'70_Duster_340
Well-Known Member
What exactly constitutes a "stroked" engine ??? Please explain in dumbass laymans terms ??
Thanks,
Kenny
Thanks,
Kenny
Ignorant question ???
- Thread starter '70_Duster_340
- Start date
-
demon seed
The Original Demon Seed
Well what I've always understood it to mean is when you take a stock engine with stock internals and change the crankshaft, or offset grind the rod journals, to give you a different stroke usually more. Like going from a 3.75" stroke to a 4.00" therefore increasing the overall displacement of the engine. At the same time you change the con rods to a different than stock length. Your overhaul displacement target will decide which crank stroke and rod length combo is used.
Terry
Longgone
John/68 Barracuda & Dart
No question is ignorant if you don`t have the answer. Demonseed did a good job at answering this one but I`ll try to add a little something. Stroking an engine involves changing the throw of the crankshaft in order to increase or decrease engine displacement. Crankshaft journal size, connecting rods, wrist pin position, and pistons can all be altered to achieve a certain stroke. Just as boring an engine makes the cylinder larger, stroking an engine makes the usable potential of a cylinder longer (or shorter).
The stroke of an engine is the measured distance that the piston travels from T.D.C. to B.D.C. This distance is part of the formula for determineing the total displacement of the engine. Here is that formula.
BORE x BORE x .7854 x STROKE x NUMBER OF CYLINDERS = Cubic Inch Displacement.
So if you increase the stroke it will make the engine's displacement larger.
The stroke of the crankshaft is determined by how far from the centerline (or main bearings) the con rod throw is. Let say you have a 4" stroke, then you con rod would be 2" from center.
A longer stroke typicly will give more low end torque. Think of a longer stroke as having more leverage. Like useing a longer breaker bar to loosen or tighten something rather then a standard ratchet handle.
On the other hand if you were to "de-stroke" your engine (shorten the piston travel) you will decrease the engine's displacement.
Ted
BORE x BORE x .7854 x STROKE x NUMBER OF CYLINDERS = Cubic Inch Displacement.
So if you increase the stroke it will make the engine's displacement larger.
The stroke of the crankshaft is determined by how far from the centerline (or main bearings) the con rod throw is. Let say you have a 4" stroke, then you con rod would be 2" from center.
A longer stroke typicly will give more low end torque. Think of a longer stroke as having more leverage. Like useing a longer breaker bar to loosen or tighten something rather then a standard ratchet handle.
On the other hand if you were to "de-stroke" your engine (shorten the piston travel) you will decrease the engine's displacement.
Ted
In some classes of racing your only allowed a certain max cubic inches so some will take a larger CU engine put a shorter than stock stroke crank to end up with a smaller displacement engine. Another reason is to achieve a large bore short stroke motor to improve rod ratio.
demon seed
The Original Demon Seed
Yup, back in 1970 Chrylser "destroked" the 340 to 303 (I think) so they could compete in the Trans Am racing circuit with the challenger T/A and cuda AAR.
Mopar318Guy
bear jew
stroked means goin to a bigger crank. with a 318 the stroke is 3.31. some people put in 360's 3.58 inch crank. or some just go for an aftermarker 4 inch crank to make a 384. just means the piston travels farther up and down i nthe cylinder. more torque. not as high of an rpm is reachable
moper
Well-Known Member
They pretty much covered all of it. I'll add...
in general, a builder will increase the stroke to lower the rpm of peak torque and/or power, and remove stroke to move the rpm of peak up. The reason is each cylinder makes "X" amount of power in one power stroke. The more power strokes in the same time you can have, the more power is transfered to the tires. If your sanctioning body or available parts don't allow more power in that one power event, by revving the available displacement faster you will make more power. This is the reason Cup cars run at 8K-9K+ now. At 350cid limit, a V8 at 7000 rpm has 56000 power events in a minute. Say, if each event is 88hp(based off a total of 700hp) thats 4,900,000 hp in a minute. If that same 700hp is at 8800rpm, that's 70,400 power events per minute, or 6,195,200 hp in that same minute, or about 20% more power along the straightaway to the tires from that same 700hp 350cid engine. Shorter strokes are more stable, less internal friction, and able to be fed with available head/intake packages(in regard to V 8s). So de-stroking makes sense in a lot of cases if you can get the parts to keep it together.
in general, a builder will increase the stroke to lower the rpm of peak torque and/or power, and remove stroke to move the rpm of peak up. The reason is each cylinder makes "X" amount of power in one power stroke. The more power strokes in the same time you can have, the more power is transfered to the tires. If your sanctioning body or available parts don't allow more power in that one power event, by revving the available displacement faster you will make more power. This is the reason Cup cars run at 8K-9K+ now. At 350cid limit, a V8 at 7000 rpm has 56000 power events in a minute. Say, if each event is 88hp(based off a total of 700hp) thats 4,900,000 hp in a minute. If that same 700hp is at 8800rpm, that's 70,400 power events per minute, or 6,195,200 hp in that same minute, or about 20% more power along the straightaway to the tires from that same 700hp 350cid engine. Shorter strokes are more stable, less internal friction, and able to be fed with available head/intake packages(in regard to V 8s). So de-stroking makes sense in a lot of cases if you can get the parts to keep it together.
