'Race' exhaust, first gen vs second gen 1100 - Suzuki GSX-R Motorcycle Forums Gixxer.com
 
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post #1 of 6 (permalink) Old 06-08-2018, 10:28 PM Thread Starter
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'Race' exhaust, first gen vs second gen 1100

Perplexed by my findings so far on various header tube diameters on 86-88 1100 vs 89-92 1100. Wondering if anyone can shed some light...

I have two sets of Yoshimura 'race' headers for the 1052 motor. One is on my 1109, and one is a duplex on the shelf. They both have an O.D. of 41mm on the header tubes( I will be selling the duplex once I repack and re-sleeve the slightly scratched cannister. But I digress...)

I have a Yoshimura 'street' system on my '91 1127. It has an O.D. of 38mm. I know it is designated a 'street' system as I talked directly with Yoshimura and they identified it as such with the serial/model #.

My confusion is that I can not find any headers/full system for the 1127 motor, of any brand, that has an equally large diameter header tube. I spoke with Hindle, and Akropovic, and both of their 'race' systems have an outside diameter of 38mm. ???

I find this baffling because either there is something mysteriously different about the 1127cc motor vs the 1052 motor that would dictate a smaller diameter header tube for RACE situations. I understand a smaller diameter header will be more street friendly with the preservation of the mid-range from higher exhaust gas speed etc. But I can not understand why a RACE system would be that much smaller.

And btw, at first glance, 38mm doesn't sound much smaller than 41mm, but it surprisingly represents a 15% difference in cross sectional area.

OR, these supposed 'race' systems are not actually so.

Does anyone out there own a header/full system for an 1127 that has a 41mm O.D., or larger, header tube diameter?

btw, the reason for all this curiosity, is I love the performance of the 41mm Yosh header on my 1109cc '86 motor. I don't feel any compromise in the midrange and I want to reproduce the same on my 1127, soon to be 1216.

Any feedback, info, witty banter, semi-critical feed-back is welcome!
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post #2 of 6 (permalink) Old 06-09-2018, 04:31 AM
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Re: 'Race' exhaust, first gen vs second gen 1100

Hi 69Neal - The internal diameters would be more useful, but even then....... I have an Akrapovic system, they produce at least as much power as any other system, but they also have a really good overall delivery. Both Akrapovic and Hindle use very thin walled stainless steel (I think Hindle are in s/s) I think if a wider header worked better they would've used it. Yoshi often use mild steel, which corrodes, so it would need to be thicker, else it would hole all the time - they also made s/s systems, but most I've seen are steel, which needs to be thicker and coated. The length of sections and shape of the collector has a big bearing on power. Many tuners used exhaust wrap to speed up header flow, so velocity is more important than header capacity much of the time. I think if you had a maxed out motor, huge capacity, majorly altered head, higher rev limits - as used on the drag strips in the 90's, the large diameter internal diameter headers would help at the top-end. That's my take on things, my motor is fairly mildly tuned, if I thought there were gains to be had with larger headers I would've bought them - but I wouldn't be overly concerned with header external diameter - GSX1400's had large looking headers, but they were double skinned (to stop bluing) and had a small internal diameter ! - they were pig heavy too..

It's likely that Yoshi altered other parts of the exhaust for the 'race' system compared with their road system to work properly - but increasing header diameter by itself doesn't necessarily mean more power and can cause poorer running lower down - more noticeable on 750 motors.

That's my long winded reply !
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post #3 of 6 (permalink) Old 06-10-2018, 06:14 AM
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Re: 'Race' exhaust, first gen vs second gen 1100

On mine it depends on where you measure the tubes. The first section from the engine down to the first weld measures 38mm and the second section from the Duplex cans to the collector are 41mm, maybe that explains it?

Those measurements came from a stainless R125RRD and surprisingly the '90-'91 750 pipe (R775RRD) measured the same!
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post #4 of 6 (permalink) Old 06-10-2018, 04:23 PM
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Re: 'Race' exhaust, first gen vs second gen 1100

Yoshi were one of the first with tapered headers, I'd forgotten that Ragnar... (getting old and senile !) I know from some of my other bikes that wide headers can introduce flat spots and not necessarily boost top-end much - GSXR1000 headers aren't big diameter, but flow well enough.
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post #5 of 6 (permalink) Old 06-12-2018, 11:58 PM Thread Starter
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Thanks for the replies guys.

That is interesting about the tapered diameters on the duplex, I will check mine more carefully, altho mine is a first gen which is not necessarily going to be tapered and I’m more curious about the second gen.

Undoubtedly the wall thickness affects the inside diameter which is what actually matters. Just easier to measure outside diameter. If Hindle and Akro use a thin wall that could equate to maybe half the wall thickness of the mild steel yosh pipes with the same O.D. Of 38mm. That would still leave an approximate 7-10% less cross sectional area of a 41mm OD mild steel header.

But more significant to me is the fact that a Yosh race header for first gen is 41mm. And a Yosh ‘street’ header for second gen. is 38mm with the same mild steel wall thickness. This is comparing apples to apples and tells me that a second gen Yosh ‘Race’ header is not going to also be 38mm.

I don’t pretend to be very knowledgeable about header tube design but I know some basics. In regards to the variables to make a header more ‘powerful’, there is length of the tubes, and diameter of the tubes.(collector shape too but for sake of argument, not as significant as length and diameter). The length of the tubes move the torque curve up or down the rpm range, but it is the diameter which determines the ultimate Peak value of the torque. It is diameter that directly affects exhaust gas velocity. Too small a diameter and optimal torque will be missed out on. Too big is not good either or the engine will not be able to achieve the rpm/flow to take advantage.

I do find it interesting that Hindle and Akro use a smaller tube as these are reputable exhaust companies. But I don’t automatically believe that these must be optimum for all applications. The second gen 1100 was not/is not a typical race track bike. certainly less than the first gen was, which had extensive Yoshimura development. So one could argue that designing an exhaust for the second gen might be targeted at broader, all round performance, despite the ‘race’ designation on some brands. What I’m curious about is what the diameter Yoshimura headers are for a second gen ‘race’ exhaust is.

Ragnar, it sounds like yours is a race version with duplex? I think Duplex was exclusively a race exhaust feature? So that is very interesting with the tapering from 38-41mm. Also, if it is stainless, it is possible that it has a thinner wall than the mild steel and therefore even larger I.D. Than the mild steel versions. Also very interesting that the 750 Yosh race headers are the same diameter as your 1100 header. Seems that they are targeting a much higher rpm torque peak for the 750. But if that size diameter is not too big for a 750.....

I think a larger exhaust tube diameter becomes even more relevant when upping the displacement ~8-10% from 1127cc to 1216cc or more.
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post #6 of 6 (permalink) Old 06-14-2018, 07:34 AM
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Re: 'Race' exhaust, first gen vs second gen 1100

Javadog?......I don't have many answers, was surpsised to see the 750 pipe the same dia also, and yes, the ones measured were both stainless. Will have to measure a mildsteel pipe and see what that shows. I do know that the Duplex cans were there to slightly increase back pressure at lower RPM's to try and maximize power, say coming out of corners. So, non-Duplex pipes from any manufacturer "may" use a slightly smaller tube diameter throughout looking for the same result.

Edit: Correct, these were the pipes measured...
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Last edited by Ragnar; 06-14-2018 at 07:46 AM.
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