Adamesh Exhaust - Loss of Torque!
 

Hi,

Yesterday I collected my car from having the Adamesh sports exhaust which removes the two rear silencers and Adamesh over axle sections fitted.

My car is a 4.2 XKR which used to be like a bullet from standstill and acceleration was pretty much immediate throughout the rev range.

The car roars now, but that is it! It has lost most of its torque and when you press the accelerator there is a bit of a delay.

I am really unimpressed. It seems I have replaced performance with noise and that is it.

Is this to be expected? Any thoughts and experiences would be most welcome.

I am seriously considering re-fitting the standard exhaust at my earliest convenience.

Thanks,
Nick

I reckon I'd do it sooner :).

Welcome to the screwy world of performance mods. I suggest you're add a chromed gas cap. I hear it is worth 30 horsepower. ;-)

As with all mods, seat of the pants measurements are a poor indicator. Do some timed runs with the torque app for similar, and if you revert, do the same to see if they are consistent with each other.

Also take into consideration the prevailing weather. Temperature and humidity do play a factor!

Hi mhminnich,

I totally understand where you are coming from, but this is too obvious to me. My car normally has the ability to "run away" you need to be aware that it is very powerful and raring to go. That has all gone, instead it is a farting growling mess!

Now where do we buy those gas caps.... ;o)

Nick

"...instead it is a farting growling mess!"

My gawd, you've turned it into a mustang! Revert now while there is still time to save you.

I know, I must hand my head in shame. Car is booked in to reverse the process! Sadly not until the 18th! I will wear a disguise until then!

Sounds like this is pretty much like when people put "drag pipes" or straight pipes on a motorcycle...you lose some of the torque when it's just a straight thru exit for the exhaust. One fix I know of is to get a hold of some stainless steel wool specifically made for exhaust pipe packing, and stuff it loosely into the exit end of the exhaust pipes. Keeping it in place requires either a screw thru the pipe, or some type of cap that is a good friction fit (the cap would probably be preferable)...or a variation of the "lollipop" that Honda motorcycles used to have....like THIS

In the "closed" position, blocking the majority of the exit, the lollipop brings up the torque of the motor by making more back pressure..in the "open" position, it supposedly increases horsepower but cuts the torque in the normal RPM band that most non-drag racers use on a regular basis. The lollipop will hold the stainless steel wool in no problem.

Just some food for thought..it would be a very inexpensive experiment, that just might work well for you.

THIS is the type of stainless steel wool I'm talking about

It's specially made to do exactly what I'm talking about above.

I too had the same experience when I fitted 200 cell cats to my old 4.2 XJ. But I could never tell whether I had indeed lost torque or if it just seemed I should be going faster due to the increase in sound. Free-flowing exhaust mods will definitely open things up at freeway speeds though.

Two years ago I got the exhaust system on my Xkr coupe 2000 changed to a stainless Milltek system. I havent experienced the decrease in torque you describe, I cannot tell any real difference from the change besides the growl of course. One year ago I also changed the intake tube to an aluminium tube from Mina Gallery. After this mod I did feel a change, throttle response was improved. But then of course my car is a 4.0, and we didnt buy the same exhaust system.

After reading some of the marathon super charger threads at this forum I learnt that after reducing back pressure you also loose boost on a Xkr. So if I were in your shoes I would rather increase boost with a different setup at the super charger to spin it faster, instead of reverting the exhaust back to stock

Regards,
Higgins

Interesting about the back pressure to boost relationship...I don't know a lot about the supercharger dynamics but this is enough for me to delve further because it does make sense to have the ability to build up pressure somewhat..like pinching a garden hose and then letting go

Not surprised
 

When I had my Corvette and was active on the Corvette forum, there were endless posts from folks doing tweaks and then complaining that the resulting performance was either worse, no discernible difference, or some difference but not worth the $. This was very common for guys installing more "free flowing" exhausts. The reduction of back pressure also reduced torque, although max horsepower was very marginally increased. What they always did get was a lighter wallet, a louder car, and obnoxious droning in the cabin so that you could not hear the stereo.

Doug

I had the same Adamesh straight end pipes and over axle arches installed on my 03 XKR three maybe four years ago now. My assessment over this time since, and given I'd had the car for the same period prior to installation, is that it's not made a jot of difference either good or bad in terms of performance. I don't often drive it like I stole it, but when I do get the Dropkick Murphys on the CD it still frightens the pants off me. Just in normal drives the overtake is as swift as it ever was. Maybe my install is the exception? but I have no complaints whatsoever. There is no drone just a lovely deep growl at low speed. Mid to high range with the windows up theres just a good hum in the cockpit, whereas stock at any speed is like you were in an electric motor IMHO.

I just had my Adamesh sport exhaust installed on my '05 XKR a few weeks ago and aside from being extremely happy with the sound, I didn't experience any noticeable loss in power. I did notice that I break traction more often from a standstill now and it took a little getting used to. The only problem I had was the clamps didn't hold after the install and it needed to be spot welded.

