Exhaust theory and my IX MR. Tapered exhaust. Fujitsubo / Supersprint.
Mar 22, 2012, 04:55 PM
#1
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Exhaust theory and my IX MR. Tapered exhaust. Fujitsubo / Supersprint.
Exhaust systems are sometimes the most controversial topic in any tuning platform. If it has an engine, you can bet many an arguement has been made over what is optimal.
Well, this go around I have decided to take what I have learned / believe and put it to the test. The system I have chosen to purchase is quite different from the norm and I hope that by sharing this it garners some good discussion if nothing else (good results hoped for as well).
So, tapered exhaust. Ugh. Ugly word around these parts right?
My system I am moving forward with is the wonderfully built 70mm/2.75in Fujitsubo downpipe fed into a Supersprint 63.5/2.5in race exhaust.
Some background. Supersprint is one of those companies whom I long wanted buy an exhaust from. This company makes common metals beautiful.
What I really admired about the Supersprint exhaust is that it starts at the downpipe. No test pipe neccessary. One less flange to deal with. Nice. The other thing was that the muffler tip is extended from the muffler itself, so no issue of it pulling in cold air, cooling the exhaust.
The whole idea behind a tapered system is that exhaust moves the fastest when hot and slows as it begins to cool. One way to help manipulate the temperature of the exhaust is the taper the system - gradually moving to a smaller pipe as it exits. This keeps the exhaust hotter and in turn the exhaust maintains a higher velocity throughout the system. This is all goodness.
I thought there could be some others out there that would find this setup interesting, so I wanted to share. I have the downpipe in my garage. The Supersprint exhaust will be shipping from Italy this week
Here's the product info page on the EVO IX from the Supersprint website:
http://www.supersprint.com/en/prod-8...4wd_evo_9.aspx
Credit to the photos, to Supersprint:
Well, this go around I have decided to take what I have learned / believe and put it to the test. The system I have chosen to purchase is quite different from the norm and I hope that by sharing this it garners some good discussion if nothing else (good results hoped for as well).
So, tapered exhaust. Ugh. Ugly word around these parts right?
My system I am moving forward with is the wonderfully built 70mm/2.75in Fujitsubo downpipe fed into a Supersprint 63.5/2.5in race exhaust.
Some background. Supersprint is one of those companies whom I long wanted buy an exhaust from. This company makes common metals beautiful.
What I really admired about the Supersprint exhaust is that it starts at the downpipe. No test pipe neccessary. One less flange to deal with. Nice. The other thing was that the muffler tip is extended from the muffler itself, so no issue of it pulling in cold air, cooling the exhaust.
The whole idea behind a tapered system is that exhaust moves the fastest when hot and slows as it begins to cool. One way to help manipulate the temperature of the exhaust is the taper the system - gradually moving to a smaller pipe as it exits. This keeps the exhaust hotter and in turn the exhaust maintains a higher velocity throughout the system. This is all goodness.
I thought there could be some others out there that would find this setup interesting, so I wanted to share. I have the downpipe in my garage. The Supersprint exhaust will be shipping from Italy this week
Here's the product info page on the EVO IX from the Supersprint website:
http://www.supersprint.com/en/prod-8...4wd_evo_9.aspx
Credit to the photos, to Supersprint:
Last edited by cbseven; Mar 22, 2012 at 04:58 PM.
Mar 22, 2012, 05:44 PM
#2
So reading between the lines, you expect to see some gains by using a smaller exhaust diameter toward the end of your exhaust system?
I think you're going to be disappointed. It is true that the diameter of your header pipes can affect your power band: smaller pipes can, in the right circumstances, increase exhaust velocity and promote better cylinder filling at the expense of top-end power. However, by the time the exhaust gases reach the last segment of your exhaust system at any reasonable RPM I would suspect the individual exhaust gas pulses are blended enough that these effects don't apply. Instead, your primary goal should be to get these exhaust gases into the atmosphere with the least pressure restriction possible. Smaller diameter tubing results in more restriction, which reduces power and hurts spool.
Furthermore, wouldn't it be more appropriate to call your setup a 'stepped' system rather than tapered? Unless I'm reading the pages wrong, it looks like you'll be mating 2.75" tubing with 2.5" tubing, etc. These mismatches are going to create serious restrictions.
