The engine is not unsprung weight. THe wheels, hubs, rotors, calipers, and a-arms are un-sprung weight. As is the rear axle and brakes.

I agree with you, but your terms are backwards.

chris

 

I would go 408 if you are spraying.

Iron 408 4" stroke, 4.03" bore, 6.125" rod

4.060 bore in an iron block isnt the most ideal for spray considering wall thickness.

With the 408 you have another overbore or two making the block much more serviceable.

My personal choice for the street would be a 4.125 stroke 4.035 bore ironblock.

It would be a torque monster and make great power from idle to 6400rpms. With the new intakes on the way and headflow numbers hitting 330+cfm it should make well over 500RWHP/490RWTQ with a hyd cam.

If you are worried about weight get a K-Member, A-Arms, and lightweight hood. That is almost 100 pounds right there.

Another option is a 3.905 bore alum 4 inch stroke 383 or 4.125 inch stroke 396.
Cheers,
Chris

 

Hey buddy, found a site that the difference is only $500, http://www.motorsporttech.com/fbody_engine02.asp

 

 

Any drag racer knows more lbs = bad.Chris I know a guy in your area with a silver Z that sprays a big shot with an alum block.My silver SS will be doing the same real soon.Any weight lost by lightweight parts up front is good but your still have 90 lbs more than necessary. :p

 

haha I know but he is asking about ironblocks.

If he picked up an ARE 4.1 bore alum short he could spray the **** out of it no problem

 

I'd go with the aluminum 387 and spin it tight. For major nitrous I'd go with the 427 ironblock.

 

It has been my personal experience that the 4.125 crank is TO LARGE and the Geometry of the motor is not good when matched with the 4.060 overbore on the ironblock. If you want to go with the ironblock and use spray, then its a no brainer, go with the 408 iron. If you go with the iron bored .060 over max. crank should be 4.00 for 414 cid. but not good if your planning to spray b/c cylinder wall thickness is an issue and you won't be able to rebuild that block without resleeving it in the future b/c no cylinder wall thickness left.

The all bore alum block would be the best revver probably make the best drag racing motor b/c of quicker revs (Grumpy Jenkins would be proud) and of course 90 lbs less weight.


Remember, IT IS ALWAYS better to make more cubes with the BIGGEST POSSIBLE BORE and BETTER to make big cubes with Biggger Bore vs. Bigger stroke, b/c of the high reving nature of a motor made with big bore and less stroke and the bigger bore will always make more power b/c they help unshroud the valves and get the heads breating better.

If you want a sig. amount of N20/spray and a great combo for street and strip do the iron 408 and stay away from cranks larger than 4.00 for the LS1 motors ESPECIALLY CALLIES!

 

Big bore + short stroke.....no question about it.....


I personally feel stroke is for HEAVY cars and trucks (i.e. my Dodge Pickup with a Cummins diesel....)......

Stroke gives LOTS of torque but it takes too long to spin up to your shift point and thus get to the next gear and that mean you go slower than if you had short stroke, spun up fast and can get on to your higher gears....

 

Whoa... whoa.... whoa....

Wait a second here.

I wanna see a valid explanation on how an oversquare motor beats an undersquare one to redline, ESPECIALLY SINCE the undersquare motor is going to have a lower redline (all other things being equal).

 

Several things:

1) Think of stroke length as tire size....the larger the tire, the harder and longer it takes to get it spinning right.....

as the stroke length increases, the distance from the center line of the crank to the center line of the rod (radius) causes the circumference of this circle (that the rod end will travel around) to increase thereby for every degree of rotation, the long stroke crank/rod end will travel farther than a short stroke crank/rod end....

Ex: 2" stroke crank (1" radius) vs. 3" stroke crank (1.5" radius)….1/3 (33%) more stoke

2" stroke = 2 * 1" * 3.142 (pie) = 6.283" distance the center of the rod end will travel in one rotation

3" stroke = 2 * 1.5" * 3.142 (pie) = 9.425" distance the center of the rod end will travel in one rotation


So right there...that’s an increase of 50% more distance for only 33% more stroke...

