View Full Version : exhaust

01-01-2012, 11:04 PM
will 496 manifolds work on a 454

01-02-2012, 01:10 AM
I asked that question in a different thread a little while ago. I wanted to know if my 496HO manifolds would work on a 502. Apparently they will work on the 454/502, but I haven't confirmed it.

01-02-2012, 06:51 AM
Yes, they bolt right up.

01-02-2012, 07:23 PM
what is the advantage of the 496 stock exhaust over 454 exhaust

01-03-2012, 11:52 AM
Nothing...one just hates to buy a new set of manifolds if not necessary or they found a deal on XYZ and want to know the compatibility. 496's had a tendency to granade so many went to a 454/502 block and want to know what fits from the old engine, etc. I am not saying the 496 was/is a lemon but I have heard the 425hp version did not have the best reputation.

01-03-2012, 01:17 PM
my question is about the exhaust not motor are the 496 stock alum manifolds better than the cast 454 manifolds

01-03-2012, 03:24 PM
Other than being lighter I highly doubt it. The 496's were not much more powerfull than their 454/502 brothers so my guess is they are just lighter. If 50lbs or less is worth the price, go for it. I bought new GLM's for $305 delivered(pair) in October. Hard to justify 50lbs or less for that price.

With aftermarket...people believe what the manufacturers claim but many for some reason ;) don't see it on their GPS after they spent $3k. When searching for new manifolds for my 454 I found this to be 97% true unless running big hp.

Carl C
01-03-2012, 04:23 PM
They don't fit. I think it was all but two bolt holes line up. That's on a 502 based 525 EFI anyway. I found the post where I tried to bolt 496 HO headers to the 525 (502 CID). Four bolt holes on each side lined up and four did not. On headers you may be able to re-drill the flange. I don't think there is any way to do this with manifolds. Anyway, this was my experience.

Dr. David Fleming
01-05-2012, 01:58 PM

Cast iron exhaust was always nice because they seemed to not warp out of shape with heat. They are HEAVY - try lifting one. The corrosion issue is severe in marine exhaust especially with salt water. Most ocean craft end up junking the iron exhaust after a few years. Closed cooling was a blessing with iron engines on the ocean.

Seriously, I replaced my iron exhaust with stainless CMI headers - some serious weight savings here. My 22ZX seemed to float better. Big iron engine in back of the boat really puts her in the water.

Carl was talking about the 525 Merc Racing engines which I think used special aluminum heads with a different bolt pattern. Maybe someone here is a little more familiar with this change. So Big Block Chevy 454/502/525 may have two exhaust bolt patterns.

Carl C
01-05-2012, 03:37 PM
I did a little checking and I guess the 496 and 454/502 exhaust bolt pattern is the same. Apparently the bolt pattern is only different on the 502 based Merc HP525EFI. That's kind of weird but that's what I'm finding out.

Now, that said, my old 496 came with all aluminum exhaust and the ports were huge. Probably as big as you would need on anything except a high hp N/A engine that needs the scavenging of long tube headers.

Anyway, I stand corrected. It does seem that 496 exhaust will bolt right onto a 454/502.

01-05-2012, 06:44 PM
my motor is a 1979 454 420 hp how do you tell what gen it is ,also so the 496 stock exhaust would work and be alot lighter, im looking for a set of aluminum takeoffs

01-05-2012, 08:17 PM
525s have a slightly different pattern due to the Edelbrock aluminum heads. It's my understanding that the 496 exhaust will bolt up to a 454/502 but the holes have to opened up a bit, as the 496s use 8mm mounting bolts and the 454/502s use 3/8". They are also aluminum as stated so they are MUCH lighter than the cast iron exhaust.

Carl C
01-05-2012, 09:38 PM
There is a cast iron 496 exhaust too. Look for the aluminum one.

01-05-2012, 11:55 PM
I know from personal experience the aluminum 496 exhaust fits a Mark IV and a Gen V 454 perfectly. The benefits are, lighter than cast, built-in runners in the manifold, dry joint between the riser in the manifold and taller better flowing risers.

01-06-2012, 09:42 AM
Dauley, make sure you confirm which material you're getting. The aluminum manifolds were only made for a few years as Merc started getting complaints about them corroding prematurely. So even though you might come across a good deal, they might either have corrosion that you don't want, or they're the cast iron model. What I don't know is whether the cast iron model has the same exact internal casting.

01-06-2012, 09:53 AM
what years did they us aluminum
a 1979 motor 454 would be what gen?

Carl C
01-06-2012, 10:37 AM
'05 was aluminum.

01-06-2012, 11:07 AM
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Gen iv, no doubt. Mark iv if you like

01-06-2012, 03:42 PM
Mark IV (Gen IV) 1965 - 1991


01-06-2012, 03:50 PM
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that is a great guide explaining the differences.

Carl C
01-06-2012, 06:04 PM
Real good reading. I thought the 502 was a truck engine but it was an "over the counter only engine".

01-06-2012, 09:24 PM
Mark iv bbc has provition for machanical fuel pump. The mark v and vi are fuel injected motors, so blocks were cast without mounting for mech fuel pump. The mark v was available in lat 90, had one in a 454ss truck. I have modified as set of the 496 risers, if revertion is a concern with with a longer duration cam you can weld extentions on the inner and lengthen the outer and dump closer to transom or make them dry to the exit. Have also cut the 496 mounting flange off and welded a new merc mounting flange to mount on sbc manifold. The 496 manifold in aluminum would make a good performance option on a warmed over motor.

01-06-2012, 10:14 PM
I don't know what years were aluminum, but my 04 was/is.

....and I would say the 496 manifolds would flow way better than stock 454 cast iron ones. The 496 manifolds flow pretty good for stock. Just check the real world HP increases from Dana's or CMI's over stock 496's. Virtually nill. That's enough proof for me.