Author Topic: Preferred exhaust for CB750 sohc race bike  (Read 814 times)

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Offline cr750

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Preferred exhaust for CB750 sohc race bike
« on: December 03, 2018, 01:54:08 am »
Hi Guys,

I am building a new vintage trackbike for myself over this winter, which I will be using for trackdays here and there and some endurace racing in Oschersleben.
Will be based on a K7 engine (standard cc - mild tune) and frame, ignitech ignition, CR carbs, alloy tanks and wheels, glasfibre seat, forks and axles to be decided ( leaning towards f1 rear (spoke/disc) and updated GL1000 front with AP or cbr calipers and cbr axles....

Anyway.....

I was wondering what the racers out there prefer for their bikes in terms of exhaust system (4-4, 4-1, 4-2-1, 4-2) ?

I am under the impression that although the street bikes and the CR750 use a 4 in 4 exhaust, actually a 4-2-1 system (triple Y) would be the 'best' system for allround performance for a  4 in line race bike that races circuits ? Reason for this I see it (4-2-1) most widely used on other (fast) vintage 4 cilinders on the racetracks in Europe ( so this motivation is both good and silly  :D )
For example I don't know if in a mild state of tune engine there's a lot of difference between using a 4-1 compared to a 4-2-1 ?

I do know there's different exhaust configs preferred for different racing ( drag - track - oval ).

I will race mostly on racetracks in Europe like Zolder, Assen, Oschersleben etc.
So tracks with a lot of bends and some straights, so I am looking at a good allround system, not merely tuned for all out power.

Can anyone tell me which system they prefer and why, preferrably form first hand experience ? ( racing yourself on racetracks or road ).
Also love to hear which suppliers you prefer in terms of exhaust systems, as I see sometime pipes cut open that simply look awfull inside in terms of welding and finishing.
Also it needs to be a system with a muffler ( or to which I can fit one), as most circuit in Europe have noise restrictions.
If I need to do some fabrication I don't mind (can weld stainless in house so fixing a muffler or an hanger is not the issue). But I do not want to build a full system with all joints myself.
« Last Edit: December 03, 2018, 01:56:55 am by cr750 »
Wanted: PERIOD cr750 or rc750 parts.
In specific; plastic cr31 velocity stacks, foot levers(+cable), rear brake. Got any of these parts or other period cr/rc750 parts/leads; Pm or E-mail me !

Ps. I know where to find the MODERN reproductions.

Offline turboguzzi

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #1 on: December 03, 2018, 01:46:14 pm »
there should be a guy in germany doing 4-2-1 for vintage bikes, cant remember his name, a link should be somewhere here in the posts.
4-2-1 supposed to be "best" config, though not many connect 1-4 & 2-3 as it should be... many build  1-2 & 3-4 which are easier to make...

Offline bwaller

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #2 on: December 03, 2018, 03:41:25 pm »
Probably best for overall power delivery to choose a 4-2-1.

Check with Kemp Archibald in Canada. The pipe is built by an ex Canadian racer Lang Hindle.

https://www.ripplerockracers.com/product/cb750-hindle-vintage-racing-exhaust-system-fits-1969-78/

Offline MRieck

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #3 on: December 03, 2018, 07:17:39 pm »
Probably best for overall power delivery to choose a 4-2-1.

Check with Kemp Archibald in Canada. The pipe is built by an ex Canadian racer Lang Hindle.

https://www.ripplerockracers.com/product/cb750-hindle-vintage-racing-exhaust-system-fits-1969-78/
Yep again.
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Offline PeWe

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #4 on: December 03, 2018, 09:51:22 pm »
there should be a guy in germany doing 4-2-1 for vintage bikes, cant remember his name, a link should be somewhere here in the posts.
4-2-1 supposed to be "best" config, though not many connect 1-4 & 2-3 as it should be... many build  1-2 & 3-4 which are easier to make...
This one?
http://translate.googleusercontent.com/translate_c?depth=1&hl=en&rurl=translate.google.com.au&sl=de&sp=nmt4&tl=en&u=http://www.schuele-maschinenbau.de/pages/ausp_klassik/cb750_rick.htm&xid=25657,15700023,15700124,15700149,15700186,15700191,15700201,15700237&usg=ALkJrhjPhCSlD7hQHrDwTrjlmSBBV2dVgg
http://www.schuele-maschinenbau.de/

Hindle 4-2-1 work fine on my street bike. 
Not that loud but will be heard when twisting. Nice deep tone.I need to make brackets for passenger foot pegs  as I did for an RC4-1 (K7 model to fit my K6 when these were available to order.)

