A bigger displacement short block will suck harder on the same openings. The heads will be a bigger restriction on a big engine vs a smaller one, but the big engine will make more total power with the same heads than a smaller engine. However, I don't know nuthin' about pulling stuff so I guess it'll take some of the truck pull guys to guide you through it. I know they like to spin high rpms so maybe a 500" deal would be better than 600" in your app. Errr, I'm guessing you're doing a truck pulling thing.

 

A larger engine will make more power with a given amount of flow, it will pump more air and make more horsepower. It won't make as much power per cubic inch as the small engine but because the displacement is higher it will force more flow through the engine.

We put this theory to the test on the dyno using Shannon's 460 Ford engine. It would make 585 horsepower with a 1050 Dominator carburetor. Just for fun we ran it with a 500cfm 4412 Holley carburetor and it made 420 horsepower. Remember that two barrels and 4 barrels are rated differently and a 500 two barrel is 40% smaller than a 500 four barrel. This same carburetor will make around 400 horsepower on a 355 inch Small block engine so the 460 engine was able to beat the 350 by 20 horsepower despite the restriction.

 

Food for thought and input. A 600 inch motor should make more power than a 500 inch motor, but the cylinder heads make about .25 hp per cfm of flow per cylinder. So how does a larger displacement motor with the same head flow make more power? The reason for this question is that the motor i want to build is limited to iron factory heads, and if i can make more power with more displacement with the same heads I will build accordingly, but if the power level is pretty well set by the head limitations no sense adding money to it with a $2k rotating assembly when my stock crank will work. Thanks for any input.

This is a common misconception. More cubic inches do not make significantly more peak HP. More cubes will however make more torque and HP at every point below the HP peak. The larger engine will also make the power in a lower rpm band given the same combination of cam and heads.

The opposite holds true of smaller displacement. Replace a 4.3" stroker crank with a 429 crank, using the same cam and heads, and peak power will be pretty much the same but at a much higher rpm.

When using heads that have limited capability, more displacement will tend to draw the rpm range down, and by time you cam it up enough to get to rpm band higher (if that's what you want) you'll lose all the torque that the added cubes would have offered if the combination was optimized for the heads being used.

 

If you take a engine simulation program and keep everything the same except bore and stroke you will get your answer fairly fast. Althought sims are not too good for predicting actual numbers, they are very good at predicting trends.

Overlay the HP graphs generated say at 466, 501, 521, 545, etc... and you will see where the point of "most area under the curve" is. I did this awhile back and in that particular instance a 521 was better than a 545. The 545 started really falling off after 5k and although had bigger numbers down low was not as balanced, nor had as much area under the curve in the range I was interested in.

Steve

 

In the real world, bigger is better, a larger engine will make more horsepower and torque with everything else equal.

 

I am building this motor for mud drags. I am needing to pull a vacuum level depending on my class, and i know it will be easier to pull vacuum with the larger displacement. This makes it easier to build the power and maintain the vacuum then. I just didnt want something that was going to be a dog because the heads wouldnt flow to the capacity of the rest of the combo. No flow no go. With iron heads flowing about 350 or so cfm what would be the ideal cubic inches to maximize the flow potential of these intake runners?

 

Schmitty,

Check out my engine build. Answer to my larger engine question, all else being equal, was a TON more torque and more HP based on previous ET's and MPH.

http://460ford.com/viewtopic.php?t=13985

Bigger IS Better :wink:

 

Bigger IS Better :wink:[/quote]

Damon,
That's what my ex wife said. :lol:

 

Damon - Bigger IS Better :wink:
Nevs - That's what my ex wife said. :lol:


Is that why she is your EX-wife

(sorry, it popped in my head an I just could not resist.)

 

In the real world, bigger is better, a larger engine will make more horsepower and torque with everything else equal.

Dave,

In the real world one matches the engine to the application...

