power characteristics.

 

[johno]

Hmmmm,  back pressure for high performance, not in my books. In my country back pressure is for old volkswagons to stop crappy exhaust valves burning out and the enemy of performance.
Its an interesting subject though, I reckon there is a thread on this forum that probably sums that debate up beautifully, a comment from an M3 mechanic looking at his 4 into 4 pipes with big diameter/ short megaphones on saying " this is the last time with these things" or something like that.

I figured they had been on a journey and it was time to change.  Kind of a shame really as I am a big fan of the beautifull noise of four pipes, there is a great clip on u tube with two old farts starting up a MV Augusta 750 at a track meet. Suffering catfish that is an awesome awesome sound.

Exhausts have evolved,
Naturally aspirated
straight pipe....when tuning ...short length top end  ( like drag), longer for more midrange( like speedway 500 bike)

Then someone discovered the megaphone,  extended and intensified the reverse pulse time back to valve
Long tapered megaphones like Honda works bikes  spread the range power advantage over a broad range, short big diam megas like Manx Norton concentrate advantage over a narrow range.

Then someone invented the 4 into 1 where the reverse pulse from one pipe is used to help another cyllinder scavenge more efficiently and a combination of inertia pulses in primaries as well as reverse wave at outlet create a slight advantage over the reverse wave of a single pipe,

Oh yes in the 1940's and 50's the sports car dudes were big on the 6 into 3 into 1 or the 4 into 2 into 1 and when Honda educated the world with an awesome 4 cylinder it didnt take long for the touring dudes to use the the 4 to 2 to 1 for strong midrange. Once again a system where inertia and reverse waves are used on the same crank plane to scavenge its brother cylinder

Then the horsepower freaks bolt on superchargers and turbos to pressure feed the air through the engine, unlike naturally asperated engines where the vacuam created by the piston moving down draws in air, the superchargers just push almost unlimited air through the engine and with that much pressure pushing through you dont need any fancy exhausts to draw the gas out it just blasts out from megga cylinder pressure. All it needs is no back pressure.

I think.

Anyway out of all that I will probably run 4 individual pipes on my salt bike , dont care about the slightly less power but to get my rocks off on the noise.......I HATE mufflers

Cheers Johno