EDIT: Here a link to another Hindle with the longer baffle as I have. Kemp at Ripplerock mentioned on my question when I ordered that most power will be achieved with the longer baffle.
Short for the wonderful song.  ;)
I ordered both baffles just for sure  8)
http://forums.sohc4.net/index.php/topic,147350.msg1720744.html#msg1720744

I can most likely remove oil filter without removing the pipes. Have not done it yet, will soon.
« Last Edit: December 04, 2018, 08:40:23 am by PeWe »
CB750 K6-76 1005cc JMR Billet block.
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Offline Old Scrambler

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #5 on: December 04, 2018, 08:20:27 am »
Also consider..............www.cyclexchange.net and take a close look at the performance exhaust page along with separate 1-4; 2-3 header page. Based on my research.........the smaller inside pipe diameter may increase power...........take a look at the F2-F3 OEM design.
Dennis in Wisconsin
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Offline PeWe

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #6 on: December 04, 2018, 08:44:40 am »
I forgot to mention that the Hindle 4-2-1 is very light.
As Kemp wrote in the other thread:
We developed a 4-2-1 to get maximum torque and horsepower, a design that Hindle has been using on all his modern era pipes. This has been really successful in dyno runs over conventional 4-1 pipes from the era. Hindle has tried the crossover many years ago and couldn't get any improvement from combining 1&3, 2&4 over 1&2 and 3&4 so we stick with 1&2 etc as we also prefer the sound in this combo with the 4cyl models. We use a 1.5 inch headers and thin wall stainless steel much like some world superbike racers for light weight, durability and cost benefit over titanium. The system is all spring mounted for easy access as we pattern our vintage exhaust models after Lang's Championship winning superbike. It's truly a blast working with Hindle to design and manufacture these vintage systems.
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Offline Tim2005

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #7 on: December 04, 2018, 11:58:46 am »
The German one could also be a Baldes, both those and the Schule are 4:2:1 some pics below (Baldes is first one)

Offline turboguzzi

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #8 on: December 04, 2018, 12:14:11 pm »
bravo tim, those are the ones i thought of
http://www.schuele-maschinenbau.de/pages/klassik.htm
http://www.baldes-auspuff.de/

baldes makes some nice frames too...

Offline cr750

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #9 on: December 05, 2018, 05:54:14 am »
Thank guys ! A lot of info to go trough.

But ok, 4-2-1 it is for the exhaust, seems no doubt about that.
Only if the combo on 1-3 / 2-4 or 1-2 / 3-4 makes any difference if I read TG and PeWe correctly.
I guess there's no real evidence to be had on that, just opnions.

Interesting frame on that last one TG !

Wanted: PERIOD cr750 or rc750 parts.
In specific; plastic cr31 velocity stacks, foot levers(+cable), rear brake. Got any of these parts or other period cr/rc750 parts/leads; Pm or E-mail me !

Ps. I know where to find the MODERN reproductions.

Offline turboguzzi

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #10 on: December 05, 2018, 11:42:48 am »
disclaimer- never had the chance to play with different systems in a dyno room, so no 1st hand experience. the theory is that 1-4, 2-3 have even 360 rotation pulses at the first Y, the second Y helps at lower revs.
1-2,3-4 have uneven pulses at 1st Y (180-540) so one cyl. "gets helped" more than the other.
for what it's worth, had the chance to see the motogp M1 yamaha naked and up close at the racing HQ and that bike was surely 1-4,2-3....
but honestly, for a mild tune like you are doing, doubt if youll feel the difference,

Offline cr750

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #11 on: December 08, 2018, 12:31:47 am »
Hey TG, I agree I will probably not notice, I am just going to source a 4-2-1
But if cost an availability are the same I will buy a 1-4 2-3 version.
You never know what the future brings :-)
Wanted: PERIOD cr750 or rc750 parts.
In specific; plastic cr31 velocity stacks, foot levers(+cable), rear brake. Got any of these parts or other period cr/rc750 parts/leads; Pm or E-mail me !

