Undersquare vs. Oversquare Engines

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moper said:
I think the issues are apples to oranges... By limiting heads to one brand and style, and camshaft, and compression.. and you eliminate maximizing each combo with the available parts for them. The stroke is the key in both cases.

#1....The LA RPMs will feed the 4" crank engine to 6500 with a std CNC program netting 270-280cfm. The suggested cam is smaller in terms or duration at .050 than I'd use. A solid roller would be more like 265-270°@.050 at .600 lift, and with taking out for lash and the nasty pushrod angles, that lift at the valve is closer to .560. Also, carb is on the smallish side. I think performance wise 520-540 at 6300 is close. I built a 416 very similar to that that made 540 with a dual plane and 950 carb, using a smaller solid roller cam. The torque peak will be higher than mine tho. I'd think 470-490tq @ 43-4400rpm would be what I'd expect.
The B wedge with it's shorter stroke and a CNC head in the 310 area will be undercarbed but not by much. But it will make it's power higher in the rpm band. I think the numbers would be similar, but slightly lower even at peak. I'd be looking for 510-525hp at 6800, with torque in the higher rpms too. I'd be looking for peak torque in the 5K area with a peak around 470 pound feet. To get things better, I'd run a higher static ratio, closer to 11.5 and a single plane intake for this one, plus a carb in the 950 area.
I have a program that uses a bunch of data points to approximate frictional losses for an engine... Interestingly, the hp it estimates being lost by the 4" is higher, but at 6600, the B wedge has the same hp loss as the 4" LA does at 6K.
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Yep, I probably should have titled this "Stroker vs. B Block", but I was trying to prove a point. I do believe (although I have no way to prove) that the B Block will out power a stroker due to the head configuration more than anything else and that the under/oversquare and rod/stroke ratios have far less to do with creating usable power than gas flow does.

Do rod ratios and bore and stroke issues make a difference? I say yes they do, but I wonder how much of a difference they truly make under 6500 rpm? I'll bet that the difference on two identical engines, with the same heads, cam and intake but different rod ratios or under/oversquare configurations would be in the single digits under 6000 rpm, with that number increasing as the revs rise.

As far as I know, none of us are building F1 engines that spin at 18,000 rpm, nor are we building 7500 rpm Mopars that we drive on the street although I'm sure some of us have built some high revvers for the track. Of course, I've been wrong before, lol.

I'm going to be starting on 2 builds come late summer and both will be LA strokers but each one will have a different purpose. One will be for my Ramcharger and one will be for the Duster. The present LA build in the RC will be dropped in the Duster as I have to have it emission checked just once to get it registered and plated as an antique then I can do anything I want to it.

I will be spending my money on getting fuel/air in and out and making sure that engine holds together at the planned rpm range rather than worrying about r/s and b/s ratios. :read2:
 
I wonder what effect the comparative mass of the rotating assemblies (namely crankshaft) would have on horsepower production.

What does a BB crank weigh?

FWIW my 5.9 magnum weighed 498 lbs when I brought it home. The Eddy heads are right at 50 pounds lighter than the stock Magnum heads.

I've been told 720 for a BB with aluminum manifold, but that's hearsay, not gospel. Could they really be 200+ pounds heavier? Right on the nose of the car?

I know a Ford FE goes about 650, which is about 150 more than a 351 (Windsor).
 
Stock 360=550#, 383-400=627#, 440-426W=670#, these weights are factory with all the cast iron hanging off them.

Terry
 
You have to remember theres a few ways to see more power out the crank. Any crank. You can reduce weights, reduce friction, machine very accurately, and focus on one area in the power curve. Do any of them, and more power will be found at the crank for that given rpm area. Lighter parts are easier to accelerate, and won't deform as stress rises with rpm, so more power is the result. You also have to remind yourself that every action has a reaction. You could make a balsa wood rod, and it would be light, but it can't work. Parasitic or frictional losses are huge. If you thinkg there's no difference, go turn a PS1C Procharger by hand... Then compare outputs from a 10psi boosted blower engine vs a 10psi turbo engine. Turbo engines make monster horsepower because they take none to drive. A blower uses as much as 25% of it's own power produced just to turn itself. The higher the boost, the worse the loss. Also as I said, frictional losses due to the longer strokes, shorter rods in shorter decks and smaller bores are much greater at lower rpms.

