Strokers

[thatchevyguy]

I've been told by a few people that it is better to build a stroker motor out of a 350 2-bolt main than it is out of a 350 4- bolt main because the 4- bolt main is made for pulling which is low rpm, i would like a few other opinions

[mr_mushroom]

i've heard that before but i've also heard that it doesn't make a difference.
since i don't have a stroker, i can't say.
i've only got .10 over on my 350.
what are you putting it in?

[GreyGoose006]

well a stroker will have a lower rev limit due to having a longer stroke, so it makes sense to me to put it into the 4 bolt enginine so that it will be as robust as possible.

you probably wont be revving it much past 4.5K anyway, and if you do, you should either put lightweight pistons and rods in it, or expect something to blow apart catastrophically.

just my

[maxwedge]

Wow, a 383 built right can run 7500 rpms if you set it up for that. What does the 4 bolt have to do with pulling low rpms other than a stronger lower end, the engine doesn't know if it is a 2 or 4 bolt, relative to torque out put.

[GreyGoose006]

well most engines can be taken up to rediculous rpms, but what i was saying is that due to the torque biased nature of a 383, and its relatively lower power than its displacement would suggest, most are used in trucks or cars that do not get driven in such a way to rev the engine as high as possible.
thats all

and i would still suggest using a 4 bolt main engine if possible because of the higher average piston speed that will be seen in a longer stroke engine

[2.2 Straight six]

if you're building an engine for 400hp upwards, you should go with a 4-bolt main engine. purely because it's stronger. many people who have 2-bolt main engines and want lots of power have a machine shop drill and tap holes and fit new caps to convert their engine from 2-bolt to 4-bolt. it's all about strength.

[thatchevyguy]

first of all grey goose a stroker is a high rpm motor and im gonna break 3000 rpm's sitting on the line with a trans-brake. and i'll hit 2nd at about 6200
this motor is for nothing but the strip, which is mostly what strokers are built for, so i have no earthly idea why you would say i wouldnt be running over 4500.

[thatchevyguy]

And max wedge you sound like you actually know somthing. See i've been setting this 1972 datsun 240z up for the strip, well i just finished hulling everything out (interior, engine, trans. etc.), and building my motor mounts i got it down to just a body and frame.i picked up a 400 turbo the other day and its getting gone through right now , im putting a 3500 stall in and im changing the valve bodies for harder shifts and more rpm, i'm supposed to pick up some 4:11 gears tomorrow, then im going to weld up the spider gears for pisitraction, but from everyone i talk to they say the rearends will hold up for awhile till i get enough money to narrow a rearend, and tub it, but i'm going to clip my fenders a bit to get some good size slicks under there, or atleast the biggest ones i can fit under there. But i'm still not to sure about what block i should build, i mean i have a 2 bolt and a 4, i guess i'm just going to have to call a tech line

[GreyGoose006]

sorry. i appologise for the confusion.
i was under the assumption that it was being used as a street motor.
most strokers i have seen are for street use

if you want the strongest engine possible, get a 2 bolt and have it machined for splayed caps.
that would be the smartest idea if you plan on running higher rpms.

strokers are not ideally suited for high rpm operation
have you ever wondered why high rpm motors tend to have low torque and high torque motors tend to not rev too high?
torque is directly related to stroke.
a longer stroke is like using a cheater bar on a wrench or a lower gear.
it will give you more torque, but at the expense of speed.
as you increase the stroke, the maximum rpms must get lower or else the piston speed will go out of control.

say your engine runs a certain piston speed at its maximum rpm.
if you increase the distance that the piston must travel, but dont give it any more time to do so, the piston speed will go up.
if your motor is limited by piston speed in its non-stroked form, then you will have no choice but to use a lower max rpm to keep the same piston speed.
you can get around this by using high quality parts, and keeping weight to a minimum by using lightweight pistons and rods.

if this engine is to be used solely as a 1/4 mile monster, then you can afford to rev the piss out of it and just rebuild it every so often when it needs it.
just make sure that your bottom end is up to the task.

if you are building an all out motor, go the extra step and use splayed caps.

[UncleBob]

Originally Posted by GreyGoose006

strokers are not ideally suited for high rpm operation
have you ever wondered why high rpm motors tend to have low torque and high torque motors tend to not rev too high?

I guess it depends on the definition of "ideal". You can take any engine and with proper modifications run them waaaaaay higher RPM than stock. Some are more forgiving than others. Drag race engines, its not uncommon to see engines with 8000+ fpm average piston speed, which is double most stock engines, and they can live like that for seasons of racing.

