Two engines.....both 427cu. Only difference in the two engines is stroke length, will one make more torque?

4.060 bore x 4.125 stroke = 427ci (longer stroke)

4.125 bore x 4 stroke = 427ci (shorter stroke)

 

this one should make more HP and TQ >>> 4.060 bore x 4.125 stroke = 427ci (longer stroke)

but the shorter stroke would likely last longer and perform better at higher RPM

 

4.1 x 4.1 = 433ci

Maybe thats better.....shorter stroke and more cubes. Not the same question I was after, but after thinking about it....that seems like a smarter build.

 

You're talking like 2 - 3% more torque on the one with the longer stroke if all things are equal.
The rod journal being further away from the crank centerline gives it more mechanical advantage (leverage) when turning the crank.

A bigger bore will likely make more peak power.

Is 3% more torque worth the downfalls associated with longer stroke?

 

My thought is a well dialed in street motor is good for about 1.27 x CID in torque at the rear tires. So your 427 options are good for about 540-550 lbs on a chassis dyno regardless of configuration. I think the longer stroke will want to hit peak torque at a lower rpm.

But like Joe said, the bigger bore should rev higher making more power, even if both make the same torque.

Edit - if you really want torque, build a ls454.

 

Using an LSX 6-bolt block.....how would you stroke/bore it for 454ci.

700 RWHP N/A possible?

 

What about a Race motor, what's the x.xx times c.i.?

 

Depends on the fuel.

Torque is basically cylinder pressure. If you hooked a load cell to the top of a piston and measured the force that cylinder pressure was forcing the piston down, you can get an accurate torque measurement.
Increasing cylinder pressure at the right moment will increase torque. Increasing cylinder pressure causes detonation. Different fuels will allow for different TQ/CI ratios.

 

I can appreciate that but for most motors there has to be some limit for the cubes with c16 for example. I think there was another thread on here in the gen 4 section about Max hp/c.i. of 2.xx or something.

 

Some diesel engines make close to 4 ft lbs per cubic inch

 

Stupid glow plugs

 

NHRA Pro Stock was around 3hp/ci before they neutered them with the RPM limit. Not sure what F1 was at, but I’m not so sure they even run gasoline anymore.

 

Think its possible to get 1.5HP/ci out of a 454ci with 11.3:1 cr. 93 octane. Hyd cam.

 

Bore 4.185. Stroke 4.100. 700 rwhp very possible. You can get 454 from gmpp. There are other vendors too. I seen a while back you could get a ls454 from shafiroff (non vendor so no link) around 6k. Then do your top end.

Edit - there is a guy with a GN iirc who hit 700 rwhp on a sbe ls7 and Darin Morgan heads.

 

Hp/cid has as much to do with rpm as torque. Torque is torque. It is a much more firm number. Make peak hp at 11000 rpm that number goes up. Hell, there are a few in the mid 400 cid making over 1000 NA.

Generally though I look at the torque number to see if I believe a dyno. 454 should be able to hit 575-580 RW tq. If you cam for rpm and get your power peak past 6500, 700 rwhp very realistic.

Another way to look at it is 850 at the flywheel. Around 1.85 hp/ci. Not a layup. But not unrealistic.

 

Exactly. The torque is kind of the litmus test for dyno results. It's a good way to tell if you have a dead cylinder if you're not making the power you think you should.

 

Displacement is displacement, for the most part. The longer stroke has a longer arm, but the bigger bore has more piston surface area exposed to combustion pressure. Applying 1 lb on a 2 ft bar is the same as applying 2 lbs on a 1 ft bar.

A 4.060" bore has a piston surface area of 12.95 in^2.
A 4.125" bore has a piston surface area of 13.36 in^2.

With the same dynamic compression ratio, air/fuel ratio, quench, and so on (hard to do, but stay with me here), let's say both engines reach a peak cylinder pressure of 1200 psi.

4.060" bore = 12.95 in^2 x 1200 psi = 15,540 pounds of force
4.125" bore = 13.36 in^2 x 1200 psi = 16,032 pounds of force

While the longer stroke has more leverage, there's less force acting on that leverage, so it's all pretty much a wash. What isn't a wash is the inertia and friction between the two. The longer stroke means higher piston speeds which means more inertia and more friction which will show as a loss of power as rpm increases.

 

Let's compare these to a baseline motor that has a 4.06 bore and a 4.00 stroke - the smaller of the two bores and the smaller of the two strokes (414.3ci).

The bigger bore gives 3.16% more force due to increased surface area (from dividing PAO's numbers).
The longer stroke gives 3.12% more force due to increased lever arm (from dividing the stroke figures).

So, big bore wins by a 0.04% margin.

Personally I just want to know why 4.125 bore x 4.125 stroke wasn't on the menu (441ci).
If you're comfortable with that bore, and comfortable with that stroke, why not use both together?

 

You also have to consider the fact that there isn't much difference in lever action at peak cylinder pressure which is ~14-18 degrees ATDC. The advantages of the longer stroke won't start to show until the crank comes around to 30+ degrees ATDC when combustion pressure is already much lower. By the time you see the full effect of the longer stroke around 70-75 degreed ATDC, the cylinder pressure is just a fraction of peak. This is also why the exhaust lobes on the cam would ideally be different between the two setups.

 

4.185 x 4.125 = 454ci

Thats what I'm thinking.....if that leaves enough wall thickness for a 250-300 progressive shot.

But where to go from there for a rebuild down the road?

I'm talking about an LSX iron block.......