Old fashioned Rev Kits

Auxiliary "valve" springs in the lifter valley, really they are lifter springs.

If you use these, do you use less spring on the valve ?

They seem like such a sensible idea. But engine builders always tell me they are unnecessary, so I've never tried them.

I always thought they would be a good idea to keep the roller wheel in constant contact with the lobe. But I could be way off base

Gus

If you pitch a pushrod the lifter stays in its bore

Not really. The valve spring controls the valve, and the rev kit keeps the lifter in contact with the lobe. Rev kits used to be standard on circle track engines but we see them less and less. We do have an engine going together now with a rev kit in it. They make sense to use but the correct lifters are hard to find. Isky used to make them for lots of different applications but a lot of those part numbers have been discontinued.

With the rev kit spring controlling the lifter, the valvespring no longer controls, or needs to control, the lifter, just the valve.

So why would you not use less valvespring ?

I have no personal experience with rev kits. But back in the day when Ford thought it was a better idea, I read an article on their philosophy. IIRC, the purpose of a rev kit is to increase the rpm limit of the engine, hence the name "rev" kit. Accomplishing this higher rpm limit with stiffer valve springs increased the stress on the entire valve train whereas the rev kit only increased the stresses on the cam/lifter. If you wanted to maintain your current rpm limit and installed a rev kit, I don't see why decreasing the valve spring would be a bad idea. But why?

My guess would be, no need to increase your RPM limit unless you also increased your cam to move the powerband up.

However, by keeping your same RPM limit, you could use less spring, which would tend to beat up parts less.

I had them on the old Max Wedge, Isky 550 Super LeGarrea,(?) in fact they helped real good, I could rotate the spring-retainer-valve with my fingers, lol, I had run them like that a few times (6800) before new ones. Amazingly no time difference with new ones. I added a bolt to center of holder since there’s no heat crossover in max heads (the springs made it bend up). It was all on there when I got engine.

I look to the 69 1/2 six pack engines as an example. Again, IIRC, the design rpm limit with the stock cam was about 5800 with the springs used. With the same cam timing events, the six pack engines have stiffer springs which raised the usable rpm limit to 6200.

Back in the M/P class days when 10000 to 12000 rpm was standard that was the only way to do it. Every M/P engine I ever saw had a rev-kit...

Given the work Ben Strader and others had to do to get the "Spinal Tap" LS to run at 11,000 rpm I wonder if the Modified Production engines from back in the day had any real valve control at those RPMs.