I hear a lot of talk on this board about torque. Low-end and high-end. I hate to make myself sound like a "newb", but is anyone out there up for the challenge of trying to help me understand what it is that torque feels like?

I've only really begun to understand how cars work within the last two years of my life. Before that, not a clue. So, despite having learned A LOT since, and having now done a lot of my own repairs, I am still missing a lot of that gut instinct a lot of you have developed over the course of years of working on these cars. The idea of trying to tune a car, or diagnose a car's problems "by ear" or "by feel" just isn't an option for me yet. I haven't developed the know how, I haven't had the experience. I'm hoping maybe someone out there can help me speed up the process.

My recently swapped engine is now running, in fact my car is driveable. But something just doesn't feel right. The engine sounds "low" to me, that's all I can say really. "Low" as in sound frequency, frequency of rumble and vibration. When I rev the engine I get a low VROOM that I'm not used to, it seems foreign to me when compared to the engine I just replaced.

When driving around town it seems almost acceptable. But I REALLY notice the difference when I'm on the highway, or going up a hill. It can handle the hill, but I feel like my engine has to go into really high RPM's to get up it. And, with the high RPM's is a deep, low VVVRRROOOOOM.

I think that if I understood the whole "high end/low end" torque thing, and what controls it, I might be able to to better understand why my engine feels the way it does.

Any advice guys? Thanks!

-Matt

Torque is rotational force.
An engine is an air pump. Depending on how the timing of the valves is arranged, it pumps most effectively within a certain envelope of engine speed. (RPM)
At it's most efficient engine pumping speed, you will generally see peak torque.
By changing when the engine pumps most effectively via the valve train and intake/exhaust considerations, you can move the peak power around. (HP)

HP = Torque * RPM / 5252

That introduces time to the description of what the engine is doing. HP is simply the amount of force that can be applied over time. Now the engine's operation can be described in terms of the Work it can accomplish.

By lowering or raising the peak torque rpm, the engine pulls harder (does more work) at the corresponding rotational speed. An engine that is set up for low rpm operation will pull harder at the corresponding low rpm.
HP figures can be increased easily by building rpm, something most of our slant six engines don't do well. They don't breath well at high revs, and the undersquare configuration doesn't lend itself well to making peak power at those speeds. (Undersquare; the cylinder bore is smaller than the stroke.)

If your engine is otherwise healthy, the cam may be retarded slightly. Just a bit will do it. By advancing the cam, the peak pumping efficiency moves to a lower RPM. By Retarding the cam, that peak pumping efficiency is moved to a Higher RPM. Within limits.

Hope that helped rather than hindered.



CJ

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Part of Tyrde-Browne Racing

HUH?

And Matty what are you trying to describe? Does the engine 'feel' "lazy"? If so I would say the timing events are slightly retarded. (thats where all the cam degreeing plays part in how the engine 'pulls')...

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Retarded cam --> higher RPM efficiency/power.
Advanced cam --> lower RPM...

Lou

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Home of Slant6-powered fun machines since 1988

CJ:
Or perhaps more simply put, Hp is a description of how fast torque can be delivered; Hp is a rate. Higher the HP the greater the amount of torque that can be applied in a given time period.

Think back to high school first semester physics where we may remember definition of torque, but if like me, a refresher is needed for this stuff.

Simply think of your arm pulling or exerting a force on the handle of a wrench while turning a bolt. The length of that handle times the force or pounds of pull assuming 90 degrees to bolt & 90degrees to handle of wrench will give you torque.

So if wrench is two feet long, and you are pulling on the end of it with 20 pound force, the torque generated to turn that bolt is [2’x 20#] = 40 lb ft. This is similar to calculating work where force times distance = work, except the force generated is rotational such as a piston pushing on a crank shaft causing it to rotate or that bolt.

Clear as mud, right? There is more!

Now Horse Power; a rate of delivery of torque, or in other words in one second how much work can be done; recall force times distance.

You may have compared different engine’s of similar displacement output from different manufactures, and noticed some have higher HP compared to torque such as 300 hp, 250 Lb ft, and the other way around 200 hp, 350 Lb ft such a diesel engine, or 300 Hp, and 305 Lb ft. a common relation of Hp to torque for an American V8.

Often engines that make big hp and less torque are high rpm engines, and low hp high torque are low rpm engines such as a stock slant six.

So a way to think of torque is; it’s the force that moves your car. The more torque the easer the car will move, the easer for it to maintain a steady speed over hills.

I don’t know if this helped you, but it kept me out of trouble for a few minutes this morning… LOL

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Thanks for the advice guys, especially Ceej and Wja jr for spelling it out for me. I wouldn't say that my understanding is crystal clear yet, but I'm getting closer.

I would say that right now, my engine is having to work harder to maintain higher speeds/go up hills. I have to feed it more gas and rev it up higher to maintain my speed.

Everything needs to be adjusted. My idle RPM is high right now, higher than it should be. Currently my distributor is set to put the timing somewhere in the 5-10 BTDC range.

Luckily, I have found a local guy on Craigslist who's big into classic Mopars. He's supposedly done a lot of work on Slants and he's offered to take a look at my car and hopefully help me get my engine/carb tuned up good. I'm going to take notes on everything he does. That will be Thursday, I'll let you all know what I learn.

Thanks again!

-Matt

Do you know the rearend's gear ratio and weight of your vehicle?
When yopu meet with your "tuner", see if he can run a compression check. It is helpful to know the engine's cranking compression, in psi.
DD

Doc, forgive me for knowing the fraction, but I have the 7 differential (is it 7.25?), as opposed the 8 (8.75?). I'm not sure of the weight of the car off hand, perhaps you have reference materials siting the weight of a stock '73 Valiant 4-door? The previous owner of my car painted over the stickers with touch-up paint.

