MTFCA Forum

You don't need any backpressure.

The size and length of the pipe might have some effect on engine performance at certain speeds.

Exactly what size and length would be most advantageous would depend on how the engine is set up as to cam, compression, chamber volume, etc, and what speed range you want to enhance performance in.

The most gain would probably be realized by improving the exhaust manifold rather than the exhaust pipe.

Improving and "tuning" both intake and exhaust to suit a particular engine and operatring speed range is where best results will be found.

Straight pipe will be too loud and ugly. And unlawful most places.

Have run a shorty 13”-15” glass pack type open bore muffler ( resonator types) with 1 1/2” inlet and outlet, using down turn exhaust pipe tip to direct sound to the pavement underneath. Nice mellow sound that gives notice when accelerating.

An exhaust cut out isn't too hard to find or expensive. You might want to try one first to see if you like or hate the noise and can always go back through the muffler if you are someplace you want it more stock.

I have never tried one so don't know they sound. Someone on here probably has and someone on here probably has one to sell if you post wanted in the classified.

Tim Moore

I replicated this accessory muffler for my Speedster with 3" x 48" tube as shown. It gives it a much more powerful sound but not sharp. It may give you what you want. I like closing it off and running it through the larger muffler but it could be built without it.
Rich "Deep Toned Racing Roar"

If you are running the type muffler which can be taken apart, you could turn the inner baffle around. That way the exhaust would go straight through instead of going from end to end because the holes would be at the back and go right out. That way if you decide you don't like the sound it will be easy to go back to stock.
Norm

Norman Kling wrote: ↑

Sun May 14, 2023 1:01 am

If you are running the type muffler which can be taken apart, you could turn the inner baffle around. That way the exhaust would go straight through instead of going from end to end because the holes would be at the back and go right out. That way if you decide you don't like the sound it will be easy to go back to stock.
Norm

Or maybe just leave the inner baffle out.

Norm,
I think that's how my muffler was constructed.
Keith

Undecided
Grabbing a spare pipe to have while I decide
Open pipe, short glasspack, or cutout. We'll see....

Listen to the sound as he revs the engine -----
https://www.facebook.com/kathy.p.brown. ... 892621554/
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Instructions to make one - modified for dual exhaust manifold
https://www.mtfca.com/discus/messages/8 ... 1530408436

A lot of speedsters run straight pipes and seem to have no problems.

Too bad Humble Howard is not still around, but maybe one of his friends in CA can help out.

DHort wrote: ↑

Sun May 14, 2023 11:08 pm

A lot of speedsters run straight pipes and seem to have no problems.

Too bad Humble Howard is not still around, but maybe one of his friends in CA can help out.

Yep, my speedster has a 3 inch stove pipe exhaust in the rear with a damper and handle. To me I think it looks neat. It serves it's purpose.

The gow job built by Gabby Garrison now runs a simple copper drain pipe strait back and sounds real nice. Don't over think it.

Just get creative!!!!!

Torque inserts...

Back in 1994 when the San Diego National tour went to Tijuana for lunch and a visit to the cultural center, when it was much easier to cross the border either way, My muffler fell apart just before crossing into Mexico! So I experienced the straight pipe for the rest of that tour. We actually got a police escort to the cultural center. When we got back to the hotel, I was able to repair the muffler.
Norm

Hi Dan,
If sound is all you are looking for as the stock manifold is rather restrictive. I run a 5' long piece of 2 1/2" with a 90* elbow turning out to the side
on my fire truck. I cut the stock pipe off & turned it down and ran it into the top of the 2 1/2" supported it with a spring from the running board.
Made a baffle out of perforated steel that made it pretty quiet so I cut some off till I got the volume I wanted.
I hope he doesnt mind . Az Terry has a simular set up on his speedster that goes into 2" tubing that goes all the way to the rear of the car. I don't
know if he has a baffle in it but it looks & sounds great, good tone & not to loud.
Hank, That is deffinetly over the top
Craig.

