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Discussion Starter #1 (Edited)
Short Velocity Stacks & Ramair Unifilters LOOSE - 60mm Open Velocity Stacks WIN

I have just returned from experimenting on the dyno.

Filtered: 77.08 bhp, 58.66 ft/lbs torque
Open stacks: 86.34 bhp, 63.51 ft/lbs torque

Shocking result with the filters. We could have messed around with the jets, but there is no way the motor would have got near the power & torque obtained with the open velocity stacks.



My engine clearly does not work well with filtered short velocity stacks.

I then fitted the Procom CDI and here are the dyno results.

Procom CDI: 88.43 bhp @ 8286 rpm, 63.52 ft/lbs torque @ 5779 rpm.
Stock CDI: 86.34 bhp @ 7681 rpm, 63.51 ft/lbs torque @ 6725 rpm.



It's interesting that max torque occurs almost 1000rpm lower with the Procom. The Procom allows more revs and hangs on to the power until our self imposed maximum. It would rev higher but we limited the revs to 8,500 rpm.

Oddly, last year we tried the Procom when the motor was at a lower stage of tune, and there was a 1bhp loss throughout the rev range. Now, I've lost a little bit between 6500 and 7000rpm and gained everywhere else. The Procom stays on, as do the open velicity stacks.
 

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Wow, I can;t believe the filters cost that much power!! Unfotunately, where I live in the country, the dirt roads would kill my engine in no time without filters.

My 904 is almost complete, the next part I am going to buy is a ProCom unit. Thanks for all the info, your posts have been alot of help to me.

I wonder what the difference in power would be between the cams you are running and the 813's I am using. Hope to hit the dyno soon when I get some good carbs.
 

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rob those are not uni filters are they the the ones you showed me if so they are not the uni filter.question is how much do the stacks add over no filter ,no stack.I been looking at the c/f din numbers and converting the air pressure and temp to the same as we use over here.Looks like it was about 46.6 to 42f and baro pressure was 29.7 to 30.18 doing the math taking your c/f numbers back to raw numbers then looking at sae c/f numbers your bike is making 80 to 85 hp with sae c/f numbers we use on the dynos over here.Not bad for a 904 .
 

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Discussion Starter #5 (Edited)
Mike

You're correct. The filters fitted were manufactured by Ramair, which they describe as uni-filters.

I'm very pleased with the performance of the Procom CDI. Funny how it didn't work well when engine work was restricted to head porting, gas flowing and skimming.
 

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mine kinda acked funny to till i got everything right.I was about to through mine away and after i got the tune right and the 2into1 on it i pluged it in for one last try and bang it picked the bike up a bunch .I think the extra timing maybe causes it to miss or something if there not right.These are the touchy motors more so then any i have ever worked on.little jet changes can make 3to5 hp when you get these motors making good hp.
 
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