2.5 vs. 3.0 exhaust manifold ?

[brookstroutr]

I've got a 3.0l Verde to go into my '84 GTV6 and wanted to know if the exhaust manifolds were different on the 3.0 vs. the 2.5 motors.

[Grant]

Yes!

3.0 manifolds are significantly larger inside. Verified this myself.

[Gabor K.]

Have not noticed any difference regarding pipe difference between the 75 3L manifold and GTV6 2.5 manifolds. The part numbers are different so there may be some minute differences, however the copper gaskets of inlet and outlet of the manifold have the same number for 2.5 and 3L. So there cant be much difference concerning exhaust flow between them.
If you are interested in improving engine breathing, and there is a lot of potential, you should consider using the CSC headers instead and bin the ineffective and heavy original parts.

[Grant]

I think it might come down to Alfa making a running change for the later 3 liter car then.

If you had the two manifolds side-by-side, you would surely agree with me. The gaskets are the same, but from then on the 3 liter manifold is much larger inside.

It could be that many 3 liters were shipped with 2.5 liter manifolds, furthering the myth that they are the same pieces. For my Verde and my Platinum, they are very different.

[La Voce]

I can confirm they are different, either will mount up to the manifold, but the difference (besides the part number) is the the bore, it's a few mms bigger in the 3 Liter.

[Potenziato]

I think that since the 3.0L manifolds are thinner, they crack easier. The Verde owner's probably replaced them with 2.5 manifolds since the availability of 3.0 ones is getting scarce.

My 1987 early Verde has the bigger 3.0 manifolds. I think it's a myth that any 3.0 came from the factory with 2.5 manifolds. The majority of cars in the USA seems to be from the 1988 model year.

[Gabor K.]

When I compared is the 3L 75 with the GTV6 manifold at the time I installed the 3L in my car. I could´nt see any difference worth mentioning.
However in the parts list there are mentioned different manifolds for GTV6 2.5, 75 2.5, Europe 75 3.0 and US 3.0 so of course if you see difference over there, you had different headers for the 3L.

On the other hand, as I mentioned , there are a lot better solutions than the original header to get today, so by changing to a CSC header you can potentially gain a 15-18 Hp. On the condition that the rest of the exhaust system is upgraded also.

[brookstroutr]

I thought I'd read some earlier posts about the 3.0l being slightly larger. I may be in the market for some when I put in my 3.0l motor. I'm doing the 'S' cams & pistons with some head work. I do not know if I want to go the CSC header route even though I've done the Ansa center and rear muffler sections. The cat is also 'hawged out' which made a huge improvement.

[Giorgio68]

Quote:

Originally Posted by brookstroutr I thought I'd read some earlier posts about the 3.0l being slightly larger. I may be in the market for some when I put in my 3.0l motor. I'm doing the 'S' cams & pistons with some head work. I do not know if I want to go the CSC header route even though I've done the Ansa center and rear muffler sections. The cat is also 'hawged out' which made a huge improvement.

[brookstroutr]

I've been in Fl for almost 2 years waiting for my house in AZ to sell which is finally going. Fl doesn't have emissions. It had passed AZ emissions, but when I got the exhaust off for inspection, I noticed the guts were clogged so I gutted the cat. Huge difference. The old ceramic cats just down right suck - POS's. I'd never use an OEM from that era. I installed free flow performance cats on the Biturbo and Euro M635CSi and they zoomed through the tough Maricopa County, AZ emissions - same as SoCal.

Cost was way cheaper and better. The BMW OEM cat is 27#s heavier, more restrictive, more heat retention, less efficient and $1200 USD vs. about $250 installed. Not stupid here. The Maser's was 3" id vs. 3.5 id and $190 installed vs. $600 for the OEM cat. Both cars have the flange connection for future R & R'ing at about $100 USD. Oh yeh, mpg increases somewhat unles you like the power increase too much.

The other reason I'll probably go with the stock 3.0l manifolds is to maintain the low-midrange torque. I street/track my cars but do not bounce off the redline as they're off their power band unless you're making a race engine.

Cheers.

[Giorgio68]

Brookstroutr,

Do you have any information where to buy that free flow cat?

Giorgio

[brookstroutr]

Giorgio,

Sorry I missed your post. Almost any decent muffler shop can set you up for the swap. As these exhausts have the OEM cat welded, I preferred to have the shop install appropriate flanges before and after the free flow cat. Thereby, allowing me to do an easy replacement and/or track pipe swap. I've used Magnaflow and Dynamax on my cars which are good and easy to locate. The stock cats are now about $450 USD and is still the same crap cats of yarn...