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Discussion Starter #1
Hi All,

I am seriously considering replacing my Precats with some Wizard Decat manifolds. At the moment funds are a bit tight but as the GT is currently in pieces getting the clutch replaced, I am tempted to just swap the manifolds over while I am in there.

I expect the manifolds would give an improvement in Power and responce but what else? Is improved reliability from lower engine bay temperatures guaranteed? Could I expect to see an improvement in MPG at all?

As funds are tight (I live in Aberdeen in the middle of an oil price crisis!), Could I realistically make any money on the old Precats? Would there be any demand from hardup alfa owners for a good 2nd hand set of Pre-cats? I am quite surprised by the condition of my cats, they don't look 80k miles old.

Any and all opinions valued.
Thanks,
 

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On the temperature side - a sheet of heat barrier over the top of the rear manifolds will stop most of it. Not tin foil, the decent multilayer reflective stuff. I'm not entirely convinced that cooking the ECU is the cause of the ECU problems - it is attached to a damn great heatsink with cooling air flowing through it when the engine is on. IMO most of the radiated heat is from the first 2 inches of the manifold, which is exposed - the cat is right at the bottom of the pipe. Don't know if anyone has put a sensor on the ECU for "before and after". If my cats melted and I needed to replace them, I'd de-cat. I wouldn't bother if everything was working.

Apparently it is a bit louder and a bit quicker - but you'll need someone who has done it to comment.
 

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If your are on the budget it would make more sense to buy some second hand from 2.5 156 CF2 or 3.0 GTV CF2, but in that case you will also need different downpipes. Wizard is straight fit of course and it already has lambda bosses welded in. I welded lambda bosses on the downpipes and it works just as good (lambda wires are long enough). I also used lambda extenders/fakers on the secondary lambdas (which are behind the cats) to avoid any dashboard errors. It works flawlessly ever since.
 

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my mine gripe with the removal of the pre cats is the sound change. You loose the lovely deep growl and gain a slightly tinny rasp.

I much prefer the sound with them in place. But can see why you would remove.
 

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I have done it, i like the cf2 route. if i had more money at the time i would have looked at doing the wizard manifolds.
I do like the oe setup though for the noise with std exhaust as the exhaust has a nice burble and growl. I have lost this now, but it sounds much better if pressing on. Yes there is a little rasp, but i like it.
 

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Don't forget the issues surrounding oil filter access with the cf2 manifolds. Its hard enough with the standard manifolds. If I was going down the catless route it would be the wizard manifolds. Besides if they are made to the same standard as the exhausts they must look fantastic!
 
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On the temperature side - it is attached to a damn great heatsink with cooling air flowing through it when the engine is on.

Apparently it is a bit louder and a bit quicker - but you'll need someone who has done it to comment.
I think the issue is massive under bonnet temps when you stop, no cool air warm air rising etc.. and the inlet manifold gets hot too even when supplying cold air..

I went the CF2 route with a wizard exhaust and it sounds ace.. but i modded the cf2 to meet the standard front pipes... then pud released his manifolds.. will swap the manifolds again at some point
 

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I did mine on my GTV 3.2 . Best to combine with a remap as you can run a bit leaner with the cf2's and add a few more BHP.
 

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My wizard manifolds are waiting to be fitted at Autolusso b'mouth. Will post when I get my beast back. First top end rebuild, clutch, queef, cam belt, air hose, lower wishbones, powerflex uppers, radiator. Only had her 1m before problem s 'appeared'.
 

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I was seriously worried about the temperature around the ecu (my loom's a bit crispy!) so I ordered some Wizard manifolds from Dan, and they're great :) I was going to do a thread showing everything in place, but I've run out of time to do the car so it may have to wait for a few months...

Assuming your downpipes are serviceable, the extra couple of hundred spent on the new manifolds is money well spent - no need to muck around with oil cooler pipe or exhaust routing, the lambda sensors just screw back in, and best of all you can fit them with the gearbox in place. Oh, and they look rather nice :thumbup:
 

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I'm looking to get the wizard manifolds soon, next month or so. Will be fitted when I have the cam belt done in the summer.
If I put these in but keep the main centre cats, will I still get the raspy noise??? I'm not a fan of rasp, just sounds like a clapped out corsa! Currently got main Decat and there is a bit of rasp. Have a Supersprint system fitted too
 

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If I put these in but keep the main centre cats, will I still get the raspy noise???
I've not fitted Wizard manifolds to a car with a Supersprint system before. However I did fit a set to a car with a Ragazzon cat-back, and it did increase the raspiness of the exhaust sound. However, it didn't increase it by as much as fitting CF2 manifolds and stainless steel downpipes would have done. CF2s & stainless downpipes from any manufacturer gives additional rasp to any exhaust, more so than Wizard manifolds and the original steel downpipes.
 

