exhaust

[river_ratj40]

i have read articles and books related to exhaust tunners and expansion chambers, and i have a pretty good idea how an expansion chamber on a 2 stroke motorcyle work. what i dont understand is how a mod 50 exhaust (that resembles a cowbell) works as an exhaust tunner. i understand that the bigger the tunner the more exhaust you can pull out of your cylinder. but it doesnt make since in my head that the soundwaves in an mod 50 exhaust tunner would keep fresh air and gas from exiting the exhaust port inside the cylinder. can anyone explain just how these tunners work in relationship to an expansion chamber. i know im hard headed and not looking at this correctly, but any help would be greatly appreciated.

[Mark75H]

Three cylinder two strokes have a unique feature that places one cylinder's exhaust port closing time just after the exhaust port opening time of an adjacent cylinder. This lets the blast from one cylinder force unburned overcharge just outside an adjacent cylinder back into the exhaust port that is closing - restoring the fuel air mixture that would have normally just been wasted out the exhaust port. This also increases the pressure in the cylinder where the piston is closing the exhaust port - so the motor has more torque from using fuel and fresh air that would have been wasted and from the increased pressure (same as higher compression ratio, but with less stress on the motor).

The degree time between cylinders on a three cylinder is 120 degrees, the exhaust open time is usually about 165 degrees, so there is about 45 degrees of exhaust port open overlap between adjacent cylinders. When the speed of the motor agrees with the lengths between the exhaust ports you get the best effect.

Engineers at Scott-Awater noticed this effect on their 63 ci triple back in the 1950's. The triple was an extension of their 40 hp twin, which barely made 40 hp ... adding a third cylinder increased the power to 60 hp. With a little work the 40 was bumped up to 45. When the same work was applied to the triple they expected 67.5 hp, but got 75.2 instead. The 7.7 bonus hp came from the triple exhaust feature.

[Roy Hodges]

so, McCulloch inherited a 75 h.p. motor , I had thought McCulloch developed it , glad you set the record straight. Thanks .

[Mark75H]

so, McCulloch inherited a 75 h.p. motor , I had thought McCulloch developed it , glad you set the record straight. Thanks .

McCulloch bought Scott during this time, but no major personel changes at Scott were made, just change in ownership and name. Brewster Atwater Jr even stayed on to the end of outboard production in the late 1960's. The 75 was brought to market during the name change transition: Scott-Atwater, Scott, Scott by McCulloch, McCulloch

Many late year 1961 60 hp Scotts were actually 75 hp with leftover 60 hp covers.

[iwanajohnson]

Engineers at Scott-Awater noticed this effect on their 63 ci triple back in the 1950's.

so there was a 63ci 3 cylinder. I had a guy telling me about this the other night and I called him crazy. what years were they made? Another question with the exhaust, as river rat said, how does the cowbell shaped desighn help performance so much? lot of good information though, keep it coming.

[Fast Fred]

the Mod50 tuner is long, the funnel shape is not as pronounced as like SST60,
:cool:

[Mark75H]

Engineers at Scott-Awater noticed this effect on their 63 ci triple back in the 1950's.

so there was a 63ci 3 cylinder. I had a guy telling me about this the other night and I called him crazy. what years were they made? Another question with the exhaust, as river rat said, how does the cowbell shaped desighn help performance so much? lot of good information though, keep it coming.

They started in 1958 and ended just before 1970. It was a very popular motor, probably 200,000 or more of them made thru the years. In 1958 they were only 10 hp behind the Merc Mark78 (which was the highest horsepower outboard you could buy), by 1969 they were only half the power of Merc's biggest motor. They were also sold thru Sears under the Sears and Elgin brands.

The bell at the end probably adds 1 or 2 hp, it is not the important part

[river_ratj40]

is there any way to figure out how long and wide to make your tunner for a 3 holer, other than the try and fail method.

[iwanajohnson]

yea, like you told me buy a monkey!!!

