Exhaust valve lift

[gregaba]

Back in the 70's we expermented with increased exhaust lift over intake valve lift on some of our race engines.
We were racing small block chev's at the time.
We would run about 20 thou. additional lift on the exhaust ie 620 verses 640.
Did not have access to a dyno at the time so had no way to confirm if this was an advantage or not.
It did seem like we had more power but were not sure.
Has anyone used increased lift on an FE engine and was there a measureable difference in power on the dyno?
Thanks
Greg

[blykins]

It really depends on the combination.  I know that’s a vague answer but every cylinder head may want something different. I use a lot of cams with more lift on the exhaust and I use a lot of cams with less lift on the exhaust.

[frnkeore]

Much of the exhaust lift, depends on the duration of the exhaust lobe. As a rule, the more duration, the higher the lift but, with all the lobes available, including lift rule lobes, you can come close to matching what you want and/or need.

FE's require more Ex duration but, the other part of it, is if you have the flow numbers, for the heads, raising the valve higher than what the max flow is, is a waist and a bit harder on the spring, as well as piston clearance, it may also require you upgrade a spring package, to accommodate just the Ex lift.

[gt350hr]

     When I ran SB Chevies in Comp eliminator ( C/ED) we ran LESS duration and lift on the exhaust because it was TOO good and over scavenged the intake port hurting power. My point is EACH and every head has it's own dynamic and what it "likes". Fords "usually " like less lift on the exhaust Brent has a really good grip on FE split durations.

[gregaba]

Thanks for the answers.
We were running outlaw late models on dirt.
The engine combo was a .125 over 400 ci with a 327 stroke crank,Brodex heads, Crower roller cam and ultra rev kit,Harland Sharp rockers,gear drive for the timing and a bunch of other stuff.
With the extra lift cam grind we were getting very competive and it didn't seem like we had quiet enough power to be a consistent winner before that.
Greg