150bhp loss would you notice???

[a1rak]

From previous post some of you will now my car has the supercharger fitted. It was all set up at Emerald and was dynoed at 530bhp. Took it to Austec where I was going to have the new ACT quiet exhaust trial on my car.
We wanted a before and after comparison of noise and power so put my car on the rollers with the original sports noisy system. 388BHP was the best we could get from the engine, to say I was pi**ed off was an understatement.
Thought long and hard about what could have changed or gone wrong. The only change was that I had fitted the CATS for a recent MOT. Austec said you may have lost 10 or 15bhp due to the CATS but never 150BHP. Anyway fitted the DECATS pipes back on second power run 530BHP. So the lesson is, if you get your car mapped by a specialist so that it is working at its best don't f**k with anything afterwards and think you will get away with it.
The odd thing was that I really did not notice on day to day driving. I will do a separate post on the new exhaust with photo's but my initial impression is very good, 96 to 98db and no loss of power. Ask TIM at ACT for more details

[Gazzab]

My cerb when down from 436 to 399 felt sluggish comparatively.

[Jhonno]

Obviously not driving it properly to not notice that!!

[Alistair H.]

I am guessing seriously blocked/knackered cats to get that sort of loss!

[a1rak]

Alistair H. said:

I am guessing seriously blocked/knackered cats to get that sort of loss!

No not at all, the CATS were fine. They obviously start reaching there flow limit around 400bhp before having a major effect on engine output. Maybe being forced induction made it much worse than normal.

[Supateg]

Is the exhaust pipe on yours 2 1/4" or 2 1/2" inc the new box?

I should be in for fitting soon after the Std Cerb goes in and Tim is happy with the new box.

So you can draw from this Std cats start limiting flow after 400bhp....interesting

- Craig

[ridds]

Std cats or aftermarket?

It's very unlikely the std cats would restrict flow at 400hp.

[a1rak]

ridds said:

Std cats or aftermarket?

It's very unlikely the std cats would restrict flow at 400hp.

Standard CATS in very good condition as they have hardly been on the car. It maybe the forced induction caused such a huge effect. The mixture was running really rich across the whole rev range with the CATS fitted so they obviously effect flow even at low RPM.
What I was really trying to get across with this thread was that if you get your cars ECU custom mapped by a specialist be it Joolz, austec or Power then you really should leave it alone afterwards as even a small change in exhaust or induction is likely to have a large adverse effect on the performance.

[a1rak]

Supateg said:

Is the exhaust pipe on yours 2 1/4" or 2 1/2" inc the new box?

I should be in for fitting soon after the Std Cerb goes in and Tim is happy with the new box.

So you can draw from this Std cats start limiting flow after 400bhp....interesting

- Craig

The exhaust has ACT Silenced DECATS, Then 2 additional silencers on the link pipe with one large transverse back box silencer. The tailpipes are 3" and the OD of the connecting pipes is 2 1/4. Much prefer the look of the transverse back box and am a lot happier with the noise levels. Will get it sound tested soon and post up the results with some pictures.

[Supateg]

Thanks for the info. will look forward to the sound test result.

Its not the restriction on the decats alone its the negative pulse they sent back up the exhaust which sapped the power.

[Brummmie]

Emerald Dyno can give VERY high figures, due to it not being able to deal with higher output engines.
This will more than likely be your problem, I can speak from experience here..

[jackwibble]

Brummmie said:

Emerald Dyno can give VERY high figures, due to it not being able to deal with higher output engines.
This will more than likely be your problem, I can speak from experience here..

But as a1rak said he removed the cats re fitted the decat pipes and it then gave 530bhp on the second run so i dont think in this case its the dyno?

[jackwibble]

Brummmie said:

Emerald Dyno can give VERY high figures, due to it not being able to deal with higher output engines.
This will more than likely be your problem, I can speak from experience here..

But as a1rak said he removed the cats re fitted the decat pipes and it then gave 530bhp on the second run so i dont think in this case its the dyno?

[jackwibble]

Brummmie said:

Emerald Dyno can give VERY high figures, due to it not being able to deal with higher output engines.
This will more than likely be your problem, I can speak from experience here..

But as a1rak said he removed the cats re fitted the decat pipes and it then gave 530bhp on the second run so i dont think in this case its the dyno?

[a1rak]

jackwibble said:

Brummmie said:

Emerald Dyno can give VERY high figures, due to it not being able to deal with higher output engines.
This will more than likely be your problem, I can speak from experience here..

But as a1rak said he removed the cats re fitted the decat pipes and it then gave 530bhp on the second run so i dont think in this case its the dyno?

This was the Austec Dyno so 530bhp is very accurate. I know the Emerald one reads high but on theirs it was 535bhp at 6250rpm last year. The engines is now run in been serviced and I lifted the rev limiter to 7000rpm.
The 388bhp to 530bhp difference was the same dyno on the same day with the same operator at the same temperature. The ONLY difference was the CATS.

[Brummmie]

a1rak said:

This was the Austec Dyno so 530bhp is very accurate. I know the Emerald one reads high but on theirs it was 535bhp at 6250rpm last year. The engines is now run in been serviced and I lifted the rev limiter to 7000rpm.
The 388bhp to 530bhp difference was the same dyno on the same day with the same operator at the same temperature. The ONLY difference was the CATS.

I miss read it, you have your answer then!
Get some Cats of something like an M5 (at a guess) that makes big power with them on.

[a1rak]

Brummmie said:

I miss read it, you have your answer then!
Get some Cats of something like an M5 (at a guess) that makes big power with them on.

to be honest I'm just going to leave the decat pipes fitted then worry about the MOT later.

[spitfire4v8]

.. or have the car remapped on one of the other 2 maps with the cats in? a quick back of fag packet calc suggests you might be losing 70hp from a very rich mixture if your cats are that restrictive..

[a1rak]

spitfire4v8 said:

.. or have the car remapped on one of the other 2 maps with the cats in? a quick back of fag packet calc suggests you might be losing 70hp from a very rich mixture if your cats are that restrictive..

hello Jools was hoping you might join in. I don't smoke but can only report on actually what happened, I understand that the CATS obviously knackered the calibration of the map and caused over fuelling and a misfire but I was just surprised by how much it affected the engine performance on the dyno. Would love you to inspect the map maybe I could email it to you and you can pass your expert eye over it.

[gerradiuk]

Paul any updates on this, really interested in how its going