| [ Total Views: 933 | Total Replies: 16 | Thread Id: 85970 ] |
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 sander288
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| posted on September 13th, 2010 at 01:00 PM |
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Mix and Matching Ratio Rockers
I was talking to a friend of mine in the UK and he has had a motor built with a fk-10 cam and runs different ratios on his inlet and outlet valves.
1.4:1 (inlet) 1.25:1 (outlet)
Is there any merit to doing this? its the first time i've heard of mixed ratios on the rockers...
The motor makes good power though so it must be ok
Cheers
Shaun
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 matberry
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| posted on September 13th, 2010 at 01:04 PM |
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Yep, no problem except you need to buy two sets of rockers .
If the balance of inlet to exhaust flow of the head is not where the engine builder wants it, this is one way to get the flow rates where desired.
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
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sander288
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| posted on September 13th, 2010 at 01:49 PM |
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So in affect, this engine builder wants more exhasut to flow out, so has allowed for a bigger ratio?
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Gracey
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| posted on September 13th, 2010 at 01:55 PM |
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Going by what you've posted "1.4:1 (inlet) 1.25:1 (outlet)" I'd say it want's less.
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matberry
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| posted on September 13th, 2010 at 03:03 PM |
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Volksie heads are inherently poor performers on the intake, and most off the shelf heads flow more on the exhaust than some heads guys want, when
compared to what can be achieved with the intake.
This combo with the 1.25's on the exhaust, is reducing the lift on the exhaust to effectively decrease the flow that he would have had if all the
same ratio's were used. It changes the flow ratio of exhaust to Inlet.
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
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Newt
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| posted on September 15th, 2010 at 12:21 AM |
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Matt,
Is it a problem if your exhaust over floweth?
Newt
It is as it is - If you didnt enjoy today, you've missed the opportunity.
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beetleboyjeff
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| posted on September 15th, 2010 at 12:28 AM |
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Yeah - you will get exhausted.. lol
From your ole' mate Jeff
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Newt
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| posted on September 15th, 2010 at 12:29 AM |
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I would have thought that that would have been better than being constipated?
Newt
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matberry
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| posted on September 15th, 2010 at 07:53 AM |
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| Quote: | Originally
posted by Newt
Matt,
Is it a problem if your exhaust over floweth?
Newt
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Well, not such a 'problem', but when your chasing every ounce of performance, and who isn't, there is a flow ratio to aim for. It's the same
principle that is used when deciding the valve sizes. A smaller exhaust valve is used as once the combustion has occured, the increased temperature
and burnt gasses don't need as much space, and this gets optimised, same for the ports and exhaust system. It's the fine tuning of these areas that
customises an engine for a specific aplication. Such as, a bigger exhaust for more power but less torque and visa versa.
And it's better than being exhausted..... and way better than constipation !!!
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
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sander288
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| posted on April 11th, 2012 at 08:57 PM |
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Reviving this old thread;
Some talk with Col at Eastern creek and also with Craig T this weekend got me thinking; Col said put some 1:1 rockers on the exhaust valves but I
though why not go bigger with the intake instead?
Would some 1.25:1 rockers on the intakes be ok with a Pobjoy 37/68 Cam?
Would anything need to be changed apart from the rocker?
Can anyone speculate as to whether this would help at all?
Cheers
Shaun
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Gracey
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| posted on April 11th, 2012 at 09:40 PM |
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I have used 1.25:1 rockers on a 37/68 cam. It works well however it puts more stress on the valve springs, so if your springs are getting old you need
to take this into consideration.
Oh yeah, I used em on intake and exhaust.
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sander288
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| posted on April 12th, 2012 at 08:02 AM |
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New springs so not worried there
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matberry
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| posted on April 12th, 2012 at 08:51 AM |
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| Quote: | Originally
posted by sander288
New springs so not worried there
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Well, be worried. See how things are in 1 or 2 thousand k's'
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE
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sander288
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| posted on April 12th, 2012 at 10:37 AM |
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Mmmmmm
Probably not worth it; given the stocks clips still in use and stock valve springs...
Might look at doing it in 12 months after the motor is settled and I've had a chance to really open it up on the track
Cheers
Shaun
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matberry
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| posted on April 12th, 2012 at 10:16 PM |
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| Quote: | Originally
posted by sander288
Mmmmmm
Probably not worth it; given the stocks clips still in use and stock valve springs...
Might look at doing it in 12 months after the motor is settled and I've had a chance to really open it up on the track
Cheers
Shaun
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Good move. Get rid of the stock clips, and shim up with a bolt together shaft kit and preferebly swivel feet adjusters at the same time. If your doing
up the heads now, the adjusters should go in now while the valve tips are all fresh.
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE
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Craig Torrens
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| posted on April 12th, 2012 at 10:20 PM |
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Just leave it as is Shaun....and just start collecting parts to build a 'real' race 1300 
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HappyDaze
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| posted on April 13th, 2012 at 07:05 AM |
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^Probably the best move^
I'd rather wear a Beetle out by racing it than by polishing it!
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