Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Which exhaust?

Just had a reply from S&S about exhaust set up.
Email as follows.

Hi, John.

There is no simple answer to your question. When tuning exhaust length, all one can really do is optimize the power over a relatively narrow RPM range. At all other RPMs, the tuned length becomes irrelevant. That being the case, here is an equation to help you determine optimal header length.

L= 950 x 233/RPM

L=Length
RPM=RPM in the middle of the desired power band

The engine wants, at a minimum, around 3000 RPM with a good cruising range being 3000-3800 RPM, so if we select 3400 RPM, we are looking at an optimal header length of 62.3"

The Morgan header pipe is 1 3/4" diameter so you can fit just about any Harley muffler to the header that you desire as long as you can rig up a bracket to mount them.

Let me know if you have any other questions.

Any thoughts?
John.

From S&S.
PS.

Two points I should have clarified. The math would include the length of the muffler as well. It is an end-to-end measurement of the entire exhaust system. Also, unless the engine has been replaced, the Morgan should have a 121" engine in it.

Have a great weekend.

Thanks John.

[quote=The Morgan header pipe is 1 3/4" diameter so you can fit just about any Harley muffler to the header [/quote]

John,

My 2012 machine has 2" OD pipe coming out of the head (after the 1.875" reduce section right at the port), and was 2 1/2" OD after the cat, before I removed it, so is now 2".

Based on most of the exhaust calculators one finds online, 1 3/4" or 1 7/8" would make more sense for this engine.

BTW-when I had the exhaust off for fab/updates, I measured the actual port diameter of the head at right about 1.375".

I was thinking about that as well. 2" makes it slightly more difficult in terms of a straight swap out as well.

If you think about cars, performance muscle type cars, if running at a drag strip the headers are always in the range of around 40", give or take a few. BUT that same car on the street has to have full length exhaust pipes, mufflers and tail pipes, which of course are a LOT longer.

So some sacrifice is required from optimal to running on the street.

Just my opinion, but I believe the larger pipes will decrease your low end torque and create some peakier and narrower torque ranges. For being street friendly, I think I would error on the smaller diameter pipes versus larger. Again, this is just my opinion on what I've read over many years of being a gearhead.

Likewise with carburetors, if setup correctly, cam, ports, exhaust etc, larger throats will give you higher peak hp, but you will lose throttle response at the lower rpms. Conversely, a slightly smaller carb will improve throttle response but cut down on peak hp. I believe I read someplace back about 20 years when the throttle body injection was coming out and some people were converting old 8-stack mechanical injection to port injection. The 8-stack induction looked cool, but most were of a very large butterfly design. The opinion back then was that as long as the injectors were feeding at the correct amount for your needs, it made little difference as to what size the butterflies were, within reason that is.

I've always thought that the pipes on the M3W were way too long for good performance, but I'm sure that tuning can be done to optimize just about anything.

I'm happy to see some experimenting with the pipes, sounds interesting.

custon pipes

[img][img]https://www.tm-img.com/images/2019/07/29/grimm.md.jpg

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Have a look at these.

They are indeed shorter, but closer to your ear.

FWTIW, when I brought my 3W'er back to Morgan New England for its 1000 mile service, Larry commented that it was the best sounding M3W he's heard and questioned what I did to it. Since the Stage 1 kit was back-ordered and I ran out of patience, I had removed the cat's and 1st and 3rd baffles but not the middle ones. My boring bit was too dull by then so that wasn't intentional. I then wrapped the headers (titanium) all the way back to the juncture and added a Stealth intake. Larry has installed a few Stage 1's and performed several bafflectomies but never removed the cats before. Consensus was that the combo of losing the cats plus retention of the longer (i.e. past the ears) stock pipes, plus perhaps retention of the middle baffle, gives the most pleasing tone. Performance increase and heat reduction aside.