Engines with lack bottom end power?

[273]

I thought the general consensus was engines that were soft down low in the rpm band was a lack of torque.
But I've been noticing that built engines of all type even high rpm still make decent power down low generally far better than a stock low power version of itself some on par or better than a mild built engine with low end power in mind. So I'm guessing there's something besides power.

This ain't about my car in particular but bottom end in general but as an example I'll use my car.

I got a 380hp crate engine with a 2800 stall and 2.xx something gears but lugs in 3rd under about 35 mph so I drive in 2nd intown no big deal. Here's an article where they dyno it makes 409hp @ 5400 rpm and 439.5tq @ 4100 rpm but at 2500 rpm it still makes 181hp/380.6tq which should be more than enough power in 3rd, that's better than a stock 318 at peak power. A stock 5.9l long block with 4bbl and 360 manifolds makes 314hp @ 4600 rpm and 407.1tq @ 3500 rpm and at 2500 rpm 185hp/398.5tq so about the same and even though it don't show it I can't see it even at 1500 rpm or so being much different. I know we're not just talking full throttle runs here but there's half throttle dyno runs making 80% of the power and more important similar power curve.

360 Crate Engine Buildup & Dyno - Mopar Muscle Magazine

Here's the stock 5.9L with different exhaust
Installing Exhaust Headers Into 300hp Crate Engine - Mopar Muscle Magazine

So I can't see it be a power issue seems to be more than enough power available, my guess it would be something to do with cam overlap? something makes it lug and makes it feel soft, yes I know gears and a better stall would fix if but why if both engines are making same power down low why does it act so different? A /6 makes way less power and would have no problem.

 

[AJ/FormS]

that's better than a stock 318 at peak powe

Maybe so but, per the factory literature
a 318 in 69 was rated 230hp@4400IIRC, (which is only 193 ftlbs torque) and 340 ftlbs at 2400 rpm :
whereas the 340 didn't get to 340 ftlbs until 3200, and peak power of 275@5500 translates to 356 ftlbs.
Engines do not make horsepower.
Engines make torque over time, and horsepower is the computed result of that.
340 ftlbs is the same no matter at what the rpm is measured at.
So then;
340 at 800 is 52hp
340 at 1600 is 104hp
340 at 2400 is 155hp
340 at 3200 is 207hp
340 at 4000 is 259hp
340 at 4800 is 311hp
340 at 5600 is 363hp

Loss of torque with rpm dropping, is usually a loss of efficiency. As the rpm drops, there is more and more time for the piston on the intake/compression changover, to push just-inducted fuel/air charge back up into the intake, thru the late-closing intake valve. This is why big cams idle at low vacuum.
Another thing that can happen, more so with headers, is, as the rpm comes down, there is more and more time, for, on the overlap cycle, for the headers to pull fuel-air from the plenum, straight across the piston and into the primary pipes. That's Idle/low speed fuel charge that never got burned in the chamber, therefore did not contribute to torque-production.
These things, with aggressive cams, can continue from idle to at what-ever rpm it takes ,to build peak vacuum, usually in the window of 1600>2200, or more with bigger cams.
A third factor is the duration of the power stroke.
The longer your exhaust duration is, the shorter your powerstroke has to be. The stock 318 has, IIRC, 122 degrees of power stroke, so by the time the exhaust opens, there is as good as zero energy left in the expanding gasses. But a long-period cam might have 100 or less degrees of power-stroke, so needless to say, there will be plenty of energy left in those gasses.
So then in these two examples there will be a difference of say 20 degrees of, what I call, Power-extraction. Obviously, at low to mid rpms, the more energy that you can extract, the more torque she will make.
Here's how the factory low-compression 318s can still make torque;
1) The early-closing intake traps the charge, and
2) the near total lack of overlap, traps the A/F charge in the intake, and
3) the very long extraction period puts as much of the energy as is possible, into the crank. but
4) the short intake period limits power-production.

