346whp @ 0 pounds of boost
12-06-2010, 08:02 AM
#61
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So according to the post you just made the debate is OVER. A big exhaust does make more power than a smaller exhaust on a Revup.
Does anyone still have a problem with my dual 3" exhaust on my sedan with stock headers?
BTW I love what you've done with the car. Bigger than the world exhaust and bigger cams and a few boltsons with a built bottom end. I'm sure Nismo would be proud and impressed if they see this. Go out there and take on some E90 M3s. I would love to see that.
Does anyone still have a problem with my dual 3" exhaust on my sedan with stock headers?
BTW I love what you've done with the car. Bigger than the world exhaust and bigger cams and a few boltsons with a built bottom end. I'm sure Nismo would be proud and impressed if they see this. Go out there and take on some E90 M3s. I would love to see that.
12-06-2010, 08:23 AM
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the point is this is a build thread surrounding a particular fully built car with all the trimmings - if you want to know the ideal exhaust setup for your setup, you'll simply need to do what the rest of us do and try 'em out for yourself, or just be happy with what you have. It's awfully impossible to compare the results of this setup to a non built one.
Last edited by Z1 Performance; 12-06-2010 at 08:26 AM.
12-06-2010, 08:35 AM
#66
And 279 whp with only an intake and the 3" headers and 3.5" single. https://my350z.com/forum/na-builds/3...-roadster.html
So it is safe to say the debate is in fact over? I think it is. Big exhaust=more power.
12-06-2010, 08:39 AM
#67
It's not really that impossible.
Take away the restrictions, without going too far and killing the velocity. That's the name of the game.
Any time you have something restricting airflow significantly, making changes to other parts will do little to absolutely nothing. Variance in dyno pulls may even lead you to believe you lost power.
Opening up the last bottleneck when everything else is already tuned for higher flow, will yield huge results. That's why our headers could make 15whp on one setup, and 40whp on another setup. It's just amazing that with the stock revup Nissan left 30+whp on the table in the exhaust system.
Take away the restrictions, without going too far and killing the velocity. That's the name of the game.
Any time you have something restricting airflow significantly, making changes to other parts will do little to absolutely nothing. Variance in dyno pulls may even lead you to believe you lost power.
Opening up the last bottleneck when everything else is already tuned for higher flow, will yield huge results. That's why our headers could make 15whp on one setup, and 40whp on another setup. It's just amazing that with the stock revup Nissan left 30+whp on the table in the exhaust system.
12-06-2010, 08:40 AM
#68
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but the car has cams...and your car doesn't
the car has headers, and your car doesn't
these factors alone make it a completely irrelevant comparison, as these factors are very large contributing factors to the ideal exhaust size and configuration
the car has headers, and your car doesn't
these factors alone make it a completely irrelevant comparison, as these factors are very large contributing factors to the ideal exhaust size and configuration
Last edited by Z1 Performance; 12-06-2010 at 08:41 AM.
12-06-2010, 09:15 AM
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In your mind, it would have made more power - and you're free to think that and have that opinion
The fact of the matter is, you don't know (nor do I), nor does anyone else unless they try it back, to back
Secondly, you're talking about 2 different cars. This is not the car that made 279 whp with just headers and an exhaust - that was a revup roadster. The car in this thread is the non revup race car. Now you're trying to draw a comparison between either of these, and a sedan with stock headers and not a single, but dual 3 inch exhaust? You want to know which will be better, you'll have to try all the combos yourself. No one is going to know otherwise
The fact of the matter is, you don't know (nor do I), nor does anyone else unless they try it back, to back
Secondly, you're talking about 2 different cars. This is not the car that made 279 whp with just headers and an exhaust - that was a revup roadster. The car in this thread is the non revup race car. Now you're trying to draw a comparison between either of these, and a sedan with stock headers and not a single, but dual 3 inch exhaust? You want to know which will be better, you'll have to try all the combos yourself. No one is going to know otherwise
12-06-2010, 12:14 PM
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Yes, but their exhaust setup is not you setup...and that too is a fact. You also don't know what portion of their mods (headers vs exhaust) are responsible for the majority of the gains.
a "big" exhaust can take many forms - and there is such a thing as too big.
a "big" exhaust can take many forms - and there is such a thing as too big.
12-06-2010, 01:25 PM
#73
I have an AP Ti single exhaust that is LOUD so I put in a silencer. When we tuned it the silencer stole 30 hp (271 vs 24x) I am putting up with the noise and enjoying my 271/262 at the wheels.
