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Replacing stock exhaust silencer - post "nat" - re-map ?


herbiemercman
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Hi Guys, I am considering replacing my exhaust silencer, it is an original Toyota NA part.

 

I wanted to keep the silencer as i did not want the engine noise to be too loud, rather just a solid burble, also the aesthetics of the four inch bore most popular tail pipes members fit are not some thing i like.

 

My question is, if i have a bespoke stainless steel twin pipe fitted with two "Burges" silencers and small chrome oval tail pipes, what is the probabilty of me needing a re-MAP? i think that the pressure drop could be very close to the current exhaust system, i am not familiar enough with how critical the Mapping perameters are? and hope some one out there could give me an opinion. Herbie.

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Hi Scooter, Thanks for prompt reply, my current silencer is in very good condition i just fancy the system i outlined in my thread. The current system has two 45mm OD pipes coming from the 70mm OD down pipe connected with a "Y" piece, and the stock silencer has the two 45mm entries.

I listen to some of the current day Audies etc, exhaust sounds, the performance ones, and they are louder but a great sound. I have never seen a MK4 with twin tail pipes, i think it will look good.

I have a tuned up Merc Estate car and had a bespoke SS exhaust fitted with a company in Birmingham, it sounds good and it took them three hours, and this was ten years back, it cost £350. Herbie.

 

MERC. TAIL PIPES> .231109 001.jpg (330.2 KB)

MERC  REARS.231109 001.jpg

Edited by herbiemercman (see edit history)
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If the pipe diameter remains the same then the resistance wont change. Therefore the flow will be the same and no remap will he needed.

 

If you change how it flows, typically through increase in size, then it will need mapping.

 

Just get an exhaust system made using the same diameter pipework and it will be a plug and play situation.

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Hi Noz, I understand about the pipe diameter being the same, but what about the two silencers having easier flow through and less pressure drop than the current stock silencer?

From your experience / knowledge of mapping are you saying that the exhaust pipes diameter are the main controlling factor?, if so, then if i removed my silencer and just had the two 45mm pipes i would not need a remap? I must admit i am struggling with this logic as i was always led to believe that the resistance to the total volume flowing through the exhaust system directly affects the manifold absolute pressure, the MAP.

I studied "Bernoull's Law" at college and i remember the equation Q = CD2 ROOT P OVER S). this means : The volume of gas flowing is proportional to the pressure and inversely proportional to the resistance. So this is why i am concerned about the resistance of the different silencers. I would like to know what you think and may be the resistance difference would have a minimal affect on the MAP pressure.? Herbie.

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Hi Noz, I understand about the pipe diameter being the same, but what about the two silencers having easier flow through and less pressure drop than the current stock silencer?

From your experience / knowledge of mapping are you saying that the exhaust pipes diameter are the main controlling factor?, if so, then if i removed my silencer and just had the two 45mm pipes i would not need a remap? I must admit i am struggling with this logic as i was always led to believe that the resistance to the total volume flowing through the exhaust system directly affects the manifold absolute pressure, the MAP.

I studied "Bernoull's Law" at college and i remember the equation Q = CD2 ROOT P OVER S). this means : The volume of gas flowing is proportional to the pressure and inversely proportional to the resistance. So this is why i am concerned about the resistance of the different silencers. I would like to know what you think and may be the resistance difference would have a minimal affect on the MAP pressure.? Herbie. PS: Just looked at your car and it looks great.

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Thanks mate. Car actually looks completely different these days! New colour. Wide arch wheel etc.

 

I personally wouldnt over complicate it. Any theory will only ever be estimation at best.

 

Silencers these days dont restrict as much as old style muffler used too.

 

I would just replicate the system using the same diameter and call it a day buddy.

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Hi Scooter, I have done some video recording of my car blasting up a hill which runs from my Pub, it sounded really good, i only managed first and second gear and i was hitting 70MPH when i braked for the bend at the top of the hill.

The tick over burble is also quite solid as well.

Anyway the only issue i had was if the resistance was too much at the top end at silly high speeds, it just feels like that, up to 130MPH (on a test track of course), it is reving and noticeably pulling well, but after that speed it just builds moderately up to the 150 / 160MPH mark.

However for every day use the acceleration in all gears, up to all speeds, is way faster than any other cars i have encountered, which was not the case with the original NA, where tuned VW Golf cars, etc, could pi--you off, so i am happy with my lot, and i do not need to get involved with a re-map. What do you think? Herbie.

Edited by herbiemercman (see edit history)
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I'm by no means an expert but I don't think you'll need a re-map from thinking about the setup. People stick exhausts on their cars all the time (and see power gains) without touching the ECU.

 

If you were having issues with boost control then maybe your exhasut was providing a big enough restriction to create back pressure. It doesn't sound like it was, so your wastegate will still open under the same boost level as before and everything will still be dealt with in the same manner. The exhaust gasses seem to be escaping quickly enough with your stock system so opening that up shouldn't make any difference...flowrate should be fairly similar.

 

A stock/BPU TT car would've been a different story however, as they rely on restrictive flowrates and back pressure to control boost levels from what I understand.

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Remap should be used as a preventative measure against any problems and not just power increase.

 

If you keep the pipe the same and the AFR doesnt change then the tune in theory will be the same.

 

If you make a flow change the map should be adjusted regardless of if you are happy with the current performance. You should always ensure you have correct fuelling.

 

It would be best to play it safe. Swap the exhaust. Have a remap. Rather than risk it or check AFR and then it's way different.

 

None of us can ensure the advice is sound and will protect your engine.

 

Get it mapped/checked with the new exhaust and cover your ass mate.

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Many thanks, Style and Noz, I understand your comments. Basically apart from a 10% thicker head gasket my set up is exactly as it was with the Mapper in South Wales who mapped all Dr Jekyll's conversions. I have covered 4,000 miles now from the NAT conversion and the performance is spot on. I have observed all the tops of the pistons and the valve faces during the cylinder head gasket job, they were in good condition.

I have "piece of mind" now and can just drive and enjoy my great machine, which you must agree was designed well before it's time.

I also think of my Brother , Adrian who bought new the TT Supra when i bought my new NA, and he gave me years of jocular banter that my car was a "whimp", he was amazed when i drove to his house and took him out in my NAT, with 100BHP more than his machine.

He was well impressed, little did i know , that he would be electricuted in his villa in Turkey, two years later, and his daughter's sold his car for £20K.

We never know "what is around the corner".

Chris Wilson , who is a very experienced guy, sorted a serious fueling / ECU problem on my Brother's car and got on well with him, Chris said good things about him after his passing and i will always remember that. Herbie.

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