Low End Torque

[matt0941]

Ok I think that I have a general understanding of horsepower vs. torque. And I also know that many people are fond of the KA-T because of its low end torque and desirable (for many) power curve. But I am still unsure of how my car will feel once I turbo the DOHC motor. Generally speaking... With the turbos that I will probably end up choosing from (T04E, T3/T4 Hybrid, GT3037) what can I expect. From this I mean, how early before the redline will I hit my torque peak, I know that a KA-T will not be optimal shifting at the red. Also does the low end torque limit this car from being a highway monster (I know that any car can do pretty much anything with enough cash, but again... generally speaking)? I am pretty much unsure of the difference that the long stroke makes on the actual acceleration of the car at high speeds. Alot of the cars that I have researched in the past (like the 300zx, MKIII + MKIV Supra, 300zx, SR20 powered 240s) have a tendancy to not be great 1/4 mile cars because of the way they are built. Granted there are 9 second supras out there, I am not denying this... I am more so speaking of wheel hop issues and that they disown any car on a roll. I would like to know how my car would handle on a roll and am pretty much looking to be assured that if some mustang revs his engine at me at 60 I will be able to hit 120 before he can tap his gas. And no I don't encourage being a moron on the highway but I don't drive 100% legally.

[cnichols]

With the torque monster that is the KA-T....if you're cruising on the highway, you're basically right in the fat part of the powerband. And, if yours turns out anything like Chris May's, there's not much difference between 3500 and 6500 (at least not compared to other cars).

You're going to have gobs of torque at basically any RPM, so don't worry about it. It won't really matter if it's an 800 hp Mustang anyway (it'll crush you)...but you shouldn't have a problem with GT's and stock Cobras. Although I wouldn't be surprised if some of the mildly modified ones put up a decent fight.

[GirlRacerS14]

I don't really know all the specifics but i can tell you from experience. Even with just 7psi on mine i spend a lot of time burning off the line and that's with a limited slip and drags. But yeah starting off the rev limiter comes quick, you barely have a chance to shift. As for the Mustangs, vettes, etc i haven't been beaten yet, but i also haven't run into anything with serious mods. Nothing against sr's, I had a '92 fastback with an sr but my personal experience says build the crap out of the KA. (Chris May's car is a perfect example. he came to the 240 meet in knox last year and that car is a beast as we all know)

[TrunkMonkey]

First of all the ka is strocked different.

the KA has a longer stroke.

The sr can redline up to 7700 rpm w/computer upgrade while the ka stock is 6400 unless you have a computer upgrade like jwt-jim wolf tech.

you're saying that you need a ecu upgrade on either car to rev higher. what point are you trying to make?

The sr is a better block as it has individual oil squirters and a better crank especially for performance.

iron blocks are better than aluminum, and both engines have excellent cranks.

If the ka motor was better japan would put them in there silvias.

so if it's from japan it must be good, right?

As far as 1\4 times sr kicks azz. Ive run mustangs into the ground, vr4s' z28 and vettes. Srs' pull hard o the highway. you dont always even have to downshift.

all these can be said about the KA also.

Besides when your talking about 8pounds on the ka block as oppossed to starting at 7 pounds stock to 14+ pounds on the sr stock block. Thats serious power.

huh?! if you keep the stock turbo on the SR you would need to raise your boost to 14-15lbs just to make the power of a KA at 8lbs. i don't get what you're trying to say here.

-demetrius

[TrunkMonkey]

from now on, if anyone has any comments related to KA vs. SR please post it in the appropriate thread.

anymore posts like this will be deleted.

-demetrius

[GirlRacerS14]

:bowdown Well put Demcj. I couldn't have said it better myself.

[I am Technoman]

Buy the way, The KA does have oil squirters.

[Structure240sx]

good job demcj u said everything i wanted to :thumbup

[matt0941]

Yea thanks demcj, the last thing I need is "What you should REALLY do is.." I have already decided on the KA as an engine and that reply really needed to be in the KA vs SR thread. And it doesn't really matter how many lbs. you are boosting, boost doesnt equal horsepower you have to take into account compression ratios. But anyways I shouldn't be talking about this, so thanks for the info cnichols and 240girl.

[WDRacing]

Its a good thing I wasn't online to catch that post first. I like to let demcj clean up after I grill them for posting complete garbage.

A stroker motor will drive just as good as any other motor on and off the highway. The KA's powerband will actually extend when boost comes on. Thats a major reason i looked at extending the rpm range through lightening and balancing the crank. But I've decided to stay on the cheaper side of things and keep i just under 8000.

