The piston will only have as much support as was designed into it when they were made. If the cylinder length is not known when the pistons are made it's just potluck whether anything will be right. I do these fairly often but I know what skirts and what break points to use. Some of the sleeved deals have longer cylinders and some don't and some are too long to hone correctly.

 

I love big bores, OldSStroker, just like you do!

I just hate small strokes!

 

Same thoughts here!!! I'd rather see a 302 SBF based 377 to get those kind of cubes and lower the CG of the motor/car to help in braking and turning...

I still haven't seen a BBSS motor make less TQ even at lower RPM, well at least where it was the bore/strokes fault. Its usually the fault of the intake runner length, cam and compression combination that's paired with it.

Bret

 

You may or may not be surprised at how many piston designers do not take cylinder length into consideration when making a piston for a long stroke motor, it's the first question i'd ask.

 

I know and no I am not surprised at all since I am right in the middle of this industry as well.

 

I have but it's not a big difference till you get extreme. You won't see much in the range of combinations we usually see in this stuff. Torque is mostly engine size dependent. This is why the BBBS will always kick *** on the BBSS though as well!

BTW I am doing one of those 380 inch SBF 8.200 deck engines right now and I've gone even further with excellent results too. lower decks are certainly better at times like you alluded too. I have one of those I did that went 185+ mph on TT5s and had 5.300 rods so that must scare the hell out of the rod ratio people!

 

Where at on a LS1 or LS2 does the stroke get too extreme? I'm talking extreme for a Open track car that will spend 30 minutes at a time running hard. I am getting conflicting info, some folks are saying that a 4.10 stroke in a LS1 is to much for my uses, some say it's not?? I will be running a 4.10 bore with a 4.10 stroke in a Darton dry sleeved LS1 block.

 

It depends on many things but I would look at the rings and such available now. The 4.100 could work if done right. Both would need to be done right. Also the 4.100 is a stupid bore. Use a 4.115-4.125 so you can get real rings.

 

I have a bore/stroke question, Erik you probably can answer with some better feedback then the average guy. I am in the process of planning out a new motor, I was going to go with a 402 iron block setup, but somethign I was thinking about doing was going a little bigger on the stroke... say to a 4.1 or a 4.125 to try to get some more CI out of it. What kind of machine work/cost difference am I looking at going with a setup like this vs a regulat 4 inch stroke 402? i was leaving the bore's at 4 inch, so that the block would have plenty of room for rebuilds in the future... so the bore is pretty much set. It's my understanding that the #8 piston will need a notch, therefore requiring the whole assembly to be balanced accordingly to compensate for the #8 being lighter.. what else will have to be done? I assume the block will need clearancing, but how much.. is it enough so that block integreity will be a concern, or is the iron that much stronger so that it can handle that?

I'm hoping to make over 500 rw on motor, thru a 4500 nitrous converter and a th400, and then later on start spraying the car, start at 100 and probably work my way up to around 200 or so, I figure that will be more then enough to get the car well into the 9's so that will be more then enough for me.


Thanks in advance for the insight.

 

So, you are saying that the 4.10 stroke is fine as far as reliability goes especially concedering my inteanded usage? Cool, now onto the bore issue. I didn't pick the bore and would agree with you that if there is a larger selection of rings present for a slightly larger bore AND you can easily do it,,, go for the larger bore. I just figure there must me a reason the guy is going with the slightly smaller bore?? Maybe he is worried about liner thickness?? I don't have enough knowledge to know but I will queery him on it know. Thanks for bringing this issue up.

 

JL,

When I do these there are no shelf pistons for that stroke so I do customs and I do them with smaller rings and they are NA only or small NOS but still work great and are strong but the skirt shape is a custom one from Wiseco for the short 5.500 cylinder. You could do a piston with a 1.2, 1.2, 3.0mm for like 200 shot or less and still be strong probably and fit it all in there.

The machine work would be the same as there is only a tiny amount of clearancing depending on rods but the piston would be around 250ish more than a shelf piston. With the shorter rings the skirt could move up on the piston a little to compensate for the stroke. The #8 piston on the Wiseco's I use already clears the reluctor as is with no work.

 

Yeah with a longer cylinder 4.100 stroke is no problem and the Eagle 4.100 is fairly cheap already. Actually you could stay at 4.100 and still get some rings but no where near the selection as 4.125 and up.

 

Erik,

Thanks, that is some good info. I may have to give you a call and inquire about some other things as well... so I can have a better understanding of what's involved in a buildup of this nature, what's really needde to get to the specific goals that I have in mind, etc.etc. The # you have listed in your sig, when's a good time to reach you?

 

Thanks for the nice worlds and I am here from 2PM to 10PM Central usually although I will be heading out early tonight to the Houston Grand Prix here tonight.

 

If you have an LS1/LS6 block, and you choose NOT to go the power-adder route, increasing displacement is about the only way I can think of to gain power, while staying naturually aspirated. Increasing displacement in an LS1/LS6 block is done most easily & cheaply by stroking. Sure, you can punch out an LS1/LS6 block, but removing the OEM cylinder sleeves, boring the block, and installing larger-bore sleeves gets expensive. Of course, you could just sell your engine, and buy a stroked LS2 crate engine.