Petzschler
→Welcome backâ†
The CRAZIEST car i ever had the pleasure of driving was a destroked 340 (2.75" stroke i think) AAR Cuda back in the mid 80s.
That thing would turn 9500+rpm without hesitation! below 5000rpm there was nothing, but holy crap the top end pull was
mindblowing. I think that engine had one of the first (prototype?) solid roller cams available for the LA.
Kenny, Great answers here. I can't really add to it. It is covered. Maybe a little to well for a basic laymen term explanation, but it is covered.
Certain racing classes will require a max CID. As stated above. But also in some drag racing classes, you'll get a weight penalty for running a big block or running , oh, lets just say a 360. If you look at the class closely, there is no weight penalty for running a 355 cid engine. De-stroking the engine clears you of any weight penalty. Further destroking to a smaller size can give you a weight break. Or just simply running a 318 for that matter can allow you to run a lighter car.
If the max cid for a class is 350 cubes, theres sevearl ways to go about getting that cid. Grab a simple Desk Top Dyno program and play around with the stroke settings for any bore size. Then fill in the rest of the basic perameters of the program to complete the fields for the dyno simulation.
Don't just watch how the power curves rise and fall, but where they do.
This will help you understand how a particual engine set up works and why some people will build an engine in a certain way for a certain purpose.
It'll probably open up a can or two of questions for you, but that'll be a good thing.
Certain racing classes will require a max CID. As stated above. But also in some drag racing classes, you'll get a weight penalty for running a big block or running , oh, lets just say a 360. If you look at the class closely, there is no weight penalty for running a 355 cid engine. De-stroking the engine clears you of any weight penalty. Further destroking to a smaller size can give you a weight break. Or just simply running a 318 for that matter can allow you to run a lighter car.
If the max cid for a class is 350 cubes, theres sevearl ways to go about getting that cid. Grab a simple Desk Top Dyno program and play around with the stroke settings for any bore size. Then fill in the rest of the basic perameters of the program to complete the fields for the dyno simulation.
Don't just watch how the power curves rise and fall, but where they do.
This will help you understand how a particual engine set up works and why some people will build an engine in a certain way for a certain purpose.
It'll probably open up a can or two of questions for you, but that'll be a good thing.
clhyer
Well-Known Member
- Joined
- Feb 24, 2007
- Messages
- 3,734
- Reaction score
- 320
Kenny,
Thanks for asking the question! While I had a basic understanding of the "how" as far as increasing the stroke; I had never thought about the decreased stroke. Thanks to everyone that responded. No day is complete unless I've learned something and it was a fun lesson today...
C
Thanks for asking the question! While I had a basic understanding of the "how" as far as increasing the stroke; I had never thought about the decreased stroke. Thanks to everyone that responded. No day is complete unless I've learned something and it was a fun lesson today...
C
'70_Duster_340
Well-Known Member
Thanks guys, I have a much better understanding now ... Still a lot to digest, but I'm printing it out and leaving it in my favorite room, where I do most of my reading :read2:
Kenny
Kenny
moper
Well-Known Member
A friend runs a 302 chevy in a Nova. He drops the clutch at 6K, and shifts it at 8500. He could run anything, he loves the small engines and huge rpms.
Petzschler
→Welcome backâ†
I agree 1000%! i'm seriously considering putting the kibosh on the "Big" SmallBlock i was goin to build, and just
do stock cube W2 headed HIGH rpm screamer. nothing like raping a 454, 460, or 440 with a 100 cube smaller engine.
LOL Kind of been there done that and loved it. Though it is tuff on the engine constantly going "There", it was allways great leaving those poor full of themselfs bastards behind LMAO hard!!!!!!
Allways kill'em off the line. Once I get to my top end redline area, they would be comin up on me like a house on fire. But it was over by then.
Longgone
John/68 Barracuda & Dart
My brother`s got a Boss 302 and although the displacement is small the heads are gi-normous with intake ports the size of a big block Chevy. That car with it`s 411 gear and solid cam is one bad little ride and revs like an electric motor. Lol! You can really feel how well the car would perform in a Trans-Am type racing circuit.
-
