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Thread: Almost new year so...

  1. #1
    Senior Member Lost it's Avatar
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    Almost new year so...

    I'm thinking naughty thoughts.

    I'm thinking I'll redo the gearbox oil change on the S type. Then do a rolling road run.

    And fit a full exhaust on it. Deleting the cats. Put a set of O2 eliminators on for the closed loop running. Then do another rolling road run.

    And keep the standard system for when it needs an MOT again.

    Legal? Barely. Chance of the car having an emission check at the road side? Next to none....

    Increase in power and torque? Possibly.
    2001 3.0 SE Auto, Satnav, winter pack. Dark Blue, all the toys.
    2004 3.0 Sovereign Estate. Winter pack. Fixed. For Sale.
    2005 Estate X type 2.2 Sport.
    2000 V8 3.2 XJ8 LWB. "Prom" car. Lovely. Should sell this one too really...
    2005 "AllyCat", 3.0 XJ6 SE.
    2000 S type 4.0 V8. Latest toy.
    VFR800A and a VFR 800F

    Still beating cancer. Trevor 2, Cancer 0.

    Sure I took the Red pill....

  2. #2
    Senior Member Lost it's Avatar
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    And my wife bought me a genuine Jaguar bonnet leaper for the S type. She says it looks like it needs one. Hmm. That old chestnut again...
    2001 3.0 SE Auto, Satnav, winter pack. Dark Blue, all the toys.
    2004 3.0 Sovereign Estate. Winter pack. Fixed. For Sale.
    2005 Estate X type 2.2 Sport.
    2000 V8 3.2 XJ8 LWB. "Prom" car. Lovely. Should sell this one too really...
    2005 "AllyCat", 3.0 XJ6 SE.
    2000 S type 4.0 V8. Latest toy.
    VFR800A and a VFR 800F

    Still beating cancer. Trevor 2, Cancer 0.

    Sure I took the Red pill....

  3. #3
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    If it reduces the back pressure you may get reduced power.

  4. #4
    Senior Member Lost it's Avatar
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    Correctly designed engines don't need, or use "back pressure". That's a well rehearsed fallacy.

    There's lots of theories. But basically if the combustion process has raised the pressure within the cylinder by whatever variant of the compression ratio it was throttled to, that and the piston accelerating upwards gives more than enough momentum for the gasses to be removed. The larger the primary the better you might think? Well, it's not quite that simple. But it's simpler with a V8 because the exhaust pulses are uniform. And as these engines aren't "flat plane" big bang motors, that's an advantage.

    There's the theory about negative pressure waves, there's the theory about the gasses impinging on an exhaust driven supercharger, there's also theories about the length of the exhaust branches. These can all be "tuned" to help the motor under certain circumstances, but it's common enough knowledge that if you change the exhaust then you also change the inlet route that your fresh air or mixture "see's" as well. And the more exhaust you get rid of, potentially there's more space in tthe cylinder for the fresh charge.

    Exhausts usually add to pumping losses, that prevent the engine spinning up quickly, a lot of research has gone into this from the likes for Suzuki, Honda, Yamaha, Kawasaki, Ducati, you name it, if they build a performance engine, they go the extra mile with the exhaust as well to try and remove as much restriction as they can..

    And especially with a supecharger, you will have more energy to remove the gasses anyway, so you'd think a free flowing exhaust would be a benefit, not a hindrance..

    The only time having an exhaust too big might create a problem is if the larger bore also has a restriction in the form of a baffle type silencer.

    In fact, regarding power outputs, back in the 1960's when the major US car makers were playing the power output war, their engines used to dump their exhaust into a chamber that was as close to vaccum as possible just to remove pumping losses.

    Basically you have to work out how much gas you need to get rid of and over what rev range and size the exhaust accordingly. Generally a 4 into 1 will give more torque lower down, (and power as it's a function of torque) a 4 into 2 into 1 will give more power at the top end as the exhaust gasses are able to leave the combustion area with less restriction.

    There are very skilled people out there that know far more about this than I do.
    2001 3.0 SE Auto, Satnav, winter pack. Dark Blue, all the toys.
    2004 3.0 Sovereign Estate. Winter pack. Fixed. For Sale.
    2005 Estate X type 2.2 Sport.
    2000 V8 3.2 XJ8 LWB. "Prom" car. Lovely. Should sell this one too really...
    2005 "AllyCat", 3.0 XJ6 SE.
    2000 S type 4.0 V8. Latest toy.
    VFR800A and a VFR 800F

    Still beating cancer. Trevor 2, Cancer 0.

    Sure I took the Red pill....

  5. #5
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    Let us know how it goes and what the the dyno results are (start with a "before" dyno, of course).

    Probably wise to tell your insurer.

    Won't be legal for public roads, but I suspect will pollute rather less than most of the cars on the roads - which are deemed legal. Ah, the madness of politicians.

  6. #6
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    You will also get better mileage per gallon. I know a person who did it to his diesel van and he was saving a litre per 100 km.
    Grumpy Old Git
    “When a government is dependent upon bankers for money, they and not the leaders of the government control the situation, since the hand that gives is above the hand that takes. Money has no motherland; financiers are without patriotism and without decency; their sole object is gain.”
    Napoléon Bonaparte

    2003 (botox) S type 3.0 sport with manual gearbox, as rare as rocking horse apples

  7. #7
    Senior Member Jim_S-V6_2004's Avatar
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    Many years ago we fitted straiht-through megaphone "silencers" to our bikes. They breathed better and I think we gained a little more power.

    It could have been wishful thinking of course, because we didn't have money to blow on power tests.

    We throttled down at night so we didn't make as much racket as the fool bikers do today with no regard for time of night nor people.

    I could quite happily swat them with a lump of 4x2.

    .

  8. #8
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    Being a petrol, if it reduces EGR as seems likely then the MPG will be worse and the in--cylinder temp higher. I doubt the latter matters on a 3.0.

    Not that MPG would appear to be the OP's interest.

    Before & after dynos will be interesting.

  9. #9
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    It will still be silenced, I'm looking for the sake of discovering just how restricted the standard boxes are.

    Gearbox oil flush again first.
    2001 3.0 SE Auto, Satnav, winter pack. Dark Blue, all the toys.
    2004 3.0 Sovereign Estate. Winter pack. Fixed. For Sale.
    2005 Estate X type 2.2 Sport.
    2000 V8 3.2 XJ8 LWB. "Prom" car. Lovely. Should sell this one too really...
    2005 "AllyCat", 3.0 XJ6 SE.
    2000 S type 4.0 V8. Latest toy.
    VFR800A and a VFR 800F

    Still beating cancer. Trevor 2, Cancer 0.

    Sure I took the Red pill....

  10. #10
    Senior Member Victor's Avatar
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    Quote Originally Posted by Lost it View Post
    I'm thinking naughty thoughts.

    I'm thinking I'll redo the gearbox oil change on the S type. Then do a rolling road run.

    And fit a full exhaust on it. Deleting the cats. Put a set of O2 eliminators on for the closed loop running. Then do another rolling road run.

    And keep the standard system for when it needs an MOT again.

    Legal? Barely. Chance of the car having an emission check at the road side? Next to none....

    Increase in power and torque? Possibly.
    At your age ?? well put all such thoughts out of your mind and concentrate on the motors. ..............besides, such thoughts are an overrated pastime and best left for t'young folk.

    Now behave.
    A very cynical grumpy old man
    Late 2004 2.7D auto
    Connoisseur of Fine Ales
    "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming - What a ride, where are the wimmin?"

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