3 into 1 pipe

[tz375]

Some of us are silly enough to reverse engineer pipes manufactured in the seventies and trying to apply modern thinking to see if we can do any better. I suspect that a smarter idea might be to see if we can find someone at a company like SLP or AAEN that has designed 3 into 1 pipes to see what they come up with.

All we know for sure is that 3 into 1 pipes from back in the day do weigh a lot less than stock and that improves performance. We know that Strader tried at least three different baffle designs including one based on his patent and we are trying a new design just for giggles.

We think we know that Bromlech, Piper and most others were simply three headers and pipe to take away gas and noise without a chamber as such.

We believe that waves form one cylinder will adversely impact other cylinders as the bike comes on the pipe but don't seem to have a firm grasp on why that's not the case in snowmobiles where they keep working up to a nice high peak.

What we don't appear to collectively know is how to cross link pipes and pulses across a collector. Maybe that's the answer - stuffing waves get so dissipated across three pipes at higher speeds that they no longer have such a strong positive or negative effect. Someone knows but that person is probably not on this board or if they are they ain't owning up to it.

I'd just chose a set of pipes that people claim work (Jemco or Swarbick) and be done with it.

I think the bottom line is if you want power, buy something that's proven and if the journey of discovery is more important than the outcome, keep cutting and welding.

[stcyr]

I thought i read somewhere that the middle cylinder has a slightly smaller displacement and that was the difference in jetting. Correct me if i am wrong but i am afraid of running the middle cylinder lean, heating it up and burning it down.

I read that somewhere too, but the bore and stroke is specified as 70mm and 64mm for all cylinders so don't believe it.

A stock GT750 is so underpowered and overcooled that you don't need to be concerned about the extra cooling that a richer main would provide to the center cylinder. Do you really want that extra unnecessary cooling at the expense of efficiency/horsepower? Add enough perfomance mods and maybe you'll want that extra cooling effect on the center cylinder.

[tz375]

Most 3 into 3 pipes specify the same jets in all 3 carbs, but Strader specifies a larger jet in the center pot - something to do with teh shorter header on that pipe causing it to run hotter.

The smaller jet in the center pot was entirely due to that split pipe on the center pot making it run cooler.

Run Jemcos and you can use teh same jets in all three but make sure your part throttle jetting is good because that's where people melt down their GT's and RDs.

[diablo]

yes i will remember to raise the needles, i was wondering why strader was running bigger jet in the center.
I also read that a k clutch basket has a bushing instead of a needle bearing, i have lots of parts, is it better to change it to needle bearing? or anything i need to know about doing so.
as on smoke riders mods, i took out the coolent bypass, i have not had any troubles at all or noticed any differance in operating temps. cheers.

[stcyr]

The smaller jet in the center pot was entirely due to that split pipe on the center pot making it run cooler.

I don't know where you got that info but the center cylinder definitely runs hotter. A leaner mixture is required because within the hotter inlet passages, the fuel atomizes better so it burns more completely. In the cooler paths, less fuel will atomize and burn so more is needed. It's the same reason you need to choke a cold engine. Racers typically richen up on cooler days and lean out on warmer days, not the other way around (I know, that's more about air density but same effect). If you use the same size jets in all 3 cylinders, the center combustion chamber temperature will be lower than what's optimum for best efficiency and nothing will be gained in terms of engine durability. Other triples, V-twins and V-4s run leaner settings on the hotter cylinders as well. Who're you gonna trust, the people who designed these fine machines or something you read on the internet?

Jetting for expansion chambers is tricky because, as you mentioned earlier, you can destroy an engine at lower throttle settings while still on the pipe.

Edit: When I refer to center cylinder heat, I'm talking about the middle of the engine as a whole but mainly the trapped heat in the crank, crankcase webbing and carburetor area. The actual cylinders and head are kept pretty much the same temperature by the water jacket. The combustion chamber temps are controlled by fuel mixture and that's what people are concerned about. The stock exhaust doesn't have the "supercharging" effect of a properly design expansion chamber so you you won't get any dramatic increases in combustion chamber pressures that would cause heat related problems under certain riding conditions.

Maufacturers tend to run the mains on the rich side and lean all the other circuits to keep emissions low. I've never seen a jap street bike released to the american public after the mid-70s that didn't do that.

Edit: I mistakenly said "the hotter the intake gases are, the better they "atomize" the fuel" but I meant it's the greater amount of fuel that gets "vaporized" in the hotter tracts which displaces more air thus requiring less fuel. This is because vapor (a gas) volume is may times greater than fuel droplets (a liquid) so those carburetors with hotter tracts can't take in as much air as the cooler ones.

