Kento

It's funny to see you getting all defensive with a long-winded reply because your first post was "taken all wrong". You had a bunch of guys jumping on your case because you didn't explain yourself properly and thoroughly enough (part of the risk of posting your "opinion" on a forum-- remember that everyone can post an opinion on your opinion). All you did was complain about the lack of low-end torque, and how the rotary "feels like a six-cylinder under 4000 rpm". But for a "rotary enthusiast", you failed to mention a sequential setup, which would help you immensely under 4000 rpm.

Funny, you don't get that idea from your original post...

Should I say it again? "Stock sequential setup" Have you ever driven an FD with it? Instead of complaining about the lack of low-end torque, why not do something about it? Go talk to KDR about converting your car back to sequential turbos. Get fatter, grippier tires, and modify the suspension to handle it.

There are a few who pounce on a person asking an "easy" question, but for the most part, I only see people referring them to the search feature or a thread link so that the person will get the answer to the questions before they're even asked. If you post something on a public forum (especially an "opinion"), you're gonna have to get used to the fact that some people are going to voice their own opinions, asked for or not.

DamonB

So it is your contention that all fast or quick cars (or powerful motors) must turn stratospheric RPM?

rpm_pwr

It helps But seriously I have no idea WTF you are talking about. I said that to me engines with torque curves that fall off badly like that feel like they are being choked and that I find them boring. Thats MY OPINION, having owned such a car for three years.

That has nothing to do with RPM, if you could get good power out of a steam engine and have good near linear torque curve OVER THE RPM BAND THAT IS USED FOR PEAK ACCELERATION I'll have one of them.

I just dont like cars that have a bootload of torque down low, but die up top. Ever driven a race car that has to pull through a restrictor? It's the same feeling. Heaps of go, but you feel like it's a racehorse breathing through a drinking straw.

I couldnt give a toss about numbers on a tacho.

-pete

KevinK2

You missed the detailed yaw analysis on page 1. If the v8 has similar max hp to an FD, and both are geared with fd gearing and final ratio specific for same top end speed at redline, the acceleration curves for ea gear will be similar. Don't need 18 speeds, just enough hp.

t-von

iTrader: (8)

I feel the same way about my cousins 98 gt Mustang. It gets of the line pretty good but, falls flat on its face above 4k

poss

iTrader: (5)

I'm not disagreeing with you jim, but then why is it faster to shift around peak horsepower rather than peak torque??

I hope we agree that given identical weight, of two cars in a race, the one with a higher torque at the wheels is going to accelerate faster. Now is torque at the wheels more closely related to torque at the engine or hp at the engine? Here and i though i had it all figured out

rpm_pwr

LOL I have NO idea what that has to do with what you quoted from me. I completely agree with you! Doesnt change the fact that you can change gears all you want, doesnt change the fact that the car will call flat on it's ***.

-pete

rpm_pwr

Finally someone gets it! I'm sorry to hear you share my pain It's kind of like the non-seq torque hole but in reverse. OK maybe not THAT bad

-pete

jimlab

Apparently, and engines that make low end torque can't make any at higher rpm, and therefore are only suitable for use in 18-wheelers.

Stephen seems to think that engines are impact wrenches, and KevinK2 can't calculate wheel rpm from two different gear ratios and come up with the fact that at an identical rate of engine acceleration over a set period of time, the car turning the wheels faster is covering more ground. OK, I've had enough.

rpm_pwr

Lucky you tacked that on the end I never said that ALL motors with low end torque can't make high end torque. I just said that I found torque curves like the one posted aren't much fun (to me). It's simply another way of saying you can have a torque deficit up high too. Jesus Jim, you missed a chance to post your torque spreadsheet!

You do realise he said:
So if they're travelling at the same speed how is one car "covering more ground" than the other?

-pete

Shinobi-X

As far as your comments go on wheelspin and driving the car, it may be your level of driving skill and experience with the FD. I don't believe too many people hammer it in 1st, with a 'small' amount of 340rwhp- much less anything higher. If you had more torque in the low end, you would be even worse off.


Honestly, how much reading did you do on the FD's powerplant before you bought the car? As much as everyone would agree that rotaries lack torque, at 1.3L (for arguments sake...), it's simply too small a displacement to really do anything about. Also, were you aware of the non-seq. setup when you bought the FD? Depending on how it was done, it's possible that you can reverse it, and go back to the seq. setup which won't have as much lag. I would suggest getting a ride, or even driving a well running seq. FD if you have not done so already. I don't know what your mods are, but if you are making 340rwhp, you will most likely be running into boost issues when going back to seq. mode. Make sure to look into whats done to the car, and read up on whats necessary to accomodate seq. mode with that much power.

