Fabiamania continued

Hey guys, just a quick update on the Fabia : Brembo Supermax discs have now been fitted front and rear along with the matching Supermax pads, at the same time Goodrich stainless braided hoses were fitted and Brake fluid changed. Braking is now intense.

June 29th sees the making of a new Turbo back exhaust, made by Tony Banks in Leeds, this will be 65 mm pipework, a 200 cell cat a resonator and muffler.

June 30th sees the girl hitting the rolling road at JBS car designs in Chesterfield for a full custom remap (stage 2) hoping for around 155 to 160 hp.

Following this at the earliest opportunity I will have vents fitted into the bonnet to allow some of the extra heat out, and the calipers need painting, later some attention to a couple of bits inside.

This will be the end of the road and I'll just enjoy it.
 

TCJBOLDIE

Moderator
Staff member
Points
697
Location
Brisbane
Car
2011 Honda FN2
Fabs It looks like there will be a few more ponies in the stable when all of your mods are i finished However I would recommend an even larger diameter exhaust system or if possible just the dump pipe to be as big as the available space allows as am sure you know bigger is better when it comes to turbos.
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
Hi, yes I have considered this and it's a tricky balance: if it was just a dump pipe and very short a large diameter would be perfect just to get the hot gas away from the car but having a full system, and trying to balance internal cabin noise with very strict UK legislation is difficult.

As you say bigger is better with a turbo, but this is only relevant to a point.

In a full system you need to get the gas away as quickly as possible (same as the dump pipe) however as you increase the diameter of exhaust pipework the gas speed slows... Imagine water flowing through a hose... Open the flow on the nozzel and the pressure drops and speed slows. Also physics and the laws of gas are also working against us too : So as a gas cools it looses energy and slows down.

So if we have a large bore exhaust over a long length, as the gasses travel along the pipe and airflow and /or rainwater air spraying the pipework, we are loosing huge amounts of heat, this is cooling the gas all of the length of the system and slowing its progress, added to the larger diameter, we have a serious problem.

By the time it exits the system it will not have any significant latent heat left, so there will be no scavenging effect because the gas will be moving so slowly.

This is exactly what we need to avoid in a Turbo engined vehicle - yes?

So to overcome this, if we keep the exhaust system pipework small-ish we can increase the speed of the gas flow through the pipe work, doing this reduces the heat loss significantly and this to helps to keep the gas speed up.

Keeping the gas speed and the gas temperature as high as possible until it exits the system is the better way for the Turbo as it keeps the flow rate high.

If it was practical : a dump pipe would be perfect but not for road use and certainly not in the UK.

The other thing which would help would be to insulate the exhaust system entirely so that it lost even less heat along its path, this would help to maintain the gas temperature even more effectively and help keep the gas speed as high as possible.

There are a shed load of calculations involved in obtaining the correct diameter pipework, but with resonators and mufflers involved to, and I don't have accurate exit gas temperature readings I have had to guesstimate the best option for balance.

A large bore exhaust over the full length with boxes would create a power loss for sure and more so during the winter as road and air temps drop below zero.

Hope this makes some sense
 
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TCJBOLDIE

Moderator
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Points
697
Location
Brisbane
Car
2011 Honda FN2
Thanks for all that well written and researched reply Fabs |B

IMO for a road legal the best result power wise is to have the dump pipe as large as possible from the turbine exit to the 2nd bend where it goes under the body / floor where it needs a tapered reducer to connect to the smaller diameter of the remainder of the exhaust system.

Ultimately the available space will determine how large the size of the most important first part of any turbo exhaust can be.
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
Hi, yes I see your meaning however the turbo dumps straight into the primary cat which hangs virtically down the back of motor taking all available space, I guess in some respect it acts like a large dump pipe its has a huge inlet flange probably some 75mm or 80mm in diameter, the new cat is only 200 cells so it will have much greater flow capacity, so hopefully this will suffice. Room is very restricted in that area so comprises have been made, and it's far from "ideal" but I am having to trust the guys who build the system to do the right thing to. I am dispensing with the secondary cat altogether and just having a center resonator and a rear muffler.

Photos will be taken.... Thank you for your advice it greatly appreciated.
 

TCJBOLDIE

Moderator
Staff member
Points
697
Location
Brisbane
Car
2011 Honda FN2
Fabs just to be clear we call the first ,say 1 metre of the exhaust that bolts to the turbine exit a "dump pipe" and the pipe that exits an external wastegate to atmosphere a "screamer pipe" that is what you will see on drag and competition cars BUT totally illegal on a street registered vehicle.
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
Yes,
The wastegate is internal on this unit and releases back into the exhaust or dump pipe, in my case this is directly into the primary cat inlet.

The pressure side/cold side of the system on this model Fabia does away with dump valves/blow off valves and has a sealed delivery pipe.
 

Fabia17

Torque Junkie
Points
322
Location
Lincoln UK
Car
Fabia Monte Carlo
Here you can see how tight everything is. The wastegate is clearly visible in the turbo outlet, with the wide flange and below the inlet for the Primary Cat.... No room to swing a cat, springs to mind.... Hahaha
 

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