[stroknsmokngt]

Omars sells a 3/1

http://omarsdtr.com/cafenew7.html" onclick="window.open(this.href);return false;

[stcyr]

Most 3 into 3 pipes specify the same jets in all 3 carbs, but Strader specifies a larger jet in the center pot - something to do with teh shorter header on that pipe causing it to run hotter.

That makes sense. A shorter header on the center means the pressure waves will return to the port sooner than the outer ones so a higher engine speed is needed to sync up with those waves. When the outer cylinders horsepower peaks and then begins to drop off, the center cylinder will continue to make power. Because of the greater charge being put in that cylinder at higher engine speeds, air flow is increased necessitating an increase in fuel.

I'd rather have same length headers so the work load is evenly distributed across all cylinders at any speed.

[tz375]

Where did you get that info on the center pot running hotter and needing a smaller jet to match the lower volumetric efficiency? As you said when you posted the edit.

Forget about the interwb, I make this stuff up as I go along- sometimes based on actual observations but that's not guaranteed.

My old Rocket 3 BSA did have a larger main jet in the center pot because we all believed that cylinder ran hotter - at least that's how we rationalized it back in ... Well that was a long time ago.

Good point about emissions and lean settings a.k.a. cold blooded bikes.

Of course CV carbs aren't quite like slide carbs and they are on the needle in most riding conditions and that's tricky for most people to jet for.

Agree totally that the best system is 3 pipes. You really don't want to see what i'm planning to test next.

[stcyr]

Where did you get that info on the center pot running hotter and needing a smaller jet to match the lower volumetric efficiency? As you said when you posted the edit.

My old Rocket 3 BSA did have a larger main jet in the center pot because we all believed that cylinder ran hotter - at least that's how we rationalized it back in ... Well that was a long time ago.

Good point about emissions and lean settings a.k.a. cold blooded bikes.

Of course CV carbs aren't quite like slide carbs and they are on the needle in most riding conditions and that's tricky for most people to jet for.

Agree totally that the best system is 3 pipes. You really don't want to see what i'm planning to test next.

I can't find the document with that info but a few days ago, I asked our Honda rep if he could verify what I read. He got on the horn and sure enough, that's the case. Long ago, when I'd rebuild used carbs on V-twins, I'd put the richer jet in the hotter running carb paying no attention to which one it was in originally. Like you say, it was logical. Then I started noticing that new unmolested bikes were just the opposite. I figured they must know what they're doing and just forgot about it. No doubt, most speed tuners think like us and just make them all the same.

I have a link somewhere with tips on jetting CV carbs that'll help cut out the guesswork. I'll post it later.

Forget about the interwb, I make this stuff up as I go along- sometimes based on actual observations but that's not guaranteed.

Hey, if you can't dazzle 'em with brilliance, baffle 'em with bullshit.

Okay, I'll bite, what're you planning to test. I'd like to try NO2, Heard it works much better in 2 strokes.

[tz375]

Nothing like that. It's just another 3 into 1 pipe and a very modified 3 into 1.

Nitrous you say.. Hmmm.

[diablo]

running leaner in the middlle cylinder because it is hotter in the crank case, very interesting.
Looking foward to those test results.
NOS on a buffalo, i bet it would rev up like an H2 & go like a rocket

[diablo]

•The clutch plates were changed from resin to be aluminium substrate
•The primary driven gear (clutch centre boss) was changed from being a bushing to be a dual needle roller

[tz375]

The later model needle rollers and smaller diameter hardened bush/spacer are an improvement and so are later clutch plates.

[stcyr]

Nothing like that. It's just another 3 into 1 pipe and a very modified 3 into 1.

Nitrous you say.. Hmmm.

I would use the 3 into 1 with the largest diameter collector and mid section. Cut it open and weld in three plates so the individual pressure waves have their own piece of the pie.

[ja-moo]

running leaner in the middlle cylinder because it is hotter in the crank case, very interesting.
Looking foward to those test results.

I might believe it, if I hadn't been modding and racing the lowly "air cooled" Kawi triples for 34 years. Jet even straight across. The cylinder that seizes the most..... The right, figure that one out.........

You have to realize that the heat is in the top of the cylinders and migrates down, losing quite a bit of heat on the way. Then you have this big lump of aluminum (cases) radiating heat. I would seriously doubt the center crankcase would be more than a few degrees different, if at all......