Mid engine Alfa 156 - exhaust question.

Road-race engines and ancillaries - general discussion
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FERRARIST
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Mid engine Alfa 156 - exhaust question.

Post by FERRARIST »

Converting my Alfa 156 2.5V6 to mid engine project, cause i'm really tired with FWD......RWD car is what i love to drive when on track.......
Well it seems that moving engine rearwards is not too hard to do,following is more complicated.....BTW roll center is almost 50/50 as you can see below pictures, i'll be able to achieve balance between 50/50 and 40/60, no power steering, my goal is between 1100 - 1150kg......
My questions about exhaust is:
I plan to use my oem exhaust manifolds and headers(will cut and extend further where the lambda probe is - yellow line in the picture below), and because oem pipe is 55mm, i think that i may use let's say 60mm......
How long the exhaust pipe must be after the lambda probe? I don't want to extend the pipes more than necessary, my plan is to rise the central pipe, split it in two and exit it where white lights on the rear bonnet is?
Had 3.2GTA camshafts on, proper remap as well.......i don't care about the noise and heat......just want to do it as light and as engine safe as possible....
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WhizzMan
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Re: Mid engine Alfa 156 - exhaust question.

Post by WhizzMan »

It looks as if you are cutting in between the primary and secondary catalytic converters? You may want to convert to a custom setup with sports cats, since that will give you much more flow and you'll need to do a lot of manufacturing anyway. The ECU is usually using at least three O2 (lambda) probes on these engines two pre-cat and at least one behind the cat, to measure if the cats are still working. I think the 156 2.5 uses four in fact. Also, a 3.0 engine but at least the 3.0/3.2 inlet base plates and inlet pipes will give you a lot more power than the stock 2.5 ones. They are restricted so the 3.0 engine has significantly more power than the 2.5. With GTA cams and a custom exhaust with sports cats you should be looking at 220+bhp.

Nice project, keep the pictures and updates coming. :)
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FERRARIST
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Re: Mid engine Alfa 156 - exhaust question.

Post by FERRARIST »

WhizzMan wrote:It looks as if you are cutting in between the primary and secondary catalytic converters?
The ECU is usually using at least three O2 (lambda) probes on these engines two pre-cat and at least one behind the cat, to measure if the cats are still working.
Yes, i plan to cut just where oem lambda is, and weld bigger straight pipe to the end......ECU use only one O2, it's CF2 engine, GTA had 3 O2's......i don't want to use cats, i just need to know if 150cm straight(with two 90degree bends) 60mm pipe(or wider) will be OK?
FERRARIST
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Re: Mid engine Alfa 156 - exhaust question.

Post by FERRARIST »

WhizzMan wrote: Also, a 3.0 engine but at least the 3.0/3.2 inlet base plates and inlet pipes will give you a lot more power than the stock 2.5 ones
Forgot to mention that i'm also using 3.2GTA intake runners and plates......both cylinder heads ported intake and exhaust sides.....
WhizzMan
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Re: Mid engine Alfa 156 - exhaust question.

Post by WhizzMan »

Ah, only one probe an no cats in the exhaust headers. You'd benefit greatly from redoing the exhaust including the headers. The stock 2.5 exhaust and in fact, most of the Alfa V6 factory exhausts have a rather small primary diameter, primaries are too short, radius bends too tight and the merge collector is shaped very inefficient.

Be aware that cutting where you want to cut now, will mean that the exhaust is bolted "hard" onto the engine with no flexible bit in between to isolate the engine motions and vibrations from those of the exhaust system. This will usually give you cracked exhaust piping within a very short time frame.

If you plan to use the stock exhaust headers, 60mm ID would probably be okay since the flow restriction of the headers is very high an what you put after those, doesn't really matter a lot anymore in detail. Make sure you make the radius in those 60mm big enough, or the bend will still rob a lot of flow. If you really want to make sure you're okay, don't merge the two banks and use two 50mm pipes.

With no silencers, I doubt there will be a lot of tracks admitting you. If I were you, I'd investigate about a setup with custom headers with 39/40mm ID for the primaries, equal length piping for those with at least 60cm length, proper merge collectors into 2*50mm ID, then some full flow dampers and possibly have the exits of the 2 dampers merge into a single secondary full flow damper. make sure the secondaries and the primaries together are about 120cm long. You can look at setups with two dampers after all the merging, or one large damper with two inlets and two exits. These figures come from proper working setups and Jim Kartalamakis recommendations in his latest V6 book. Do not go larger in diameter with the primaries and secondaries or you'll lose velocity and that's a bad thing. These are rough length estimates and should be calculated precisely for your setup and depend on what merge collectors you are using and what routing you will choose. This is what I would be looking at myself and I know it won't be found for pocket change in your local Halfords bargain bin. However, a setup like this will give you a noise level that will probably be acceptable for most tracks and plenty of power, if executed correctly. There are some manufacturers that make headers for these engines that you could possibly use for the primary stage, but since your layout will require the rest to be custom built, I think you' be better of just getting a proper setup designed and built by someone that knows their stuff and can take your unique layout into account from the start of the design.
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FERRARIST
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Re: Mid engine Alfa 156 - exhaust question.