Matt, try comparing your car to a Camaro or somthing please. I hate Mustangs...lol.

WD

[matt0941]

What fits into the category of a stroker motor?

Matt, try comparing your car to a Camaro or somthing please. I hate Mustangs...lol.

WD

I own (and am trying my damndest to get rid of ) a mustang but I would MUCH rather have a cobra than an SS. Out of the F-bodies the mustang is the best IMO, the trans am looks like a cartoon and the Camaro is mexican. Sorry to be so prejudice but it's true.

And I think what I was trying to get at is the fact that alot of muscle cars and such tend to get great 1/4 mile times but their trap speeds can be like 94mph. While some Supra has a higher 1/4 time, his trap speed is 112mph. I would prefer the Supra because on the highway it would beat the muscle car and if that track were extended any farther the Supra would disown it. Even though that is completely hypothetical I think it suits Import vs Domestic rather well. I want a highway car that will accelerate FAST 60-120. How would you guys rate a KA-T powered car for this exact purpose. The previous responses have been VERY helpful either way. But could you compare it as a highway car vs. another car that you have had experience with that would make a good comparison or something? Thanks.

[WDRacing]

A stroker motor os any motor that has any exceptionally long stroke. Take the KA for example, the stroke on the KA is quite a bit longer then its rival the SR20. The longer stroke allows for a greater volume of a/f to be consumed at lower rpms. It also increases the cubic inches of the motor without using larger pistons and having the block over bored.

The KADET will run strong on the highway at any speed.

The LS1 powered Chevy's have owned every Mustang built in the 1/4 and around the track until Ford installed a friggin blower on there new Cobra. But for the price of the Cobra, there is a really nice turbo kit made for the LS1. At 8 psi the Camaro's are hitting low 10's...lol. Makes me wonder why I love imports so much.

WD

[C-Kwik]

A turbo will actually follow form with the NA version's torque curve. Once boost hits max, the volumentric efficiency of the motor plays a major factor in the way it feels. In the case of a KA, it still feels like it weakens a bit up top. Right about 4000 RPM you get a nice surge of power and then diminishes as you hit redline. Still feels strong though, and probably still better to wait to shift until at or about redline. An exception to this is if you use too small a turbo and it begins to really choke the motor and/or gets very bad adiabatic efficiency.

As far as wheelhop, most RWD imports use a rear subframe mounted on rubber bushings. It provides comfort and less road noise but allows a lot of movement, especially as you increase HP. But that's only a small part of why it's hard to launch a car like this. You can eliminate wheel hop by replacing the subframe bushings, but it's hard to control the camber change as the suspension compresses. This causes the contact patch to diminish. And when you increase power, it only gets worse. You can stiffen the suspension to decrease the movement, but then you limit some of the weight transfer. It's a constant struggle to find a good balance of everything on any car.And what is worse is that many of the highly modded turbo cars tend to have less low-end torque. So you start running into problems of either bogging, or revving too high and and spinning tires like crazy. I'm already haveing traction problems at only 6.5 psi. My tires are rock hard now, so we'll see if it gets any better once I replace them.

[WDRacing]

Not that I've personally ported the IHE on the KA, but I'm quite sure after that is done, the top end performance will increase greatly. The stock intake runners are small and long. Which means they're filled with factory cast imperfections as well as room for tubes to increased in diameter.

Not to mention getting everything gasket matched.

WD

[SLIMMY240]

another thing you should maybe look at is your gears. i think about everyone agrees the ka will have plenty of torque. but if your highway racing you may look into gears. i think the stock ka transmission will go to around 140 without the govenor (if you got one, unfortunately i do). i know they used to do alot of highway racing in dallas, and there was a 90 240sx runnin around with a sr, and on one race that i saw he raced a z06 vette with alot of bolt ons and 2 stage no2 kit. they raced for $2000 from a 20mph roll, they got back and the 240 took his money and left. we were talkin to the guy in the vette he said that he sprayed twice and the at around 180 he gave up because the 240 was still pulling away. i heard someone say the 240 was running around 25psi, but still 180 is impossile on stock gear ratio. so you might wanna check that out.

[cnichols]

I've seen different gear ratios, but never one for high speed. I know Nissan Motorsports offers 4.3x and 4.6x gears which I don't see how anyone could hit 180 with.

