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Discussion Starter · #1 ·
I recently posted a message at various forums asking about how to get the most low end torque out of my '79 ZX, and I've gotten alot of responses telling me that I shouldn't be worried as much about low end torque but rather the high end. I want my 280 to be a real street fighter in a small package. So I was wondering, should I concintrate on the low or high end?
 

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Discussion Starter · #2 ·
> I recently posted a message at various
> forums asking about how to get the most low
> end torque out of my '79 ZX, and I've gotten
> alot of responses telling me that I
> shouldn't be worried as much about low end
> torque but rather the high end. I want my
> 280 to be a real street fighter in a small
> package. So I was wondering, should I
> concintrate on the low or high end?

for street use low end torque is always much more useful. high end horsepower is great for the freeway or the racetrack. it's just more difficult to make low end out of a small displacement motor like the l28. the 3.1 liter engine build is a good way to build low end, as well as raising the compression ratio and installing a better cam.
a good person to talk to is bob hanvey. he's built some strokers and has done the p-79 head modifications. you can view his site at <A HREF=http://www.geocities.com/MotorCity/Track/6997>http://www.geocities.com/MotorCity/Track/6997</A>/. he also post here quite a bit.
 

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Try this comparison

> for street use low end torque is always much
> more useful. high end horsepower is great
> for the freeway or the racetrack. it's just
> more difficult to make low end out of a
> small displacement motor like the l28. the
> 3.1 liter engine build is a good way to
> build low end, as well as raising the
> compression ratio and installing a better
> cam.

That information is true, to a point. Try doing a comparison between the Acura Integra GS and GS-R. Both of these cars use a 1.8L DOHC, but the GS has 140hp, while the GS-R has 170. Also, the torque from a GS is about 125ft/lbs and the GS-R is about 110ft/lbs. The main difference between these two engines are the cams and intake manifold.

So, why is the GS-R faster??? The reason is because it has more hp, and produces it at a higher rpm. This means that the engine can remain in any given gear for a longer time, and produce more mph (work/time aka hp). While it may lack low-end launching capability, it makes up for it once it reaches high rpm. It is better to make torque at a higher rpm to take advantage of this, so that when you shift, you land right back into the 'fat' part of the torque curve, which keeps you moving. So, a torque curve that peaks higher is better than one that peaks lower, once you're moving.
But, a low-end torque is better to GET moving initially. This is why semi's produce only [email protected], but produce over 500ft/[email protected] of torque. But, this is why they have 13speeds!! Having more hp, would make them faster and reduce the need for so many gears, but then they would have more trouble to get moving. Make sense??

Basically, you want enough low-end torque, to get you moving, but don't want all of it in the low-end. You want the torque curve to keep extending, so that when you shift you are still climbing in torque, rather than having already peaked. This means you need hp, to get the rpms up and enable you to shift at a good rpm.
 

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Discussion Starter · #4 ·
Re: Try this comparison

here's another comparo. the new honda s2000 vs. the bmw m roadster. i chose these two cars because they make the same amount of horsepower, but in two different ways. they also weigh close to the same. let's start with the honda- now depending on what you read, this car makes 240 hp @ 8500 rpm and 159 lb-ft torque @ 7500. the car has a curb weight of somewhere between 2500 and 2800 lbs. the 0-60 time is between 5.5 and 6 seconds. i haven't read about a quarter mile time yet. the bmw on the other hand makes 240 hp @ 6000 rpm and 236 lb-ft torque @ 3800 rpm. the 0-60 time is between 5.1 and 5.3 seconds. the 1/4 mile time is 13.7sec/ 101 mph. also bear in mind this car weighs almost 3100 lbs, at least 300 lbs more than the honda. looking at the numbers, the bmw should win anywhere on the street and in a drag race, but the honda should pull higher top speed numbers.
 

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Make HP and gear accordingly

That is the adage of a famous Corvette tuner,although I can't remember which one.Make the horsepower but have the gear to get you movin' at low rpm.If you alredy have a 3.90 gear and 5 speed the only way to get more gearing at a cost effective price is to swap tranny input shafts this way your effective gearing can be changed as if the rear end was a 4.37 or 4.65(in first three gears and 5th ;4th is unaffected due to 1:1) .I've posted this before so i wont go into the details.But the bottom line is it works and allows the use of big cams which kill low rpm torque but make killer HP.So, make HP and gear accordingly. Later,norm
 

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Exactly my point!