I bought a 1.5 to 2 inch adapter and a length of 2 in pipe. Planning on subbing the pipe for the muffler to try out... Maybe tomorrow if I can get to it.

TSC sells tractor mufflers that sound great and you can find them normally with the right diameter either in the store or their online services.

Hank

I'll stop at TSC in the a.m. to check. Thanks Hank

I'm thinking about the bark the 8n I run each summer.... neat sound.

TSC muffler is the FO-11. They usually have to order it for you. I buy 2 at a time.

Muffler is off the car. Settled on a 1.5 in to 2 in coupler into a length of 2 in pipe. I'll run this for a bit and see how it goes.
I drove the car this afternoon, it accelerates and pulls very nicely.
....and it sounds "nasty awesome too!"

Back pressure??

hah wrote: ↑

Wed May 17, 2023 9:29 pm

Back pressure??

Not much.
I have to take it for another ride to really compare muffler/No muffler. Results to be reported here.

Search torque inserts...may help

I made a modification to my homemade muffler.
The open 2 inch pipe is now closed with a 1.5 in to 2 in reducer, welded to the 2 in tube. The reducer was welded with the 1.5 in end inside the 2 in tube. This has created the necessary back pressure much like the stock muffler.

Although the low rpm torque has improved, I'm finding it's still not as good as the stock muffler. It needs a bit more back pressure.
Further R/D to follow this week.

I have found "the recipe...."
-1.5" to 2" coupling to go into existing 1.5" stock pipe.
-18" length of 2" pipe welded to 2" side of coupling.
-1.5" to 2" coupling to go into the end of the 2" pipe, but weld it backwards with 1.5" side inside. The 2" end of the coupling becomes a 2" extension.
-->then three 3/4" nuts stacked to block part of the outlet as pictured.

The restrictive area of the nuts has brought the engine back to life! The motor now has crisp throttle and leaps forward and pulls well when spark is advanced.

Going to drill the exit of the pipe and stack them on a 1/4" bolt.

It's still very loud. But I have now achieved what i had hoped to.

Hope you can enjoy the "recipe" on your car/speedster!

Make a turned down exhaust tip from exhaust pipe. Instead of using the nuts, calculate the amount of reduction you get from using the nuts, then slightly crush the outlet tip to get the same reduction in pipe size. Having the outlet turned down should help a little with the noise level by pointing the exiting exhaust at the road instead of expanding out the back.

Good point! Will look into that this week.
I found that the outlet has to be about 30% smaller than the inlet.
I based my initial calculations on measurements of a stock muffler.
The number ratio reduction I calculated I tried to achieve with the nuts, on the premise that it would be easy to add or subtract nuts to facilitate changes in back pressure.
This was a fun project for sure! ****TUNEABLE SHOTGUN MUFFLER!!!******
"SPEEDSTERS SHOULD BE SEEN AND HEARD!!!"

You do not want backpressure. You want VELOCITY.

I'm getting great performance out of it as is....
So your saying I should run a 1.5" or even a 1.25" pipe all the way to the rear? Free flowing but smaller diameter?

I'll probably regret entering this, but here goes:

learning about and understanding the effects volumetric efficiency, scavenging, and backpressure on exhaust systems will save 90% of experimentation (or more)

I understand volumetric efficiency and back pressure, please explain scavenging? I hope your regret is not needing to explain.

Hello John

I could give a worthy explanation (but would undoubtedly miss any number of details), so to save inevitable criticism, second guessing, and a lot of typing, I'll route you to these guys who have it covered in spades: https://www.enginelabs.com/engine-tech/ ... nd-theory/

If it's backpressure you want, just squash the stock pipe half shut just ahead of the stock muffler.

Zoom,Zoom Dykes motor suggestion--

You may have made a choice and decision for your exhaust system.

