Choosing the right stroke for a 340

-
340inabbody

340inabbody

FABO Gold Member
FABO Gold Member
Joined
Jan 31, 2018
Messages
807
Reaction score
400
Location
Arizona
So it looks like there are some options on the length of stroke one can get in a particular crank rod piston combination. From what I gather.....the longer the stroke the more displacement BUT also the increased risk of interference on the assembly. What are the trade offs to be made? What is your experience with the amount of stroke you have used and recommend etc. Looking for a 340 application in particular.

Lets talk stroke....
 
How much cylinder head do you have vs how much power you would like to make vs how many rpms you would like to turn....gear and transmission.

If you have good heads ...then maybe the transmission and gear is the decider.
Lower cruise rpm, stroke it.
 
Stock stroke is great for factory iron X or J type heads if you want it to keep pulling at high rpm. If you're running aftermarket heads, I really like the 3.58 inch stroke, for 368 to 379 cubic inches depending on bore size.
 
What about de-stroking to 305 and revving to 8-9000 RPM
 
destroking requires a much...much heavier piston....not good for revving....
 
340inabbody said:
So it looks like there are some options on the length of stroke one can get in a particular crank rod piston combination. From what I gather.....the longer the stroke the more displacement BUT also the increased risk of interference on the assembly. What are the trade offs to be made? What is your experience with the amount of stroke you have used and recommend etc. Looking for a 340 application in particular.

Lets talk stroke....
Click to expand...
The popular 4.00 stroke has zero issues with interference except with a stock style connecting rod at the bottom of the cylinders. This is also the case with other stroker kits that have exceeded the normal 4.00 stroke.

The rod is ether not to use the OE style connecting rod and/or grind the bottom of the cylinders for clearance for the connecting rods. This grinding is normal and does not cause any issues.

The ability of an engine to “Rev” is not limited to the size of the stroke but more so the thickness of your wallet since there are 500 CID pro stock engines with a greater size stroke and larger piston reving well past 8500 rpm.
 
Yeah, the 2.9 inch stroke used in the trans am engine would have required some boat anchor pistons back in 1970. Ross and CP can make some fairly light pistons for such a setup now, but I don't see it being a good option unless there was a 9 inch deck height block available. I've always been more than impressed by the stock stroke in a 340 with X heads, though. Even in a heavy 1973 B body with 3.55 gears.
 
You can always increase the length of the connecting rod to offset some piston height.
 
When Chrysler got back into nascar, the motor developed into a 48 degree valve train.

they didn’t do that for amusement.

valvetrain stability is a large factor in 8-9K rpm motors and reliability and endurance.
 
340,
No substitute for cubic inches & stroke is one way to do it. As far as which heads to use....
If you used stock 340 heads, then a stroker will make about the same HP with those heads, but at a lower rpm. Torque will be higher though.
 
rumblefish360 said:
The popular 4.00 stroke has zero issues with interference except with a stock style connecting rod at the bottom of the cylinders. This is also the case with other stroker kits that have exceeded the normal 4.00 stroke.

The rod is ether not to use the OE style connecting rod and/or grind the bottom of the cylinders for clearance for the connecting rods. This grinding is normal and does not cause any issues.

The ability of an engine to “Rev” is not limited to the size of the stroke but more so the thickness of your wallet since there are 500 CID pro stock engines with a greater size stroke and larger piston reving well past 8500 rpm.
Click to expand...


Not exactly. A Pro Stock engine has a bore that ranges from 4.600 to almost 4.700 and the stroke is adjusted for the size of the bore. So...with a 4.600 bore the stroke will be right at 3.75. If you end up at a 4.700 bore you’ll be at a 3.600 stroke to stay under 500 inches. So for what they are, the Pro Stock engine uses a very short stroke and a big bore.
 
Garrett Ellison said:
Stock stroke is great for factory iron X or J type heads if you want it to keep pulling at high rpm. If you're running aftermarket heads, I really like the 3.58 inch stroke, for 368 to 379 cubic inches depending on bore size.
Click to expand...

Those are nice combos, but budget wise for a street build I would just build a 360 rather than drop the coin for those.
 
Garrett Ellison said:
Stock stroke is great for factory iron X or J type heads if you want it to keep pulling at high rpm. If you're running aftermarket heads, I really like the 3.58 inch stroke, for 368 to 379 cubic inches depending on bore size.
Click to expand...
Absolutely! But my thoughts are if you're going with a 3.58 stroke, then just start with a 360 and save yourself the cost of a stroker crank for the 340. In that case, a set of pistons and you're there. Even if you want a bigger bore than you feel comfortable with in the 360, sleeve it and go big (under $80 a hole locally).
Hmm... now I'm thinking of a 273 block sleeved to a 340 bore with a 360 crank with the mains turned down... and being able to just keep pointing out the "273" cast into the side of the block to all the 5.0 blue oval boys...
 
Last edited:
Rat Bastid said:
Not exactly. A Pro Stock engine has a bore that ranges from 4.600 to almost 4.700 and the stroke is adjusted for the size of the bore. So...with a 4.600 bore the stroke will be right at 3.75. If you end up at a 4.700 bore you’ll be at a 3.600 stroke to stay under 500 inches. So for what they are, the Pro Stock engine uses a very short stroke and a big bore.
Click to expand...
I stand corrected on the pro stock combination that makes up there displacement but will also say I have seen larger stroke engines rev very high.
 
rumblefish360 said:
I stand corrected on the pro stock combination that makes up there displacement but will also say I have seen larger stroke engines rev very high.
Click to expand...


That’s for sure. I remember when the 632 became all the rage. The lowly 572 was now the ***** little sister to the 632. And they mostly stayed under 6500. Now, 8500 is nothing for those things. Maybe higher because I haven’t done one in a while. Stroke length doesn’t always mean you’ll have a low rpm tractor engine. They will rpm.
 
70aarcuda said:
destroking requires a much...much heavier piston....not good for revving....
Click to expand...
3.20 stroke !

20211129_144337.jpg
 
You must log in or register to reply here.
-

Back
Top