Ram, in terms of packaging, i think the big block have the knod. They can fit larger ports where they are located already, and they are wider, giving more intake port volume for that size. This is for street type, 6500redline engines. Above that.. the small block simply have more heads available (Cup car/sprint car R&D), along with better valve angles and lighter parts among other things. I still think the ultimate cross breed car (street/strip/road race) is an LA stroker A body.
 
wow Talk about a lot to digest ! this is a great thread I guess the most important thing for me here is that I seem to be on the right path with keeping my LA now not to hijack but why is everyone so stuck on the 360 ? whats wrong with stroking my 318 and still having a numbers car ? can't I overbore it for a bigger displacement than 390 and do I really need to ? wouldn't I be better off spending the money to open up my 360 heads for more flow ? after all isn't a motor just like a pump ie more flow is more everything ? sorry to ask so much at once but I read somewhere that de-stroking adds horsepower what kind of comparison would that be for a cross breed car ?
 
ok personally i woul go with the 400 block and have it built with a lightened rotating assembly,balanced,blueprinted for 7500-8000rpm runs nothing better than when that little jerk in a honda civic tells you that he has a rpm advantage and his honda goes to 8 grand and you just smile and tell him so does yours :toothy10:

i love the look you get after that plus nothing sounds sexier than a v8 wrapping out to 8k :) :) :)
 
360Z28 said:
Moper,
the reference to F1 engines is that they go totally against todays thinking of what the ideal bore/stroke-rod ratios should be. i just thought it was interesting! 750+hp and only 250-300ft-lbs of torque will lay waste to most cars on the 1/4mile lol.
cheers

dgc333,
then they couldn't have used a long enought rod with a shorter piston..otherwise it woulda been significant. you wouldn't happen to have a link would you? or specs on what they did?
cheers
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The 454's were built with custom pistons, the difference between the two was the position of the wrist pin; lower in the piston for the short rod and higher in the piston for the long rod. Stroke was the same, bore was the same, compression was the same as was the head and cam.

I want to say it was Car Craft but it could have been Hot Rod that did the article, I get both magazines. In any case the article was to tray and prove or disprove the theory that a higher rod length to stroke ratio would make more power and in this case it didn't.

Regarding an F1 car you have to remember that Horsepower is nothing more than a mathematical expression of the rate at which torque is being generated or HP = Torque (in ft-lbs) x RPM / 5252. This is why every single HP/torque curve intersects at 5252 RPM. Drop that F1 motor into a 3000-3500 lb street car and it won't make enough torque to get the car moving and if it does a kid on a BMX bike could beat it in the 1/4 mile. Ever notice how those cars pull out of the pits (same for NASCAR Sprint Cup cars) they rev the snot out of the engine and drop the clutch to get the tires spinning. The torque at low rpm combined with the gearing needed for top speed just won't allow the vehicle to pull away from a stop any other way. You have to have a torque curve appropriate for the application.
 
I agree with moper in regards to an LA stroker in an A-body being a great road racing package due to the low weight and high torque output. My X's dad has been building road racing cars for the SCCA and other circuits since 1966. In the couple years that I had the chance to pick his brain he taught me that torque was key in getting out of the corner before the other guy. Look what this guy can do with an engine that he never really brings up much more than 6K and it's a big block hemi. Note what RPM's he's turning as he pulls out of a turn. Turn up your volume!:

http://www.youtube.com/watch?v=Bj1RB6_497c

http://www.youtube.com/watch?v=7D4dpsC8eVE&feature=related

Here's his website: http://www.glennbunch.com/

Hemi.jpg
 
Nice thread fella's!
EM says that S/B Mopar iron heads well outflow the Bigblock irons.
Hopefully they will do a Stroker S/B against a 400 B/B Mopar with irons.
They already did a Mopar 383 B/B against a Chevy 383 stroker S/B.

But the best yet was the 'hogged out' S/B Eddy heads!
90hp over standard Eddy casting...:drama:

Stroker Poly 402 is the way to go now...
Best iron head ever made (non-hemi)!!!:mob:
 
While the Poly head design has great potential, the head itself is limited. A fella on FABO went nuts on his with interesting results. Note, he milled the rocker stand down/off, I forget.
Click here; CNC Ported 318 Poly Heads
 
Sometimes I think you guys get over thunk in the over thinking dept, I AM LOST

To me this is a simple A or B, like the OP started out with.

The OP is NOT gonna be installing a turbine, F1 engine, Stude or ever a Ford SOHC

He IS going to be building a SB Mopar vs a B/ RB Mopar. Seems to me it gets back down to "simply".............

What is the bang for buck out of what the OP has to work with and is willing to spend? In "my house" that is ALWAYS the bottom line LOL

In a mild build does a B / RB have better head potential than an LA at the same dollar figure?

That would be one of my "questions" if I had a SB and a B/RB "lying around"
 
In simple terms engine output at all speeds is determined by intake valve size or actually circumference.
Even at low rpm it is the most important factor. And intake valve size is basically determined by the bore size.
F1 engines are impressive but not as impressive as the budgets to obtain that performance. Typical gasoline is about six pounds per gallon, I think a gallon of “91 octane pump” fuel for F1 weighed over nine pounds. Fascinating tech in F1 but I can’t apply it to anything.
 
