jeepinbassist
CB750 Member
Have any of you guys done a baffle delete or bored out the inside of your exhaust. I'm thinking about doing something like this and would like to know what you guys have tried. Pictures if you have them.
-
🎁 Enter the August Vintage CB750 gift card giveaway! It's easy... Click here, post something, and you're entered into the drawing!
Exhaust Mods
- Thread starter jeepinbassist
- Start date
-
- Tags
- custom dohc exhaust fabricating tools
jeepinbassist
CB750 Member
Stock pipes. On mine I can look inside and see nothing removable.
falondin
CB750 New member
depending on the year of your bike you can remove the baffle and ride without it. I know here in NC if a vehicle is 35 years old it dont have to be inspected. It sounds great without them.
madmtnmotors
CB750 Addict
Depending on their condition and the year of the bike you might want to reconsider. The 4-into-4 aftermarket reproduction pipes for the 69-78 SOHC CB750's start at $1200 and can go as high as $2000:
http://www.davidsilverspares.com/CB750K6-FOUR-1976/part_188994/
You can get an aftermarket 4-into-1 all stainless steel for $350 shipped and save your stock pipes (if they're worth saving):
http://www.delkevic.us/index.php?ro...r+and+Stainless+Steel+4-1+Headers&SKU=COM2775
amc49
CB750 Guru
The later '79-83 DOHCs sound like sh-t with any baffle work at all, and they unlike many earlier bikes have solidly welded in baffle elements that have you pretty much destroying the exhaust to do any mods at all on them. Most of the baffles are welded quite solidly to the outer case and you will destroy that removing them.
Not only that, it often makes the engine run worse and simple jetting does not correct it, the actual tuning has been changed and any remains left of baffling after you find out how hard it is then makes the exhaust flow MUCH worse.
Don't ask how I know that...................
Thinking on the early SOHCs the baffles simply unbolt and come out. Definitely NOT true on the later ones.
Not only that, it often makes the engine run worse and simple jetting does not correct it, the actual tuning has been changed and any remains left of baffling after you find out how hard it is then makes the exhaust flow MUCH worse.
Don't ask how I know that...................
Thinking on the early SOHCs the baffles simply unbolt and come out. Definitely NOT true on the later ones.
Depends on the version of exhaust on sohc bikes. The early exhaust was basically a straight through pipe with a glass pack type insert. The 341 series had some baffling but still better then the last couple of years. As years went on honda added more baffling that could not be remove, but a long drill bit will go a long way in making less restriction lol
amc49
CB750 Guru
Yeah, how pretty much all the Japanese bikes have gone, they have unitized the exhaust pipes to make it much harder to mod them, no more bolt in baffles. Violation of law (emissions and sound level) and they are doing what they can to stop it.
Mcbuckets13
CB750 Member
I took the baffles out of my 92' CB750 nighthawk and it sounded crappy and ran crappy too. It was definitely louder, but not the right kind of loud that shows off your bike, rather the kind that makes people think "look at this idiot". Get a performance pipe, definitely worth the investment and gives you a torque/hp boost as well
amc49
CB750 Guru
BTDT. And being you commonly cannot remove ALL of the baffling it is very common for them to run like crap.
Witness post #7. Early on how they did things. Modding THOSE can help. But once they start looking for so quiet you can't hear it standing next to it then the pipe will be so baffled there is no way they can actually be 'tuning' the exhaust other than by back pressure only and back pressure tuning is NOT wave tuning , which gets you 5X the power. Wave tuning pretty much is impossible in that sort of extensive baffling other than in small increments like area control can give. Just like with a car. Why if you look around to pick a nice header rather than whatever one just 'fits' you can build a nice big chunk of torque that was not there before in a bike. On a Kerker I had on my DOHC it was easy to mod the baffle to make a whopping increase that was instantly feelable, throwing the OEM baffle back in immediately made that disappear. It all went back to the basic baffle design, that one had a thousand small holes instead of the cheaper much more common bigger fewer holes and in so doing it made removing the baffle fiberglas EXTREMELY worthwhile, it let the baffle becomes invisible to let the rear megaphone work almost identical to no baffle at all.
When I used to build 'streetrace' cars you could pick up 75+ hp. by simply removing the full length pipes to just run header mufflers, They alone can be tuned to pull maybe 90% of the power an open header will make out of them. No way will you ever do that with full length pipes to the back of the car and name any of the top brand trick mufflers you want there, it won't happen.
Witness post #7. Early on how they did things. Modding THOSE can help. But once they start looking for so quiet you can't hear it standing next to it then the pipe will be so baffled there is no way they can actually be 'tuning' the exhaust other than by back pressure only and back pressure tuning is NOT wave tuning , which gets you 5X the power. Wave tuning pretty much is impossible in that sort of extensive baffling other than in small increments like area control can give. Just like with a car. Why if you look around to pick a nice header rather than whatever one just 'fits' you can build a nice big chunk of torque that was not there before in a bike. On a Kerker I had on my DOHC it was easy to mod the baffle to make a whopping increase that was instantly feelable, throwing the OEM baffle back in immediately made that disappear. It all went back to the basic baffle design, that one had a thousand small holes instead of the cheaper much more common bigger fewer holes and in so doing it made removing the baffle fiberglas EXTREMELY worthwhile, it let the baffle becomes invisible to let the rear megaphone work almost identical to no baffle at all.