[Fast Fred]

well, seein that nobodys takin a swing at this:eek: :cool: . this is what i got,
thare is two styles, the Header, like 49 and the 56, and the troff, like the Mod50's, Yamaha, Hot-sue.

i'm thinkin that when one cyl Fires it's exhaust, the squese ( thinkin the turns in the header of the 49 make up most off the squese) holds it up just long enuff
to presureize the exhaust for the closin cyl above. and that helps it out more
on the scavagin than the reflection only.

stinger stock exhaust is dif', but for the rest, this gets ya some ware close.

under the exhaust addapter, the exit hole of the exhaust, what ever the dieamiter is X7 long (if rectangle or oval go with the longest mesurement, you can all way make it shorter, not easy to make it longer) with 2 1/2 X the exit hole area, about, goin out :cool:

[Mark75H]

well, seein that nobodys takin a swing at thisi'm thinkin that when one cyl Fires it's exhaust, the squese ( thinkin the turns in the header of the 49 make up most off the squese) holds it up just long enuff to presureize the exhaust for the closin cyl above. and that helps it out more
on the scavagin than the reflection only.

http://www.boatracingfacts.com/forums/showpost.php?p=31717&postcount=2

.

[Fast Fred]

ya, thats what i'm thinkin is happin, just like that.:cool:

[river_ratj40]

ive got two motors. a 98 model 56 ci johnson, and a 81 model 2 cyl evinrude. both with very different exhaust. ive seen the tunners in some big v-6 moters and a mod50 tunner. i was wanting to know which one was the best. im going to run all exhaust throught the midsection. no pipes. both motors will be set up with jet pump, so low end torque is a must. im just trying to understand how exactly everything flows through.

[Fast Fred]

thinkin mite have just the thing for the 2cyl. kinda 2X4, the UPS dude has been vary dissapointin as of late.:( :( :o :eek: :cool:

[iwanajohnson]

thinkin mite have just the thing for the 2cyl. kinda 2X4, the UPS dude has been vary dissapointin as of late.:( :( :o :eek: :cool:


You've got to be kidding me that frigging order isn't in yet!!!!!!!!!!!!!1

[river_ratj40]

Fred...


im interested in the 2x4 for the 2 cyl. if you get it.;) just let me know. good luck with the ups dude...

[Fast Fred]

Ups dude's stock is up,but not by much, thay cracked a LU goin to Canada for me, but that some thin else,the 2X4 1/2 set up sittin right hear, got some shots in the cooker for ya, finishin up on one that someones waitin for, your in thare,
i'll post when out of the cooker:cool:
thanks
FF
:eek:

[river_ratj40]

i had a neighber order a set of fourwheeler wheels. he got 2 through fed x, lost one during shipping, and found one on the side of the highway going home. that would suck...

[Fast Fred]

:cool: check this,
http://img20.imageshack.us/img20/7904/p4050012yb5.th.jpg (http://img20.imageshack.us/my.php?image=p4050012yb5.jpg)
http://img153.imageshack.us/img153/1340/p4050014gp0.th.jpg (http://img153.imageshack.us/my.php?image=p4050014gp0.jpg)
http://img92.imageshack.us/img92/9909/p4050016xu7.th.jpg (http://img92.imageshack.us/my.php?image=p4050016xu7.jpg)
http://img170.imageshack.us/img170/5514/p4050018at8.th.jpg (http://img170.imageshack.us/my.php?image=p4050018at8.jpg)
http://img169.imageshack.us/img169/5145/p4050019kl4.th.jpg (http://img169.imageshack.us/my.php?image=p4050019kl4.jpg)
keepin it carbrareted

[Fast Fred]

:eek: :cool: :eek: http://img293.imageshack.us/img293/4744/p4050020ut1.th.jpg (http://img293.imageshack.us/my.php?image=p4050020ut1.jpg)
and some udder ones:rolleyes:

[iwanajohnson]

:eek: :cool: :eek: http://img293.imageshack.us/img293/4744/p4050020ut1.th.jpg (http://img293.imageshack.us/my.php?image=p4050020ut1.jpg)
and some udder ones:rolleyes:

are these carbs ran like this or are they just sat on top of each other?

