[SD455DJ]

Originally Posted by KSZR

Dennis,

My 72 Lemans with 400 .030 over, 068 cam, cast iron intake, log manifolds, HO racing carb and distributor kits, dual snorkel, crush bent quiet exhaust, 3.55 12 bolt, 200 4R does a best 1/4 mile on my dragy of 14.59 at 95.

Going to upgrade to a 2.5" Pypes mandrel system, which sounds like a huge improvement.

What would I gain by going to ram air manifolds over logs? Wondering if its worth it.

Kent

Kent, Certainly RA manifolds will help with a 3-8 hp & lb-ft of torque gain through the rev range of 2000 rpm and above, especially the larger outlet repops (RARE's 2.45" ID outlets). All exhaust manifolds benefit from 2 1/2" mandrel bent headpipes (Pypes makes them for logs and RA's) to make the most power gain along with mandrel bent pipes to complete the exhaust system. Going to RA manifolds (either stock 2.1" or the 2.45" oversized) will accommodate more power gains in the future should you decide to upgrade your engine, so, IMHO, it's never a bad idea if you can afford it...but, the 68-72 std. A-body log manifolds hold their own on relatively stock builds. I'd be more tempted to open up the outlets to 2.2" on your logs (stock outlets are 1.875" and 1.95)" and save your money if you don't have future plans to make more power with your 400 (B-Man has an excellent thread on opening up his log manifolds and making his own 2.5" mandrel bend headpipes). I think logs are fine up to 350 hp, however, the law of diminishing returns kicks in fast at 350 hp. I know my XV 400 engine that made 380+ hp would have made 400 hp on the dyno with RARE 2.5" manifolds. I didn't open up the outlets on the log manifolds since I race it at the Pure Stock Drags and have to be legal.

Your 400 will be quicker by 0.1 to 0.2 seconds (I think Ccass mentioned this earlier in this thread) quicker with just the manifold change and you'll get another .0.2 to 0.3 second drop with the full mandrel bent Pypes exhaust system.

Dennis