ok stroker guru's, gig this one

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mtandrews

mtandrews

beware the Ides of March
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alright we all know that doing the stroke on the 360 versus a 318 nets more cubes as well as torque (given all things equal) and is cheaper to boot. Yeah I know about the 340 but if you ain't got one and are willing to pay a small ransom for one, you have my blessing(s). 360's are plentiful but not as plentiful as 318's but I digress. My question is durability. I was told that a 408 is not a good choice if you are actually going to "drive" the car because the piston for the 408 is too short to actually rack up mileage on because the short piston wears out the cylinder wall faster than a taller piston. Now I don't know this by experience it's what is told to me by owners of the 408's and a few builders that I know. Well, what about the lowly 318 stroked to a 390ish size? Do they suffer the same piston rocking problem or do they have a taller piston from the pin to the dome? My way of thinking is if they do AND you plan on actually logging some miles on your mill maybe the added cost of a smaller mill might be the ticket. Anyone knows if the pin to deck height of 318 strokers have a taller/shorter/same pin to dome height?
 
Hmm.. Interested in learning this aswell.
 
all the LA engiens (318, 340, 360) share the same deck height...and the same rod length...

therefore...the piston compression height is going to be the same with the 4 inch stroke...which will shorten the skirt...so the only thing different between the 3 engines is going to be the bore size...and whether you have flat or dish piston.

4 inch stroker pistons will have a Compression height around 1.47 inches....that is the center of piston pin to top of piston...
 
mtandrews said:
alright we all know that doing the stroke on the 360 versus a 318 nets more cubes as well as torque (given all things equal) and is cheaper to boot. Yeah I know about the 340 but if you ain't got one and are willing to pay a small ransom for one, you have my blessing(s). 360's are plentiful but not as plentiful as 318's but I digress. My question is durability. I was told that a 408 is not a good choice if you are actually going to "drive" the car because the piston for the 408 is too short to actually rack up mileage on because the short piston wears out the cylinder wall faster than a taller piston. Now I don't know this by experience it's what is told to me by owners of the 408's and a few builders that I know. Well, what about the lowly 318 stroked to a 390ish size? Do they suffer the same piston rocking problem or do they have a taller piston from the pin to the dome? My way of thinking is if they do AND you plan on actually logging some miles on your mill maybe the added cost of a smaller mill might be the ticket. Anyone knows if the pin to deck height of 318 strokers have a taller/shorter/same pin to dome height?
Click to expand...

318 and 360 blocks are the same deck height, same rod length so if you use a 6.123 rod in both and a 4" crank in both you'll have identical piston C.H.
What your hearing about wear and driveability is bullshit. A stroker sb mopar had a C.H. of around 1.465...plenty!
Pistons only rock in the bores if you leave excessive piston to bore clearance. The 318 stroker will be down in HP by about 15 due to the smaller piston.
Good luck!
Brian
 
Because it doesn't cost much more to stroke a small block these days when rebuilding, it is a popular option for more power. Other than using a little more fuel are there any downsides? Has anyone with a stroker in a driver had problems with durability? I haven't seen any threads stating any.
 
ou812 said:
318 and 360 blocks are the same deck height, same rod length so if you use a 6.123 rod in both and a 4" crank in both you'll have identical piston C.H.
What your hearing about wear and driveability is bullshit. A stroker sb mopar had a C.H. of around 1.465...plenty!
Pistons only rock in the bores if you leave excessive piston to bore clearance. The 318 stroker will be down in HP by about 15 due to the smaller piston.
Good luck!
Brian
Click to expand...

:cheers: I agree.
Most engine builders are thinking about the Chevy which has a 9.025 deck height wit the same 4in stroke and a 6in rod C.H. is 1 inch which will have more problems with skirt problems.
 
I read somewhere that if you put 1/8" holes in the skirt area of the piston it will help to stop the piston from rocking. Has anyone else heard of doing this?
 
What do you consider "high mileage"? I know of a few that are passing 20K miles including years of intermittant strip time. You will not get 100K from them. But for most of us, something like 4-5 years of 3-5K miles a year is acceptable. They do loosen up faster. Usually because ring stability gets worse witht he short piston. But it's not a question of tons of oil use or big problems. They just wear faster. Even a performance built factory displacement suffers from faster wear if you're out hammering on it.
 
I would guess the type of piston will have a lot to do with how much rocking you will have in the piston and how quickly the engine wears. A forged piston will have more piston to wall clearance and rock more than a cast or cast hypereutectic piston that uses less clearance.

