Cf3 precat delete - Alfa Romeo Forum
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(Post Link) post #1 of 11 Old 24-07-16 Thread Starter
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Cf3 precat delete

Sorry for asking this I'm sure similar questions have been asked dozens of times, but there has been some very helpful people on this forum for me so far.
The current spec of my 03 156 is as follows.
1.6 ts with air box resonator deleted and v6 intake pipe fitted, bmc filter in the standard air filter housing, 2.0 ts throttle body, 2.0 ts cam shafts, ragazzon exhaust from the cat back with small ragazzon middle box and ragazzon back box alfisti edition.
The car drives, pulls and sounds great for a 1.6ts but the next step I want to take is removing the precats.
This is where I have a few questions.
I read that one option is to modify a cf2 down pipe to suit the lambdas etc.
But I was thinking about either cutting out the precats and welding in 2 pieces of pipe in their place
Cutting open the tops of the precats, remove each cat and then welding them back closed leaving 2 empty chambers and an original look.
Would 2 empty cat chambers have less performance gain than welding in 2 pipes? Or would both options give identical results?
With the precats removed, will the car get louder than it currently is?
How will the precat delete effect emissions results when it comes to getting the car tested?

That is all my questions for the moment
The sooner I get this done then the sooner I can maybe get the car mapped.
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Easier Idea. source the manifold off a CF2 156 and weld in a replacement Lambda Boss.

Don't hollow out the cats, you will really screw up the pressure/turbulance in the system.
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Don't hollow out the cats, you will really screw up the pressure/turbulance in the system.[/QUOTE]

That is very interesting. So would the pressure/turbulence be affected if the centre section cats were removed/hollowed out? I understand how removing the precats could cause an issue - but what if the centre ones were hollowed out - rather than fit a decat straight pipe? Just curious. Would that affect the pressure?

What is the advantage of fitting a staight decat pipe over merely removing the cats from the existing pipe? Sorry if I am getting this totally wrong!
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(Post Link) post #4 of 11 Old 25-07-16 Thread Starter
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So I may go in search of a cf2, thanks.
How about noise? Will it change?
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Cut the cats out, weld in tube. Don't bash the innards out of the cat (as Ransoman said) because it leaves a big empty expansion chamber for the exhaust gas to flow into, it will lose energy here and have to be pushed out by the crankshaft.
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(Post Link) post #6 of 11 Old 25-07-16 Thread Starter
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Thats what I would have thought but I was just making sure.
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Wow that's a lot of effort on a 1.6, what kind of bhp is it pushing out with those mods? Will you remap after decat Ting?
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(Post Link) post #8 of 11 Old 26-07-16 Thread Starter
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Its not that much effort really though.
I wanted a 1.8 or 2.0 but the right one never came up for sale here in Ireland after a very long search.
The cam shafts were the biggest pain but myself and a friend managed it in an evening.
As for power increase.... I haven't a clue on numbers but its nippy for a 1.6.
Its a shade quicker than a 140 tdi passat if thats any comparison.
I plan to have a rolling road map done when I get the precats deleted.
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Yup, been there done that with the cats. My hands were bloody stumps for days after. Car sounded tinny and lacked poke. Had more poke with!!!
I struck lucky and got an already modded cf2 manifold. Took a few days for the ecu realised something had changed, then it started to improve. Then got better and better.
Centre decat makes life even more silly, but also not tree friendly.
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With the mods it should push over 140hp with a remap inc the decat delete.

Get a lightened crank pulley and it'll see over the 140hp easy. It'll still be a revvy little thing. But torque on the 1.6 is the issue. The shortercrank of the 1.6 hahampers it. The 1.8 is the better ts all round I reckon. Having all three of the ts displacements.

But the 1.6 gearbox is short. Which is why you bounce the thing above the red easily. Also the 1.6 has no varible intake manifold. Which does make a difference.

The 1.6 should easily rev past 8k in balance. But the weak thing here and the limit is the hydraulic tappets. You get valve float. Do although the 1.6 feels like it could spin forever the valves won't. Then to take advantage of those revs you'd need a wilder cam. Then you keep hitting safe ceilings and theres only so much you can get from a 1.6.

Its a good engine in standard trim the ts and nicely tuned. But you can get into mega money trying to achieve numbers yhe bigger engines just do with ease.
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(Post Link) post #11 of 11 Old 06-08-16 Thread Starter
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Where would I get a lighter crank pulley?
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