Valve spring recommendation needed
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More Turbo
Joined: Oct 2009
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From: West Plains, MO
Valve spring recommendation needed
I'm building a 390 for my '65 F-350 dually from a pile of parts acquired over the years. Basically, a low-compression truck engine that will never see over 4000 rpm. With the 4.88 rear end (and a brownie I added with an 0.85 OD) it turns about 2600 rpm at 60 mph. Stock 1.73 rocker gear, valvetrain, 2-barrel intake/carb, etc. (Budget build). 
I have available a mild new-in-box Crane 260-2H (260/272 seat, 204/216@.050, .501/.533 lift hydraulic) and lifters that I'd like to use. Looking for a valve spring recommendation that doesn't require spring seat or other head machining. Most of the commonly available "FE springs" won't handle the .533 exhaust lift. Thoughts?
I have available a mild new-in-box Crane 260-2H (260/272 seat, 204/216@.050, .501/.533 lift hydraulic) and lifters that I'd like to use. Looking for a valve spring recommendation that doesn't require spring seat or other head machining. Most of the commonly available "FE springs" won't handle the .533 exhaust lift. Thoughts?
Cargo Master
Joined: Oct 2020
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According to their specs that Comp Cams spring has a rate of 415lbs/inch and installs with 109lbs @ 1.800. With .533 lift that gives you an open load of 330lbs. This is too much and your cam will go flat. You need something that'll give you about 80lbs on the seat and around 230-250lbs open loads.
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Joined: Oct 2009
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From: West Plains, MO
Thanks! I was planning to use a taller installed height with +.050 locks. At 1.850 that's 88# on the seat, and 312# open. Probably not enough seat pressure, but plenty of over-the-nose.
I looked at this table: https://help.summitracing.com/app/an...ail/a_id/4784/
Also: https://www.enginebuildermag.com/201...ring-pressure/
And from this article: https://www.dragzine.com/tech-storie...ring-pressure/
(In particular: A normal flat tappet cam core is limited to about 145-155 pounds seat and 400-pounds open pressure. The simple reason is the material; cast iron cannot stand more pressure and will go flat. It cannot handle the same pressures as a roller cam, which is made out of steel.)
Although this article is intended for drag racers, I certainly wouldn't try to run 400 lbs.!
There appears to be considerable debate on this subject (as usual)... check out some of these widely differing recommendations: https://www.fordfe.com/valve-spring-...e-t166497.html
I think somewhere around 110-120 on the seat, but less than 300 at max lift, would work. If I can find a single spring of the proper diameter, that is...
Do you know of one?
I looked at this table: https://help.summitracing.com/app/an...ail/a_id/4784/
Also: https://www.enginebuildermag.com/201...ring-pressure/
And from this article: https://www.dragzine.com/tech-storie...ring-pressure/
(In particular: A normal flat tappet cam core is limited to about 145-155 pounds seat and 400-pounds open pressure. The simple reason is the material; cast iron cannot stand more pressure and will go flat. It cannot handle the same pressures as a roller cam, which is made out of steel.)
Although this article is intended for drag racers, I certainly wouldn't try to run 400 lbs.!
There appears to be considerable debate on this subject (as usual)... check out some of these widely differing recommendations: https://www.fordfe.com/valve-spring-...e-t166497.html
I think somewhere around 110-120 on the seat, but less than 300 at max lift, would work. If I can find a single spring of the proper diameter, that is...
Do you know of one?
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More Turbo
Joined: Oct 2009
Posts: 596
Likes: 58
From: West Plains, MO
The Comp 924 might be a better choice, but I'm not sure if the spring seats will need machining (dual spring)... the FE Forum post I linked suggests that it doesn't. Guess I will wait until I have time and room to disassemble the heads and do some measuring!
https://www.summitracing.com/parts/cca-924-16
https://www.summitracing.com/parts/cca-924-16
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