When I used to build 'streetrace' cars you could pick up 75+ hp. by simply removing the full length pipes to just run header mufflers, They alone can be tuned to pull maybe 90% of the power an open header will make out of them. No way will you ever do that with full length pipes to the back of the car and name any of the top brand trick mufflers you want there, it won't happen.
madmtnmotors
CB750 Addict
Witness post #4. It was this post that motivated me to respond one year ago before I realized this thread was already two years old at that time. According to jeepinbassist's profile he has not logged in here since November 2014.
Not to say that the thread is irrelevant, just that the original poster has likely made a decision by now (at least I hope so!) and is not likely to see these or future posts based on his inactivity here.
Observation over, let the discussion continue!
Not to say that the thread is irrelevant, just that the original poster has likely made a decision by now (at least I hope so!) and is not likely to see these or future posts based on his inactivity here.
Observation over, let the discussion continue!
amc49
CB750 Guru
For the general public.....................it seems how well it runs and sounds has much to do with the type of exhaust flow there, if a straight through type then it will do better, if the mod kills part of an exhaust 'loop' though you can get a much crappier result and most now use loops and splitting since that kills more noise in the confined space there. It's utterly amazing how simply defeating one loop can so open the outright noise up in some of them. On the F it was really bad sounding too, it had no basis in what a normal nice sounding exhaust sounds like, being a high flat 'blatting' sound that grated on your ears instantly.
The spark plugs actually got darker as well, meaning richer, meaning I LOST power there. I had a header for it within a week, no way was I gonna drive that new bike around sounding like that.
Honda wasn't kidding on the exhaust mod sticker on the bike when they said mods might hurt performance. Who knows, they may be setting those loops up in such a way that removing the easiest part actually messes the bike up worse, knowing how people commonly are.
The spark plugs actually got darker as well, meaning richer, meaning I LOST power there. I had a header for it within a week, no way was I gonna drive that new bike around sounding like that.
Honda wasn't kidding on the exhaust mod sticker on the bike when they said mods might hurt performance. Who knows, they may be setting those loops up in such a way that removing the easiest part actually messes the bike up worse, knowing how people commonly are.
Manufacturers spend tons of R&D$ on the exhaust tuning, not only for sound regulations but to enhance power. And then we go and screw it up by drilling holes in baffles etc 
Any modern exhaust I agree that alterations will hurt performance or modify the power band. My CBR954 has an exhaust diverter valve in the collector, changes from a 4-2-1 at lower rpms then goes 4-1 up higher. If you delete it or unhook it, it definitely makes lets lower end. The first 750's with the 340 exhaust did increase power when the baffle was removed, always had to go up about a jet size and would pull noticeably stronger, also had the best exhaust note of any bike I have ever heard. Honda is one of the best at making a quiet exhaust that still produces good power.
Any modern exhaust I agree that alterations will hurt performance or modify the power band. My CBR954 has an exhaust diverter valve in the collector, changes from a 4-2-1 at lower rpms then goes 4-1 up higher. If you delete it or unhook it, it definitely makes lets lower end. The first 750's with the 340 exhaust did increase power when the baffle was removed, always had to go up about a jet size and would pull noticeably stronger, also had the best exhaust note of any bike I have ever heard. Honda is one of the best at making a quiet exhaust that still produces good power.
amc49
CB750 Guru
They have the advantage of that dyno that sometimes shows things in exhaust tuning that make no sense but the effects are there solid as a rock. Like hitting a wall just right to greatly kill noise but not flow, sometimes that flaws with as little as 1/8" difference in the distance spec. I always wondered why they used essentially a glasspack BEFORE all the exhaust looping in the back of the DOHCs, the construction made no sense as the baffle was incredibly holed to then have glass but in only about a 1/8" space again, it shouldn't work packed tight and close like that but it apparently does something. I cut that section out to recover that drilled section as it makes excellent low flow loss baffling on other things.
My view is still pretty much that if you can remove something to have a straight through shot it generally can run better but now with all that direction changing that no longer works. I used to trim baffle length more and more on bigger Yam 2 strokes back in the day and if you stopped at the right length you picked up a whopping chunk of torque that disappeared again with the use of a stock baffle. The same idea worked great on Kaw 3 cylinders too. Maybe half the power of a good set of expansion chambers picked up for only a little work.
Oh yeah, if you go to messing with the variable volume pocket like on that CBR or Yamaha EXUP you WILL be f-cking it up. They spend millions just trying to find out the critical volumes for tuning like that. Just like the intake resonation chambers so many cars now use to reduce intake drone and increase low rpm torque at the same time. The area in those things does not accept modifying at all other than generally badly.