There is definitely something wrong here. I just drove my car 30 miles to a friends house. It acted very strange on the highway. Didn't want to let me go past 50-55 MPH. If I were to have pushed it any faster the engine would have been very very loud. It was also running "rough" at these high speeds. Also, my engine got hotter (right under half way on the gauge) cruising at 55 than my old engine ever did, even on a trip into Boston on a 95 degree day! There should be no reason for this heat, I blasted all of the rust out of this engine with an air compressor. There should be no blockages in there. When I got off the highway, temp came right down to normal. Something isn't right!

I will definitely check the compression tomorrow and report back. Thanks.

-Matt

Well I'm not gonna give you any fancy technical advice. But depending if you have a stock exhaust or not. It's gonna have somewhat of a low tone. Mine is straight piped with a glasspack it has a deep quiet rumble at idle and has a very loud throaty roar when you rev it up. My "power" doesn't really kick in till after 2k rpms. Then I really get cruising. I've never had a problem on the hwy, been able to go speedometers top speed of 85mph a few times no sweat. However it doesn't like hills. There is a hill by my house that I go up sometimes. It's got a pretty good slope to it, I have to shift down to second and take it up to 3k before I go to 3rd. But I have a truck so I got more weight. Like I have come to realize and someone on here told me, a slant has a sound of it's own. Oh and one more thing, yes the engine will get louder the faster you go, at 65mph mine runs at about 2800rpm it's pretty dang loud. Especially when your floor dosent have any insulation:D

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Current truck: 98.5 Ram 2500 ccsb, sport, 24v cummins, 5spd, 4.5" lift, 35's, 5" straight pipe.

Having the needle pointing right under half way on your temp gauge isn't bad at all. You don't want it running too hot but running too cool can cause a lack of power and mileage.

Whats your rear end gear ratio? Check the inspection cover on the rear end. There might be a metal tag on it that will say 2.76 or 3.23 etc. Let us know what you find.

Also are you 100% sure the engine was running rough or could it have possibly been a vibration from your wheels not being balanced?

Your '73 Valiant 4-door weighs between 3200 and 3500 pounds or so, depending on equipment. It almost certainly left the factory with a 2.76:1 ratio in the 7¼" rear axle.
Sounds to me as if your transmission isn't shifting out of second…or possibly not even out of first! Drive it up to 45 mph from a standing stop and count the shifts. If you do not feel a 1-2 shift around 10-17 mph and a 2-3 shift between 25 and 32 mph, you've got transmission issues.

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Too many people who were born on third base actually believe they've hit a triple.

Fixed it. Typing too fast or something.

CJ

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Part of Tyrde-Browne Racing

Sorry for the delay guys, I had a busy day. Thanks for the info Dan. It's probably safe to assume I have the 2.76:1 ratio. I looked under the car at the differential but couldn't see any numbers. Might have to jack the car up to get at them. Either way, my Valiant was one of the bare-bones models... didn't come with any frills, so I think it's pretty safe to make assumptions about it.

Dan, you are so right about the transmission. Have you, or anyone ever heard of a transmission that neglects to switch gears in the rain? I didn't put two and two together earlier, but it's been raining heavily here today and yesterday. I specifically remember a time months and months ago where my transmission didn't want to switch when I was driving on the highway and the roads were significantly wet. Safe to assume this is probably a sign of a failing transmission, eh? Although, the good news is, I have a total of 3 other transmissions to choose from, 2 in my garage and 1 in my parts car. Not looking forward to doing a swap, but if I have to I will.

I just drove the car 30 miles home after hanging out with my friend for the day and the problem I experienced earlier was significantly better this time. I suspect my transmission shifted normally into 3rd gear this time around.

Engine was still running hotter than I'm used to, but is that to be expected of an engine with new rings? Most of the Slant's I've driven in the past have rings that are worn to hell. I guess it would make sense that good compression would create more heat.

At a stop, in neutral, I accelerated my engine up into very high RPM's and yeah, it is a little rough at very high RPM's. There's a shake about it. But, this engine hasn't been fine tuned so we'll see if some timing and carb adjustment won't change that. I should also note that I have an exhaust leak about halfway along the pipe, right in the center of my car. Is it possible for an exhaust leak to affect engine performance? If I lean down next to my car when it's running I can hear a pop pop pop that seems to coincide with slight stutters in my engine. This is true of both my current engine and the one I replaced.

So, to summarize, my car needs work! It never seems to end, but I don't mind, cause I love my car! I'm gonna get this bugger where it needs to be.

Thanks guys!

-Matt

Your engine is misfiring; that's what's causing the roughness — time to go through and check all the secondary ignition components (distributor cap, rotor, plug wires, coil wire, coil, spark plugs) and go through all the tune-up components again. Tune-up parts and technique suggestions in this thread.

Your transmission not shifting could be a minor issue or a major one. Start with a kickdown linkage adjustment. Loosen the 7/16" bolt near the top of the rod that runs from the manifold bracket down to the transmission, and shorten the rod (the bolt and its square washer slide once loosened -- you want to slide the bolt towards the front of the car). Try about a half inch. That's going to be too much, but we're trying to isolate the cause of the problem here. Tighten the bolt and go drive. If the car now behaves more normally or short-shifts into third at an inappropriately low speed (basically the opposite of your present problem) then you know a more precise adjustment of the kickdown linkage is called for.

Come to think of it, make sure the linkage is assembled and installed correctly. And did you use the thick or the thin gasket between the carburetor and the intake manifold? It needs to be the thick one or you'll have effectively lengthened the kickdown linkage and caused a no-upshift problem.

You do have the three books described in this thread, right?

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Too many people who were born on third base actually believe they've hit a triple.