Visual difference in 302 vs 347?

Got the heads off as well. Here are the pics and following that will be the numbers in text.










Top of the heads:
8A18 289 WF



Under the heads:

3A 289 C80E

and

1A 289 C80

 

Also, as you can see in this pic, the pistons aren't domed as I once thought. Hard to see down in the plug hole with a flashlight, lol. Anyone know what pistons these are?

 

Looks like those heads have been ported and polished. Might be keepers afterall. Definately so if they are and after you have screw in studs and guide plates installed and get rid of the rail rockers. The pistons look like the stock O.E pistons used in 68. Not sure about the broken castin in the distributor hole, but that might be kosher, they punched out a ragged hole in the front of the lifter valley wall in the small blocks, I'll have to look at the two blocks I've got left to see what they look like there. Are there any numbers stamped into the piston tops ? If there are, that'll be the overbore size. No numbers, it's likely a std bore block.

 

Tomorrow I plan it putting on my engine stand and dropping the oil pan. I am interested to see if there is any metal in it. Could someone have possibly chiseled it away a bit, to make room for a larger distributor rod? (Like the HEI that was on it) Another thing, why do the heads have two different numbers on the bottom of them. Mis-matched? Or a different number for a different side of the block?

 

I don't see any work on the intake side, but looks like they do have new exhaust valves(maybe intake as well and they're just sooted up)...... Unless someone built a 289 in a '70s block, I'll guess those are the pistons used in a '76 302, remember that block was cast in 1976, heads are much earlier...

 

Look at the chamber walls, they've been polished and not their original contours. The 72-76 302 pistons had dished centers that were at least a quarter inch deep. The ones in the pics are much shallower.

 

You cannot simply put a larger distributor body in an engine block. Could be someone tried though. It's normal to have some different numbers on two matching heads. The casting (engineering numbers) are the same (C8OE) that's what counts. Look for the overbore sizes stamped into the piston tops. Those are not the pistons used in the 76 blocks. The date codes in the rocker gallery should be close to being the same dates if they came from the same engine. It's the number/letter/number(s) combo next to the valve cover rail that looks like a "screwed in tag" that's actually cast into the head.

 

Looks like a casting hole. They needed to make a hole when getting the engine block out of the casting. Does it look like the other end of the hole will be in this location?

 

well crap... from the looks of it.. only 1 head has had some work done? Look here and compare to the others. Then compare to the other head which looks completely untouched.



If that's true and the pic's aren't deceiving?.. those heads will cause compression variations to be all over the place from cylinder to cylinder and even worse from side to side. Not good at all.

also.. those heads are well over 60cc's(they look like the lo-po 63cc version) and would not be considered anything remotely close to a performance casting unless you start grinding and slicing to get them flowing more and squeezing tighter. Laying the chamber walls back only makes matter worse for compression too.

Pistons are low compression smogger versions too(granted.. maybe not as bad as some of the mid-70's crap.. but nothing to write home about nonetheless). I'd guess they are aftermarkets with at least an -10cc volume(including the valve reliefs).. and to make matters worse.. they look to be down in the hole at least .015 - .020 too.

Hate to say it.. but from what I see there.. you'd be lucky to hit 9-1 compression with that setup(I'd guess closer to 8.75'ish MAX). And what's worse.. the cam gear looks to be pretty thin too and should be replaced.

 

Thanks for all the helpful replies. I'll have more info and pics this evening when I take the rest apart after work.

 

Also, if you were in my place with this block and heads, what would you do? I'm not going to be competing in hardcore drag racing. I may take it for a few passes on our local street car nights, but that would be all. The main concern is that I want it to sound good, and have a bit more power than usual. I'm used to driving it with a 250 in it, lol. So with just the motor I've posted, blows my previous power out of the water. I don't want to go too crazy on hp. Mainly I want a good sounding street car, with just enough pep to justify the sound.

 

if you just want a good/healthy running smallblock?.. 300-325 horsies will shove you around just fine in such a light little car. Very easily attainable with that shortblock despite its compression shortcomings.

Just need to be sure that the block viable as it is(cleanup and rering?).. or can be safely overbored to .030-.040 depending on where it's at now. If it's already at +30.. the bore will usually need to be really nice to clean up any potential barreling and get a +40 out of it. If it already at +40?.. I wouldn't mess with it as going to +60 can be problematic unless its sonic checked first. Be sure to get some decent hypereutectic flat tops since they aren't too pricy and would be fine for that power level(up to about 400HP) qand will bring the compression up too.

So.. does that one head with the red arrow above have that chamber wall laid back more than the others?.. or is it just sooted up and deceiving the eye from here? If it is?.. I'd say junk em' and get a better casting to start with. If it isn't chopped differntly than the others?.. just tank em'.. have the exhaust smog bump ground out.. do a good 3-5 angle valve job.. and cut about .030-.040 off them(I usually go to about .050 but best to keep it more minimal since they may have been nipped before already). They guy doing the head work should be able to tell you what they'll safely allow without getting into the valves edge.

If you really want to get compression up any more than that?(compression is good everywhere in the power band but comes with a higher gas price).. you'll need to nip the block to achieve a 0 deck height.

Or... you could leave the block alone and go with some thinner than typical Cometic head gaskets at around .028-.030 thick. That extra .010-.015 thou of quench will be well worth the extra $200 bucks if you're wanting that last bit of compression out of the deal. I'd lean towards having the block decked myself.. but have done both(0 deck and thinner gasket) and they flat out run at any rpm to make the motor feel bigger than it really is.

Or.. you could just run some small domes with the parts you have(on a fresh bore of course).. and let er' rip. Maybe not the most efficient way to go about reaching a 10-1 compression ratio.. but pretty good bang for the buck without all the other machine work(milling/decking or thinner gaskets to raise compression) being needed.

IMHO.. 9.5-1 should be more than enough to achieve that above mentioned power level.. but 10.5-1 REALLY wakes these little motors up big time. The one on my stand right now will likely end up well north of 11-1(with thin gaskets) and will surely sing up alongside the angels using a big cam.. yet still be fully streetable due to such good off idle response with all that beautiful compression. Keep your cam around 225'ish duration and it will be a nice street motor with plenty of gumption to go eat some Chevy lunch when you want to let it eat.

 

Very helpful information. Much appreciated. I'm going to find out what kind of cam is in it today after work. I don't have much left to take apart.

 

I missed the variation. Good catch. I only focused on the obvious that they were worked. Those look like the 9 to 1 pistons used from 68 to 71. Definately not the 72-76 units.

 

If you really want a low buck setup, it's hard to beat an Explorer 5.0, there are still many of these sitting in the J'yards that have life left in the motor. You can pull these, remove the intake setup and the FEAD, replace the intake with an RPM or Stealth, top it with a 600 Holley. You'll need a steel geared distributor to match the roller cam. Leave the stock cam in, but replace the rockers with full roller 1.7's. This will get the lift up to .445/.473. The duration is 256/266 in these cams with a 116.5 LSA. Add some headers to it and you'll have a torquey little small block very much like the old 289 Hi-po but with better manners. It'll melt the rubber down on the rear everytime you nail the pedal. I had one like this in my 89 Ranger backed by a Toploader 4 speed and 3.73 rear. I never had a problem lighting up the 275/60's on the rear. That Ranger weighed in at 3550 lbs with me in it. In a Mav, it would be a screamer with 500 lbs less weight.