So last year, I put a straight through stainless steel exhaust on my 2000 XKR Conv, very nice I thought, but after a while to be honest I think it's too noisy by far now, it's ok for boy racing and your mates, but let's face it I am way past all that and my wife moans about the noise too lol. Not only that I think the lack of back pressure probably does not match the ECU that well and so they say you can't have the older cars re-mapped without a replacement ECU and a pile of money. I also don't actually think it drives any better with virtually no back pressure either, if anything I think it's probably worse with less power now.

1. Has anyone got any ideas and advice about the above?




So I intend to purchase & fit 2 of the 4 boxes I removed and re-fit. The easy option would be to reinstall the rear boxes, leaving straight through under the rear seats.


2. Do we think that will be ok? Or are you supposed to fit the awkward boxes under the rear passenger seats and leave the rear straight through? or does it not really matter? It will be a bit quieter regardless I hope. I only wanted a bit of a roar from that old V8 as it was far too silent with the original exhaust, but this straight through pipe makes your ears ring and it growls and spits at lower speeds and on long journeys it drives me absolutely nuts!

 

If it bothers you that much, just leave the exhaust in place and fit some restrictors in the tail pipes, I got some from Ebay but never fitted(got used to the noise eventually). Much easier than replacing the exhaust and that squashed section over the rear subframe has to rob some power

 

I run a mina gallery under axle rear quad tail pipe rear boxes which retains main centre box but eliminates the boxes in front of rear axle. Very happy with it. I think you would be happy if you refitted rear most boxes and left out those under rear seat area.

 

But what did you do about your ECU? Does yours run fine without any adjustments to the ECU then? I don't think less back pressure gives you anymore power unless you have the car re-mapped you know?

 

Did nothing with the ECU you dont need to. The reduced restriction means that the cylinders are evacuated more effectively and with less power overhead from the engine. That in turn means theres more space for the incoming air to take up and the fueling is proportionally measured to the incoming air flow. The ECU only has to make addition adjustments if it detects an imbalance, ie., too much or too little O2 in the exhaust. a free flow exhaust does nothing to change this.

 

So its probably the noise that's driving me nuts then lol, I think some new rear boxes will fix that, leave out the nasty ones under the seat, they probably restrict the most flow. I also noticed those huge counter balance weights at the rear when I fitted mine rear pipes, must be worth loosing those things they weight about 10Kgs each side, did you loose yours?


Cheers.

 

The stock exhaust flows enough for 600hp+ (just look at Avos' XKR) so if you're looking for power gains in the exhaust you are probably looking in the wrong place.

And for sure too little backpressure can have negative effects, I've heard it many times before...

 

Dont know anything about any counter balance weights, I didn't see anything or knowingly remove any

 

No, I just wanted it to sound a bit sportier, but for me it's too much now and hurts my ears lol, going to get some new rear boxes to quieten the beast down a bit.
I can recommend however the lower enlarged supercharger puller mod that makes a big difference on the 4.0 XKR

 

I cant really see the point in carrying out a power upgrade and then take it away by fitting a rear silencer. you might as well just return it all to stock

 

Well according to Cambo they go up to 600Bhp on a standard exhaust, so it won't hurt hopefully, I just cant bear the noise, it's far too noisy now, wakes up my neighbours as well lol.

 

maybe they can but what would they get if they took away the restriction provided by the stock exhaust. You can make the engine develop whatever you fancy if you have the money so saying someone has got 600hp with the stock exhaust is a bit of a red herring

 

I used to see similar situations over on the Corvette Forum when I owned my 1995. The first "mod" everybody wanted to do was replace the perfectly fine exhaust system, usually at a cost of $1,000 give or take. Not only were "performance increases" negligible, at best, but in short time the owner would post complaints about excessive noise or drone in the cabin.

This is one of the worst bang-for-the-buck modifications if you are looking for anything other than noise.

Doug

 

Sorry but I have to disagree with this. The worst mod is a K&N filter, there are many documented tests done on the net which show no gains, yet few that show any gains. However with the exhaust there are significant gains mainly due to the removal of 4 silencers and also the pinched section over the rear axle. I would agree that increasing the pipe diameter significantly is a waste of money and probably counterproductive. Removal of the silencers and the pinched section is good for about 15-20hp. If you have an XK8, it is probably your cheapest way of increasing HP. Unlike other cars , there are no alternative cams available, no gas flowed heads, larger valve options and so on. Other than cats and exhausts, you are pretty well stuffed

 

Yes, I love the noise pulling away but that drone over distance is awful, so 2 rear boxes it is going to be my Xmas present this year, with my enlarged supercharger lower pulley this car is quick enough.

 

A K&N filter will last forever, clean it every 3 months or so and that is it. You will never have to buy another air filter

 

K&N filters are sold primarily on the premise that they give more power whereas they give little if any. As for the cleaning part, every 3 months? are you serious? The standard item should be changed out every 20-30k. The extra cleaning you are doing is probably shortening the life of the filter allowing larger particles to enter the engine.
K&N Air Filter Review - Debunking the Myths (and why OEM is better)

 

The only thing a K&N filter will do is put oil onto your MAF sensor and make dirt stick to it, making it perform worse.

 

Yes, but they make some people feel better.

 

Can you give me some proof, evidence or otherwise convince me that modifying the exhaust is going to provide 15-20hp? On a car that is probably just making 300hp at the wheels?

Because I don't believe you...

If you said change the old clogged up cats for some 200 cells and you'll recover 15-20hp that was lost, i'd believe you.

If you told me that removing one of the silencers and fitting an x-pipe or some sort of crossover would give 10 or so hp, i'd believe you.

But the rest of the exhaust is fine for a 370hp engine. A twin 2-1/4" exhaust system flows plenty for that sort of power level, even with one or two crappy bends in it...