TECH-'56 Olds 324 to 346...cheap!!

I'm building a '56 Olds 324cu.in. for my '40 Ford.
I bored my block to 4" (.125 oversize).
I was fucking around with a couple of new pistons on the table and
made a strange discovery.One piston was for a '56 324 and the other one was for a '57 371cu.in. engine.
I pushed one wrist pin halfway out and slid it halfway into the other
piston to observe the known difference in stroke of the two engines.
To my surprise the deck height of both pistons was identical!
Seems like the only thing that would explain this mystery would be
that the '57 rods were actually shorter than the '54-56 324 rods.
I don't know that answer yet but I was able to put my 4" bored
324 together with '57 4" standard bore pistons and rings,which are
readily available and relatively cheap!
KEEP THE ROCKETS BLASTING!

 

i dont see how this would be possible?
the stroke on the 324 is 3.437 and the stroke on the 371 is 3.68

if they had the same bore? i m just screwing my head up the more i think of this. if this is so and the rods are shorter on the 371 then the block must be shorter, which might make sense because of the need for spacers to make intakes fit. i just cant get my head around this must be the beer. ill tell you what im gonn go to the garage and grab a 60 over 324 piston and measure it, i dont know the compresion but its a flat top. ill measure from center of wrist pin to top. cory

 

Sounds crazy don't it?
However,I have put the crank and pistons in to try my theory.
With '56 crank and rods,and '57 std. pistons,they just come flush
at top dead center!

 

found this in the the tech section, if this is so the rods are the same length and this is getting huh.

Cranks+Rods The 1949-1956 almost same ( different
bolt size for flywheel and damper). 1957-1958 ¼ inch stroke, larger mains, rods
narrower on crank, external balance. 1959-1964 larger mains and rods longer.
The 57 crank (mains turned down) with 57 rods will fit 49-56 engine for ¼
stroke. Can do the same with 59-64 crank with offset grind of rod area for more
stroke and put into 57 engine.

 

I saw that post the other day about some guy that had compiled alot of early Olds info.
98% of it was correct to my knowlege(?) but I did see 2 or 3 things
stated there that I recognized as being inaccurate.

 

i just went and measured some of my 324 pistons and they measured 1.96 to 1.98 from wrist pin center to the top of piston. Do you have any 371 pistons you can measure. this was not super accurate measurement just a eyeball. cory and i dont know the compresion, i do know there is a differance in the heads on the 56 and 57 the 57s have bigger chambers which might mean the piston comes out of the block to make the difference. remember im a novice not a expert at all but if this is true this would be great even better for me if this resulted in like a 7 to 8 compresion ratio for my next blown olds build. cory

 

Top of 324 piston to center of pin =1.875-1.878
Top of 371 piston to center of pin =1.895-1.898
Deck is .25 higher on 371,,rod length is the same at 6.625
371 rods are around .94 in width --324 are close to 1.0
You will gain a tad of compression by using 371 pistons

 

hhmmmm........

 

this makes me wonder if the oldstock jahns pistons i used were 371 pistons. they were a standard 4" flat top. this is great information i dont see why anyone hasnt brought this up before. Don im glad you chimed in and answered all the questions. hey seymore ive got a 346 olds in the forty getting ready to drop a dual 4 on it and put a st10 behind it. cory

 

When I was having my 324 assy. balanced last month
by a famous longtime balancer in north Texas(the
famous Wayne Calvert in Denton,TX.)I told him what
I was doing with the '57 pistons in the '56 block,and
he said he discovered they would work back in the
60's and had built one just like it!
He passed on something else that I didn't know.He
said that a certain year Chry. hemi rods can be used
to replace the early Olds rods,and they are lighter.
He couldn't remember what year rods...too long ago.
BTW I am aka RocketMan.
MickeyD

 

Yes, Oldsmobile made it easy on hot rodders--you can bore a 303 .125 and use standard 324 pistons, too. If only they hadn't changed the camshaft and lifter diameter........

 

I notice that you are in Arlington.I'm in McKinney.
Are you into early rocket engines?
That's kind of a rhetorical question I guess.
What kind of cars are you building/driving?
MickeyD

 

Yes 331 and 354 rods can be used , not as beefy as olds , but you can lighten olds rods without giving up any strength.

 

This thread couldn't of come at a better time for me. I'm in the midst of pulling my '54 324 apart and I've been looking into piston options. If this is the case with the 371 pistons, I may plug those in my '56 motor as well.