You need some back pressure in an engine, the trick is finding the right combination of parts to achieve your goals.
You need some back pressure in an engine, the trick is finding the right combination of parts to achieve your goals.
12-06-2010, 02:21 PM
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I have an AP Ti single exhaust that is LOUD so I put in a silencer. When we tuned it the silencer stole 30 hp (271 vs 24x) I am putting up with the noise and enjoying my 271/262 at the wheels.
You need some back pressure in an engine, the trick is finding the right combination of parts to achieve your goals.
You need some back pressure in an engine, the trick is finding the right combination of parts to achieve your goals.
No engine wants backpressure actually....the engine does want velocity of air, both in and out. Your silencer increased your backpressure, by forcing all that air that the heads exhaled to eventually find their way out of a much smaller orifice than without it. That is adding backpressure....you saw the net result. At the same time, the silencer essentially is creating a bottle neck, which also slows down velocity (and if severe enough also can choke volume). That's how it's reducing volume, etc, but it comes at a price.
Last edited by Z1 Performance; 12-06-2010 at 02:23 PM.
12-06-2010, 03:13 PM
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Please correct my if I'm wrong but arnt they using 2.5" primaries for the headers and y pipe into the 3.5" exhaust?
I also just want to say I appreciate all the work sg is doing and that they are actually sharing it with us dispite all the bitching about dynos. I feel lucky they are sharing the amount of information they have given us.
I also just want to say I appreciate all the work sg is doing and that they are actually sharing it with us dispite all the bitching about dynos. I feel lucky they are sharing the amount of information they have given us.
Last edited by lemmiwinkz; 12-06-2010 at 03:16 PM.
12-06-2010, 06:43 PM
#80
Regarding torque/horsepower:
Torque and horsepower have a defined relationship. If you know either torque or horsepower, and you know RPM, you will know the other variable.
To get more horsepower, you need either more torque, or more rpm.
Torque is basically maxed out by the displacement of the engine. The relationship between torque and engine displacement is basically describing the engines efficiency. Brake Mean Effective Pressure (BMEP) lets us compare engines of different displacement:
To put the VQ in perspective for you, my engine with the non-revup lower plenum was making close to 290 lb-ft of torque at 3.5 liters:
The formula for BMEP is simple, and it gives us somewhat of an idea of the potential torque we should be able to expect out of a certain displacement, when comparing it to racecar engines of similar breed:
BMEP = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)
So, taking 290 lb-ft of torque and 213.5 cubic inches we get: 204.83 (the unit is PSI). Now that is to the wheels. If we want to just be conservitive and assume another 10% at the engine: 319 lb-ft the BMEP is 225PSI
Now to compare to race engines:
Formula 1: ~220PSI
Nascar Cup: ~219PSI
Corvette Z06: ~165PSI (advertised numbers)
Porsche 911 GT3: ~206PSI
Looking at the BMEP by itself, it looks like we have the most amazing engine in the world! And it shows that it's making a HUGE amount of torque compared to most race tuned naturally aspirated engines.
Now that I've made the VQ look like a better engine than formula one, I must continue to explain the details:
We're missing a big chunk of the picture. It's much easier to make greater torque at LOWER rpm, than it is to make that same torque at higher RPM. This is because the faster you spin the engine, the more losses you rack up with friction (bearings, cams smashing valves, pistons on cylinder walls etc) and pumping losses (that's why pulling a vacuum in the crankcase frees up power at high rpm).
The reason the BMEP is lower on the F1 and Nascar cup engines, is because they have tuned the engines to spin at high RPM, and the goal is to make the torque (and horsepower) as high as possible at those higher RPMs. That means sacrificing low and mid-range torque to make the engine efficient in those areas. The tuning comes in all sorts of different forms, like header design, cam sizing and timing, intake runner diameter and lengths, etc.
So naturally the peak torque falls, and the BMEP goes down with it. Since the engine keeps making torque at higher RPM, the horsepower goes up (a very significant amount). Using sequential gearboxes with close gears, you can keep the engine operating at high RPM and the loss of low-end torque no longer matters since you're never there!
Is it funny what I described is EXACTLY what modern auto manufactures are doing with their 7 and 8 speed automatics to make up for their high revving engines with fairly small powerbands? (Think of how low the torque is on the new G37/370z 3.7's, but how high the horsepower is). Honda has been doing it forever of course, except with VTEC they can keep a ton of low end power compared to what it would be like if it was always on the big cam.
