3" exhaust outcome on N/A

[mad_sb]

nameless lost torque and a little hp when they went from 3" back down to production 2.5" when they were testing one of the long tube 4-2-1 header versions. It wasn't a huge loss, but the 3" made more power everywhere vs the 2.5 IIRC.

Originally Posted by johnbradley

If I get in trouble for this I am blaming all of you



Please keep in mind this is just the prelimn. I have mountains of data to go through and figure out why it is what it is.

Originally Posted by johnbradley

10-13 ft lbs down low, 4-5 thru some areas of the powerband. If I knew why after the first flash the torque is up in the dip but then reverts ( I assume electronic interference since its repeatable) after that on the very next pull I can lessen the dip. I am almost willing to pay for the explanation but I am not sure that it would be shared if its known.

Originally Posted by johnbradley

Video will be a little ways out. Final numbers with the smaller exhaust 188/153 and a best torque run of 186.7/157.2. I'll have the dyno sheets off to Nameless to sort through after I go grab some lunch....3 hours no food sucks. So as you would expect smaller exhaust made less power, but only really seems to have dropped below 4500 for the most part.

[StormTrooper]

I'm really curious to see what the newest batch of nameless headers will do since they seem to keep getting better each revision.

My guess is that since tuning has been figured out during prototyping they've made gains above the rest of the field. Could be me wishing it though.


Personally I dislike the canister (fart can) look and would lose a few HP just to not have one.

[topazsparrow]

Originally Posted by ZDan

You won't lose torque due to "lack of backpressure" with a big exhaust. Big myth, that...

But then again, I seriously doubt that a 2.36" exhaust would be holding a 7400rpm 2.0L NA motor back.

Put it this way, the 6.0 liter V8 in my FD makes 465rwhp through a 3" OD single exhaust. I don't think a 2.36" exhaust is going to be a problem for you.

Yes and no. Backpressure is a myth... or rather the incorrect term. The loss of scavenging is the reason for a loss in TQ at lower RPM's. an exhaust that is too big WILL lose it's ability to scavenge.

[Dephective]

I don't like the setup of the 60s and the 60r would be far too loud with header + full exhaust for some tracks, let alone DD. Noise isn't my primary concern at all, but I don't like the passenger exit, or the muffler being inline. I haven't gotten a good view of the rear with the 80 but I'm sure it will be acceptable at least. I also plan for FI down the road, so the 60 just isn't an option for that kind of money.

[Dephective]

and thanks for the info on nameless 3" dynos. That has lessened my concerns quite a bit. I trust Nameless's research and development.

[jamesm]

i don't see why anyone would use a 3" exhaust when no one makes a 3" overpipe. your flow is limited to the flow capacity of the smallest part of the exhaust. if there's a 2.5" overpipe in there, you aren't going to flow any more than a 2.5" exhaust would anyway.

i'm sticking to 2.75" since there is an overpipe available in that size.

[Tansey86]

Originally Posted by jamesm

i don't see why anyone would use a 3" exhaust when no one makes a 3" overpipe. your flow is limited to the flow capacity of the smallest part of the exhaust. if there's a 2.5" overpipe in there, you aren't going to flow any more than a 2.5" exhaust would anyway.

i'm sticking to 2.75" since there is an overpipe available in that size.

If you have a 2.5" overpipe and the rest of the exhaust is 3" it will flow much better than a full 2.5" system. The phrase " its only as strong as its weakest link " doesn't apply to exhaust diameter.

[FR-S Matt]

Originally Posted by jamesm

i don't see why anyone would use a 3" exhaust when no one makes a 3" overpipe. your flow is limited to the flow capacity of the smallest part of the exhaust. if there's a 2.5" overpipe in there, you aren't going to flow any more than a 2.5" exhaust would anyway.

i'm sticking to 2.75" since there is an overpipe available in that size.

That's technically not true. I'm currently having one made along with a midpipe. There are no overpipes being made that *fit* both LHD/RHD. There is a 3" solution though for LHD.

[jamesm]

Originally Posted by Tansey86

If you have a 2.5" overpipe and the rest of the exhaust is 3" it will flow much better than a full 2.5" system. The phrase " its only as strong as its weakest link " doesn't apply to exhaust diameter.

that's not true. the maximum flow rate of a tube is dependent upon it's minimum radius. you can have 1000 feet of 3" pipe, and if you have one inch on 2.5" pipe in the middle, the whole thing can't flow more than that 2.5" section in the middle. this is the principle on which flow restrictors (like 'boost pills') work. the 2.5" section doesn't magically have more cross-sectional area just because it has 3" pipe on either side of it. in fact, it'll flow less than a straight 2.5" would do to the fact that it's now no longer ideal (i.e. all smooth, same diameter pipe).

