cam questions

67chrrybucket

Well-known member
Im building my 200 im looking at cams i needed to know if you degree the cam +4 will that change the ivc? Im trying to figure out how far to mill my log head to keep my DCR in the right place. Also if i get a 108 lsa its going to be a 104 by the time its advanced? :unsure: thanks in advance
 
HOwdy:

Awww, now I see where you are coming from. Briefly, no. Advancing or retarding the cam profile will not have an effect on CR. The static as well as the dynamic CR are effected by cam duration- from when the intake closes to when the exhaust opens.

ON lobe centers, no. Again, advancing or retarding the cam timing will not alter the lobe angles. But know that lobe angles will effect cylinder pressures and vacuum. Tighter lobe angles offer less overlap, the time that both the exhaust and intake are open. This results in higher engine vacuum, a smoother idle and, in general more torque. Wider angles go the other way.

Advancing and/or retarding a cams timing will effect when peak torque and peak horsepower occur. in theory, Advancing cam timing will increase low end torque and peak HP will happen at a lower rpm. Retarding cam timing will reduce low end torque and increase the rpm of peak HP.

Please note this is a very brief cover and, again many factors must be considered for the final outcome.

Hope this helps.

Adios, David
 
Tighter lobe angles offer less overlap, the time that both the exhaust and intake are open. This results in higher engine vacuum, a smoother idle and, in general more.
David i believe you meant the opposite.
67chrrybucket no one can recommend a camshaft without knowing everything about your engine. Which includes transmission type & rear end ratio.
 
when advanceing or retarding cam timing Lobe seperation angle does not change but intake centerline does , changing the intake centerline on a cam does effect dynamic compression ratio a little by allowing the intake valve to close (for example advanced 4 degrees from 110 to 106 ) earlier on the compression stroke creating a little more cylinder pressure.retarding does the opposite, all of the street cams I have used have a 110 degree intake centerline regardless of the LSA, most companies including Clay Smith recommend degreeing the cam to 106 Intake centerline for a little more low end torque on the street. Also the tighter the LSA of a perticular grind the more over the more overlap there is. with the same cam profile the 108 LSA will idle rougher than a 110 and a 112 will be ever smoother. The 108 has more peak torque and a lower powerband but may be and issue when running an automatic with a stock coverter due to the Idle quality. regardless of which cam you choose go through the added time to degree it properly. some companies sell there cams with an advertised ICL but also grind the advance in the cam, comp specs show their HE series street cams with a 110 ICL but they grind 4 degrees of advance from the factory, clay smith grinds theirs strait up.also I have degreed a few that were off by a couple of degrees which is not uncommon. Check out this article for more info. http://www.classicinlines.com/SelectCam.asp
 
Oops!!!! Thanks for catching my mistake. Once again, I need to think before I write and reread and rethink before I send. Sorry for the misinformation.
 
The "plan" for the engine is a 68 200 with .030 over pistons forged (hopefully) dished +7 cc late model larger log head with 1.75/1.50 valves direct mount 2 barrel holley 350 (might have it e85 converted) dui distributor 1.6 ratio rockers and a 6-8psi supercharger. Im using a 3 spd toploader with a 3.50 9" rear i was thinking of using a 264/274 hyd cam with 108 lobe center if im missing something?
 
67chrrybucket":3aumi492 said:
The "plan" for the engine is a 68 200 with .030 over pistons forged (hopefully) dished +7 cc late model larger log head with 1.75/1.50 valves direct mount 2 barrel holley 350 (might have it e85 converted) dui distributor 1.6 ratio rockers and a 6-8psi supercharger. Im using a 3 spd toploader with a 3.50 9" rear i was thinking of using a 264/274 hyd cam with 108 lobe center if im missing something?
If you are supercharging the engine, you need a 114 L/C camshaft or close to that.
 
I see any reason why i want to run a114 LC ,i was planning on mostly driving on the street so i was looking at what would put it in a good rpm range and the 108 LC looks like the rpm the 200s run best
 
the wide lobe separations are usually used with forced induction because when during the overlap period you can blow you fuel air mix Though the engine right straight into the exh. This also makes it look like your blower or turbo is too small as well.
As far as advancing the cam, it probably wouldn't be needed unless you blower is set up to only make boost at higher rpms.
 
I know your post was camshaft choice, but since you are going to supercharge it you also need a black box to dial back the total ignition advance when under boost conditions.
Will-Does10's could help you in this area.
 
67chrrybucket":1g79buhj said:
So with the engine setup the same way n/a without forced induction a 108 L/C would be a good choice?
No, either build the engine for N/A or build it for a supercharged design.
For a street car i would not recommend a 108 L/C camshaft. Unless you want a very very rough idle.
I'm not trying to be sarcastic, but from your questions you need professional advice for each type of build.
 
67chrrybucket":2eygjgfs said:
So with the engine setup the same way n/a without forced induction a 108 L/C would be a good choice?

I know you gave some of the engine parts specs. What is the compression going to be?
 
67chrrybucket":6suda2cv said:
Well if i go natural aspiration 9.5/1, supercharged 8.5/1
I would zero deck the block & install the flat top tempo pistons to get 10.5 natural aspirated.
You will pick up an additional 10-15 HP. You will have to use premium gasoline anyway so might as well get the best.
When i stated professional help i was really thinking the best choice would be a machine shop with the owner or at least one of his machinist be at least over the age of 50 so he has more experience on this old engine.
Good luck on your build.
 
Nope, i ran a 10.4 engine for several years.
I ran a 274 camshaft with 195# cranking compression. I ran 93 octane gas with no problems.
You need to make up your mind which head you are going to use. An aluminum head will tolerate high compression better than an iron head.
 
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