Now look at what that does to crank/rod end velocity at say 6500RPM.....

2" stroke @ 6500RPM = (6.283" * 6500RPM)/12(feet)/60(seconds) = 56 feet/second

3" stroke @ 6500RPM = (9.425" * 6500RPM)/12(feet)/60(seconds) = 85 feet/second

Once again....50% (actually 52%) increase for only 33% more stroke….

it takes time (and power) to accelerate "X" amount of mass to a given speed....so the faster (longer distance) the crank/rod end needs to travel, the longer and harder its going to be to spin up to any given RPM.....


2) then take all this information and consider what it does to a piston, piston rings, the rods, etc....(stress) and the downside of long stroke starts to really scream at you....




know its long....but you did say you wanted a valid explanation and nothing does it better than math

 

Fire off the math stud, I'm a degreed mechanical engineer with enough calculus/statics/dynamics/mechanics of materials under my belt to choke a horse.

Your whole treatise missed one (very important) fact... the longer stroke results in a longer applied moment to the crank and therefore more mechanical advantage. So, for a given explosion in the cylinder, at a given rpm which must be below the critical point at which the advantage of the bending moment is cancelled out by the added moment of inertia due to the longer stroke, the longer stroke makes more torque AND more power.

There is a crossover point on this curve and a categorical rule stating that bigger bore is always better is flat-out WRONG. Remember, a bigger bore also means a higher moment of inertia due to a higher mass (bigger piston) WAY out on the end of that rod. I might get a bigger explosion out of it (due to the bigger bore) but there is a balance between this and the added mass.

One more thingy... up to that critical point described above, the longer stroke motor will rev faster. It just can't top out as fast (rpm-wise).

 

Explain this to me because I don't agree.....


two engines of equal/close CID (383 stroker vs. 388 all bore), the stroker motor will increase RPM slower than the all bore....now...when you step up to a 427 (stroke AND bore), you are probably loosing some of the "spin up" ability due to the longer stroke, but the increased HP/TQ produced might/probably overcomes that (don't know about that)


I didn't forget that....since I was not talking about which one makes more torque, I didn't see any point in stating the above....

You are right the longer stroke provides a longer moment arm and as such more twisting force that can be applied to the crank/trans/drive shaft/etc....


What I stated above is that longer stroke causes the crank to in essence travel a farther distance per degree of rotation during a revolution....thus it takes more time to accelerate the rotating assembly up to a higher RPM (go from 1000RPM to 2000RPM)...



Like anything, you can go on either extreme and find a situation that will discredit.... .....(ex. 5" bore X 0.25" stroke....won't do crap...)....

Your average engine is not too far off from being square (bore = stroke)....


Remember, a longer stroke means higher mass (more iron) WAY out on the end of the throws....




What I'm getting at is all things being equal (CID, HP, etc...) the shorter stroke engines tend to accelerate faster....now if one engine makes a significant amount more power than another (250hp vs. 500hp), then that skews the results (again, the 383 stroker vs. 388 all bore idea....both make ~ 500rwhp...the 388 should spin up faster...)....




Now what kind of car an engine is put into also has a big impact on acceleration.....a big bore/short stroke engine in a 4,500LB boat of a car might not have the torque required to get the tub moving and as such need really high gears.....BUT...the engine is still accelerating fast (get to shift points fast)....



Final point I would like to make (before I get into an argument with anyone)....nothing personal….if I'm wrong, let me know.....I still have a ways to go in life before I know everything...

 

I like the all-bore/offset crank setup the best. Best bang for buck, no added weight, and can still handle a 200 shot fine. thats my dream setup.

 

Chris,

Sorry, didn't mean to be a *****. I come off that way some times, and didn't mean to.

In order:

"Explain this to me because I don't agree.....

two engines of equal/close CID (383 stroker vs. 388 all bore), the stroker motor will increase RPM slower than the all bore....now...when you step up to a 427 (stroke AND bore), you are probably loosing some of the "spin up" ability due to the longer stroke, but the increased HP/TQ produced might/probably overcomes that (don't know about that)"

The longer throw at the crank spplies more torque to it on the power stroke. That being the case, the engine will overcome whatever load is holding it back more quickly up to the point that the difference in moment of inertia takes over. Up to that point, the stroker is making more torque AND more horsepower. Because we have to assume the loads that have to be overcome are identical in both examples (mass of the car, gearing, etc...) the only reasonable conclusion is that the stroker spins up to that point faster - it accelerates harder.


