A couple of months ago i perchased a 72 f 250. The previous owner had swaped the old 6 cyl out for a 460 and c6 but the camshaft went out and i supposed he no longer wanted to bother with it so he sold it to me. I replaced the cam with a performance cam. i am not sure what the lift is on it but i do know it is more than the stock one at around .5". after some truobles with the tranny caused on my part i have got the truck running. i go to time the truck by ear just to get it going at first but when i timed it to 10btdc the idle speed decreased. it does not backfire but im curious as to why 10btdc does not produce the best engine idle. could it be that turnig the distributor advances the timnig causing the engine rpm to increase? i did pop the valve cover off and set the balancer to tdc and both valves on the #1 piston were closed so i believe i did the cam instalation right. i read another article in which another guy with a 460 said it did not turn over well while starting and someone suggested the timing could be off. my 460 also seems to be sluggish in starting but i figured this to be the fault of my battery which i dont think is very good anymore. i'm wondering if anyone could tell if i have a problem in my camshaft alignment or if a motor will naturally increase idle speed if the distributor is moved passed 10btdc. Any suggestions on this would be greatly apreciated.

 

was the vacuum advance hooked up when you timed it? it shouldnt be.

 

How much Cam? Too big a cam will screw everthing up for stock settings.

 

no, the line was disconneted and plugged when i timed it, thanks.

 

I am not sure how much lift it was. i mesured it with a caliper just because i wanted to see if it was bigger than the stock cam but did not get the size of the lobe but i think it is somwere just under .5". how much cam would be too much?

 

its the duration and lobe separation that will screw with idle... the tighter the lobe separation and longer the duration the worse the idle. it could have an advance or retard ground into the cam too, so id check the specs on the cam and maybe get a degree kit.

 

Half an inch is ALOT of of lift for a cam. Like darrin1999 said lobe separation and duration have alot to do with idle. A " fat " cam will produce a very lumpy idle. Depending on duration you will have to adjust timing accordingly. Also did you install the cam cam straight up or advance or retard it. Just for example I have a 73 Ranchero with a 351C. I installed a comp cam with .480" of lift and it puts out just over 400 hp. I would not trust your micrometer to much on a cam.

 

Post Script.

I installed my cam with 4 degrees of advance and my initial timing is set at 5 deg' btdc. Where as the book calls for 8 deg' stock. I have a 9.5 to 1 compression ratio And yes my idle is lumpy but the truck is very fast and will blow corvettes away off the line. Even though a 351C is more of a top end engine.

 

stock cam for a 460 is .487 lift, and i think 198 duration,108 intake lobe centerline, and i think 110 lobe separation. the only one im sure of though is the lift. the cams for the fuelie 460s have more lobe separation- either 112 or 114 i cant remember

 

you must have some steep gears and a high stall converter to go with the big cam.

 

I installed the cam stright up. All i know about the cam is that it is a step up from the stock. when i bought the cam the guy at the speed shop just said it was a performance cam and didnt give any warnings about running it with a stock setup. my biggest question would be is the truck idling rough because of the cam or bad timing. i knew the idle would be rough but wasnt sure. so the cam gives the truck an unsteady idle? and, is this much cam to much for a stock motor or can i get by with it.

 

P.S. i have also heard to time it to 10 btdc. does anybody notice it runs better at 8 btdc.

 

it sounds like your cam may have advance ground into it and/or has too much duration and/or you have other engine issues... you need to get the cam card for the cam or at least the brand and part number so we can look up the specs and tell you wether it should have a rough idle or not. 10 degrees is just a safe starting point. 10 degrees initial and play with it from there. make sure the advance is disabled when you set base initial timing.

 

I have 4:10 butt gears with 2200 stall. My cam has a pretty long duratin ( can't find my cam card ) For a non- roller cam.