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
matberry 路
Yep, no problem except you need to buy two sets of rockers馃槀.
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.
sander288 路
So in affect, this engine builder wants more exhasut to flow out, so has allowed for a bigger ratio?
Gracey 路
Going by what you've posted "1.4:1 (inlet) 1.25:1 (outlet)" I'd say it want's less.
matberry 路
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.
Newt 路
Matt,
Is it a problem if your exhaust over floweth?
Newt
beetleboyjeff 路
Yeah - you will get exhausted.. lol
Newt 路
I would have thought that that would have been better than being constipated?
Newt
matberry 路
Newt wrote:Matt,
Is it a problem if your exhaust over floweth?
Newt
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 !!!馃槀
sander288 路
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
Gracey 路
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.
sander288 路
New springs so not worried there
matberry 路
sander288 wrote:New springs so not worried there
Well, be worried. See how things are in 1 or 2 thousand k's'
sander288 路
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
matberry 路
sander288 wrote: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
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.
Craig Torrens 路
Just leave it as is Shaun....and just start collecting parts to build a 'real' race 1300 馃槈