[Fast Fred]

i was goin through the box, just slid that top set on thare, i had a set on a Moda, that had a stripped jet screw:eek: , was lookin for the right fix.:cool:

[Roy Hodges]

Man, you just ruined it for me. I thought you had a new secret 2stage ,12 barrel carbonation setup for the 3 hole looper.

[iwanajohnson]

Man, you just ruined it for me. I thought you had a new secret 2stage ,12 barrel carbonation setup for the 3 hole looper.

that is the secret it really is gonna be runnin 12 barels, on nitro methane:D :D :D haha!!!!

[Roy Hodges]

Because- have you heard what Nitro sells for? last time i heard, about a year or so ago, it was $30/gallon. And, i bet you have to buy more'n a gallon, or maybe it's more.and from what i hear, 2 strokes can 't take much percentage of nitro in the mix, maybe 10% ; 15% MAX. Lon Stevens told me years ago , that his 60 cubic inch, full house 6 cylinder Mercs used a gallon of fuel (alky) a minute ! into that he added Blenzall gold label, which contained some nitro benzene, and some racing Castor @ 32-1 mix.

[Fast Fred]

so took that top set,changed the Jets, put them on a Mod56 and Fired it Off.
:eek: :eek:
as she cameup online, hittin at 20deg, bolted to the bench, in the shop
she pulled up to about 1500, no foot, on a hose, over a bucket.
i Cracked it a few times,Dam, the thing Is BadA$$, Sounded like Wow.:eek: :cool:

saw one once, never did hear it run.

Got the 12 venturi, they are the ones under neath, two in each hole,:cool:

[Fast Fred]

http://img152.imageshack.us/img152/8346/p4120009mi4.th.jpg (http://img152.imageshack.us/my.php?image=p4120009mi4.jpg)
:eek: :eek: :cool:

[Fast Fred]

got some other exhaust stuff:eek:
http://img135.imageshack.us/img135/2153/p4120003py8.th.jpg (http://img135.imageshack.us/my.php?image=p4120003py8.jpg)
http://img87.imageshack.us/img87/2853/p4120005le3.th.jpg (http://img87.imageshack.us/my.php?image=p4120005le3.jpg)
http://img141.imageshack.us/img141/952/p4120006dx0.th.jpg (http://img141.imageshack.us/my.php?image=p4120006dx0.jpg)

[Roy Hodges]

http://img152.imageshack.us/img152/8346/p4120009mi4.th.jpg (http://img152.imageshack.us/my.php?image=p4120009mi4.jpg)
:eek: :eek: :cool:............................................ .................................................. .................................................. ................SO ; This..........is the famous "Bench Test ?

[Fast Fred]

not sure how "Famous" it is:eek:, but ya thats the first fire spot.:cool:

[iwanajohnson]

as the doctor in frankenstein would say....IT'S ALLIIVVVEEEE!!!!!

[Fast Fred]

insured for 5000bucks, check it before the truck drives away, in outboard fome
on a skid, roped down to the skid, spun in clear plastic, with blue rope over the hole thing.:cool:

[iwanajohnson]

insured for 5000bucks, check it before the truck drives away, in outboard fome
on a skid, roped down to the skid, spun in clear plastic, with blue rope over the hole thing.:cool:

sounds great!so your sayin it's on it's way? beam me over a tracking number in a pm if you get a chance. thanks.:D

[Fast Fred]

i got to catch up to the shippin dude, he gave me two slips, but i put them boath on it,they tryed losin some stuff on me once, cuzz they ripped the tag off,so i get two on thare for um,:cool:

[Roy Hodges]

Hows our old friend AL Bundy doing ?

[Fast Fred]

not sure ware Al's at, i'm hangin out with Peg, buildin a Moda:cool:

[iwanajohnson]

everones got somethin for peg. I still say yall could do better. plastic surgery has came a long way since then!

