I've experienced valve float at about 5000 RPMs. I'm running an XE269HR cam and with .533 lift with 1.6RR its almost hitting the .540 Max from the 1.47 TF Heads springs. At least I think its valve springs. The exhaust note changes and it seems like I'm freewheelin. Also my MAF readings drop as soon as this happened. What springs do you reccomend next? Thanks.

 

I'd say get some stiffer valve springs! What springs does Comp recommend for that cam ? I would buy those springs!

 

Duh i should have thought of that... Thanks I'll look into it

 

There are several factors that contribute to valve float:

1. RPM;
2. Valve spring seat pressure;
3. Valve spring rate;
4. Mass of valve train components;
5. Acceleration rate of the cam lobe/ramp.

Presuming that you don't necessarily want to reduce the engine RPM, you are left with a combination of altering the valve springs, camshaft, and/or valve train mass.

Valves themselves are probably the heaviest components in the valve train, along with lifters. Since lifter mass is difficult to alter, most people look elsewhere. The typical 1.94" intake valve goes in the 110g range. Aftermarket stainless valves can shave 10-20 grams from that, and hollow shaft/sodium filled valves can cut nearly another 5-8 grams.

The valve spring retainers are also a place to reduce mass. Stock steel retainers are usually around 21½ grams. Stock exhaust valve rotators are more like 37g - 15+ grams of useless dead weight that only works against your valve train. Add that goofy little stamped steel oil shield over the top of the spring and the 'O' ring that sticks to the valve, and you have another 10.2g of useless mass that the springs have to control. Eliminating the old seals and installing positive seals allows you to dump 10g. Eliminating the exhaust valve rotators sheds 16g from half of the valve train. Lightweight steel retainers usually go about 16-17g, and titanium retainers are less than 13g.

Push rods are often overlooked, but where the stock steel plain-end push rods weigh in at around 48g, CrMo steel push rods are actually stronger while saving over 10g - they measure 37g.

Add together all the wasted material that the cam has to move and the valve springs have to control, and by selecting lightweight components, you can shave almost 35g from each valve train - or about the mass of a good push rod.

If you want to split hairs, you can use sing valve springs instead of duals or dampered springs, since ½ of the mass of the spring is also moving on every valve actuation.

Rocker arms are another item that moves, and adds to the overall mass. And while aluminum may seem like the best choice on the surface, forged steel rockers with intelligent design are far stronger than aluminum and actually lighter in reciprocating mass than 99% of aluminum rockers. They'll lighten the load and better handle the heavier springs and loads of an aggressive cam profile.

Since you have a roller cam, you can safely increase the valve spring pressure and rate without inducing lobe damage. Just don't overlook the advantages of taking some of the fat out of your valve train.