Power and more of it

Submitted: Sunday, Feb 29, 2004 at 22:09
ThreadID: 10904 Views:1150 Replies:7 FollowUps:5
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I was just wondering what the limitations/considerations were with increasing power output from ones engine. I have heard tell that a bigger exhaust will give me more power, mate has a Defender and put a 2.5" exhaust on and Truckster has a 3" (2.5"?) one and it helped but why? Does it allow the gases to get out faster hence allowing more fuel air mixture in and a bigger bang?

If the fuel is limited on intake electronically then how do you get more power out the other end without remapping the engine management system ala D-tronic?

Its amazing what wafts thru ones mind when wandering around the Motor show...

Any clues would be good.

ThanxLife ISN'T like a box of chocolates...it's more like a jar of jalapenos.
What you do today, might burn your bum tomorrow."
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Reply By: Eric Experience. - Sunday, Feb 29, 2004 at 22:18

Sunday, Feb 29, 2004 at 22:18
Bonz.
You are on the money. There is an increase in niose, but very little else if you just fit a bigger pipe. In Trucksters case he has a turbo so that is a different story. Eric.
AnswerID: 48697

Follow Up By: Bonz (Vic) - Sunday, Feb 29, 2004 at 22:21

Sunday, Feb 29, 2004 at 22:21
My mate has a turbo too as have I ..... so whats the difference in the story?Life ISN'T like a box of chocolates...it's more like a jar of jalapenos.
What you do today, might burn your bum tomorrow."
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FollowupID: 310496

Reply By: awill4x4 - Sunday, Feb 29, 2004 at 22:26

Sunday, Feb 29, 2004 at 22:26
The larger exhaust doesn't usually give much more of an increase of absolute power. What it does do, is allow the turbo to spool up faster which in turn changes your torque curve usually allowing more power earlier in the rev range so that by seat of the pants driving, the response is improved.
Regards Andrew.
AnswerID: 48698

Follow Up By: Bonz (Vic) - Monday, Mar 01, 2004 at 18:12

Monday, Mar 01, 2004 at 18:12
Seat of the pants stuff is pretty important I reckon, if it feels faster/torquier then hopefully it isLife ISN'T like a box of chocolates...it's more like a jar of jalapenos.
What you do today, might burn your bum tomorrow."
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FollowupID: 310574

Reply By: Martyn (WA) - Sunday, Feb 29, 2004 at 23:25

Sunday, Feb 29, 2004 at 23:25
Bonz,
With a smaller exhaust the exhaust gas back pressure is greater so more waste gas remains in the cylinder after each power stroke, a larger exhaust allows the waste gas to escape easier, with a turbo you are again forcing more air into the cylinder, this in turn pushes more waste gas out and depending on the camshaft profile may keep the inlet valve open to get a greater volume of air into the cylinder which mixes with the fuel vapour creating a bigger bang, more heat, more power etc etc etc Hence why racing motors have no mufflers and exit the constraints of a pipe as soon as possible, they want all the waste gas and some fuel out into the pipe hence the backfiring you hear of unburnt fuel flashing off in a hot exhaust on the overrun. Does this help at all????? Keep the shiny side up
AnswerID: 48703

Follow Up By: Bonz (Vic) - Monday, Mar 01, 2004 at 18:06

Monday, Mar 01, 2004 at 18:06
Sure does Martyn, it means that when the exhaust is stuffed a bigger one'll go on, as will a snorkel when the ensuite is built...DON'T ASK!Life ISN'T like a box of chocolates...it's more like a jar of jalapenos.
What you do today, might burn your bum tomorrow."
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FollowupID: 310572

Reply By: Wayne (NSW) - Monday, Mar 01, 2004 at 08:37

Monday, Mar 01, 2004 at 08:37
Bonz

The other replies have spoken about getting the air (exhaust) out .Getting the air in will also help. Fitting a snorkel will help force air into the turbo and there fore increase torque.

I did notice an increase in torque, when driving on the sand dunes at Stockton Beach , after the exhaust was increased to 2.5", the new exhaust had a lot of the bends taken out and all the mufflers removed.

WayneAlways Out'N About
AnswerID: 48716

Reply By: Wayne (NSW) - Monday, Mar 01, 2004 at 09:43

Monday, Mar 01, 2004 at 09:43
Bonz,

I was once told for power " there is no substitute for cubic inches"

I know it is not politically correct but cubic centimetres has not got the same sounding impact.

WayneAlways Out'N About
AnswerID: 48723

Follow Up By: Bonz (Vic) - Monday, Mar 01, 2004 at 18:07

Monday, Mar 01, 2004 at 18:07
Yes Wayne I leaned that a long time ago after I slipped a few chicken sock CUBES into the petrol tank of my old Falcon, went like rocket...... WHOOSH - BANG!!Life ISN'T like a box of chocolates...it's more like a jar of jalapenos.
What you do today, might burn your bum tomorrow."
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FollowupID: 310573

Follow Up By: Wayne (NSW) - Monday, Mar 01, 2004 at 18:16

Monday, Mar 01, 2004 at 18:16
Bonz,

ROFLMAO

WayneAlways Out'N About
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FollowupID: 310578

Reply By: ianmc - Monday, Mar 01, 2004 at 10:09

Monday, Mar 01, 2004 at 10:09
I have had a 2.5" exhaust on my Triton 2.5td for some time together with a straight thru muffler and the fitter did a great job in minimising bends.
As advised the turbo acts as something of a muffler so the noise level is only slighlty increased, low speed torque is improved a little, but top speed remains about the same but this may be due to gearing & engine characteristics I feel.
It cost me $250 but the pipe used was thin & probably resonates a bit. I would go for a heavy guage pipe & muffler if possible & probably greater life.
AnswerID: 48725

Reply By: Member - Bradley- Monday, Mar 01, 2004 at 10:44

Monday, Mar 01, 2004 at 10:44
Best way to think of an engine is as a big air pump.. gas in / gas out. Atmospheric pressure will push gas into an engine but the exhaust stroke of the cycle has to 'push' the gas out so to speak. of course the gasses are hot and therefore expanded, so they will need to move at speed to evacuate to combustion chamber. Exhaust headers are designed to 'scavenge' the gases and help remove combusted gases from the chamber to allow for more fresh gas on the next cycle. The exhaust pipe should be of a large enough diameter and minimising any sharp bends , the bends should be mandrel bent as this does not decrease the internal diameter of the pipe and reduces frictional losses from the bend. With turbos, go for an incresed diameter from the outlet flange onwards, with an internal divider for the wastegate gases. For max power use a custom header manifold as well ( $$) upgrade turbo etc ($$$) There is also a lot of thermodynamics involved but i'm sure as hell not going into it here. lol. Hope that didn't confuse too much.Just killin time till easter...............go and play in the dirt, instead of workin in it......
AnswerID: 48727

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