Can I Use A Late 400 Block In My Early Gto?
I enjoy the magazine. It has a lot of good information I hope to put to use sometime in the near future. I'm a greenhorn and I just started restoration on a '67 LeMans convertible. My questions arise from an answer given in your "Tech Q & A" from the July '07 issue. I recently purchased a 400 motor to replace the stock 326. I was told this would be a good candidate and bolt right in. The block number is 500557, "WA" is stamped on the front, and the date code is B187. The heads are No. 46 and date codes are L028 and K218. I think this works out to a 1977 motor and '68 heads.
Reading about the 500557 engine blocks having narrower main saddles, oil pan rails and thinner cylinder walls, I'm just a little concerned about rebuilding it, to find out later I could run into problems. I'm looking to increase horsepower comparable to that of a '67 GTO. Would this engine and head combo be a good fit? I know I need motor mount adapters. Do these work well without any other fabrication? Any information would be greatly appreciated.
T. J. Spottek
Via Internet
Rocky Rotella responds:The No. 500557 casting is certainly at a disadvantage when compared to an earlier block for ultra high-performance applications, but that doesn't suggest it's inadequate when used in moderate combinations. As long as your machinist is confident that your particular block shows no signs of fatigue, and it doesn't need more than about 0.040-inch overbore, you shouldn't have any problems using it in the 350- to 400-hp build you're planning.
Many of the late-'70s Pontiac blocks did not receive all the cast-in engine mount bosses found on the earlier castings, but getting one to fit your early application isn't overly difficult. One company that offers a conversion kit designed specifically for that purpose is Performance Years (www.performanceyears.com). PN RFE139B is the correct part number for your application, and it retails for $45.
The No. 46 cylinder heads contain small diameter valves (1.96/1.66 inches) and pressed-in rocker studs, but have a combustion chamber volume around 75 cc, which should produce a compression ratio near 10.0:1 on a 400ci. Any competent machine shop should be able to install 2.11/1.77-inch valves and tap the existing rocker stud bosses for threaded studs. With a mild port clean-up to blend the bowls into the new seats, the heads should flow on par with, or slightly better than, a typical large-valve D-port casting. When you factor in the combustion chamber volume, these castings should easily help you meet your performance goals.