Ps. I know where to find the MODERN reproductions.

Offline Grumpyoldgit

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #12 on: December 08, 2018, 05:21:51 am »
That Hindle System looks great!

Offline MRieck

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #13 on: December 08, 2018, 06:39:09 am »
That Hindle System looks great!
I have one sitting in the box....it looks well made and is pretty light. Win-win
Owner of the "Million Dollar CB"

Offline Tracksnblades1

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #14 on: December 09, 2018, 10:35:37 am »
Barring any top trade secrets, what primary pipe OD diameters are you guys seeing on your exhausts....?
I've measured a few in the barn. Don't have any under bed. 😎
My late 70 early 80 Yoshimura 4-1 has 1.503 OD primaries, (single wall chrome)
1977 cb750f stock has 1.378 primaries (dual wall chrome ?)
1978 cb750f stock has 1.378 primaries (dual wall chrome ?)
2014 cb1100 stock has 1.409 primaries (single wall ss)

I always thought the old RC pipes had some of the largest primary ODs.
A few of Kennys pipes have that old RC look going on.
The old dual overhead cam Hondas seem to share the same aftermarket exhaust regardless of displacement....?

What do some of your exhaust primaries measure on your rides, big bores and really big bores...too.....?

Thanks and have a great Sunday.
« Last Edit: December 09, 2018, 10:42:27 am by Tracksnblades1 »
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Offline PeWe

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #15 on: December 09, 2018, 11:10:12 am »
My Ripplerock Racers Hindle 4-2-1 has very thin pipes and nice bends, like art. ID must be relatively wide.
I remember my old RC4-1, pipes looked really fat on outside but was not that light.

Different applications have different needs  I suppose. A modified street bike that often is ridden in town and need to work fine on and from lower rpms work must likely better with not too unrestricted exhaust. Good response from 70kph-150kph important when passing slower going cars.
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Offline Tracksnblades1

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #16 on: December 09, 2018, 05:21:53 pm »
My Ripplerock Racers Hindle 4-2-1 has very thin pipes and nice bends, like art. ID must be relatively wide.
I remember my old RC4-1, pipes looked really fat on outside but was not that light.

Different applications have different needs  I suppose. A modified street bike that often is ridden in town and need to work fine on and from lower rpms work must likely better with not too unrestricted exhaust. Good response from 70kph-150kph important when passing slower going cars.

I see the work of art in your pictures. Excellent craftsmanship. I read in your previous post the Hindle has the 1.5" primaries. Mounted on your 1005cc K, I would say that exhaust note is in a bigger hurry to exit those 1.5" primaries as compared my 76f 736cc with the same.....
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Offline PeWe

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #17 on: December 10, 2018, 03:16:06 am »
My Ripplerock Racers Hindle 4-2-1 has very thin pipes and nice bends, like art. ID must be relatively wide.
I remember my old RC4-1, pipes looked really fat on outside but was not that light.

Different applications have different needs  I suppose. A modified street bike that often is ridden in town and need to work fine on and from lower rpms work must likely better with not too unrestricted exhaust. Good response from 70kph-150kph important when passing slower going cars.

I see the work of art in your pictures. Excellent craftsmanship. I read in your previous post the Hindle has the 1.5" primaries. Mounted on your 1005cc K, I would say that exhaust note is in a bigger hurry to exit those 1.5" primaries as compared my 76f 736cc with the same.....

The strange thing is that the baffle has a rather big hole all the way thru it and still not that loud. The silencer function is working with that perforated inner tube and "wool" around it as dampening and insulation keeping the baffle cool when pipes are hot. That's why the baffle is still not golden as the header that became colored after 1 hour or less.
My old 4-1 (Alfa) has not that wide hole, but still louder and sharper sound when twisting.

Interesting subject and hopefully others that have tried various dimensions and constructions can contribute with their experiences.
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CB750 K2-75 stock looking project started 2017

Offline turboguzzi

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #18 on: December 10, 2018, 03:57:55 am »
it's not as precise as with inlet ports, but also in exhaust pipes too big can be too much as essentially you are slowing down gas speed in the tube, losing the possibility to use it to help with scavenging. And diameter is not all, it's the ratio of diameter/length of primary tubes /length of secondary tube, not to mention the cam you are using.
Without knowing the application, road race, drag, street, etc. really hard to say that one diameter is "best". Very likely that best for track use is way smaller than you'd think
in case it helps, this is what a guy who used to work with Muzzy on Rainey's bike (GPZ750, so dims shouldn't be far off for a cb750...) told me:
"The pipe was a Kerker tapered 4-1 with 27" primary pipes. 1.375"-1.750" 2.5" baffle in the meg"

John Robinson "4 strk tunning book has quite a few formulas and internet is full too.

