Avenger 85 question

[ImpulseRocket]

Yes I can. Typical transfers and piston of a CG.

Your transfers have a cut out at the bottom.
View attachment 206696

Your piston already makes a provision for that with the bottom half+ of the piston missing.

View attachment 206697

The typical CG engine needs a hole at the bottom of the transfers for the fresh charge to travel up, whereas the avenger engine doesn't need the hole as the charge will use the gap along side the piston to get to the transfers. HTH.

I am pretty sure the Avenger design is borrowed from a Saw or something similar. The partially closed divided transfers were always the one odd thing about this cylinder I never understood. I can only assume they opened up the bottom to try and get better intake flow to the lower transfers, but they wanted to try and retain as much piston stability as they could. Compromise design.

 

[Chainlube]

I am pretty sure the Avenger design is borrowed from a Saw or something similar. The partially closed divided transfers were always the one odd thing about this cylinder I never understood. I can only assume they opened up the bottom to try and get better intake flow to the lower transfers, but they wanted to try and retain as much piston stability as they could. Compromise design.

What it looks like to me, is they were trying to match it up to a CG case and cast it a little different. Probably could have use an adaptor plate instead, just cover the transfer holes with it.

 

[GW's Motorized]

From what I see the phantom had a better internal design as it is based on the ms380/460 design.

 

[ImpulseRocket]

From what I see the phantom had a better internal design as it is based on the ms380/460 design.

The cylinder port design of the stihl Saws allows them to have a smaller lower case size and higher pop pressure than the typical case port design seen on most 2 strokes. It has ups and downs just like any design. Makes for a higher intake charge velocity which results in a larger volume of air/fuel in a shorter time span which helps both with cylinder evac and swirl which results in better efficiency and torque. The cost is mainly a more limited potential for high flow volume, and thus less peak power at higher rpm.

This is why the Phantom pulls like a truck at the lower rpm but still winds out to about 9500 where it peaks and then falls like a rock. vs the Avengers higher peak hp rpm (lower peak horsepower).

The transfers of the Avenger are dimensionally and volumetrically bigger and operate with lower pop pressure. The transfer shape and design on the Avenger is very good, which is why it too has a good torque curve. Peak isn't quite as low in the rpm range, but it is broader overall.

I prefer the Stihl saw design because it was created for an engine that needs to make it's best power under load, at lower rpms when it starts bogging down on a cut... kind of like my fat butt sitting on the Bike. It's power curve also matches the limitation of the yd100 bottom end better in terms of longevity (lower operating rpm range) and due to it's efficient burn gets rather amazing fuel economy when run at part throttle just toodling around.

 

[ImpulseRocket]

Mine is flat and so is the Phantom 85 piston.

The Phantoms chamber was copied from the ms460 saw, which also runs a flat top piston. It's squish band is the right shape to work with a flat top. What he is saying is the Avengers chamber shape doesn't seem to match a flat top piston design for an ideal squish band.

 

[Wyvern]

The cylinder port design of the stihl Saws allows them to have a smaller lower case size and higher pop pressure than the typical case port design seen on most 2 strokes. It has ups and downs just like any design. Makes for a higher intake charge velocity which results in a larger volume of air/fuel in a shorter time span which helps both with cylinder evac and swirl which results in better efficiency and torque. The cost is mainly a more limited potential for high flow volume, and thus less peak power at higher rpm.

This is why the Phantom pulls like a truck at the lower rpm but still winds out to about 9500 where it peaks and then falls like a rock. vs the Avengers higher peak hp rpm (lower peak horsepower).

The transfers of the Avenger are dimensionally and volumetrically bigger and operate with lower pop pressure. The transfer shape and design on the Avenger is very good, which is why it too has a good torque curve. Peak isn't quite as low in the rpm range, but it is broader overall.

I prefer the Stihl saw design because it was created for an engine that needs to make it's best power under load, at lower rpms when it starts bogging down on a cut... kind of like my fat butt sitting on the Bike. It's power curve also matches the limitation of the yd100 bottom end better in terms of longevity (lower operating rpm range) and due to it's efficient burn gets rather amazing fuel economy when run at part throttle just toodling around.

