i have a 355 setup with a 216/228 .454/.480 lift cam in it now and a 750 holley double pumper. i have it adjusted perfectly to the cam. i am going to be swapping over to a solid 236/236 .495 lift comp cam and i want to know when i put it all back together if it shoudl be close to where it was or shouldi have to start all over again.

joe

 

the whole idea behind getting a bigger cam is moving more fuel.

anyway, there are alot of people who retune thier carbs for the day(depending on temp, humidity, etc). you definatly need to tune the carb if you change anything in the engine.

 

The main jetting will be the same or real close.
should be something like 70's pri and 80's sec.

Because of the lower idle manifold vacuum with the bigger cam you may want to install a different power valve.
If, with an automatic your manifold vacuum is say 5.5" while idling in gear, install a 4.5" power valve.
This adjustment will ensure the power valve stays closed at idle while in gear.

More important than the carb is the ignition timing. the bigger cam will want a different ignition curve. It will want the same amount of ignition advance at WOT but will like a lot more advance at idle.
You can achieve this by limiting the travel of the mechanical advance. On cars with even bigger racing cams; they need so much initial timing that it is practical to lock out the mechanical advance curve altogether. thus 32 to 36 deg advance at idle and 32 to 36 deg at WOT.
You can still use the vacuum advance although it may need adjustment.

You can tell if your car needs more initial timing a t idle with your new bigger cam if, it tends to run hot at idle or low speed after the the cam swap. the increased amount of EGR from the larger amount of overlap causes the fuel to burn slow at idle and low speed requiring more initial ignition advance. A slow burning
late timed motor will overheat the cylinder walls and valves while running.