exhaust pipe length - Wrist Twisters
 
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post #1 of 23 Old 09-17-2010, 08:55 PM Thread Starter
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exhaust pipe length

hey guys, ive got an interesting question. In a couple of months i want to do the pcIII+exhaust combo. I know alot guys here love the dual undertail pipes, much respect to that, although i kinda fancy the look without them. i think it really shows off the curve of the tail.. but each to their own.

so here my question, does pipe length from the where the headers join to make 1 pipe matter in terms of perfomance? I like the look of googleit's bikes, where a single exhaust is mounted to the rear pegs, very sexy. but ive also seen a couple of hornets with an exhaust under the engine. does this damage the engine in anyway? bare in mind i will be getting it dyno tune with a pcIII. any advice on this subject would be greatly appreciated.

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post #2 of 23 Old 09-17-2010, 10:04 PM
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The 900rr, which was the first bike Honda used this engine on, came with 4-1 single exhaust. So as far as going into 1, there shouldn't be any issues there. Probably more power if you get the 900rr headers, right can, and proper PC3 map.

Just going off logic here... but I don't think you can damage the engine going 4-1. As far as going out the back by the passegner foot peg or putting a can underneath the swingarm GP style, don't know if how that will effect performance or cause issues with the motor.

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post #3 of 23 Old 09-17-2010, 11:18 PM Thread Starter
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cheers andrewebay1. yea i was looking at a 900r exhaust which had the 4-1.

i like the look of the exhaust under the engine , like how buells do it. not sure how it would sound though. i guess any information on this too would be most valuable.

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post #4 of 23 Old 09-17-2010, 11:54 PM
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Yes the mid-pipe lenght will make a difference - or to be correct the mid-pipe volume.

Sounds like you are proposing to pretty much eliminate the mid-pipe and mount a muffler straight after the 4-2-1 part of the header - I suspect you'll gain some top end and loose some bottom/mid range. A PC111 tune will help, but .......

900rr header with the mid-pipe is not a issue as you'll find the midpipe length and volume is not far off the stock 919 - if you consider the Y pipe on the 919 is two slim pipes and the 900rr has one fat one.

Headers make the biggest difference and to do the Buell style you'd want to look at some how incorporating a suitable volume of mid-pipe prior to the muffler. Do-able for sure but I'd be inclinded to consider some form of header modification that sweeps them left or right (not central as per the stock set-up) so there is room to have a mid-pipe flick back 180 degrees to enter the muffler near the front of the engine with final exit at the rear. Buell hides all this shit in a big black heavy muffler.

I've a picture a work of a clean under engine canister with twin shorty mufflers on a 919 - I'll post it on Monday.

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post #5 of 23 Old 09-18-2010, 08:42 AM
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Originally Posted by AllanB View Post
Yes the mid-pipe lenght will make a difference - or to be correct the mid-pipe volume.

Sounds like you are proposing to pretty much eliminate the mid-pipe and mount a muffler straight after the 4-2-1 part of the header - I suspect you'll gain some top end and loose some bottom/mid range. A PC111 tune will help, but .......

900rr header with the mid-pipe is not a issue as you'll find the midpipe length and volume is not far off the stock 919 - if you consider the Y pipe on the 919 is two slim pipes and the 900rr has one fat one.

Headers make the biggest difference and to do the Buell style you'd want to look at some how incorporating a suitable volume of mid-pipe prior to the muffler. Do-able for sure but I'd be inclinded to consider some form of header modification that sweeps them left or right (not central as per the stock set-up) so there is room to have a mid-pipe flick back 180 degrees to enter the muffler near the front of the engine with final exit at the rear. Buell hides all this shit in a big black heavy muffler.

I've a picture a work of a clean under engine canister with twin shorty mufflers on a 919 - I'll post it on Monday.
Wave theory is dependent upon length.
Flow velocity is dependent upon diameter.
When it comes to headers and collectors in particular, it's all about lengths and diameters and zero about the resultant volumes. The only volume specific component in the entire exhaust system is the the muffler, or mufflers as the case may be.