I also read that you are talking about wheelspin as the turbos kick in. The thing is, in seq. mode, the transition with your car may be a bit much if you are not experienced. Honestly, the FD may not be the car for you (but in any car with a good deal of power, low weight, inadequate tires, etc. you will get wheel spin).

I'd say the best bet for you, would be to drive a near stock, seq. FD to get a feel for how the car operates naturally. Then you can judge if seq. mode with your power level is something you want to deal with. There is no need to get defensive, but it sounds like the FD doesn't have enough of what you want, in many areas where you want it. V8 swap?

maxcooper

The torque at the wheels in a given gear are directly related to the gear ratio.

Optimal shift points are where the torque at the wheels curve in the lower gear crosses the torque at the wheels curve in the higher gear, or when you hit the redline. You shift when the torque at the wheels in the next gear will be equal to or greater than the torque at the wheels in your current gear.

CarTest has a "Drive Power in Gear" graph that will show a plot that aids in understanding if you want to see it.

-Max

maxcooper

I almost posted last night that I found driving cars with torque curves that drop off a lot on the way to redline, boring. This is a typical characteristic of engines that have a high torque-to-HP ratio. It is no fun when the car gets slower as you rev the engine out. That feels quite backwards to me. The shift shouldn't be the climax of the acceleration curve. I prefer if it peaks a bit after the shift but stays relatively flat the rest of the way out. I even find the rev to redline anti-climactic on high-revving engines if the torque curve drops off a lot. I am glad rpm_pwr posted his feelings, which are the same as mine on this matter. It doesn't make the car any faster or slower (necessarily), but engines whose torque curve is sloped downward for the range you accelerate in aren't as much fun to drive. I don't want to dig gears for my main enjoyment; I want to let the engine scream.

The inertia that comes with large displacement (required for beefy low-end torque) is also a downside from the "driving experience" perspective (and again, has little to do with actual performance). It feels like the flywheel is 50 lbs too heavy, and I love my light flywheel. Heavy rotating assemblies give the engine a "clunky" feel.

Torque proponents often bring out driving feel as a justification for their engine preferences, but good low end torque is not the only part of the driving experience that matters. I am definitely NOT saying that I think low end torque is worthless. I like low end torque. But producing it often comes with some downside in these other areas.

-Max

DamonB

RPM is not a requirement of horsepower, but for two identical engines the one that spins to higher RPM will make more power. At the same time two engines may have the same horsepower with one turning much less RPM. Given that, the engine with less RPM must have more torque (otherwise it would make less power). The higher torque motor can run with longer gear ratios than the other and yet still acheive the same speeds in the same amount of time. A motor makes power. Whether it it reaches the top of its power band and "falls on its face" at 5000, 8000 or 10,000 RPM makes no difference; all motors have an optimal range. The purpose of a multi geared transmission is to try and keep that motor operating within its power band at all vehicle speeds. If gearing and motor characterisitics had nothing to d with speed you could judge every car merely by the redline on the tach.


That's perfectly alright with me, it's everyone's choice. My point was that the "feel" you describe does not translate to more or less power.

In recent years racing motors spin to higher and higher RPM. One reason is that in most racing organizations the engines are limited to a fixed displacement and number of cylinders. Given a fixed displacement the only way to get more power is to spin the motor faster. This will make the motor peaky in its power curve and place even more emphasis upon the gearing selection due to the narrower power band. Lots of power available, but at the expense of having to shift often.

KevinK2

prior jim:

"Simple math dictates that if torque at the axles is the same for each, the car in the higher gear will cover more ground at any given rpm because it will have a higher wheel speed"

recent jim:

"...and KevinK2 can't calculate wheel rpm from two different gear ratios and come up with the fact that at an identical rate of engine acceleration over a set period of time, the car turning the wheels faster is covering more ground."

you changed your original statement.

1st case was based on equal torque at the axle. equal axle torque means equal tractive force at contact patch for same dia tire, giving equal acceleration for same mass cars. acc'n = mph change per sec. the taller geared car will not pull away from the other.

2nd case is identical ENGINE acceleration, never mentioned in the prior post, and indeed contradicts the equal axle torque reference. If equal engine acceleration exists, the taller net geared will pull away, and the axle torque will be higher for that car.

