Power Valve

**Chaz** · 01-05-2023, 10:52 AM

I had a 1974 Maico 400 radial when I was a kid. Start in first, second, it didn't matter.
Torque from idle till it wouldn't rev any higher. If it fell off the curve .. I didn't really notice it and probably should have shifted already. Plenty of over-rev to it's total design of, carb, case volume, cylinder and pipe.

Most pipe builders get pushed into a corner (myself included) of building (more HP) as R+D continues .. until the acoustics outrun the useful airflow of the rest of the package, and are then dubbed as being dud's.

Gordon Jennings wrote a book on two-stroke tuning. There was a second volume on just expansion chambers. Plenty of information on what builds low end torque in his writings.

Variable exhaust timing was a great idea. Some stuck with the use of dirtier oils, but synthetics were accepted practice by then.

Wayne Taylor had the right idea.

**cali kid** · 01-05-2023, 11:52 AM

Originally Posted by chaz

i had a 1974 maico 400 radial when i was a kid. Start in first, second, it didn't matter.
Torque from idle till it wouldn't rev any higher. If it fell off the curve .. I didn't really notice it and probably should have shifted already. Plenty of over-rev to it's total design of, carb, case volume, cylinder and pipe.

Most pipe builders get pushed into a corner (myself included) of building (more hp) as r+d continues .. Until the acoustics outrun the useful airflow of the rest of the package, and are then dubbed as being dud's.

gordon jennings wrote a book on two-stroke tuning. There was a second volume on just expansion chambers. Plenty of information on what builds low end torque in his writings.

Variable exhaust timing was a great idea. Some stuck with the use of dirtier oils, but synthetics were accepted practice by then.

Wayne taylor had the right idea.

bad ass!

**cali kid** · 01-05-2023, 12:09 PM

Originally Posted by cali kid

bad ass!

Those power valves are Rotax, real simple to hook up. 3 liter Merc. Was this motor ever completed?

**moatorbotin** · 01-06-2023, 02:42 PM

Originally Posted by rude tim

I think that space is the biggest obstacle that would need to be overcome on a multi cylinder 2 stroke block. There just is not enough room to put the control mechanism on the cylinders. Obviously they would have to be electronic controlled which makes the space problem even worse. Having raced 2 stroke bikes for years I can tell you It would be bad ass to have it working correctly. Power valves made a bigger difference that the reed valves as far as creating a broader power band.

Why do they have to be electronically controlled? The PV on my KTM isn't. (Is it a multi cylinder thing?)

**rude tim** · 01-06-2023, 07:03 PM

The 2 stroke boat engines have the cylinders turned so the exhaust port is not 90 degrees from the crank.

**H2OPERF** · 01-06-2023, 07:31 PM

The g2 is 90deg the cylinders are not canted down, I have a 3.4 block some day we will see what it will do. kinda hard to make an adapter with the exhaust on the left of both banks but it will go on the stv some day..

**H2OPERF** · 01-06-2023, 07:39 PM

small g2 powervalve set up.. they were on track but brp did what they do best.

**ksfastman** · 01-07-2023, 12:51 AM

Expansion chambers do not kill the bottom end.

**rude tim** · 01-09-2023, 07:35 PM

Originally Posted by ksfastman

Expansion chambers do not kill the bottom end.

Expansion chambers are built to specific power bands. If you build the pipe for a top end port map you will loose some bottom end and vice versa for a low port timing motor and pipe. They make more power than an exhaust chest design but they will narrow the power band some. Boats do not have the ability to shift gears therefore in “normal boating conditions” an exhaust chest provides a better overall power band as it uses the other cylinders to scavenge the exhaust/ draw in the intake and pulse to stuff the extra fuel/air back in to the cylinders.

**ksfastman** · 01-09-2023, 08:27 PM

Originally Posted by rude tim

Expansion chambers are built to specific power bands. If you build the pipe for a top end port map you will loose some bottom end and vice versa for a low port timing motor and pipe. They make more power than an exhaust chest design but they will narrow the power band some. Boats do not have the ability to shift gears therefore in “normal boating conditions” an exhaust chest provides a better overall power band as it uses the other cylinders to scavenge the exhaust/ draw in the intake and pulse to stuff the extra fuel/air back in to the cylinders.

A so so expansion chamber is going to make more power than the chest the OEM's use. The problem is where are you going to mount/route the chambers, Rec boaters aren't going to want pipes outside the cowl/mid. A dedicated slippy pipe per cylinder with water injection would be awesome.

**oldschoolltv** · 01-09-2023, 08:35 PM

I was looking for the pictures of the one Wayne was working on, he was one of a kind.

**ksfastman** · 01-10-2023, 08:21 PM

Originally Posted by Chaz

I had a 1974 Maico 400 radial when I was a kid. Start in first, second, it didn't matter.
Torque from idle till it wouldn't rev any higher. If it fell off the curve .. I didn't really notice it and probably should have shifted already. Plenty of over-rev to it's total design of, carb, case volume, cylinder and pipe.

Most pipe builders get pushed into a corner (myself included) of building (more HP) as R+D continues .. until the acoustics outrun the useful airflow of the rest of the package, and are then dubbed as being dud's.

Gordon Jennings wrote a book on two-stroke tuning. There was a second volume on just expansion chambers. Plenty of information on what builds low end torque in his writings.

Variable exhaust timing was a great idea. Some stuck with the use of dirtier oils, but synthetics were accepted practice by then.

Wayne Taylor had the right idea.

Wow, what ever happened to this engine?

**ksfastman** · 01-10-2023, 08:23 PM

Originally Posted by ksfastman

Wow, what ever happened to this engine?

That's like OB porn!!! Lol

**Glastron1987** · 01-21-2023, 10:16 AM

I wonder if making the tuner variable would be an easier/simpler modification and still give you most of the gain?

**Chaz** · 01-21-2023, 10:51 AM

Originally Posted by ksfastman

Wow, what ever happened to this engine?

Last I heard, it was still in Wayne Taylor's shop. I know the twins were offered pretty good money for it .. but they weren't interested in selling it ...

From what I remember, it's a 2.6L

Glastron1987

I wonder if making the tuner variable would be an easier/simpler modification and still give you most of the gain?

An oldie, but goodie ...

http://www.bridgestonemotorcycle.com...ou_really6.pdf