I just finished and installed a slightly modified stock 4bbl intake and the difference was totally worth the effort. The modifications I made were opening up the plenum into two oval openings just like a modern edelbrock manifold as well as a little porting to ease the passages in the plenum , adding a 1 inch phenolic spacer and blocking the exhaust passages through the manifold. The plenum was opened up on my milling machine so any machine shop can handle this very inexpensively. The difference was amazing to say the least. Also, I'm using a edelbrock 750 cfm carb.
Wow! I'll have to try that! Was that a 4 hole spacer? And where and how did you block the ex heat passages? I wonder how much just a spacer would help.....
Modified nailhead manifold I used the same carb and spacer as I did on the previous manifold. I used a die grinder to re-shape or contour the spacer between the primary and secondary holes so that the air/fuel mix didn't have such a sharp turn to make out of the spacer towards the front or rear ports. I actually had to fatten the jets after the mods. As I mentioned earlier, the throttle response right off idle all the way through full throttle was greatly improved. The car feels totally different. I would hazzard to guess that this setup would be on par with or better than the rare 66 Q-jet combo. As for the exhaust block off I used thin pieces of steel with some non hardening and non- sylicone sealer and placed them over the holes on the intake gaskets. These thin steel plates are just big enough to cover the exhaust cross over port on the manifold so they won't get pushed up inside of the manifold.
I've already got a nice 1" aluminum spacer to try out after I baseline the car:grin: It should increase port velocity and promote a more complete a/f mixture, if my calculations are correct of course Any pics of the modified manifold? I have a 66 q-jet setup as well but I want to try EVERYTHING to squeeze every tenth out of my car:Brow:
Modified nailhead manifold Sorry, I didn't take any pictures but as I mentioned earlier, I made it look just like a edelbrock manifold with two oval openings instead of the four individual holes. If you just place a 1 inch spacer on the stock manifold, the primary holes of the stock manifold are too small and will cause a restriction or bump in the road for the air/fuel mix, so they'll have to be opened up to match the spacer. Also I tapped the holes (where the exhaust crossover exits around the primaries)with a 1/8th inch pipe tap and 2 pipe plugs with some J-B weld to block any leaks at those holes. I hope this helps.
66gscov4sp,Go for it, but make sure you can still close the hood with that superwildcat air cleaner assembly or whatever your using. I know that the Offy 2X4 manifold is taller and poses hood clearence problems.
Jeff: On the nailhead list I believe it has been shown that the 2 inch spacers don't work near as well as the 1 inch. or at least that is how I remember the tread. Mike
