The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: berger on 21.01. 2020 22:54

Title: two into one exhaust system
Post by: berger on 21.01. 2020 22:54
I did not go to the pub yesterday *eek* because once I get stuck in to bike things time goes by. I have heard many different opinions on power output with either two separate exhausts or a two into one. what are the opinions of you  wise and enlightened people out there about a two into one giving a bit more power or less power than two separate exhausts? cheers *beer*
Title: Re: two into one exhaust system
Post by: berger on 23.01. 2020 01:14
Siamese exhausts vs twin exhausts- performance. ?

Title: Re: two into one exhaust system
Post by: Nourish on 23.01. 2020 10:43
I believe that a 2 into 1 exhaust system improves bottom end performance and so popular with the side car and trials crowd.
I think it helps by drawing out the gasses, as one cylinder empties it creates a vacuum in the opposite port.
Title: Re: two into one exhaust system
Post by: lawnmowerman on 23.01. 2020 10:55
Lots of different opinions on this one. Bear in mind the orginal RGS had a siamese exhaust of larger bore where the track option was smaller twin pipes.
Some say the siamese pipes aid scavenging, some say the twin pipes give better breathing.
Some bikes like the older BMWs and Commandos had a twin pipes with a balance pipe linking them and some "performance" systems have a twin pipe going into a single pipe and then back out to twin silencers.
There was also a phase of open pipes with no silencers for racing machines until noise regs were introduced.
I think the main things seem to be looks, and setting the carb up correctly to the exhaust system chosen.

Jim
Title: Re: two into one exhaust system
Post by: RDfella on 23.01. 2020 17:13
Two into one looks cool - and you only need to buy one silencer!
Title: Re: two into one exhaust system
Post by: Nourish on 23.01. 2020 19:34
Ok if you've only one carb!
Title: Re: two into one exhaust system
Post by: JulianS on 23.01. 2020 19:55
Tried both over the years and not noticed much difference. Twin pipes a bit noisier and may give the illusion of going faster. 2 into 1 good for clutch access.

Did have carb trouble with 2 into 1 and goldie silencer, would not tick over reliably. Sorted by change to standard silencer.

Getting a 2 into 1 which fits is the real problem. Some of the commonly advertised 2 into 1 systems are a poor fit, the rose on the left pipe not seating squarely at the head, poor fit in the head and a slight kick up at the end of the pipe bringing the silencer too close to the pillion footrest.

Now using an ebay purchase of a nice 2 into 1 stainless made back in the 1960s by a company called TT Tubecraft.
Title: Re: two into one exhaust system
Post by: chaterlea25 on 23.01. 2020 21:28
Hi All
Quote
Getting a 2 into 1 which fits is the real problem. Some of the commonly advertised 2 into 1 systems are a poor fit, the rose on the left pipe not seating squarely at the head, poor fit in the head and a slight kick up at the end of the pipe bringing the silencer too close to the pillion footrest.

That's for sure  *razz* *angry* *work*

At least it was with the Stainless system I bought ,
Although with SS it was able to be reworked to fit
A lot of work produced a very nice result (to my eye anyway  *smile*)

John
Title: Re: two into one exhaust system
Post by: Joolstacho on 23.01. 2020 22:27
Wasn't the siamese system first designed for sidecars - (no pipe on LHS to interfere with chair frame etc) ?
Title: Re: two into one exhaust system
Post by: JulianS on 23.01. 2020 22:44
Had one of these, type A years ago. Fitted OK but the weld at the pipe joint soon rusted.
Title: Re: two into one exhaust system
Post by: Black Sheep on 24.01. 2020 07:18
Biggest problem is getting a good fit. You can end up scraping metal off the exhaust ports in the attempt (alloy head only). Not good. Essential if you have a sidecar though to stop the passenger going deaf.
Title: Re: two into one exhaust system
Post by: Rocket Racer on 25.01. 2020 03:22
On a solo for the UK and commonwealth countries, a RH only system means better cornering clearance on left handers! I personally like the siamese with a goldie muffler, but agree finding a decent off the shelf fit unlikely. I had a set made locally to fit (then chromed) and also prefer the daytona twin/ flat tracker style but obviously the latter not so good if seeking stock appearance.
The chrome pipes done for a super rocket.
No noticeable performance differences, I can pull over 7k on either exhaust type
Title: Re: two into one exhaust system
Post by: bsa-bill on 25.01. 2020 09:52
siamese would certainly fix the problem of silencers being different distances from the rear wheel, I find the only way I get mine the same is to spacer the timing side out so far the kickstart lever won't operate without gouging its way into the silencer  *sad2*
Title: Re: two into one exhaust system
Post by: muskrat on 26.01. 2020 06:00
G'day fellas.
In my opinion each cylinder should have it's own carb & exhaust for performance. With a single carb feeding two cylinders the difference between siamese and twin exhausts is negligible.
Cheers
Title: Re: two into one exhaust system
Post by: RDfella on 26.01. 2020 12:47
Diameter of exhaust pipes and distance between exhaust valve and join is critical. The lengths must also be identical. When the length / diameter have been correctly calculated taking regard of valve timing and revs at which max power is desired, a power increase will ensue. Get them different or random lengths and power loss will likely result.
Title: Re: two into one exhaust system
Post by: berger on 26.01. 2020 14:09
after reading old and new posts I will not be messing with the old rusting 2 into 1 now, but I will be taking note of pipe measurements when putting the reverse cone--- not for road use exhausts on