Re: free drop of Indy 440-1 ?
[Re: johnnyd]
#2325303
06/22/17 04:24 PM
06/22/17 04:24 PM
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Joined: Jan 2003
Posts: 14,506 So. Burlington, Vt.
fast68plymouth
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With off the shelf Ross pistons at zero deck and uncut Indy heads, you can run a pretty long duration cam.
Are you trying to run something particularly long or with a really tight lsa?
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: free drop of Indy 440-1 ?
[Re: johnnyd]
#2325324
06/22/17 04:54 PM
06/22/17 04:54 PM
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Posts: 131 Boston, MA
johnnyd
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yeah- so many thing affect the clearance it can be tough to predict. And like maxi says, it's not necessarily at TDC so a simple calculation can't work. I was thinking of Comp 23-770-9. The builder has used the 23-758-9 before in a similar engine and thinks the larger cam will cause P/V issues. I don't want to cut the pistons at this time. 23-770-9 http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=751&sb=2The basics- 323 duration with 108 lobe separation and intake centerline .690 lift
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Re: free drop of Indy 440-1 ?
[Re: johnnyd]
#2325328
06/22/17 04:59 PM
06/22/17 04:59 PM
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Joined: Jan 2003
Posts: 14,506 So. Burlington, Vt.
fast68plymouth
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Yeh, 289@.050....... That's iffy at best.
I'd say shoot for a little slower lobe, about 280@.050 max, 108lsa, then mill the heads some if there's room.
The 770 cam would have about .050 less p/v clearance than the 758 cam, with 1.5 rockers if both installed at the same c/l.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: free drop of Indy 440-1 ?
[Re: maxi426]
#2325348
06/22/17 06:03 PM
06/22/17 06:03 PM
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Joined: Jan 2003
Posts: 31,050 Oregon
AndyF
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Someone please correct me if I'm wrong, but I don't think that valves necessarily hit pistons at exactly TDC That is true but the cam info is published for TDC so that is what you work with. If you know valve drop and cam lobe lift at TDC then you can figure out how deep the valve pockets need to be. That is why Ross is asking for the valve drop of the head. A cam might have 0.200 lobe lift at TDC. With a 1.50 rocker arm you have 0.300 gross valve lift at TDC. Then you need to know your valve drop, head gasket thickness, desired valve to piston clearance and valve lash and you can figure out the depth the valve pocket needs to be.
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Re: free drop of Indy 440-1 ?
[Re: johnnyd]
#2325498
06/22/17 11:42 PM
06/22/17 11:42 PM
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Joined: Oct 2005
Posts: 8,882 Ontario, Canada
Stanton
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That is true but the cam info is published for TDC Where do you find that info? I don't think I've ever seen cam data that says what lift is at TDC.
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Re: free drop of Indy 440-1 ?
[Re: Stanton]
#2325541
06/23/17 01:08 AM
06/23/17 01:08 AM
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AndyF
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That is true but the cam info is published for TDC Where do you find that info? I don't think I've ever seen cam data that says what lift is at TDC. For Comp Cams you need to look at the lobe profile catalog on the website. Not the regular catalog, but the lobe profile one. It will have lobe lift at TDC for a couple of different centerlines. Every engine combo I build I measure the valve drop at TDC with the engine fully assembled. That way I know exactly how much clearance I have between the valve and the piston at TDC. Once you know that number you can calculate what your valve to piston clearance will be for any cam lobe. If you are good enough at your calculations you don't even need to measure the VP since it will be exactly what you calculated it out to be. I always double check but it is usually within a few thousands of what I calculated. Lobe lift at TDC is related to duration more than lift. Most people assume that high lift cams will have less VP clearance but really it is the big duration cams that you have to watch out for. That and rocker arm ratio! The longer rocker arm ratio will absolutely eat up VP clearance. Anyway, the information is all published so you just have to look for it and know what to do with it....
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