 

[67Dart273]

There is no actual thing as horsepower. Horsepower can NOT be measured!!! Torque is the only thing that can be measured. ALL HP figures are a MATHEMATICAL PRODUCT of torque compared to RPM (in the case of engines)

For a better understanding, consider the mathematical constant in the HP formula, and the fact that ALL torque/ HP curves have a common marker at that constant which is 5252

HP = torque X RPM / 5252

There is, therefore, only two ways by which an engine can make more horsepower. That is A: make more torque, and/or B: make torque at a higher RPM

 

[273]

Maybe so but, per the factory literature
a 318 in 69 was rated 230hp@4400IIRC, (which is only 193 ftlbs torque) and 340 ftlbs at 2400 rpm :
whereas the 340 didn't get to 340 ftlbs until 3200, and peak power of 275@5500 translates to 356 ftlbs.
Engines do not make horsepower.
Engines make torque over time, and horsepower is the computed result of that.
340 ftlbs is the same no matter at what the rpm is measured at.
So then;
340 at 800 is 52hp
340 at 1600 is 104hp
340 at 2400 is 155hp
340 at 3200 is 207hp
340 at 4000 is 259hp
340 at 4800 is 311hp
340 at 5600 is 363hp

Loss of torque with rpm dropping, is usually a loss of efficiency. As the rpm drops, there is more and more time for the piston on the intake/compression changover, to push just-inducted fuel/air charge back up into the intake, thru the late-closing intake valve. This is why big cams idle at low vacuum.
Another thing that can happen, more so with headers, is, as the rpm comes down, there is more and more time, for, on the overlap cycle, for the headers to pull fuel-air from the plenum, straight across the piston and into the primary pipes. That's Idle/low speed fuel charge that never got burned in the chamber, therefore did not contribute to torque-production.
These things, with aggressive cams, can continue from idle to at what-ever rpm it takes ,to build peak vacuum, usually in the window of 1600>2200, or more with bigger cams.
A third factor is the duration of the power stroke.
The longer your exhaust duration is, the shorter your powerstroke has to be. The stock 318 has, IIRC, 122 degrees of power stroke, so by the time the exhaust opens, there is as good as zero energy left in the expanding gasses. But a long-period cam might have 100 or less degrees of power-stroke, so needless to say, there will be plenty of energy left in those gasses.
So then in these two examples there will be a difference of say 20 degrees of, what I call, Power-extraction. Obviously, at low to mid rpms, the more energy that you can extract, the more torque she will make.
Here's how the factory low-compression 318s can still make torque;
1) The early-closing intake traps the charge, and
2) the near total lack of overlap, traps the A/F charge in the intake, and
3) the very long extraction period puts as much of the energy as is possible, into the crank. but
4) the short intake period limits power-production.

Agree

But what I'm trying point out is my engine make more torque (380tq@2500rpm) than a stock /6 273 318 even 340 and 360 at 2500 rpm and ties the 300hp crate engine all which should be able to drive in 3rd at in town speed and pull from stock stall speed without feeling soft why can't mine?

Now the question isn't just about my engine you look at the dyno result of any built engine most make strong power down low. Look at the 5 or so 318 builds that make from 282hp to 477hp all make 335-355tq around 2500 rpm 50-70tq over stock 318 at 2500 rpm. The ones making 355tq are the biggest power one 425 hp and 477 hp with the biggest cams flowing heads etc..

So my question is what would make these engine seem softer down low (rpm) when there obviously making good power down there?

 

[Brooks James]

More torque, cheap, 100 shot of nitrous, plate kit

 

[273]

There is no actual thing as horsepower. Horsepower can NOT be measured!!! Torque is the only thing that can be measured. ALL HP figures are a MATHEMATICAL PRODUCT of torque compared to RPM (in the case of engines)

For a better understanding, consider the mathematical constant in the HP formula, and the fact that ALL torque/ HP curves have a common marker at that constant which is 5252

HP = torque X RPM / 5252

There is, therefore, only two ways by which an engine can make more horsepower. That is A: make more torque, and/or B: make torque at a higher RPM

Call it whatever you want, don't want it to turn into tq hp thing, really want figure out what's going on, my guess would be overlap but don't know exactly how.

 

[273]

More torque, cheap, 100 shot of nitrous, plate kit

it's why question, not how to fix, engine already makes a good amount of torque. (380tq@2500rpm)

 

[273]

Even if you look at the stock 273 commando build it makes like 275tq @ 4000 rpm and pretty flat from 2700-4300 rpm, a 2bbl version would make even less torque and compare the 273/292 473hp @ 7900 rpm and 334 tq @ 7100 rpm, makes 255 tq @ 3500 rpm less than a 20 tq difference. I imagine 473hp would need high stall and deep gears not to fall on it's face even though it's probably on par with a 2bbl 273 and way above /6 torque at low rpm's especially 170 making even way less , my 380tq is miles above this.

 

[Rat Bastid]

There is no actual thing as horsepower. Horsepower can NOT be measured!!! Torque is the only thing that can be measured. ALL HP figures are a MATHEMATICAL PRODUCT of torque compared to RPM (in the case of engines)

For a better understanding, consider the mathematical constant in the HP formula, and the fact that ALL torque/ HP curves have a common marker at that constant which is 5252

HP = torque X RPM / 5252

There is, therefore, only two ways by which an engine can make more horsepower. That is A: make more torque, and/or B: make torque at a higher RPM

Engines (good engines) make more power with less torque after peak torque.