I have always understood a small block will make torque / HP at a higher RPM than a big block, in other words, the small block may or will make the same torque / HP as a big block, but it will be screaming at a higher RPM to do it.... Of course I may be completely off on this. Most big blocks I have had the experience of driving or riding have always been pretty torquey.
 
Dartswinger70 said:
I have always understood a small block will make torque / HP at a higher RPM than a big block, in other words, the small block may or will make the same torque / HP as a big block, but it will be screaming at a higher RPM to do it.... Of course I may be completely off on this. Most big blocks I have had the experience of driving or riding have always been pretty torquey.
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The engine is ignorant of its architecture.

Making the assumption of equality in everything, a bigger bore and shorter stroke will always make more power than a smaller bore and longer stroke of the same displacement.

There is no way a 400 inch small block with a 4.200 will make the same power as a 400 inch big block with a 4.400 bore.

Bore spacing is critical and you just can't get the bores far enough apart with what is called small block architecture.
 
Unless your dad own's the local bank, the bottom line question is which engine gives you the usable (streetable ,, for me) power for the least cost. Interesting discussion.
 
For the most part building cid with bore size is more advantage then stroke. Bore size is the ultimate limit to power.

It allows for better breathing more rpm and longer rods.

Now for torque everyone always goes on about the crank multipying effect. 4" vs 3.38" which is true but totally disregard that the the 400 bb has more pistons area then the 360/408 given more pressure applied to the crank to be multiplied. Which pretty much equals out.

Head wise the bb has more port area given the bb a definite advantage. 360/408 struggle to breath. The 400 bb has thr ability to make as much if not more low end power cause stroke is really no advantage as I explained earlier but also the 400 bb has better breathing ability and allow for longer intake runners. Plus the 400 bb has the ability to turn way more rpm over the 360/408 given it way more potential for power.

The only advantage for the 360/408 is size and weight. But for that extra weight your getting a way stronger block. If you were to build a race block 360/408 the weight advantage would disappear.

Even 383 have more potential.
 
Why does the longer throw of the stroker crank have no advantage?

How does the Sb stroker not have the ability to rev like the B.B. 400?

Even though it was a Chevrolet motor, the engine Masters episode of the 383 stroker first at 400 B block was very good.
 
rumblefish360 said:
Why does the longer throw of the stroker crank have no advantage?

How does the Sb stroker not have the ability to rev like the B.B. 400?

Even though it was a Chevrolet motor, the engine Masters episode of the 383 stroker first at 400 B block was very good.
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The reason the 4" doesn't have the advantage over a lesser stroke. Especially in this comparsion because of different bore size. It the 400 bb has more piston area then the 360/408 sb so for the same amount of fuel being burnt the 400 bb will have more downward force going to the crank than the smaller bore sb. So the 4" stroke will be multiplying lesser downforce than the larger bore bb which means both should put out about the amount of torque for a given revolution.

But in the case of the 360 3.58 crank vs 408 4 crank. They both have the same bore size, there for the same downward force. So yes the 4" stroke will produce more torque at a given rpm. So the 4" stroke only has an advantage at low end power, but that only matters if deep gears and high stall is an concern. But if you factor in piston speed the 3.58 can always spin faster than the 4 always able to make up the difference if your willing to spin it. So bore size really becomes the limit, cause bore size limits valve size which limits airflow which limits hp. Obviously for this to matter were talking about taking things to the max.
 
Long stroke small bore is a truck motor. I just love tellin that to Pontiac guys and watch the top of their head blow off.
 
RustyRatRod said:
Long stroke small bore is a truck motor. I just love tellin that to Pontiac guys and watch the top of their head blow off.
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Me too!!! The Pontiac guys get really weird when you say stuff like that to them.

I also like to point out the battery is on the opposite side of the starter. The fuel pump is on the opposite side of the fuel line.

If I really want to whack them out I say it's a camaro with different sheet metal.
 
ramcharger said:
The 400 B engine is oversquare, the bore is larger than the stroke. The LA stroker is pretty much square in the configuration that I gave. it would be undersquare @ 426 with a 4.125 stroke.
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oversquare would be the other way , longer stroke than bore !!
 
dgc333 said:
FWIW, one of the car rags built to identical BB Chevy 454 motors except for one with a low rod ratio and one with a high ratio just to see what the difference would be. They made almost identical power, as close as any two engines can be.
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-BUT, the long rod engine had a hair less cyl wall loading than the shorter rod engine!
 
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