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post #6 of 23 Old 09-18-2010, 09:34 AM
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Quote:
Originally Posted by mcromo44 View Post
Wave theory is dependent upon length.
Flow velocity is dependent upon diameter.
When it comes to headers and collectors in particular, it's all about lengths and diameters and zero about the resultant volumes. The only volume specific component in the entire exhaust system is the the muffler, or mufflers as the case may be.
volume is a function of length and diameter.... it just explains the two

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post #7 of 23 Old 09-18-2010, 12:15 PM
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The 919 engine is not really that highly tuned and any difference in performance between pipes/cans/systems would be negligible.

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post #8 of 23 Old 09-18-2010, 12:34 PM
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Quote:
Originally Posted by nd4spdbh View Post
volume is a function of length and diameter.... it just explains the two
Sure, volume is a function of length and diameter.
But simple volume is not the target characteristic for exhaust design, nor a standalone design element - if the exhaust system is intended to enhance performance. (Again, mufflers aside)
Header and collector lengths and diameters are.
Exhaust gas velocity is function of diameter.
Exhaust gas pressure fluctuations are primarily a function of lengths.

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post #9 of 23 Old 09-18-2010, 12:37 PM
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The 919 engine is not really that highly tuned and any difference in performance between pipes/cans/systems would be negligible.
You can easily kill the midrange of a 919 with a lousy pipe, just like you can kill any engine's power with a lousy pipe.
4 into 1s are notorious for a mid range flat spot if tuned for peak.

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post #10 of 23 Old 09-18-2010, 02:13 PM
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Quote:
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The 919 engine is not really that highly tuned and any difference in performance between pipes/cans/systems would be negligible.
Most of the aftermarket slip on cans - yes - they all are approximately the same lenght and tend to have cores around the 2 inch diameter. However not all are equal - if you look at the Sato & Yoshis you'll also see that they have taken the time and expense to offer a smooth transation in diameters on the mid pipes. Compare this with a D&D that looks like the mid-pipe was stolen from your mums vacumn cleaner ......

As he is discussing the header & mid-pipe and this is where it will alter the bikes performance and how it is delivered.

Re Volume - correct I was presuming there would be some reasonable length in the mid-pipe not bolting a metal bucket on the end thinking it will offer enough volume! My bad with my explination. For the cleanest state of tune you'll want to replicate in some form the stock diameter and lenth or the 900rr's.

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post #11 of 23 Old 09-18-2010, 02:21 PM
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Quote:
Originally Posted by mcromo44 View Post
You can easily kill the midrange of a 919 with a lousy pipe, just like you can kill any engine's power with a lousy pipe.
4 into 1s are notorious for a mid range flat spot if tuned for peak.
You can not kill the midrange, that is a little bit of a exaggeration.

Yes, you can put a little blip of a flat spot in it, that is as simple as installing a stock 900RR head pipe.

Many people mistake that little flat spot as a bump in performance when it comes off it, that is a mistake.

Check all the dyno charts, there are a zillion of them out there, pipes make a marginal difference on the 919.

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post #12 of 23 Old 09-18-2010, 04:30 PM
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Originally Posted by FJ1200 View Post
You can not kill the midrange, that is a little bit of a exaggeration.

Yes, you can put a little blip of a flat spot in it, that is as simple as installing a stock 900RR head pipe.

Many people mistake that little flat spot as a bump in performance when it comes off it, that is a mistake.

Check all the dyno charts, there are a zillion of them out there, pipes make a marginal difference on the 919.
You're talking 900 RR headers ,while I'm painting the theoretical extreme of 4 inch primaries 2 inches long and 1/2 collector that is 2 ft long to make a point.
Decent pipes won't screw things up badly, we are on the same page in that respect.
As for dyno curves, seemingly small blips at full throttle are not indicative of partial throttle characteristics. Typically, if it's off a full throttle it just gets worse at partial throttle. It's similar in effect to Air / Fuel ratios. If you tune for full throttle max power, you'll be down below 13: 1 for sure, higher 12s being the norm. But engines tuned that rich tend to run a bit "flat" under partial loads, and just aren't happy there in terms of response. Modern ignitions and fuel injection have reduced the effect, but it is still there.

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post #13 of 23 Old 09-18-2010, 06:21 PM
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Is it as simple as shorter pipes = bigger diameter?

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post #14 of 23 Old 09-18-2010, 06:47 PM
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Quote:
Originally Posted by honda ng gingsa View Post
Is it as simple as shorter pipes = bigger diameter?

in a simple answer.........no.