I think you're going to be disappointed. It is true that the diameter of your header pipes can affect your power band: smaller pipes can, in the right circumstances, increase exhaust velocity and promote better cylinder filling at the expense of top-end power. However, by the time the exhaust gases reach the last segment of your exhaust system at any reasonable RPM I would suspect the individual exhaust gas pulses are blended enough that these effects don't apply. Instead, your primary goal should be to get these exhaust gases into the atmosphere with the least pressure restriction possible. Smaller diameter tubing results in more restriction, which reduces power and hurts spool.
Furthermore, wouldn't it be more appropriate to call your setup a 'stepped' system rather than tapered? Unless I'm reading the pages wrong, it looks like you'll be mating 2.75" tubing with 2.5" tubing, etc. These mismatches are going to create serious restrictions.
Mar 22, 2012, 06:47 PM
#3
On a turbo car, smaller exhausts simply have a higher pressure drop and will make less power.
There is diminishing gains with larger exhausts after a given point though and a smaller exhaust will usually be more quiet. Thus ideally, you'd want the smallest exhaust that doesn't hurt power.
I can tell you from experience though, 2.5" is going to hurt you badly above 300WHP.
There is diminishing gains with larger exhausts after a given point though and a smaller exhaust will usually be more quiet. Thus ideally, you'd want the smallest exhaust that doesn't hurt power.
I can tell you from experience though, 2.5" is going to hurt you badly above 300WHP.
Mar 22, 2012, 08:26 PM
#4
My wife is worried about me. But, she doesn't understand guys like us, does she?
You're on the right track, bro. Keep up the good work.
Mar 22, 2012, 09:51 PM
#5
back when I was running a 16g in my 89 mirage turbo I went from 2.5 to 3.0 exhaust. leaving the muffler shop was extremely disappointing. the car did not pick up power and spool like EVERYONE on the internet will tell you, all it did was loose a butload of torque. car was waaay more fun with the 2.5 on the car.
years later went to a dyno session with a friends talon to watch his exhaust upgrade day. he had a 3.0 downpipe and 2.5 catback. on the dyno he dropped the exhaust and installed a full 3 inch. both catbacks were from burshur racing. first pull with no tuning changes the car lost 6whp and 20ft/lbs of torque.
I have read a 1000 post on turbo exhaust . "bigger is better, period" I laugh at all 1000.
normally aspirated folks clearly understand the correct size exhaust nets the greatest horsepower. exhaust is a series of pulses. when those pulses are spaced close enough additional torque gains will be found as the pulses pull on each other and help evacuate the exhaust.
bicyclist also understand the principal. its called drafting.
what turbo guys dont understand is the pulses are still there on turbo cars. the turbine does not eliminate them. you only have to put your hand on the exhaust tip to feel them.
there was a honda in scc that made 550 whp through a 2.5 inch exhaust. it tracked high 10s at 135 fwd.
there was also guy a few years ago that has a 16g making 420hp/430tq through a 2.5 exhaust.
I say give the kid a break. let him play.
years later went to a dyno session with a friends talon to watch his exhaust upgrade day. he had a 3.0 downpipe and 2.5 catback. on the dyno he dropped the exhaust and installed a full 3 inch. both catbacks were from burshur racing. first pull with no tuning changes the car lost 6whp and 20ft/lbs of torque.
I have read a 1000 post on turbo exhaust . "bigger is better, period" I laugh at all 1000.
normally aspirated folks clearly understand the correct size exhaust nets the greatest horsepower. exhaust is a series of pulses. when those pulses are spaced close enough additional torque gains will be found as the pulses pull on each other and help evacuate the exhaust.
bicyclist also understand the principal. its called drafting.
what turbo guys dont understand is the pulses are still there on turbo cars. the turbine does not eliminate them. you only have to put your hand on the exhaust tip to feel them.
there was a honda in scc that made 550 whp through a 2.5 inch exhaust. it tracked high 10s at 135 fwd.
there was also guy a few years ago that has a 16g making 420hp/430tq through a 2.5 exhaust.
I say give the kid a break. let him play.
