Is this cam a horrible choice?

[mlowry1260]

I agree that changing valve springs is easy. If these heads are used, at least lap the valves. You should set them up by installed height at a minimum. I use a valve spring micrometer. The best way is at a shop where they check & balance the installed height & check spring pressure.

If you need to do this as cheaply as possible, borrow a spring compressor & a spring micrometer & set them up at the same installed height using shims. Lap the valves to make sure you have a good seal at the seats. Clean everything twice & make sure you get all the lapping compound off of the heads/seats/valves.

[Tony71502]

So, explain to an engine newby how you check installed spring height, lap valves, or install shims?

I know how to replace valve springs and that would be no problem. But I figured you had to replace more than just the spring, and something in there requires machine shop work.

[Killercanary]

To properly replace the valve springs you have to know their installed height so that you ensure that you have enough seat pressure. Installed height is the distance between the spring pocket on the head and the bottom of the valve retainer. Basically you put in a valve, spring cup, retainer, and lock and set it up so that the valve is in the closed position but there is no valve spring in place. You then measure from the top of the spring cup to the bottom of the retainer to determine your installed height. You then use a valve spring pressure checker to see how much lbs of pressure the spring exerts at that installed height. If its too much then you can use things such as +.050" locks, different retainers, etc to raise the installed height which will lower your installed spring pressure on the seat. If its not enough you can run spacers under the valve spring pocket to shorten the installed height to raise its seat pressure. You must be careful here though to ensure that you do not end up with coil-bind in the spring at max lift as that can be catastrophic. I'm not sure what the OEM spec is for seat pressure on stock heads, nor do I know what it is for the B cam, but I'm sure you can find that out somewhere. Most cams will tell you what minimum spring pressure is needed, this is determined by a number of factors such as ramp rates, duration, etc. I doubt you'd need anything over 120lbs on the seat for a B cam and stock heads, and that may even be a bit high.

Time, mileage, and heat all degrade spring pressure so when you hear of old tired valve springs all this means is that their pressures are reduced from when they are new. For instance if you put in your new springs and they have 120lbs on the seat when installed and you pull them out a few years down the road and re-check them they will be a good bit less than that. This is the major cause of valve float with high mileage stock heads. Add boost from a supercharger and it makes things even worse as you have pressure trying open the valve which also reduces springs pressure. With some simple mathematics you can get an idea of how much spring pressure you lose per lb of boost by figuring out the area of the valve and the amount of boost you are running to determine what pressure opposite of the valve spring is being exerted and subtract that from your installed seat pressure. the bigger the valve, the worse this is and the more spring pressure is needed to counteract it.


You can do all of this yourself, the only special tools needed are a valve spring compressor, a magnet to get the locks out, and tools to get the installed height measurements and valve spring installed height pressures. If you can determine your installed height with a mic you may be able to take your springs to a machine shop and have them check them for your installed height measurement as most people do not own a valve spring pressure checker.

[Tony71502]

Well I'm going to just have Broughers install the valve springs. The question is which ones to buy? Do I go with the trickflow stock head upgrade kit that lowry linked?

Or do I go with Ford racing A-50 springs and B-50 retainers which was recommended from a member on a different forum. I need to learn how to shop for valve train parts. :)