Never ridden a Phantom, but with the Avenger, there is only a small dead-spot off of idle, once you get moving it's got tons of pull, the last 3rd being especially willing, I'm 300lbs and it pulls just fine with a 36T.

I have seen that split in ports before in nitro-model engines (basically 2 stroke diesels)

 

[ImpulseRocket]

Never ridden a Phantom, but with the Avenger, there is only a small dead-spot off of idle, once you get moving it's got tons of pull, the last 3rd being especially willing, I'm 300lbs and it pulls just fine with a 36T.

I have seen that split in ports before in nitro-model engines (basically 2 stroke diesels)

I know it pulls strong too. Peak torque is close to the same and they both have strong torque curves. The Phantom makes 1 more hp (5 vs. 4) but it peaks it's 5hp sooner than the Avenger peaks it's 4hp, which perfectly lines up with what I said.

The Phantom also has a much smaller intake port at the flange whilst making it's extra horsepower. When I port matched my intake flange to the reed block, which is the same port shape as the avenger, it probably added another 25% more area. My theory is the smaller intake port size and the nearly 2mm squish gap was added to restrict the power some amd/or keep the heat more reasonable, because the design of the ms460 saw they used makes 7hp with a restrictive stock saw muffler. Even with a stock Phantom exhaust I am fairly sure my bike makes close to that 7hp figure with the work I have done. If I installed a 18 to 20mm carb I know it would make at least that much.

 

[Wyvern]

I know it pulls strong too. Peak torque is close to the same and they both have strong torque curves. The Phantom makes 1 more hp (5 vs. 4) but it peaks it's 5hp sooner than the Avenger peaks it's 4hp, which perfectly lines up with what I said.

The Phantom also has a much smaller intake port at the flange whilst making it's extra horsepower. When I port matched my intake flange to the reed block, which is the same port shape as the avenger, it probably added another 25% more area. My theory is the smaller intake port size and the nearly 2mm squish gap was added to restrict the power some amd/or keep the heat more reasonable, because the design of the ms460 saw they used makes 7hp with a restrictive stock saw muffler. Even with a stock Phantom exhaust I am fairly sure my bike makes close to that 7hp figure with the work I have done. If I installed a 18 to 20mm carb I know it would make at least that much.

Where do you think the bottleneck is in the Avenger?

 

[ImpulseRocket]

Where do you think the bottleneck is in the Avenger?

Without port timing and duration numbers along with other details here and there I couldn't tell you. I could speculate, but I am not a fan of doing so.

The person importing and selling them made claims of "better port timing" than the Phantom but never released the numbers to the public. A lot of people make the mistake of thinking timing figures alone are the key to efficiency and power, and most of them are partially wrong.

As a person who understands the vast ocean that is things that affect power, I can tell you that port timing and duration is only a single factor out of many. It's no different than guys that stick a huge cam and giant carb on a small block chevy engine to make more power vs. The guys that spend the money on an intake and cylinder head engineered to deliver higher flow volume while maintaining charge velocity and proper swirl but run a much smaller street friendly cam. Both ways can make the same power, but one will be a much better engine all around.

 

[GW's Motorized]

I know it pulls strong too. Peak torque is close to the same and they both have strong torque curves. The Phantom makes 1 more hp (5 vs. 4) but it peaks it's 5hp sooner than the Avenger peaks it's 4hp, which perfectly lines up with what I said.

The Phantom also has a much smaller intake port at the flange whilst making it's extra horsepower. When I port matched my intake flange to the reed block, which is the same port shape as the avenger, it probably added another 25% more area. My theory is the smaller intake port size and the nearly 2mm squish gap was added to restrict the power some amd/or keep the heat more reasonable, because the design of the ms460 saw they used makes 7hp with a restrictive stock saw muffler. Even with a stock Phantom exhaust I am fairly sure my bike makes close to that 7hp figure with the work I have done. If I installed a 18 to 20mm carb I know it would make at least that much.

If the phantom V4 is a 2 piece and has a good rep when it comes out, I'm gonna get one and mod out my V3 to see how much I can get out of it with "bolt on" parts (meaning carb, pop top piston, and a kx85 or similar pipe welded to the phantom flange.)