| makofoto | 09-16-2005 12:25 AM |
Making more AX HP ...
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I've got a particularily fast event coming up ... where every bit of power is going to count.
Will I gain any HP taking off my ProDrive muffler ... the rest of the cat-less exhaust is 2.5" Stromung straight pipes, Scooby Sport ceramic coated DP, APS Up-Pipe ? Stock turbo, Ecutek dyno tune, 94 octane ...
Should I have a additional straight pipe made for the axle back end of my exhaust ... or just a curved end pipe ...
Will I gain any HP taking off my ProDrive muffler ... the rest of the cat-less exhaust is 2.5" Stromung straight pipes, Scooby Sport ceramic coated DP, APS Up-Pipe ? Stock turbo, Ecutek dyno tune, 94 octane ...
Should I have a additional straight pipe made for the axle back end of my exhaust ... or just a curved end pipe ...
| Scoobie Doogie | 09-16-2005 01:05 AM |
Hmmm...Turbo cars me thinks less exhaust=better. Put an elbow on the end of your down pipe would be the most HP. Plus you'd save some more weight.
Dave
Dave
| makofoto | 09-16-2005 01:34 AM |
Even with Turbo cars ... I think Inertial Flow ... through a certain length of exhaust pipe is helpful in creating a fairly constant sucking flow of gases ... which helps with throttle response at mid to high revs ...
| Scoobie Doogie | 09-16-2005 01:53 AM |
Exhaust gas velocity only matters on N/A car because they need the scavenging effect of the exhaust pulse to pull more air into the combustion chamber for more power. Turbos=forced air so no need for exhaust past the turbo outlet. Actually the BEST exhaust on a turbo is a bell.
Dave
Dave
| DrBiggly | 09-16-2005 12:21 PM |
Eh, take it off. A few pounds and perhaps an HP or two. :)
-Biggly
-Biggly
| jmott | 09-16-2005 12:47 PM |
[QUOTE=makofoto]Even with Turbo cars ... I think Inertial Flow ... through a certain length of exhaust pipe is helpful in creating a fairly constant sucking flow of gases ... which helps with throttle response at mid to high revs ...[/QUOTE]
nope.
a little horn on the end of the turbo works best
nope.
a little horn on the end of the turbo works best
| jmott | 09-16-2005 12:48 PM |
[QUOTE=Scoobie Doogie]Exhaust gas velocity only matters on N/A car because they need the scavenging effect of the exhaust pulse to pull more air into the combustion chamber for more power. Turbos=forced air so no need for exhaust past the turbo outlet. Actually the BEST exhaust on a turbo is a bell.
Dave[/QUOTE]
even on NA cars these days it is rare to see an exauhst with too little backpressure.
especially with variable cam timing being so common
Dave[/QUOTE]
even on NA cars these days it is rare to see an exauhst with too little backpressure.
especially with variable cam timing being so common
| dwx | 09-16-2005 12:54 PM |
When I tested my SM car with the muffler on and off, the difference was negligible, and that was with a Prodrive oval tip muffler, which is not straight through. Taking it off isn't really going to hurt anything though.
Boost == Power.
Boost == Power.
| makofoto | 09-16-2005 01:17 PM |
>>>difference was negligible<<<
NO it isn't ... it's MUCH louder ! :eek: :lol:
... so you guys don't think that exhaust flow helps spool up and thus throttle response in a Turbo car ...
Dang ... I had my Db meter with me last weekend but forgot to check sound levels w/o my muffler. Some of our local events have started to get strict with sound levels. I had a friend kicked out of an event (twin charged SM Mini) ... with another car (SS Z-06) ... he had to add his 90 degree tips after receiving a warning.
Barco ... did my car sound that bad on course ... as Max thought ? It did sound cool in grid ... I had some people convinced I had a 2.8 stroker engine ... ;)
NO it isn't ... it's MUCH louder ! :eek: :lol:
... so you guys don't think that exhaust flow helps spool up and thus throttle response in a Turbo car ...
Dang ... I had my Db meter with me last weekend but forgot to check sound levels w/o my muffler. Some of our local events have started to get strict with sound levels. I had a friend kicked out of an event (twin charged SM Mini) ... with another car (SS Z-06) ... he had to add his 90 degree tips after receiving a warning.