[Fast Fred]

goin over to Stellwagen:cool:

[iwanajohnson]

fred ya still haven't moved far enough away from the cold weather!

[Fast Fred]

they is sayin she has landed:cool:

[iwanajohnson]

they is sayin she has landed:cool:

they landed with it and was happy to see it at the house but I think they threw it down and landed the plane on it. haven't personaly saw it yet but I heard it's in rough shape. power pack's busted and carbs are broke. not the news i wanted to hear thismornin. hope fedex pays up quick on insurance claims cuz they're gonna need to get me some parts.:confused:

[Roy Hodges]

They "test " the packaging by giving the M1A1 Abrams drive over test, then recheck with a 40 ton steam roller followed by the Cat D-8 bulldozer and finally a "DROP test " from their 747 at 37,000 feet ? Now ,anything sent by the P.O. gets a "SERIOUS" test, they don't play around. No sirree .

[Fast Fred]

they will be Payin!, take pics of it, we'll call Dave for some NEW carbs and a power pack, and any thing else that looks dirty. Losers:mad:
gave my shipper the heads up,it's covered for 5000bucks.:mad:

[iwanajohnson]

they will be Payin!, take pics of it, we'll call Dave for some NEW carbs and a power pack, and any thing else that looks dirty. Losers:mad:
gave my shipper the heads up,it's covered for 5000bucks.:mad:

hey fred yea it sux. I called fex ex and they're comin to pick it up to take to local depot to do a damage inspection. looks like they laid somethin on it and the driver said there was a possible damage slip worte out. looks like were gonna have to file a claim for it though. I'll get back with ya after I find out what this guy says today.

[Fast Fred]

let me know what the scoop is,:( ,

[iwanajohnson]

everyone should start boycotting fed ex!!!! they're keeping me off the water:mad:

[iwanajohnson]

alright back to the point of this thread which is exhaust. has anyone ever tried a mini expansion chamber that goes in the midsection? by any conventional thorught it would work better than an exhaust tuner that goes in the mid. anybody got any thoughts on this. ps. everyone should boycot fed ex.

[Mark75H]

A normal leg is not long enough or big enough inside to accomodate a working expansion chamber for one cylinder ... multiply the diameter times three for three pipes and add a foot or two to the length for proper length and you might squeeze something in

[iwanajohnson]

A normal leg is not long enough or big enough inside to accomodate a working expansion chamber for one cylinder ... multiply the diameter times three for three pipes and add a foot or two to the length for proper length and you might squeeze something in

so your sayin that the sound waves would be goin back into the cylinder too quick and it wouldn't be any good?

[Mark75H]

Yes

[iwanajohnson]

has this been tried or is this just a basis off of book knowledge?

[Fast Fred]

fedex sayin, they got ya covered.:) :cool:

[Mark75H]

has this been tried or is this just a basis off of book knowledge?

Are you saying something must be tried to prove that it will not work?

"Book knowledge" is often the result of other's hard work, trial and error.

A motor with the port timing and rpm range you are using - will need a set of pipes that will not fit inside the housing.

You are certainly welcome to build the device you have envisioned and see for yourself ... but if that is your approach ... why are you bothering to ask?:cool:

[iwanajohnson]

fedex sayin, they got ya covered.:) :cool:

that's great news to hear. if ya see this today fred gime a call. sam not tryin to dog ya was just askin there, you know more than I do and I don't know much about expansion chambers. sorry that came across wrong. I just still don't understand how a tuner that is just a pipe that flares out at the bottom can help to get your back pressure. that's what I was sayin more than tryin to say ya was wrong there. thanks

[Mark75H]

That is a much more direct question that is a lot easier to answer :)

The little pipe that flares out at the bottom provides more back pressure than nothing. The flair may help back pressure stay nearly the same over a wide range. Fishing/pleasure motors can't be fully optimized as far as tuners go because the outboard manufacturer has no control over whether the motor will be used on a 200 pound boat or a 2,000 pound boat. The tuner has to be able to flow enough to avoid damaging the motor in either case.

