225 Odd fire: Limits compared to B4B Even fire

C

CTX-SLPR

Active Member
Joined
Feb 4, 2004
Hello All,

Continuing to work on my very slowly moving LSR project and the supply of standard bore 3.8 blocks seems to be low at least that I can find without serially buying blocks. 225's in need of a freshening do come up more frequently though and with a 3.75in bore, that means that even an already 0.030in over engine is still game for a 3.800in bore. However how much strength am I loosing first in choosing a 225 vs. a 231 and secondly how much from boring it 0.050in over?

General Thoughts?

Thanks
 
CTX-SLPR said:
Hello All,

Continuing to work on my very slowly moving LSR project and the supply of standard bore 3.8 blocks seems to be low at least that I can find without serially buying blocks. 225's in need of a freshening do come up more frequently though and with a 3.75in bore, that means that even an already 0.030in over engine is still game for a 3.800in bore. However how much strength am I loosing first in choosing a 225 vs. a 231 and secondly how much from boring it 0.050in over?

General Thoughts?

Thanks
Click to expand...
Essentially the 225 and 231 blocks are the same strength wise. Additional strength over the 231 v6
comes from the 225's odd fire crankshaft and the bore spacing is centered over the rod throw. 225 v6 have a deck hight similar to the early even fire 231 v6 blocks and the cooling passages are different in the 225 v6 vs the later even fire 231 v6.
 
The 225 was bored .050 when Buick went to the 231 odd fire engine, so it will take the overbore. The limiting factor will be the heads, which have very small valves. The 225 also oils the rockers through the shaft. The 231 oils through the push rods. The 2,3,&4 cam bearings in the 225 were also smaller than the 231 making cam availability a problem. The early 231 odd fires were pretty strong if you can find one. Again, the heads are not great. I would go with an even fire 231. The parts availability is so much better. Get a copy of Pat Ganahl's V6 Performance book. I had an odd fire 231 with a 4 barrel intake and headers in my Toyota pickup for years. Replacing it with an even fire 231 V6 made a huge difference. I just sold that engine since I went to the 274 stroker engines a few years ago.
 
I have a 2.660 oddfire Moldex crank already for my 181cid destroker and will be running 8445 heads on top. Cam is an open question and if I need to modify the cam bearings to fit a more modern camshaft (solid roller for example) I'll have to think about that. I have 3.800in bore flat top pistons but they are a bit deep in the hole even with a healthy shave on the deck (9.526 vs. 9.547) and relies on 0.018in shim gaskets to make it work with a 0.035in piston to head clearance.

What does it take to put a later camshaft in the early odd fire blocks?

Is there a cooling passage mismatch with the earlier blocks running later heads? I didn't see any notes on TA about putting the "tall port" head on the oddfire block for the coolant, just the rocker oiling.

Thanks
 
8445 heads will only work on 1977 and newer blocks according to Pat Ganahl's book. The crank you have should fit 77 and up blocks if the main bearings are the same size. You would need rods to match the crank pin size and they would have to have zero offset. An odd fire cam can be custom ground, but I doubt there are any cast cores left. It may have to be billet, but the chain and gears are available. A late model N/A block may be the best choice. There are still plenty of those around and lots of parts like 14 bolt girdles, ported heads, and intakes like the KB.
 
Correct, the odd fire early blocks coolant passages are not in line with the later 8445 heads.
 
Well that pretty much eliminates one of those as a foundation. Guess it's dealing with finding a stock bore 231.
 
If you find a standard bore 231 block, will you be able to bore it and still stay within your cubic inch limit? I have used a .004 ceramic coating on standard bore piston skirts to take up clearance on standard bore blocks so they did not need to be bored. I was lucky enough to hone them straight and round and get the clearance right.
 
I will be able to bore it 0.030in over and stay in my limit (183.99cid) but it's skin of teeth close. I already have some marginally workable 3.800in bore pistons though hence the search for a matching standard bore block. Ceramic coating might be a way to account for a block that has some wear.
 
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