Offline cr750

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #19 on: December 11, 2018, 06:15:26 am »
On the subject ( while I am waiting on a plane in your lovely country TG); does anyone know if a CBR f3 exhaust would fit in terms of diameters on our our beloved cb750 ? Not like plug and play, but I mean in terms of diameters of the headers etc ? It seems to me that is stock a 4-2-1 and a stainless version could be had from a scrap yard in my area. A hacksaw and some Tig welding could deliver a cheap racing exhaust.
Wanted: PERIOD cr750 or rc750 parts.
In specific; plastic cr31 velocity stacks, foot levers(+cable), rear brake. Got any of these parts or other period cr/rc750 parts/leads; Pm or E-mail me !

Ps. I know where to find the MODERN reproductions.

Offline turboguzzi

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #20 on: December 11, 2018, 06:28:32 am »
not unheard off, Riccardo and Rene did exactly that in their racers. Rene is longer active here but he fitted a CBR600 system to his 500/4. Riccardo might have used one of a CBR900, not sure.

Offline Don R

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #21 on: December 11, 2018, 07:55:45 pm »
 I have a couple pipes to check, Hooker 4/2, unknown Yoshi clone 4/1, twin cam Vance and Hines 4/1 drag pipe. I'll measure some OD's.
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Offline 754

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #22 on: December 11, 2018, 09:23:30 pm »
My turbo header has small primaries,  , unequal length. Then a 2 inch pipe I think, to a megaphone..
 Seems far more torque than a 4 into 1 Hooker..
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Offline Tracksnblades1

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #23 on: December 12, 2018, 05:52:49 am »
it's not as precise as with inlet ports, but also in exhaust pipes too big can be too much as essentially you are slowing down gas speed in the tube, losing the possibility to use it to help with scavenging. And diameter is not all, it's the ratio of diameter/length of primary tubes /length of secondary tube, not to mention the cam you are using.
Without knowing the application, road race, drag, street, etc. really hard to say that one diameter is "best". Very likely that best for track use is way smaller than you'd think
in case it helps, this is what a guy who used to work with Muzzy on Rainey's bike (GPZ750, so dims shouldn't be far off for a cb750...) told me:
"The pipe was a Kerker tapered 4-1 with 27" primary pipes. 1.375"-1.750" 2.5" baffle in the meg"



John Robinson "4 strk tunning book has quite a few formulas and internet is full too.

A mini megaphone to a bigger megaphone. Sounds like them guys had some 2 stroke tuning experience with diverging cones. One more converging cone and they would have had an expansion chamber with a Long lead pipe.
« Last Edit: December 12, 2018, 08:19:30 am by Tracksnblades1 »
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Offline cr750

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #24 on: December 12, 2018, 10:49:21 am »
Thnx TG, interesting ! I pmd Riccardo a while ago. Dunno if he is still a active here ?
While we are at it.. does anybody know of a supplier like https://www.coneeng.com/motorcycle_components.html but then in Europe ? Can find enough for car exhausts, but not so much bike related in terms of separate parts to build your own.
Wanted: PERIOD cr750 or rc750 parts.
In specific; plastic cr31 velocity stacks, foot levers(+cable), rear brake. Got any of these parts or other period cr/rc750 parts/leads; Pm or E-mail me !

Ps. I know where to find the MODERN reproductions.

Offline turboguzzi

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Re: Preferred exhaust for CB750 sohc race bike
« Reply #25 on: December 12, 2018, 11:30:55 am »
I build for my supermono an exhaust system using bent and straight parts from a 600 supersport 4-1 and it wasnt that much fun, and that's just one cyl (albeit twin port exh). doing a 4 cyl, accounting for all the angles, lengths, spatial position while you tack everything together is going to be a nice little nightmare... not to mention welding thin-wall tubing challenge. really doubt the benefit vs headache...

 

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