Exhaust tuning question

motthomas · #1 2nd July 2010, 12:37 PM

Any exhaust tuners on here?

This is a bit on the technical side so bear with me...

I was looking at getting a cheap stainless exhaust system off ebay for the mc22 seeing as my stock headers are rusting. I emailed yer man looking for dimensions so I could compare it to the stock system and see how it would perform. I have "Four Stroke Performance Tuning" by A. Graham Bell so I decided to run the numbers and compare where the stock system and the ebay system were placing the power.

Bell gives an equation in his book which says that the primary pipe length:

P=((850xED)/rpm)-3

P is pipe length in inches
ED is 180degrees+position before BDC the exhaust valve opens
rpm is the rpm which the exhaust is tuned to

So first off I threw in the stock pripary pipe length into the equation along with ED=209 since in the mc22 the exhaust valve opens 29degrees BBDC.

The result I got was that the stock system seems to be tuned to only 5240rpm!
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Thats seems pretty low to me given that the mc22 produces max torque @ 11500rpm and max power @ 14500rpm.

So I ran through the equation again looking for the primary pipe length if the exhaust were to be tuned to the 11500rpm and it came out to only 320mm!

Basically my question is did honda deliberately design the exhaust to give a boost to power in the lower revs at the expanse of overall power? Or is Bells equation outdated and theres a better way of doing things now? Im just throwing it out there in the hopes that someone knows something about this tuning malarky!
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Black Rabbit · #2 2nd July 2010, 01:10 PM

What you talkin' about Willis???
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revenga · #3 2nd July 2010, 01:11 PM

Wouldn't be surprised if honda did it to beef up the low and mid range

jimgoose · #4 2nd July 2010, 03:23 PM

Ever ridden a real racebike? I mean a full-fat, no-messing, close-ratioed, flatslide-carbed racebike that never had lights. They are nasty, nearly unrideable brutes when taken out of their proper environment, and your MC22 would be rather similar if Honda didn't tweak the header lengths to give it a little bit of pork lower-down. Also, having the optimisation there gives a better, cleaner burn, which I'd imagine helps with the EU emissions regulation - that's typically tested at around those revs, and is why most biggish bikes have a bit of a flatspot around there.

How does the primary header pipe length on the eBay system compare with the stock setup, BTW?

corkgsxr · #5 2nd July 2010, 06:39 PM

Originally Posted by jimgoose

Ever ridden a real racebike? I mean a full-fat, no-messing, close-ratioed, flatslide-carbed racebike that never had lights. They are nasty, nearly unrideable brutes when taken out of their proper environment, and your MC22 would be rather similar if Honda didn't tweak the header lengths to give it a little bit of pork lower-down. Also, having the optimisation there gives a better, cleaner burn, which I'd imagine helps with the EU emissions regulation - that's typically tested at around those revs, and is why most biggish bikes have a bit of a flatspot around there.

How does the primary header pipe length on the eBay system compare with the stock setup, BTW?

like one guys drag ducati i saw, 30 hp at low revs then for the last 2.5k it went up to 200 odd hp

all it was for was drag racing.

motthomas · #6 2nd July 2010, 07:59 PM

Originally Posted by jimgoose

Ever ridden a real racebike? I mean a full-fat, no-messing, close-ratioed, flatslide-carbed racebike that never had lights. They are nasty, nearly unrideable brutes when taken out of their proper environment, and your MC22 would be rather similar if Honda didn't tweak the header lengths to give it a little bit of pork lower-down. Also, having the optimisation there gives a better, cleaner burn, which I'd imagine helps with the EU emissions regulation - that's typically tested at around those revs, and is why most biggish bikes have a bit of a flatspot around there.

How does the primary header pipe length on the eBay system compare with the stock setup, BTW?

I realise the power would need to be a bit more spread out in a road bike rather than all slapped onto one spot higher up the rev range but I really didnt think there would be that much of a gap between the power/torque area and the exhaust optimisation area. Especially when the carbs are optimised for higher up the range...
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The ebay system looks to be tuned to 5970rpm so slightly higher up the range than stock. Ive to check the size of the exhaust port on the head though because the ebay headers are wider than stock so if they end up bigger than the ports there would be a sudden expansion problem right at the ports.

But Ive already decided not to chance that system because Im not sure I trust the quality of stainless and welds coming from HongKong and sold on ebay!
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Considering a completely custum job from a reputable local fella will only set me back 200squid more.
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Im just curious about the whole tuning thing now.

j-hornet250 · #7 2nd July 2010, 08:19 PM

if you can get a set of stainless headers made up for 200 i'll get a set at the same time

motthomas · #8 2nd July 2010, 08:46 PM

Originally Posted by j-hornet250

if you can get a set of stainless headers made up for 200 i'll get a set at the same time

Sorry man, I meant 200 on top of the price for the ebay system and thats 280.
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Though I was quoted that for an entire system so headers collector and end can so Im sure if you just wanted headers made up it would be cheaper. Ill PM you the number.
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jimgoose · #9 3rd July 2010, 11:55 AM

Originally Posted by corkgsxr

like one guys drag ducati i saw, 30 hp at low revs then for the last 2.5k it went up to 200 odd hp

all it was for was drag racing.

That would be a bit of an extreme case, but yes, that's the sort of setup I'm referring to.

jimgoose · #10 3rd July 2010, 11:59 AM

Originally Posted by motthomas

I realise the power would need to be a bit more spread out in a road bike rather than all slapped onto one spot higher up the rev range but I really didnt think there would be that much of a gap between the power/torque area and the exhaust optimisation area. Especially when the carbs are optimised for higher up the range...
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The ebay system looks to be tuned to 5970rpm so slightly higher up the range than stock. Ive to check the size of the exhaust port on the head though because the ebay headers are wider than stock so if they end up bigger than the ports there would be a sudden expansion problem right at the ports.

But Ive already decided not to chance that system because Im not sure I trust the quality of stainless and welds coming from HongKong and sold on ebay!
To view pics on this biker's forum - your post count must be 2 or greater.
Considering a completely custum job from a reputable local fella will only set me back 200squid more.
To view pics on this biker's forum - your post count must be 2 or greater.
Im just curious about the whole tuning thing now.

Maybe you're starting to overthink this a bit? If 'twere me, I'd clap a decent (possibly even used) full-system from a reputable manufacturer on there and have the fueling seen to - that is, properly rejetted and dyno-d.
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