Post by FERRARIST »

WhizzMan wrote: Be aware that cutting where you want to cut now, will mean that the exhaust is bolted "hard" onto the engine with no flexible bit in between to isolate the engine motions and vibrations from those of the exhaust system. This will usually give you cracked exhaust piping within a very short time frame.
First of all thanks for your advices.....
I have already one 60mm flexible pipe in order to prevent problems described by you.....
WhizzMan wrote:If you plan to use the stock exhaust headers, 60mm ID would probably be okay since the flow restriction of the headers is very high an what you put after those, doesn't really matter a lot anymore in detail. Make sure you make the radius in those 60mm big enough, or the bend will still rob a lot of flow. If you really want to make sure you're okay, don't merge the two banks and use two 50mm pipes.
Sounds OK, but i guess both banks must be merged because the lambda must read from all 6 cylinders......anyway if not a problem to use 60mm "merge" pipe, to avoid restrictions i may use bigger as well, right......
WhizzMan wrote:With no silencers, I doubt there will be a lot of tracks admitting you.
What we had here to drive on, can hardly be called "a track"......We drive on Serres circuit as well and have no problem with them......and as you may hear from this year's event my car was noisy.....http://youtu.be/RH8qResYPR8 :)
WhizzMan wrote:If I were you, I'd investigate......
Don't get me wrong, and no offense to you, but......
- i can't invest in a project that was never done before with Alfa 156, have no idea if the whole conception work fine or not.....
- if this works OK, i dont plan to use only 2.5V6 - have 2.0TS engine and Fiat Coupe 20VT - all engines interchangeable on 156's - that's why i rather prefer to invest in suspension and slick tires(very hard to find proper ones here in Bulgaria) - i don't plan to use this car in Monza, Spa, SIlverstone or any other really fast track.....
- maybe silly excuse for someone, but some people here in my country must work at least half year, just to be able to pay for the price for the custom exhaust work that you describe above.....:).....i do this just for "very serious fun and hobby"......
As i said - no offense to you - we don't know about each other's situation and point of view.....i just ask for some advices......
WhizzMan
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Re: Mid engine Alfa 156 - exhaust question.

Post by WhizzMan »

Ah, this is in Bulgaria, that makes the "rules of engagement" quite different indeed. The fact that you spent money on GTA cams and chip tuning for just a few more BHP (GTA cams are hopelessly purpose made for a long stroke engine with way too small valves and cost hundreds) did lead me to believe you were willing to spend hundreds to gain just a small bit of power.

I think people have rear-engined several tipo-C based Alfa's before and the Alfa V6 is a popular donor for Lancia Stratos replica Kit cars. You may want to investigate there for more information on getting the engine to behave properly. Stephan from Squadra tuning has built a proper bi-motore 916 GTV. He uses the complete front suspension including engine mount points and top struts welded into the rear, with adjustable rods on the steering arms to control the toe-in. You could get a front end for a 145/146/155/916 to put in your rear. The 156/147/GT front end probably is too large on top with the dual wishbone configuration.

If you have budget for it, get a Q2 differential, you'll be getting lots more power on the road with that. Alternatively, get a 20VT setup, those have a visco and allow for way much more power than the 2.5 V6.
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FERRARIST
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Re: Mid engine Alfa 156 - exhaust question.

Post by FERRARIST »

WhizzMan wrote:Stephan from Squadra tuning has built a proper bi-motore 916 GTV.
I saw that project, but way too heavy car for a track use......anyway quite impressive....
WhizzMan wrote: He uses the complete front suspension including engine mount points and top struts welded into the rear, with adjustable rods on the steering arms to control the toe-in. You could get a front end for a 145/146/155/916 to put in your rear. The 156/147/GT front end probably is too large on top with the dual wishbone configuration.
I did the same, using entire front frame from Alfa 155, with subframe and wishbone setup, however i'll made 2 custom wishbones in near future, custom rods for adjusting rear tracking waits the rose joints ordered from McGillmotorsport......156/147/GT front is way too heavy, double wishbone setup is useless because rear wheels wont steer.....
WhizzMan wrote:If you have budget for it, get a Q2 differential, you'll be getting lots more power on the road with that. Alternatively, get a 20VT setup, those have a visco and allow for way much more power than the 2.5 V6.
Yes, looking for used but in good shape Q2 locally, and if unable to find will buy either new Quaife or Q2......
Thanks....
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