Custom Exhaust System
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Joined: Nov 2011
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From: Europe
The stock exhaust system is very resitrictive. You don't make an engine moving that kind of air that quiet without a TON of restriction. 2" exhaust for a 370 hp car is very small, even if it is true dual all the way back. I would consider dual 2.25" a minimum, and dual 2.5" is better. You can make a bunch of power simply by eliminating a few of the mufflers, as 2 is plenty, but it will be much louder. Depends on if you can stand some more sound or if you want to maintain the quiet cruiser demeanor. Another thing to consider is that the stock exhaust is VERY heavy. If you go to a custom 2 muffler system, you can drop something on the order of 40-60 lbs of weight. I would not expect spectacular gains out of an off the shelf cat-back. It will be better than stock due to slightly larger piping diameter, more attention paid to pathing that does not cause kinks, and less restrictive mufflers. But they are still in general 5 muffler systems, so you are still limited by that. from what I have gathered from posts with back to back before and after dyno graphs, an off the shelf cat-back is worth about 10-15 crank hp and much better sound. So if you need to relace a system as in your case, they are a great idea. But they are not really worth the effort IMO if you still have a good system underneath your car. If you can stand the extra sound (or are actively seeking a more aggressive sound), a custom system seems to be the way to go, so you can run larger diameter piping and less mufflers for a significant restriction and weight reduction.
Oh, and as others have said, the stock cats are VERY restrictive. That's where there's BIG gains to be made for power in the exhaust. Moving up to some high flow race cats will help, but if you're in an area with no emissions testing or at least lax enforcement of it, no-cat downpipes can yield some massive gains.
Oh, and as others have said, the stock cats are VERY restrictive. That's where there's BIG gains to be made for power in the exhaust. Moving up to some high flow race cats will help, but if you're in an area with no emissions testing or at least lax enforcement of it, no-cat downpipes can yield some massive gains.
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From: Sunny Southport UK
If you're getting heat soak then go for it.
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From: KC
Just makes me wonder what Avos would make with a proper exhaust for that kind of power 
He'd probably see at least 30 more hp at the crank with a nice no-cat dual 3" system. But it's also pretty cool that he's making that much power while keeping it nice and quiet with the factory exhaust. Taking that sleeper style to the next level
He'd probably see at least 30 more hp at the crank with a nice no-cat dual 3" system. But it's also pretty cool that he's making that much power while keeping it nice and quiet with the factory exhaust. Taking that sleeper style to the next level
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Joined: Mar 2010
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From: Tampa
Just makes me wonder what Avos would make with a proper exhaust for that kind of power
He'd probably see at least 30 more hp at the crank with a nice no-cat dual 3" system. But it's also pretty cool that he's making that much power while keeping it nice and quiet with the factory exhaust. Taking that sleeper style to the next level
He'd probably see at least 30 more hp at the crank with a nice no-cat dual 3" system. But it's also pretty cool that he's making that much power while keeping it nice and quiet with the factory exhaust. Taking that sleeper style to the next level
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From: on-the-edge
Ahem ... first, the stock exhaust *is* 2.25 inches OD and it is not "true dual" as there is a join at the front most silencer. It actually benefits from the join, but it is not what is understood to be "true dual" as that term is conventionally applied to completely isolated piping for each bank.
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From: KC
The individual pipes go down to 2" in several places, although you are correct that the OD is usually 2.25". But that's why I consider it a 2" system, the engine in general only cares about the choke point. And the banks do merge at the first muffler/silencer, but they never go down to one diameter like most factory exhaust systems, where they merge into one pipe and then split out again at the back for aesthetics. The cross sectional area through the merge silencer never goes below that of the two pipes that go into it, so it can be considered a true dual with a crossover.
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From: NY
I have measured it and it's 2" OD for most of it or less. Where it goes over the axle it's only 1 7/8" and some have said 1 3/4"
Oh, and as others have said, the stock cats are VERY restrictive. That's where there's BIG gains to be made for power in the exhaust. Moving up to some high flow race cats will help, but if you're in an area with no emissions testing or at least lax enforcement of it, no-cat downpipes can yield some massive gains.
