black_knight

iTrader: (1)

I heard a few people mention that a long stroke had some specific disadvantages. They said that a 3.9 bore with a 4.125 stroke would have "unfavorable" piston speeds and rod ratios.

Would the same thing hold true for ANY bore with that stroke? Would a 4.01 bore, for example, have an easier time with that stroke? Or would it be the same?

Bo White

iTrader: (59)

Stay above a 1.55 rod/stroke ratio and personally I do not like strokes that are larger in size than the bore but that is just me.

black_knight

iTrader: (1)

How is rod/stroke calculated? Does bore size factor into it directly or indirectly?

Bo White

iTrader: (59)

Take the rod length and divide it by the stroke, like the short (stock)rod 400 SBC r/s ratio was 1.48 . The problem about strokers is the more stroke you run on a given block the lower the ratio will be because the block is only so tall.

gollum

iTrader: (1)

Which ever piston diameter that utilizes the longest piston skirt seems best? Which one that would be , I don't know. But I would not go over 4" stroke.

Midrange torque is awsome with simple 382 (3.8976 bore, 4.00" stroke) when cammed correctly. I have seen as much as 436 rwtq @4500 rpm with a mild 221/221 cam. Allowing use of 3.42-3.73 gear to keep piston speeds and rpm's low (shifting at 6000). And since your rpm's are lower, you will not need veryhigh valve spring pressures to controll valvetrain.

All this with stock ls1 throttle body, stock MAF, and ported heads.

grinder11

iTrader: (1)

I agree. I believe that one other thing to keep in mind here is the fact that not only is a longer skirt desirable here, but as you increase bore size, you are also increasing the bearing area, however slight, to more effectively deal with the longer strokes increased load on the piston. To exaggerate, if you had a 3 foot diameter piston, there is much more area to distribute the pressure of the less favorable rod/stroke ratio. It would lower the lb. per sq. inch that the longer stroke crank could load the skirt. I can remember several years ago a magazine ran a test on how effectively a piston transferred its heat to the cylinder wall. Most people are of the opinion that an engine will run hot and possibly seize if the piston/cylinder clearance is not "loose" enough. These tests proved just the opposite. The tighter the piston to cylinder wall clearance was, the cooler the engine ran due to less blowby and the aluminum piston being able to dissipate its heat more rapidly into the cooler cylinder wall as a result of the closer tolerance. Of course, this was true only up to a certain point, as eventually the clearance would not be sufficient enough to allow for expansion of the more rapidly expanding piston. Then....DISASTER!! This is especially true for a forged piston. Years ago, the rule of thumb was not to exceed 4,000 surface ft. per minute of piston travel. With modern technology and the vastly superior rings available, this figure has risen. But all things equal, side loading and a long stroke will mean more rapid cylinder/ring/piston wear. But there are those who would argue that with a well designed long stroke crank, optimized rod length, proper cam timing and lift, with quality pistons and rings. along with the right rear end gearing and transmission (The total combination), you wouldn't need a 7,000 R.P.M. motor.

black_knight

iTrader: (1)

So... Yes? Bigger bore does dissipate some of the issues with long stroke?

black_knight

iTrader: (1)

I guess I'm still confused. If a bigger bore helps, and a 4" stroke is ideal for a 3.8976 bore, then what would be an ideal stroker for a 4" bore?

Full-Force

iTrader: (11)

I dont like any of the strokes in our engine config myself. I would like to see bores in excess of 4" with strokes no more than 3.5. Longer stroke makes pistons move faster and moves the power lower in rpm's. I would like to turn a stock motor to 7 grand safely and you could if the stroke wasnt so long. I know there are some of us who do in fact turn stock bottoms over 7 but I still wouldnt like to. These 4" strokers are making for some hella torque motors I would think.

grinder11

iTrader: (1)

I am glad I am not the only one who feels the way you do! I totally agree with you on this, and am surprised that more have not voiced the same opinion. I truly love these engines, but wouldn't it have been nice if G.M. would have made them all at least 4.0 bores and offered a 4.125 bore option, grinding various length strokes along the way to arrive at the desired displacement? A 427 could be ours for half the price. I think they may have been shooting for a little more low end grunt and maybe midrange too so they slapped in a little longer stroke from the get go. I am also sure however, that they must have tried mucho combos in prototype and there has to be numerous reasons they arrived at the final figures they did. As far as the answer to the previous posts, there is no "right" bore for a given stroke. I was simply trying to say that a bigger diameter will allow for more bearing area of piston skirt, thereby reducing, and minimally, I might add, the rods loading affect in the cylinder walls. Think of it as a snow shoe for your cylinder walls!!!

