Thread: 781 heads

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Ive got a 75 454 that has casting #781 heads on it. Im trying to find out the cumbustion chamber size of these heads.
Mortec says 118cc.. while my Federal mogul/SpeedPro catalog & a big bloc Chevrolet book I have shows that that # is 110 cc. If anyone knows for sure, or has more sources please let me know. John

John the 781 heads are 118cc they are a open chamber oval port they are a really good head they flow really good, I had a set on my bracket car 433 cid (396 60 over with 454 crank) no big cam 595 lift 294s comp cam and a 850 holly 10 to 1 and it would run mid 11,s
those are good heads keep them they are getting hard to find.

For your infos Those heads where used on the 454 1973@1985 The had 2.06 Intake and 1.72 Exhaust and a 113cc chamber.
They also had the open chamber.

Any other question write me back at tekno_x80@hotmail.com

Any one have the correct answer for this cause I have 781 head as well to mate to the TRW L2349F pistons I bought. I bought these haveing been told by the TRW tech rep that the 781 heads are 118CC which gets me between 9 and 10:1. If they are 113cc Im gonna have to find other heads. So anyone with facts and can give the correct answer for me and the guy who originally posted this I would appretiate it. I may buy after market heads regardless but would like to know for reference regardless.

yep, I geuss your right..I was just curious at this point.

As I typed my last post the one thing I was guessing may happen is that one of you experts would say to just get a ccing burett kit. I know, I know you are correct, but thought I would take a shot anyway.

I have only done maybe 5 or 6 motors in my life and once I am done with this 454, my only other motor that I want to do is a 250 inline 6cyl for a 66 step side pick up w/a three speed on the tree. Reason I say this is cause I dont see myself building a whole lot more motors where I would need the cc ing kit. If its gonna cost me 150 for that kit I just may as well put the money towards new heads, instead of using these 781's that who knows what has been done to them.

Tech inspector thank always though cause your various posts are always an education

I agree with erik427.I have set of 781's on my BBC and I remember researching chamber volume.I admit I can't remember the source but I definitly remember 118cc's.

Boy somebody is really making money on a $100 cc kit. I used the one at Joe's Machine Shop on my 882 SBC heads and the burette was a cheezy plastic model, I guess so it wouldn't get broken working around iron parts. The last time I checked a glass burette for chemistry work was about $40 and probably $50 now. If you are worried about the cost of the kit just BORROW a (more accurate) glass burette from a high school chemistry lab and make your own cover plate from hardware store plexiglass. Just drill out a hole about 1/4" diameter in the plexiglass, do the cc-ing and return the burette. I'll bet it is possible to do this for under $10. As far as the sealing goes, any good mechanic should be able to run his/her hands through his/her hair and get enough grease to seal the bottom of the plexiglass?? (Just kidding, I sold the oil rights to my hair to Exxon!)

Don Shillady
Retired Scientist/teen rodder

Stepside, the 781's are 118 cc as cast...that may vary by a couple cc's, so you should still check, but it's definitely not 113 unless they've been milled. I just checked my 781's this very afternoon, I did every other chamber on each head, 3 were 118 cc, one was 117cc...and that could be due to mis-measuring a bit. And forget the burette...for occasional cc'ing, just buy a big plastic syringe, a tach shop or supply store for horses or cattle should have one...30 or 40 cc's is good, 60 would be better. Just fill it with a water/rubbing alcohol mix (flows better) and I put a few drops of food coloring it it, makes it easier to see. The syringe is accurate if filled correctly. Suck the water up into it just past the mark that you want, then tap the air bubbles out and bring the water to an even amount. (50cc, 30cc, whatever size it is) Do the plexiglass thing as mentioned above, and shoot the water into the chamber till it's up to the hole. (dont forget a spark plug in the hole) Keep track of how much you put in, and you''re done.....check a few to be sure.

K cool thanks for the info Johnny