The debate over under-square, square, and over-square engines will probably go on as long as internal combustion engines continue to be made. GENERALLY SPEAKING (in other words, there are exceptions to every "rule"), over-square engines are sometimes referred to as "horsepower" engines. They make horsepower, and lots of it, by being able to rev the pi$$ out of the engine; however, take a close look at the area under the torque curve of an over-square engine.

Under-square engines are sometimes referred to as "torque" engines. They do not need to be reved to produce gobs of torque, and, as stated above, unless you get ridiculous with stroke length, you do not give up a lot in the ability to rev. Now, take a look at the area under the torque curve of an under-square engine.

So, right away, we can see that there at least two different ways to make "power".

If you choose to stroke an LS1/LS6, it has to be done correctly. The OEM heads have to go (or get a damn good porting job), it'd be a good idea to go with an aftermarket intake, a more aggressive cam, larger throttle body and MAF, and it would probably be wise to go with an all-forged rotating assembly. A reasonably stroked LS1/LS6 (say, 3.905 X 4.00) will yield somewhere around 383 CI, and give up very little in rev capability, not that that matters...when you build a stroker set-up, you already know you're going to make power without having to rev the pi$$ out of the engine.

BTW, this leverage arm/crank throw business being the sole reason for strokers producing more torque than a square, or over-square engine is mostly bunk. Torque is a product of displacement and BMEP. The major reason a stroker produces more torque, is because you've increased it's displacement. There's been plenty of experimental work done to prove that longer throw cranks/stroker rods have a negligible effect upon torque production, as compared to an engine's displacement/BMEP. Hey, I didn't make up this "rule"; someone a whole lot smarter than I am figured it out. I just read it, and it made sense to me.

 

There are plenty of 346 cube LS engines making gobs of torque and hp NA. If you spend all the money to increase the displacement, and don't have adequate breathing, you aren't going to see much gain. Put your money into breathing.

Yep, torque is the product of displacement and BMEP, and power is torque x rpm. As you pointed out bore and stroke ratios don't have much effect on torque production with a given displacement and breathing. Doesn't that negate the oversquare = horsepower, undersquare = torque theories?

You are presenting it both ways. Which idea do you buy?

 

Airflow equals horsepower and bigger bores allows more airflow. Bigger strokes allows you to take advantage of that airflow whatever it is by avoiding valvetrain limitations which ultimately limit you on engines where you are lucky enough to have real heads.

If your heads suck your stroke won't have as much impact on performance. If you have good heads then the stroke will definitley make more power and more area under the curve.

 

I believe the original question was: Is it worth it to increase stroke, with a given bore size. This was never a question of "should you add stroke or should you add bore?"

So again, to the question: Is it worth it to increase stroke, with a given bore size?

The answer is, as long as your heads will support it, YES. If you can fit the stroke in there, and aren't limited by class rules, then YES it will make more power than the same bore and less stroke.

If it were me, and I could use any stroke I wanted for a given set of heads and bore, I’d stroke it MORE and rev it LESS. (yes, that’s the exact opposite of what some have suggested) I’d make the same power as Mr. Rev-happy at peak but toast him under the curve while enjoying a more reliable engine and not having to change out my valve springs constantly. The only concern is fuel economy, but that’s what they made 6 speeds with double overdrive gears for. Unless you’re racing in a class that limits displacement, then why the hell not do it like that?

I can already hear the complaints: "oh, but you can't rev it very high like that! I want to rev it to the moooooon!" These complaints are easily disarmed. Ask the question: "Why?" Why are revs so important to you? Is your goal to make revs or is it to make power? (talk about losing sight of the forest for the trees...)

There are limits, mechanically, to how much you can stroke a motor, obviously, and when you're talking about high boost it complicates matters with cylinder pressures.

But, as a general rule: given a fixed bore, the winner of the race is the guy with the larger stroke. Whoever said that they want LESS cubes and LESS stroke for a given bore, ("I wish they'd release a short stroke LS7") just get the hell out of here right now. No, seriously, leave. Go get a Honda and rev it up however high you want if you think RPM's > displacement. Meanwhile, us sane people who live in the real world will continue to use stroke, make power, and spank your @$$ at the strip.

Oh, and in the LS1 world, it’s completely non-controversial that a 4” stroke will run all day long and isn’t any kind of a problem for the motor. Somewhere north of there is where things start getting complicated.

That's my $.02. I'm not an expert but I'd like to think everything above is simply common sense.

 

I think that is what people are wondering about "Something north of a 4 inch stroke". I think everyone accepts that a 4 inch stroke is OK. What about a 4.100 or a 4.125??

 

Fastest n/a six speed car is a 4.125 stroke. I'd pm him with any questions of longevity etc. Further, gm put a 4" stroke in the ls7. If GM did this they would be of the understanding that no problems will arrise whatsoever in longevity i'd venture to say. That being the case going past 4" stroke is probably not that big of a deal if things are done properly.