99bluefirebird

iTrader: (8)

So I am thinking I will have to change my short block soon, considering options mainly from TSP. What are the disadvantages to a 383 stroker LS1 instead of the 346? Is it just fuel mileage, or longevity, or torque sacrifice, or piston to valve clearance? Lets say this is comparing 383 stroker LS1 to 364 (larger bore) LS2.

99bluefirebird

iTrader: (8)

I know many people have both LS2's and 383 strokers that can help me out here...

Grimes

iTrader: (3)

In terms of why GM didn't do it, probably because at that point in time it would have been harder to hit fuel economy standards or emission standards. Now they have larger lsX's from the factory, so go figure.

gmguy4life

I agree. There is like three ways of meating those standards and make power; small engine with FI(ford) or large displacement with small cam conservitive tune(GM) or large displacement short stroke but sacrafice torque(Euro). just my .02

Stang's Bane

iTrader: (22)

Stroke does not necesarily equal torque. Displacement equals torque, whether it comes from bore or stroke.

One of the biggest, if not THE biggest is cost. GM has been using basically the same 3.622 stroke crank since 1997. It is a cast crank so it is very inexpensive compared to the cost of a forged piece. Look at the LS7, it has a 4" stroke and it has a forged crank. The extra stress placed on the crank from the increased stroke would make a forged piece necessary and that cost would not significantly drop no matter the amount of production. A larger bore block is a tooling cahnge and that is about it. The more engines they make, the less the amortized cost per engine is. JMHO

gmguy4life

True. I agree with your statement also about cost. In terms of equaly sized n/a motors with the same cam/tuning the one with the larger stroke usally have more torque. I was speaking more about how companys try to balance hp and emissions.
I think an oversquare motor has a greater impact on emissions, fuel econ compared to a square, near square,and undersquare motor aside from tuning and cam selection.

Old SStroker

Is it time to open that can of worms again?

Why would you use the same cam in the same displacement short stroke and long stroke engines? Why does the longer stroke engine of the same displacement make more torque?

gmguy4life

Man don't read to far into it. It was an example how more force on a rotating assembly makes more torque. You know what torque is don't you, it is a twisting force.
I did not disagree with the guy above, he was right. You are getting off subject .
Example just look at some Euro V8 and V10's and see how much more torque they make over a american V8(LS1/2) not that much sometimes less, we tend to have more stroke. They have short stroke high horsepower engines.

THE_PROFESSOR

This goes back to leverage. When the crank is at the horizontal positon, it is easy to see that the larger stroke crank will develop more torque from the conn rod. However, places more demands on crank, rods, block, due to more piston accelerations and more extreme angles.

All things being the same, a stroker is a torque machine, and a bore is a rpm/head flow engine. This is not conjecture. More bore means more effective valve area, which increases valve area flow by a squared factor.

It would certainly be advantageous to plan for a different engine characteristic with a different cam, perhaps a higher lift to overcome less valve area, with a lower duration to compliment the lower torque range. Or just get forged and force it to rev. BIG fun!!

For a 10% increase in displacement, plan on a more than 10% increase in torque (346 --> 383). Unless head/intake flow become a restriction.

As for efficiency, expect more airflow pumping losses, but an ability to run higher compression. Not sure how this balances out, certainly someone has plotted dozens of engines and found a trend..........

GM had to sit down quite early in the design process and decide bore/stroke values. They undoubtedly had this trend plot in front of them.

3.4camaro

iTrader: (1)

Cuz they have less displacement, that's why they make less torque.

THE_PROFESSOR

that hurts

mzoomora

iTrader: (36)

The LS1 is a longer stroked engine than the one it replaced. Old 5.7's were 4.00" bore by 3.48 stroke, LS1's are 3.90 x 3.62. Given the same displacement I would rather have a larger bore, but there are benefits for both.

2 main disadvantages to a stroker-
Higher piston speed for same rpm
Larger bores unshroud valves more (not really a disadvantage to a stroker, just a benefit of more bore)

This is an old argument that was beaten to death not to long ago.

THE_PROFESSOR

Velocities do jack. We are all right now hurtling thru space at around 60,000 feet per second. Fear not, your pistons will survive and your head will not lop off. Good thing you are flying in perfect synchronization with the objects around you, huh. It would suck to smash into that wall at a mere 6000 feet per second.

Mean piston speed is simply a representation in the hot rod industry to simplify what happens in between the stopping that occurs at every bottom and top dead center. What happens is called acceleration and deceleration. And of course from Newton's first law, Force = Mass X Acceleration, forces are what are required to bring about these accelerations. Forces create stresses, deflections, and eventually failures. Catastrophic is usually the case.

With a larger stroke comes more accelerations, as the piston must generate a greater displacement at a fixed amount of time. Yes, the result is a greater average piston speed.

jfman

iTrader: (6)

After looking at a stroker crank next to a stock crank I cant help but to notice that because of the larger stroke. The bottom of the rod has to push in a less direct way at the begining of the compression stroke. I'm not familiar with technical terms but the angle from the rod to the bore of the cylinder is greater than with a stock stroke.

Think if you had to manualy compress a piston on the compression stroke with a handheld rod (lol). You would want that rod to be as parallel to the bore as possible to make it easier to compress. The higher the angle from the rod to the direction of the bore, the harder it is to push. A bigger stroke make that angle greater.

THE_PROFESSOR

jfman, you are correct!! As that angle increases, more and more energy is dissipated in the form of piston scrub against the cylinder wall. We can find this proportion of force lost with simple vectoring, using sine and cosine with respect to the angles. This is why the rod must be longer as the stroke is increased. As the two are lengthened, the position of the piston pin relative to the rings changes, forcing the pin into the area where the rings are, higher and higher up the body of the piston. The piston effectively has to absorb these increases in length, as the piston cannot simply pop out of the hole.

There is a finite boundary where this can go. However, if the deck height is increased this allows more stroke, the accompanying longer rods, and heightened torque and displacement. I am personally for this option, with the valve covers sticking out of the hood. I am currently lobbying GM to create this block, alas they are not listening. Join me, together we have a stronger voice!

4" is apparently as far as GM will go with the LS blocks. 4.125 is available aftermarket, but we can easily see that reliability could very well be sacrificed.

jfman

iTrader: (6)

If you raise the deck height then the intake manifolds wont fit anymore because the heads will be furtehr apart lol ! Of course GM can figure that out I'm sure.

Now I'm thinking one day they may retire the old BBC based 8.1 and come out with all aluminum new gen big block

Websy21

iTrader: (34)

That would be awesome

Old SStroker

Prof, that's Newton's Second law. I'm old enough that Isaac taught our Physics 101 class. He had a thing for getting numbers correct.



Listen to the man.


I told you it was a can of worms...and much misinformation. Have at it!

THE_PROFESSOR

Touche', Stroker , u got it.

i guess everything i said is misinformation, then?? After all it is that simple, right??

mzoomora

iTrader: (36)

Piston speed affects durability of an engine and increases wear. The original question was why hasnt GM done it, and that is a good reason. You can say it doesnt mean jack, but when they are warrantying engines it matters to them.