Alfa Romeo Forums banner

1 - 9 of 9 Posts

·
Registered
Joined
·
4,501 Posts
Discussion Starter #1 (Edited)
The 3.45 litre will be due for a new cat here soon. I would like to go with some Euro/low-restriction/high-flow-whatever cat (already have the Remus at the rear and the performance of the standard stainless steel 164 24 valve header up front can not be improved upon in much of a measurable fashion...)

Any suggestions?

By the way, visually mine is due for replacement (it has a hole burned right through the core), but that aside - don't discount the value (or should I say the necessity of replacement as a wearable maintenance part!) We had a big-bore 147 burn two pistons before we figured out that it was a blocked cat causing it!
 

·
Registered
Joined
·
6,087 Posts
JJ,
Low restriction/hi-flow simply means that the cat is large enough so that the spent gases don't choke the exhaust process. Reputable manufacturers use good (and pretty much the same) materials. Hence, the real question is size and shape. With your engines, the flow of spent gases has to be considerably more than the typical V6 Alfa engine, so ideally you need an exhaust system that is larger in diameter than stock, and the cat that fits the larger diameter piping would also be larger than stock.

I don't know if you have done any formal testing, but I would venture an educated guess that you would ideally want and exhaust that is larger than stock by 1/4" to 1/2" in diameter... I'm not sure what you have now, or if the diameter you are using is the same as the OEM diameter, but one thing you could do is look at the size that other marques, with similar engine outputs are using... I would use that size cat, and then double check the shape to make sure it fits properly.

One last thing - I wouldn't place much weight on quality of a cat based on price. If you cut open a cat that is not too expensive (such as one from Magnaflow) and compare it to another pricey unit, you will wonder why there is such a big difference in the price... and realize that it hasn't much to do with the cat's quality or performance...

Best regards,
 

·
Registered
Joined
·
4,501 Posts
Discussion Starter #3
Thanks - yeah - I dunno...

Long conversation here about air velocity and port sizes on the 24 valve motors that are already too large for the 3.0 (Alfa kept valve sizes and port sizes exactly the same on the 3.2 GTA because they found that the ports were too big to begin with...)

We make horsepower by putting 2.5 litre 24 valve heads (with 3.0 valves and MILD porting of the 2.5 sizes) on 3.2 engines!

Point is too much port there to begin with, what's a bigger exhaust path on rearward going to do for you!? It's only with our 3.45 litre 24 valve motors that we start mild porting and on a 3.7 that we go any bigger really and even then, we use a stock 24 valve header on the transverse-mounted applications (164/156/166/147...!)

Good thoughts on the cats though!

Jason, what do you have? Jason - anybody? Hello? Earth to Jason... :D
 

·
Registered
Joined
·
460 Posts
How about getting to rebuilt? There are several of this list who have had their cats rebuilt and re-certified for reasonable expense.
 

·
Registered
Joined
·
54 Posts
hmm exhaust size. Well first off I would say just throw a test pipe in there to get rid of your poor blown cat. Use it while you're doing all the tuning. Then I would look into some serious exhaust changes.

I did not get a good look at your remus exhaust and such but take for example my fiat spider. 1.8 liters using a 2.5" mandrel bent exhaust. When I first built the exhaust I suspected it would be too big but since I might turbo it later it might work out well. After building the system, and talking to the guys at burns stainless, 2.5 was the perfect size for my high revving engine, they said I could even go to 3" for a little more hp and a little loss of torque. This nearly blew me away since the original exhaust had a 1.53" ID. Cross sectional area of a 2.5" vs 1.53" is 4.9in^sq vs 1.84in^sq!

So now, considering your 3.45 liters are almost double the size of my fiat engine, I would think 3" or 2 pipes with at least the same about of cross sectional area will be needed. Also that 3.45 should be revving pretty well, just another factor to consider.

I don't think, however, that your primary runner sizes will have to be changed like you said. The stock 24v header system works well. I think the most benefit to be gained is in a tuned collector for the 2 secondaries into 1 and out into the rest of a larger exhaust. Beyond that you will be looking into completely customized headers, but the cost/benefit ratio is high.

Oh and if you think the remus sounds good.. just wait till you have a straight through custom exhaust. The Fiat sounds like no other Fiat I've heard before. Quiet when you want it to be, non-droning, and loud as hell when you get on it. First exhaust that overcomes the intake noise. lol

Hope this helps... you spend your money. :p
 

·
Supporting Vendor
Joined
·
4,423 Posts
Low restriction/hi-flow simply means that the cat is large enough so that the spent gases don't choke the exhaust process. Reputable manufacturers use good (and pretty much the same) materials.
Enrique,

While that used to be true, I'm not sure it is anymore.

The really high $$ cats these days have a metal matrix core, which supposedly flows much better than even the best high-flow ceramic matrix core cats. These have only come to market in the last few years, and are quite expensive.

The reason you want a small cat that flows well is a large one can really eat up your ground clearance.

I have had good luck with Random Technologies cats...

http://www.randomtechnology.com/index.html

Joe
 

·
Registered
Joined
·
5,459 Posts
Joe,

Which model do you use? Is it universal? I see no section for Alfa romeo...oh well...
 

·
Registered
Joined
·
133 Posts
random

What you should know is that Random does a good job at marketing but they are not a manufacturer; they simply purchase aftermarket converters and resell them. This includes the relatively new metallic substrate models with 200 and 300 cells per square inch cell densities and 2 mil foil thickness.

Look up converter manufacturer's websites and you will find what you need at fair prices.

:)
 
1 - 9 of 9 Posts
Top