Fun fact (from my exhaust installer), that the Adamesh exhaust will actually have a different sound than domestic exhaust systems due to the type of metal used. Adamesh uses German metal which is more pure and produces a different sound than less pure domestic metals. Maybe someone here can confirm it is actually true but the sound it produces is far more exotic than I have heard from modern mustangs or other muscle cars.

I would highly recommend the Adamesh sport exhaust to anyone looking for their car to finally sound how it looks.

Hi Redeye and boatdrnx,

Thanks for sharing your experiences. Redeye I agree the stock exhaust is so quiet it can be like driving an electric car. You do hear a bit of super-charger whine under hard acceleration but not much more.

Boatdrnx do you have both the over straight end pipes and the over axle pipes. It has been suggested the that over axle pipes reduce the back pressure.

I did call Adamesh and spoke to a gentleman who told me most people buy these for noise and they have not tested before and after HP gains on a dyno! I found that very surprising, I certainly would do that if I was selling a modified exhaust.

Currently I am considering going to a custom exhaust shop in Ashford to see if they can do something about the over axle pipes to reintroduce some back pressure or it might be time to go back to the drawing board.

nick from thanet.

I have both the over axle and straight end pipes and didn't notice a difference with performance.

I think the equaliser to any possible lack of back pressure is playing the Dropkick Murphys. The jags ECU just seems to tap into the CD player and away we go! :icon_pala:

Since you have a 'boosted' engine I wouldn't think you should lose much bottom end torque. Of course if your ecu had adjusted itself to the best possible combination of variables prior to this change there should be a change in performance and probably not a positive one until it relearns and adjusts those variables. Others indicate they didn't suffer your current situation so with hope the relearn will solve your issue. Good luck!

wj

HI, does anyone know the expected period over which the ecu will relearn its new parameters after an exhaust change?

Shamelessly borrowed these thoughts from multiple sources, mostly to create enlightenment, discussion, and debate. Might be a little bit of rambling here but it’s late….:

When you reduce back pressure in an exhaust pipe, you will lose torque in the lower rpm band. On the plus side, (especially with the supercharger), you should see a horsepower gain on the higher end.

Reducing back pressure reduces exhaust gas velocity, which reduces scavenging. On street-driven, or low rpm engines, some back pressure is good. On a single-cylinder engine, this keeps the air/fuel charge in the cylinder from being pulled out during valve overlap. On multi-cylinder engines, the exhaust pulse from one cylinder can affect the air/fuel charge in another cylinder. The back pressure from the manifolds, pipes, and mufflers helps to even out the exhaust flow for better low and mid-range power.

A properly designed, tuned exhaust system will actually create a low pressure pulse at a specific rpm range so that when the exhaust valve opens on the next cylinder the exhaust will be scavenged from the cylinder much more efficiently. This cannot happen without some regulation or restriction on the exhaust gasses. The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it (like when you put your thumb on the end of a water hose to attain more velocity).

This causes the first group of gases to actually suck out the following set of gasses. Here’s how it works: the expulsion of the first set of gasses leaves an empty void behind itself. The next set of gasses are pulled into the void. The third set of gasses get pulled into the void created by the second set of gasses. And so on and so on. If the diameter of the exhaust pipe is too large, or if back pressure is reduced too much, there will be no void left by the gasses and therefore the scavenging chain will not occur (on the low end).

While you will not lose torque all together, you will lose torque in the lower rpm band, while theoretically gaining more power higher in the rpm band. You should also notice the engine rev more freely. You are in sense un-choking the engine by going with less restrictive exhaust. The motor will be able to exhale the spent exhaust fumes much easier as the motor works harder when the rpms climb higher, therefore creating more power by running more efficiently.A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but will create unacceptably high amounts of back pressure at high rpm. Thus if your power band is located 2000-3000 RPM you'd want a narrower pipe than if your power band is located at 8000-9000 RPM.

Back pressure at its most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust will flow backwards, which is not good. The trick is to have a setup that has as close to zero back pressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters and muffler sets are designed so that they are best suited to a particular RPM range (remember the pulses!). Many engineers try to work around the RPM specific nature of pipe diameters by using set-ups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb back pressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM. High technology snowmobiles have also used a variable exhaust that increases or decreases back pressure as required for maximum performance at different rpm.

With a stock exhaust system, your 2003 XKR doesn't develop peak torque, (387 ft lbs), until it reaches 3,600 rpm. In contrast, a Ford pickup engine is engineered to develop peak torque down around 2,500 rpm, which gives it massive pulling power off the line. So now, with lowered back pressure, you are experiencing lowered exhaust velocity and subsequent lower response (i.e., torque) at lower rpm’s. Maybe you could retrofit a Ferrari or BMW exhaust system to get the best of both worlds.

For some more interesting thoughts on back pressure and deep exhaust tone, click here: exhaustbackpressure