long inlet manifold

GoldenMotor.com

Davezilla

New Member
Mar 15, 2014
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San Antonio Texas
I haven't used one myself, but they do offer an increase in bottom end torque, but they also lose a lot of top end power so it really depends on your build and how you intend to ride the bike... for all out speed I wouldn't recommend this one, but if you need climbing power or a strong bottom end and speed is less important, the long intake delivers... for strong top end power and top speed you'll want the shorty intake, these are easy to port match to the intake port and easy to bore out to match the carb size, the stock shorty intake is only 13mm inner diameter, but can be bored out to 16mm for better top end performance, it made a very noticeable difference on mine.
 
Dec 11, 2014
628
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Tucson
I have seen some long manifolds on big horsepower, reed valved, moped top end bikes with big carbs fully custom built. As well as z manifolds just to clear the seat tube. As for performance gains unless the length is precisely timed and I have no knowledge of that on the intake side it might help with velocity but not breathing. I am running as short and big as possible at the moment but I have only been working on top end power with the stock Chinese jug.
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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memphis Tn
It's been my experience that some chinadolls will show improved low end with a long intake,
But it usually cuts top end power a bit.
Every engine is different so you will need to experiment to find the proper length for your needs.
Experimentation is easily done with simple heater hose and hose clamps to find the wanted length, than fab it up in steel.
But again, not ALL motors will show any changes or improvement.
 

2door

Moderator
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Sep 15, 2008
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Littleton, Colorado
Just curious. I'll be the first to admit I'm no 2 stroke high performance expert and the principle might be different than an automotive 4 stroke. However It's been my experience that it's the opposite of what Maniac says. I've seen these guys running around on the steets with huge tunnel ram intakes with a couple of 4 barrels sitting on top. They have absolutely no bottom end. If they try to come away from a stop sign hard the engine usually caughs and stumbles until the revs come up and then, and only then does the intake begine to work for them. But who wants to drive on the street at 3000 rpm or better?

Why would a China Girl react differently to a long intake on the bottom end of the power band?
Not knocking you, Maniac. As I said, I'm not a 2 stroke expert by any means. I'm asking because I don't know.

Tom
 

Mike B

New Member
Mar 23, 2011
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Central CA
They're just over carb'ed, happens all the time. We all know that a a 600 CFM Holly is the right deal for a 327 on the street, a 750 is good for a big block.

Two 4V's is over carbed, it's a race set up.
 

YesImLDS

Member
Jun 29, 2013
960
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Columbia, Missouri
Just curious. I'll be the first to admit I'm no 2 stroke high performance expert and the principle might be different than an automotive 4 stroke. However It's been my experience that it's the opposite of what Maniac says. I've seen these guys running around on the steets with huge tunnel ram intakes with a couple of 4 barrels sitting on top. They have absolutely no bottom end. If they try to come away from a stop sign hard the engine usually caughs and stumbles until the revs come up and then, and only then does the intake begine to work for them. But who wants to drive on the street at 3000 rpm or better?

Why would a China Girl react differently to a long intake on the bottom end of the power band?
Not knocking you, Maniac. As I said, I'm not a 2 stroke expert by any means. I'm asking because I don't know.

Tom
I don't really understand it either I remember on my first build I had a exteneded intake, but it was something I made myself and it ran perfect and had instant acceleration, but once I put a shorty intake on it my low end slightly decreased, but the top end increase by quite a bit, talking like 4mph on the top end with a 36T. I know intake spacers are popular with cars and I even have on on my own car. It's a 3/8" spacer, but is good for 30 ft lbs of torque at 4000 rpm when the SRV valve on the intake manifold pops open. Anyways that's enough car talk. I would think it would have to do with the mixing of the fuel and air in the low end?

It doesn't make any sense to me, but that's my personal experiences with it.
 

Slogger

Member
Sep 8, 2014
544
4
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nohio
I can tell you the 4" long offset manifolds will definitely increase bottom end power. They make it pull through corners and in the midrange really well. The engine will run out of power at about 5500 rpm, though.
Even going down a steep hill mine refuses to rev higher than that with its long manifold. It's like a rev limiter.
Members of the 20 mph club would love one of these. I need to pedal up to 6 mph, then the engine pulls away cleanly, and that with a 29" wheel 40 tooth sprocket gearing pulling a 260 pound pilot.
It goes 28.4 mph tops. Since I need to keep it under 25 for the cops I like it a lot.
 