> here's another comparo. the new honda s2000
> vs. the bmw m roadster. i chose these two
> cars because they make the same amount of
> horsepower, but in two different ways. they
> also weigh close to the same. let's start
> with the honda- now depending on what you
> read, this car makes 240 hp @ 8500 rpm and
> 159 lb-ft torque @ 7500. the car has a curb
> weight of somewhere between 2500 and 2800
> lbs. the 0-60 time is between 5.5 and 6
> seconds. i haven't read about a quarter mile
> time yet. the bmw on the other hand makes
> 240 hp @ 6000 rpm and 236 lb-ft torque @
> 3800 rpm. the 0-60 time is between 5.1 and
> 5.3 seconds. the 1/4 mile time is 13.7sec/
> 101 mph. also bear in mind this car weighs
> almost 3100 lbs, at least 300 lbs more than
> the honda. looking at the numbers, the bmw
> should win anywhere on the street and in a
> drag race, but the honda should pull higher
> top speed numbers.

OK, the Honda: [email protected], 159ft/[email protected] Look at where peak torque is. When you shift, you are going to fall WAY below the peak torque. You'll probably fall around 5500-6000 when you shift. This is not very good, and hurts acceleration. But the Honda still has 0-60 of 5.5-6.0 why?? This is due to the HP. Because once it is in a gear, it can stay in that gear for a long time, this makes up for the utter lack of torque. I would bet You can probably hit 40mph in 1st gear. Probably hit 60mph @6500-7000rpm in 2nd. This proves the importance of gearing.

Now the BMW: [email protected], 236ft/[email protected] So if you shift @6000, you drop to @4000, which is right smack in the 'sweet spot' of the torque curve. So the BMW is making peak torque at a very useable rpm. The BMW will require shifting sooner than the Honda, but will pull harder in each gear compared to the Honda.

So, the moral of the story is:
The BMW needs to shift to stay moving, while the Honda can stay in a gear for a long time, but suffers when you shift. Great example of hp vs. torque.
 

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Discussion Starter · #7 ·
Re: Exactly my point!

> OK, the Honda: [email protected], 159ft/[email protected]
> Look at where peak torque is. When you
> shift, you are going to fall WAY below the
> peak torque. You'll probably fall around
> 5500-6000 when you shift. This is not very
> good, and hurts acceleration. But the Honda
> still has 0-60 of 5.5-6.0 why?? This is due
> to the HP. Because once it is in a gear, it
> can stay in that gear for a long time, this
> makes up for the utter lack of torque. I
> would bet You can probably hit 40mph in 1st
> gear. Probably hit 60mph @6500-7000rpm in
> 2nd. This proves the importance of gearing.

A couple of things, if you want acceleration, shift after your peak torque not 500-1000RPM before it. Also, your HP peak is where you'll experience the best acceleration for a given speed, so if you have a smooth torque curve then you also want to shift at your HP peak. In the case of the honda, a good idea would be to shift a bit after HP peak so your revs don't fall too far below the torque peak in the next gear. Simply: HP peak = best acceleration for a particular speed, torque peak = best acceleration for a particular gear.

> Now the BMW: [email protected], 236ft/[email protected] So
> if you shift @6000, you drop to @4000, which
> is right smack in the 'sweet spot' of the
> torque curve. So the BMW is making peak
> torque at a very useable rpm. The BMW will
> require shifting sooner than the Honda, but
> will pull harder in each gear compared to
> the Honda.

> So, the moral of the story is:
> The BMW needs to shift to stay moving, while
> the Honda can stay in a gear for a long
> time, but suffers when you shift. Great
> example of hp vs. torque.

But considering the BMW has more torque, the BMW would be geared lower and probably finish its gears at about the same speed as the Honda, I suspect the BMW would be slightly faster(assuming equal weights) because of the wider torque curve the figures indicate.

Project#2501
 
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