if i buy this cam and these roller rocker arms, what will my effective lift be for intake and exhaust?

Question

Cam=http://store.summitracing.com/partdetail.asp?part=SUM-K1105

RR= http://store.summitracing.com/partdetail.asp?part=SUM%2D141507&autoview=sku

I am trying to do a low buck build on a gen1 sbc 327 with Summit vortec heads that say they can handle a maximum of .520 lift..

Will these other parts work?

Vortec heads= http://store.summitracing.com/partdetail.asp?part=SUM-151124

Answer 1

If you divide the advertised lifts by 1.5 you'd have a cam lift of .310 intake and 325.333 exhaust.
Multiply both of these lifts by 1.6 and you'd wind up with .496 intake lift and 520.533 exhaust lift.

The big question is: Which Chevrolet Vortec heads are you buying? Chevrolet has only two versions that have the ability of accepting a total lift of .530 out of the box without modifications.
The first is Chevrolet part number 25534421. It has 185 cc intake ports and 56 cc exhaust ports.
The second Vortec number is 25534431. The intake ports are 215 cc and the exhausts are 84 cc.
Both of these cylinder heads have 66 cc combustion chambers. ---- With flat top pistons you'll be very close to 10.0 - 10.3 compression ratio.

Now the big choice! Which head would you like to choose? Bigger may look better on the outside but the little 327 likes all the velocity you can shovel in and that means the small ports will give you more low end torque. By all the numbers of the camshaft you have chosen I'd go for the 185 intake runners.
I really like the cam you have chosen because of the usable torque and rpm range.
If it were me I'd triple check the roller rocker arm's sweep across at least one valve first to be sure the contact of the roller starts fully on the end of the valve toward the intake manifold and ends it's sweep fully on the valve at the max valve lift.
My advice to you is stick with a 600 cfm Holley or smaller with vacuum secondaries.

We have dirt late models with 356 inch Chevy motors, Dart 49 cc Platinum heads with 200 cc runners, modified Willy's 500 CFM carburators that scream to 7,600 RPM.

My point is the seemingly small carb with vacuum secondaries will do wonders.

Good luck with your project!

Answer 2

In general, Yes, they will work. Typically Chevy's come with an advertised ratio of 1.5 but they are actually closer to 1.45. If you take the specs Summit gives (465/488) which it states is arrived at using the stock ratio and divide it by 1.5 you get the actual lift of the cam which is 310/325. Now multiply that times 1.6 and you get 496/520. Got it? Good!

Answer 3

The max lift on the intake and exhaust side will stay the same as the cam specs as long as you stay with the 1.6 rocker (which is standard for majority of cars and the general measure for all heads) and you do not enlarge your intake valves about 1.94 and the exhaust valves about 1.60.


Hope this helps