The truth about 3inch exhausts on Na Cars
- Thread starter 7MA61
- Start date
Im running my Apexi N1 exhaust with a 3" straight through system (no cat, res, nothing!) and theres no backpressure and my torque is shit. Its also VERYYYYY freakin loud, Its going on my GTE next month and my NA is getting the GTE stock system.
JustAnotherVictim
Supramania Contributor
Mine was loud too, but it didn't sound like that. I had my 3" exhaust on my car when it was NA and loved it. I remember when I first got my 3" exhaust everyone bashed and flamed me and basically 1/50 people agreed with me that 3" exhaust was better. It's funny how things have changed since then, and now there's dyno proof! 
It would be nice if we could see a before/after torque curve. Or did I skip over that? Those kw and kph graphs don't help me much. Not to mention they're almost a year apart.
I do not believe there was ever any doubt that a larger exhaust will make more power overall. That would be silly. A bigger exhaust will make more power but that's not the only criterion why a 2.5in system is usually recommended.
You're not going to make much power with an NA, period. If low end was sacrificed with this 3in exhaust to make an extra few hp on top, I don't think it's worth it which is why 2.5in catbacks are commonly used on an NA.
I do not believe there was ever any doubt that a larger exhaust will make more power overall. That would be silly. A bigger exhaust will make more power but that's not the only criterion why a 2.5in system is usually recommended.
You're not going to make much power with an NA, period. If low end was sacrificed with this 3in exhaust to make an extra few hp on top, I don't think it's worth it which is why 2.5in catbacks are commonly used on an NA.
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Mine @ 97Db would Kill birds in flight make small children scream and cry and shatter Bricks in walls under boost
I HATED it and it was only a matter of time before I was defected..
I HATED it and it was only a matter of time before I was defected..
Joe compare the graphs, there isn't a low end loss at all, the entire power curve is up. Of course you shouldn't expect much from an NA, but this is good hard proof that you should get a 3" exhaust for your NA, especially if you plan on going turbo later so you don't have to buy another exhaust.
AGlobalThreat said:
I fail to see how, people's dynos show that kind of difference between two runs in the same session even more so after a few days.
I agree. After doing the kw > hp conversion, before and after power is 152.2hp and 154.4hp respectively with the dynos being more than a year apart.
That isn't sufficient evidence that the 3in exhaust did anything at all.
I could dyno my car twice within 10 minutes and get results with more variance than that.
From the before/after dyno posted, it doesn't seem like the 3in exhaust did anything but make the car louder.
That isn't sufficient evidence that the 3in exhaust did anything at all.
I could dyno my car twice within 10 minutes and get results with more variance than that.
From the before/after dyno posted, it doesn't seem like the 3in exhaust did anything but make the car louder.
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The car has repeatedly run the old figures of between 108rwkw and 113.5 rwkw(being the highest it made after the ecu install) with the old exhaust on various dynos at various intervals so its not a case of that, not to mention it pulls better towards the limiter then before pretty much anything above 6000rpm used to be pointless as torque/tractive effort went way south.CRE said:
As for any loss in bottom end torque, it feels just as snappy down low if not more so I fit the gas on corner exit and its more likely to want to step out then before.
The only reason I went three inch was to free up the top end for when the BC cams go in, that and I needed a new cat and muffler anyway.:biglaugh: . Realistically this isn't a street car so anyloss in bottom end ie below 3000rpm is a moot point on the track.
Oh and the old exhaust wasn't exactly quiet either, this one is just a bit louder
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i dunno if i could run a loud ass exhaust on my car ive had a car with a horribly loud exhaust and i think ive grown out of that so ill prolly be going with 2.5
nice numbers tho and thanks for posting this! i love how your car sounds i just dont think id do it to mine if i had to live with it
nice numbers tho and thanks for posting this! i love how your car sounds i just dont think id do it to mine if i had to live with it
Fuzz420 said:
I'd say louder.
I was there during said dyno session.
He definately had a gain in horsepower and torque without a muffler.
I've got to say, out of all the cars that I recorded dynoing that day, this includes some insane, higher horsepower Supras, his was hands down the loudest car at WOT without a muffler and 2.5". :icon_bigg
Now Aaron, tell us all if it was worth it without the muffler? :biglaugh:
A year apart huh? A dyno can have 5 horsepower difference with no changes between pulls.
Your losses. Still waiting to see a stock exhaust, HKS sport exhaust, and a quality 3 inch like you tested on the same car, on the same day. Or at least close and corrected.
edit; So a 3" inch exhaust yields almost 2 horsepower. Wow. I am trying to remember if I have an old test of a 7MGE bolt on test, or if one was done. I will be looking it up when I can. Because you should pick up 10 across the board as big as the stock mufflers are.
