Thread: cam purchase

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Well I did it bought the cam today for my 305 224 230 duration 477 480 lift and 110 lobe sep ........well....? What do u fellas think too big too small ,put it in retarded or advanced ?

Before I awnser that can you give the degrees after bottom dead center when the intake valve closes?

What is the chamber volume of the heads in cc's ? is the motor basicly stock, rebult or modified in any way ? S

ahhh......you went with the XE268H Comp. Not optimum for that small of a motor but I will be great for what you are doing. If you plan on revving it any make sure you get the right valve springs. You might need a highter stall speed converter for it to idle in gear. Try it first though.

Put it in straight up or "0 degrees". Comp puts +4 in all there cams.

I forgot "3 on the tree". Never mind the converter stuff.

at .006 61 after abdc................heres the hole deal here...
gross lift intake exaust
.477 .480
duration .006 tappet lift 268 280
valve timing at .006 open close
intake 26btdc 61abdc
exaust 72bbdc 27 atdc
specs for intake 106.0 center line

duration at .050 intake exaust
224 230
lobe lift .3180 .3200

lobe seperation 110


the engine has been balanced bored 30 over and some minor head work edelbrock intake ,street master ,and rams horns, 600 cfm vac secondary , approx 9.5to1 ,3 on the tree and approx 3.73 rear gears ,heads have been milled just enuff to clean em up, good valve job ,and some bigger valves and springs and teflon seals,and a taller installed height on the exaust valves.The cam I removed looks alot bigger than this 1 I am installing .040 more lift and a hole lot more duration than the new cam ,the old cam looked like the big end of a egg and the new 1 has ramps that look more like tear drop.The old cam looks really extreme on the duration.the old cam was not a stock item.

The springs and their installed height have to be right for the new cam. If you dont use the right parts, dont expect the cam to work right, or your warranty wont be honored either if it doesnt work out.

well after putting the intake valve closing angel into the equation, the 305's 3.46 dynamic compression stroke is now 2.790 inches so to get your dynamic compression ratio crank this stroke into the compression equation to get your dynamic compression ratio.

Well now I am pretty much completely freaked out went and got the rhodes liftersand they say it knocks 10-15 degrees off all the stats soooo.....224/230 duratoin at .050 should drop to214/220..or possibly even 209/215 and the abdc @61 should drop to 51 to 46 degrees I also have a 3 key way timing roller chain should i move the key way to retarded or advanced to help with retarding the abdc of 61 degrees on the intake. I read a article that sayes moving the timing crank gear forward and backwards helps low or high depending on which position?This cam nonsence is turnin a fun first time build into a headache!!!! Help Southerner!!!lol

Yessss, cam profiles are a challenge aren't they ? Dont worry though, I have been mechanicing for 30 odd years and I am still learning new tricks. The latest one being the term dynamic compression ratio, This more accurately describes whats happening in the engine cylinder in the real world.

Now I have to do other things at the moment, but concentrate on the fact that you do not get compression untill the cylinder is sealed. Then I will get back on line with a number of different combustion chamber and cam profiles with a nifty formula, the results could be quite intriqueing. S

Yessss, cam profiles are a challenge aren't they ? Dont worry though, I have been mechanicing for 30 odd years and I am still learning new tricks. The latest one being the term dynamic compression ratio, This more accurately describes whats happening in the engine cylinder in the real world.

Now I have to do other things at the moment, but concentrate on the fact that you do not get compression untill the cylinder is sealed. Then I will get back on line with a number of different combustion chamber and cam profiles with a nifty formula, the results could be quite intriqueing. S

"should i move the key way to retarded or advanced"

My advise would be to install and degree the cam in according to the grinders instructions to establish your baseline. You can change it later if you feel you need more bottom end or more top end.

Thnx Tech ,I get to goin on this stuff and I start thinkin it all set in stone,I want to get it right....but changin the cam or even a advance and retard is not that big a deal after the motors done. and thnx for your time too Southerner!!!Ilook forward to hearing what u were talkin about in the last post........................also I can not be in that bad a boat ,this is only 1 cam size bigger than comp said to use in my application,I just figured with iron heads and rams horn exaust ,that was why they said the 262.This can and will be upgraded ,I just do not wanna pop and blow fire thru the carb untill I get headers or possible some heads.I could always put the 4 speed granny low back in also I guess its just silly to think I am gunna bolt this monster together and not have to do anything to it again,because now that I think of it even motors that run well get pulled apart ,thats just the nature of hot roddin I guess.

Tech's right...

All you are doing when you advance or retard the cam in theory is move the curve up or down 500rpm....

In a heavy car I would advance it....more so than anyone else would but....you have to be careful.... the more you advance the more you invite the death rattle ( detonation) and the 305 is already prone to rattle....

I would strongly suggest degree'n in the cam and run it straight up for starters....

Did you check with the cam company on the recommended springs and installed height? Also, dont advance or retard it without knowing what you are doing it for, and see what they say first. Advancing will increase your bottom end a little, but it will also decrease your piston/valve clearance. You cant just do things like this without knowing the consequences.

http://www.co.jyu.fi/~rax/lobe.htm