Compared to stock with 4 cats I imagine?
By the time you compare it to piggies (and possibly an x-pipe in the stock exhaust) the difference won’t be that significant. ~200 horsepower through a 2.3(?) In. pipe isn’t leaving much on the table really. Particularly because the stock manifold are excellent.
Yes, compared to stock. I also have 2 cats in the main cat position.
Your rationale is that 2.36" is sufficient and the stock exhaust isn’t leaving anything on the table for NA. Reality says otherwise.
JC, You assume a lot of things and I like that you rely on math and calculations, which I also enjoy, but you have to look deeper than that.
You’re assuming the 2.3" piping isn’t crushed in sections and there aren’t shitty bend that adversely affect flow. Most of us know that there are so in reality you could gut the cats and add an X-pipe but you would be trying to polish a turd.
The JHM exhaust isn’t successful based on it’s diameter alone, I think we can all agree on that. The success of the system really depends on the designer knowing the engine and the concepts of exhaust tuning…just like we always discuss with their B6/7 S4 headers.
I feel that the gain of a 2.75" exhaust is actually decreased when a car is supercharged.
For example:
Going from an OEM to a full 2.75" catback NA will have a larger gain than
Going from an OEM to a full 2.75" catback while supercharged.
I’m not saying the increased size isn’t needed for efficiency, but the delta is larger while NA.
This is apples to oranges, but take not of the B8 S4…headers and exhaust add almost nothing.
This is one of the companies that you were arguing for in your other thread.
The fact is they really don’t care about making power, they just need their dyno to show that they make power or increase performance. As long as the guys in Europe stay happy buying dyno sheets, then all is good and MRC will pump their custom tunes, P&P intake manifolds, cold air scoops, and undersized exhausts…they should just hope their customers don’t have a run in with a JHM car because it’s usually pretty embarrassing.
The B8 S4 bears this out. The exhaust seems to deliver very little gains.
Supercharged, I believe one of the fastest times on a JHM stage 1 car was running a stock catback and JHM downpipes. Trapped 118.
Same goes for the APR test car…didn’t it have stock catback? Ran 11.15 @ 125
Yes, pretty much. Rather a well designed 2.36 inch exhaust than a crappy 2.5 or 2.75 inch one (not the JHM obviously before you jump me again - there are more “large” options i.e. Supersprint)
The stock Audi exhaust really is quite good. They will have spent a lot of time designing that component - albeit with multiple targets not just outright performance. A lot more thought went into it than with most aftermarket solutions. It’s not a “turd” by any stretch of [euroswagr’s] imagination. The Audi main cats are also very good, no reason to replace those at all.
[quote] the stock exhaust isn’t leaving anything on the table for NA.
[/quote]
I didn’t say “nothing”. I said not much. I can believe your JHM exhaust gained you about 20 horsepower. I also believe at least half of those gains are due to the absence of the 400cpi primary cats. Those are by far the most restrictive component. Every time I see them I can’t believe you wouldn’t gain >10hp without them on a 400hp engine. A stock exhaust with an X-pipe in the right location (I’m sure JHM did considerable research in finding the optimal spot for the X) will not leave much left to be gained by increasing the pipe diameter. This is guesstimation territory but I would say maybe 5 hp. Really depends on the precise design of the exhaust, it’s a complicated science where you need both velocity and low (but not too low) backpressure.
Anyway, looking forward to see what my car gains without the precats. I just picked her up and she certainly sounds better, but was stuck in traffic pretty much the entire way home.
Bottom line OPs car runs great, sorry for the accidental derail.
actually, not anything has been contracted to create a new word, and that word is…
…NOTHING!
I got that much, but I didn’t say either of those did I?
[quote=myself]the difference won’t be that significant.
[/quote]
How you went on interpret that as zero or nothing or not anything I’m not quite sure.
Dude, you like to think out loud…but you can’t accept being wrong. You will argue in circles just so you don’t “seem” wrong.
So you said the stock exhaust would be sufficient without cats and an X-pipe
Now you’re saying a well designed 2.36" exhaust would be sufficient, which is it?