Mar 23, 2012, 01:14 AM
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"Stepped" exhaust are very interesting stuff indeed, but it's very important that you consider the configuration of your car and test the exhaust for backpressure values.
If you look at the Supersprint system, especially for NA cars, you'll notice that often the diameter progressively decreases going downstream.
This is because during the testing a constant diameter exhaust brought a big drop in backpressure, and low and mid range torque was worse than stock.
The technical explanation why a stepped exhaust works is found in the temperature and density, toghether with heat transfer, of the gasses.
As the gas goes toward the back it gets colder and heavier, it slows down and has more intertia (worse pickup and throttle response, also worse spool up time in turbos).
Reducing the diameter you have a smaller gas volume and also much less pipe wall, so heat trasfer is lower. The mass of the exhaust gas in the pipes is proportional to something between ^3 and ^4 of the diameter.
Obviously this is valid only if the steps have progressive slopes between different diameters and the top end power doesn't suffer.
The Supersprint exhaust, which has 2"75 (70mm) pipes, has been developed to be fitted on stock or mildly tuned Evos, so stock turbos and power up to 350, maybe 370.
It's been developed measuring the temperature and backpressure values on the exhaust line on the dyno, and it sure increases the power by 20+ hp on a stock car, whiteout torque loss at low rpm or worse spool up.
This is the dyno chart on the official website, but it includes also the manifold!
Obviously if you want around 400 hp or more this exhaust is just too small.
That's the reason why a 3"15 (80mm) system exists!
If you look at the Supersprint system, especially for NA cars, you'll notice that often the diameter progressively decreases going downstream.
This is because during the testing a constant diameter exhaust brought a big drop in backpressure, and low and mid range torque was worse than stock.
The technical explanation why a stepped exhaust works is found in the temperature and density, toghether with heat transfer, of the gasses.
As the gas goes toward the back it gets colder and heavier, it slows down and has more intertia (worse pickup and throttle response, also worse spool up time in turbos).
Reducing the diameter you have a smaller gas volume and also much less pipe wall, so heat trasfer is lower. The mass of the exhaust gas in the pipes is proportional to something between ^3 and ^4 of the diameter.
Obviously this is valid only if the steps have progressive slopes between different diameters and the top end power doesn't suffer.
The Supersprint exhaust, which has 2"75 (70mm) pipes, has been developed to be fitted on stock or mildly tuned Evos, so stock turbos and power up to 350, maybe 370.
It's been developed measuring the temperature and backpressure values on the exhaust line on the dyno, and it sure increases the power by 20+ hp on a stock car, whiteout torque loss at low rpm or worse spool up.
This is the dyno chart on the official website, but it includes also the manifold!
Obviously if you want around 400 hp or more this exhaust is just too small.
That's the reason why a 3"15 (80mm) system exists!
Mar 23, 2012, 06:28 AM
#7
94, what kind of 2.5" exhaust makes 500+? A 2.5" downpipe? Ok, I believe it without a second thought.
A 2.5" catback that bends around a fuel tank and rear axle like a normal FWD exhaust?
I can say from experience, on a 2G FWD DSM, my car wouldn't make more then 320ish and the boost would not go any higher. I dropped the catback (still on a 2.5" downpipe) and the car instantly picked up 6mph and boost went up like 5 psi. It was a Tanabe exhaust though, so maybe my experience is simply based off a ****ty exhaust to begin with?
That exhaust above, if it is the EVO fitment adds two 90 degree bends though which is pretty significant. If the muffler sat on a 45 and had a single 45 degree bend instead of the two 90s, I'd believe it could probably work considerably better then the exhaust I had.
As for everything else in here though about cooler exhaust gases...if you actually do the math on it instead of guessing, I think you will be surprised on the outcome.
A 2.5" catback that bends around a fuel tank and rear axle like a normal FWD exhaust?
I can say from experience, on a 2G FWD DSM, my car wouldn't make more then 320ish and the boost would not go any higher. I dropped the catback (still on a 2.5" downpipe) and the car instantly picked up 6mph and boost went up like 5 psi. It was a Tanabe exhaust though, so maybe my experience is simply based off a ****ty exhaust to begin with?