You could probably get a little extra punch with a reduced size tuner, but to optimize it, you'd have to do it yourself :)

[iwanajohnson]

i get what your sayin about them havin to make a generic tuner. I've got a shorter one made. was just look at a book on expansion chambers and wondered if the pipe in the mid was possible.

[Mark75H]

why would you make the tuner shorter? do you think it is too restrictive?

an internal expansion chamber would be possible, but only if the leg was longer - much longer. Plus the leg would have to be fat enough for three expansion chambers. Back in the days of the Kawasaki triples a lot of 3 into 1 pipes were tried, but none worked as well as 3 separate pipes.

[iwanajohnson]

[QUOTE=Mark75H;33668]why would you make the tuner shorter? do you think it is too restrictive?

i run a jet pump so I need a lot of low end and that's the best way to get it out of those exhaust tuners. this is the style were runnin

[Fast Fred]

thats a screamer pipe. jet pump, purpose specific, 2to 1 gear reduction, pump
stall after 6000 rpms crank speed, more exhaust pressure sooner, need her to get on the powerband rightaway. long pipe hear would be best :cool:

[Fast Fred]

did see a header bolted to the bottom of the exhaust adapter, it turned out the back through the back of the mid, and then a bit up with an expando-can on it,
was tall but it worked. looked like a baseball bat .:cool:

[Mark75H]

Shorter would most likely hurt bottom end at the expense of a minor gain on top end ... I thought you wanted more accelleration?

[iwanajohnson]

Shorter would most likely hurt bottom end at the expense of a minor gain on top end ... I thought you wanted more accelleration?

on a jet pump ya start out with our motors from a dead stop and just grunt the low end to get tbe boat out of the hole and plane the boat out and then crack the throttle in for the top end. all this is cut by 1/3 with the foot.

[iwanajohnson]

a lot of what I know about the tuners and needing to be shorter for the low end is what I've been told by various people. the pictue I put on is the picture of what most people build and put in their boats, I've never built one so I was just kind of asking around to get an idea of how they worked or what could work better!

[RichardKCMo]

Rules, Rules!!!
If everyone runs the same thing, pretty much even. Some orgs. change rules a lot when certain people win a lot.

I sure hope you keep us apprised as thing go on since you only have one race, its only about 3 hrs for me to spectate.LOL
RIchardKCMo

[iwanajohnson]

oh I've already stepped out of the box from doin everything the same way, I just gotta see if it works. fed ex de-commisioned my motor last week by droppin somethin on it, just waitin on them to pay for some stuff so I can get it on the boat and really prove how bad it is. boat races are this august 4th or 7th. try gatorjetboats.com for the exact date but it's close, I'll keep ya posted on when they are. keep an eye on the jets section on thread outboard jet in progress and that's my boat bein started, you might have already saw it but we'll definatley keep ya posted an ya should come watch the race, and I'll keep tryin to think of somethin different to make it a little more interesting.

[Fast Fred]

work the weight transfer, as she comes on plain, Do NOT LET OFF the THROTTLE. drive through it,when she settles down, hit the NOS:cool:

[river_ratj40]

If You Cant Drive It Wide Open, Dont Drive It All!

[iwanajohnson]

If You Cant Drive It Wide Open, Dont Drive It All!

that's sort of the theme song, if we can get it on there and goin we'll see if we can keep true to that.

[Fast Fred]

some one was hackin on my Moda runnin bench, so i'm makin an other one:eek: :cool:
http://img510.imageshack.us/img510/4489/p5100009oi6.th.jpg (http://img510.imageshack.us/my.php?image=p5100009oi6.jpg)

[Fast Fred]

check the timin, check the burn,:cool:

[Fast Fred]

Moda runnin stand:cool: :eek:
http://img501.imageshack.us/img501/5347/p5250019qs5.th.jpg (http://img501.imageshack.us/my.php?image=p5250019qs5.jpg)