What valve springs should i choose?

[Bruce Robles]

Comp probably knows better than anyone, call them. Why reinvent the wheel?? I agree with the rest, call a reputable engine builder who does this everyday and use their expertise. I know you want to do it yourself and you think you'll save money if you do, you won't. What's so important about 8000 rpm??? Are you racing or just having fun?? If you are racing, you need help. If your doing this for fun, get some good advice, get it built, and start driving the thing. You don't seen to be very knowledgable in the basics, i.e.
"will a 351 cam fit in a 302?". There ton's of interchangeable parts that fit both, and there are as many that don't, but look like they will work.
You will wish you never started this project and you'll get disheartend. You won't enjoy it if there are problems.
Have concidered a crate motor from Ford or another source? A good reliable crate engine will add value to your car when you want to sell it.

Good Luck.

[blykins]

Comp doesn't know, that's the problem. When you call their tech line, you may very well be speaking to a kid that has never assembled an engine, but can read a catalog.

It's best when questions like this arise to call/email an engine builder that does this everyday.

[Caprimaniac]

We are indeed going racing and we will indeed do all engineservice & rebuild in house.

Why don't we need some experts to do the work for us? For one, we're amateurs. Which means; we go racing when everything is working & in order. We're not going to every race, whatever the costs. There might be some person in this part of the world that could do the service needed, but this person I have not heard of or met yet. You see; there's a HUGE difference between US and the rest of the world regarding professional engine builders. Here in Norway, you don't come by them every day. And car racing is not very large; there were alot going on in the 70's, but calmer these days. But; it's getting busier. Besides; I am semi- pro, which means all experience is good experience. I admit the only downside is the lack of some basic machinery for skimming heads, cylinder boring, centerline measurements etc. fortunately, we have good friends helping out on such matters.


Let me come to the point here! Long since I posted and something has come up that I'd like to ask the experts.

While dismantling the Vic Jr. heads I discovered that under the valve spring discs, there are shims of different thickness for the exhaust VS inlet valve.

The springs and hardware for ex and in are identical and as I understand effective installed gheight should be identical. Have they taken into account temperature differences between and hence the effective length of the two? In other words; should you consider factor of valves stretching or being shortened while checking installed height on (aluminium) heads?

(I would assume that the aluminium is swelling more than the steel valve, and more at the ex than on the in valve?)

The other approach is: Inlet valve needs a little more preload, hence the thicker shim, shorter installed valve and higher closed spring rating, to account for the heavier valve. (2.02 VS 1.6")

would be interesting to know, as assembly of new valvesprings start very soon.

[blykins]

Unfortunately, install height is not always the exact same between intake and exhaust valves. One valve may be shorter than the other....one valve may receive a different angle valve job than the other, etc. You should always check between the two.

You are correct in that the exhaust valve is lighter and thus doesn't need as much spring pressure. However, that side is not one to be experimenting with, as if your exhaust valve floats, there's a very good chance that it will contact the piston as it's coming up and the end of the exhaust stroke.

If I were in your situation, I would measure each install height, calculate what you want your open/seat pressures to be, lay your shims out for each valve, then assemble.

[Caprimaniac]

Originally Posted by blykins

Unfortunately, install height is not always the exact same between intake and exhaust valves. One valve may be shorter than the other....one valve may receive a different angle valve job than the other, etc. You should always check between the two.

You are correct in that the exhaust valve is lighter and thus doesn't need as much spring pressure. However, that side is not one to be experimenting with, as if your exhaust valve floats, there's a very good chance that it will contact the piston as it's coming up and the end of the exhaust stroke.

If I were in your situation, I would measure each install height, calculate what you want your open/seat pressures to be, lay your shims out for each valve, then assemble.

Yes, Brent. I totally agree with you; it will have to be checked for every valve / spring installed.

The dismantled heads were put together at Edelbrock. All the exhausts had same shim, which were different from the ones, also all identical, at the inlet. I thought therefore it was one reason for this. anything of what I mentioned or, as you say, a difference in length or valve seat depth.

I checked the Summitcatalogue just now, and they don't list any different lengths on the two... Oh, I will have to measure to know, anyway...

And I will not experiment with less spring preassure on the exhaust side, promise!

Thanks again