496HO detonating at high revs after fitting Dana exhaust
01-08-2012, 06:17 PM
#11
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Then you have experienced what most others experience, no gain. The original exhaust flows pretty good, especially for a stock motor. Too much advertising in the claims of mph gain. When BT says that a pair of CMIs on a 496HO will give you 3-5 mph, I don't know where he gets that from, never seen it myself.
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01-08-2012, 06:49 PM
#12
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[QUOTE=Cartscarts;3588694]It seems the guy who fitted the headers did not open the water taps and the engine was getting hot. Opend the taps and changed plugs and all running ok.
I'm not sure what water taps are, but if you are referring to the home-depot style water shut off valves supplied with the Dana's they are supposed to be closed and not open.
I called bob at Dana specifically to ask this verification question when I installed mine last year. He said he did not have the time to tell me the ins and outs of the Dana exhaust, just leave them closed. He also told me all of that should be in the instructions, after telling me call with any questions.
Love the Dana's, but that dude's a Dcik.
I'm not sure what water taps are, but if you are referring to the home-depot style water shut off valves supplied with the Dana's they are supposed to be closed and not open.
I called bob at Dana specifically to ask this verification question when I installed mine last year. He said he did not have the time to tell me the ins and outs of the Dana exhaust, just leave them closed. He also told me all of that should be in the instructions, after telling me call with any questions.
Love the Dana's, but that dude's a Dcik.
01-08-2012, 10:04 PM
#13
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Cartscarts:
I would say something is still wrong with that 496HO equipped with its Dana Header exhaust as the engine should pull to 5000rpms or so if the set up and prop are correct and the engine is really getting the fuel it needs and running correctly. That 300 or so rpm he is loosing is definiltely costing 2-3mph.
Best Regards
Ray @ Raylar
I would say something is still wrong with that 496HO equipped with its Dana Header exhaust as the engine should pull to 5000rpms or so if the set up and prop are correct and the engine is really getting the fuel it needs and running correctly. That 300 or so rpm he is loosing is definiltely costing 2-3mph.
Best Regards
Ray @ Raylar
01-08-2012, 10:28 PM
#14
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fixx
1) make sure the exhaust ports on the danas line up with the exhaust ports on the cylinder head..
2) The engine wont rev to wot if your injesting water (reversion)
saw this last year, check your plugs b4 you start it...
2) The engine wont rev to wot if your injesting water (reversion)
saw this last year, check your plugs b4 you start it...
01-10-2012, 10:33 AM
#15
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Never seen any good come out of changing out the stock exhaust on any 496HO I know of but have seen them cost the owners a new engine before due to reversion. Claims of gains on a stock HO are nothing more then a gimmick to sell product.
01-10-2012, 11:26 PM
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Fact or Opinion?
ZP'd:
I respectfully have to totally disagree with you on exhaust headers for Merc 496 engines. I have done direct tests on many headers in a controlled test basis ( on dyno and in boat)of unbolting stock Merc 496 exhaust manifolds and bolting on certain brands of marine aftermarket (true) headers and I can assure you tha some make more power than the stock manifolds, in some cases as much as 35-45 HP more!
Will this kind of power increase always translate to more speed in any given boat, hell no! some boats need nearly 20Hp to gain 1 mile per hour of speed and without proper setup, prop rework and driver training (trimming) the results will sometimes seem almost negligible.
As for the so called reversion issue from headers, you will usally see that exhaust water backup into a marine engine is more from poor exhaust routing out of the header, around captains call and silent choice switchable systems, sharp S-tube bends and tip design and lengths as well as exhaust outlet drop heights, than it is from the header itself.
Camshaft changes coupled with header installations can sometimes be the real reversion culprit and not the header installed.
You hopefully as an expierenced header user will have a lot of factual basis for your statement and not just parroting what you read in internet posts of other users, or dockside ramblings of a few so called marine header experts.
Lets all be careful to say on OSO what we KNOW and not so much what we HEAR?
Best Regards,
Ray @ Raylar
I respectfully have to totally disagree with you on exhaust headers for Merc 496 engines. I have done direct tests on many headers in a controlled test basis ( on dyno and in boat)of unbolting stock Merc 496 exhaust manifolds and bolting on certain brands of marine aftermarket (true) headers and I can assure you tha some make more power than the stock manifolds, in some cases as much as 35-45 HP more!
Will this kind of power increase always translate to more speed in any given boat, hell no! some boats need nearly 20Hp to gain 1 mile per hour of speed and without proper setup, prop rework and driver training (trimming) the results will sometimes seem almost negligible.
As for the so called reversion issue from headers, you will usally see that exhaust water backup into a marine engine is more from poor exhaust routing out of the header, around captains call and silent choice switchable systems, sharp S-tube bends and tip design and lengths as well as exhaust outlet drop heights, than it is from the header itself.
Camshaft changes coupled with header installations can sometimes be the real reversion culprit and not the header installed.
You hopefully as an expierenced header user will have a lot of factual basis for your statement and not just parroting what you read in internet posts of other users, or dockside ramblings of a few so called marine header experts.
Lets all be careful to say on OSO what we KNOW and not so much what we HEAR?
Best Regards,
Ray @ Raylar
Last edited by Raylar; 01-10-2012 at 11:36 PM.