Barco ... did my car sound that bad on course ... as Max thought ? It did sound cool in grid ... I had some people convinced I had a 2.8 stroker engine ... ;)
| PossumK | 09-16-2005 02:04 PM |
Your car was pretty loud, but not as loud as that one white Integra on Sunday (Was that your SM competitor?). My ears were ringing every time it passed.
| BlkWRXWag | 09-16-2005 02:31 PM |
I suspect it was over the limit Mako, but that may be just be subjective since it was such a God awful noise!!!!
| makofoto | 09-16-2005 02:51 PM |
Yeah that was Tetsu ... he's in first ... I'm in 2nd place in our local SM Championship ... but after dropping events ... Casey Quinn is still in first with his 440 hp Camaro and 335 Kuhmos!
I'm still playing catch up in the Decibel Dept. :D
I'm still playing catch up in the Decibel Dept. :D
| buzz313th | 09-16-2005 03:29 PM |
IMHO
Any volume of air that is keeping momentum on the output side of the turbo will help create a decrese in air pressure, The longer or larger the volume of air, the greater the energy (As long as there is no bottleneck) At higher RPM's I feel that throttle response would be quicker and snappier than if that "Inertial flow" was not existent.
A turbo spins by having higher pressure at the input side than the output side. The bigger the difference the more energy available for the turbo. If the Inertial flow helps the NA cars because of a scavenging effect, then the same to certain extent would also help a turbo car. With a wide enough exhaust, the back pressure is minimal at initial engine acceleration. But once the mass of air has built a certain velocity, that energy is being used to further lower the airpressure behind the turbo.
Obviously, this theory cannot be proven until tests are done on a dyno, but either I belive this to be the case.
JB
Any volume of air that is keeping momentum on the output side of the turbo will help create a decrese in air pressure, The longer or larger the volume of air, the greater the energy (As long as there is no bottleneck) At higher RPM's I feel that throttle response would be quicker and snappier than if that "Inertial flow" was not existent.
A turbo spins by having higher pressure at the input side than the output side. The bigger the difference the more energy available for the turbo. If the Inertial flow helps the NA cars because of a scavenging effect, then the same to certain extent would also help a turbo car. With a wide enough exhaust, the back pressure is minimal at initial engine acceleration. But once the mass of air has built a certain velocity, that energy is being used to further lower the airpressure behind the turbo.
Obviously, this theory cannot be proven until tests are done on a dyno, but either I belive this to be the case.
JB
| Calamity Jesus | 09-16-2005 03:50 PM |
[QUOTE=buzz313th]If the Inertial flow helps the NA cars because of a scavenging effect, then the same to certain extent would also help a turbo car. With a wide enough exhaust, the back pressure is minimal at initial engine acceleration. But once the mass of air has built a certain velocity, that energy is being used to further lower the airpressure behind the turbo.[/QUOTE]
No. See, a NA car's exhaust works with pulses. A valve opens and a rush of exhaust flows out and down the primary tubes, through the collector and out toward the tip. If tuned properly, the next exhaust valve will open as a vacuum is starting to build up in the primaries from the previous pulse's race to the tip. This helps pull the exhaust out of the new valve opening.. and so on and so forth.
When you put a turbo in the mix, you've got constant positive pressure in the primaries. The exhaust can only be pushed out of the cylinders because there is no vacuum to help draw it out.
The turbine itself dampens the exhaust pulses like a valve. Imagine dumping water down your sink.. you can dump bucket loads at a time, but only so much can squeeze down the drain at a time. Since there isn't one pulse to pull out the next pulse, there's no advantage from a longer pipe.
We don't need dyno results. Look at the FWD dragsters.. they make incredible HP from small engines and dump their exhaust and wastegate separately using the shortest length of piping they can to get it outside of the car (usually exiting on the side of the front bumper).
No. See, a NA car's exhaust works with pulses. A valve opens and a rush of exhaust flows out and down the primary tubes, through the collector and out toward the tip. If tuned properly, the next exhaust valve will open as a vacuum is starting to build up in the primaries from the previous pulse's race to the tip. This helps pull the exhaust out of the new valve opening.. and so on and so forth.