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It is fairly easy to eliminate the rasp. OEM V6 exhaust systems with CF2 manifolds, had an additional silencer right after the main cat (it looks like one big silencer), so in total the car had three silencers. So when I made CF2 conversion on my 3.2, I used OEM cat (from 166 3.0 CF2), and I have no rasp whatsoever. CF3 system has 4 cats and they are therefore enough to eliminate the raspy metallic sound.

Here is the photo of 166 CF2 exhaust system:
 

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I've not fitted Wizard manifolds to a car with a Supersprint system before. However I did fit a set to a car with a Ragazzon cat-back, and it did increase the raspiness of the exhaust sound. However, it didn't increase it by as much as fitting CF2 manifolds and stainless steel downpipes would have done. CF2s & stainless downpipes from any manufacturer gives additional rasp to any exhaust, more so than Wizard manifolds and the original steel downpipes.
I've got scorpion SS down pipes too, the originals crumbled away! ?
 

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If you want better manifolds while keeping your growl I think the SuperSprint ones fit the bill don't they. Their system is the growliest I've heard. If I could afford it I would put the full SS system on with the powerloop back box - sounds amazing
 

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It is fairly easy to eliminate the rasp. OEM V6 exhaust systems with CF2 manifolds, had an additional silencer right after the main cat (it looks like one big silencer), so in total the car had three silencers. So when I made CF2 conversion on my 3.2, I used OEM cat (from 166 3.0 CF2), and I have no rasp whatsoever. CF3 system has 4 cats and they are therefore enough to eliminate the raspy metallic sound.

Here is the photo of 166 CF2 exhaust system:
Mmm, that's a good idea, when my GTA exhaust falls to bits (I seem to end up replacing my exhaust system at least once a year whatever I drive) I might have to see if I can get a custom one made with an extra silencer after the cats (if there's room).

And back to the OP's questions - I've been told the original manifolds are quite hard to shift so don't expect to make much back on them through Ebay. Also I wouldn't expect much in the way of a MPG boost (probably even with a remap); after all even a 10% improvement on b*gger all is still b*gger all ;) But long-term reliability should be improved, esp if the manifolds are heat wrapped or expensively ceramic coated, and I'd have thought a remap would release a few more bhp, presumably quite a bit more if combined with a bigger throttle body / plenum work to improve breathing throughout.
 

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If you want better manifolds while keeping your growl I think the SuperSprint ones fit the bill don't they. Their system is the growliest I've heard. If I could afford it I would put the full SS system on with the powerloop back box - sounds amazing
The SS ones require a mortgage to buy so won't be going down their route. I've the powerloop fitted with unsilenced centre, and yeah it's very growley.

Wondering if, Decat manifolds, standard main cats, silenced centre and powerloop will eliminate rasp. I do t mind a little bit of rasp, but not a lot...

Heat wrap is the way to go, I seen a comparison between wrap and ceramic coating, the ceramic was only margainly better. Literally 3 degrees in engine bay temps...
(Zircotec - Plasma sprayed ceramic thermal coatings)
 
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Discussion Starter #18
Thanks everyone. Very helpfull replies. Today I unbolted the old rear bank manifold, what a horrific job, the designer clearly hated mechanics! I will make the decision to replace once I have managed to get it out of the engine bay and had a good look at the old one, but it isn't easy.
 
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Thanks everyone. Very helpfull replies. Today I unbolted the old rear bank manifold, what a horrific job, the designer clearly hated mechanics! I will make the decision to replace once I have managed to get it out of the engine bay and had a good look at the old one, but it isn't easy.
It's a much bigger job getting it out than unbolting it; you'll definitely need to drop the subframe for a start. I had the gearbox off so mine slid out sideways, but maybe you'd be able to get it out by unbolting the engine mounts and either dropping the engine a bit or moving it forward.

The decat ones just slide easily in and out though (at least with the subframe off) - my box is back in and I did a trial fitting of mine before taking them out to reshape the heat shields to fit.

Here's what they look like with the original heatshields slightly reshaped to fit. Shiny :thumbup:
 

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Thanks mj2k. Very helpfull.

Yes, despite the manifold being unbolted, there is almost no movement at all. I just managed to lift it up enough to get a socket/wrench onto the the rear engine mount upper bolt and out.

Once the gearbox is off I should be able to swing the engine forward enough to get it out. I am hoping to find they are cracked as i have always had a ticking that quetens down quickly and the engine bay always smells hot.
 
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