Re: 496HO - Best RPM for Max HP
 

Our Dyno runs on the stock 496HO motor on a merc ECM with no modification shows that peak horsepower develops at about 4900rpms and peak torque develops at 3900 rpms. Generally speaking the best overall speed with a 1.5 ratio in the average non-ventilated bottom boat will probably be had at about 5100 rpms which is just below the magic 5250 number in fresh water. This is however dependant on a lot of variables like x dimension, hull type, weight, prop type, prop tuning and trim condtion. I don't think their is one rule that works for all boats, experimentation is the only real answer. Just one little trick for some of you 496HO owners, remove your stock stainless risers off your merc manifolds and remove the restrictor plate. We have found that this is good for about 15 -20HP on the dyno. Might give most of you a mile an hour with the right prop work. Hope this info helps!
Ray @ Raylar

Re: 496HO - Best RPM for Max HP
 

Raylar, what hp were you seeing at the crank on the dyno? Thanks.

Re: 496HO - Best RPM for Max HP
 

Hey Ray: I'm intersted in your comment about removal of the restrictor plate. This year I removed the riser from the manifold on one side to make the removal of my exhaust diverter a little easier. I know there was a riser gasket that I replaced, but I don't recall seeing any type of "restrictor plate" that I could have removed. Was I in the right spot or is the plate to be found somewhere else? Interested in knowing as some extra hp might get me to a milestone. Thanks alot.

Re: 496HO - Best RPM for Max HP
 

We saw about 418 to 430HP on the dyno at the crank on the 496HO at between 4900 and 4950 corrected. the torque came in between 470 and 486 lb/ft. between 3800 to 3900 rpms corrected. This was run with 87 octane pump gas and with stock Merc 496 exhaust system. the motor would pull about 5200 rpm and hit the rev limiter about 5225rpm. Our best dyno runs with our BP103 kit ( heads, intake, and cam) came in at 533HP at 5000 rpms and the torque at 601 lb/ft at 4100 rpm corrected with the stock Merc ECM and 80 MM throttle body and a set of our Tri-Y stainless headers. The restrictor plates are found mostly on the 2001 and 2002 496's. I think they were designed as some sort of anti-reversion plate. they were in between two gaskets at the riser base to manifold and with openings tapered out towards the riser. On our first stock engine dyno pulls they were in and they killed about 15 -20 HP between 4500 and 5000 rpms. Mercury may have opted to delete these in later motors, I am not sure, but I have talked to several 496 owners who have found them installed. If you don't have them, all the better.

Re: 496HO - Best RPM for Max HP
 

Thanks for taking the time to respond and help us out Ray.

Re: 496HO - Best RPM for Max HP
 

i was running 28's and was consistently right under the rev limiters at 5100-5150, changed to 30's picked up a couple mph gps... and boat runs around 4850 now...engines seem to like being a little overpropped... my acceleration is better now and hole shot the same..
Don

Re: 496HO - Best RPM for Max HP
 

Is this nascar? I don't think that is really considered a restrictor plate. Yes it may reduce exhaust flow out the motor. However it should help keep that water from running back and sitting nice and warm next to your exhaust valve. The idea is to steam off any water that will get that far back into the exhaust, before it gets to the cylinder head. I would probably say for 15 hp this is not a good recommendation. However, If you are doing other upgrades to your 496ho not a bad idea. If you go that far though you might as well go for a good set of exhaust headers. (CMI,CMI,orCMI)

Re: 496HO - Best RPM for Max HP
 

Update, I hit 68.5 gps with 2 people with a 28 bravo @ 4600 On mullet this summer. Wasn't able to do it again, even alone. Put my 26 back on and ran 67 gps @ 5100.
I guess the 5100 is ok.
Smitty I'll have to wait until spring, I'm putting it away. I do think it will work.
I don't think worrying about reversion is worth 1 mph unless someone is sure it wont hurt, and how big of a job? John

Re: 496HO - Best RPM for Max HP
 

The thought was the the very light weight would put less burden on the motor and the 1.36 would get us up to higher speeds, no so as I found out. Would putting the 24P on get me to the same place while keeping the 1.36 or should I swap the gears and it that a big deal> thanks.

Re: 496HO - Best RPM for Max HP
 

The thought was that with the light weight less burden would be on the motor and the 1.36 would bring higher speeds, not true as I found out. Would using the 24P get me to the same place or should i switch the gears and is that a big deal?