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Old 02-26-2008, 06:46 AM
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Just a curiosity question on cams.

Whats the "generally accepted" amount of lift that you can go before valve spring bind becomes a problem? (Or is that to "engine specific" to really have a guideline on it?)

And, at what duration do you begin to get a bit of idle lope?

Thanks!

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Old 02-26-2008, 08:38 AM
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Curiosity

My son has a Comp Cam 260H Hyd in his 350 and I can just barely hear a cam.
Centerline is 110
Duration @50 is 212
lift is .440

Bob
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Old 02-26-2008, 09:32 AM
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the old school rule was to keep it below .550"... but that really has no meaning anymore. As far as lope goes that is a factor of overlap, duration, exhaust system, intake, compression, etc... so there's no hard and fast rule their either...
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Old 02-26-2008, 01:33 PM
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Some engines hot coil bind at .440" lift, others can easily take .700" or more. Its a product of valve stem length, head design, spring design, and retainer design.

Overlap is the biggest factor in lopey idle, and the biggest factor in overlap is cam duration and LSA. You could have a 200* cam that lopes with a tiny LSA, and you can have a 240* cam that doesn't lope with a wide LSA. It also has to do with displacement. Smaller engines make the cam seem "bigger," so the same cam specs that make a 350 have lope won't make a lopey idle in a 454. Idle ignition advance plays a huge part as well. More initial timing will smooth out some lumpiness.

I'll be putting a 222/230 cam on 112 LSA in a 383 and I expect modest lope. Its an LT1, so the EFI can be tuned for each; I could keep the idle at 950 and put lots of idle timing in and smooth it out, or I could drop it to 850 and pull out some idle timing and make it really lopey.

I got a teeny lope from a 218/224 cam on 110 LSA in a Big block, (notice less duration, but narrower LSA, so similar overlaps) but I had lots of initial timing. I could have lumped it up by reducing initial timing but I didn't want to.
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Old 02-27-2008, 05:29 AM
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Quote:
Originally Posted by curtis73
Some engines hot coil bind at .440" lift, others can easily take .700" or more. Its a product of valve stem length, head design, spring design, and retainer design.

Overlap is the biggest factor in lopey idle, and the biggest factor in overlap is cam duration and LSA. You could have a 200* cam that lopes with a tiny LSA, and you can have a 240* cam that doesn't lope with a wide LSA. It also has to do with displacement. Smaller engines make the cam seem "bigger," so the same cam specs that make a 350 have lope won't make a lopey idle in a 454. Idle ignition advance plays a huge part as well. More initial timing will smooth out some lumpiness.

I'll be putting a 222/230 cam on 112 LSA in a 383 and I expect modest lope. Its an LT1, so the EFI can be tuned for each; I could keep the idle at 950 and put lots of idle timing in and smooth it out, or I could drop it to 850 and pull out some idle timing and make it really lopey.

I got a teeny lope from a 218/224 cam on 110 LSA in a Big block, (notice less duration, but narrower LSA, so similar overlaps) but I had lots of initial timing. I could have lumped it up by reducing initial timing but I didn't want to.

Thanks Curtis! But I'll show my ignorance here;;; What is LSA ?
Thanks again, and I appreciate the other responses.
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Old 02-27-2008, 07:05 AM
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Lobe seperation angle.
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Old 02-27-2008, 07:25 AM
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Farmer,
If you give us information on what engine (make, model, year) you want to add a cam to and what you are expecting from it, then maybe we can help.
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Old 02-27-2008, 12:29 PM
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Thanks 454; I've already done that and so many folks on here just helped me a tremendous amount. (at the time I was here under another name, Lloyd wv I think, and my computer crashed. I couldn't recover the name and PW so I re-registered under the present name)

The build I was doing was a 302 ford, building for HP and then planning to step up my rear gearing as a way of seeing how high I could get the mpg figures. I used a crane cam 210 duration, .469 lift. ---- I need to change carb jets yet, and then get a good reading on my mpg. Once I do that I'll report back to all of you guys on just what specifics I built into the engine and the resulting mpg figures.

Have a good day!
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Old 02-27-2008, 12:39 PM
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that sounds like a cam that might lope a little bit on a 302 and deliver decent mpg on the highway and maybe slightly less around town compared to stock. However, it should make noticeable more power than a stock cam. should pull to at least 5500 rpms in a 302. This is assuming about a 110 lsa.
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