Topic: MAC 4/1 Baffle Mod 750K8

[brewsky]

Before popping $50 or so on a “performance baffle” from MAC, I decided to try a home made version first.

The baffle funnels all 4 pipes thru a crimped tube section of about one square inch area. No wonder they say “no re-jetting is required”!

First (stage 1) was 6 - 5/16 holes drilled in the narrowed section of the baffle. Test ride detected no change in noise, power, or flat spotting, and the onboard A/F meter showed no change in readings at any throttle position from previous readings.

Second (stage 2) was enlarging the opening with a Dremel on one side, and adding 2 more holes on the other. Test ride pending weather…

By the way, an 8” bolt with vice grips attached to the threaded end make a perfect slide hammer for baffle removal.

[LesterPiglet]

If you haven't modded the other (rear) side of the baffle I can't see it making much if any difference.

[mrrch]

I modded my baffle by grinding some slots in the baffle more to change the sound than trying to add any performance(I wanted a bit more rumble)

[brewsky]

Les,
I did open up the other side also with drilled holes, .......probably doubled the restricted opening area or more. Going a little at a time so as not to get obnoxiously loud.

[Jerry Rxman Griffin aka MuthaF'er]

My thought is to cut that sucker in half ie take the front half off. I have one but I haven't done anything with it. Looks like it would create a lot of back pressure since it does not exit directly.

[flybox1]

Les,
I did open up the other side also with drilled holes, .......probably doubled the restricted opening area or more.

thats all well and good, but your EXIT hole is still the bottleneck. 
until you open this up, you've really done nothing to change back pressure. 
youve just rerouted the flow to the bottleneck.

[LesterPiglet]

I meant the exit hole. You opened up one side but still have the 1" exit.

Edit. Ah, I see now. I thought both tubes had that flattened hole.

[brewsky]

Fly,

The interior was narrowed to 0.98 sq inches at the crimp restriction in stock condition.

The modified interior restriction is now 2.1 sq inches, and the flow has a straight thru shot instead of making a 360 degree turn to escape.

True, the exit end of the muffler is still restricted to 1.72 sq inches total, but it is almost twice as good as before.

The exit diameter is 1.48", and I can't tell if MAC's "performance baffle" is any larger diameter or not, but it doesn't look like it in the photo.

[Elan]

Funny I was just getting ready to do this on the same exact baffle.  I was planning on just drilling holes into the plates on each end to allow more flow.

[Elan]

My thought is to cut that sucker in half ie take the front half off. I have one but I haven't done anything with it. Looks like it would create a lot of back pressure since it does not exit directly.

It would be tough getting it back in perfectly centered this way I would imagine.

[brewsky]

Funny I was just getting ready to do this on the same exact baffle.  I was planning on just drilling holes into the plates on each end to allow more flow.

I thought about that at first, but was afraid it would alter the sound to make it tinny or shallow.
Years back I cut the guts out of one, only to have to install a drilled plate back in the end.
The sound was terrible.

[brewsky]

My thought is to cut that sucker in half ie take the front half off. I have one but I haven't done anything with it. Looks like it would create a lot of back pressure since it does not exit directly.

That well may be the best in the long run.....I'm just trying to inch my way in reversible stages in case I get to a performance or sound level I don't like

[lucky]

Check out this design.
From Cycle Shack.
They sell single baffles also.
I have one in my 1978 CB750K.

[mrrch]

I added a second screw and nut 180 degrees from the original locating screw for the baffle (it helps with the tinny/rattle sound, with only the one screw it can rattle)
Mine sounded ultra sweet without the baffle (I never rode it, did did some rev ups in the shop,probably would not run right plus the neighbours would hate me

[brewsky]

Well, it definitely sounds and seems to run better with the altered(stage 2) baffle in rather than out.

The sound is a little louder, but not that much, and there don't seem to be any flat spots. No decel popping either, even with the baffle removed.

With the baffle removed, it is headache city loud, and the response seemed flat, even though the A/F ratios didn't change much.

May just leave it there and get back to the jetting exercise.

I was a little surprised at how little change there was in A/F readings between full baffle in and open muffler test runs.

See last runs....#7, 8, and 9

[lucky]

Very interesting findings Brewsky!
I am surprised too.
So the baffle alters the sound but not the A/F ratios.
You would think the back pressure would change the A/F ratios.
But the sensor is in the muffler and that is a important fact too.

Thanks for posting your results.

[derelicte]

Might as well ask here...  My 750 came with a mac 4-1 and I was looking at the same performance baffle because right now it is not baffled, and indeed headache loud.  PO had it running well though - will I probably need to mess with the jetting to keep it running right with the added baffle?

[brewsky]

My guess is with the performance baffle, you may not need to change jetting at all.