[matt0941]

another thing you should maybe look at is your gears. i think about everyone agrees the ka will have plenty of torque. but if your highway racing you may look into gears. i think the stock ka transmission will go to around 140 without the govenor (if you got one, unfortunately i do). i know they used to do alot of highway racing in dallas, and there was a 90 240sx runnin around with a sr, and on one race that i saw he raced a z06 vette with alot of bolt ons and 2 stage no2 kit. they raced for $2000 from a 20mph roll, they got back and the 240 took his money and left. we were talkin to the guy in the vette he said that he sprayed twice and the at around 180 he gave up because the 240 was still pulling away. i heard someone say the 240 was running around 25psi, but still 180 is impossile on stock gear ratio. so you might wanna check that out.

Thats what I am all about man, I am going to race for titles....

Fast & Furios, lol Im just kidding :rockon

[matt0941]

A stroker motor will drive just as good as any other motor on and off the highway. The KA's powerband will actually extend when boost comes on. Thats a major reason i looked at extending the rpm range through lightening and balancing the crank. But I've decided to stay on the cheaper side of things and keep i just under 8000.

WD

I am a bit confused about the torque peak and redline, revlimiter on the KA-T. If the rev limiter kicks in at 6,200rpm (correction?) when is the torque peak usually reached... a bit after this? And I have heard that you don't really need to shift at the redline due to the fact that the torque peak hits at a bit above 7,000rpm and then the redline is shortly after. Can someone confirm these numbers and also tell me why anyone would want to extend the RPM range if you are past the peak anyways.

[WDRacing]

The ideal thing to do would be to put your car on the dyno, look at the torque curve and the HP curve. The torque curve will drop off before the hp, thats just physics. But also look at where the hp curve begins to drop off, where it drops is your best shift point. That way your next gear is right in the middle of the torque curve.

Oh the torque peak should never be after the redline, but if you car has low end torque and the to curve still doesn't peak till after the redline, you have a sweet motor. Won't happen though.

WD

[C-Kwik]

I am a bit confused about the torque peak and redline, revlimiter on the KA-T. If the rev limiter kicks in at 6,200rpm (correction?) when is the torque peak usually reached... a bit after this? And I have heard that you don't really need to shift at the redline due to the fact that the torque peak hits at a bit above 7,000rpm and then the redline is shortly after. Can someone confirm these numbers and also tell me why anyone would want to extend the RPM range if you are past the peak anyways.

While it is theoretically possible to build an engine that could have a torque peak beyond redline, I doubt you'll ever find that this is the case. At least not with a stock motor. It would be rather pointless to build an engine to breath best beyond redline since you'll never see it then. If you modify the motor so that it puts the torque peak beyond redline, then it would be very wise to increase redline, assuming the motor can handle it.

Torque peak on a stock KA occurs at 4400 RPM according to Nissan's rating. The highest redline I've seen on any KA is 6900 RPM. The peak torque is occuring way before that.

There could be a number of reasons to increase redline. If there is still power to be made, then it may extend your powerband some. Keep in mind for a given amount of torque, the higher the RPM it is made in, the better. As an example, lets consider an electric motor. They tend to make the same amount of torque all the way to it's maximum RPM. You'll find that while torque is the same, HP will increase directly with RPM. So the more RPM you have, the more HP you have. internal combustion engines do not have perfectly flat torque curves. Typically it rises to a peak and then starts diminishing. Even though it diminishes, due to the nature of Hp being greater with RPM(for a given amount of torque), the HP rating after the peak torque can still be higher than at peak HP. And in most motors, this is typical.

The reason that HP rises with RPM, is because it's a measure of potential. Frankly, HP is one of the most misleading terms when it comes to rotating engines. Torque is the force that actually accellerates your car. The higher the torque, the faster you will accelerate. So the best acceleration in each gear occurs at peak torque. But some smart guy thought up a device called a transmission. It has many gears that allow the motor to have more leverage. Lower gears allow you to put more torque to the wheels, and therefore you will accelerate faster. Notice your car accelerates its fastest in first gear? So why do we care about HP? Well, since the HP is a number that takes into account torque and acceleration it can tell us more abouot how well it uses the leverage yout transmission provides. Typically, the longer you can stay in a lower gear, the more torque you can get to the wheels at any given time. All motors will get to a point where the speed is mechanically limited, or get to a point where the torque has diminished so much that shifting to the next gear would give you more torque to the ground. Ideally, you would want to shift at the point where the torque measurements at the wheels in each gear crosses the curve for the next gear.

