1981 Mint 400 Flareside Race Truck

Very true, Bob.  I was aware of the equation, but was thinking backwards.

So, the torque and HP will be equal if the torque peaks at 5252 RPM.  And if the torque value is less than the HP it means the torque peak is at less than 5252 RPM.  But if the torque value is higher than the HP value then it means the torque peaks higher than 5252 RPM.  Did I say that correctly?

To put this into perspective, I tout Dad's engine as having 400 HP and 500 ft-lbs, but without telling what the RPM is for either.  However, since you are always quoting the torque peak, then you have enough info to solve the equation: 400 HP comes from exerting 500 ft-lbs of torque at 4200 RPM.  And 350 HP comes from exerting 400 ft-lbs of torque at 4600 RPM.

So, Dad's engine has more 25% more torque but only 14% more HP than the Mint engine.  That's because the torque peaks at 9% lower RPM than the Mint engine.

Gary Lewis wrote

So, the torque and HP will be equal if the torque peaks at 5252 RPM.  And if the torque value is less than the HP it means the torque peak is at less than 5252 RPM.  But if the torque value is higher than the HP value then it means the torque peaks higher than 5252 RPM.  Did I say that correctly?

To put this into perspective, I tout Dad's engine as having 400 HP and 500 ft-lbs, but without telling what the RPM is for either.  However, since you are always quoting the torque peak, then you have enough info to solve the equation: 400 HP comes from exerting 500 ft-lbs of torque at 4200 RPM.  And 350 HP comes from exerting 400 ft-lbs of torque at 4600 RPM.

Hmmm? Trying to understand this... 4.9L with ~120 HP and ~260 ft. lb. torque @ ~1600 RPMs?

260*2425/5252=120

In other words, the 260 ft-lbs has to be at 2425 RPM to get 120 HP.

Thanks, Gary.

Gary Lewis wrote

....  So, the torque and HP will be equal if the torque peaks at 5252 RPM.

True, the horsepower at the torque peak will be equal to the torque if the torque peak is at 5252 rpm.  But unless the engine has a REALLY peaky torque curve the torque will be not be falling off as fast as the speed is increasing.  So the peak horsepower will be higher than the peak torque, and at a higher speed

Gary Lewis wrote

And if the torque value is less than the HP it means the torque peak is at less than 5252 RPM.  But if the torque value is higher than the HP value then it means the torque peaks higher than 5252 RPM.  Did I say that correctly?

You are almost (but not quite) backward.  First of all, if the torque peak is above 5252 rpm, then the horsepower at the torque peak will be higher than the torque.  For example, an engine making 400 lb-ft of torque at 6000 rpm is making 457 hp at 6000 rpm.

But in reality you can't simplify it that much.  Because an engine with torque less than hp can still have the torque peak below 5252 rpm if it has a very flat torque curve.  For example, an engine with a torque peak of 200 lb-ft at 4000 rpm might only drop off to 190 lb-ft at 6000 rpm, which would be 217 hp.

You can use the 5252 to give you some tendencies, like if torque is higher than horsepower that you don't have a screamer.  But the variability in the shape of the torque curve keeps you from being able to pinpoint it.

And that gets to an error in your later hp and torque calculations...

1986F150Six wrote

Hmmm? Trying to understand this... 4.9L with ~120 HP and ~260 ft. lb. torque @ ~1600 RPMs?

Gary Lewis wrote

260*2425/5252=120

In other words, the 260 ft-lbs has to be at 2425 RPM to get 120 HP.

That would be true if the torque and power peaks were at the same engine speed.  But that would only be true if the engine had an exceptionally peaky torque curve.  Generally the torque falls off fairly slowly as you speed up past the torque peak, so the power is actually going up as the torque goes down.

For instance, this engine might make 260 lb-ft  at 1600 rpm, which would be 260*1600/5252=79 hp.  But it might only be down to 210 lb-ft by 3000 rpm, which would be 210*3000/5252=120 hp.

That illustrates a useful take-away.  Peaky engines can be a kick to drive, but broad torque and power curves are more pleasant.  One way you can tell by engine ratings whether the engine is peaky or broad is to look at the rpms at the torque and power peaks.  If they are close together, then the engine is probably pretty peaky.  But if the power peak is at an engine speed significantly higher than the torque peak, then it's probably pretty broad.


Oh, and by the way, some might notice that I say "lb-ft" while others say "ft-lbs."  Torque comes from multiplying the force (lbs) applied to a lever arm (ft).  And multiplication doesn't care which order you go in, so ft multiplied by lbs would be mathematically the same thing.  So neither lb-ft or ft-lb is incorrect.  However, energy is also described in units of force times distance.  So to avoid confusion, in the English system of units engineers and scientists use "lb-ft" for torque and "ft-lb" for energy.  But as I said, mathematically they are identical, so it really doesn't matter.

So, I drive a truck with a rather flat torque curve engine that operates well below the claimed 120 HP, since I rarely drive beyond 2500 RPMs.

It never accelerates quickly, is pleasant to drive [slowly!] and when placed under a strain [load], the engine can be "heard" to say, "is that all you have?"

 

Bob - I clearly didn't fully comprehend that of which I typed.  

But, I do think I understand what you said.  And, well said it was.  So, I'll leave it at that and cease and desist.  

David - Yes, your engine is happy down low, has a flat torque curve, and yet rarely reaches 2425 but probably never does that at full throttle so never produces its max power.  It just putt putts along, quite happy to be driven by an almost grandfather.  

1986F150Six wrote

So, I drive a truck with a rather flat torque curve engine that operates well below the claimed 120 HP, since I rarely drive beyond 2500 RPMs.

It never accelerates quickly, is pleasant to drive [slowly!] and when placed under a strain [load], the engine can be "heard" to say, "is that all you have?"

Keep in mind that the speeds I picked for the torque and power peaks were picked sort of at random so I could illustrate the math.  The real point is that you need to know those speeds to really understand the characteristics of your engine.  (Actually you need the power curve, showing power at all engine speeds to REALLY understand the characteristics.  But if all you have is the torque and power numbers, knowing the engine speeds they correlate with is helpful.)

wow...i am infatuated with frank vessels beast. thank you for sharing!

curt milinder was the owners name i bought this truck years ago from him it now lives in las vegas

Cool!  Is it still your truck?  If so, can you get more pics?  Anyway, can you tell us more about it?

Bringing back and old thread from the dead for anybody new that hasn't seen these pics from the absolute glory days of the Bullnose! From the Mint 400 in Las Vegas 40 years ago. The 138HP 351M was never made to look so good, before or after, eh Gary Lewis??

What I love seeing.  Im on a group that posts 80s/90s truck builds as my goal for my truck is a 80s/90s themed setup.

Nothing says 70's / 80's more than hundreds of people just standing beside the track, literally a few feet away from a 3500lb lump of steel flying through the air, on the ragged edge of losing control at any time.

If you give it time and distance even 138 HP can get things rolling.  

As for the people, I've been there, done that.  Not on that race but on other races.  

ooohhhh. i gotta build me one o those!!!!!

mat in tn wrote

ooohhhh. i gotta build me one o those!!!!!

Idea I had was to source another '82 F150 like mine but gut it and build a strict mudding/offroad 4x4 version of my truck same rims and all and use my truck to trailer it.

i like the way you think

lol Yep I just wish I had the money and time to do all these ideas.  I know it would be interesting having them both built exactly the same one just a bare bones off road truck and the other the tow vehicle.

I keep building the toys and not the tow vehicles. no trailer queens here