If I have 1.8 ratio rockers and want to stay just under .650 max lift. What size cam can I get?

Ok I'm no cam Wizard but if you take your max lift and divide it by you rocker ratio it should tell you the lobe lift you need.

So .650 * 1.8 = .361 Lobe lift

If I'm wrong somebody speak up .



Dan

Edit fixed decimal point.

Dan,

Your decimal is in the wrong spot. It should read .361.

Alan

Dan's right to an extent....... excluding the decimal point misplacement........ however

due to the geometry of the rocker arm, you won't get the calculated actual lift with that. I'm assuming you are trying to follow cttpa rules, so if you want to get as close to 650 as you can then do this.

get a dial indicator, mount it solidly on your head, take all the lash out of your current cam and measure the total lift by placing the indicator on the rocker arm directly above the valve in the same plane as the valve movement. get a total lift and compare it to your advertised lift of your current cam. set up a ratio and determine how far over 650 advertised you can go and still maintain 650 actual.

now i run 1.73 and you are running 1.8..... the bigger the ratio, the more you lose from advertised to actual lift. when i ran my 728 cam, my actual without any lash was .667, and now i run a 672 and my actual is about 638. again, with the 1.8 rockers, you can expect to lose a bit more.

that will give you a starting point and then you can call your cam guy and know what your max advertised lift can be, and go from there.

sean

So maybe a cam close the size of your old cam would work in mine since I run the 1.8's. Yes?

My math from Sean's and Dan's post...

Sean was losing .04 to .06 from advertised lift to actual. If you are going to lose more with your 1.8 rocker, add .06 to .07 to your actual lift... .650 = .710 to .720... devided by rocker ratio...
should give you an advertised cam lift of .394 and .400

that's with estimating that your loss would be close to Sean... the only way to know for sure is by measuring.

no doug, i think you misunderstood

with a 1.8 rocker, you'll lose more from advertised lift to actual lift with a cam that is advertised using a 1.8 rocker compared to a 1.73 rocker.... my advertised cam lift is for a 1.73 ratio......

basically doug..... if you go with a max lift of .772 or less advertised, you'll most likely be fine with actual lift..... but again.... you need to keep that in mind when you call the cam guy and have a cam made for your application.

sean


ps.... what olchev is saying is absolutely correct with the exception that his increase to .06 - .07 is probably stretching a bit........ I wouldn't play it that close for two reasons

1. the actual lift isn't as accurate as you think
2. when your talking .001 too much is illegal ..... i'd put in a better fudge factor then that.