You also still haven’t touched on your rationale about exhaust size with a supercharger. You are guessing and assuming everything, but testing has shown your guesses are incorrect…but you still argue.
Did you just contradict yourself in the same post?
[quote=JCcan’tbewrong]The Audi main cats are also very good, no reason to replace those at all.
[/quote]
[quote=JCcan’tbewrong]I also believe at least half of those gains are due to the absence of the 400cpi primary cats. Those are by far the most restrictive component.
[/quote]
I think he meant pre-cats when he said primary cats.
Yes, thank you. Audi calls the pre-cats primary catalysts too FYI. And the 400 cpi was there in case of doubt.
I’ve never measured the standard exhaust, I took the 2.36 number in a quote from Saki as I have no reason to doubt it.
I may be wrong on the superchargers vs NA exhausts, I am out of my depth on that as I’ve really dealt with turbo cars before. No problem conceding that. The thing with superchargers is that they (correct me if I’m wrong again) pretty much flow a fixed amount of air/engine speed depending on the size pulley you use. With turbos the turbine itself is a huge restriction in the exhaust which superchargers do not have. As such it seems reasonable you can get away with a lot more in terms of exhaust undersizing without impacting the power numbers too much. Maybe 1 or 2 degrees less timing which don’t do much. An NA car needs all the help it can get to breathe a little better, that’s certainly true. But my point stands that the absolute gains made by larger piping are relatively small. We have some idea how much the precats alone are worth (And I just recorded useful data about that) and we should attribute at least a small horsepower gain to the X crossover as well if we assume it to be well designed. Not that much left to attribute to the diameter of the piping if the entire pie is only 20hp (number borrowed from Saki again)
Can a moderator break this exhaust talk off this thread please.
JC just so you know all of this has once again. Already been tasted. 2.75 vs stock catback on same OEM cats. The properly built 2.75 picks up a dyno recorded 18-23 Hp. Is been shown time and time again.
Would indeed be nice if this could be split off from this thread.
[quote]JC just so you know all of this has once again. Already been tasted. 2.75 vs stock catback on same OEM cats. The properly built 2.75 picks up a dyno recorded 18-23 Hp. Is been shown time and time again.
[/quote]
Saki said his car picked up about 20hp by going to a full 2.75 inch catted from stock. That’s a full system not catback.
I’m not arguing that there isn’t a horsepower gain, there is. But if you look at all the other improvements a JHM system has over stock (no precats, x-pipe, probably better resonator/damper flow) there isn’t much left to attribute solely to the increase in diameter itself. If JHM felt like wasting their time on making a point they could probably design a 2.5 inch system that comes within a few HP of the 2.75 version.
Either way my car with just piggies has picked up roughly 2/3rds the gain of Saki’s car when he upgraded the entire exhaust. So out of 20 horsepower total you’re left with about seven and some of those might be coming from the X crossover section and better bends. So my “5 hp” guesstimate for the diameter increase seemed not overly pessimistic.
If I was a betting man, I’d bet JHM tested both size exhausts. You’re also making all of these comparisons based on stock tuning. Maybe anything bigger than 2.5" on a stock tuned car is pointless, but that wasn’t what JHM and other companies were shooting for, they wanted to maximize NA performance.
I’ve had my pre-cats gutted for a few months…there is no way in hell I would ever say they provided me 14hp, if anything sound is most noticeable.
Didn’t your mechanic remove your torque limiter and mess with the tuning?
So you really can’t attribute these gains to just the gutting of your pre-cats…remove the torque limiter on a completely stock car and you’d probably see similar gains.
No my torque limiter is still there, stock Audi map. I’d have been disappointed with the results otherwise!
I definitely want to take mods one by one and evaluate - and it seemed a better idea to do this before rather than after a remap.
Have you timed or dyno’d your car before and after? 10 horsepower doesn’t feel like much on these cars, barely detectable by a butt dyno if at all. But the stopwatch doesn’t lie.
