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Old 12-24-2004, 01:00 PM   #1
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Default The different 1965 421 engines

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
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Old 12-27-2004, 10:20 PM   #2
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Old 01-30-2005, 12:03 AM   #3
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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
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Old 01-30-2005, 10:54 PM   #4
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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.
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Old 02-16-2005, 10:15 AM   #5
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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
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