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post #15 of 23 Old 09-18-2010, 07:11 PM
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Quote:
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in a simple answer.........no.
Echo Echo

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post #16 of 23 Old 09-19-2010, 04:03 AM
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Haha, OK. watching the discussion as develops.

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post #17 of 23 Old 09-19-2010, 02:31 PM Thread Starter
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hope i havent started a figthing thread. lol

sweet so the under engine exhaust could be a little hard as i dont plan on modfying the headers, that would be a mission. I do like the look of a single low side mounted exhaust and a guy up here in auckland does beautiful custom exhausts, soo will need to investigate into that.

so from what i gather pipe length is v.important. I remember hearing about this too from some kawasaki mechanics a while back where they did a custom job for a cbr1000rr. They made a low side exhaust with alot of pipe wrapped around each other. look wicked and sounded even better.

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post #18 of 23 Old 09-19-2010, 03:09 PM
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check out this thread - it is a NZ bike too.

https://www.wristtwisters.com/f94/var...ipe-24685.html

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post #19 of 23 Old 09-19-2010, 03:09 PM
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Quote:
Originally Posted by veEnom View Post
hope i havent started a figthing thread. lol

sweet so the under engine exhaust could be a little hard as i dont plan on modfying the headers, that would be a mission. I do like the look of a single low side mounted exhaust and a guy up here in auckland does beautiful custom exhausts, soo will need to investigate into that.

so from what i gather pipe length is v.important. I remember hearing about this too from some kawasaki mechanics a while back where they did a custom job for a cbr1000rr. They made a low side exhaust with alot of pipe wrapped around each other. look wicked and sounded even better.
The best under engine exhaust I have seen is in this thread
https://www.wristtwisters.com/f94/my-...f800-1995.html


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post #20 of 23 Old 09-19-2010, 03:12 PM
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Yeah but he has engine mounted crash knobs .

Bawahahahahahahahaha

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post #21 of 23 Old 09-19-2010, 04:27 PM Thread Starter
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Quote:
Originally Posted by marylandmike View Post
The best under engine exhaust I have seen is in this thread
https://www.wristtwisters.com/f94/my-...f800-1995.html

the single sided swingarm is absolute sex!

i somehow never fancied the bellypan on the hornets, but i like the clean look of of the under engine exhaust i must say.

cheers allanb. ive seen this thread before. i might go for something alittle smaller to emphasize the tail of the hornet a lil more, whilst following the lines of the tail. i just love the tail without the twin underseat exhaust.

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post #22 of 23 Old 09-19-2010, 05:33 PM
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Quote:
Originally Posted by veEnom View Post
hope i havent started a figthing thread. lol

sweet so the under engine exhaust could be a little hard as i dont plan on modfying the headers, that would be a mission. I do like the look of a single low side mounted exhaust and a guy up here in auckland does beautiful custom exhausts, soo will need to investigate into that.

so from what i gather pipe length is v.important. I remember hearing about this too from some kawasaki mechanics a while back where they did a custom job for a cbr1000rr. They made a low side exhaust with alot of pipe wrapped around each other. look wicked and sounded even better.
No fighting, just different perspectives. Length is very important. Diameter to lesser extent within typical range of variations. A bit more insight on this. V-8 car hot rodders would buy "race" headers and put them on their street cars. Even if the engine was fairly maxed out in terms of build, for the realities of driving the car on the road, the headers had primaries too short and too fat. Meanwhile, the same header manufacturer would have a "street" range of header with, are you ready, longer primaries and small diameters. Part throttle and low to mid RPMs were stronger, and the ONLY sacrifice was true full throttle peak power RPM modes of use - which is rare on the street but what you'd be doing at Friday night bracket racing.

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post #23 of 23 Old 09-19-2010, 05:38 PM
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Found em in my collection of 919 Hornet images. The low-pipe black one has some form of mid chamber after the header not unlike the current crop of sports bikes with little moto-gp mufflers. I wonder if it is a mid pipe doing a 180 degree bend to get the length before exiting and they have covered it in a tidy case.

And a couple of cool high-pipe ones just for good measure.
Attached Images
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File Type: jpg GP_BLACK2.jpg (113.4 KB, 19 views)
File Type: jpg MC15 Hornet.jpg (81.8 KB, 14 views)
File Type: jpg orangeracing-02.jpg (80.1 KB, 16 views)

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