How helpful would piston skirt coating be (especially with a forged piston that has more clearance to start with)?
 
it's the side loading due to angularity [at 90*] from a poor rod ratio with the 4'' sb motors.

also pin location which keeps the piston more stable in the bore, mopar tall decks allow long rods to be used=good rod ratio, along with taller pistons/lower pin heights/pin bores.----ring stability
higher nickel blocks could fight this [cyl wear] better but the majority are not.

if you wanna rev the snot outta something build a motor with a 1.80 or better [1.80-2] rod ratio.
 
moper said:
What do you consider "high mileage"? I know of a few that are passing 20K miles including years of intermittant strip time. You will not get 100K from them. But for most of us, something like 4-5 years of 3-5K miles a year is acceptable. They do loosen up faster. Usually because ring stability gets worse witht he short piston. But it's not a question of tons of oil use or big problems. They just wear faster. Even a performance built factory displacement suffers from faster wear if you're out hammering on it.
Click to expand...
I drive my cars, I put about 15,000 miles on my 68 Fury III a year. It's not a stroker but it's a trouble free 383 with a stock rebuild. I have 3 318's laying around and 1 360.
 
Ok, so how many miles on the car this is going into? If you drove the 68 for 1/2 the time that's only 7500 miles...lol Also bear in mind that when the cars were new they werent expected to go for 100K miles. There are ways to gey more powre with std discpacements but again, they are not going to help you go 100K miles ..lol.
 
moper said:
Ok, so how many miles on the car this is going into? If you drove the 68 for 1/2 the time that's only 7500 miles...lol Also bear in mind that when the cars were new they werent expected to go for 100K miles. There are ways to gey more powre with std discpacements but again, they are not going to help you go 100K miles ..lol.
Click to expand...
My Duster is going to get all of the miles. My plan is to pull my Fury "off line" for some much needed modifications and bodywork which should take me 1 - 2 years (no powertrain work though, that's rock solid). On the mileage the manufacturers intended, I don't know.... Every Duster I've had I have put no less than 100,000 plus miles on them. My family put at least 80 miles a day on a 69 New Yorker for 10 years(!) with very little in the way of wrenching outside of normal wear and tear. We got lots of land to cover down here in Texas :-D. I think if you do real maintenance on them they'll give ya lots of trouble free miles... I understand there is a tradeoff in everything but I'm still checking every angle.
 
OK, so are you some sort of closet genius? I always learn from your threads and you ask questions that are almost always well founded. Just wanted to say thanks....
 
Here is a picture...shows the difference in skirt length and designs...

from the far left is a KB847 .....390 4.00 stroke ..3.94 bore disc stroked 318 1.47 CH
next is a KB107 360 3.58 stroke....4.03 bore flat top standard stroke 1.67 CH
next is a ProTru 408 4.00 stroke 4.03 bore disc stroked 360 1.47 CH
next is a wiseco 408 4.00 stroke..4.03 bore flat top...stroked 360 1.47 CH
 

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Well, if you are seriously concerned with long life, I would do the 360 and let the power fall where it may. Strokers are pushing away from factory design that had to keep things simple and minimize wear. Mopars did well because the blocks have good iron and the pistons were always really tall and stable, among other things. So I'd build a nice solid 360 and go have fun. If it's a good enough running 360 you can always throw a 408 pie tin on it...lol
 
OK I hope I dont get laughed at for this....I dont know alot about motors, my brother is the mechanic. In the past my daily driver was a honda civic si. From time to time I would check out some performance stuff in mags and online for imports. I remember for engines that were getting turbo'd they would( im not sure if this is the correct terminology) "sleeve" the cylinder bores to make them stronger....handle the added stress from the turbo. would that work or could it be an option with this? or am I totally on the wrong track? just throwing it out there, like i said, i dont know much about motors lol!
 
i rather build the 408 and put the 360 pie tin on it...LOL
 
The modern blocks are cast much different. The aftermarket supports them with special sleves and deck plates to make them stringer, or to go with bigger than factory bores. I sleeve blocks when the sonic test says one or two holes are thin even if there's no particular problem visible. The sleeve material is better and you end with a stronger more consistent bore. This is why NHRA mandates a max number of sleeves. Otherwise racers would be doing just that...
 
FANTOM;

I'm not totaly sure what the import crowd is doing. But if you read something about them sleaving the blocks cylinders, perhaps, there installing them for a huge jump in bore sizes.


In laymans terms, a sleave is the actual cylinder, that you view. The sleave replaces a worn out cylinder. Thicker the better for a stiffer cylinder wall that doesn't flex or flex's less under load (Wide Open Throttle)

I don't know what displacesments are available or what can be done to them. Our engines only have so much room to expand. If there engines can go from a 3.5 inch bore to a 4 inch bore with this trick, well, I'd say that is a huge jump in size for these guys.

What they can do with additional stroke, IDK?
 
Do the longer strokes have a longer dwell angle that affects how the piston loads the cylinder wall?
 
I've heard of people boring 318 blocks to 360 and even 340 bore sizes. That would save some on the cost of pistons, but the extra machining for that much bore might offset what you save on the pistons. You could do a stroker with a 3.79 (I think) stroke, which would bring the pin down some to cut down on rocking.
 
A 4" stroker has less dwell time due to higher piston speed.

MT here's something to ponder.

The SB Mopar stroker that uses a 4" stroke and 6.123" rods has a rod ratio of 1.53"

The 454 Chevy uses a 4" stroke and a 6.135" rod for a rod ratio of 1.53"

So it seems the stroked Mopar is in the same range of a stock 454 Chevy and the 454 lasted good.
 
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