G or J???

taguy1979 · June 28th, 2004, 10:41 PM

Alright I am wondering how much of a difference there is between G heads and J heads I know the G's are supposed to flow better but I am getting conflicting info on whether they have big valves or small valves in them. I think G heads came on a 71 455 what was the compression ratio for a 71 455? I am wondering because I wanted to know of the pistons in the 71 would have smaller dishes in them then my 74 J head 455. Would it be worth it to swap to the G heads?

[ June 29, 2004: Message edited by: taguy1979 ]</p>

Oldsguy · June 29th, 2004, 05:45 AM

taguy, As I have said before to others, for a more precise answer than mine, go to realoldspower.com. I am not trying to push members here over to there, but you can get an answer to THAT QUESTION easily over there.

What I know is this, the compression ratio will depend upon the application of the engine, ie, 2bbl or 4bbl, toro, "W" machine, 442, or just plain vanilla wrapper Oldsmobile????? My Delta was of the latter type, 2bbl plain vanilla wrapper Delta 88. The cr was 8.5:1 or perhaps a little less.

About your heads, I would say the Gs would be better than the Js, the Js were the least desireable BBO heads of all. I am not sure about the size of the valves but probably both heads had hardened exhaust valve seats. If you plan on rebuilding the heads anyway go with the Gs, if you don't, go with the Gs. If you DO rebuild the heads and replace the valves, be sure to have hardened seats installed on the exhaust side. If you can find some C heads, those were reported to have the best flow numbers of all stock BBO heads but it would really depend upon your intended use and application and the rest of the engine anyway. Lots of variables to consider.....

taguy1979 · June 29th, 2004, 07:10 AM

Thanks... I have been trying to get back into the Realoldspower>com forum since last night but it keeps telling me that there is some error. I know the motor with the G heads was a 4 barrel I was so shocked from finding heads that weren't J heads that I forgot to check anything else about the motor. I guess I will see what else I can find out about it.. Thanks again [img]smile.gif[/img]

Oldsguy · June 30th, 2004, 10:35 AM

No problem, any time..

June 29th, 2004, 05:45 AM	#2 (permalink)
Oldsguy Hot Rodder at heart Administrator Join Date: May 2004 Location: Lees Summit MO Posts: 5,315	taguy, As I have said before to others, for a more precise answer than mine, go to realoldspower.com. I am not trying to push members here over to there, but you can get an answer to THAT QUESTION easily over there. What I know is this, the compression ratio will depend upon the application of the engine, ie, 2bbl or 4bbl, toro, "W" machine, 442, or just plain vanilla wrapper Oldsmobile????? My Delta was of the latter type, 2bbl plain vanilla wrapper Delta 88. The cr was 8.5:1 or perhaps a little less. About your heads, I would say the Gs would be better than the Js, the Js were the least desireable BBO heads of all. I am not sure about the size of the valves but probably both heads had hardened exhaust valve seats. If you plan on rebuilding the heads anyway go with the Gs, if you don't, go with the Gs. If you DO rebuild the heads and replace the valves, be sure to have hardened seats installed on the exhaust side. If you can find some C heads, those were reported to have the best flow numbers of all stock BBO heads but it would really depend upon your intended use and application and the rest of the engine anyway. Lots of variables to consider..... __________________ Dan '77 Cutlass Supreme '46 2 door "The rocket 455.....it's a sledgehammer approach to a thumbtack world" LuxBlue of HAMB.

June 30th, 2004, 10:35 AM	#4 (permalink)
Oldsguy Hot Rodder at heart Administrator Join Date: May 2004 Location: Lees Summit MO Posts: 5,315	No problem, any time.. __________________ Dan '77 Cutlass Supreme '46 2 door "The rocket 455.....it's a sledgehammer approach to a thumbtack world" LuxBlue of HAMB.

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June 28th, 2004, 10:41 PM	#1 (permalink)
taguy1979 Junior Member Join Date: Jun 2004 Location: Calgary alberta Posts: 4	Alright I am wondering how much of a difference there is between G heads and J heads I know the G's are supposed to flow better but I am getting conflicting info on whether they have big valves or small valves in them. I think G heads came on a 71 455 what was the compression ratio for a 71 455? I am wondering because I wanted to know of the pistons in the 71 would have smaller dishes in them then my 74 J head 455. Would it be worth it to swap to the G heads? [ June 29, 2004: Message edited by: taguy1979 ]</p>

June 29th, 2004, 07:10 AM	#3 (permalink)
taguy1979 Junior Member Join Date: Jun 2004 Location: Calgary alberta Posts: 4	Thanks... I have been trying to get back into the Realoldspower>com forum since last night but it keeps telling me that there is some error. I know the motor with the G heads was a 4 barrel I was so shocked from finding heads that weren't J heads that I forgot to check anything else about the motor. I guess I will see what else I can find out about it.. Thanks again [img]smile.gif[/img]