Reed Valve In Airbox

[gmustangt]

Looking to have a discussion on the reed valve in the airbox , its seams this is incorporated in Polaris new 850 Boost. Is this the key to improved bottom end?

1. The reed valve is only open under vacuum and closes up under boost?
2. Bottom end sees more air when under vacuum , better filling the cylinder, better response etc.
3. This means you are pulling in hot under hood air in these cases?

Anyone have any before and after experience of adding a reed? is it a noticable differance? and the key to better bottom end.

 

[Clarke673]

I can't even explain how impressed I am in the complexities polaris undertook on this kit. I have been working on my own to make something like they just came out with. Pics copied from snowest and polaris. I'll let other do the debating and come back later

Ps. Can't wait to cut that box up and try to work out a proper tunnel dump!

 

[gmustangt]

Skidoo is similar with the a separate intake for preboost / low throttle.

these intakes seem to be the main difference from the after market kits we are used to.

makes you think that’s where the better bottom end comes from , and I can understand why.

 

[Sheetmetalfab]

Looking to have a discussion on the reed valve in the airbox , its seams this is incorporated in Polaris new 850 Boost. Is this the key to improved bottom end?

1. The reed valve is only open under vacuum and closes up under boost?
2. Bottom end sees more air when under vacuum , better filling the cylinder, better response etc.
3. This means you are pulling in hot under hood air in these cases?

Anyone have any before and after experience of adding a reed? is it a noticable differance? and the key to better bottom end.

I think the reed valve is only a small part of the equation.

According to VOHK Mid pipe wastegate is the biggest piece of the puzzle.

Controlling that with fueling makes the 2T turbo work with low octane.

 

[gmustangt]

I think the reed valve is only a small part of the equation.

According to VOHK Mid pipe wastegate is the biggest piece of the puzzle.

Controlling that with fueling makes the 2T turbo work with low octane.

Wastegate really won’t have anything to do with low end vacuum throttle response.

fwiw I built a pro 6 years ago with wastegate off the pipe , has its advantages but not low end.

With the comp. housing being the choke point on the bottom end because the wheels aren’t spinning fast enough , getting more air in through the reed valve makes sense under vacuum, fill up the cylinder . Then close the valve once there’s positive pressure

 

[Sheetmetalfab]

Wastegate really won’t have anything to do with low end vacuum throttle response.

fwiw I built a pro 6 years ago with wastegate off the pipe , has its advantages but not low end.

With the comp. housing being the choke point on the bottom end because the wheels aren’t spinning fast enough , getting more air in through the reed valve makes sense under vacuum, fill up the cylinder . Then close the valve once there’s positive pressure

I don’t assume your experimental pro build used electronic solenoids controlled separately from the turbo.

I understood they use the wastegate to allow for an exhaust outlet unobstructed by the turbine wheel.

This should help bottom end power.

The old psi pipes with center dump always had great bottom end.

 

[TRS]

I believe it needs the pipe dump while in the NA mode. When the reed opens in the NA mode you cannot have pipe pressure. It will fill the cylinder with exhaust. It definitely will affect scavenging.

 

[gmustangt]

@Sheetmetalfab no i never had electronic controlled wastegate , and ya id agree the external gate on the pipe allows for better flow in to the turbine.

@TRS hmm that one seams backwards to me , if the wastegate is open with no boost you are wasting the energy to spin the turbo. reed or no reed there is air coming through the throttle bodies , it doesnt know or care where its coming from, so reversion would happen anyways. Typically there would always be pipe pressure before intake pressure even on the turbos we are used to today.

Good discussion

 

[Sheetmetalfab]

@Sheetmetalfab no i never had electronic controlled wastegate , and ya id agree the external gate on the pipe allows for better flow in to the turbine.

@TRS hmm that one seams backwards to me , if the wastegate is open with no boost you are wasting the energy to spin the turbo. reed or no reed there is air coming through the throttle bodies , it doesnt know or care where its coming from, so reversion would happen anyways. Typically there would always be pipe pressure before intake pressure even on the turbos we are used to today.

Good discussion

I think trs was referring to “turbine wheel pipe pressure” being much less with the large wastegate available to make it match “naturally aspirated pipe pressure” and have N/A bottom end response.