If you consider about 10hp BIG gains, then yes. And that's with cat-less downpipes.
The exhaust and cats look restrictive. But in reality, each only add about 10hp on stock cars.
Replacing the intake from the throttle body forward with 3.5" tubing and a large cone filter yields about 30hp. That's with unrestricted exhaust already done. Probably less without exhaust. Do all three and you'll get a nice gain.
Here's another thread in addition to the ones posted earlier:
https://www.jaguarforums.com/forum/x...results-74595/
Oh, and as others have said, the stock cats are VERY restrictive. That's where there's BIG gains to be made for power in the exhaust. Moving up to some high flow race cats will help, but if you're in an area with no emissions testing or at least lax enforcement of it, no-cat downpipes can yield some massive gains.
The exhaust and cats look restrictive. But in reality, each only add about 10hp on stock cars.
Replacing the intake from the throttle body forward with 3.5" tubing and a large cone filter yields about 30hp. That's with unrestricted exhaust already done. Probably less without exhaust. Do all three and you'll get a nice gain.
Here's another thread in addition to the ones posted earlier:
https://www.jaguarforums.com/forum/x...results-74595/
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Joined: Jun 2012
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From: KC
I'd be extremely surprised if the cats were worth that little. They are extremely closely coupled, small through diamter, and the inlets and outlets are badly designed. I have no direct experience in the Jag world, but I just can't see the elimination of a restriction of that level only being worth 10 hp. I'm planning to make some custom catless downpipes here in the spring/summer. I'll of course do before and after dyno runs and report the results. I'm planning some intake mods as well, and I'll test those as well. I want some definitive, properly tested results so we can end all the hearsay.
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From: NY
I have direct experience with this since I dyno tested before and after when I replaced my cats with downpipes. That thread is actually mentioned above. Conditions were identical. Improvement was 11hp, but that is actually misleading because the second dynos were run to a higher rpm. If you look at the same rpm's, then the gain is only 7hp.
Modern catalysts aren't that restrictive anymore. Of course if your current cats aren't in good condition, then higher gains could be had. Mine were in good condition with low miles.
A proper test would compare NEW stock cats with the aftermarket ones. But no one ever does that.
Modern catalysts aren't that restrictive anymore. Of course if your current cats aren't in good condition, then higher gains could be had. Mine were in good condition with low miles.
A proper test would compare NEW stock cats with the aftermarket ones. But no one ever does that.
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Joined: Jan 2013
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From: Lincolnshire UK
Finally got the car back with the cat back exhaust fitted looks good, sounds quite as requested but has a very bass type of tone to it now, not a bad thing. Peformance feels stronger under hard foot down, I wouldnt say faster just stronger if that makes sense, maybe due to me loosing power before cause of my 8 holes, maybe cause its so cold here at the moment or maybe cause its given me another 10/20bhp. However before I had noticed poor mpg figures which I put down to my exhuast, this doesnt seem to have improved, could this be down to something else or thr fact its -1 degrees C atm?
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From: on-the-edge
I must have a different exhaust then. Mine measured 2.25" OD using digital calipers. All the part numbers are Jaguar.
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From: NY
Only the short section in front of the first/center silencer is 2.25" The rest of it is 2" and less over the axle.
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From: on-the-edge
Mitutoyo digital calipers zero'd and set to read in decimal inches.
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From: NY
What year is yours? Either Jaguar changed the size or your calipers are off. I measured with calipers as well and went and double checked the measurements. Verified that my calipers read accurately.
In front of center silencer is 2.13", not 2.25"
Everywhere else is between 1.9" and 2"
Smallest part of the bend over axles is 1.7"
All measurements are outside diameter.
In front of center silencer is 2.13", not 2.25"
Everywhere else is between 1.9" and 2"
Smallest part of the bend over axles is 1.7"
All measurements are outside diameter.
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