 

Regarding boring the 303's and 324's; I talked to
Joe Mondello ("...there is none higher!!") with the
question "will a .125 overbore lead to overheating on
a street rod engine?".
He saya "no problem..it will still have enough cyl.
wall thickness left for a .030 bore again for another
rebuild in the future.
FYI,I just had my '56 cam core reground by Schneider Cams in San Diego.
$100 for a regrind or $200 for a new one.
Great work and about a 2 day turnaround.
MickeyD

 

Moderators-- is it possible to add this thread as an addendum to the Olds Rocket tech thread?

 

MikeyD.... I'm knee deep in Olds motors here... 12? I think. I've got too many cars at the moment, but the Olds powered ones would be my pickup & a '50 Olds coupe

 

my 51 303 block is at 4" and it never goes above 170 deg. im thinking that i have the 371 pistons in it. they were old stock so im not for sure.

 

303 can be bored out to use 371 pistons? rad. i'm helping a friend build a 303 and we're trying to come up with a game plan for building a bad ass 303. this post rules

 

any pics Cory?? I saw your '40 in that other thread....

you punched it to 4" no problems? everyone seems to be weary about punching the 303s to 4" but hell, I'll try one next go 'round!

 

i didnt have a choice really, the old hot rod motor already had 60 over 324 pistons in it. from what i heard from the old timers and those here on the hamb is that the 324 was the same block as the 303 so i figured if it would work on that then why not try it as for running hot my motor never went above 170 all sumer till about two weeks ago when one day she shot through the roof i didnt know what the hell happened pulled the new rebuilt water pump and the propeller spun on the shaft spot welded it up good to go. fusuick part. i bought my pistons of a old guys shelf in california, jahns, been setting there for years he said, so i thought they were a custom set but i bet there 371 piston they fit so i didnt do any measuring. im pulling the 10 heads this winter to port polish and match em, so ill pay a little more attention to where there at. gonna try to use dons info. ive got my offy dual four which is gonna replace the 3 97's. cory

now what im wondering is if i can get a new set of 4" 371 pistons and cut them down to 7.5, 8 to 1 compression for my 671 blown 303 ive got setting here, and are the stock rods good enough for the blower.

 

Bones, the stock rods will work if you prep them by using good bolts, ARP-mopar, shot peen and resize big ends. Run at least .012 side clearance on them. Get forged pistons, cut .03 off the top but leave them at stock height under the squish area of the head. Stock cast pistons will crack from wrist pin into the skirt under boost at anything over 8 to 10 pounds. Use a .037 head gasket-coat with alum paint , install wet. Get heads to cc out to around 72-74 cc--run dist locked at about 32 to start and play later.

 

I didn't know about an "Olds Rocket tech thread".How do I find that?
I'm new here and kinda computer dumb.

 

here's the Olds Tech thread...

and here's the Tech archive....

 

Thanks for the tip Seymour!

 

nice posts!

someone should compile all good rocket info into one clear post with tabells etc, ALOT of awesome olds info around here on hamb, to much to find it here and there... if i get some time over i'll dig into it

 

God I love it when DON WOW posts wisdom for us. I am looking at starting the assembly of mine this spring when I get home.
Eric

 

btt
Here's a tidbit that '49-56 Olds engine builders may
need to know;
Before you send your bare block to the machine shop for cleaning,be sure to take the 2 front oil
gallery plugs out and keep them for the rebuilding.
The one that goes on the passenger side has a small
hole (~ 1/16") drilled in it to shoot oil on the timing
chain.
The youngsters in the shops nowdays will send it
back to you with Chevy style solid plugs in it and the
chain won't get as much oil as it needs.
Try to find an origional if the loose them for you!
MickeyD

 

YES! Pull all your plugs because the machine shop may not return them!!!

On a side note, does anyone here know if the 303-324 front oil galley plugs (behind timing chain) are the same as 303-455 Olds???? They look the same at first glance, but I've never verified if they are exactly the same or not.


Don Wow-- Can you verify if the rod bolts for 303-324 should be 318-360 Mopar or 361-440 Mopar? I've forgotten. Also, can those be used for '57-8 371 Olds rods?

 

Nate, the 49 to 56 rods with the 49 rifle drilled being odd man out are the same. All will take 354-392-440 rod bolts, 57 58 371 are just a hair smaller in width on the big end, around .06 , other than taking a different bearing you can can use the same bolts in the 371 as you can in the 303 and 324. If the early rods are ground for side clearance they can used in a 371 because they are damn near the same. I never checked the galley plugs -----yet----- but i've got all ,303 to 394 and 260 to 455, and everthing in between. Would'nt surprise me if they match up.