I know this thread is almost 2 months old, but there are a few things in it I wanted to correct.
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Originally Posted by serialk11r
SUB-FT86, you can easily get 160lb-ft (at the crank, no drivetrain, relatively constant at low speeds) with a low rpm optimized cam I think...maybe that's something you should look into. This car essentially has a racing cam. The low rpm torque sucks, but fuel economy will be pretty good because of it. Can't buy a sports car and expect the engine to be tuned for low rpm, that's called a truck/SUV :P The beauty of compromise: sometimes you get something good out of it as a side effect.
Matador, may I direct you to the Engine Tech thread?  |
I wouldn't call it a race cam, race cams have a very high lift and aggressive cam profiles to help airflow. They get lopey down low, idle poorly, etc unless the motor has something like i-Vtec, VVTL-I, etc. From what I can tell, the FR-S doesn't have those issues. It's not a low lift cam, but it's not a race cam either. It's a high lift cam with a mild profile, not a race cam with race profile. I'm sure the aftermarket will take care of that though, like they always do. Of course, whether that's a good idea for someone depends on their goals for the car. Toyota/Subaru went with a cam with higher lift which still kept good idle and low rpm characteristics. It looks like the motor lacks a dual camp profile, so they can't go too high with the lift and timing without causing idle and low rpm issues the general public won't appreciate.
Also, as was stated, you certainly can buy a sports car and expect it to have good low rpm numbers. Plenty of Sports cars are tuned for low rpm power. Heck, the Toyota MR2 turbo is sports car with good low rpm power numbers. The turbo begins to spool very quickly, by 2500rpm you are building significant boost and by 3000rpm you've hit full boost. Also, it's an example of a sports car with good low rpm power number from the Toyota family.
The FR-S was designed after the AE86, which was a high rpm NA car. The car was really designed in that image. It wasn't meant to be a sports car with down low numbers like Toyota's MR2 turbo was, it was designed to be a sports car with a smooth, high revving NA power band like the AE86 was. If it's anything like the other high revving NA cars.
Quote:
Originally Posted by serialk11r
Well not exactly. I know the example you like to use is the G35. The G35 has so much more power over a wimpy 2L engine car that you were probably satisfied with the low rpm performance, even if it could've been better at high rpm. I don't know how the G35 performs, but I assume it is going to make good torque at high rpm because it goes on the 350Z, which is supposed to be a real sports car.
When you have something like VVEL on the VQ37VHR, you can have a no compromise torque curve because the duration is adjustable. This is the only exception. With something like VTEC, Honda loses valuable fuel economy points if it wants to boost the low rpm torque, so they own't do it. Most sports cars are built by companies which do not have the sophisticated systems to produce good torque all around, so they are tuned for high end power. I am fairly sure this is an accurate trend, as when you look at the car's size vs. the torque curve when the same engine is used across a lineup, the smaller cars typically get tuned for higher rpms. It only makes sense, because horsepower is basically what sells a sports car, and not for a bad reason! The good torque is always available at 30mph and up, which is more than enough for most people.
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Plenty of manufactures have systems which control time, duration and lift these days. i-Vtec from Honda (the performance version found in the RSX-S and Civic Si), VVT-LI from Toyota, MIVEC from Mitsubishi, i-AVLS from Subaru, Audi Valvelift and VarioCam Plus from Porsche all change lift, timing and therefor duration depending on the engine conditions. Cam phasing and cam changing are both pretty common these days. It allows the manufacturer and engine tuner to maximize the lower end of the rpm range and the higher and of the RPM range without compromise.
In fact, considering Toyota and Subaru both produce motors which use these technologies, I was hoping they would implement them into the 86/FR-S/BR-Z. When Mitsubishi implemented their Mivec for the Evo starting with the Evo 9 and up, the powerband and output became much better. It's the same reason the Honda's respond to power and boost so well throughout the powerband. It allows them to optimize the engine tune throughout the powerband.
An NA 2.0L motor is always going to have lower torque output, so they make up for it with a higher redline and higher RPM breathability. This is where high lift cams come in handy. Cam phasing and dual cam profiles help even further, since they allow good low rpm drivability while also allowing good high rpm breathability.
Quote:
Originally Posted by serialk11r
Um, you can't have "higher torque than hp", because the 2 are measuring different quantities :P
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Of course you can have higher peak torque than peak HP. As DMDZK pointed out, it just depends on where the peak numbers occur in the powerband. If horsepower peaks before 5252, the motor will have a higher peak torque output than peak horsepower number. If the horsepower peaks after 5252 rpms, the motor will have a higher peak horsepower number than peak torque number. If it occurs around 5252rpms, the output will be fairly sqaure (same peak HP and peak torque numbers). HP is just torque * rpm/5252, so which is higher (HP or torque) really just depends on WHERE in the powerband the peak HP occurs.