De-cats for the V8V ... AKA the epiphany!

[nickv8]

Today was finally the day - the V8V found its voice. And boy... what a voice!

Shortly after buying the 2014 V8V from AM Bristol in May, it was back to have a V12VS exhaust fitted. Unfortunately even following the best efforts by AM Bristol, it just couldn't happen due to the rear-mounted manual gearbox radiator. ( Previous write-up.)

The clear alternative was to get the car de-cat'd using the official AM retro fit kit which replaces the secondary cats.

Must I admit I was a bit reluctant as even though I wanted to make the car more vocal when pressing on, I didn't want it to sound shouty at every moment including starting up and creeping away from the neighbours. I figured that's exactly what the de-cats would do.

On the plus side, the de-cat option was a third of the price of the full V12VS exhaust (both prices including fitment). So, after a bit of advice from fellow PH'ers plus hearing alternatives including the V8VS and GT12 Vantage(!) setups at local events I lumped for it.

I needn't have worried. In fact, I should have had it done on the day of collection! Oh my... oh my!!!!!!! To paint the picture...



I must have looked like a loon for the first few miles. I was genuinely laughing at how great it was.

Seriously - if you think your V8V lacks a little on the audio scale, just do it. Don't delay. I can't wait to take Vantage beyond 3-4,000 revs again. Truly addictive.

Interestingly, it doesn't appear to have any downsides. It's not boomy or noticeably noisier in the cabin (and I doubt outside) when not stomping on the right pedal. The Sports button now makes a real difference, so if you want to sneak around, resist temptation and leave those exhaust valves alone.

Most likely the best money I'll ever spend on this car

Footnote: huge thanks to AM Bristol as always. Extremely professional service, prompt, friendly (they were as pleased to show me the stunningly beautiful V12 Vantage Zagato they had in the service bay as I was to go weak at the knees staring at it), really good price, etc. They also managed to work on the warranty tweaks without the slightest fuss including a new rear light (misted up), fuel cap stickiness and some other odds and ends. And really carefully washed the car following my dirty (roads!) weekend in Wales.

[shinjuku]

Great read!

I was considering the V12 backbox, but it doesn't fit on the 4.3L V8 due to the oil cooler in the rear section I believe?

Would love a video of your car now.

I know exactly what you mean btw—it's funny what an exhaust does

[bogie]

LOL

I experienced the same thing when I upgraded my 2006 Vantage to a 2012 last year, the secondary cats really dulled down the noise level. There was no official parts back then so Larini cat replacement pipes were fitted. Now its just how it should have been when it left the factory. With the valves closed its not really noticable but with them open it sounds like a V8 should.

Has to be one of the cheapest most rewarding upgrades for a 4.7 Vantage

[telum01]

My grey V8V had high-flow cats and muffler on it when I bought it. Sounded bloody brilliant *colonial cough*.
My red V8V was totally stock when I bought it. Exhaust note was a pile of soggy chips (I don't know if that works Britishly).

High-flow cats are a "no brainer" recommendation for anyone wanting to get an overall better sound out of their car. The units still have cats, so you don't have a crazy, obnoxious noise or that raw-fuel smell some cars get when catless, and you're still being somewhat environmentally conscious. Meanwhile, you're reducing weight from the car, getting a little more power, and getting a more throaty sound throughout the rev range.

If the catalyst material is high quality, you shouldn't have any check engine lights or fault warnings, so that's a bonus.

Just my quick schpeal since I'm so excited to get high-flow cats on my red Vantage in the near future

[Gday2]

Video with lots of sound please!

[HBradley]

nickv8 said:

Today was finally the day - the V8V found its voice. And boy... what a voice!

Shortly after buying the 2014 V8V from AM Bristol in May, it was back to have a V12VS exhaust fitted. Unfortunately even following the best efforts by AM Bristol, it just couldn't happen due to the rear-mounted manual gearbox radiator. ( Previous write-up.)

The clear alternative was to get the car de-cat'd using the official AM retro fit kit which replaces the secondary cats.

Must I admit I was a bit reluctant as even though I wanted to make the car more vocal when pressing on, I didn't want it to sound shouty at every moment including starting up and creeping away from the neighbours. I figured that's exactly what the de-cats would do.

On the plus side, the de-cat option was a third of the price of the full V12VS exhaust (both prices including fitment). So, after a bit of advice from fellow PH'ers plus hearing alternatives including the V8VS and GT12 Vantage(!) setups at local events I lumped for it.

I needn't have worried. In fact, I should have had it done on the day of collection! Oh my... oh my!!!!!!! To paint the picture...



