[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

[KSZR]

Originally Posted by SD455DJ

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

Thanks! I'll go for the RA manifolds and 2.5 X Pypes system.

My goal is to be faster than my wife's Mach E in the 1/4(13.8)! Fun!

What is the next step without just going to a stroker? From reading posts maybe 2801 or 2802 cam? Worth it over the 068?

3.73s might be nice over the 3.55s since I have overdrive.. But the 200 4R does have a much lower 1st gear than a T350 or T400.

Kent

[SD455DJ]

Kent, Might as well ante-up for the 2.5" outlet RA manifolds since you are going that route along with the Pypes mandrel 'X' system. Can't go wrong there and it will support more power down the road (up to 500 hp easily). I personally would get the kit without the mufflers and purchase the 18" case DynoMax UltraFlo's or Magnaflow's separately, which are both straight-thru design, yet fairly quiet, but support lots of power. I have both and they both perform very well.

I see you have #16 heads and I'm assuming the '68 large valve variety. I would certainly follow the same recipe we did on the XV 400 engine on yours. With the large valve heads with .040" quench, lower 10's for static compression, the 2802 cam, etc., I would expect an easy 420 hp/480 lb-ft torque. With your new exhaust system and a fuel delivery system to match, you should have no problems running high 12's at 106+ mph. I'd stick with the 3.55's for a while since your first gear multiplication ratio is 9.7625 with the 200R4's 2.75 first gear...that's like having 3.90 gears with a TH400/TH350! You will have a major traction problem with this build...and lots of fun!

Dennis

[KSZR]

Originally Posted by SD455DJ

Kent, Might as well ante-up for the 2.5" outlet RA manifolds since you are going that route along with the Pypes mandrel 'X' system. Can't go wrong there and it will support more power down the road (up to 500 hp easily). I personally would get the kit without the mufflers and purchase the 18" case DynoMax UltraFlo's or Magnaflow's separately, which are both straight-thru design, yet fairly quiet, but support lots of power. I have both and they both perform very well.

I see you have #16 heads and I'm assuming the '68 large valve variety. I would certainly follow the same recipe we did on the XV 400 engine on yours. With the large valve heads with .040" quench, lower 10's for static compression, the 2802 cam, etc., I would expect an easy 420 hp/480 lb-ft torque. With your new exhaust system and a fuel delivery system to match, you should have no problems running high 12's at 106+ mph. I'd stick with the 3.55's for a while since your first gear multiplication ratio is 9.7625 with the 200R4's 2.75 first gear...that's like having 3.90 gears with a TH400/TH350! You will have a major traction problem with this build...and lots of fun!

Dennis

Very cool! Thanks for your input. Lots to think about!

Would Rhodes lifters make sense with the 2802? Just thinking about retaining the nice Pontiac low end torque and drivability.

Kent

[SD455DJ]

I don't think you will need Rhoads with the 2802 cam and 10.0 to 1 compression in the 400. So far, we've never had any issues with the lifters that come with the Summit cam kits (supposedly Johnson Hy-Lifts), and I'm not a fan of their 'sound'.

Dennis