Well engine is about done

Engine is dang near done. Came up with 316 ci all said done, not to bad since it started out as a 201. Running buick valves, nice port job and all that needs to be done is a cam grind or find a good ground cam for 1800-2000 rpm range. The big question is that I can run a custom intake/header, would this be any benefit over reworking the stock manifold? I was going to run 1.625 id tubing for the intake side and smooth the transition from the carburetor to the intake. What are your opinions on a custom header/manifold? Thanks guys!

Down in that low of an RPM range the exhaust header really won't be much of an advantage....but you're going to build one anyway because the original type intake manifolds really suck and it happens to be easy to do.

The neck is to short, the air has to turn a sharp 90 degrees and the air coming out of the carb is still not really attached to anything after going around the throttle shaft and plate.  Then the manifold pulls the air completely opposite directions on the overlap of half of the intake cycles..... left- right -right -left -left- right-right- if you were standing looking at the manifold.

Yeah, with work the manifold can flow some decent air.  With work the carb can.  Bolt them together and see what you get, you'll be disappointed.

So fabricate a small plenum and intake manifold.  Put some thought into it to get the flow pattern right.  You won't be able to build the runners long enough on the exhaust to give much of a "tuned exhaust length" benefit though as the RPM is so low it will resemble a cell phone tower.

The good news is with a decent intake the engine will be able to tolerate a little more duration on the intake lobe of the camshaft than it could with the factory type cast manifold.  The bad news is that it doesn't much matter what valves are in the head or how smooth or shiney the ports are.  There's still only so much air that is going to get yanked and pushed around that  90 degree corner in the head and there's very little radius to that corner. 

Down at the 2000 RPM range the engine has a lot of time to breathe.  The mistake you will likely make is to use to big of tubing for the exhaust.  Use 1.625" or 1.5" OD on the intake but the exhaust can likely benefit from 1.375" to scavange better.  The other thing is a small collector diameter, there's 4 even pulses with time to evacuate, a large diameter collector and pipe is going to kill speed, and loss of this airspeed will kill scavanging.  Smaller is better.  Don't think that the engine is 1/2 of a 632 cid big block V8, it's no where close and it fires evenly where the V8 does not and needs a larger collector.

Something to think about is that I only ever had a 1.875" outlet on the collector on the header I built for mine......when I ran an updraft carb.  I ran the exhaust tubes in a rotational firing order, meaning that the tubes went around in order rather than firing across from one another.


Edited by wi50 - 08 Apr 2014 at 11:47pm

Boltz-
cant offer any help with the intake but was curious what you went with for rods, bore, stroke etc.?  if my brother ever gets some money we can finish his build.   so far we are going to be 4.155x5.4. did you convert to full flow oil are are you keeping bypass system?


Edited by CAL(KS) - 11 Apr 2014 at 4:09pm

thanks, good luck.  my help most likely came from the same individual   we are using H rods also.  wish i was close enough to drop by the shop, we would probably have more done lol.

Edited by CAL(KS) - 12 Apr 2014 at 8:07am