Megaphones
- Thread starter RacerDave
- Start date
Mike
Lifetime Supporter
I don't understand the question? A lot will have to do with your collector size and location in relation to the rear opening. You know what your collector size is right? You could then take measurements to the rear opening making sure it can still open and close without making contact. I have two sets of megaphones. Both are 3" dia at the collector. One set tapers to 4" and the other to 4" and then back to 3 1/2" with a reverse cone roughly an inch in length.
This will be interesting.
I made some megaphones for my 40 and I tossed them.
I never persued it any further because I felt the eng didnt require it.
I have made several collectors over the years and they have always gained power.
My benchmark is exit dia is double the entry, the length is 2/3 the primary length.
I then cone back hard on the exit and this brings the mid range back and retains the peak.
I couldnt fit it in ,so I thought I would be cunning and calculate the volume of the meg that I would like and put the volume into a meg that I could fit.
It lost about 15-20rwhp from memory, I would say the merge was to great and it lost gas speed effecting the scavange.
It would be interesting to see what others came up with and not just peak power.
Mid range is more important.
Jim
I made some megaphones for my 40 and I tossed them.
I never persued it any further because I felt the eng didnt require it.
I have made several collectors over the years and they have always gained power.
My benchmark is exit dia is double the entry, the length is 2/3 the primary length.
I then cone back hard on the exit and this brings the mid range back and retains the peak.
I couldnt fit it in ,so I thought I would be cunning and calculate the volume of the meg that I would like and put the volume into a meg that I could fit.
It lost about 15-20rwhp from memory, I would say the merge was to great and it lost gas speed effecting the scavange.
It would be interesting to see what others came up with and not just peak power.
Mid range is more important.
Jim
Jim:
My thought train was that the megaphones were used to create a Venturi because the collector seems to be reduced in diameter in comparison with the diameter of say a drag racing header collector.
I had 180 headers on my Chevy powered oval track car in the 90s the collectors were 3.5 inches and I used a merge muffler that had a 5 inch diameter ID.
My thought train was that the megaphones were used to create a Venturi because the collector seems to be reduced in diameter in comparison with the diameter of say a drag racing header collector.
I had 180 headers on my Chevy powered oval track car in the 90s the collectors were 3.5 inches and I used a merge muffler that had a 5 inch diameter ID.
Dave
This is my take
Megaphones originate on motorbikes, they found that more pipe length gave power and a wider band due to a longer negative and positive wave .
With a bike you have no where to go to increase the length so along came the megaphone.
The neg pressure comes from the gas passing down the primary pipe at high speed, the merge collector will help with this due to the venturi effect in the design thats why they waist the tail down to increase the gas speed.
When the gas enters the megaphone it will slow because the volume in the pipe is increasing this will increase the length of the pos/neg and secondary wave and help with the scavange in the higher rpm.
Unfortunatly the mid range falls off because as per usual we cant have everything.
Putting a very steep reverse cone on the exit will bring this back due to the waves hitting it and going back down the pipe at lower eng speed(basicly changing the timing of the waves).
I found on my 40 that it loves triple pass mufflers, I have tried several combos and it keeps coming back to triple pass mufflers.
I truely believe it is the length.
I would say that is why the 40s ran a megaphone because the system is to short and the neg/pos and secondary wave is effected.
My collector outlet is 50mm, same as the primary pipes, it is a ventury.
It doesnt kill it I rev it to 6500 and its still going.
I will make a trombone system after the collectors one day to see what it does.
I tried straight pipes at 2 1/4 but it lost mid range.
Your auger will kill the waves.
I have made mufflers with a megaphone inside them. the megaphone was made from perforated sheet and I used fiberglass mat in the box.
jim
This is my take
Megaphones originate on motorbikes, they found that more pipe length gave power and a wider band due to a longer negative and positive wave .
With a bike you have no where to go to increase the length so along came the megaphone.
The neg pressure comes from the gas passing down the primary pipe at high speed, the merge collector will help with this due to the venturi effect in the design thats why they waist the tail down to increase the gas speed.
When the gas enters the megaphone it will slow because the volume in the pipe is increasing this will increase the length of the pos/neg and secondary wave and help with the scavange in the higher rpm.
Unfortunatly the mid range falls off because as per usual we cant have everything.
Putting a very steep reverse cone on the exit will bring this back due to the waves hitting it and going back down the pipe at lower eng speed(basicly changing the timing of the waves).
I found on my 40 that it loves triple pass mufflers, I have tried several combos and it keeps coming back to triple pass mufflers.
I truely believe it is the length.
I would say that is why the 40s ran a megaphone because the system is to short and the neg/pos and secondary wave is effected.
My collector outlet is 50mm, same as the primary pipes, it is a ventury.
It doesnt kill it I rev it to 6500 and its still going.
I will make a trombone system after the collectors one day to see what it does.
I tried straight pipes at 2 1/4 but it lost mid range.
Your auger will kill the waves.
I have made mufflers with a megaphone inside them. the megaphone was made from perforated sheet and I used fiberglass mat in the box.
jim
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When you analyse the valve timing and lift there is really never anymore than fully open exhaust valve at one time in a 180° system so the secondary/tail pipe does not need to be large, conventional american non crossover headers fire @ 90°,180°, & 270° intervals in the same collecter, so volume of exhaust gas in collecter varies & you have to size to suit the 90° interval.
Jac are you referring to me?.
Tom here is a pic,they are truley just a run of the mill muffler.
When I made the system I had to pass a tight DB reading.
I got the mufflers from the local muffler supplier with no intensions of keeping them after the test.
After making several setups and made no real gains they went back on.
I did make a track version that has no cats.
It gains 10 rwhp with out cats and drops about 20kg from memory.
Primarys 2"
collector tail 2"
mufflers 2.25"
Jim
Tom here is a pic,they are truley just a run of the mill muffler.
When I made the system I had to pass a tight DB reading.
I got the mufflers from the local muffler supplier with no intensions of keeping them after the test.
After making several setups and made no real gains they went back on.
I did make a track version that has no cats.
It gains 10 rwhp with out cats and drops about 20kg from memory.
Primarys 2"
collector tail 2"
mufflers 2.25"
Jim
Attachments
sorry I made an error ,collector tail is 2.25 not 2"
I also noticed I stated in post #6 that I had made several collectors over the years but that should be megaphones.
I need to start proof reading.
Jim
I also noticed I stated in post #6 that I had made several collectors over the years but that should be megaphones.
I need to start proof reading.
Jim
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