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new exhaust and manifold


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#16 Dan

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Posted 11 February 2005 - 08:47 AM

EFi cars always get less mileage than carb'd cars - the EFi system chucks in loads more fuel than is needed in order to keep the cat working properly throughout the rev band (that's why fuel injection and the CAT is not so good for the environment as stoopid government types think it is).

#17 998dave

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Posted 11 February 2005 - 09:21 AM

Ok, im confused, i found an old mini mag which had the catalogue in, and there was a part which said the average mpg was 47!! i thought mpg went down with a stage one not up, mine only does around 35-40.

A stage one kit works by allowing the engine to work more efficiently. To do this the system basically allows easier breathing (air flow), into and out of the engine. Thereby increasing volumetric efficiency (the amout of the cylinder filled and used during combustion).

Also, by splitting the inlet and exhaust manifolds heat transfer is reduced, and this means the inlet charge is that bit cooler, therfore more dense, and so can operate with more fuel, and again produce more power through increased efficiency.

Now your engine is running more efficiently, presuming it's been tuned correctly, a rolling road is advised, you have more bsfc (brake specific fuel consumption), that is the amount of power your engine produces per unit fuel it consumes.

This then means you can dawdle along at lower speed in a higher gear then before, and not have the gnine coughing or struggling. And when you do want power the engine can produce more per unit fuel then before as it's cooler, and not having to ovecome all those big pumping losses associated with the original manifolds, pipes and filter.

That help?

Dave

#18 998dave

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Posted 11 February 2005 - 09:25 AM

EFi cars always get less mileage than carb'd cars - the EFi system chucks in loads more fuel than is needed in order to keep the cat working properly throughout the rev band (that's why fuel injection and the CAT is not so good for the environment as stoopid government types think it is).

catalyst needs the engine to peform as close to stoichiometric as possible. Lambda is equal to one. that is there is just enough air to burn all the fuel, and vice-versa.

A non-cat mini can run slightly rich at lambda equal to 0.9 that is there is a little bit extra fuel then the air can burn, but that's okay because you never burn it all anyway as it's never properly vapourised in the inlet charge anyway. At lambda 0.9 the engine can produce more power, and still get through the emissions regulations.

lambda is the AFR (air:fuel ratio) measured by an exhaust gas analyser.

Dave

#19 Jackman

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Posted 11 February 2005 - 10:29 AM

Thanks for that dave, i understand alot better now, i think ill save up and wait for a one years no claims before i do it, currently i can go into 4th at 30 so that should do me fine for now.

#20 psycho mini driver

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Posted 11 February 2005 - 12:45 PM

so would a stage one on an spi increase economie aswell as performance?

#21 998dave

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Posted 11 February 2005 - 03:25 PM

In theory yes, however, the SPi is a lot more modern then the older carbed engines, so i would imagine rover had sorted some of the problems, for instance your exhaust system won't strangle the engine so much anyway.

Although, MiniSport advertise one, you could just read their info. on it, they have example power curves too.

#22 Dan

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Posted 11 February 2005 - 06:58 PM

OK I shouldn't have said that EFi is less economical, I should have said that CATs are.
There was a paper published on this once, I can't remember when or who by though. The problem with the cat is that, as you say 998Dave, they need to remain at the stochiometric ratio (14.7:1) so that there is no unburnt fuel or oxygen remaining in the exhaust gas after the combustion stroke. But without one you can do one of two things:
You can either lean the engine off and burn less fuel (some reciprocating piston engines can even run as low as 20:1 air/fuel ratios without problems) which gives better economy if you don't mind the reduction in power output.
Or you can enrich the mixture slightly which will also give greater economy. I know that sounds like a contradiction but it does work. Basically, if the engine is producing more power then you don't need to keep the revs so high. With a lower engine speed the reduction in the quantity of fuel burned more than makes up for the increase in mixture strength. Which is the same effect that provides greater economy out of a stage 1 kit.
So the Stochiometric ratio is the most efficient burning of the fuel, in that it is all combusted away while still within the cylinder, but it is not the most efficient use of the fuel.
But the only way you could see the result of this on an EFi car having removed the CAT is to remap it, ignoring the lambda sensor and effecetively over fuelling.

I wish I could find this paper now, there were loads of other reasons why CATs are inefficient (especially when coupled with government anti pollution legislation) and encourage pollution and fuel over-use rather than help the situation, and why lean burn engines (which the A-series technically is anyway) are a far better solution.

Edited by Dan, 11 February 2005 - 07:03 PM.


#23 998dave

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Posted 11 February 2005 - 07:07 PM

wooo...
we agree.... one BIG reason - cat's only work when hot... :cry:)

Dave

#24 Badoff

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Posted 11 February 2005 - 11:18 PM

just to get back to the original thread. yeh all you should need is the rubber hangers unless you had to cut the rear hanger off the subframe to get your centre exhaust on, i know i did due to the annoying rattle it was making. is your car injection? does it still have a standard 1 piece exhaust and inlet manifold?

#25 998dave

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Posted 12 February 2005 - 11:54 AM

just to get back to the original thread.

where's the fun in that?

#26 psycho mini driver

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Posted 13 February 2005 - 04:34 PM

i have it all fitted now, new down pipe, decat and a classic rc40 exhaust, just need to fire gum the joint where the exhaust meets the decat pipe

#27 Madmax

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Posted 13 February 2005 - 07:32 PM

excellent stuff mate, lets see some pics of that new rc40!

#28 psycho mini driver

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Posted 13 February 2005 - 09:10 PM

i will get some up asap, the car is shut away for the night now, but will get some hopefully when i get in from work tomoro. its great as it looks old skool and small, but it roars, i was surprised! it is a little quieter than my twin dtm, but not much.

#29 psycho mini driver

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Posted 13 February 2005 - 09:15 PM

also, this manifold is slightly shorter, and it doesnt hang as low as the old one, which is very good, no more scrapeing, but its tucked up so high, it almost fouls the body where it bends, i think it might knock, but not 100% if it is here, anything i can do? or will it stop?

#30 Badoff

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Posted 13 February 2005 - 11:14 PM

Make sure you have the bracket that holds the bottom of the manifold to the diff housing and it should be ok.




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