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I am lloking to get a slip on only and I was wondering what everyone thought was good quality at a decent price. Most people here have full exhaust, i just need a slip on. Any insight would be helpful on this.
 

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TWO BROS
 

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HMF all the way. Check out their numbers on HMFENGINEERING.com
 

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Originally posted by DaNNNNNy9@Jul 28 2004, 10:54 PM
HMF all the way. Check out their numbers on HMFENGINEERING.com
you do know those numbers are put up there by HMF dont you......"a warrenty is only as good as the box its written on"........sort of speak B)
 

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I am lloking to get a slip on only and I was wondering what everyone thought was good quality at a decent price. Most people here have full exhaust, i just need a slip on. Any insight would be helpful on this.[/b]
I would remove the baffle and put hte HRC endcap on instead of buying a slip on. To my knowledge the slip ons don't make much more power than the the reomved baffle. I would do the HRC end cap and save up the cash and buy a full system instead.
 

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Originally posted by joe1l@Aug 1 2004, 09:43 PM
QUOTE
I am lloking to get a slip on only and I was wondering what everyone thought was good quality at a decent price. Most people here have full exhaust, i just need a slip on. Any insight would be helpful on this.
I would remove the baffle and put hte HRC endcap on instead of buying a slip on. To my knowledge the slip ons don't make much more power than the the reomved baffle. I would do the HRC end cap and save up the cash and buy a full system instead. [/b][/quote]
this is true. both joe and dez are right. from what we all know about the 450r, a goog first step w/o the option of a full pipe would be to use the HRC or similar end cap and open up your air box with no lid or a modification then re-jet. this will make some noticable difference until your ready for the next step... full pipe, cam, and maybe a higher compression piston.
 

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If it's a gain on bottom end you want, you could put on a more restricting slip-on than the end cap and stock muffler[/b]
Not necessarily true.

There's a lot of misconceptions out there on "backpressure", restriction, and the true issue, velocity.

Any slip on should show a nice gain down low, even versus the HRC cap. Why?

To answer that question, we must understand why "backpressure" is not good for low end as commonly believed.

Most confuse the attributes of velocity with backpressure. Backpressure kills power period.

The reason this is confused is because when comparing pipes of similar design, ones that are setup to optimize low end power create backpressure on the top end. Small diameter pipes keep low RPM exhaust velocity high, creating a scavengening effect that draws more spent exhaust gasses out of the cylinder and more fresh mixture in, but when the exhaust volume raises, the pipe may be too small to flow well, producing backpressure on the top end. People then associate "backpressure" with bottom end power.

Now lets say you have a nice open pipe that makes good power across the board. Throw a stock silencer on there that makes the exhaust take two or more 180 deg turns - which causes backpressure at all RPMs - guess what happens to velocity, it goes down the toilet -- everywhere.

This is especially critical on an engine with a fairly "wild" cam - probably mostly so on engines with lots of overlap that need all the help they can get drawing in a fresh charge at lower RPMs. I've dealt with some 400EX's that wouldn't even run with any type of stock silencer - even a gutted one that flowed every bit as well or better than a 450R HRC setup.

So.... In this case, it's very likely that no matter what slip on you put in place of the stock pipe, you will likely realize an increase in bottom end power, while at the same time, increasing top end power. Especially if you're not running a stock cam.

The HRC end cap, while good still leaves room for improvement -- it's passages (the stock silencer) are still relatively small and there is no direct path out for the exhaust, it must still make it's way thru at least two chambers (I can't remember exactly).

In my past experience, the difference may not be huge- there will likely be a difference. It's also my experience that changing the header will not make a huge difference either. All in all, with a 4 stroke, unless the pipe is ridiculously restrictive or the engine just refuses to run, there are only relatively small gains to be had with changing a pipe - especially if you're used to 2 strokes.
 

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I have to disagree because I have dyno sheets of a HRC kit/stock cam and full pipe vs. the same bike with an HRC end cap ... There is a gain everywhere; not just on top ... It's about 1.5 HP on bottom, 2HP in middle, 2.5 peak and almost 3 on over rev ... So there IS a pumping loss in the stock header with the stock cam with NO overlap ...[/b]
You must remember that a slip on will fall somewhere between those figures -- more than likely, closer to the full pipe side than the HRC side. You changed two variables when you made the comparison above - you changed the type of silencer and you changed the header at the same time, so those results can't be used to examine the effects simply adding a slip-on silencer versus a full pipe setup.

The gains you saw on the bottom were due to what I was talking about with removing the restrictions in the path the HRC silencer has --- they most likely aren't coming from a larger diameter header tube. The gains thru the mid and top are also partially from opening the silencer end (remember the HRC cap does not flow like a slip on silcencer - a quick step behind an idling bike will quell any doubts you may have as to which is carrying more velocity at idle, imagine the difference as flow goes up)

To compare exhaust length and diameters and their effects on how the engine runs, you must make an apples to apples comparison of either a free flowing open silencer on both systems or a partially open setup like the HRC cap on both systems.
 

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I think there is validity in changing the tuned length as well as increasing the header diameter.

However, I also believe there is power to be gained just by adding a slip on (over the HRC) if someone wants to save the additional $200 over going with a full pipe to get every last ounce of power available to them.

As far as the HRC setup goes -- with the stock 450R silencer Honda changed the internal design of the silencer body over what they have used in the past -- with the 400EX, removing the end cap did little to nothing. So, yes, changing from stock to the HRC cap does make a substantial improvement over the stock plugged up silencer - it removes the 180 degree changes of direction in the exhaust flow and opens the whole system up a good bit --- but the exhaust still has to pass thru chambers and it's exit path is not linear (i.e. the pulses will still bounce off the internal walls of the chamber before exiting). In my past experience (and in running the logic thru my head), while this improves overall flow for better top end, it doesn't necessarily do a whole lot for bottom end scavenging because the pulses are still being "disturbed" before their exit.

I've tested an HRC type setup verses an open, slip-on type silencer on my 400EX (among several other pipes) and while there were definitely gains by going with the HRC type setup, there were more gains by using a slip on -- primarily noticible in the bottom end.

Now... You mentioned that the YFZ has lower peak flow --- how was that determined and/or what exactly are you referring to, the pipe or the head? While the YFZ head does likely have better low lift flow, it does not flow as well as the TRX head overall --- especially on the exhaust side where the valves are significantly smaller. Who's to say the YFZ wouldn't run better or develop more torque with a smaller header?
 

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Now if only we could talk the exhaust makers to weld a small bung in every pipe near the muffler inlet so us guys could run an O2 sensor kit ...[/b]
That would be nice wouldn't it?

I'm getting ready to weld a bung into my HMF header for fine tuning - be nice if there were one there from the beginning...
 
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