"I didn't forget that....since I was not talking about which one makes more torque, I didn't see any point in stating the above...."

Torque is power. You know the equation. And it isn't just peak power, it's area under the curve. The true test is which motor has more area under the curve in the useable powerband at full throttle, not which one makes more power up top. I fully agree that the all-bore motor will tend to have an advantage at high rpms, but I have yet to see anything from any reliable source that an all-bore 382 is quicker than a 382 stroker UNLESS that added bore allows bigger valves. Furthermore, where EXACTLY is that point? It might be at 6600-6700 rpm, which is about as high as most folks really want to go anyway for the sake of reliability.

Even with bigger valves, one could increase duration of the cam on the stroker motor and make up part of the advantage by holding the valve open longer.

 

These are the kind of post that really make this site stand out... good job folks.

Oh and I went 427 just cannot wait to get it done

 

hmmm....never looked at it that way.....

 

I like where this post has gone. I have discussions like this everyday and I think I can present a few good points.

First off I hope we can all agree that POWER is what wins races. Its not rpm, or revving speed, all else considered equal it comes down to power.

Secondly, many people wont agree with this but RPM is just a necessary evil when producing power. It does nothing good for the engine. It just makes it less reliable and requires running a less efficient drivetrain.

Side by side two engines of equal displacement, one with big bore short stroke, and one with small bore big stroke, the big bore engine will be able to make more power. It will be able to use larger intake valves and breathe more efficiently while having more area on top of the piston for the cylinder pressure to act upon.(There is however a point where the cylinder becomes so big that flame front travel takes too long to travel the distance and efficiency suffers) Since it can breathe better and can work the heads better at any given piston speed it will be able to process more air and fuel and therefore make more power. This engine will make more power per cubic inch and in classes with weight per cubic inch will have a better power to weight ratio. There really is no replacement for displacement and I would always want as big an engine as possible that would still let me run a good power to weight ratio but when building that engine for racing I would always want as much bore as I could reasonably get.

Quick revving in neutral means very little. Though I will admit that very light internals will free up some power at the track that might not be seen on the dyno at the controlled acceleration rates they use.

As for RPM, two engines of equal power where one makes its power at lets say (700 hp @ 6500 rpm) vs (700 hp @ 9000 rpm)
If these engines are tested in the same car and have the same power to weight ratio, and are each geared optimally to their power bands the one making power at the lower rpm will come out on top.

This is peak power at roughly 39% higher rpm. It will take about 39% lower gear to run in its power band than the lower rpm engine. The first loss is through the drivetrain.
Whatever power loss was seen before through the drive train will now be greater by the square of the rpm increase. The engine will now also have to sweep through its operating range faster (due to the lower gears) to increase the wheel speed by the same amount in the same amount of time. This increases the inertial losses seen from having to accelerate the internal mass of the engine and the mass of the drivetrain at a faster rate. This can be seen on Engine Dynos when you lose power slightly each time you increase the step rate of the test and on a chassis dyno when you show a power loss at the wheels just by going to a numerically higher gear ratio. Both these scenarios are where the lighter weight internals can show a power increase by reducing these inertial losses.

The great thing about the big inch engines is that they are much more efficient with better BSFC's and lower friction than the small high winders and they are way more reliable in every way.

The last thing is that when you are considering holding the valves open longer in the big stroke little bore engine you need to remember that the little bore is limiting valve area and breathing efficiency of the head and the long stroke means it will reach critical piston speed at a lower rpm. After that point you will just be losing power and increasing reversion problems by holding the valves open any longer than necessary to reach that limiting engine speed.

Hope that helps
Dan.

 

I think just about everyone will agree on that.....

 

Good reading guys.I realize I'm not as smart as I thought.You don't see this detailed stuff on the other site.