Cam and valvetrain longevity....??? low duration high lift...
10-05-2016, 04:49 PM
#1263
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Join Date: Sep 2007
Location: Clarks Summit, Pa.
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10-05-2016, 05:18 PM
#1266
Gold Member
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We machined the bushings for a .903 lifter.
I was locked into using the 55 cam and decided the lofter upgrade was a good investment.
That said, I wonder if it would be worth it to make the mods in a fresh build. I know you have to start with an aftermarket block, but most probably already are anyhow.
10-05-2016, 05:30 PM
#1267
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I have and do use a 55mm/.904 combo on a regular basis. We are doing some 1075's with those mods right now. That is certainly the way to go if you are scratch building one. All of the ones that I mentioned above were already assembled, so it wasn't really an option to machine them for the larger cam and lifters. They would have to come all the way apart to do that.
Eddie
Eddie
10-05-2016, 05:39 PM
#1268
Gold Member
Gold Member
Hey Eddie.
So, the advantage of a 55mm is still worth it even in a relatively low RPM marine application?
Is the main advantage the better geometry with the larger base circle?
Also, what are you using for cam bearings on the 55mm stuff? Roller of Babbitt, is what I'm wondering, not so much manufacturer?
So, the advantage of a 55mm is still worth it even in a relatively low RPM marine application?
Is the main advantage the better geometry with the larger base circle?
Also, what are you using for cam bearings on the 55mm stuff? Roller of Babbitt, is what I'm wondering, not so much manufacturer?
10-05-2016, 05:52 PM
#1269
Platinum Member
Platinum Member
8620 is carborized to 60-62rc scale, .100" deep. Thats Mike Jones spec after he heat treats a camshaft.
From Harold Brookshire
There is a limit to how far you can regrind a cam, or even the initial grind.
Cams are made to a given lift, duration, and LSA, and then heat-treated, either carburizing (8620) or induction-hardening (other steels ending in -50 or higher). How long, and how deep, the heat-treat goes is very important. Many cams have only .080" or less of heat-treat.
Cams can generally be ground +/-3* in LSA, and +/- .025" in lobe lift. These are the more important numbers.
So this means you cannot regrind a .370" lobe lift, 106 LSA cam into a .450" lobe lift, 112 LSA cam. The grinding process with go through the heat-treat on both the nose, and on the sides. You can't grind a 106 LSA into a 108 LSA, then later try for 104, or 110. You'll go through the heat-treat.
If you keep the LSA the same, or just a 1* difference, keep the lobe lift close to the original, you'll be much happier. The actual shape of the lift curve has more importance than either of those two.......
I had also read, GM, had a spec of .180 deep when finished.
From Harold Brookshire
There is a limit to how far you can regrind a cam, or even the initial grind.
Cams are made to a given lift, duration, and LSA, and then heat-treated, either carburizing (8620) or induction-hardening (other steels ending in -50 or higher). How long, and how deep, the heat-treat goes is very important. Many cams have only .080" or less of heat-treat.
Cams can generally be ground +/-3* in LSA, and +/- .025" in lobe lift. These are the more important numbers.
So this means you cannot regrind a .370" lobe lift, 106 LSA cam into a .450" lobe lift, 112 LSA cam. The grinding process with go through the heat-treat on both the nose, and on the sides. You can't grind a 106 LSA into a 108 LSA, then later try for 104, or 110. You'll go through the heat-treat.
If you keep the LSA the same, or just a 1* difference, keep the lobe lift close to the original, you'll be much happier. The actual shape of the lift curve has more importance than either of those two.......
I had also read, GM, had a spec of .180 deep when finished.
Got motor back to my shop, pissed around testing all kinds of stuff, found with intake manifold off I had TONS of oil blowing around top of lifters when they were in right spot. Turns out this merlin 2 block I had had fairly short lifter bores and they had a massive radius at top that allowed lifter band to enter it allowing oil to blow out with no resistance (morels), this was back in like 2005 I think and they just wasn't alot of info on what worked and didn't work at time. Pulled cam out, sent it back to Cam motion and they reduced base circle either .050 or .100, re-installed cam in motor, had great oil pressure, ran that motor for a little over 100 hours before upgrading it another 170 hp or so, cam looked perfect when it came out, saving it to go back in that POS merlin block one day, so if cam was already cut from a core with a certain range THEN reduced even just .050 all the way around it either had to be cut thru the heat treat or re heat treated to last 100+ hours ran at 185/190 seat and 460 open with morels to still look like new??
10-05-2016, 05:54 PM
#1270
Registered
At this point Tim you need to ask yourself will you really be happy with a low 70mph boat that cost 3 times what you planned to get it there???? At the time your build made sense and if everything worked out you could have enjoyed the reliability for years and saved your money. But things have changed.
I would take some time to carefully consider upgrading boats, or adding forced induction.
I honestly believe you will not be satisfied unless you hit 80mph next.
Seriously
I would take some time to carefully consider upgrading boats, or adding forced induction.
I honestly believe you will not be satisfied unless you hit 80mph next.
Seriously