Horsepower is real. It’s what makes cars go quicker and faster.

 

[Rat Bastid]

There is no actual thing as horsepower. Horsepower can NOT be measured!!! Torque is the only thing that can be measured. ALL HP figures are a MATHEMATICAL PRODUCT of torque compared to RPM (in the case of engines)

For a better understanding, consider the mathematical constant in the HP formula, and the fact that ALL torque/ HP curves have a common marker at that constant which is 5252

HP = torque X RPM / 5252

There is, therefore, only two ways by which an engine can make more horsepower. That is A: make more torque, and/or B: make torque at a higher RPM

BTW…
P
L
A
N

 

[RustyRatRod]

It is also completely dependent on WHAT engine you're talking about. Some were not designed for bottom end torque. Some were designed for peak torque in a higher RPM range, like for instance, some 4 cylinders. So trying to "get" bottom end torque from some engines will always be a challenge at best. Anything can be built for "more" bottom end torque, but getting a lot of it from some engines will always be a challenge, since some are simply not designed for such.

 

[toolmanmike]

I know this is a 440 but Nick was having trouble reading low rpm torque on his dyno because it wasn't designed to read that much torque at rpm below 3000.
Nearly 600 ft/lb at 3000 and like most torque curves, you can see them low, they peak, and then reduce with rpm. This one was coming down at 3000 when the readings started. No idea where it was at a lower rpm. It was all about the long ram intake. Lots of low rpm torque, just as designed.

 

[Jeep Guy]

It sounds to me like you are having a gearing issue. You stated that you have 2.xx gearing. That is high gearing(low numerically) and will rob some bottom end, but give you better characteristics on the highway...lower rpm at 70mph and better gas mileage for example. On an episode of Roadkill on Motortrend TV, they had a similar issue. The engine would barely spin the tires due to a highway friendly gear even though it was a decent sized V8. If you figure out your tire diameter on you vehicle and get your gearing in the 3.35-3.55 range, you can still get decent rpms on the highway, but improve the bottom end. If your vehicle is an in-town, weekend cruiser, then you may even want a 4.10 final drive. What your doing is moving your torque numbers down lower with the numerically higher gearing. You will build power quicker and go through the gears quicker. This, of course, will cause higher rpm on the highway and use more gas as your rpm will be higher.

There are online calculators where you can enter your transmission gearing ratios for each gear (1st, 2nd, 3rd, 4th) along with the outside diameter of your tires along with your engine's desired rpm and it will show you what the rpm will be at certain speeds based on the final drive ratio you enter. You can find what is acceptable for your type of driving. Generally, you want somewhere in the low 2,000's for your rpm on the highway, but if it is a stop light to stop light weekend warrior, you may not care.

Here is a simple calculator from Spicer...

Spicer Transmission Ratio RPM Calculator

Use the Spicer Transmission Ratio RPM Calculator to determine your engine’s RPM based on the transmission gear ratio, tire height, MPH, and ring and pinion gear ratio.

spicerparts.com

 

[rumblefish360]

@273 What size tire, gear, transmission, converter stall, flash point, cars weight, carb and header and exhaust size?

 

[273]

It is also completely dependent on WHAT engine you're talking about. Some were not designed for bottom end torque. Some were designed for peak torque in a higher RPM range, like for instance, some 4 cylinders. So trying to "get" bottom end torque from some engines will always be a challenge at best. Anything can be built for "more" bottom end torque, but getting a lot of it from some engines will always be a challenge, since some are simply not designed for such.

Take the 6 318 builds one makes 282hp with xe262h 3 make about 400 hp with cams from xe268h to 280h all 4 make 335tq at 3000 rpm and one makes 425hp with xe275hl 355tq at 3000 rpm and the 477 hp comp solid 247/247 .622/.592 makes 350 tq at 3000 rpm and 335 tq at 2500 rpm over the stock 318 2bbl dyno 282 tq at 3000 rpm and 292 tq at 2500 rpm.

So I think it's safe to say all the modded engines make as much if not more torque under 3000 rpm and definitely makes more at 3000 rpm by 50-70 tq and way more above, the 477hp made 45tq more at 2500 rpm more than stock 318.

Conventional wisdom says bigger cam heads etc.. should be weaker less torque no bottom end especially with a 318 needing deep gears high stall not to fall on there face and not saying these engines don't need gears and stall but it obviously ain't from a lack of low end torque, why is it then some of these engines will fall on there face be a dog down low without gearing and stall. They all make good power down low, better than most stock A body engines.

