231 odd fire power...

Anyone know what the power ratings were for the 75-76 231 oddfire? I would imagine they are similar to the 225 but just wondering. Thanks in advanced.

 

I know the compression ratio is lower and pretty sure the hp is too. If was gonna do it over, I'd have rebuilt the 225 and forgot about the 231. Next time. Just my opinion from my exper. Get Pat Ganahls book on the V6's before you do anything.

 

Wild guess. 105hp? Maybe 110hp?

 

from Pat's book..... in '75. bore increased .050 to allow the odd fire to share the same piston as the Buick 350. 225 bore= 3.750. 231 bore =3.80, 225 compression ratio is 9.0:1 vs that of OF 231 at 8.0:1.

 

160 hp IIRC

 

According to the casting numbers this is a 75-76 which shows it to be a .050 225. I hope that is true cause i swapped the 225 flywheel on to it. They looked similiar but the 225 felt heavier. Intakes look same. Hope compresion isnt 8.0-1 but that could explain the hard starting(ontop of milage and wear). The idea was to bore it 50 over to share buick 350 assembely line space....so does that mean connecting rod, pistons.etc are the same as 350's? Thanks guys.

 

Yup Evenfire 105 --115 with 1979 heads

HP rating was changed so don't compare to the 160HP oddfire which was measured by the old standards. I have no idea what the translation would be. I don't see any reason why the 231 odd fire wouldn't be close to the 225 oddfire. It was smogged more so that could make it worse

 

FYI

The old 225 usually had 9:1 pistons- too high a ratio for current gasoline anyway.

It should be run on 110 octane gasoline. If so you could get 160 hp at the crank with a stock engine. Notice this was measured at the crank- and with out accessories--(no alt, no water pump belt. no ac and no fan)
Probally something like 130 hp at the rear wheels--- and less in four wheel drive. Friction from the transmission, accessories, waterpump and fan takes away a lot of Horse Power.

By the time the 231 came Horsepower ratings were measured at the rear wheels-- not the crank--- and measured with accessories running. The rating was about 110 to 100 horse power. And ofcourse the 231 had 8:1 pistons. So the 231 is more powerful than it the rating suggests at face value. I suppose about 120-130 horsepower at the crank.

I suppose you loose about 20 horse power with 8:1 pistons compared to 9:1s. But you have a hard time running 9:1 without special gasoline.

If you put 9:1 pistons in a 231 odd or even fire, you would have to run high octane gasoline to get the power increase. If you ran low octane gas like 85 you would have to retard the timing a lot to get the engine to run with out detonation (quite distructive to the engine). So you would be back down to lower horsepower anyway.

Even if you have a stock 225 with 9:1 pistons-- you best run the best octane gas you can fine-- like 90+ and retard the timing a few degrees. And add octane booster to the tank. Also older engines were designed with soft valve seats, so unleaded gasoline is hard on the valves.

The main issue today is gasoline octane. So if you run gasoline that is eazy to find you have to stick to 8:1 pistons anyway. So you have less power potential than engines used produce in stock form back in the 1960s

 

http://www.gnttype.org/general/v6hist.html
http://tech.oldsgmail.com/eng_buick.html
http://tech.oldsgmail.com/buick_mod.html

 

zactly, and even though it may be difficult to get consistant octane levels its easy enough to pour a little octane booster in the tank. That always seemed to work to appease the sins of the refinery in a pinch. This worked fine on all of my classics that I've owned over the years since they took lead out and forced us to live with lower octain or inconsistant fuel .I also found on any of my 225s always ran fine on 84.

 

my 70 225 runs fine on reg gas, but i do think the seats have been changed to allow for unleaded gas without damage. not real sure though. i always run octane booster (when i remember) but i really dont notice to much of a differance, alwasy thought it was just in my head