JMSII Does anybody know what kind of compression ratio one would have if he bolted an early set of 401 heads (#3196291) on a later (1976) motor with stock flat top pistons? Also, what's a fair price to pay for a set of these heads? (used, not fresh) And one last thing, could a person use a set of Harland-Sharp rockers on these studs without machine work? Thanks Guys!
tufcj The 76 401 has dished pistons if they are factory. Factory compression was 8.25:1. The 291 heads would put it at around 8.75-9:1. 291 heads are bringing $300-400 a pair from the last few sets I've seen on ebay for rebuildable cores. Yes, you can use any roller rockers on these heads without machine work. You will need to change out the studs to a Chevy style, and get pushrods that are hardened for guide plates. The heads are cast so the pushrod holes act as guide plates. Make sure you use AMC rockers, as the Ford style don't have the lower edge clearanced correctly. Bob tufcj
82Waggy tufcj wroteThe heads are cast so the pushrod holes act as guide plates. I've seen several people suggest this, but I'm not so sure it is a good idea to rely on the cast slots when using roller rockers. I've got a pair of 090 castings that have the slots but they don't look to be very well centered.
tufcj I've got 291 heads on both my AMX 390 and Jeep 360. Both are running Crane gold roller rockers. The Jeep is a mild lift (Edelbrock) cam. It's been fine for over 40K miles. The AMX has a .525 lift, 292 duration cam in it. It only has a few hours of run time on it, but no problems. I didn't see any centering problems with the rocker/valve on either engine. Bob tufcj
fuzz401 I have the 6090 with crower roller rockers with about 120 1/4 mile passes and 600 road miles and no problems at all
82Waggy Well, that's good to know. What pushrods are you guys running? Fuzz, are you running the stainless Crower rockers?
fuzz401 crower SS rockers what they look like my contact pattern on the valve tip crower push rods made to my length
82Waggy Not sure how critical it is, and you guys seem to be doing OK with what you are doing using the cast slots (no guide plates), but some think it is an advantage to stabilize a roller rocker as high up the pushrod as you can get without hitting it. Reasoning seems to be that rollers don't often have as wide a contact surface with the tip of the valve stem as a non-roller (stock type) rocker, and it is therefore not as forgiving of being off center as a stock rocker is.
jeepsr4ever Hard to say if that .75" of height on a 7.800" long pushrod would make much of a difference in a motor that sees less than 8 grand. Taking in account any flex you could assume that the guideplate would work better but the chromoly pushrods are pretty stout. The slot in the heads have worked great since they were first made after all arent the greater percent of chevy heads the same way?
82Waggy Like all of this splitting hairs stuff, guess it depends on how crazy you are getting with spring pressures and such. If I was going to start pushing over 6000rpm on a regular basis I would probably go with 3/8 pushrods - requiring that the slots be drilled out and guide plates be installed anyhow. Does seem to make sense to grab the pushrod as high as possible but .75" is likely a non-issue for most applications. For those that don't know, 502 and other bridged heads do not have slots