The turbine wheel will still get some flow to keep it spinning, just not excessive pressure (which would cause the reversion)

 

[Wheel House Motorsports]

The cool thing with the electronically controlled pipe dump WG is the ability to instantly manipulate things. Your not stuck thinking about opening position vs boost PSI. If you read through the polaris pattents they have a lot of info about their whole smart boost system or whatever the trade name is. TONS more calucations and corrections being used vs a turbo added OEM unit and 1 dimensional WG.

With the reed valve and the wastegate cracked at idle this allows the motor to affectively bypass the turbo almost completely allowing for SOME RPM to be built and then feed the turbo. Again this is just speculation on how it all operates and is mapped but illustrating the hard parts I see, the patent info and how I see it coming together.

The bottom end is very strong and smooth coming on from an idle to WOT. once your riding at all above the engagement RPM on them its explosively fast and responsive. The boys at polaris had the pre-production units ripping and I know they are still continuing to fine tune mapping and correction tables to make it even better wherever possible. For its performance in this state I am blown away. every NA sled even after a year or two always benefits from more mapping and time on the snow.

 

[Sheetmetalfab]

The cool thing with the electronically controlled pipe dump WG is the ability to instantly manipulate things. Your not stuck thinking about opening position vs boost PSI. If you read through the polaris pattents they have a lot of info about their whole smart boost system or whatever the trade name is. TONS more calucations and corrections being used vs a turbo added OEM unit and 1 dimensional WG.

With the reed valve and the wastegate cracked at idle this allows the motor to affectively bypass the turbo almost completely allowing for SOME RPM to be built and then feed the turbo. Again this is just speculation on how it all operates and is mapped but illustrating the hard parts I see, the patent info and how I see it coming together.

The bottom end is very strong and smooth coming on from an idle to WOT. once your riding at all above the engagement RPM on them its explosively fast and responsive. The boys at polaris had the pre-production units ripping and I know they are still continuing to fine tune mapping and correction tables to make it even better wherever possible. For its performance in this state I am blown away. every NA sled even after a year or two always benefits from more mapping and time on the snow.

Every video that shows rpm on the gauge is locked on 8450-8500 in a pull.

No variation.

(Makes me think boost psi is tied directly to peak operating rpm. ?)

 

[gmustangt]

The cool thing with the electronically controlled pipe dump WG is the ability to instantly manipulate things. Your not stuck thinking about opening position vs boost PSI. If you read through the polaris pattents they have a lot of info about their whole smart boost system or whatever the trade name is. TONS more calucations and corrections being used vs a turbo added OEM unit and 1 dimensional WG.

With the reed valve and the wastegate cracked at idle this allows the motor to affectively bypass the turbo almost completely allowing for SOME RPM to be built and then feed the turbo. Again this is just speculation on how it all operates and is mapped but illustrating the hard parts I see, the patent info and how I see it coming together.

The bottom end is very strong and smooth coming on from an idle to WOT. once your riding at all above the engagement RPM on them its explosively fast and responsive. The boys at polaris had the pre-production units ripping and I know they are still continuing to fine tune mapping and correction tables to make it even better wherever possible. For its performance in this state I am blown away. every NA sled even after a year or two always benefits from more mapping and time on the snow.

Good points , they can be opening and closing the WG based on other sensors from idle to WOT.

Aside from that they must see the need for added air , thats why the reed.

 

[Wheel House Motorsports]

Every video that shows rpm on the gauge is locked on 8450-8500 in a pull.

No variation.

(Makes me think boost psi is tied directly to peak operating rpm. ?)

The 850 motor LOVES that RPM. I've been running my NA one there for 2 years and its where it wants to be.

Nice thing if your targeting an absolute pressure (maybe even with a tiny bit of correction for IAT) basically targeting a Mass air flow. from sea level to 10k it should be holding the same RPM ALL the time if done right.


The reed valve helps give the motor just the slightest gulp of air again to bypass turbo and spool up quicker. As I said, in riding them they ahve a nice meaty torque curve and ROWDY response in and out of boost.

 

[madmax]

As far as your Question 3 goes, I’d be willing to bet the air coming in from the hot turbo is at a higher temp than what the air box reeds are going to pull in on the back or the air box. So I wouldn’t be concerned with “hot under hood air” entering the crankcase.
Also, a lot of turbo builders have tried the “reed in air box” design over the years, it’s never worked out very well. Very different now with a very specific reed design coupled with the computer controlled ignition, fuel and waste gate.