HP is a calculated number. It is much easier to determine how fast a car will be from looking at this number than looking at just the peak torque number. If I were to say a motor had 150 lb-ft of peak torque, it would be hard to determine how fast the car is. It could end up being a motor that spins at 1 RPM but makes 150 lb-ft of torque with a 1 RPM redline. This would not be useful for nothing more than turning something that needed an exact output of 150 lb-ft of torque at 1 RPM. You could have 50 gears, and chances are you'ld never get moving very fast at all. 150 lb-ft of torque at 1 RPM is .028 HP btw.

Now lets consider I tell you that a motor makes 150 HP. It may make 150 HP even at 1 RPM. But at that one RPM, you would have 787,800 lb-ft of torque. Now, even with some seriously tall gears, I'm sure you could accelerate a car with some decency with that much torque.

For the sake of argument, lets assume we have two motors that have a perfectly flat torque curve. Both makes 150 HP. The first one has a redline of 100 RPM and the 2nd can rev to 1000 RPM. The 100 RPM would make 7878 lb-ft of torque. The 1000 RPM motor would make 787.8 lb-ft of torque. If we took the 1000 RPM motor and used a gear ratio of 10:1, you'ld be making 7878 lb-ft of torque(ignoring any drivetrain losses), at 1/10 the speed of the motor. It would actually have the same torque and HP curve as the 100 RPM motor after the gearing. If the gearing were matched so that each motor hit redline at the same wheelspeeds, they would accelerate the same. Even though the 1000 RPM motor made 10 times less torque, it can make the same HP because it can make use of the leverage additional RPM's give. And as you see it is quite linear. 10 times more RPM with 10 times more leverage with 10 times less torque acheived the same results.

Sorry this is so long winded, but I didn't want to leave anything out.

[WDRacing]

Jesus C-Kwik...I think I'm actually dumber now. Or atleast thats the way you made me feel..lol.

WD

[cnichols]

Why is this man not a moderator?...I followed everything...but definitely learned something.

[matt0941]

Thanks alot for the information, you get an A for effort.

the HP rating after the peak torque can still be higher than at peak HP.

...but here are you sure that you did not make a typo?

[C-Kwik]

Actually, I meant the HP rating after the peak torque can still be higher than the HP at the peak torque RPM.

Sorry about that. I'm not an editor.

[matt0941]

On a stock 5-spd 240SX technically is the best point to shift (for racing... if you would ever race stock :rolleyes) right at 4,400rpm? Seems kinda weird.

[erich]

-snip- lets consider an electric motor. They tend to make the same amount of torque all the way to it's maximum RPM. You'll find that while torque is the same, HP will increase directly with RPM. So the more RPM you have, the more HP you have.

This is the only bit of misinformation the your post. Electric motots make the most torque when stalled, i.e. 0 rpm. They make 0 torque maximum rpm (whatever that may be) or the armature would continue to accelerate.The amount of torque generated by an AC induction motor (the kind in just about every plug-in electric appliance) is determined between the phase angle between the magnetic fields of the armature and the stator. if I remember correctly it is at 30 degrees or so. On a side note electric motors have zero efficiency at 0 rpm and max rpm with a nice arc up and down through peak efficiency at mid rpms.

p.s. This all goes out the window with cpu controlled variable phase AC motors but I digress.

erich

[S13Ka24e]

On a stock 5-spd 240SX technically is the best point to shift (for racing... if you would ever race stock :rolleyes) right at 4,400rpm? Seems kinda weird.

No it would be to shift to when you release the clutch for the rpm's to drop to 4400 rpm.

[matt0941]

I thought you wanted to shift at torque peak and ideally switch gears so that RPM's fall flat in the middle of the torque curve.

[C-Kwik]

This is the only bit of misinformation the your post. Electric motots make the most torque when stalled, i.e. 0 rpm. They make 0 torque maximum rpm (whatever that may be) or the armature would continue to accelerate.The amount of torque generated by an AC induction motor (the kind in just about every plug-in electric appliance) is determined between the phase angle between the magnetic fields of the armature and the stator. if I remember correctly it is at 30 degrees or so. On a side note electric motors have zero efficiency at 0 rpm and max rpm with a nice arc up and down through peak efficiency at mid rpms.

p.s. This all goes out the window with cpu controlled variable phase AC motors but I digress.

erich

I'll take your word for it on this one. I only made assumptions based on dynographs i have seen in some magazine article about electric car motors. I don't think it was an actual dyno chart, but rather the theoretical one. But it was just used to make the point.

[matt0941]

:squint sooooo someone wanna answer my Q?