My view is still pretty much that if you can remove something to have a straight through shot it generally can run better but now with all that direction changing that no longer works. I used to trim baffle length more and more on bigger Yam 2 strokes back in the day and if you stopped at the right length you picked up a whopping chunk of torque that disappeared again with the use of a stock baffle. The same idea worked great on Kaw 3 cylinders too. Maybe half the power of a good set of expansion chambers picked up for only a little work.
Oh yeah, if you go to messing with the variable volume pocket like on that CBR or Yamaha EXUP you WILL be f-cking it up. They spend millions just trying to find out the critical volumes for tuning like that. Just like the intake resonation chambers so many cars now use to reduce intake drone and increase low rpm torque at the same time. The area in those things does not accept modifying at all other than generally badly.
ridersup
ridersup
750K exhuaust mods
This is is my 78 750k with an original 70's Jardine 4 into 1(unequal length) header. The header originally went straight back. Cut off @ 4-1 ,welded a set of automotive 3-1/2" collectors w/ a 3" exhaust tip. Used 1/2 of the original baffle into the new pipe (single pin holds the baffle for quick removal). Certainly not a scientific approach . Very inexpensive, and allows quick experimentation or mods. Currently #115 main jets - up 3 on pilot jets. Has individual pod filters. Dyna coils. 14/48 on the sprockets. Idles great ,starts with out the choke. Revs to 9grand cleanly. plugs(e3) read good. Of course gas milage has suffered. No freeway cruiser, but quick/fun street setup.
This is is my 78 750k with an original 70's Jardine 4 into 1(unequal length) header. The header originally went straight back. Cut off @ 4-1 ,welded a set of automotive 3-1/2" collectors w/ a 3" exhaust tip. Used 1/2 of the original baffle into the new pipe (single pin holds the baffle for quick removal). Certainly not a scientific approach . Very inexpensive, and allows quick experimentation or mods. Currently #115 main jets - up 3 on pilot jets. Has individual pod filters. Dyna coils. 14/48 on the sprockets. Idles great ,starts with out the choke. Revs to 9grand cleanly. plugs(e3) read good. Of course gas milage has suffered. No freeway cruiser, but quick/fun street setup.
Last edited:
If you drop the pilot jet two sizes you will probably gain back some fuel economy. If it starts without the choke your idle circuit sounds way too rich. I have never had to go up more then one size on pilot jets...ever even on my big bore stuff.
amc49
CB750 Guru
X2, starting up with no choke needed at cold engine says idle is too rich.
X2 on going up too, the engine simply does not really see hotrod parts at idle since it is realworld choked about 99% by the closed carb. Why the difference in idle jet from say on the DOHC is only from 35 to 38 and engine size changes from 750 to 1100.
And E3 plugs? You won't be getting accurate readings off them, they are too cold even when they are right. Could tell you why but it would take 100 pages. Best tuning thing you could do there is dump those plugs.
That header to begin with was one that didn't have a whole lot of science applied to it. A car header grafted onto bike and much lacking there. The primaries are whopping too long and the collector too big, automotive engines run in totally different ways than bike ones do.
X2 on going up too, the engine simply does not really see hotrod parts at idle since it is realworld choked about 99% by the closed carb. Why the difference in idle jet from say on the DOHC is only from 35 to 38 and engine size changes from 750 to 1100.
And E3 plugs? You won't be getting accurate readings off them, they are too cold even when they are right. Could tell you why but it would take 100 pages. Best tuning thing you could do there is dump those plugs.
That header to begin with was one that didn't have a whole lot of science applied to it. A car header grafted onto bike and much lacking there. The primaries are whopping too long and the collector too big, automotive engines run in totally different ways than bike ones do.
ridersup
ridersup
Exhuast mods-ridersup
Thanks for the very reasonable response/info. This setup is not for everyone, just an experiment with left overs ,not at a great cost. Not all engine builds require the same thing. Building is at the very least adapting/experimenting. This setup is surely not for all applications. HONDA race development pointed out parameters for primary & collector tube length in the very early 70's (which 'Jardine' did not meet). This setup works for me as of now-at most levels. Not competing with anyone here. Everyones experiences with builds can help some at sometime-not all ,all the time, but can be appreciated at all levels... . just a note...Please keep comments tactful as always and not shoot personal opinions in Emails..Thanks to all.
Thanks for the very reasonable response/info. This setup is not for everyone, just an experiment with left overs ,not at a great cost. Not all engine builds require the same thing. Building is at the very least adapting/experimenting. This setup is surely not for all applications. HONDA race development pointed out parameters for primary & collector tube length in the very early 70's (which 'Jardine' did not meet). This setup works for me as of now-at most levels. Not competing with anyone here. Everyones experiences with builds can help some at sometime-not all ,all the time, but can be appreciated at all levels... . just a note...Please keep comments tactful as always and not shoot personal opinions in Emails..Thanks to all.
????? all comments sounded ok to me
ridersup
ridersup
Private Emails sir. Lets Leave it at that..Thanks.
Similar Threads