I am sure JHM tested different sizes. And I am sure there was a difference between sizes in terms of performance. No reason for them not to make it 2.75 inch even if it only gained half a horsepower (probably more than that, but you get the point). Better for marketing purposes as well.
On tuned cars the larger exhaust could make a bit more of a difference, yes.
I have a few 3k-8k logs of my car before the JHM 3R clutch and gutted piggies, but if I test it again I won’t be able to attribute all of the gain to the piggies.
To be honest I just plan on enjoying this car and following the modification path that I know works. I’ll definitely make some drag strip passes this season, hopefully the end result of that won’t require a flat bed like the last time.
You’ll probably think, wow that’s crazy to just trust the testing that others have done, but I look at it as EASY and almost pointless to do my own. When I decided to start modding my B7 S4, there was a ton of great testing and information out there. I chose my parts/tune based on that…and I tested those upgrades at the drag strip. I established a decent baseline stock and also had a dyno performed. I added my parts and did some more testing and another dyno, same place, similar conditions. My acceleration data and dyno data lined up very well. There were no surprises and my gains were comparable or better than what others found. It was a fun experience, but I doubt I’ll do anything other than 3-8k pulls or the dragstrip for this car.
Makes perfect sense. I think you’re doing it the right way.
I’m just looking at which parts make sense and which are the most crucial. I’m not finding the exhaust crucial to my goals. People like me who are on another continent altogether can’t conveniently use JHM as a one stop shop for everything. Getting a tuning cable sent over, sure. But big and heavy items are a different thing altogether and unfortunately the current exchange rate makes all of it insanely expensive. 1 or 2 years ago when I got a dollar and a half for a EUR the pricing would’ve been great. Now that we’re close to parity with the USD, no way.
At this end I would have to get a Sachs performance clutch and flywheel and they’re excellent. (though I’m not going that way until the car is retired from daily driving - Moscow is a 24/7 traffic jam)
(side note: I don’t think the clutch/flywheel would make much difference in a 3-8k test. The biggest gains from reducing flywheel mass are when the revs are rising very quickly. So most performance gained in 1st, then 2nd, and by the time you get to 6th it’s basically nothing)
As far as tuning goes, I’m not sure if I’ll stick to a stock map with the torque limit removed or get a proper remap. The places I would use in Europe are still far away from here and they don’t tune remotely. With JHM my concern is a (perceived) lack of user experiences in road racing conditions where you’re basically either full throttle or into the ABS for half an hour straight. That’s what I will use the car for in the future. Not merely 12 and a half seconds of hard acceleration. I don’t have much reason to assume it would be a risk - the ECU has a ton of safety features - it’s just that a small amount of uncertainty multiplied by the cost of a new engine is still a considerable amount.
Good thing the OP pretty much abandoned this thread already, we’re well off into a tangent once again.
How are you evaluating your gain? I know how I evaluated mine…a rough guess. I don’t think you should hang your argument on a number I threw out.
Mine is based on picking up a consistent 2 tenths and 2 MPH of trap speed at the drag strip. It’s actually more like 2.5 of each. Generally a car will need about 10 hp per tenth/MPH at this level. Or 10 whp. So to that end, I picked up 0.24 tenths and 0.23 MPH over my stock best when I added the exhaust. Does that mean 25 hp/25tq? Not sure. It’s a rough estimate.
I have no idea how you are measuring this.
what was your dyno delta? did you test at the strip when you were stock?
I’m only comparing the few performance metrics we have adequate data of (3-8K test)
I didn’t want to calculate or argue about how much horsepower gain there was exactly. But I think 20 hp is a fair guess, it will be in the right ball park whether it’s 18 or 26, we know it’s not going to be that much different.
My car did 2x7.95 and 2x 8.0 seconds in the 3-8K before when it was colder. It did 7.75 and 7.77 yesterday. I believe from youtube I found some of your results which were 8.0 stock and 7.7 with the full exhaust? This test doesn’t show very well where in the rev band most gains were made so how much actual peak HP we gained is impossible to guess. And it wouldn’t even be that relevant as peak numbers don’t mean that much. But to see the area under the curve we need a dyno obviously.