low end performance?
low end performance?
Hi, I just got an '89 240 (auto), I'm coming from the 300ZXTT world and I know nothing about modding naturally aspirated engines. Is there anything I can do to improve performance under 3500 RPM, just to make it a bit quicker for day to day driving? Would an intake or headers help? It seems that most of the exhausts for this car that I have looked at have 2.75-3" diameters, which my guess is would lose the backpressure and kill low end performance - are there any out there that are narrower? Also, just out of curiousity, I've seen a number of posts about "upgrading" to 300ZX brakes, yet those brakes are unconditionally hated by 300 owners, do they really perform well on the 240?
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C-Kwik
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Why do you care about low-end? If you're driving hard, you'll never see much below 4000. You might find more power from swapping to a DOHC KA and using a Manual transmission.
Backpressure, or the lack of has no direct impact on low-end performance. It's the lack of exhaust gas velocity that kills low-end. Pick too large a pipe and the gases exiting the motor will slow down. This affects the scavenging effects of the header nd you lose low-end. As you go to higher RPM's, you get more airflow and the exhaust velocity gets higher and the scavenging effects come back. While in theory, it's possible to acheive good scavenging with zero backpressure, in the rear world, it is hard because engines work throughout a range of airflow and exhaust systems tend to have bends. 1-2 psi of backpressure is acceptable. The Apex'i N1 exhaust was tested by SCC and showed no loss of power in the low-end, even with it's rather large piping.
the 300ZX is about 3600 lbs. The 240 is about 2800. It's more than enough braking for the 240. Compare the 300ZX brakes to a stock Supra TT and there is a huge difference in size and construction. Especially considering the Supra is actually lighter then a 300ZX TT. Also consider, most 240's aren't doing low 14 to 13 second 1/4 miles. On a race track, it will not be as fast at the end of a straight, therefore the brakes from a 300ZX are quite adequate. Weight and heat directly impact how much energy a rotor has to absorb.
Backpressure, or the lack of has no direct impact on low-end performance. It's the lack of exhaust gas velocity that kills low-end. Pick too large a pipe and the gases exiting the motor will slow down. This affects the scavenging effects of the header nd you lose low-end. As you go to higher RPM's, you get more airflow and the exhaust velocity gets higher and the scavenging effects come back. While in theory, it's possible to acheive good scavenging with zero backpressure, in the rear world, it is hard because engines work throughout a range of airflow and exhaust systems tend to have bends. 1-2 psi of backpressure is acceptable. The Apex'i N1 exhaust was tested by SCC and showed no loss of power in the low-end, even with it's rather large piping.
the 300ZX is about 3600 lbs. The 240 is about 2800. It's more than enough braking for the 240. Compare the 300ZX brakes to a stock Supra TT and there is a huge difference in size and construction. Especially considering the Supra is actually lighter then a 300ZX TT. Also consider, most 240's aren't doing low 14 to 13 second 1/4 miles. On a race track, it will not be as fast at the end of a straight, therefore the brakes from a 300ZX are quite adequate. Weight and heat directly impact how much energy a rotor has to absorb.
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C-Kwik
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S13's tend to be lighter. According to Manufacturer's rated curb weights. S13's being closer to about 2700 lbs. the S14's are closer to about 2800 lbs. This is without a driver, but with all fluids to max including gas.
Trying to drive a car hard in the low-end can cause more problems. Consider for a given speed, the car in a higher gear will have more load(or resistance) at the flywheel or torque converter. The KA has a relatively broad torque-band and makes nearly as much torque at the low-end as it does in the mid-to high end. If you kick-down to a lower gear, you will get more torque to the wheels with less resistance at the flywheel.
Proof of this is to drive a car with a clutch on the verge of slipping. I could slip the clutch simply by flooring it at 2000 RPM just by mashing the gas(clutch is already engaged). I'd try the same in 1st gear at a higher RPM even and it would hold. Not to say that you should drive like me and shift at redline everytime, but if the car is going to be driven somewhat mildly, I'd just let it kickdown a gear and use the power when you need it. But then, that's just me.
Trying to drive a car hard in the low-end can cause more problems. Consider for a given speed, the car in a higher gear will have more load(or resistance) at the flywheel or torque converter. The KA has a relatively broad torque-band and makes nearly as much torque at the low-end as it does in the mid-to high end. If you kick-down to a lower gear, you will get more torque to the wheels with less resistance at the flywheel.
Proof of this is to drive a car with a clutch on the verge of slipping. I could slip the clutch simply by flooring it at 2000 RPM just by mashing the gas(clutch is already engaged). I'd try the same in 1st gear at a higher RPM even and it would hold. Not to say that you should drive like me and shift at redline everytime, but if the car is going to be driven somewhat mildly, I'd just let it kickdown a gear and use the power when you need it. But then, that's just me.
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I am Technoman
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- Joined: Fri Nov 22, 2002 6:49 am
- Car: ???
K-kiwk My custom ehxaust sounds so sweet. I use a hotshot header with no cat . The hotshot collector is 21/2 in and bolts to that hollow looking cat so the hot air expands wide and gets forced into a smaller back pipe thats only 2 1/4 inches no resonator just a big *** Borla stainless muffler.
so basicly what in trying to say is my exhaust flowsreally really fast.
I wanna record a 5grand rev for you guys to hear!
so basicly what in trying to say is my exhaust flowsreally really fast.
I wanna record a 5grand rev for you guys to hear!
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I am Technoman
- Posts: 979
- Joined: Fri Nov 22, 2002 6:49 am
- Car: ???
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I am Technoman
- Posts: 979
- Joined: Fri Nov 22, 2002 6:49 am
- Car: ???
I have a Tanabe Super Medalion Hyper-spec exhaust (yes, it sounds ricey, but its really nice..) its 60mm diameter (about 2.25",) so there's plenty of exhaust gas velocity, I lost no low end with it, gained some that I actually lost with the hotshot headers...anyway, I got the tanabe exhaust for $450 shipped brand new, and its full T304 stainless steel, excellent build quality, sounds nasty, and fit perfectly...I highly recommend it. C-Kwik...not everyone likes revving the piss out of a poor SOHC KA24E that's stock...they weren't meant for it, they aren't race-car engines. i like torque...I like stepping on the gas at 2500 rpm and being shoved back in the seat...But I also love bringing mine up to 5.5 grand, but not often, because my car has 92k miles, and I'd rather not decrease the life of the engine...