I must have looked like a loon for the first few miles. I was genuinely laughing at how great it was.

Seriously - if you think your V8V lacks a little on the audio scale, just do it. Don't delay. I can't wait to take Vantage beyond 3-4,000 revs again. Truly addictive.

Interestingly, it doesn't appear to have any downsides. It's not boomy or noticeably noisier in the cabin (and I doubt outside) when not stomping on the right pedal. The Sports button now makes a real difference, so if you want to sneak around, resist temptation and leave those exhaust valves alone.

Most likely the best money I'll ever spend on this car

Footnote: huge thanks to AM Bristol as always. Extremely professional service, prompt, friendly (they were as pleased to show me the stunningly beautiful V12 Vantage Zagato they had in the service bay as I was to go weak at the knees staring at it), really good price, etc. They also managed to work on the warranty tweaks without the slightest fuss including a new rear light (misted up), fuel cap stickiness and some other odds and ends. And really carefully washed the car following my dirty (roads!) weekend in Wales.

Nick, could I ask what the procedure cost?

[nickv8]

HBradley said:

Nick, could I ask what the procedure cost?

It's around £650 which includes the AM de-cats, new gaskets, clamps and fitting. Best thing is that this would not affect the AM warranty.

If you're interested, you may wish to contact Kyle McLoughlin, Parts Advisor at AM Bristol - t. 01179 007 007 (only just realised the tel number when copying out from his business card!)

My insurance charged £19 extra annually for this mod which is OK IMHO. But all these figures pale into insignificance compared to the smiles/miles ratio of the new noise

[nickv8]

shinjuku said:

Great read!

I was considering the V12 backbox, but it doesn't fit on the 4.3L V8 due to the oil cooler in the rear section I believe?

Would love a video of your car now.

I know exactly what you mean btw—it's funny what an exhaust does

Exactly! The noise adds at least 50mph to any gear

I would assume the manual 4.3 V8V also has a rear mounted gearbox radiator so your AM-derived options are reduced.

Would also like to record a video, but it would have to be on the move above 4k RPM. Need somebody who can hold a mic very firmly LOL!

Edited by nickv8 on Thursday 17th August 16:48

[HBradley]

nickv8 said:

It's around £650 which includes the AM de-cats, new gaskets, clamps and fitting. Best thing is that this would not affect the AM warranty.

If you're interested, you may wish to contact Kyle McLoughlin, Parts Advisor at AM Bristol - t. 01179 007 007 (only just realised the tel number when copying out from his business card!)

My insurance charged £19 extra annually for this mod which is OK IMHO. But all these figures pale into insignificance compared to the smiles/miles ratio of the new noise

Thanks Nick, very tempting!! I'm wondering what difference it'll make to a V8VS?!

[nickv8]

HBradley said:

Thanks Nick, very tempting!! I'm wondering what difference it'll make to a V8VS?!

As the V8VS has a slightly different exhaust, the end result is likely to be different too. But from my initial sample (70 miles in mixed roads including motorway, familiar fast A roads and sweeping B roads), I think it's safe to say it simply adds extra audio "texture" when pressing on especially beyond 3k RPM. Not the full pops and bangs, but then I wasn't after the "turn it up to 11" effect.

I haven't done the Fuse 22 trick as there are moments I want to creep and GT cruise, so to me it's a safe bet, especially at this price point and reverse-ability. Stay out of sports mode and keep the revs low, and the Vantage does it's magic as a GT. But now it has the option to get more angry in a perfectly British gentleman kinda-way

[bogie]

You will have trouble running full decat pipes on a 4.3 , it will trip the MIL and fail MOT

On a 4.7 you have extra pair of "pre-cats" without O2 sensors, these are the cats that are being replaced in this instance. You still keep the other cats in place. I did mine for £400 from Larini.

On a 4.3 you need sports catalysts to replace the primary cats which are more like £1500 a pair + fitting

[LordBretSinclair]

bogie said:

On a 4.7 you have extra pair of "pre-cats" without O2 sensors, these are the cats that are being replaced in this instance. You still keep the other cats in place. I did mine for £400 from Larini.

Exactly - best mod ever !!!!

[BamfordMike]

bogie said:

You will have trouble running full decat pipes on a 4.3 , it will trip the MIL and fail MOT

On a 4.7 you have extra pair of "pre-cats" without O2 sensors, these are the cats that are being replaced in this instance. You still keep the other cats in place. I did mine for £400 from Larini.

