MG TF 135 SAIC Sports Cat - MG-Rover.org Forums
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post #1 of 35 (permalink) Old 05-04-2017, 13:20 Thread Starter
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MG TF 135 SAIC Sports Cat

I am somehow convinced that the current cat is holding the car back a bit (totally unscientific conviction). The car has done 55,000 miles so I don't think the existing cat is pristine either although I don't have any reason to think that there is anything wrong with it. That said, the bug is inside me know to get rid of it and replace it with something better.

Is Janspeed the only company that makes sports catalysts? Are they type approved or is a sport cat by definition not approved? I am not looking for just a pipe, just something a bit more free flowing. What are the available options (if any)? Is OEM like for like the only legal option?
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post #2 of 35 (permalink) Old 05-04-2017, 18:41
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Correct me if Iím wrong but doesnít the SAIC car have two cats?
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post #3 of 35 (permalink) Old 05-04-2017, 18:43 Thread Starter
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Originally Posted by barkingdog View Post
Correct me if Iím wrong but doesnít the SAIC car have two cats?
So they say, I don't know of what *exactly* things look like but the word is that there is a pre-cat and a cat. I had the backbox/downpipe/manifold replaced with Daytona so I have a feeling the pre-cat was gone when the change was made. Sounds a bit amateurish but I don't have a way of looking underneath the car.
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post #4 of 35 (permalink) Old 05-04-2017, 18:48
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That sounds right. The pre cat removal, (according to the powers that be) does improve things. I doubt a sports cat would make a huge difference.
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post #5 of 35 (permalink) Old 05-04-2017, 19:18 Thread Starter
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Originally Posted by barkingdog View Post
That sounds right. The pre cat removal, (according to the powers that be) does improve things. I doubt a sports cat would make a huge difference.
Still though, if the cat was to go, what should replace it?
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post #6 of 35 (permalink) Old 05-04-2017, 22:25
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Not so sure about how much a de cat or sports cat excercise would improve the performance on a K series in my experience...

Last rolling road day I was at one of the guys with an Elise S1 with a standardish K series engine did back to back runs - The first run he had his cat installed and got the results and while other people did their runs he removed his cat and replaced it with a free flowing de cat pipe then did another run to compare figures. The results showed he lost 1 BHP and gained 1 ft/lb torque with the cat removed so basically there was no point in removing the cat.
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post #7 of 35 (permalink) Old 06-04-2017, 09:38 Thread Starter
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Not so sure about how much a de cat or sports cat excercise would improve the performance on a K series in my experience...

Last rolling road day I was at one of the guys with an Elise S1 with a standardish K series engine did back to back runs - The first run he had his cat installed and got the results and while other people did their runs he removed his cat and replaced it with a free flowing de cat pipe then did another run to compare figures. The results showed he lost 1 BHP and gained 1 ft/lb torque with the cat removed so basically there was no point in removing the cat.
I've read these reports, I was just wondering whether the story is different for the SAIC models.
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post #8 of 35 (permalink) Old 14-04-2017, 11:47
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Today I took off the cat which had sucked a briquette into the exit hole causing serious power loss over 4000 rpm. Top bolt on the left was a nightmare!!! MY2000 VVC.

Replaced it with a shiny new decat pipe.

So the exhaust system now comprises of a Direnza 4-2-1 SS manifold and downpipe. TT MK7/2 SS back box with decat pipe.

I firmly believe that the VVC does not lose any power when fitting a decat...On the contrary. I have not RR the car but I know my car like the back of my hand. She now does 35 in first, before decat she was 30. She now does 70 in second, before decat 64. She now does 95 in third, before decat 90. She now does 115 in fourth, 110 before decat. All on a private road of course.

Also...I have this small section of road that I test all my cars on, it's a few hundred meters long. Before the decat Molly reached 78mph on this road...Time and time again. First run following decat she hit 84mph!

There you have it...Not very scientific I know but I also know for a fact that my torque has improved throughout the rev range...Increased mph in every gear and the sound....Well that's another story!!!
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post #9 of 35 (permalink) Old 14-04-2017, 12:03
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Is it better because it is decatted or because you've removed the defective part?

