Hey all,
In my relentless search to find my own perfect '65 Bonneville i have run into a small bump in the road.
I've always known that in 1965 the two different engine sizes available were the 389 and 421. HOWEVER, i thought the 421 only came in one flavor which would be the Tri-Power. However I recently ran accross a seller who claimed his untouched (i.e. same engine as always) '65 Bonneville has what he called, "the small 421." He claims it was NOT tri-powered (it had a single 4-barrel carb). I asked him about the different 421s and he said there was :
his 421 (4-barrelled)
a tri-power 421 (more power than his)
and another Tri-Powered 421 (this was the best engine available that year).

Does anyone have any more info on the various 421s available for 65? I knew the 421 tri-powered was the best for '65 but i didn't know there were various 421s available that year.

If anyone does know about these: What'* the difference between them? Does making it a three-carb set up instantly make this '4-barrel 421' a full-on Tri-Powered engine? And if so, what is the difference between the last 2 of the 3 421s i noted above?

I'm so intrigued by it all! Haaha
-Mike Diaz :P

Here ya go!

http://www.pontiacserver.com/aw65bonne.html

Thanks a question tho:

the article says "Power for these full-size models ranged from a 256-horsepower, 389-cid V8 with a two-barrel carb, up to a pair of three-deuce 421s packing 356 and 376 horsepower, respectively. "

But I'd like to know what the difference was between those 2 421s. Was it just the intake? One supporing 3 carbs, the other supporting just one?
The guy i talked to selling a 421 bonnevillle claimed his engine was the "small 421" with the single 4bbl carb. I wasn't sure if that means the block was different or what.. i'm sure one of our knowledgable peeps here knows!

Talk to me people,
mike diaz

There were three versions of the 421. A 338 HP w/ a single 4BBL and 356, & 376HP Tri Power(3x2BBL) carb set up. The intake is obvously different between the 4BBL and 3x2.
http://www.pontiacpower.net/intake01.html
The exhaust manifold was the same for each http://www.pontiacpower.net/exhaust01.html
But the 376HP 421 carried the moniker SD for Super Duty. It had a special cam and also inluded a forged crank, rods, and pistons. I'm sure the valves were bigger too.

I don't know what the reference to a "small" 421 means. To me, anything larger than 6.5 Liters (389 cu.in.) is a big block engine. They 421 was replaced by the 428 and then the 455 later on.

The base 421 had 10.5 compression and a AFB.
The 2 higher versions had 10.75 compression and Tri-Power among other things.
Anyone of them are real runners including the 389s.
In my opinion, I always thought the AFB ran the best.
These'* one for sale over at P-Y board, it looks real nice.

http://forums.performanceyears.com/e...1/m/2801063001