The main objective of a stroker engine, really, is to increase engine size. Sometimes its more advantagous than bore, such as when sleeve thickness is too thin for higher output with a larger bore. Basically, you expand the variable that is more effective for your end result.

Even if you do limit the RPM between a stroked motor and a non-stroked motor, you will still make more power, in theory with the stroked motor, so a race engine or street engine, can both see very worthwhile reasons to use that approach.

anyway....splayed caps, definitely. Or go with an LS2 if you want a lot lighter engine with a much stronger engineered bottom end. But as always, cost is an issue

[kevinthenerd]

Originally Posted by thatchevyguy

first of all grey goose a stroker is a high rpm motor and im gonna break 3000 rpm's sitting on the line with a trans-brake. and i'll hit 2nd at about 6200
this motor is for nothing but the strip, which is mostly what strokers are built for, so i have no earthly idea why you would say i wouldnt be running over 4500.

A long stroke results in a higher mean piston speed. If you're racing and you're limited to displacement, a big bore with a short stroke will win every time. This will give you more rpms for a given piston speed. The mean piston speed (2*L*N) is the main thing that affects things like motor longevity and cam setup. (Look up the Jones equations.)

[kevinthenerd]

Originally Posted by GreyGoose006

well most engines can be taken up to rediculous rpms, but what i was saying is that due to the torque biased nature of a 383, and its relatively lower power than its displacement would suggest, most are used in trucks or cars that do not get driven in such a way to rev the engine as high as possible.
thats all

and i would still suggest using a 4 bolt main engine if possible because of the higher average piston speed that will be seen in a longer stroke engine

You can raise the power band of any motor by getting more agressive cams and opening up the ports. The motor operates most efficiently at a particular port velocity. That port velocity is achieved earlier with small stock ports.

[kevinthenerd]

Originally Posted by GreyGoose006

if you want the strongest engine possible, get a 2 bolt and have it machined for splayed caps.
that would be the smartest idea if you plan on running higher rpms.

The 2-bolt mains are thicker than 4-bolt mains. Splaying the end caps requires the bolts to break in shear before anything moves. This means that your careful measurements of main bearing clearance won't change during the operation of the motor, which is very important considering the crank is going to want to twist and warp every which way when the engine is under full load.

[kevinthenerd]

Originally Posted by UncleBob

I guess it depends on the definition of "ideal". You can take any engine and with proper modifications run them waaaaaay higher RPM than stock. Some are more forgiving than others. Drag race engines, its not uncommon to see engines with 8000+ fpm average piston speed, which is double most stock engines, and they can live like that for seasons of racing.

The main objective of a stroker engine, really, is to increase engine size. Sometimes its more advantagous than bore, such as when sleeve thickness is too thin for higher output with a larger bore. Basically, you expand the variable that is more effective for your end result.

Even if you do limit the RPM between a stroked motor and a non-stroked motor, you will still make more power, in theory with the stroked motor, so a race engine or street engine, can both see very worthwhile reasons to use that approach.

anyway....splayed caps, definitely. Or go with an LS2 if you want a lot lighter engine with a much stronger engineered bottom end. But as always, cost is an issue

Limiting the RPM and displacement, your bore to stroke ratio makes little difference for the actual power developed. There are some considerations, though. In a big bore motor, your mean piston speed is lower and your rod to stroke ratio is usually longer, meaning that the maximum piston acceleration is less (for less force on the journal bearings and other components.) The big bore motor will lose more in heat transfer than a square motor because of the increased combustion chamber surface area. (Ceramic coated pistons and thin compression rings can help with this.) With the higher rod-to-stroke ratio in a big bore motor, the piston will accelerate more rapidly from TDC, resulting in a slightly improved intake charge initially. The higher mean piston speed of a stroker will require more agressive cams.

With that being said... if you're not limited in your displacement and you're already all bored out, by all means stroking is a great way to go. If your piston can handle more speed than your valve train, then stroking may be your only way to get more out of your piston speed.

[GreyGoose006]

[quote=kevinthenerd]A long stroke results in a higher mean piston speed. If you're racing and you're limited to displacement, a big bore with a short stroke will win every time. This will give you more rpms for a given piston speed. The mean piston speed (2*L*N) is the main thing that affects things like motor longevity and cam setup. (Look up the Jones equations.)[\quote]
exactly
just look at the chevy 302
4 inch bore
3 inch stroke

biggest bore of any sbc (excepting the 400, which is not a true sbc. i know i'll get flamed for saying this, but its true)
it also has the one of the smallest strokes

in "stock" form, it will rev past 9K.
that was using 1970s technology