 

[273]

It sounds to me like you are having a gearing issue. You stated that you have 2.xx gearing.

I know my car has a gearing issue, this ain't about my car directly just using as an example,

The take away my engine makes 380 lbs-ft at 2500 rpm a stock cammed magnum makes 385 lbs-ft at 2500 rpm which is way more then enough torque more than any stock /6-360 all those engine will work fine with 2.xx and stock stall why won't mine? I'm obviously making more than enough power down low.

 

[273]

@273 What size tire, gear, transmission, converter stall, flash point, cars weight, carb and header and exhaust size?

26/2.xx/727/2800 stall/3100lbs/800 cfm/1 3/4/2.5

My question is built engine even ones operating in higher rpm bands seem to make more than enough low end tq/hp 1500-3500 rpm generally more than stock why some are soft down low? Generally people go on about torque but I've noticing lately most of these engines make good low end torque more than enough they shouldn't be a dog down low. So my guess it would probably overlap or some other cam spec but not exactly sure why? but doesn't seem to me be a torque/hp problem.

 

[273]

Engines (good engines) make more power with less torque after peak torque.

Horsepower is real. It’s what makes cars go quicker and faster.

Did you have any thoughts on why? I figured you'd be able to.

It's always been described as lack of low end torque/power but as I've start to notice most mild to fairly wild engines have good low end numbers, single plain intakes bigger cams etc.. generally trade low for top end but even then these engine still make pretty good low end number generally better most stock A body engines, so my guess it ain't a lack of tq/hp down low but something like overlap or some other cam spec? That makes some of these engine feel like a dog down low.

 

[rumblefish360]

26/2.xx/727/2800 stall/3100lbs/800 cfm/1 3/4/2.5

26/2.xx = a 26 inch tire & 2.?? Gear ratio?
Then a 2800 stall in a 3100 lbs car with a 800 cfm carb, 1-3/4 headers with a 2-1/2 exhaust.

Correct?

Your problem is the whole package is a disastrous mismatch.
You’ve been told this before. What’s the problem?
The way the car is set up, I can run my *** to the ‘60 foot mark quicker than your car can. You’ve been told how to fix this issue before.

My question is built engine even ones operating in higher rpm bands seem to make more than enough low end tq/hp 1500-3500 rpm generally more than stock why some are soft down low? Generally people go on about torque but I've noticing lately most of these engines make good low end torque more than enough they shouldn't be a dog down low. So my guess it would probably overlap or some other cam spec but not exactly sure why? but doesn't seem to me be a torque/hp problem.

For the most part, you love to argue with myself tells g us we are wrong, twisting words around and manipulating words we say out of context to prove your point and others shoving your opinion and guessing as right and we are wrong.
And yet again you come here looking to fix an issue that you have been told you’re wrong on several times.

So tell us, how are you right, I’m wrong, but your car is slow as molasses dripping from a spoon on a cold January night?

 

[273]

26/2.xx = a 26 inch tire & 2.?? Gear ratio?
Then a 2800 stall in a 3100 lbs car with a 800 cfm carb, 1-3/4 headers with a 2-1/2 exhaust.

Correct?

Your problem is the whole package is a disastrous mismatch.
You’ve been told this before. What’s the problem?
The way the car is set up, I can run my *** to the ‘60 foot mark quicker than your car can. You’ve been told how to fix this issue before.

This thread ain't about my car, I know what needs to be done, I'm going with dual plain and less cam and possibly gears down the road.

i'm using as part of the example cause it fit's with what i'm trying to zero in on, plus it's known factor for me.

For the most part, you love to argue with myself tells g us we are wrong, twisting words around and manipulating words we say out of context to prove your point and others shoving your opinion and guessing as right and we are wrong.

If you say so

And yet again you come here looking to fix an issue that you have been told you’re wrong on several times.

This 1st time I brought up this question, I don't know answer but nothing you said so far has anything to do with what I asked.

So tell us, how are you right,

right about what?

I’m wrong, but your car is slow as molasses dripping from a spoon on a cold January night?

No **** the guy bought it from geared and stalled wrong, still got nothing to do with the question.