[Dephective]

Originally Posted by jamesm

that's not true. the maximum flow rate of a tube is dependent upon it's minimum radius. you can have 1000 feet of 3" pipe, and if you have one inch on 2.5" pipe in the middle, the whole thing can't flow more than that 2.5" section in the middle. this is the principle on which flow restrictors (like 'boost pills') work. the 2.5" section doesn't magically have more cross-sectional area just because it has 3" pipe on either side of it. in fact, it'll flow less than a straight 2.5" would do to the fact that it's now no longer ideal (i.e. all smooth, same diameter pipe).

Incorrect. This applied to an incompressible liquid, not gases.

Temperature of gases coming directly out of the manifold are considerably hotter than what comes out at the end of the pipe. Higher temperature means more space is needed. Which is why cat-backs don't do much for power unless it was the biggest restriction in the system. Why do you think headers make more power than any other exhaust modification on N/A. Downpipes make the most on FI, because temperatures are hottest right after the turbo.

This is why we see differences in power/torque with the variance of piping diameter in headers i.e stepped diameter. These variances change the exhaust gas velocity.

The straw theory doesn't apply here. There is more to "flow" than just the amount of gas can move through.

I didnt think there would be an issue, I was just trying to confirm from those that had more experience with n/a than myself. This isn't my first rodeo.

[jamesm]

Originally Posted by Dephective

Incorrect. This applied to an incompressible liquid, not gases.

Temperature of gases coming directly out of the manifold are considerably hotter than what comes out at the end of the pipe. Higher temperature means more space is needed. Which is why cat-backs don't do much for power unless it was the biggest restriction in the system. Why do you think headers make more power than any other exhaust modification on N/A. Downpipes make the most on FI, because temperatures are hottest right after the turbo.

This is why we see differences in power/torque with the variance of piping diameter in headers i.e stepped diameter. These variances change the exhaust gas velocity.

The straw theory doesn't apply here. There is more to "flow" than just the amount of gas can move through.

I didnt think there would be an issue, I was just trying to confirm from those that had more experience with n/a than myself. This isn't my first rodeo.

You're right that when you throw in temperature and all that things change a bit. You can reduce the diameter the further you get from the head and maintain the same pressure. In any case, you wouldn't want the smallest bit in front (like the overpipe in our case).

[Dimman]

Nice to see how far general knowledge of NA tuning has advanced on the internet...

[jamesm]

Originally Posted by Dephective

Incorrect. This applied to an incompressible liquid, not gases.

Temperature of gases coming directly out of the manifold are considerably hotter than what comes out at the end of the pipe. Higher temperature means more space is needed. Which is why cat-backs don't do much for power unless it was the biggest restriction in the system. Why do you think headers make more power than any other exhaust modification on N/A. Downpipes make the most on FI, because temperatures are hottest right after the turbo.

This is why we see differences in power/torque with the variance of piping diameter in headers i.e stepped diameter. These variances change the exhaust gas velocity.

The straw theory doesn't apply here. There is more to "flow" than just the amount of gas can move through.

I didnt think there would be an issue, I was just trying to confirm from those that had more experience with n/a than myself. This isn't my first rodeo.

You're right that when you throw in temperature and all that things change. You can reduce the diameter the further you get from the head and maintain the same pressure. In any case, you wouldn't want the smallest bit in front (like the overpipe in our case).

My point remains though. A 2.5" overpipe isn't going to flow as much air as a 3" overpipe just because you bolt a 3" front pipe to it, and all of the exhaust still has to go through it, it's still the limiting factor so to speak.

[Dephective]

Originally Posted by jamesm

You're right that when you throw in temperature and all that things change a bit. You can reduce the diameter the further you get from the head and maintain the same pressure. In any case, you wouldn't want the smallest bit in front (like the overpipe in our case).

You're misunderstanding my question. Like someone corrected me earlier on the terminology, not back pressure but the scavenging effect is considerably lessened with too large of a diameter exhaust for n/a (generally speaking). I know that this is the case with lower displacement cars most of the time. I haven't seen any research into exhausts with a larger than 2.5" diameter on a N/A FRS/BRZ. The changes brought about by having a header + 2.5" piping til the cat-back might just be enough so that the 3" from there on might be overbored on this application. I'm not sure that's the case, I was just looking for info to confirm or refute that logic.