Okay.. I have read that the *ideal* exhaust size is 2 inches for a ga16. Is that ideal for high rpm or low? I want my car to stay fairly peppy.. I do NOT want to have to redline to get any power.. Should I get 1 3/4 mandrel instead?
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2" is the optimal size for the GA16. Any bigger, you lose the constant flow of pressure which puts more work on the engine to PUSH the exhaust out (like trying to sip water through a 2 1/2" wide straw..or PVC pipe). If you go any smaller, you're building too much backpressure and restricting the flow (like sipping water through one of those little coffee mixer straws). I have 2" exhaust and my low end is better than ever. I can peel that f**ker GA16 out with an auto and 205mm wide tires (something I couldnt do before, even on stock 170 tires).
2" is the optimal size for the GA16. Any bigger, you lose the constant flow of pressure which puts more work on the engine to PUSH the exhaust out (like trying to sip water through a 2 1/2" wide straw..or PVC pipe). If you go any smaller, you're building too much backpressure and restricting the flow (like sipping water through one of those little coffee mixer straws).
Agreed....I like your analogy
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I do NOT want to have to redline to get any power
I don't know about the ga16 but there is a lot of extra power to tap into at the higher rpms in the sr20de if you can get your hands on a JWT ECU or G20 ECU. Check out the dyno chart for your car to learn where you begin to lose power on the rpm scale. However; if you have mods. then you throw off the stock hp/torque curve. You can always dyno it yourself to figure it out.
Unfortunately, we own 4 bangers and redlining is kind of the name of the game.
Remember also that exhaust pipe sizing is more dependant on how much power your engine makes than on displacement.An engine with a given horsepower level-no matter what the size- will always need a certain pipe size(although it may be larger on a engine with more internal mass due to power lost to internal friction ,reciprocating mass and pumping losses).A 400 hp 350 Chevy will have roughly the same airflow requirements as a 400 hp SR20.This is because in order for an engine to make power, it must combust a given amount of fuel and that amount of fuel also needs a given amount of air to burn properly.All fuels have a given amount of energy per given volume(measured in BTU's or British Thermal Units) and no matter what you do,this will remain a constant.So, while a 1.6 liter 115 hp engine may be optimized at a certain pipe diameter, it is because of power output and not engine size that it does that.That's my lesson for today!
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Last edited by himilefrontier : May 18th, 2003 at 02:26 AM.
Please supply some evidence to support this statement... I'm not sure that I agree at this time. Your sipping from a wide straw analogy doesn't make much sense to me. Lets take electricity... the larger the wire diameter, the less the resistance for a given length of wire. Why wouldn't this apply for an auto exhaust? Hell, people at the dragstrip run open headers to race... according to your thinking... that must be awful.
2" is the optimal size for the GA16. Any bigger, you lose the constant flow of pressure which puts more work on the engine to PUSH the exhaust out (like trying to sip water through a 2 1/2" wide straw..or PVC pipe).
true, the bigger you go, the less backpressure and resistance. Resistance=bad and it is important to get rid of it as much as possible. Unfortunately, exhaust gasses and electricity are 2 different things. With a n/a engine, only one thing pushes the exhaust gas out and that is the piston. The exhaust valvs open and the piston pushes out the fumes using some of the engines energy.
When you have a smaller exhaust, backpressure is your biggest enemy. With a larger exhaust, you get rid of that resistance, however there is a problem, in your exhaust system, that piston gets a bit of assistance by a suction within the exhaust system.
Like I said, you can best understand it by thinking about a straw with water. Something you probably remember from elementry school, imagine 2 glasses sitting on 2 different steps of a staircase. The glass that is higher up is full of water and the one on the lower step is empty. If you take a U-shaped straw and stick each end in each glass and you start the flow by sucking the water from the lower end, the water will continue to flow into the lower glass until the top one is empty. This is all done because a velosity has been created and gravity has chosen the direction of the flow. (If you still cannot imagine it, think about siphoning gas out of a fuel tank).
back to the car, the exhaust system works the same way, the flow of gases also has velocity within the pipes and therefore, there is a suction that literally pulls the exhaust gases out of the cylinders freeing up the engine of the old gases and taking some stress off the piston. Now, a 1.6Litre can only create so much exhaust at a time (especially at low RPMs), so if the exhaust is too big, the gases move slower (there is more space to fill) which means the velosity is slower and the suction is less (once again putting more stress on the piston). also, it i's too big, there may even be some reverse flow going on within the pipes b/c there just isn't enough exhaust to fill up the pipe completely.
well of course, the 2" is dyno proven to be the optimal size for a N/A GA16DE. If you have a turbo on the car, things change. With a turbo, bigger is better. The gasses are being forced in and foced out, so there is no need for the suction of a properly tuned exhaust system.
Nonsense, who says exhaust gasses and electricity act totally different??
How about electricity and water?... they act the same... the bigger the pipe... the more water you can get through it with a given water pressure. Same for electricity... the bigger the wire diameter... the more current can flow through the wire for a given pressure(Voltage). Now why would exhaust gasses through a pipe act any differently...
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Originally posted by 1997 GA16DE Unfortunately, exhaust gasses and electricity are 2 different things.
Originally posted by bgriffey Nonsense, who says exhaust gasses and electricity act totally different??
How about electricity and water?... they act the same... the bigger the pipe... the more water you can get through it with a given water pressure.
yes, but if there is not enough water to fill that pipe completely there will be air in the pipe. I'll try to do some kind of image, I'm not explaining this well.
OK, what you have shown here has to do with turbulence. I'm not sure this applies when the inside of the pipe is very smooth. Turbulence has to be started by something in the airstream. I know of no such object inside the pipe that would start such a phenomenon...
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