David Gordon

iTrader: (1)

I have a 395 and beleive me there is no reason to turn it over 6500 max. I usually shift at 6200 and that is plenty.

black_knight

iTrader: (1)

Although the bigger bores would be REALLY cool to give us more options, I can tell that we are looking for very differant combos. I'm going mostly steet some strip and you're obviously looking for a race setup. I can respect that.

So more bore helps a little?

So...

1) Does a re-sleeved 427 have the same issues as a 395 all-stroke, or is it under control at that point?

2) Can all of the long-stroke issues be solved by lowering the rev limiter, or will some issues remain even if the engine is not revved up high?

3) A lot of people have told me that 4" is the limit. How much of that is due to actual mechanical issues and how much is due to them simply being like full-force and liking to rev it up?

grinder11

iTrader: (1)

I guess what I am trying to say is that it isn't really out of control in either application. It's just that the longer stroke you go, the more piston speed/friction/horsepower loss/wear you get. With two engines running at the same RPM, a longer stroke will exhibit all of these traits compared to a shorter stroke. I recently spoke with and had work done by Wheel to Wheel Motorsports here in the Detroit, Mi. area. They are great and I am glad they are not that far away from me for advice and/or taking my car there for a labor intensive job. Kelly is the tech/rep I have met and gone through there. VERY HAPPY with the first class effort they make and the finished product!I told him I am in process of buying a 395 stroker assembly from a forum member here. He was very much of the opinion that ANYTHING over a 4.00 stroke was something they were not interested in pursuing, and you could just tell he was frowning on this set-up. I have my own beliefs on this and while most everything he said is correct (Actually, all of it!), I am still going to go for it. But I am also going to sleeve it to a 4.125 bore and end up with a 440 or 441, I forget which. Like the other guy earlier said, there is no need to rev it past 6200-6300, as it is pulling real hard at that point. It is really a personal decision. I like engines with real good low end and midrange torque, but don't want a tractor. If it pulls hard from 1800-2000 up, but can still pull hard at 6300, I got my cake and can eat it too!

black_knight

iTrader: (1)

Well, I have my own ideas about how to go with the large cubes... I mean once they start getting up there, you are past the limits of where a hydrolic roller can go. If you want to stay with hydrolic, then one option would be to NOT spin it so high, in which case a large stroke seems to make sense...

I'm just wondering about how much it's going to scrape and tear itself to pieces and if a larger bore alleviates this. No solid answers on my questions yet, I notice, just opinions. And those are fine (and, by the looks so far, all valid for their respective applications), but they don't really answer my questions.

LOnSLO

iTrader: (15)

Most guys have their own opinion on which is better. My opinion is, money is the issue. I would think that everyone would like a 441 or higher cube LS1. But can everyone afford it? no. My personal view is to get as much cylinder volume as possible if you can afford it. Are you going to drive this motor 100,000 miles or more?
The Smokey Yunick way of thinking is to go short stroke, big bore, and rev it to 9500 rpm. The Pro Mod way of thinking is to go mega cube (big bore and even bigger stroke). So who is right? They both make a ton of power.
Just FYI - I rev my motor over 8000 rpms all the time. Will it last 100,000 miles? No. Does it make power up there? YES.

Freiburger

Within the realm of possible/practical bores and strokes for common streeet/strip V-8s, bore-to-stroke ratios do not matter at all when it comes to power production, especially on an engine with cylinder heads as good as the LS1/LS6. Nothing but cubes matters. And for a given displacement, rpm potential is defined by the cam profile and head flow limitations, not by the stroke.

For those who disagree, and many will since my opinion is an uncommon one, show me the test data that proves your theory.

DF

LOnSLO

iTrader: (15)

I agree 100%. Good post Dave.

black_knight

iTrader: (1)

I am no expert, but I have heard enough to know that the LS1 is (hydraulic) valvetrain limited more than limited by piston velocity, even with a long stroke.

I was more talking about oil consumption and friction wear on the engine. And whatever else the problem is with > 4" strokes.

LOnSLO

iTrader: (15)

The main problem with larger than 4" strokes is the piston design. The compression height of the piston gets smaller as stroke length increases. A piston for a 4.250" stroke on an LS1 looks ridiculous.

black_knight

iTrader: (1)

Yes, that would be a problem. What is the usual solution?