When you put a turbo in the mix, you've got constant positive pressure in the primaries. The exhaust can only be pushed out of the cylinders because there is no vacuum to help draw it out.
The turbine itself dampens the exhaust pulses like a valve. Imagine dumping water down your sink.. you can dump bucket loads at a time, but only so much can squeeze down the drain at a time. Since there isn't one pulse to pull out the next pulse, there's no advantage from a longer pipe.
We don't need dyno results. Look at the FWD dragsters.. they make incredible HP from small engines and dump their exhaust and wastegate separately using the shortest length of piping they can to get it outside of the car (usually exiting on the side of the front bumper).
| dwx | 09-16-2005 03:57 PM |
[QUOTE=buzz313th]IMHO
Any volume of air that is keeping momentum on the output side of the turbo will help create a decrese in air pressure, The longer or larger the volume of air, the greater the energy (As long as there is no bottleneck) At higher RPM's I feel that throttle response would be quicker and snappier than if that "Inertial flow" was not existent.
A turbo spins by having higher pressure at the input side than the output side. The bigger the difference the more energy available for the turbo. If the Inertial flow helps the NA cars because of a scavenging effect, then the same to certain extent would also help a turbo car. With a wide enough exhaust, the back pressure is minimal at initial engine acceleration. But once the mass of air has built a certain velocity, that energy is being used to further lower the airpressure behind the turbo.
Obviously, this theory cannot be proven until tests are done on a dyno, but either I belive this to be the case.
JB[/QUOTE]
In a best case scenario, you want zero backpressure after the turbo. That creates the largest pressure differential. The larger differential allows the turbo to spin faster at lower rpms, which increases both throttle response and lag times. In a perfect world you'd want as large of a pipe as possible coming off the turbo, properly sized to the exhaust housing and which follows other constraints like packaging, noise, etc. It should also be very short and just dump out to atmosphere.
Turbos on Subarus are generally not that large and the benefit you see going from say a 3" exhaust to a 3.5" exhaust is minimal. You just aren't pumping that much exhaust out. Like Beaverboy said, on turbo drag cars that use very large turbines, they use 4-5" exhaust piping that generally dumps out the shortest path it can.
Any volume of air that is keeping momentum on the output side of the turbo will help create a decrese in air pressure, The longer or larger the volume of air, the greater the energy (As long as there is no bottleneck) At higher RPM's I feel that throttle response would be quicker and snappier than if that "Inertial flow" was not existent.
A turbo spins by having higher pressure at the input side than the output side. The bigger the difference the more energy available for the turbo. If the Inertial flow helps the NA cars because of a scavenging effect, then the same to certain extent would also help a turbo car. With a wide enough exhaust, the back pressure is minimal at initial engine acceleration. But once the mass of air has built a certain velocity, that energy is being used to further lower the airpressure behind the turbo.
Obviously, this theory cannot be proven until tests are done on a dyno, but either I belive this to be the case.
JB[/QUOTE]
In a best case scenario, you want zero backpressure after the turbo. That creates the largest pressure differential. The larger differential allows the turbo to spin faster at lower rpms, which increases both throttle response and lag times. In a perfect world you'd want as large of a pipe as possible coming off the turbo, properly sized to the exhaust housing and which follows other constraints like packaging, noise, etc. It should also be very short and just dump out to atmosphere.
Turbos on Subarus are generally not that large and the benefit you see going from say a 3" exhaust to a 3.5" exhaust is minimal. You just aren't pumping that much exhaust out. Like Beaverboy said, on turbo drag cars that use very large turbines, they use 4-5" exhaust piping that generally dumps out the shortest path it can.
| Scoobie Doogie | 09-16-2005 06:50 PM |
Thanks for the backup Beaverboy and dwx.
Dave
Dave
| makofoto | 09-16-2005 10:15 PM |
O.K. ... well I tried running without the ProDrive muffler last weekend ... just one run ... didn't want to melt my rear half shaft boot. Didn't notice much difference ... but it did sound great ... made my half SM car sound more like the real thing! :-)
So I'll see about having an angle end piece made for the end of my down pipe ... so I can run with the sound blasting away from the timing motor home/start ... and give that a try next weekend ...
