Effects of valve lift - worth it going higher?

[harkes]

Hi

Is there any rule of thumb for performance gains from increased valve lift? I am now making 189hp@8400 with 8,5mm lift. Its rather expensive to go "shim under bucket" for lets say 10,5mm lift if it does not really give a bigger bang.

- Niels

[harkes]

Got a fast answer from Ken at Catcams. He estimates 5% = 198,5hp....gotta reach the "magical" 200

Worth it...not really
Want to do it...of course!

[totta Crolla]

"The effect of this constriction shows up as a pressure drop through the intake valve. So why don't we just open the intake valve further? Because when the valve is lifted a distance equal to 1/4 its diameter, the area of a cylinder around the valve (that the fuel/air charge passes through, not the engine cylinder) is equal to the area of the valve face and intake port (ignoring the valve stem). See Figure 1. Mathematically, the area of the cylinder is (2 (PI) r)(d/4). Since d = 2r, this evaluates to (PI)r2, which is the area of the intake port. Experimentally, the amount of additional flow through the intake port increases very slowly as the lift of the valve increases beyond 1/4 of the valve diameter"

Stolen from here:

http://www.eaa1000.av.org/technicl/engemp/engemp2.htm

I'm guessing that the Cat cams man is assuming you will fit larger valves to suit the higher lift.

[jondee86]

You can see some good info on valve lift vs flow here...

http://club4ag.com/forums/viewtopic.php?...734#p64307

Cheers... jondee86

[oldeskewltoy]

I just finished a head using 10mm lift with stock buckets and shims.... The cams are from Ted's they are their KK108E cams. I sent an email to them explaining that from what I always understood 9mm+ required something other then stock bucket/shim. They assured me that there KK108E cams work perfectly fine on stock buckets and shims... take that for what its worth....

[totta Crolla]

Catcams say the same thing for their 9.5mm lift cams.
I guess you need to relieve some of the head casting for 10mm lift ?

[harkes]

@totta Crolla
Exactly as you say. Catcams has no problem selling even 290/11mm with shim [u:56702c9b37]over[/u:56702c9b37] bucket. I actually just bought this (7105141) kit with uprated springs second hand but I think the profile might be too agressive. Having my current cams measured as I dont want a new cam with higher peak torgue than my current. Will be interesting to see how much the higher lift will give.

[totta Crolla]

harkes Wrote:@totta Crolla
Exactly as you say. Catcams has no problem selling even 290/11mm with shim over bucket. I actually just bought this (7105141) kit with uprated springs second hand but I think the profile might be too agressive. Having my current cams measured as I dont want a new cam with higher peak torgue than my current. Will be interesting to see how much the higher lift will give.

If you are interested and your cams turn out to be too aggressive then I might be up for a swap with my Catcams 7105138's

[harkes]

@totta
Thanks for the offer but the cams have has never been installed so I can have then exchanged for a minor fee at Catcams. My engine currently makes max torque at 6100rpm which is a good match with my 9000rpm redline. It looks to me like the xxx138 is a bit too dosile to take advantage of my rpm range(?)

[totta Crolla]

harkes Wrote:@totta
Thanks for the offer but the cams have has never been installed so I can have then exchanged for a minor fee at Catcams. My engine currently makes max torque at 6100rpm which is a good match with my 9000rpm redline. It looks to me like the xxx138 is a bit too dosile to take advantage of my rpm range(?)

No problem, my current engine is set up for gravel rally where torque at a lower rpm is an advantage but I intend to race the car later in the year so I can now afford to go more aggressive with the cams and general power output.