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Cam question
Posted: Mon Apr 15, 2019 1:09 am
by Krooser
Say you have a cam recommended for your application that has a lift of .500. And you have a cam with virtually the same duration, LSA and timing events but the lift is .565. What would be the advantages/disadvantages to the higher lift?
This question came up last night while bench racing with a couple friends...
Re: Cam question
Posted: Mon Apr 15, 2019 1:24 am
by PackardV8
With cam questions, the answer is always, "It depends."
What is the application? The valve diameter? The RPM range, and so it goes.
Re: Cam question
Posted: Mon Apr 15, 2019 2:09 am
by GARY C
Providing you have valve train stability and the head doesn't have a problem up there I would put my money on a power increase across the board and possibly extend the rpm range one to two hundred rpm.
Re: Cam question
Posted: Mon Apr 15, 2019 2:19 am
by superpursuit
The general answer is more power. This is providing your flow increases with the extra lift and your engine can use the extra flow. It's always easier to answer a question like this if you give an engine type that you are referring to. The downside is more work for the springs. On engines that meet the above conditions this is generally referred to as 'free power' as it usually does not have any other adverse effects to talk about.
Re: Cam question
Posted: Mon Apr 15, 2019 4:29 am
by digger
probably lose a tiny bit of bottom end if you test it at low enough rpm. even with the same seat durartion the "effective" duration is a slighty larger and more reversion is bound to take place at some rpm down low, just isnt as severe as with actual added seat duration
Re: Cam question
Posted: Mon Apr 15, 2019 10:49 am
by CamKing
In many cases, the added lift will make more top-end power, and carry it a little longer.
Here's some cases, where it won't.
If the port gets turbulent above .500" lift, the added lift can hurt the power everywhere.
If it's a hydraulic, the higher acceleration rate to get the added lift, can cause the lifter to collapse sooner, making the power fall off sooner.
If you're limited on spring pressure, the higher acceleration could cause valve float sooner.
If you're limited to flimsy pushrods, the added spring pressure required to control the added lift, could cause pushrod flex, and cause seat bounce, and hurt the power.
If you're limited to stock rockers, the added lift, and added spring pressure required for that added lift, could cause valvetrain issues, and cause valve float.
Re: Cam question
Posted: Mon Apr 15, 2019 10:55 am
by PackardV8
CamKing wrote: ↑Mon Apr 15, 2019 10:49 am
In many cases, the added lift will make more top-end power, and carry it a little longer.
Here's some cases, where it won't.
If the port gets turbulent above .500" lift, the added lift can hurt the power everywhere.
If it's a hydraulic, the higher acceleration rate to get the added lift, can cause the lifter to collapse sooner, making the power fall off sooner.
If you're limited on spring pressure, the higher acceleration could cause valve float sooner.
If you're limited to flimsy pushrods, the added spring pressure required to control the added lift, could cause pushrod flex, and cause seat bounce, and hurt the power.
If you're limited to stock rockers, the added lift, and added spring pressure required for that added lift, could cause valvetrain issues, and cause valve float.
Exactly, Mike. Those who've been around a while have seen instances where switching from 1.5 rockers to 1.6 or 1.65 rockers increased lift from .500" to .565" but the result was all those problems you listed.
Re: Cam question
Posted: Mon Apr 15, 2019 6:35 pm
by Krooser
We never thought of all the potential problems like turbulence, skinny pushrods and the like.
Hard to imagine a 12 pack would cloud our thought processes..
Thanks.
Re: Cam question
Posted: Tue Apr 16, 2019 11:27 am
by CamKing
Krooser wrote: ↑Mon Apr 15, 2019 6:35 pm
We never thought of all the potential problems like turbulence, skinny pushrods and the like.
Hard to imagine a 12 pack would cloud our thought processes..
Thanks.
Hell, you should hear about some of the fantastic innovations I've designed, until I wake up the next day, sober, and realize they would never work, impossible to produce, or were invented decades ago.
Re: Cam question
Posted: Tue Apr 16, 2019 12:07 pm
by ClassAct
CamKing wrote: ↑Tue Apr 16, 2019 11:27 am
Krooser wrote: ↑Mon Apr 15, 2019 6:35 pm
We never thought of all the potential problems like turbulence, skinny pushrods and the like.
Hard to imagine a 12 pack would cloud our thought processes..
Thanks.
Hell, you should hear about some of the fantastic innovations I've designed, until I wake up the next day, sober, and realize they would never work, impossible to produce, or were invented decades ago.
Yup. A few bottles of liquid brains and I'm a genius. That's why I gave that up 26 years ago. My genius was killing me!
Re: Cam question
Posted: Tue Apr 16, 2019 1:39 pm
by 77cruiser
ClassAct wrote: ↑Tue Apr 16, 2019 12:07 pm
CamKing wrote: ↑Tue Apr 16, 2019 11:27 am
Krooser wrote: ↑Mon Apr 15, 2019 6:35 pm
We never thought of all the potential problems like turbulence, skinny pushrods and the like.
Hard to imagine a 12 pack would cloud our thought processes..
Thanks.
Hell, you should hear about some of the fantastic innovations I've designed, until I wake up the next day, sober, and realize they would never work, impossible to produce, or were invented decades ago.
Yup. A few bottles of liquid brains and I'm a genius. That's why I gave that up 26 years ago. My genius was killing me!
I've had ideas come out of a bottle.
Re: Cam question
Posted: Tue Apr 16, 2019 10:22 pm
by DaleHays
In addition to all the great considerations from Mike, couple others to add:
1) If the higher lift causes an issue with valve to piston clearance (say you already have the engine together - and are pondering cams). Yes that can be fixed - just not fun to tear an engine down for it.
2) Dependent upon the engine, RPM range, port size etc --- the engine design may not actually be able to use the flow and/or the fuel. An extreme example would be my old Flathead Ford race engines - even in a totally ported and full race prepped block, just can't get any more flow above about .500 lift in almost any situation. So - what to do . . . we then think about opening the valve faster (opening ramp profiles) and also about adding duration.