hey guys, I have a set of sbc heads with a casting # 3973487X also Jl 61 stamped. Anyone have info on these heads? I've looked online and I've found about 4 different answers. Please help me out if you have info on these. thanks
they would be worth rebuilding if the guides arent shot or they are 2.02's, guides adds up to plenty of $, the 75 cc chambers arent gonna help you much.
good heads the x makes the port runners larger than regular 487's,had them on my stock 72 blazer 350 engine.
The primary appeal was that the intake ports were slightly larger than a std. 487 casting....handy for class racing like NHRA Stock Eliminator where you are restricted to using only certain casting numbers. There is also a 461X casting as well, same deal but better & with smaller chambers than the 461. To the average guy it doesn't mean a whole lot...they are OK as they are, but nothing I'd look for in particular one way or the other.
thanks for the help. These heads have been rebuilt once, but it was when I was young and dumb and I don't remember if they are 2.02's or not, but I hope they are. Anyway I'm going to rebuild this motor again and want to use these heads. Would anybody suggest grinding them down to get a smaller chamber? Just runnin' flat tops and a 268 comp cam. thanks again for the help
Well, I'd cc the chambers, equalize them, & at least clean up any mold lines, etc. in there....& then surface them flat. Then cc them again. If you are going to replace the pistons, I'd probably look at flattops with only two valve reliefs, vs. four. It will gain a tad bit of compression, easily enough. Unfortunately they are more expensive than the four-relief pistons. If you are not opposed to hypers, look at the KB231 which will work nicely. The KB120 has one common relief which will give slightly less compression, sometimes cheaper, though. If you are not going to use new pistons, then, depending on what the final chamber size is, and what head gasket you use....you may want to mill them a bit more. However, with that cam, don't go nuts with cutting them....that cam will not bleed off a ton of cylinder pressure at low rpm. Stick with a final static comp ratio of around 9:1-9.2:1 & you'll be fine. There is a pretty accurate calculator on KB's website. Either 1.94 or 2.02 valves will be OK..and, if I might offer a small suggestion- I'd look at either something in Comp's Xtreme Energy line, or the new Lunati Voodoo cams. Either one has modern lobe designs & technology. The 268 Comp has been around since about 1977, updated a few times...good enough cam, but time's passed it by. Take a look at this: http://store.summitracing.com/partdetail.asp?part=CCA%2DCL12%2D238%2D2&autoview=sku Use Comp's recommended springs, & step up to quality "long-slot" rockers, or even Comp's cast Magnums. I've not tested any of the Chevy SB Xtremes....but we gained over 10 hp & 15 ft.-lb. of torque everywhere in the curve from 1500-5500 using an Xtreme 274/286 over the Magnum 280, in a BBC 402. Not gobs, but everything helps, & if you are buying it new, they're the same price. My exp. with other Xtremes has been much the same, as well as others...though one builder I know who uses custom grinds in most everything used to use the Xtreme lobe profiles, but now prefers the Lunatis- likes the ramp designs for their quietness & feels the power is equal.
fabulous info homespun! Already have a 268 high energy cam and lifter set I couldn't pass up for $90, but still looking for low dollar piston set.
The KB120s are around $173 from Summit; the KB231s are about $240. KBs are the best of the hypers; the Sealed Power or Speed Pro hypers have a dubious rep for disintegrating under load. I will not use them, for anything, but others have had OK luck. If you want to over build a bit, Speed Pro forged pistons run anywhere from $280- $370, but it's overkill. Cast pistons used to be decent enough, but most of the companies have been sold so many times over the past 10 years that it's hard to tell where stuff is made anymore. Badger still seems to care about quality, if you can find them. Like this: http://cgi.ebay.com/ebaymotors/S-B-...ryZ33623QQrdZ1QQssPageNameZWD1VQQcmdZViewItem Some .040s out there also, for $60. Cast pistons will not take a whole lot of beating, or detonation, but if you do your part they will work pretty well. I'd also use a used GM HEI (not the ProComp junk) & check it, clean it, & use a common recurve kit to quicken the curve a bit....most people overlook the ignition, but you can gain a ton of response & power if you are willing to play with it a bit to get it dialed in. You can usually get a decent boneyard HEI & a kit for $25 or less...add a MSD coil if you want, or not, & some decent wires, & you're good to go.
I am going to be running these on my 383 Blown Small block. 75cc makes me end up with 8.4 to 1. Machine shop said everything stated above. I can't wait to see how they run. Tim
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