So I'll see about having an angle end piece made for the end of my down pipe ... so I can run with the sound blasting away from the timing motor home/start ... and give that a try next weekend ...
| makofoto | 09-18-2005 02:47 AM |
Do you guys think it's safe to run with the exhaust removed after the downpipe, ie. without an angled end tip ? I wanted to do a few runs without the exhaust ... to see how it felt ... whether it was worth having a end tip made to attach to the downpipe.
By Safe ... I mean ... what's going to happen with the hot exhaust gases just venting after the downpipe ?
Or ... should I leave the short mid pipe (no cats) ... so I have a bit more pipe ... and more support ... the end of the downpipe isn't supported ...
... but with the short mid pipe ... maybe I would be blasting the gas tank ?! :-(
By Safe ... I mean ... what's going to happen with the hot exhaust gases just venting after the downpipe ?
Or ... should I leave the short mid pipe (no cats) ... so I have a bit more pipe ... and more support ... the end of the downpipe isn't supported ...
... but with the short mid pipe ... maybe I would be blasting the gas tank ?! :-(
| Storm | 09-18-2005 11:39 AM |
Check to see if the exhaust has to exit beyond the driver as in stock/SP rules. Slap a turndown on the end and runnit!
Jay Storm
Jay Storm
| neuspeed | 09-18-2005 12:57 PM |
HKS is the straightest cat back you can buy.. If you're in SM why don't you P&P the turbo or VF34/22 it? Do you have headers?
| makofoto | 09-18-2005 01:03 PM |
Only driving SM locally ... going back to STX next year ... one year on R tires will be enough. :-)
We do have a fellow who is developing a SM STI ... bigger turbo, etc. He's already at over 400+ hp to the ground. He's only on 245/45/17 710's @ the moment ... next ... we need to fit bigger rubber ... been in touch with Joel/Stompy.
We do have a fellow who is developing a SM STI ... bigger turbo, etc. He's already at over 400+ hp to the ground. He's only on 245/45/17 710's @ the moment ... next ... we need to fit bigger rubber ... been in touch with Joel/Stompy.
| makofoto | 09-19-2005 12:16 PM |
Organizers announced that they are going to be monitoring sound levels ... and told a fellow SM competitor not to bother to show up for one run before being told he couldn't run. That fellow said he wouldn't be able to do anything about his loud, 100+ db exhaust. I could do a run during Saturday's practice ... and if my noise is objectionable ... replace my muffler ... we'll see.
| solo-x | 09-19-2005 12:52 PM |
just curious, but how much time do you think a handful of hp will give you? imo, you'd be better off focusing on your driving instead of worrying if you'll get dinged for sound. i've done the whole scramble-to-put-your-exhaust-back-on-after-failing-sound thing and it is one major distraction. maybe i've just got ADD...
nate
nate
| makofoto | 09-19-2005 01:02 PM |
Of course ... but I've got plenty of time on Saturday to test ... and I don't necessarily want to put 12 more runs on my Kuhmo 710's ... so I'll have time to make adjustments/put back exhaust.
| Patrick Olsen | 09-20-2005 04:41 AM |
Sometimes I pop my hood between runs to cool off the engine. I'd bet I'm gaining about as much power as removing the muffler will gain you.
Pat Olsen
'97 Legacy 2.5GT sedan
Pat Olsen
'97 Legacy 2.5GT sedan
| makofoto | 09-20-2005 11:46 AM |
huh ?! of course we pop the hood and spray down the IC ... that gains you a lot more power ... but ... we WANT IT ALL! :-) ... we need it all ...
I'm up against two 440 HP Camaros with 315 and 335 710's ... and a 400+ hp to the ground STI ... on a track designed my Guy Ankeny for the local GRA Corvette club ... although he will be running his full on tube frame Camaro ... that he just used to win AP at the Nationals last week. I'm currently in 2nd place ... and am scratching and clawing to stay there! :devil:
I'm up against two 440 HP Camaros with 315 and 335 710's ... and a 400+ hp to the ground STI ... on a track designed my Guy Ankeny for the local GRA Corvette club ... although he will be running his full on tube frame Camaro ... that he just used to win AP at the Nationals last week. I'm currently in 2nd place ... and am scratching and clawing to stay there! :devil:
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