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This rear box has a pressure activated release that only opens when the car is going full chat.....

 

So around town the flow is through the centre bore, then at speed the spring is compressed opening the entire rear end.

 

Clever stuff ;)

 

post-2-1213812611.jpg

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Is it the same as a "Power Valve"?

 

M/Bikes well Yamaha have used these for years on the YZF EXUP( EXhaust Ultimate Power valve).It takes away flat spots and gives more mid range power/performance gives smoother acceleration and better fuel economy if correctly adjusted.

 

;)

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Don't know... I have never seen this before... The owner says it's to control the noise at low revs.

 

It was on the Skyline we calibrated today.... Personally i prefer the full sound version ;)

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Is it the same as a "Power Valve"?

 

M/Bikes well Yamaha have used these for years on the YZF EXUP( EXhaust Ultimate Power valve).It takes away flat spots and gives more mid range power/performance gives smoother acceleration and better fuel economy if correctly adjusted.

 

The Yamaha YPVS or Yamaha Power Valve System was used on the RD350 & RD500 Two-Strokes. It was a simple valve

that had 2 positions (& the small amout of time to change between the two as it was a rotating valve system) directly in the

exhaust port before the exhaust header and changed the way the exhaust gases interacted with the expansion chambers.

This gave the bike less of a light switch power delivery the older RD350LC had (see below)

I am sure this will bring back some memories !!

 

RD350LC

1,000rpm = nothing :D

 

2,000rpm = nothing :D

 

3,000rpm = almost nothing :confused02:

 

4,000rpm = slightly better than nothing :crying:

 

5,000rpm = still only just better than nothing B)

 

5,999rpm = oh I think there is possibly more than 50cc at work here, yes something is happening :worried:

 

6,000rpm = OMFG THIS BIKE HAS JUST GONE BERZERK & THE FRONT HAS COME UP & SMASHED THE CLOCKS INTO MY CHIN !!! :o HOLD TIGHT !!

 

7,000rpm = I CAN GET USED TO THIS !!! :party:

 

7,250rpm = THIS IS BETTER THAN SEX B)

 

7,251rpm = Brick wall all over :o

The YPVS valve made the useable power come in slightly earlier, and finish slightly later.

I had a brand new one of these in 1991 and for a couple of thousand revs in the power band it was pure two-stroke nirvana.

Shame some bugger smashed me up the backside whilst stationary @ a roundabout in 1993 and wrote the bike & my back off !!

 

The EXUP valve first used in the late eighties is a similar kind of device, used soley on 4 cylinder Four-Strokes (normally with a 5 valve per cylinder head).

This time a valve was further down the exhaust system, underneath the bike where the 4 header pipes connected, before the single exhaust

exit pipe. This valve altered the way the exhaust power pulses were reflected back towards the cylinders (scavenging effect)

and the way the power pulses exited the exhaust, giving good low-down torque and the high RPM power required.

This Yamaha deemed this to be the perfect compromise to the problem of an engine @ high rpm giving good horsepower, but lower

down the rev range being very weedy & lacking torque, or vice versa. The EXUP giving both low down torque & high rpm power, a kind

of best of both worlds. An exhaust solution to the car manufacturers VVT-i or V-TEC etc.

 

This system (thread topic above) seems just to be noise related I think, but may have a slight power increase when fully open as it is flowing more gas.

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This rear box has a pressure activated release that only opens when the car is going full chat.....

 

So around town the flow is through the centre bore, then at speed the spring is compressed opening the entire rear end.

 

Clever stuff B)

 

I've got a new system going on next week with electrically controlled centre silencers. Switch in the centre console does nice sound to NASCAR to suit the occasion. That and some tubular manifolds and sports cats.

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I've got a new system going on next week with electrically controlled centre silencers. Switch in the centre console does nice sound to NASCAR to suit the occasion. That and some tubular manifolds and sports cats.

 

Now that i have to see/hear B)

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This rear box has a pressure activated release that only opens when the car is going full chat.....

 

So around town the flow is through the centre bore, then at speed the spring is compressed opening the entire rear end.

 

Clever stuff ;)

 

post-2-1213812611.jpg

 

fairly sure thats make by APEXI ... not cheap though

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