Exhaust Mod late model NH 750

[Bob H]

The old forum had an exhaust mod known as the "Tim Hodge" mod, you can see a video of the result here

My exhaust is stock. I have had loud bikes before. In 1976 I had a Kawi Z1 with a 4 in to 1 exhaust that sounded amazing, but I no longer want to wake up the world.

Anyway, I have PDF's of the mod but it seems to have disappeared from the internet, the various other sites that had the mod appear to have gone down.

The old mod started out with this:
This modification was pioneered by mail list member Tim Hodge. Tim became
somewhat of a legend because of his simple modification that opens the exhaust up,
allowing a more mellow sound and some midrange performance improvement. 

(Dean) did the "Hodge mod" on his own Nighthawk several times - experimenting
with different size holes and settled on five 3/8" holes per side (note that on my
funnel though, my innermost hole is partially covered by the baffleplate--I should
have moved this hole away from the end a little more). The beauty of this mod is that
it's nearly invisible from the outside, thus preserving the good looks of the stock
exhaust system.

From: Tim Hodge
I'll start with the end of the story: MISSION SUCCESS!! A nice mellow exhaust note (not
too loud, not to soft) with an additional benefit. That annoying soft-spot in the midrange
torque curve has improved too! Yes, there is a small top end sacrifice, but I don't typically
run the bike up to 7000 rpm anyway.

This actually was a very easy mod to accomplish.
1) The hardest part was drilling out the four steel rivets that hold the end caps on each side
of the exhaust system. Make sure you have a good sharp drill bit!
2) Next, using a pair of Vise Grips give a sharp pull to the inner circle of metal where the
exhaust gases come out. Have someone hold the bike steady while you do this step.
3) What you now have in your hands looks like a 7 inch long funnel. Now do the other side.
Set them down for a while. We'll get back to them later.
4) Important, reach inside with a pair of tongs and remove the remains of the old pop rivets.
5) Clean out the rivet holes, so they will accept the new rivets. (I used aluminum in case I
had to open them back up at a later date.)
6) Now back to the 7 inch funnels. A drill press would help here, but it is not mandatory.
Drill four 1/4 inch, staggered holes along the length of both funnels in the longer tube
portion. Deburr the holes with a file. The larger the holes, the more of the exhaust gases
will by-pass the normal baffling path and "escape" to the outside world.
7) Place the funnels back into the system, use four pop rivets on each side and that's it!

As a side note: I did mine in two stages. The first time I drilled four 3/16 holes in each
funnel. I tried that for a week, but didn't get the desired effect (wasn't loud enough). So I
reopened the system and drilled out the four original holes to 1/4 inch. I figured I had done
it once why not a second time.
I am very happy with the results. The mod has been in for about a month now. No ill effects
have shown up. The plugs are still a nice color which means to me that I did not lean out
the motor.
As a warning: I would suggest that you don't open the holes much more than I mentioned.
3/8 might work, but you should then install a jet kit which would richen the fuel/air
mixture.
Tim
1999 cb750 (slightly modified)

[Bob H]

These images were freely available on the internet when I saved them to my hard drive in 2012, they were originally posted in 2000.











A comment was made in 2000 that he drilled the hole at the narrow (left) end too far to the left.
Next it goes back together.


Comments were made about the need for a very sharp drill bit as the center of rivet is very hard steel.
Some people had difficulty separating the parts, had to use WD-40 and hammer.
There was a caution about loose bits from drilling out the rivet going into the exhaust pipe.

[mollusc]

Nicely done!  Thanks for saving this and for posting it.

[Pete in PA]

I like the pic of the inside after the baffle is out.

Doesn't help understand the route the gas takes through each muffler though.

Is there anything archived that can be reposted on drilling the airbox?
Any gains to be made?

Although tempted to try these mods, they are permanent unless you can find replacements. I wouldn't mind more power.
Still wish they made an identical bike to this but an 1100. Everything else the same.

Dont hear about any "big bore" kits either.

[mollusc]

I have never heard of anybody drilling airboxes.  If people want to do mods on that side they either stupidly throw it away and go with pods, or they make modifications to the snorkel/change the filter mount so that a K&N can be used.

[Bob H]

Is there anything archived that can be reposted on drilling the airbox? Any gains to be made?

I don't remember seeing anything about that. I suppose if someone really wanted to extract more power they could jet for velocity stacks (pods). I think everyone wants more power, no matter what bike they have - but at the end of the day I remind myself that 100% of my riding is on public roads.

Still wish they made an identical bike to this but an 1100. Everything else the same.

I think the closest you would get is the CB 1100. I remember when they showed up at a local Honda dealer around 2013. Instantly I fell in love, but I think they only had spokes the first year. I thought of all the bikes I previously had, cleaning the spokes - and blew it off.



Then they came out with cast wheels and a 6th gear... but I was happy with my 750 and had recently sold a much faster 86 VFR because the devil on my shoulder kept making me ride too fast on public roads.

Looking back at it, the CB 1100 was (and is) very cool because you could get an air cooled in-line 4 that wasn't ancient with stored bike syndrome (clogged fuel, etc.)



https://www.cycleworld.com/2014/02/05/2014-honda-cb1100-deluxe-first-look-review-photos/

http://cb1100forum.com/forum/index.php

https://www.bennetts.co.uk/bikesocial/reviews/bikes/honda/honda-cb1100-2012---on-buyers-guide#:~:text=Honda%20CB1100%20(2012%2D2016)%20%2D%20Buyer's%20Guide

[Pete in PA]

The CB1100 is close.  FI, heavier, adjust valves, too small gas tank, etc. Target missed.

[mollusc]

Is there anything archived that can be reposted on drilling the airbox? Any gains to be made?

I don't remember seeing anything about that. I suppose if someone really wanted to extract more power they could jet for velocity stacks (pods).

Really, really dumb idea.  The debates about pods on CV carbs seem to be mostly rational physics-based arguments about how pods cannot deliver consistent non-turbulent flow equally to each individual carb, followed by retorts of "well I'm going to do it anyway" and then a For Sale ad on Craigslist stating that the now-unrideable bike "just needs carb work."
Some people do claim to have been able to overcome the flaws of pods with meticulous tuning and adjustments; personally I think these largely amount to dumping in a ton of fuel in order to mask the stutters and dead spots.

[Pete in PA]

Yeah, I know better then to try pods. They don't work with CV carbs. because there's no CV going through them.

Just back from a ride, would like more power, but can live with this. It's all my past 1100 or bigger bikes since 1987 swaying me.