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Author
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Topic: Installed Height
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 10-22-2001 06:21 AM
   
I don't know if this is a brain teaser as such (although it's teasing me a little), but here goes.I need to work out what installed height to put my springs in at. Cam is a solid 250/257 @0.050 with 0.622/0.647 lift. Springs are Isky 8005. The Isky sheet says 1.875. The cam card says 1.92 (doesnt say which spring). I know it's all about open and closed pressures. But what pressure do I need?? (and how do you work it out?) Paul
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 10-23-2001 05:49 AM
No takers??? Well on my own initiative I did some investigating and was told by 2 seperate sources I would need 130-140lbs on the seat. Went down to my machine shop with the springs and tested them. [email protected]. Thats what I need  I'd still like to know how the 140lbs figure is derived, and more importantly how much variation in height is allowed, ��.010?? Paul
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bluestreek
Gearhead Posts: 1724
From: Athens,GA
Registered: Jul 2001
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posted 10-27-2001 11:12 AM
140# installed pressure on all coils with no coil bind at full lift is what you're after..
Less insatlled height would mean more overall pressure and tighter coil tolerances at full lift, and more height would mean less spring pressure and more coil tolerance.. Shims can be used to DECREASE installed height and bosses can be machined in the heads to INCREASE installed height.. Installed height may have to be adjusted to get the pressure.. When installing a high lift cam, you should also check for coil bind at full lift, to make be sure that there is at least .020 clearance between the spring coils.. If there is any chance of coil bind, then head machineing is necessary to bring them to the desired height that you can work with. .100 piston to valve clearance is also mandatory on high lift cams, and should be checked with a shim that will equal the compressed thickness of the new head gasket..
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 10-28-2001 04:30 AM
Thanks Bluestreek.Paul
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Stewart
Gearhead Posts: 9743
From: Monterey, CA Mustangsandmore Member #437
Registered: Apr 2000
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posted 12-13-2001 03:38 AM
TTT
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SteveLaRiviere
Administrator Posts: 43151
From: Saco, Maine
Registered: May 99
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posted 12-13-2001 05:36 PM
Thanks, Stewart! ------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
'97 Probe GTS 2.5L DOHC Christmas shopping? Why not use the
M&M Bookstore?
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Stewart
Gearhead Posts: 9743
From: Monterey, CA Mustangsandmore Member #437
Registered: Apr 2000
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posted 12-14-2001 01:12 PM
You're welcome, Big Kahuna.haven't heard that one in a long time! Stewart
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Moneymaker
Administrator Posts: 25883
From: Lyons, IL, USA
Registered: May 99
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posted 12-14-2001 03:47 PM
The "old" standard of .100 PTV has been upgraded to about .050. New cam, lifter and spring technology allows quite a bit less without fear of contact. ------------------
Alex Denysenko
Co-Administrator and Moderator
NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00 & '01
Fleet of FoMoCo products
Moneymaker Bio
US Class Nationals link
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Rustang
Gearhead Posts: 733
From: Clarion PA
Registered: Nov 2000
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posted 12-19-2001 06:35 PM
BE CAREFUL! You should always check both the closed and open pressures recommended by the cam supplier, and they should be checked at the spring heights specified. You need to check both conditions because this will verify the spring has the proper spring rate. You can take a wimpy stock 75# windsor spring and shim it up to 140#, but the spring rate would still be that of a stock spring.
For example, if the stock windsor spring has a spring rate of 1000lb/in and is installed at 140# seat, at .500 lift you would have increased spring force by 1000lb/in * 0.5= 500lbs. With the 2000 lb/in spring, you'll have increased spring force by 2000lb/in * 0.5 = 1000lbs. So at .500 valve lift, you would have 500+140=640lbs for the stock spring, versus 1000+140=1140lbs for the correct spring! That's 44% more effective spring!!  ------------------
'68 mustang 351 clevor- 10.92@124
'67 Stang, 351W -11.18@118
'69 351C Torino-14.90@100
'78 Pickup 351W-15.56@88
'79 Pickup 460 ET=??
http://www.rustang-racing.cityslide.com/contents/contents.cfm/712231
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Just Strokin
Gearhead Posts: 754
From: Tuscaloosa, Alabama
Registered: Dec 2001
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posted 12-21-2001 01:18 PM
The cam card installed height/pressure is based on the springs they recommend. You have purchased different springs, so you go by the data sheet for the Isky springs. Install them at that height and then check for coil bind at full open @ .0000" lash. Make sure the inner sping doesn't bind also.
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 12-22-2001 10:24 PM
Thanks guys. Paul
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