If you put a head on a engine that will be done at 4k it may not be of use regardless of the power number. A bigger engine is only better until the pumping losses exceed its lung capacity or cause the port to go turbulent
I think Carl's post does a good job of touching on this, to quote:

"When using heads that have limited capability, more displacement will tend to draw the rpm range down, and by time you cam it up enough to get to rpm band higher (if that's what you want) you'll lose all the torque that the added cubes would have offered if the combination was optimized for the heads being used."

That is the only point I'm trying to make.

Steve

 

Well I'll be the dissenting opinion. I don't believe a larger motor will necessarily make more power with the same induction. It's a function of cubic inches, volumetric efficiency, and rpm. Changing one of those variables will also change the other two so you can't look at any one of them in isolation.

A larger motor with otherwise the same parts will reach peak volumetric efficiency at a lower rpm. Peak torque should be more and horsepower from the low end up to a point will be higher.

However, the same induction on a smaller motor will allow it to make peak volumetric efficiency at a higher rpm. Since horsepower is a function of rpm, the smaller motor could make more peak horsepower.

Here's a comparison of two motors on Dynosim with the same induction, cam, etc. Granted it's just a simulator, but it illustrates what I'm talking about.

436 cid---------------------------466 cid
rpm-------------------hp--------------
2500----254-----------------------270
3000----316-----------------------334
3500----382-----------------------400
4000----445-----------------------460
4500----493-----------------------507
5000----537-----------------------539
5500----560-----------------------545
6000----547-----------------------496
6500----502

avg. 2500-5500=427-------------avg. 2500-5500=436
avg. 2500-6000=442

The larger motor makes more hp up to the point that it's greater cubic inches are offset by it's inability to "feed" them. The smaller motor can "feed" it's fewer cubic inches effectively at a higher rpm. It makes more torque at high rpm and therefore more hp. So if you run the smaller motor to a higher rpm you can even make more avg hp. Just not over the same range. On the other hand if you run the smaller engine to the same lower rpm as the big motor (like 2500-5500) the bigger motor will make more avg. hp.

I don't think you can make a comparsion of two completely different motors just by switching a carb from one to another. You'd have to have the same actual motor with the same heads, intake, cam, etc. and only changing the cubic inches with a different rotating assembly. I realize that'd be hard to do unless you'd won the lottery and could just throw money away for the sake of curiousity. I need to start playing the lottery :lol:

Just my opinion,

paulie

p.s. I edited the dyno chart to make it easier to read

 

LOL me 2 on the lottery. That is an interesting comparison. I think IMHO that the larger motor there would have a better et on a dragstrip because it is still going to move the car/truck at a better acceleration rate though, because of the more power it is making under the peak. I believe that I am going to evaluate my budget here and try to optimize to a 4.3 or 4.5 stroke. The only thing that is nagging me is a forum member backwoods ( I think) has one of the nastiest sounding motors in the mud pits that i have heard. I wish I had a block capable of a 4.5 bore. That motor is very responsive and winds very strong, all on a stock stroke. I dont need tons of torque like a pullin rig, but lots of high end hps, and a flat torque curve. I'm thinking pro stock motor that gets real muddy.

 

LOL me 2 on the lottery. I dont need tons of torque like a pullin rig, but lots of high end hps, and a flat torque curve. I'm thinking pro stock motor that gets real muddy.

Me 3 on the lottery. I keep telling my wife she needs to refine her strategy. She's obviously doing something wrong, because we haven't won yet. :lol:

You're going the wrong direction with the crank. Get yourself a 3.59" 429 crank and watch the rpm's zing! The short stroke will give you the added benefit of lower piston speeds resulting in less stress on the rotating assy per rpm.

 

Big is better...then again bigger than big aint always the best path . Using Damon's engine as an example....he went to a 534" from a 466"...it's in a very sweet spot [i.m.o.] the 500-540 range , for the heads etc that he has . If Damon put a 4.500" crank in the engine w/o changing ANYTHING else could his package , at that point , be harder to hook and may or may not have more top end....could be .