Your losses. Still waiting to see a stock exhaust, HKS sport exhaust, and a quality 3 inch like you tested on the same car, on the same day. Or at least close and corrected.
edit; So a 3" inch exhaust yields almost 2 horsepower. Wow. I am trying to remember if I have an old test of a 7MGE bolt on test, or if one was done. I will be looking it up when I can. Because you should pick up 10 across the board as big as the stock mufflers are.
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Yes but I wasn't going from a stock muffler now was I, a standardish 7mge on the day made 100.7rwkw (had extractors and 2.5inch cat back on an auto cressida). Not to mention the largest gains in a system specifically on an NA car are in the extractors and they remained the same because well you can't get much better then what I have anyway.Nick M said:
You also have to remember the car was dyno tuned on the 2.5inch exahust, and you can clearly see between the two curves that the afr's have gone to shit slightly leaner which is good but in general they are all over the shop. I'm sure with some more dyno time and tuning the 3inch exhaust would yield a higher gain. We are talking about a fixed state tuned ecu here with no afm so it can't adjust anything without user input.
But thats a moot point because I'm not getting it tuned again to the cams go in (i'm not made of cash).
Your system is costing you power. A smaller system, but bigger than stock mind you, would increase velocity, which would increase scavenging.
2.5" was already too big.
2.5" was already too big.
Err the stock exhuast on an MA61 is 2 1/4 inch Nick saying a 2.5inch is too big is rediculous.Nick M said:
We are talking about a car running 10.7:1 comp, heavily ported head, twin throttle bodies, balanced bottom end etc etc.
2 1/4 inch is a perfect size exhaust for a built 4age sprinter/corolla not a modded 3L six.
My previous system showed a flat torque curve from 1500rpm to 5000rpm which definately puts end too any argument that a 2.5inch exhaust is too small.
Dyno dynamics dyno have close toa 25% drivetrain loss. So whilst my figure look low they aren't actually.
Any properly built and tuned engine does not require a significant amount of back pressure.
My old setup with a 1500rpm launch liberated at 14.789 second 1/4 at 93.29 mph with a race weight of 1382kg or 3040lbs including driver. Using a drag calculator this equates to 186-193rwhp in American figures.
Freudian slip?7MA61 said:
The sport exhaust from HKS is 60mm, which is about 2.36 inches. That is probably a good choice. When an company makes a tuned exhaust for a naturally aspirtated car, they are sold for stock applications, or an assumed 100% V.E. 180 CID engine does not need 3 inches until beyond fuel cut.
That is some heavy gutting to hit 3000 lbs. What is missing?
And the constant discussion on the boards is that a 3 inch exhaust is needed on a stock 7MGE. That is, was, and will be horseshit.
You read the MA61 bit ie MK2 didn't you:doublebir Thats full weight, spare tyre rear seats and full tank of fuel in, car had sound deadening removed though but had a gravel rust proofing sprayed inside afterwards anyway.Nick M said:
As for a HKS exhaust, a I couldn't be fucked handing over the cash for one and 2 they don't make them for MK2 anyway.:nono: . Given that my engine is not stock why would I run an exhaust that is designed for a stock application anyway. To suggest an off the shelf exhaust is any better then something I can welded at a shop that has been in the performance exhuast business for 30 years is also a wee bit silly.
The car needed a new exhuast, the old one had a few scrapes when the car was lower and the muffler had a large carbon buildup. Given that a turbo build is not out of the question in the future I decided to go 3 inch because its means spending less money later on on yet another system.
as for the other sheet (tractive effort or torque at the wheels on the right) pretty much flat and the same figure from 2000-5000rpm
Any point in arguing about losing low end torque is still pointless when I'm throwing in 272's with 8.68mm lift, optimising top end potential is everything atm, this is my second car and essentially race car, I couldn't give a rats about a torque hole below 2000rpm because well last time I raced it probably was under there for .2 of a second off the line, and sat over 6000rpm for majority of the hill climb winding out first and second gear.
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No. I assumed all discossion on here was for the MA70. I don't pay attention to the screen names.
For what it is worth, the stock torque curve is already flat.
And an exhaust sold as a kit has far more research in it, than a muffler welded up with madrel bend pipes. It isn't even comparable.
If it werer a turbo car, that would be a different story. Pressure always tries to equalize, and the manifold has a shitload of pressure in it. So eliminating as much as possible in a turbo car is the way to go.
Good luck with the project.
I mentioned it in the post you commented on the low weight and clearly the vid if you watched it which I doubt is of a MK2:icon_conf .Nick M said:
I completely agree with you that for street use and for 99% of NA owners on here that a 3 inch exhaust on an NA car is just silly. Comparing my 7mge to 99% of 7mges on this forum is also pretty pointless because not many are anywhere near as modded the only exceptions being the guy with the homebuilt ITB kit and the 101mm stroke 7mge.
The thread was just made because my graph clearly shows that the common misconception of the loss in bottom end power with a bigger exhuast, yeah the gains aren't huge but it still hasn't lost power.