 

[Phreakish]

Part of it is relative power.
Making stock torque levels will never really feel powerful. It feels "soft" because 2k more rpm and suddenly you're pinned in the seat.
Part of it is the ability to rev. A dyno can load an engine to a greater or lesser extent than the chassis will depending on the car weight. Making the "same" torque on the dyno isn't the same as making the "same" in the car. Engines in a car are often able to rev quicker than a typical dyno pull let's it.
A big part of how quick an engine can rev is the weight of the rotating assembly (from the balancer to the wheels), part of it does come down to cam timing.
More duration and a late closing intake will affect the amount of work the piston can do. Typically the effect is pretty negative in the low rpm range (low momentum in the air column), but the gains are substantial in the upper revs. Resonance, wave pulses, and dynamic compression are all involved. It would take a thesis paper to explain it all in depth.
At the end of the day a torque engine doesn't like to rev, and a hp motor does.

 

[273]

Part of it is relative power.
Making stock torque levels will never really feel powerful. It feels "soft" because 2k more rpm and suddenly you're pinned in the seat.

That's was one of the aspects I thought might come into play

Part of it is the ability to rev. A dyno can load an engine to a greater or lesser extent than the chassis will depending on the car weight. Making the "same" torque on the dyno isn't the same as making the "same" in the car. Engines in a car are often able to rev quicker than a typical dyno pull let's it.

There's a major piece of the puzzle missing

A big part of how quick an engine can rev is the weight of the rotating assembly (from the balancer to the wheels), part of it does come down to cam timing.
More duration and a late closing intake will affect the amount of work the piston can do. Typically the effect is pretty negative in the low rpm range (low momentum in the air column), but the gains are substantial in the upper revs. Resonance, wave pulses, and dynamic compression are all involved. It would take a thesis paper to explain it all in depth.
At the end of the day a torque engine doesn't like to rev, and a hp motor does.

I was thinking it had something to do with overlap something where the cam got to get past a certain rpm heard it called (cam comes on) or something like that and even though it's making enough tq/hp the engine just lazy below a certain rpm cause of overlap duration etc.. basically resisting revs.

 

[Phreakish]

That's was one of the aspects I thought might come into play

There's a major piece of the puzzle missing

I was thinking it had something to do with overlap something where the cam got to get past a certain rpm heard it called (cam comes on) or something like that and even though it's making enough tq/hp the engine just lazy below a certain rpm cause of overlap duration etc.. basically resisting revs.

I wouldn't blame the overlap as much as duration. The less the valves are closed, the less time available to extract power/work from the chamber pressure.
If the intake valve closes well after bottom dead center, at low revs there's less pressured/density to compress. Effectively a "lower dynamic compression". This helps reduce pumping losses at high rpm, but without more static compression it makes the engine super soft down low.

Widening the lsa doesn't help this one bit. Advancing the **** out of the cam can though. There's still some loss of power extraction because the exhaust will open sooner but the gain in "dynamic compression" is usually better than the loss of work extracted by the piston due to the early exhaust. Getting the right static compression is even better.

Overlap, or a narrow lsa, can actually get gain back torque below peak due to the supercharging effect it can create. Of course, too much of a good thing is a bad thing too.

An engine needs to be built for a purpose. That purpose needs to be well constrained, and then from there the cam and heads and exhaust can be put together in an intelligent manner. Throwing "torque parts onto torque parts" doesn't go very far.

 

[273]

I wouldn't blame the overlap as much as duration. The less the valves are closed, the less time available to extract power/work from the chamber pressure.
If the intake valve closes well after bottom dead center, at low revs there's less pressured/density to compress. Effectively a "lower dynamic compression". This helps reduce pumping losses at high rpm, but without more static compression it makes the engine super soft down low.

Widening the lsa doesn't help this one bit. Advancing the **** out of the cam can though. There's still some loss of power extraction because the exhaust will open sooner but the gain in "dynamic compression" is usually better than the loss of work extracted by the piston due to the early exhaust. Getting the right static compression is even better.

Overlap, or a narrow lsa, can actually get gain back torque below peak due to the supercharging effect it can create. Of course, too much of a good thing is a bad thing too.

An engine needs to be built for a purpose. That purpose needs to be well constrained, and then from there the cam and heads and exhaust can be put together in an intelligent manner. Throwing "torque parts onto torque parts" doesn't go very far.

Thanks, exactly the type info I hoping for

 

[Bewy]

273,
You are a thinker & that is good.

If you are going to compare low end tq, the 'oomph' factor, between engines, two other factors have to be considered: car weight & drive train [ gearing ].

It is useless to compare one engine's tq to another if these factors are different. It becomes an apples to oranges comparison. With auto trans cars, the c'ter stall needs to be factored in. Quoted stall speeds are just that. A larger engine that has more tq at/near the stall speed will cause the c'ter to have a higher stall speed.

So many variables to take into account if you are going to make a real comparison.