JHM rs4 stage 1 supercharger kit

B6/7 S4/RS4
#141

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)

#142

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.

#143

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.

#144

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.

#145

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.

#146

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.

#147

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.

#148

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.

#149

what was your dyno delta? did you test at the strip when you were stock?

#150

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.

#151

Remember I am referring to my S4

The dyno delta was pretty close to 40hp/40tq from stock to JHM tune/full catless 2.5"/only IM spacers

Stock my best was 13.7@100-101mph (That could have improved, but it was a pretty consistent baseline)
with the same mods as I had on the dyno I ran 13.14@105 or so, but I probably had a little more left (should have matched your 12.99)

So the drag strip results delta was a little better than what the dyno showed, but that could have been more influenced by me learning to drive a little better thanks to some tips…

If we look at one of the fastest stock time of 13.46@102 and similarly modded times (you and Farmer Bob) 12.99@107 and 13.03@106 the 40hp/40tq, maybe a little more, is bang on.

I never dynoed after the JHM intake manifold, but I went 12.86@106.5. That night the only thing that kept me out of the 12s was leaving on ESP.

#152

With full exhaust my best 3k8k was 7.6 seconds I believe.

Stock I don’t think I ever was as low as 8.0

#153

I’ve only done two stock 3-8K in the RS4, I think best was 8.2

Maybe I’ll go out and get one tonight, it’s pretty cool outside today.

#154

I have EB werks full exhaust( JHM was NOT avaible for sale at the time) and i did a dyno before and after exhaust kit install, and the gain was 14/16 WHP done at same dyno!