valve lift

[:madaz:]

I am in the process of getting custom cams made up for an engine, and was thinking this; how much valve lift can be obtained past standard figures? I am using aftermarket springs and retainers, but am staying with hydraulic lifters. Say for example that an engine has .35" lift, is it possible to get a cam that has say .42" lift? In reality, the greater cylindrical area created between the valve and seat by that extra .07" of lift will be substantial, therefor allowing for greater flow at all rpm to allow for more torque throughout the rev range, which is what this engine needs for its application. Is it viable to increase the lift without major head modification in the way of valve seats/valves etc?

[RedMist]

I wouldnt bother speculating in regards to lift.

This will however depend on ... the type of engine you are running? The duration of the cams, your intended application, the type of cam you are developing (ie billets, reduced base circle, welded), headwork to some extent, intake and exhaust modifications, the rate of the aftermarket springs you are running... etc.

Its really best to discuss this with your cam grinder.

Hydrolic lifters?

[:madaz:]

sorry i forgot to mention its a mazda engine, but i ask on these forums because i believe they are far superior in the amount of knowledge than others.

the head has extensive port work and oversized valves and uprated springs. I have spoken to the head specialist about this but i also like to get an opinion from a public point of view, as you never know what may questions may arise!!

mazda engines have hydraulic lifters as standard, and the person who did my headwork argued that they will be fine in the application, although i was originally of the understanding that they wern't suited to bigger duration cam/higher engine rpm.

[RedMist]

Generally hydrolic lifters arent good for high RPM engines. I'm not familiar with the Mazda lifters so its hard to speculate as to what will happen.
As your head has been ported I gather you have a flow chart for it. As such you know how much lift you should be pulling before flow drops off.

As it appears you are generating a race engine I would go as much lift as as flow and valve to piston clearances allow. Duration, however will have more of an effect on how much air you get into this engine. I run 304 degree ramp to ramp in my race car with 10mm lift(at the valve). Its not something I would like to run on the road as its expensive to run and a pain in the arse until 5k RPM where power comes on in a big rush.

If you are looking at road perhaps a milder cam around the 275 degree mark with less lift would be suitable.

Best bet to either ask multiple cam grinders or someone who has worked your particular engine before.

[Grrrrrrr!]

In addition to what Redmist had to say dont forget to supply your cam guy with the full details of the new springs you are running.. if you go high enough in lift you may run into coil bind problems, springs loosing tension and all sorts of fun problems. Its really something that should have been sorted out before the head was ported so whoever did the porting knew what limits they were working within.

[:madaz:]

cheers for the info guys, yes i will be talking to the head and cam guys further discussing it but its good to get your opinions!! its quite interesting how i have to work the information out of the dude im dealing with, he dusnt explain much. But not to worry he does have a good reputation at the end of the day!