Hello all, after being a member on the UK Jaguar forums I thought I'd give this one a go too.

15 years of english salty roads have finally taken their toll on my exhaust and it has over 7 holes, so its time for a new system, as Jagaur want more money for a standard one I thought Id go custom.

Question is if I get a cat back system what sorta BHP gains can I expect if any. Ive been reading a few other american forums and I set up like mine with panel filter and said custom exhaust system other people are pulling between 400-412bhp on the dyno, any truth behind this?

The system Im looking at it called PowerFlow (not sure if you get this over there).

 

Hi L80OUS, welcome to the USA forum.

I'm guessing from your post you have an XJR of 1998 vintage? if you fill in your car details in the USER CP you'll get more answers.

I've a Paramount ss system with FIA race catalytic converters, and wouldn't make the BHP you're quoting on it's own. TBH I'd think 10-15bhp for a decent exhaust is more realistic. If you added a pulley, either upper or lower then it might make 400bhp.

We're talking going up from 2.25" to 2.5" - some sections on mine are 3" over the rear axle, gives it that 'basso profundo'....

I'd like to see the posts of getting 42bhp from just an exhaust filter combo...

 

Yes sorry forgot to mention it is a 98 X308 XJR

Heres the link for what I was referring to including dyno graph:-

https://www.jaguarforums.com/forum/x...es-dyno-41275/

 

Ah, SteveM's car has a custom air intake, I think a larger diameter, as it lets more air through the engine, he actually states in post 7 the exhaust didn't add much. A custom intake will definitely add power and there's a number of fabricated ones discussed on here...mainly in the S type thread, but some on 308's.

 

Surely you cannot get all that power out of an air intake? In them sorta temps? Gonna do more harm than good, maybe loose power, 30bhp from an air filter?

 

Well,.....if you can supply MORE cold air (the colder the better!) to the engine, AND to make possible for the engine to blow out the gasses easier (no cats, bigger pipes, less restricted mufflers, etc.), you WILL get 40-50 more BHP. Neither the "cold air intake", nor the "custom exhaust" will do it on it's own.
I've played with this on several 911 Porsches, and on the Mini Cooper, and I dynoed the custom setup. On my VDP? Why bother? It's a "short limo", and it has plenty of power for what it is.
Good luck in your quest.

 

Okiedokie...
...So with a K&N Panel Filter and Customer exhaust system (cat back) what can I be expecting to gain on 370BHP?

 

Dunno, stick on rollers and post back with the print out...

 

That might be the perfect solution to disappointment :-)

Best guess?

 

Most probably much less than 370BHP after those mods.

 

Nice thanks for the most helpful comment, now byebye thanks for comming

 

Have you dynod your car? Most of us have seen 320-360BHP as stock and not very much more with small mods. Including me.

 

Surely theres something wrong with your car if you have 320BHP, 360BHP @ stock yes but as little as 320? Id be worried.

 

That's the real life. The cars have had about 360-370BHP as new and after 10-15 years and let's say 80-100K miles real output is in that range. Catback gives nice sound, but since the orginal one is not very restrictive, gain will be less than 10BHP. 200cell cats are better investment. K&N panel filter was dynod by one member here and got 2-3BHP more when using orginal intake tube.

 

OK thanks well at least I wont loose power with this setup as I probably am at the moment with my 7 holes, getting this power back and a 10-12BHP increase would be welcome. I may get the Cats done at a later date.

 

One of many intake discussions,
https://www.jaguarforums.com/forum/x...-system-82710/
Have you thought about pulley upgrades?

If you want a real power hike, look at Avos posts and twin screw kits, never mind 40bhp, how about 200bhp safely. Big league, supercar slayer tackle that

 

Also regarding the last 2 posts:

With regards XJR-99 comments about the power being down on older cars, my mate has a 2000-reg XJR that had an engine rebuild 50k ago, my car has now done 154k miles, we had a little drag race starting at 30mph (2nd) to 100mph, the cars where the same and I mean there was hardly an inch in it, surely going from what XJR-99 said his should be around the 370bhp mark (less milage) and mine isnt, so why was the performance simular. Imo a well maintained and serviced engine shouldnt loose much BHP.

With regards to the pulley I also looked into this, my mate as mentioned above a month or 2 later after this drag race he went and got a lower pulley fitted, we re-raced and again there wasnt much difference in it, this time he pulled about half a car length on me, no big gain to say this mod was ment to give around 10% increase for an x308. So again not worth it imo.

 

Big lower pulley just gives the power at lower RPMs.

 

Yeah, I ran a DA adjusted 13.94 @ 102.5 adjusted for
humidity, on rotten old all-season tires and the
traction control on. At 100k these engines (or the car)
don't seem to be losing power.

(Car and driver ran 13.9 @ 103 new. MT did 13.7 @ 103.8.)

 

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.