why do people complain about over 4 inch strokes
08-14-2018, 05:49 PM
#1
why do people complain about over 4 inch strokes so people like to say that 4 inch is the maximum stroke on the gm blocks with shorter sleeves (basically everything but the ls7 and lsx i believe)......most people say 4.1" strokes pull it out the bottom too far......im not questioning that.....makes sense....
but then when people get blocks with longer sleeves, and then wanna run a 4.1" or more stroke, people then respond negatively and wanna talk down on that and get upset about pistons speeds.....ok valid point....im no engine guru but can understand why this could be an issue......
so why does no one bitch about going from the 3.622 stock strokes all the way up to a 4 inch stroke (approximately an 8.5% stroke increase) but many report piston speeds are to much when going from a 4" to a 4.1" (approximately a 2.25% stroke increase)?
im asking because im planning a build with a sleeved ls2 and wanna weigh all my options out.
but then when people get blocks with longer sleeves, and then wanna run a 4.1" or more stroke, people then respond negatively and wanna talk down on that and get upset about pistons speeds.....ok valid point....im no engine guru but can understand why this could be an issue......
so why does no one bitch about going from the 3.622 stock strokes all the way up to a 4 inch stroke (approximately an 8.5% stroke increase) but many report piston speeds are to much when going from a 4" to a 4.1" (approximately a 2.25% stroke increase)?
im asking because im planning a build with a sleeved ls2 and wanna weigh all my options out.
08-14-2018, 06:38 PM
#2
TECH Senior Member
The ONLY concern besides those mentioned above would be the additional side thrust caused by the increased rod angle from the longer stroke, and I'm not sure that is even an issue.
08-14-2018, 07:00 PM
#4
TECH Veteran
Bottom dead center is the main reason complain. And out the LS engine family the iron 6.0 motors have the shortest sleeve from GM.
08-14-2018, 07:47 PM
#5
TECH Senior Member
It has to do with rod-length to stroke ratio. The longer the stroke, the longer the rod needed to avoid excess side thrust. I know on some SBC's back in the day were some ridiculous strokes where the side thrust became an issue. Not sure that same issue would exist with the more sane strokes being used on LS's.
08-14-2018, 08:30 PM
#7
Lots of Posts = Lots of Internet Wizdum
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08-14-2018, 08:41 PM
#8
see this is one of my examples......im sure the piston speed difference is huge going from a 3.62 to a 4.00 but nobody bitches.....then u have this guy defying what everyone says u shouldn't do and he's happy......just doesn't make sense to me
08-14-2018, 08:42 PM
#9
it may be just one of those myths that someone said that 4.1 is no good for piston speeds but 4.0 is A ok.....and then everyone jumped on the wagon.....but im trying to avoid the sleeve length topic and work at debunking this speed thing
08-14-2018, 08:48 PM
#10
Like KCS basically said, its total BS. Its one of the biggest propagated myths out there. Piston design and rod design alone as well as bearing, block, and lubricants have changed so much its pretty much a non-issue.
427 ls3s are pretty outstanding.
427 ls3s are pretty outstanding.
08-14-2018, 09:23 PM
#11
Don't get too hung up on piston speed; it's not actually all that important. The fact of the matter is that the loads on a piston increase at a greater rate with RPM than with piston speed. For example, my 4.250" stroke engine has an average piston speed of 4250fpm at 6000RPM. Assuming the piston, pin, rings, and locks weigh 570g, I'm looking at a max load of about 3678lbs on the piston and pin as it crests TDC. Alternatively, a 3.267" stroke engine would need to turn about 7800RPM to reach the same 4250fpm, but the load on the piston and pin will be 4247lbs. Not to mention the oiling system and valvetrain are a lot happier at 6000 RPM versus 7800RPM.
08-14-2018, 09:36 PM
#13
08-14-2018, 11:11 PM
#15
TECH Resident
If you build it right you can do almost anything. If you build it wrong everything is a problem. Slapping a random Chinese kit into an aluminum block that's been bored to the edge of its life makes sideloading a major concern. Putting good internals into a strong and true block makes for a happy engine. That's why you're going to see people that "broke the rules" and paid for it while others went even more extreme and had no issues at all.
08-15-2018, 02:48 PM
#20
I haven’t gone over 4000RPM yet since I haven’t finished tuning it. I’ll be installing a new set of headers and true duals this weekend, then finish up street tuning.