Hey all,

My head is back from the shop and they successfully put in the 1.70/1.44 valves, 7/16" exhaust seats, and took a bit off (.060 total). I also had them do 2 comparisons on the springs I had to see what kinds of pressures I had at .465 lift, which is what my Erson 280 cam has.

At .500 lift, here were the spring pressures at the seat:
stock springs: 125 lbs/in
340 Erson springs: 300 lbs/in

The head shop said that 300 is definitely a bit high for what I want, so I was wondering if a set of 318 springs would be good, or if I should just go with stock springs?

My build is going to be a 9.5:1 long rod motor, probably in the 240 cu/in range on a 90% street/10% track car.

Thanks in advance for your recommendations. I don't want to prematurely wear the cam with really high spring pressures. Thanks in advance!

MJ

Replacement 318 valve springs are the same as slant 6 springs so no gains there. Comp Cams #970 valve spring is 80 lbs at 1.700" and just over 200 lbs with .485" lift. Comp #903 has the same 80 lbs at 1.700" installed height and seat pressure, but would bump the open pressure to 222 lbs. 101/272lbs are the closed and .485" lift loads for the Comp 901 spring which is most like the original 340 springs and does not seem excessive to me.

Did the machine shop measure the installed height and measure the spring load at that height? The actual installed load may be a little less than the numbers indicate.

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Joshua

Why not call Tom, at Erson, and get the correct springs for that cam?

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I asked Don Brewer at FBO that question (he was invaluable in setting up my /6 specs). He replied that it's not changing the oil that wears down the cam, and not spring pressure. I don't know, but it sounds like it makes sense. I used Mopar performance P4120249 springs, and they seem pretty crisp.

That load sounds too high for 340 springs. Maybe height installed is too low? Stock 340 springs should be perfect for that cam and they are cheap. Keep in mind that the load at 0.465" is actually 0.445" with lash, and they are probably measuring 0.500" actual (would be 0.520" cam with lash). Your loads will be lower. I would probably just use the Erson springs you have and be done with it. No worries about cam wear, IMHO.

Your stockers are a bit light.

Lou

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Home of Slant6-powered fun machines since 1988

Personally.... I tend to use lighter spring loads and never had any valve float issues, even on low block SL6 engines that rev to 7000+ RPMs

Thanks all for your replies.

Charlie, these were the springs that Tom recommended, but I was worried he was a little too aggressive for what I was planning.

Thanks Lou, I think you're right I wasn't thinking about the actual height, and I'll check the install height with Doug.

MJ

It looks like you might be right in there after you check those springs at the actual opening. Besides they are often not what the sheet says exactly, they should be checked.

I don't like higher than needed pressures either, unless it is an engine that I want to rev well past peak power. And then the cam and guides do suffer and even the pushrods and rockers might need an upgrade. Some stock diameter chrome moly pushrods might not be a bad idea for your engine. Nothing too fancy, just some insurance when you wind it up. Getting the geometry correct is a very worthwhile detail, and you can do that at the same time.

You do need enough pressure with the valve closed. I think what you have is pretty basic for a good street performance engine. We are throwing around lighter valves and rockers than most V-8s, but are still pretty close to the same as far as valve train. At least 100 lbs on the seat and not over 120, about 265 - 275 open should be plenty. Too low on the seat can make it weak at the top end and help burn exhaust valves if they bounce too much on closing. I would not set them up at 80 lbs on the seat to try to lower the open pressure if the springs are too stiff. That is stock cam territory.