When you fit a cat for the MOT you can give it another test run to see how it compares.
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post #10 of 35 (permalink) Old 14-04-2017, 15:08
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The figures I quoted were consistent for months before the cat collapsed. The cat was damaged (I believe) when the TT back box was fitted. Once the cat failed it was a dramatic instantaneous event. Performance dropped massively in a moment. 16 months ago I had a mk1 vvc which performed virtually identical to Molly (pre decat), my brother has had 2 vvcs...all very consistent. On my car the decat pipe has made a noticeable, recordable difference.
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post #11 of 35 (permalink) Old 14-04-2017, 20:13
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Fair enough but the only accurate test would be back to back on the same car.
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post #12 of 35 (permalink) Old 14-04-2017, 20:40
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After purchase I ran the car for several weeks and she was running spot on, beautiful. Then I upgraded the throttle body to 52 mm and fitted a cold air feed enclosed induction kit. I noticed an excellent improvement in the car. Then I fitted the manifold and TT MK7 back box. A subtle difference was noticed with these additions, she had more torque and revved much more freely....At this point she was running perfect and I was used to the mods....Then after about a month (driven daily) the cat started to rattle but there was NO drop off in performance whatsoever. Then on a country road blast she suddenly started choking up at about 4500 rpm...Literally just like that, one second revving as free as a bird then bang...Choked. I took her straight home at low speed. Replaced the cat with the decat pipe and as soon as I took her out I noticed a considerable difference...Not a slight imagined dream...A very real difference, so I ran my usual tests, hit the rev limiter in every gear and sure enough, about 5mph more in every gear....I don't need to convince myself or anyone else. Replacing the cat with a pipe was the best mod I have done to Molly, period.
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post #13 of 35 (permalink) Old 14-04-2017, 22:23
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Originally Posted by esotericman1967 View Post

She now does 35 in first, before decat she was 30. She now does 70 in second, before decat 64. She now does 95 in third, before decat 90. She now does 115 in fourth, 110 before decat. All on a private road of course.
Max speed in the lower gears will be entirely dependent on RPM (before the rev limiter kicks in) and not power or torque! A decat pipe will not change the rev limiter!

All F's and TF's will hit rev limiter in 1st, 2nd and 3rd gears, and possibly 4th gear also.

If the max speed has increased it must mean the engine was not reaching max RPM which would indicate that the old CAT was strangling the engine massively. The car would have been virtually un-drivable if you could not hit the rev limiter in 1st gear. Just fitting a new CAT would have got it back to full RPM and hence full speed in the lower gears.

In fifth gear top speed is limited by the power and torque of the engine, as well as driving conditions, so a DECAT might make a difference there.

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post #14 of 35 (permalink) Old 15-04-2017, 00:05
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Peter....Just look at all the mgf acceleration videos on YouTube. Particularly the turbo mgtf's they hit 70 in second gear without even red lining....So would you kindly explain that to me please?
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post #15 of 35 (permalink) Old 15-04-2017, 04:29
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Anyway... what IS important is that you are very happy with your car and the way that it now runs and performs.

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post #16 of 35 (permalink) Old 15-04-2017, 15:26
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Originally Posted by esotericman1967 View Post
Peter....Just look at all the mgf acceleration videos on YouTube. Particularly the turbo mgtf's they hit 70 in second gear without even red lining....So would you kindly explain that to me please?

  1. Put car in first gear.
  2. Accelerate
  3. Car will go faster and faster then....
  4. Rev limiter kicks in and car stops accelerating.
  5. Put car into second gear.
  6. Accelerate
  7. Car will go faster and faster then...
  8. Rev limiter kicks in and car stops accelerating
  9. Put car into third gear.
  10. Accelerate
  11. Car will go faster and faster then...
  12. Rev limiter kicks in and car stops accelerating (Usually when you are overtaking and the twt accelerates to stop you passing )

Not tried it in fourth or fifth gear (I bottle out at 90mph), but presume same result. (of course all on private roads in controlled environment )

In second gear a standard TF VVC will hit 66 mph before rev limiter kicks in at 7450 rpm (all assuming standard wheels and tires).

Have not modified my car for turbo, so can not comment if rev limiter or gearbox were changed.

Of course the car might be more responsive, or quicker with a de-cat, but top speed, in the lower gears, will not change as a direct result.

Glad you are happy with the improvements you observe.

Peter
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post #17 of 35 (permalink) Old 16-04-2017, 22:34
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Improvements in power/torque/weight will get you to top speed quicker in gears, but will not give a higher top speed, unless the car was failing to reach the red line, then you did have a serious problem.


I had a sports cat on the TF160, but I am back to standard cat now and can't say I noticed that much difference.
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post #18 of 35 (permalink) Old 17-04-2017, 08:21
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Power shouldn't affect gearing at all, but if the cat was partially blocked then at high rpm when air flow is critical then it could have been stopping the car from hitting the true limiter.

Have access to dyno & ramp facilities in Manchester if folks want to check before/afters. Been meaning to do it on my ZR VVC for a while but currently on axle stands getting built up for the 'ring this year

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post #19 of 35 (permalink) Old 21-04-2017, 14:13 Thread Starter
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I guess the ambition to fit a sports cat to the car seems a bit moot anyway given that as it seems nobody sells them.
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post #20 of 35 (permalink) Old 25-04-2017, 10:15 Thread Starter
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CJJ - did you have any issues when fitting the sports cat to your LE500 TF? Any incompatibilities with the sensors etc? Was your sports cat a Janspeed?
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