Slogger

Member
Sep 8, 2014
544
4
18
nohio
Just curious. I'll be the first to admit I'm no 2 stroke high performance expert and the principle might be different than an automotive 4 stroke. However It's been my experience that it's the opposite of what Maniac says. I've seen these guys running around on the steets with huge tunnel ram intakes with a couple of 4 barrels sitting on top. They have absolutely no bottom end. If they try to come away from a stop sign hard the engine usually caughs and stumbles until the revs come up and then, and only then does the intake begine to work for them. But who wants to drive on the street at 3000 rpm or better?

Why would a China Girl react differently to a long intake on the bottom end of the power band?
Not knocking you, Maniac. As I said, I'm not a 2 stroke expert by any means. I'm asking because I don't know.

Tom
It has to do with the totally different intake/exhaust scavenging/volumetric efficiency between a piston ported 2 cycle and a poppet valved 4 cycle engine. A while back I read a long-haired article somewhere, but the finer points elude me..
Pressure waves and resonance, blah blah blah.
But they do work- at low rpm, there's a big loss on top.
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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memphis Tn
It has to do with the totally different intake/exhaust scavenging/volumetric efficiency between a piston ported 2 cycle and a poppet valved 4 cycle engine. A while back I read a long-haired article somewhere, but the finer points elude me..
Pressure waves and resonance, blah blah blah.
But they do work- at low rpm, there's a big loss on top.
Well said slogger. Lol!
"Pressure waves and resonance, blah blah blah.
But they do work- at low rpm, there's a big loss on top."
But again, not all will show any improvement. It depends on the individual engines port timing and a BUNCH of stuff I forget.
 

Davezilla

New Member
Mar 15, 2014
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San Antonio Texas
Its still typical even in a 4 strokeV8 to make more torque they make these extra long inlet tubes going into each cylinder.... look at most fuel injected engines and you'll see this... the longer the inlet tubes, the more velocity can be generated which means lots of torque from a rather low rpm. These inlet tubes are usually so long that the tubes have to fold over themselves in order to fit under the hood a d in the engine compartment. If these inlet tubes were straight, they would need to be anywhere from 18 to nearly 30" long depending on engine size. These inlet tubes are also rather narrow to keep the velocity as high as possible, and some even taper down as they get closer to the head.

Now with that known, lets look at a typical tunnel ram where each inlet tube is only about 6 to 8" away from the head and these tubes are very wide in comparison the tubes run up to a large open plenum and each tube inlet is about 3" wide x 2" wide tapering down to the inlet size at the head, which usually needs to be ported to match the tunnel ram. The inlet runners are rather short even compared to a single or dual plane manifold, there are no curves or very slight curves as the runners just go straight up to a massive open plenum just under 2 rather large carbs... these will let a small block engine Rev up to 10,000 rpm with the right cam and large enough valves...
When you look at a tunnel rammed 350 then compare the runner length to a 5.0 Ford and compare the top end horsepower of the tunnel rammed engine to the bottom end torque of the fuel injected 5.0 you will see how this still holds true...

Now on a 2 stroke or 4 stroke engine, this runner length and diameter can be taylored to match an engines other attributes to make lots of torque down low, lots of power up high, or good all around power that's not quite as extreme down low or up high.
you can also run a medium length intake with a larger carb and taper it gradually down to the intake ports size to gain good torque without restricting the top end, the ideal taper here is usually somewhere around 1.5 degrees.... this can be noticed on sportbike engines like the gsxr, r6, r1, ninjas, and honda cbr series bikes where the intake is as straight as possible and has a slight taper all the way from a velocity stack all the way to the inlet valve.
By looking at these type engines as well as the stronger 2 stroke engines and looking at the similarities it can become easier to decide how to set up your intake to match the rest of your engine depend ding on if you want a strong top end, a strong bottom end, or a compromise of a little of both...
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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memphis Tn
My understanding is that you try to time the column resonance with the intake closing.
The idea is you get a bit of extra charge packed in when the moving airflow column slams into the closing port and starts a reflection wave which you then use the same way as a tuned pipe pressure wave by tuning length for maximum effect.
A boost bottle can help with finding the sweet spot by making the air column act larger than you have physical intake tract room for.