327 chevy crank in 400

snipped-for-privacy@hotmail.com (James Hatfield) wrote in news: snipped-for-privacy@posting.google.com:

A longer rod gives you a longer dwell at TDC, thus allowing higher cylinder pressures to build from the explosion of the air/fuel mixture. This results in significant torque gains. This is the reason people use the Ford 6.2" rods in these motors. Make sure your pistons are designed for the rod you plan to use. The compression height of the piston is different for the two rods.

Well THAT is an interesting question! Nate and others have addressed most of the things I would have immediately asked. The interesting thing to me is that you're proposing sort of the opposite approach to the "383 Chevy" build where you put a 400 crank in a 350 block, and that has an intriguing advantage.

Here's what I mean. The stock 400 is the worst of all things small-block Chevy. Its got the siamese bores, and the shortest rods on the longest stroke you can get other than a custom crank, and its got the smallest (proportional to displacement) cooling capacity. The "383" Chevy build-up addresses one aspect of that by taking the siamese bores out of the picture since it uses a 350/327 block. It still has the horrible long-stroke/short rod combination of the 400 bottom end, but since its usually used for competition, longevity isn't as big an issue and the cylinder wear from the short rods and high side-loads can be tolerated. In my mind, the 283, 302, and 327 were the best all-around versions of the SBC because they have the best rod-ratios, but they're SMALL. Just not a lot of displacement there. Your build proposal will have the respectable (not as good as Mopar or Buick, but still respectable) rod-ratio of a stock 327, but with some extra displacement from the big bore. If you build it right it should "feel" kinda like a 340 Mopar, which is also a big-bore/short stroke engine and runs like a scalded wildebeest.

The things I would look at really hard (other than those already mentioned) are 1) can you get decent compression without either custom pistons or custom (longer) connecting rods, given your available choices of heads? A short stroke/big bore motor can be stout, but its GOT to have compression to do it. It can't putt its way through life like a tractor engine the way a long-stroke/small-bore engine can with low compression. 2) Cam choice- most Chevy grinds are going to be tailored to the more common chevy builds. Talk to a good cam company about changes to work best with the big bore/short stroke setup 3) Use the best available head gaskets so that the siamesed bores don't blow the head gasket between cylinders, thats a 400 SBC weakness that you are just going to have to live with. 4) Custom balance job- don't expect to stick 400 pistons on that crank/rod setup without getting the rotating assembly re-balanced big-time 5) Cost, cost, cost. Start adding up the custom things you'll have to do this way as opposed to finding another

327 block or getting a complete 350. Can't you still pick up Chevy 350s at Eckerd Drugs on the aisle right by the cotton balls? :-)

just got another thought... isn't a 307 basically a small bore 327? might find an early 70's 307 for cheap in a junkyard as that is a really unloved version of the SBC. Should be a large main crank unless my memory is failing (please correct me if it is)

Steve is right about balancing though and don't forget about quench area

- piston should be within a few thou of the deck at TDC or it just won't work right. To me this says custom pistons right off the bat because I'm guessing that trying to parts bin this you may get a good CR, or a good deck height on your pistons, but not both at the same time unless you are incredibly lucky or persistent.

nate