 

So, was it a bad decision on my part to go with a 572 instead of a 528? Granted this is a blown alcohol motor going in a tube chassis car. Chris

 

we run a 557 with iron cj's with no port work in the mud and when you hit throttle it goes to 5500 and stays there no matter what you throw at it and it pulls 14'' OF VAC @ 1000rpm. Mud takes big time torque to compete and win go big you won't reget it. The only guy that gives him any trouble is a freind of ours that runs a 582 short deck bbc with heads that flow just under 400cfm (cast iron dart pro 1's). We never dynoed the 557 but the bbc dynoed @ 749 hp @ 6500 and 762 lbs. of torque @ (forgot). I really hate to say it but that dam chevy runs hard.

 

Port those CJ heads and I bet you will be the one giving that chevy a hard time :!: 8)

Steve

 

our motor cost 6k carb to pan his cost 13k carb to pan :lol: Its fun when the chevy guy gets beat by 70's ford technology. We got some ideas in the works to get 557 a little stronger :wink: 8)

 

I havent seen the truck with the 557 run but I caught the shortbox with the 605 in ravenna, Veeeerrrryyy impressive. I'm not sure if I will run the midstates events, none very close to me long way south and west of your events. A lot of the stuff around me run by their rules though. Have you ever done the short stroke stuff, and if you did was it competitive? I'm trying to build a motor on the short end of a budget, but if it takes a little more to do it right I will. I just dont want to try several times wrong and finally end up with one that works. The cj heads are impressive and I'm hoping to score a set of them. Nothing tastes better than a roasted chevy with a little mud sauce. The dodges scare the heck out of me though, them boys have some awesome stock peices to chose from, but so do we thank god.

 

I must be missing something if the Mopars have "awesome stock pieces". I've never seen them. Now I do think they make good running street parts, but for cubes and rpm... no thanks, nothing like putting a fair small block head on a big block(440).

JMHO! Bret

 

LOL Bret. I'm thinking iron hemi heads that can handle 1000 hp not an even comparison though. I'm hoping to Mud Drag for Christ. Keep up the good work.

 

Bigger will make more power

466 on dyno around 580hp 580ftlb done at 6200,557 667hp 694ftlb done at 6200.Both had a set of home ported doves.Bigger will allways make more given the same head. Wes Littrell

 

Here's the way I feel that this works, like it or not, a larger engine will always pump more air and make more horsepower. I know it's frictional loses are slightly higher but it's going to pump more air no matter how restrictive the cylinder head. How is this possible? Doesn't the port saturate more quickly on a large engine? Yes...

But, think about this for a minute... Lets say that a smaller engine with a given cylinder head forces the head to flow at it's maximum for a short period of time during the induction cycle at high rpm. Every cycle it goes up and then essentially clips the top of the flow curve, flattens it out on top. The valve opens, the engine pulls on the port, flow increases up to a point where it levels out. Now we take the same head and put it on a larger short block. What happens? The valve opens the amount of flow goes up and maxes out at the same level as before, pretty much. BUT, it gets to that maxed out point more quickly because the engine pulls harder on the port, thus it spends more time flowing at it's maximum than with the smaller engine. The demand is greater so it gets it moving more quickly and it holds it there for a longer period, pumps more air and makes more power.

Remember the test we did on the dyno using Shannon's 460 with a tech legal 4412 two barrel. That carburetor has never made more than about 400 horsepower on my dyno while running on a 355 inch engine with a cam that's pretty optimized, high 14:1 compression etc. Just bolting it onto a 460 with 11.8:1 compression it put out 25 more horsepower! How can it do that?

Now I know that gaining 25 horsepower by adding 100 cid isn't dramatic but 25 horsepower IS 25 horsepower and that means that the big engine will go faster than the smaller one even with the little carburetor, about 6 inches of mercury in the intake at wide open throttle and a power peak at about 5500rpm. Remember too, a 4412 is rated at 500cfm but it's only 50% as big as a 750! A fun and interesting test don't you think?

 

Well Said Dave,

The Larger engine will fill the cylinders more efficiently.

 

At what rpm ?