Any thoughts on 2 into 1 extractors Vs. 2 into 2? I am contemplating dumping boith my head pipes into a single Jemco megaphone of the following design. 1/5" OD head pipes into 1.5x1.5 x 1.75 collector then from 1.75 to 2 inch into a 2" x 12" x 3" Megaphone. Any opinions out there?
Todd Henning tested everything and the THR/Jemco setup is probably the highest horsepower solution given: 1. ease of bellypan placement per the rules 2. the rest of the THR engine combination of cam, porting, carbs etc. My own [ limited-no dyno] research indicates the 1.5 primary pipe size is too big for the stock ports. but the guys running that pipe on the CB350GP bikes say it works. the 2-into-one question is probably more of a packaging/weight compromise issue. I have the THR/Jemco setup but had to add an inch to the front of the meg to get the footpegs comfortable......Jesse ran a reworked 2-into-1 vintage Hooker on his stocker and lapped Jennings 5 seconds faster than my v1 so none of this probably matters too much.....
I'd say that sounds about right.....I doubt with my stock engine and limited racing experience that I will know the difference..lol!
Hey Brad, its hard to argue with dyno testing....especially when 1 of the 2 choices has not been tested. I believe the THP setup "goes with" the Jemco's. Personally, I like a 2 into 1. In general, it seems to be a torqueier pipe. I've also read where the collector helps scavange from the other cylinder. The pipe I run has staggered tube dia's. I beleive 1 3/8 (or 1/4) out of the head and down past 1st elbow.....then goes 1 1/2....down to a collector. The dimensions of the mega are also very important. I dont have any data....but Dean and I have been discussing the topic, and also running some kind of test. Anyhow, I like my 2 into 1...but I've never heard anything negative about Jemco's.
Multis into 1 work when the exhaust timings are equadistant to each other in terms of crank revolution. so a 4 :2 :1 works best when you group cylinders with this characteristic. Taking it down to a 2:1, the cylinders should exhaust 360 degrees from each other...Triumphs do that, CB350's are 180 cranks. Not optimal. Could a 2:1 be better than a 2:2? Maybe, but best? not likely.
off-topic but related: BUB built an exhaust system for my Suzuki GR650 [180 degree twin] in 1984: it was a 2:2 with a crossover, and one side always ran richer than the other. I told Denis about it and he told me to stick a spacer with a smaller hole in it at one end of the crossover to restrict flow thru to the other side there: it worked--both sides then burned the same. I never saw a problem with a crossover like that on any 360 degree twin, or BMW boxer. The question is, would the uneven pulses thru a cb350 2-into-1 affect anything? I will compare the plugs from Jesse's bike at Jennings and report back......
update: both plugs look identical....I think this means that even though the 2 sides merge, they are not communicating with each other, [they are both minding their own business]
CharlieYs plugs always seemed to look the same too with his custon 2-1. I'm not sure how well it works being as the builder didn't know what the crank design was. Maybe that doesn't matter that much? I know Kenny uses a nice Maney 2-1 on his Norton but that has a 360 degree crank. Does that even make a difference? I mean both bikes still only ignite every 720 degrees.
Yes, my plugs look even too...it may have something to do with collector placement within the run. Dean, I think Charly / Jesse's bike has that 2 / 1 on it you saw on ebay. I recall when I removed my CL pipes and bolted on that Hooker 2 into 1 there was a difference in power....nothing astronomical...maybe it was a combo of less than half the weight + alittle power?....I noticed slightly more Unfff in mid range, like coming out of a corner....maybe not "More" power, but "Different" power, different places. I didnt notice any diff between the Hooker and the 2 into 1 I had made.....sounded different.... My current 2 / 1 has equal primary tube lengths that are definetly longer and straighter than the hooker, along with the staggered tube diameters....that hooker had a wild headpipe config....maybe it was like that for a mechanical reason (crank timimg)? I'll be running what I have for awhile.....at least until I make the move to a fairing...I think I will have to do something different then.