That exhaust above, if it is the EVO fitment adds two 90 degree bends though which is pretty significant. If the muffler sat on a 45 and had a single 45 degree bend instead of the two 90s, I'd believe it could probably work considerably better then the exhaust I had.
As for everything else in here though about cooler exhaust gases...if you actually do the math on it instead of guessing, I think you will be surprised on the outcome.
Last edited by 03whitegsr; Mar 23, 2012 at 06:32 AM.
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Mar 23, 2012, 08:33 AM
#8
normally aspirated folks clearly understand the correct size exhaust nets the greatest horsepower. exhaust is a series of pulses. when those pulses are spaced close enough additional torque gains will be found as the pulses pull on each other and help evacuate the exhaust.
bicyclist also understand the principal. its called drafting.
what turbo guys dont understand is the pulses are still there on turbo cars. the turbine does not eliminate them. you only have to put your hand on the exhaust tip to feel them
bicyclist also understand the principal. its called drafting.
what turbo guys dont understand is the pulses are still there on turbo cars. the turbine does not eliminate them. you only have to put your hand on the exhaust tip to feel them
What you are suggesting is that by properly sizing the exhaust pipe, you can produce a resonance effect that will produce low-pressure and/or high-pressure pulses at the exhaust ports of the engine at just the right time. This is certainly feasible, and is a familiar concept to anyone who has worked with high-performance 2-stroke engines.
However, there are three problems with this: First, any resonance-based effects are also centered on a certain frequency (in other words, a certain RPM). Away from this frequency, the effect degrades significantly and can actually be detrimental at other frequencies (RPMs). This results in a 'peaky' power band.
Second, to make reasonable use of the pulses, any such stepped/tapered design must sit very close to the exhaust ports (e.g. in your header, pre-turbo). If these steps are toward the cat-back of your exhaust, then the pulses must travel from the exhaust port, through the headers, through the turbo, down the down pipe, through your exhaust, then bounce back through all of the same tubing without becoming too 'spread out' or taking too long such that the engine is already in another cycle. Unlikely.
Finally, if you're actually going to pull all of this off, then it's going to require a lot of math and testing. Piecing together random exhaust parts and hoping for the best isn't likely to net gains.
But even if we ignore all of that, it has been shown over and over again that a larger diameter exhaust on a turbo car not only increases spool, but increases airflow through the motor. What you are suggesting is that you are going to increase airflow through the motor across the power band by switching to a smaller pipe diameter, and that's just not possible.
Mar 23, 2012, 08:41 AM
#9
TurboXS did this about ten years ago on the WRX and found that on a car that makes ~300whp, tapering the exhaust toward the axle-back actually did make the most power in their beta testing. YMMV.
I've never seen Supersprint on anything non-German. Good luck with your testing!
I've never seen Supersprint on anything non-German. Good luck with your testing!
Mar 23, 2012, 11:11 AM
#10
The general direction bigger is better, works for 98% of the setups... but there is always limits... so I'd say 3" will suit 99.98999% of ppl
Mar 23, 2012, 12:58 PM
#11
It doesnt work. Even with a testpipe dump added, it loses 20whp/20 ft lbs and 1000rpm of spool. Granted this was on a car that made 535whp on an HKS exhaust/2.4/3586/pump, (also not the best flowing exhaust) but the results are still relevant.
Going smaller never helps, except for noise, backpressure still gets you. If I really have to I will grab the dyno sheets, but the simple answer is No.
Going smaller never helps, except for noise, backpressure still gets you. If I really have to I will grab the dyno sheets, but the simple answer is No.
Mar 24, 2012, 02:38 PM
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http://www.burnsstainless.com/rd-250-350-18-304-l.aspx
Gardus, do you happen to work at Supersprint? Just curious, cause I noticed you're from Italy. If so, very cool.
Also, thanks for chiming in with the background information on how these exhausts are developed. Supersprint definitely puts a high level of rigor into research / development for their exhaust systems... The quantitative research backing these designs is what sets Supersprint apart from the rest. One more week until the system arrives!
Now just need to get the transition on order and find a good welder. Anyone else in northern Alabama that knows of someone who can lay down some good welds?
Last edited by cbseven; Mar 24, 2012 at 02:40 PM.