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Author
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Topic: Valve spring seat pressure.
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Big Block Capri
Gearhead Posts: 125
From: Essex, Ontario, Canada
Registered: Nov 2000
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posted 03-08-2001 07:34 PM
   
What is the maximum recommended seat pressure for stock valve seats? We just had a couple of sets donated to our cause but I'm worried that they may be too heavy. We've been running our springs at 140 at insatlled height and it looks like the new ones may be closer to 190. I really don't want to destroy the heads...we've been through a lot together and having hardened seats installed isn't in the budget. Any help is good help guys.------------------
Paul Garant
"No replacement for displacement."
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Moneymaker
Administrator Posts: 19611
From: Lyons, IL, USA
Registered: May 99
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posted 03-08-2001 07:38 PM
350 lbs. works fine with stock FoMoCo seats.  ------------------
Alex Denysenko Co-Administrator and Moderator NHRA/IHRA/SRA member
Fleet of FoMoCo products
Moneymaker Bio
US Class Nationals link
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Big Block Capri
Gearhead Posts: 125
From: Essex, Ontario, Canada
Registered: Nov 2000
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posted 03-08-2001 07:43 PM
I just breathed one GIANT sigh of relief. Thanks Alex!------------------
Paul Garant
"No replacement for displacement."
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Big Block Capri
Gearhead Posts: 125
From: Essex, Ontario, Canada
Registered: Nov 2000
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posted 03-08-2001 09:41 PM
Does the same thing apply if the stock seats have been machined for larger valves?------------------
Paul Garant
"No replacement for displacement."
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n2oMike
Gearhead Posts: 1468
From: Spencer, WV
Registered: Jan 2001
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posted 03-08-2001 10:38 PM
Really, it's the aggressiveness of the cam that determines how hard the valves are slammed onto their seats. All the valve spring does is make sure the vale is doing what the cam says. You could put a 1000 pound spring on a stock cam, and it wouldn't be any harder on the seats than it would with the stock springs... but the cam and lifters would probably be screaming for their lives. It's not the valve spring that causes the valve seats grief, it's the cam (and it's profile) that requires those springs. Regardless of the seats, you're going to get a lot less life out of a valve job that has do live with a large by huge roller spinning a billion rpm, compared to a more moderate grind. If you want to run the big cam, be prepared to do the maintainence. ------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/motorcitymustang/cmml/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
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Moneymaker
Administrator Posts: 19611
From: Lyons, IL, USA
Registered: May 99
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posted 03-09-2001 02:05 PM
Yes Paul. Also, Mike is very correct in regards to maintainance. You must keep an eye on your valve job. A bad valve job will do more damage to your seats than 5000 lbs. or pressure or 1.999 lift cam will. ------------------
Alex Denysenko Co-Administrator and Moderator NHRA/IHRA/SRA member
Fleet of FoMoCo products
Moneymaker Bio
US Class Nationals link
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Ryan Wilke
Gearhead Posts: 1368
From: Stanton, Michigan 49707
Registered: Oct 2000
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posted 03-09-2001 03:19 PM
....and what is the 'best' way to keep an eye on your valve job? Would that be a simple compression test or leak-down test? Ryan
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steve'66
Gearhead Posts: 6150
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 03-09-2001 03:59 PM
Best way is to adjust your valves regularly. When and if you find the gaps closing up, it's probably a sunken valve.  SteveW [This message has been edited by steve'66 (edited 03-09-2001).]
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Moneymaker
Administrator Posts: 19611
From: Lyons, IL, USA
Registered: May 99
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posted 03-09-2001 07:17 PM
Keep a critical eye on the spring pressure and replace them when they loose 40 lbs. or more. As the spring looses pressure the valve has a tendancy to bounce around. On car testers are cheap. Also be fanatical on valve lash as Steve recomends. I set my valves every three runs. ------------------
Alex Denysenko Co-Administrator and Moderator NHRA/IHRA/SRA member
Fleet of FoMoCo products
Moneymaker Bio
US Class Nationals link
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kid vishus
Gearhead Posts: 4254
From: middle of NC
Registered: Oct 2000
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posted 03-09-2001 07:40 PM
wow, every three runs?!? I feel lazy now, I check mine every other week. And hardly ever have any change. But I only run 250# on the seat, and don't turn as much rpm as you do.
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n2oMike
Gearhead Posts: 1468
From: Spencer, WV
Registered: Jan 2001
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posted 03-09-2001 09:17 PM
Damn, I only set mine around twice each summer... but my seat pressure is around 130lbs, and around 300 open. It's just 236/248 @ 0.050" and around 0.560" gross lift on the intake and exhaust. It sees plenty of street miles, and gets zinged up to 7000 rpm fairly regularly.
What kind of rpm are you guys pushing? ------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/motorcitymustang/cmml/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
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kid vishus
Gearhead Posts: 4254
From: middle of NC
Registered: Oct 2000
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posted 03-10-2001 07:18 AM
Mine sees 7500 every week, 220-235 passes a year. But everything is as light as we could get without buying exotic stuff. I have titanium retainers and keepers, undercut valves, crower stainless rockers, and a Jomar stud girdle to tie it all together. And no street miles.
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Moneymaker
Administrator Posts: 19611
From: Lyons, IL, USA
Registered: May 99
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posted 03-10-2001 06:47 PM
Yes even with a shaft rocker system, scalloped titanium retainers and keepers, and 250#'s of ultra lightweight Manley Grand National springs, I still check and set my valve lash every three passes. I rarely ever must adjust more than two or three rockers, but I also check spring pressure and do a physical examination of the springs at the same time. The entire process doesn't take over an hour and gives me peace of mind. Remember that I also see over 9000 RPM on every run. ------------------
Alex Denysenko Co-Administrator and Moderator NHRA/IHRA/SRA member
Fleet of FoMoCo products
Moneymaker Bio
US Class Nationals link
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F551
Gearhead Posts: 171
From: Manitoba, Canada
Registered: Nov 2000
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posted 03-10-2001 07:33 PM
Paul - we have been running springs open @ 360 for about 10 years with no problems on stock seats (Crane / Crower).190 closed seems a lot - what cam are you going to? Roller? ------------------
Fred
68 Mustang 500CID/Powerglide - "No Tubs"
86 Mustang GT Cobra
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Moneymaker
Administrator Posts: 19611
From: Lyons, IL, USA
Registered: May 99
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posted 03-10-2001 07:51 PM
If I ever got below 200#'s on the seat I'd be in real trouble. I change them at 220#'s. Anyone need any good used high dollar pacaloy springs? ------------------
Alex Denysenko Co-Administrator and Moderator NHRA/IHRA/SRA member
Fleet of FoMoCo products
Moneymaker Bio
US Class Nationals link
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Big Block Capri
Gearhead Posts: 125
From: Essex, Ontario, Canada
Registered: Nov 2000
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posted 03-11-2001 07:31 PM
Fred,
We're running a Comp Cams solid grind that has .640 lift with our 1.73 rockers. I just dug up the cam card and, to my surprise, it shows 260 duration at .050 lift. I really hadn't paid a lot of attention to that until we started addressing the agressiveness of the cam lobes. We launch the car at only 2000 and shift at 5800-6000 and it pulls about 6300 through the traps. I'm going to install the donated springs and keep a close eye on the valve lash. It used to be a once a month ritual but we'll be paying MUCH more attention to the situation.------------------
Paul Garant
"No replacement for displacement."
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