Back on topic - to make horsepower, REAL horsepower (like 100whp per liter), you NEED to sacrifice torque (or have variable everything). That's why you will see my racecar build going up in power and down in peak torque (or at least staying the same). The peak torque used to be higher than it is now, despite the fact that it's making 15 more horsepower. Because we've used an intake manifold and cam that sacrifices sub 5000rpm torque for more torque (and as a result MORE horsepower) at 6000rpm+
So to summarize:
290 lb-ft of torque at 5000rpm is no where near as good as 230 lb-ft of torque at 7000rpm. The graph to display that relationship, is called horsepower.
(290lb-ft of torque @ 5000rpm = 276hp)
(230lb-ft of torque @ 7000rpm = 306hp)
This post really got out of hand. Sorry!
Torque and horsepower have a defined relationship. If you know either torque or horsepower, and you know RPM, you will know the other variable.
To get more horsepower, you need either more torque, or more rpm.
Torque is basically maxed out by the displacement of the engine. The relationship between torque and engine displacement is basically describing the engines efficiency. Brake Mean Effective Pressure (BMEP) lets us compare engines of different displacement:
To put the VQ in perspective for you, my engine with the non-revup lower plenum was making close to 290 lb-ft of torque at 3.5 liters:
The formula for BMEP is simple, and it gives us somewhat of an idea of the potential torque we should be able to expect out of a certain displacement, when comparing it to racecar engines of similar breed:
BMEP = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)
So, taking 290 lb-ft of torque and 213.5 cubic inches we get: 204.83 (the unit is PSI). Now that is to the wheels. If we want to just be conservitive and assume another 10% at the engine: 319 lb-ft the BMEP is 225PSI
Now to compare to race engines:
Formula 1: ~220PSI
Nascar Cup: ~219PSI
Corvette Z06: ~165PSI (advertised numbers)
Porsche 911 GT3: ~206PSI
Looking at the BMEP by itself, it looks like we have the most amazing engine in the world! And it shows that it's making a HUGE amount of torque compared to most race tuned naturally aspirated engines.
Now that I've made the VQ look like a better engine than formula one, I must continue to explain the details:
We're missing a big chunk of the picture. It's much easier to make greater torque at LOWER rpm, than it is to make that same torque at higher RPM. This is because the faster you spin the engine, the more losses you rack up with friction (bearings, cams smashing valves, pistons on cylinder walls etc) and pumping losses (that's why pulling a vacuum in the crankcase frees up power at high rpm).
The reason the BMEP is lower on the F1 and Nascar cup engines, is because they have tuned the engines to spin at high RPM, and the goal is to make the torque (and horsepower) as high as possible at those higher RPMs. That means sacrificing low and mid-range torque to make the engine efficient in those areas. The tuning comes in all sorts of different forms, like header design, cam sizing and timing, intake runner diameter and lengths, etc.
So naturally the peak torque falls, and the BMEP goes down with it. Since the engine keeps making torque at higher RPM, the horsepower goes up (a very significant amount). Using sequential gearboxes with close gears, you can keep the engine operating at high RPM and the loss of low-end torque no longer matters since you're never there!
Is it funny what I described is EXACTLY what modern auto manufactures are doing with their 7 and 8 speed automatics to make up for their high revving engines with fairly small powerbands? (Think of how low the torque is on the new G37/370z 3.7's, but how high the horsepower is). Honda has been doing it forever of course, except with VTEC they can keep a ton of low end power compared to what it would be like if it was always on the big cam.
Back on topic - to make horsepower, REAL horsepower (like 100whp per liter), you NEED to sacrifice torque (or have variable everything). That's why you will see my racecar build going up in power and down in peak torque (or at least staying the same). The peak torque used to be higher than it is now, despite the fact that it's making 15 more horsepower. Because we've used an intake manifold and cam that sacrifices sub 5000rpm torque for more torque (and as a result MORE horsepower) at 6000rpm+
So to summarize:
290 lb-ft of torque at 5000rpm is no where near as good as 230 lb-ft of torque at 7000rpm. The graph to display that relationship, is called horsepower.
(290lb-ft of torque @ 5000rpm = 276hp)
(230lb-ft of torque @ 7000rpm = 306hp)
This post really got out of hand. Sorry!