Exhaust mods

[Billy Bobtail]

I would like some opinions please the exhaust on the car is due for renewal, due to the bobtail any off the shelf exhaust would have to be modified to fit so i started thinking about something less restrictive. My belief (born out of 30 years plus in engineering and theoretical knowledge is that a diesel does not need any more back pressure than the turbo provides and that the freer flowing downstream of the turbo the better
The easier it is for the engine to pump out the gases the more power is left to push the vehicle along.
But (and it's a bigger but than an overweight elephant) a friend who has vastly more practical surf knowledge than me reports that a surf that had the small rear box removed initially seemed better but then suffered a performance loss including the kickdown characteristics being altered, reversion to the stock exhaust resolved the issues.
Is it possible for the quicker spooling speed of the turbo when "learnt" by the ECU to have a negative effect?
It was always my belief that the small back box was more to do with resonance than anything else.
Please don't simply rubbish my friends opinion because it happened - I would like considred opinions and experiences please.
Thank you.

[Albannach]

Which car?

Have a look at THIS post for some theory.

[Albannach]

Did your mate Dyno the Surf?

[Billy Bobtail]

Hi, thanks for the link and although the theory is based on a motorcycle petrol engine a lot of the common sense is sound - pumping losses, harmonics, reflected waves, etc. Fuel for the debate if you will pardon the pun.

I do not think the car was dyno'd, the chat I had suggested it was all to do with how the car drove and felt on the road compared to the stock exhaust. Not sure of exact model but believe 3.0 auto.

I like to try and understand the engineering underpinning changes and the engines response to the changes and in this example theory and practice seem slightly at odds.

[BUSHWHACKER]

Yes, the small rear silencer is just a resonator and has nothing to do with the engine's performance.

All you need for your truck is one of those universal glass pack style mufflers ( 18" ish long, round or oval shaped, with the perforated tube down the centre) fitted directly after the flex joint and a 90 degree bend to exit out in front of the rear wheel.
The turbo will spool up much quicker and the truck will feel more sprightly, especially when pulling away from a standstill.

Did did this to my 2.4 years ago, although I used a second hand middle silencer from a Transit, and the truck performed much better. I sold the exhaust to another member on here when I done my engine swap.

[J i m s t e r]

Mine failed a pre-emptive MOT yesterday on corroded centre box, which I was half expecting. It means I can put on a full stainless system

Any thoughts on what to go for/avoid? No cat required as it's an import.

[BUSHWHACKER]

Mine failed a pre-emptive MOT yesterday on corroded centre box, which I was half expecting. It means I can put on a full stainless system

Any thoughts on what to go for/avoid? No cat required as it's an import.

No Cat required as it's a diesel.

[J i m s t e r]

So should I go with the rear silencer or not? Based on the above, it seems like I need one.

[Billy Bobtail]

Thanks for the replies folks.

I was hoping that a few of the guys (or gals) that had modified exhausts would of responded with their experience of the results they found.

I am still looking into the theory side of things and as of yet can find no reason for any loss of performance other than the possibilitiy of the balance between the ECU diesel pump inputs and the air inputs being altered.

Need to find out a bit more about how "intelligent" the ECU is and its capability to learn or adjust for altered readings.

Would be nice to arrive at the optimum solution for the driving and laning I do, convinced that the must be improvements to be had - but then Toyota dont employ chimps as designers and engineers so who knows.

[Nukes25]

I just cut my exhaust off in front of the big muffler, and just piped it 90degrees out in front of the rear tire... idling and free revving, it sounds good, but under load it gets the loud gurgly garbage sound, I'm looking into fitting a glasspack just in front of the exit, see if it helps drop the loud sound under load..

as for performance, stock I was avg 26mpg, ( 265/70/15 tires, 4.10 gears, stock exhaust), I'm now on 33's with 4.56gears, and the open dumped exhaust, and mileage is still averaging 26ish, or 10liters/100km