Here is one from an early Dykes manual 12th edition - too you may want to review ...
Scientific Design of Exhaust and Intake Systems (Engineering and Performance),
by Philip Hubert Smith (Author), Phillip H. Smith (Author), John C. Morrison (Author)
Putting the hobby back another 60 years (c).

A lot of speedsters run straight pipes. They sound good but they all have a certain RPM range where they get kinda raspy. A more engineery guy could talk about pressure waves and such but all I know is it just happens. Adding an auger in the pipe can mitigate the problem by breaking up the waves. I don’t think back pressure is an issue in a model T. Don’t the Montana 500 cars run short open pipes?


Andy

TXGOAT2 wrote: ↑

Mon May 22, 2023 8:35 am

If it's backpressure you want, just squash the stock pipe half shut just ahead of the stock muffler.

I apologize if I've been scatterbrained and unclear as to what I am looking for.
I'm looking for at least the same performance and response in both throttle and timing advance as the stock muffler, but with a speedster style open sounding exhaust.
Although the suggestion to crimp the pipe before the muffler is great, that will not provide the loud exhaust sound sought for.
My set up is now achieving all the goals of the project.
The car is now very responsive and pulls well at low RPM, and it sounds loud!

"... I don’t think back pressure is an issue in a model T...."
Andy
[/quote]
All I can tell you is that my straight thru shotgun muffler, it's basically a glass pack with nothing inside, with 1.5" inlet and outlet, did not provide any power under 1800 rpm, until I baffled it with the stack of nuts on a rod as mentioned previously.

I began with a 1.5" to 2" flange with 18" of 2" pipe.
The engine sounded "nasty" good, but it lacked any power and did not accelerate well in high gear at all.
Closing off the outlet down to 1.5" seemed to be an imrpovement.
Then I measured and calculated inlet/outlet ratio on the stock muffler. I found that in order to mimick the stock muffler restriction profile, I had reduce the outlet by about 30%. I achieved this reduction by adding the stack of nuts, with the idea I can add or subtract restriction by adding or subtracting nuts.
I calculated approximately 3 nuts would be very close to the 30% restriction goal.
And that did the trick! Car now is very responsive in both throttle and timing.
And the best part.... It's pretty loud, but not wildly like it was in the beginning with the open 2" tube and no restriction. More of a "refined" loud sound that allows the engine to perform well. I'm happy.
Hope this helps someone else.

But I don't see how a wide open pipe will perform well unless you wind the motor up in high rpm.
For me, I've found back pressure is low rpm torque.
I understand the velocity issue exists too.
But it's a model t, all glorious 20hp of it, and it's supposed to be fun. And it certainly is!

Any gain will be made by exploiting inertia of the moving gas column in the exhaust system. You don't want back pressure in the system. Ideally, you obtain negative pressure at each exhaust port just as the exhaust valve opens.

Good technical explanations on what causes back pressure, why its exists and why its unwanted
Exhaust Back Pressure: Myths Busted https://low-offset.com/guides/exhaust-back-pressure/
Difference Between Headers and Exhaust Manifolds https://low-offset.com/workshop/exhaust ... s/#headers
-- this is what is needed
The Exhaust Scavenging Effect https://low-offset.com/guides/exhaust-scavenging/
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Other and there are much more information
Exhaust Talk: What’s Better, 4-1 or 4-2-1 Headers? https://low-offset.com/workshop/4-2-1-h ... 1-headers/

Hi Dan,
You seem to get more seat of the pants performance input than I do. I'm going to go out on a limb here. Every time you change the flow
characteristics of a engines exhaust you change more than the sound. If you think of an engine as a air pump and you increase the flow
out of the engine you will increase the flow into it also. This will effect to a small amount the fuel mixture & timing. Maybe you should
concentrate on adjusting those instead of tuning them with the exhaust flow you may get better results. Just something I have learned
from racing small 2 & 4 stroke engines that involve a lot of exhaust tuning. We used to call it the pipe of the month club.
Craig.