SPOautos

Actually your impact wrench is a good example as it wouldnt do much work if it didnt turn rpms.....and in addition if you want to get a bolt down a real long stud real fast you'd need to turn fast rpms. Turning it with a lot of force but very low rpms makes each turn fast but makes the overall speed slow cause its not covering much ground without the rpms. Using the same amount of tq with high rpms is going to generate much more work and accel much faster. Surely you already know this and understand the basic concepts behind work and hp.....I think your just wanting to argue with us hehe

STEPHEN

DamonB

It's not covering much ground because it is direct drive. If it was geared up through a transmission it woud turn the bolt very quickly. Power is power. Whether it come from torque or RPM.

SPOautos

You might not have meant this statement to the degree that you said it but actually rpm is a requirement of hp. tq x rpm / 5250 = hp so if you take tq x 0 your going to get 0

I understood the point you were trying to make about tons of tq and low rpm or small tq and high rpm I just wanted to clarify that first statement so someone didnt get confused.

STEPHEN

SPOautos

EDIT*

Gearing it to create more acceleration is going to cut off your top speed and depending on how far you need to go still end up slower.

However, going back to my example of 1:1 for simplicity, if they make the same amount of tq but one turns 2000rpms and one turns 4000rpms your going to get twice the work (accel) from the later.

STEPHEN

DamonB

Of course. If the torques are the same and one is spinning twice as fast it is making twice the power. My point with the impact gun was that if it had a whole lot more torque than was actually needed to turn the bolt then it could be geared to turn that bolt a whole lot faster. That's exactly what a transmission does: It trades off torque at the wheels for higher RPM as the mass of the car is accelerated.

Be careful of relating acceleration to work; doing twice the work does not double the acceleration. One is work over time, the other the rate of change in work over time. They are not linear to eachother.

DamonB

Lower gearing will cut off top speed but will increase acceleration. You're automatically assuming it to be slower and that's incorrect; over what distance is every bit as important.

Simple example is drag racing. Cars with higher trap speeds get beat to the finish line all the time. Why? Because the car with the slower trap accelerated at a higher rate in the beginning of the run.

DamonB

RPM is no more a requirement to make power than torque. Given the fact that you multiply the two together you can see you can get exactly the same power by having 5 ft pounds X 100 RPM as having 50 ft pounds X 10 RPM. Power is the same in either case and obviously if either is zero you have no power. One is not more or less important than the other as far as making power is concerned.

SPOautos

Exactly, if you have the same tq at low rpms and high rpms your going to be faster in the high rpms which was my entire point. Jim made the comment that with a V8 having the lowend tq there isnt a need for downshifting. I made the comment that downshifting puts him in the higher rpms where he will have more acceleration and that tq over time is the way to make acceleration not just flat out tq. Then he commented by saying I thought a car engine was an impact gun when lead me to use the impact gun demonstration to show how it would benifit from higher rpm. The point about if it had a trans was really irrelevant to an impact gun cause it doesnt.

ANYWAY, its the tq x rpms that creates acceleration not just tq alone. Tq alone wont create anything and rpms alone wont create anything. You can make less tq at higher rpms and be MUCH faster than a ton of tq at low rpms. This was my point. If someone wanted to make the same hp at 2000 rpms that i make at 6000 they would need to have 1081 lbs of tq. Its going to be much harder to make that kind of low rpm tq versus making 1/3 that amount at a higher rpm. And they are going to accelerate the same all other things being equal.

STEPHEN

SPOautos

I didnt say that either was more important that the other. I said that rpm is a requirement cause you said it was NOT a requirement. I was mearly correcting that statement and even mentioned that I realized you didnt mean it to that degree I just didnt want someone to get confused and think they could make hp with no rpm.

STEPHEN

DamonB

Not if the gearing is designed to take advantage of each motors response...The motor making high torque and low RPM will be able to maintain acceleration with a much lower gear ratio than the other motor; it won't have to turn high RPM to keep up, the gearing will do that. As long as the gearing suits each engine's power characteristics the speed of the two cars can be made the same.

Top Fuel dragsters are the fastest accelerating cars on the planet and they turn considerably less RPM than just about all other open wheel race motors. They do this while acheiving higher top speeds and all the while turning massively tall tires compared to other racing cars. How is that possible? Hmmmmmm.

Gears are levers. Give me a lever long enough and I will move the earth with my own two hands.


Sorry. I meant to say RPM is not the sole requirement of power and later provided examples of two motors making the same power but with very different torque vs. RPM.