UK Magazine MCM March 1982 CB900F Exhaust Test

Posted: Tue Apr 26, 2011 10:05 pm

This is a scan of the Power Pipes test in Motorcycle Mechanics Fortnightly magazine of 3rd-16th March 1982. This was a UK magazine.

Posted: Wed Apr 27, 2011 12:35 am

Interesting article.

Best pipe only gives 2hp over stock, seven pipes gave less hp than stock, Even though they all are louder, which seems to indicate less restriction.

Did the stock system have the crossover in Europe like the later model U.S versions did?

That sure says something about proper pipe dimensions.

What are the odds that the guys that randomly "customize" their pipes for looks wind up making LESS power?

Posted: Wed Apr 27, 2011 9:08 am

f4fast wrote:

Interesting article.

Best pipe only gives 2hp over stock, seven pipes gave less hp than stock, Even though they all are louder, which seems to indicate less restriction.

Did the stock system have the crossover in Europe like the later model U.S versions did?

That sure says something about proper pipe dimensions.

What are the odds that the guys that randomly "customize" their pipes for looks wind up making LESS power?

I think only the very late ones had the crossover, most models were 2 x 2:1.

I think the general rule on exhausts is "you can't beat the factory". I would suspect that most people with aftermarket exhausts (except where there is a proven increase) have traded weight and style for an increase in noise and a reduction in torque and bhp.

Twinstar Joined: Oct 09, 2008 Posts: 195 Location: Iowa

That's an interesting article.

The stock pipes are double walled. Would that possibly keep the exhaust gases from cooling down as much before they exit vs. the single wall headers?

Since the tests were on a stock bike, would the 4-1's require head porting, or some other significant change to the rest of the engine, to actually show a performance benefit over the stock exhaust?

Posted: Thu May 12, 2011 9:02 am

I think the factory pipes are double walled for cosmetic reasons (no blue pipes) rather than performance, but as you say, they might contribute to slowing the cooling.

I think that both induction and exhaust are tuned and matched systems, with some limited flexibility. By this I mean we know that you can change exhausts, but if you retain the standard carbs and airbox the system will be able to self-compensate (because the system is based on CV carbs).

However I think that to get the real benefit of a 4:1 (or any better flowing exhaust) with the improved (hopefully) scavenging at higher rpms you would need to address the induction side, either by changing the carbs, or by "improving" the flow through the head, or both.

Posted: Fri May 13, 2011 11:53 pm

stock pipes are heavy but have them on my 9 and am pretty sure I am gonna use a set of stock 11 pipes on the cafe bike........because looks and ground clearance are more important, at this point, than performance. The article however lends credence to thier use.

Posted: Sat May 14, 2011 12:21 am

Now allow for aftermarket carbs,ported heads,etc still true.

The fastest pipe I had was the one on the 955cc bike I sold. It had a 2" shorter primary than the normal Denco on my 1100F. All of these were the diamond collectror with a pyramid inside. The collector and primary pipe diameter correct,with a 7 degree megaphone. The fast pipe was a tricone 7 degree to 12 degree and the loudest open pipe ever made. You could tell the difference just changing the megaphone from single taper to tricone.

Now none of these will pass a sound check,track or street so all you are doing is comparing the ability to make a good "muffler". All a cannister is equivalent to an additional length of straight pipe.

When I was racing these pipes went under the bike and a rule change no longer passed ground clearance. I had to install a Vance and Hines "sidewinder". These were complete open no baffles and the V&H SLOWED the bike down .3sec. This is a significant loss about equal to the change of 13 to 1 compression to 10 to 1.

The funny part is on a lowered drag bike and turning toward the pipe never hit the ground,but the V&H drags easily.

As I said jebbysan has the pictures of the 955 on this web site somewhere. You cannot really see the shorter primary compared to the normal one. If someone wants to duplicate these I can send my "spare" if I get it back.

No one made the power a Dennis Dean Denco pipe makes. Dennis has a doctorate in accoustics and worked for Matsushita way before he did exhaust systems.

So strange most people were just pipe benders and no regard what ever for power.

Posted: Sat May 14, 2011 9:26 am

sonicrete wrote:

So strange most people were just pipe benders and no regard what ever for power.

In the context of the article, you have to think of the market these were aimed at - which wasn't fractions of a second of genuine competitive performance - but about bragging rights down the local pub about why your UJM was better than the other blokes UJM. These were built down to a price to sell in a niche market that was price/brand sensitive - product development investment would probably have been kept to just making sure you could mount it to the bike it was intended for, with just the one hammer, while still keeping a profit margin!

At least they guarenteed a good supply of original exhausts are still locked away in "dad's garage" all across this fair island Very Happy

Posted: Sat May 14, 2011 12:20 pm

To many people out there don't have a clue how pipes work nor do they care. Most want the look and the sound. You can"t flow more air out than you can get in. It is a pretty simple principle. SUCK, BANG, BLOW Exclamation

It's always cool to read articles on our bikes. Keep em comming.

Posted: Sat May 14, 2011 3:43 pm

atomic wrote:

To many people out there don't have a clue how pipes work nor do they care. Most want the look and the sound. You can"t flow more air out than you can get in. It is a pretty simple principle. SUCK, BANG, BLOW Exclamation

It's always cool to read articles on our bikes. Keep em comming.

You are corret breath in breath out BUT add carbs (fuel/air mix) ignition and correct extraction for peak STOCK perfomance......i guess. worked on my harley and seems to works on my 11. My 1000f is highly moded but i have nothing to compare it with as i got it that way. then again I never race them in any fashion.