On a 4.3 you need sports catalysts to replace the primary cats which are more like £1500 a pair + fitting

4.7L up to production date around late 2010 has the same exhaust system configuration as 4.3L - no cats in manifold and a downstream cat which has a primary cat / an air gap / secondary cat in same can. Meaning 4.7L with that hardware spec cannot fit decat pipes without the MOT or MIL issues you state.

The post 2010 4.7L configuration has primary cat in the manifold which is monitored by Oxygen sensors for in / out conversion efficiency. The secondary cat further downstream (not "pre cat", anything termed as 'pre cat' will be monitored by Oxygen sensors) is not monitored so will not throw a MIL and the secondary cat can be bypassed by fitting a decat pipe because the "pre cat" in the manifold is doing enough conversion to pass MOT. But because the pre cat / manifold cat remains, back pressure reduction is minimal when eliminating the secondary cat so performance increase is not that great, and is mainly done for improved exhaust note reasons - GT8 was built with decat pipes and factory stated 10BHP over stock model.

For owners with 4.7L around the hardware change date, the easy way to identify exhaust spec is to see if there is an EGR valve on the inlet manifold. EGR valve present = 4.3L exhaust hardware meaning a 200 cell cat and ECU remap will return a great power and noise gain. No EGR valve present on inlet manifold means if owner wanted more umph, manifolds and cats are needed, or if just a noise increase with modest power gain is desired, fit secondary decat pipes.

[leerandle]

Mike, great explanation. I was wondering what the different engine/exhaust configurations were just in case of next car upgrade

[bogie]

thanks for clarifying mike and correcting my terminology on the cats.

I wasnt aware that some 4.7s had the early exhaust configuration.

What exactly was the purpose of the change ? what do the secondary cats do ?

...not much I guess if we can replace them with straight pipes ?

[Wayne95]

BamfordMike said:

4.7L up to production date around late 2010 has the same exhaust system configuration as 4.3L - no cats in manifold and a downstream cat which has a primary cat / an air gap / secondary cat in same can. Meaning 4.7L with that hardware spec cannot fit decat pipes without the MOT or MIL issues you state.

The post 2010 4.7L configuration has primary cat in the manifold which is monitored by Oxygen sensors for in / out conversion efficiency. The secondary cat further downstream (not "pre cat", anything termed as 'pre cat' will be monitored by Oxygen sensors) is not monitored so will not throw a MIL and the secondary cat can be bypassed by fitting a decat pipe because the "pre cat" in the manifold is doing enough conversion to pass MOT. But because the pre cat / manifold cat remains, back pressure reduction is minimal when eliminating the secondary cat so performance increase is not that great, and is mainly done for improved exhaust note reasons - GT8 was built with decat pipes and factory stated 10BHP over stock model.

For owners with 4.7L around the hardware change date, the easy way to identify exhaust spec is to see if there is an EGR valve on the inlet manifold. EGR valve present = 4.3L exhaust hardware meaning a 200 cell cat and ECU remap will return a great power and noise gain. No EGR valve present on inlet manifold means if owner wanted more umph, manifolds and cats are needed, or if just a noise increase with modest power gain is desired, fit secondary decat pipes.

Mike, what does an EGR look like? Can you post a picture

[BamfordMike]

bogie said:

thanks for clarifying mike and correcting my terminology on the cats.

I wasnt aware that some 4.7s had the early exhaust configuration.

What exactly was the purpose of the change ? what do the secondary cats do ?

...not much I guess if we can replace them with straight pipes ?

4.3L V8 had to pass EU4 emissions regulation which isnt stringent enough to require a catalyst close to the engine, and was passed by having a cat further downstream (better for power than a catalyst in the manifold). The first brick in that cascade design can is 900 cell per square inch, the second brick in the same can is 400 cell per square inch, the 900 cell brick is more heavily loaded than the 400 with precious metal content and is doing most of the conversion work to pass the regs, the rear brick is pretty much needed to pass 100k deterioration factor when the conversion of primary brick degrades over time / mileage.

4.7L went into sale at EU4, so kept the same downstream cascade cat hardware as 4.3L, but when new model Vantage S came out, that car had to pass EU5 regs which pretty much can't be passed without a catalyst very close to exhaust port output, this is because after cold start catalysts don't start converting gas until the brick reaches about 330deg C. EU4 downstream cats achieve conversion after about 20ish seconds, EU5 test is failed if conversion isn't achieved after about 5-10 seconds hence the need for cats in manifolds.

4.7L at EU4 spec was 420 BHP, oddly some might say, Vantage S EU5 with its restrictive manifold cat is also 420BHP, this is because the EU5 manifold has better primary pipes for more power than EU4 meaning a neutral outcome with inclusion of cat in manifold.

