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J

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Discussion Starter #1
Just knicked this from AO.com

http://www.squadra-tuning.com/aanzuigbuis_modificatie_145_155.htm

would it help much ya reckon? for better airflow?
Note Alfa part number 90917628

Anyone wanna check that's still available nowadays.

I know MrT did the same sorta thing to his 156... the v6 pipe piece is straight like this alternative one...where as his standard one is like the first pic in that link. Dunno if it makes much diff... that was b4 he got the sports exhaust tho... did add a wee bit noise :D

Surely must help if not very slightly.

The price of the shorter unit was only about a tenner for the 156 one... I shouldn't see the one pictured being any more expensive.

BTW it is in dutch.. but the pictures speak just as well.

j
 
I

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Discussion Starter #3
Part number is 60617628 and is available.

Cost is £1.99 incl VAT.

Part is only listed for 145/6 though.

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Ian H
 
M

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Discussion Starter #4
The extra airbox thing on the original pipe is there to help increase low down torque I think. I remember reading a piece about airflow and other shee-ite, and how these boxes affect torque figures.
You might find the car a bit less drivable around town unless you keep the revs up, which is where you may find the only benefit.

Again, not sure how it all ties in but, apparently you get an increase in torque if you narrow the exhaust manifold outlets which leads me to believe that increase in torque is gained by making the engine work harder...sort of....???

Someone put me straight please.

Marlon
 
E

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Discussion Starter #5
Changing the diameters and lengths of inlet and exhaust manifolds has to do with improving breathing, but not by making the engine work harder. It's the ram effect of air flowing through the inlet pipes at the right speed, and the extraction of as much exhaust gases as possible through a suction effect just before the exhaust valves close. It's all a matter of managing the pressure waves created by the opening and closing of the valves.
That's why the more recent versions of the twinnies have variable inlet manifold length. At low revs the inlet pipes are long to create the ram effect, at high revs the pipes are short to reduce friction losses and improve breathing.
 
M

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Discussion Starter #6
Are you talking about the variator altering the inlet cam timing ????
If so, the early 8 valve TS engine also has this, albeit a different design (even my 75 had it).

Marlon
 
E

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Discussion Starter #7
Ehm, no. I'll try and be a bit clearer.

Variable inlet pipes are not the same as variable valve timing, although the aim is the same, ie getting more air+fuel into the cilinders by making use of the inertia of the air.
When an inlet valve closes, the air flowing down the inlet pipe is suddenly halted, creating a pressure peak in front of the valve. This pressure bounces back and forth between the valve and the plenum (air chamber from which the individual inlet pipes originate). If the pressure wave arrives back at the valve at the same moment that the valve is open, the pressure wave will force more air into the cilinder. This can be achieved in two ways:
1. by adjusting the timing of the valve opening (variable valve timing)
2. by adjusting the distance the pressure wave has to travel (variable inlet pipe length)

The latter is particularly effective at low engine speeds, which is why variable manifold systems have long inlet lengths at low revs, and short lengths at high revs where the friction in the inlet manifold becomes significant.

The exhaust manifold works in a similar way. When an exhaust valve opens, the exhaust gases create a pressure wave traveling from the exhaust port into the exhaust manifold. Tubular manifolds are designed in such a way that the pressure waves traveling down the manifold from the individual ports work together to create a suction effect. This increases the amount of exhaust gases extracted from each cilinder, which in turn leaves more room for fresh air/fuel mixture, which gives you more wheelspin in third gear.
This also explains why you shouldn't go over the top when choosing the diameter of the exhaust system. If the pipes are too large, the velocity of the gases drops too much, reducing the extraction effect because the slow-moving gas doesn't have sufficient inertia to "pull" the remaining gas from the cilinders.
So now you can start laughing at the idiots in their civics with two stovepipe-sized exhausts banging on every bump in the road. They cost you money as well as power.
 
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Discussion Starter #8
Cheers. That all makes sense to me. Just didn't know the 16v TS had variable inlet pipe length thingy doo dahs.

Marlon
 
J

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Discussion Starter #9
I understand ok with the exhaust pulse wave stuff.

The inlet pulse stuff... does that mean you can get a unit which is mechanical and adjusts itself in respect to revs and load?

Or is the intake just 'optimised' and the pulse setting doesn't change at all and just gets faster with the revs... so you have it either pulse in phase or out of phase.

Is the unit just 'tuned' to give better performance lowdown the revrange? but not as good higher up the rev band.
Can you then adjust the lengths/retune it to maybe not give as good performance lower down but stronger pull/better airflow at the higher revrange?

Does anyone kinda understand what i'm getting at?

Is it as simple as unbolt this one.... and put in this one... may not be a good bottom end but it 'breathes' better and goes like a rocket top end?

el gringo.... what do ya reckon.. is it a one setting does all? or can you tune it to go better at diff rev levels.

rgrds

j
 
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Discussion Starter #10
First of all, this system was never fitted to the 155. It was introduced on the 156 and 145/6 around '97, and only the 1.8 and 2.0 16V engines have this system, not the 1.6 or the V6. The engines have motronic M1.5.5, instead of the M2.10.3/4 fitted to the 155. So it's not possible to retrofit it to a 155. Well, anyhting is possible given a bargeload of dosh, but there you are.

As for the "variable" bit, it's actually an on/off system. Below 4960 (really!) rpm, the air has to travel through a curved inlet pipe from the plenum to each inlet port. The length of this pipe is such that the pressure waves are more or less in phase with the valve opening intervals. This gives good torque.
Above 4960rpm, a flap is opened which allows the air to take a shortcut, so to speak, bypassing the long curved pipe. This maximizes the amount of air available at the inlet port, for maximum power. At these engine speeds the pressure pulses are too slow, and actually reduce cilinder filling because the pulses are out of phase.
So it's either long or short inlet pipes. The lengths of the two inlet tracts are optimized for their respective rev bands. This means that the length is a compromise across the rev band rather than the exact optimum for a given number of revs.
Ideally the length should be varied continuously across the revs, but that is (was?) only done on racing engines. These were fitted with sliding intake trumpets operated by the accelerator.

As for the tuning possibilties, unless you change things like the camshaft timing, valve size and lift, etc, I wouldn't think that changing the 4960rpm to something else will help (much). I assume that the factory engineers figured out where the ideal cut-off point is. Then again, it may be a compromise between engine power, emissions, driveability, mpg etcetera. Which leads to the chip tuning issue, which I won't go into here.
 
J

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Discussion Starter #11
cheers El G

i actually understand what yer on about.

i didn't think it would make much differance.. just looknig for slightly better breathing top end.

so basically, replacing the airbox with the shorter pipe (at the stop of the thread) that would probably loose mid/low range torque and may aid top end breathing.

cool... i'll leave as is... for now... dun dun dun!!!! :D :D

rgrds

j
 
M

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Discussion Starter #12
I understood all that too !!!
Cheers el g, that's really quite interesting.

Hey J, we can astound mister T with our new knowledge of his engine.....

Marlon
 
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