The Lotus Cars Community banner

Status
Not open for further replies.
1 - 10 of 10 Posts

·
Registered
Joined
·
1,358 Posts
Discussion Starter #1
Original thread located here- http://www.lotustalk.com/forums/f154/exige-s-stock-exhaust-decat-dyno-runs-65648/



Yeah, I don't have any.

But I read for hours and hours looking for definitive results that going decat adds overall HP.

I read that decat tends to reduces low end torque/hp but gains up top (general statement)
I read it is louder.
I read it weighs a little less.
I read it will cause a CEL.
I read a lot of 'I think it feels faster'.

Can anyone point me to a dyno before/after decat? I could not find one actual measurement of backpressure before and after either. The only dyno numbers I read were from old posts from a manufacture's website.

Also, on the subject of the CEL, many threads just 'stopped' with people accepting they will get a CEL no matter what method they tried to use. Has anyone gone decat and gotten no cat-related CEL in > 1000 miles? If so which method worked?

I am aware this should be for track only. I am not concerned with sound, I am strickly concerned with performance gains.

Thanks!
 

·
Premium Member
Joined
·
3,738 Posts
You'll need to tune for gains -- I'm in the process of doing this but I have an EFI unit so I'll do the tuning myself. If you don't tune for it, you'll not see any gains (and probably why you don't see any dyno numbers).

I have a chunk of road that I use for data logging -- easy to repeat my testing and it's real world not dyno-world ;) Can't give you dyno type numbers, only differences in Accel G's and time/speed from A to B.

I'm using decat because I plan to go to the track this weekend and the primary reason is to reduce heat build up and increase noise so that it's easier to rev match (heal/toe) -- not doing it for any performance benefits.

Rob.
 

·
Registered
Joined
·
10,000 Posts
unfortunately its rare to come across a car thats only been decatted between runs.

i do have a dyno of car with a stock cat/exhaust vs a car with no cat and different exhaust. but nearly always its going to be different exhaust/headers.

the cel thing is partly luck, backpressure, flow, burn, fuel type related, thats why there are so many varying results with it, the resistor method only works on unsophisticated units, the L bend pipe only works if the amount of measured HC's is reduced by enough in that pipe.

the only thing i've seen for sure is that some of the sport cats are worse than the stock one.
 

·
Registered
Joined
·
1,358 Posts
Discussion Starter #4
Thanks for the replies. Ok, well, I did read 100x that a cat-back exhaust really gives no HP gains - only subjective better sound / less weight from stock.

Charlie I know your instructions are to, "say no to headers!" unless the ECU is tuned for it.

So basically, going decat or changing anything between the header and exhaust tips = zero HP gain.

That is a bummer because now I have no car-related weekend project. :( However, it will save me some money! ;)
 

·
Premium Member
Joined
·
3,738 Posts
Don't know about zero HP gains since no one has done a dyno run on just decat alone.

I did gain 4 wHP going from stock muffler to an Arqray Twin on stock ECU -- this I did have dyno'd. But the Arqray Twin is loud even with the stock Cat. And my Arqray Twin lasted 13 months before it had an internal rattle (just out of warranty).

If you want a cheap weekend project, get a 3.1" pully - that will give you some gains even on a stock ECU.
 

·
Registered
Joined
·
10,000 Posts
i dunno if i'd agree with that a test pipe does not give gains, thats not what we've seen on the sc kits at all, we've certainly seen a loss with the wrong cat.

unfortunately its complicated because it usually ties with the exhaust, look at that cup car 255 dyno i did with a gotham 265, for instance.

plus you might get some HP since its a lot less heat.


don't change the pulley unless you remap it.
 

·
Premium Member
Joined
·
3,738 Posts
I thought I read some folks here went from a 3.2" to a 3.1" on stock ECU with reliable gains (no flash)?
 

·
Registered
Joined
·
10,000 Posts
not that i'm aware of, phil used to tell people to change it and it'd be ok, but he changed his mind after a year or so, i've always stuck to the same story.

increase boost, increase's fuel pressure, increased fuel pressure, more fuel comes out of the injectors.
 

·
Registered
Joined
·
1,358 Posts
Discussion Starter #9
Ahhhhhhhhhhhh! I am back where I started. rotfl

I guess I will not know until someone with a basically stock car / exhaust goes decat and dynos their car. :(

I remember the cup car dyno plot, not sure I get what you are trying to tell me however. I was going to ask earlier but did'nt... is the S260 cup, the 270E, etc cars just the same exhaust that is on 06+ Exiges? Or is it stock with a test pipe? Or is it a different exhaust altogether?

I also subscribe to the "don't change the pulley" club.. without a tune.
 

·
Registered
Joined
·
10,000 Posts
well the cup 255 is basically the same car as an exige S, so with the same tune, they'll make the same power on the dyno, so if you look at my cars dyno with just the tune, since i had a stock exhaust/cat and that dyno it'll tell you the difference between a stock car and an exhaust and decat change.

unfortunately i'm not sure which exhaust the car had, and as i said i dont have just a decat difference, that i can remember.
 
1 - 10 of 10 Posts
Status
Not open for further replies.
Top