The emissions test is about 20 minutes duration and is a series of accelerations / idling to simulate real world use. The last acceleration in the test is quite long and loads up the engine, cleaning up the gas the primary cats can't cope with on this final part of the test is pretty much the secondary cats only purpose, and same as EU4, secondary cat also helps out with deterioration compliance when primary cat ages at 200k miles.

If the factory sell a car (GT8) without the secondary cats, one can only guess for that model they massively increased precious metal loading of primary cats to comply with regs.

Once the car is sold, the compliance to regs sort of turns irrelevant because laws in the U.K. (EU zone is different) only stipulate MOT compliance, which a 200 cell per square inch cat with the most meagre of precious metal content will breeze through.

For folk who wish to modify for more umph or better sound the hardware specs give the following options.

4.3L can only upgrade with high flow cats, or better flowing manifolds and high flow cats for absolute max gains.

4.7L EU4 = same as 4.3L

4.7L EU5 = secondary decat just for noise, or better flowing manifolds (no primary cat) and high flow secondary cats for absolute max gains.
But, if that spend was too much investment, because the manifold is already reasonable primarily pipe design, keep it but remove the primary cat and fit a high flow secondary cat

[BamfordMike]

Wayne95 said:

Mike, what does an EGR look like? Can you post a picture

Exhaust Gas Recirculating valve is on left of throttle body, the black round component in middle of pic. On a 4.7L EU5 spec car the inlet manifold has the mounting hole cast / blanked off, the car in pic has upgraded exhaust manifolds so has a blank plug fitted in the valve because some performance increase comes from deleting EGR, but normally coming out of the valve is a pipe which links valve to exhaust manifold.

EGR pretty much only helps a engine reduce Nitrous Oxide emissions, it doesn't help with other pollutants. When the 4.7L moved to EU5 spec (cat in manifold) from EU4 (cascade cat downstream), the cat in manifold took care of enough NOx meaning EGR wasn't needed - good job too because EGR makes engines feel lacklustre when accelerating due to a certain % of combustion gas is already 'spent'

[jonby]

BamfordMike said:

If the factory sell a car (GT8) without the secondary cats, one can only guess for that model they massively increased precious metal loading of primary cats to comply with regs.

If that's the case, in relation to which you lay out what seems to be a very reasonable argument, presumably one could on a GT8/12/AMR car change the primary (only) cats for some which are less restrictive

If so, would there be much in the way of potential gains and is it commercially viable to change those cats which are presumably more costly (timewise) to access than the rear/secondary cats

The big question your theory does raise is in relation to power packs fitted to V12VS. Those power packs don't 'uprate' the primary cats, so does that mean a V12VS with power pack has less restrictive cats and potentially, more power, than a GT12/V12 AMR car ? Or is your assumption about primary cats geared just to V8 engined cars ?

[BamfordMike]

jonby said:

If that's the case, in relation to which you lay out what seems to be a very reasonable argument, presumably one could on a GT8/12/AMR car change the primary (only) cats for some which are less restrictive

If so, would there be much in the way of potential gains and is it commercially viable to change those cats which are presumably more costly (timewise) to access than the rear/secondary cats

The big question your theory does raise is in relation to power packs fitted to V12VS. Those power packs don't 'uprate' the primary cats, so does that mean a V12VS with power pack has less restrictive cats and potentially, more power, than a GT12/V12 AMR car ? Or is your assumption about primary cats geared just to V8 engined cars ?

Im not offering an assumption or a reasonable outline based off the hardware I see in front of me and some powertrain knowledge. For Gaydon gen1 V8 and V12 you just need to understand who the architect was.

Yes, for GT8/12/AMR cars remove the primary cat, remap the ECU so a MIL isn't thrown and hey presto, 40 ish BHP gain for the cost of about 15 hrs labour - cost effective. Also, as CraigV12VS car has shown, even newish cars suffer misfire which can cause engine to fail after ingesting a broken up cat, so with increased noise, removal of primary cat has many benefits. On that subject most German car makers steer clear of the cheaper ceramic material cat (fitted to Aston's) opting for a metallic foil construction cat because they seldom crumble into pieces and risk being ingested by the engine.

The V12VS power pack retains the same catalyst / exhaust manifold, pretty much identical to a 2004 DB9, the power pack is ECU, inlet manifold and secondary de cats. The inlet manifold won't offer much if anything, the decat on V12 probably 10-15 BHP, meaning and as has been concluded on another thread, when the cork of the primary cat is left in place, it might be? better off getting any competent fab shop to knock up a pair of secondary decats and spend the not so insignificant difference on something else.