i like gil it's a great product for the $ and price is not bad. my last set's lasted 12 yrs. or so. they also provide exel. performance. i have the dry-pipe's with muffler's, sounds great.

any updates to the 496 testing? would like to see how the cmi's compare to the dana's. Also, would like to see the results using cmi e-tops.

See post #1...It goes into comparision of the Dana's but not the new CMI's. I've come to the conclusion on any stock engine the results will be minimal.

"Results are in. I’ve finally completed some comprehensive dyno testing of a 496HO and various exhaust systems. It’s rather lengthy so I published it on our web site. Please check it out. I spent all the time and effort for you guys. Go to www.fullthrottlemarine.com and click on high performance projects.

Bob"

Here is a dyno test I did this summer. It is a prop shaft test on a stock 496 Mag HO and a second test after adding CMI sport tube headers. Disregard the A/F data, the wideband was not connected to the dyno during this test.

Bob

That is pretty impressive. I have to say, I was skeptical but now I am going to order a set...

Thanks BobL for the dyno info. I have been waiting to see some numbers that looked this good.

Bob, so am i understanding that the cmi's were essentially the same as the dana's performance wise?

Thanks for all the work and knowledge on the 496's!

I would say yes to that. Might be a couple of hp difference but you'd never notice it. So it comes down to cost, fitment and bling. Dana wins in the first 2 cases. But, you can't beat the looks of the CMIs. IMO

Dana recommends increasing fuel pressure on late model HO's to keep from going lean in the midrange when using their exhaust. Does this also apply to CMI's or other true headers?

Yes, whenever a true set of headers or header manifolds is installed on a 2004 or newer 496 MAG or HO engine the air fuel ratios should be rechecked if possible at full throttle, if not at least increase the fuel pressure about 3-4 lbs to help get the WOT fuel ratios closer in line.
Mercury used a different fuel program in the newer 496's since 2004 that was to help eliminate the "fat" rich condtion that appeared in earlier engines and caused a lot more transom soot and such.

Best Regards,
Ray @ Raylar

Thanks Ray! :ernaehrung004:

Any dyno tests with Imco Powerflow exhaust system for the 496HO? Had them on my 454mpi in my old boat and I loved the look and the sound. Considering upgrading my exhaust manifolds--DANA, CMI E tops, IMCO. Can't decide!!

The stock Merc exhaust is pretty decent on the 496's. I've not tested any other brands of exhaust but I'd be surprised if there was much improvement over the stock exhaust with turbulators removed. I've got a couple of 496 builds going on this winter if anybody wants me to test some other manifolds, I'd be glad to try them.

Different engine packages can use different header units
 

Imco's Powerflow manifold and riser combination with the seperate exhaust ports in the riser are a very good manifold design and should be similar in power to the Dana and CMI sporttubes in power levels. The problem with the Imco units is these 4 tube risers are quite a bit taller than the Dana, CMI or even Merc stock risers and may be a hatch clearance issue on a lot of boats, not to mention they are not yet set up for a kit that remounts the brackets, sensors, remote oil filter, ecm and such an an install would be a lot of custom fabrication and cost on a Merc 496 engine. Keep these issues in mind when converting the exhaust on a Merc or Volvo 496 in any boat.

Best Regards,
Ray @ Raylar

I believe Ray is refering to the IMCO powerflow plus exhaust. These and the Stainless marine Gen III manifolds seem to make excellent power from what I've seen. But like Ray said, they don't have a turn key kit to fit the 496. I was thinking along the lines of the regular powerflow, thumper, eddie mairne and stainless marine systems not being much of an improvementover the stock Merc 496 manifolds.

Sorry dont mean to hijack the thread , do you guys know if the intake and timing cover gaskets are reusable on the 496s ,and can the timing cover be removed with out dropping the oil pan?merc and gm manuals dont mention oil pan removall,
thanks and sorry about the questions,
seems you guys have knowledge on the 496s

I do know that the intake gasket is reusable but,I do not know if the timing cover is i would guess not.

Yes all those gaskets are reusable if you are careful during disasembly and yes the timing cover can be removed w/o dropping the oil pan.

Just read this whole thread and it was very interesting. Especially the part about the turbulators. My thoughts on this are I wonder if instead of removing them entirely, trim them down so that there is roughly 1/8"-1/4" of the "lip" left on them to capture any condensation that might form and still letting the exhaust flow better.

Seems reasonable, maybe I'll test it out. I'll be dynoing an engine next month with stock exhaust. Of course it's just a guess as to how much material you'd have to leave to be effective?? I've never had a problem with them removed, so you really wouldn't know if they were doing any good. I'm tearing down an engine that has about 400 hrs running without turbulators. I'll give it a close inspection for water damage.

Obviously the aftermarket headers don't have turbulators so what is used for protection or is it a non issue with anything else other than factory merc manifolds?

+1

I was kicking around the idea of CMI's (for the sound and bling as I don't really care about the extra 1-2 mph) but my mechanic recommended I leave it alone. The boat is kept on a lift and he felt the turbulators were a good thing.

Still trying to figure out how this would affect anything when it is stored on a lift. I remember you telling me this before.

I'm certainly no expert and he was talking over my head half the time, but the way he explained it was you're more likely to get condensation when the boat is stored on the water. The turbulators are there to collect and burn off condensation before it gets back into the motor....at least I think that's what he was telling me.

I am no expert either however this may be a case of overkill by Merc. I read somewhere that the turbulators only came into play when a boat was used at very cold temp such as just above freezing. This would make sence. Maybe someone has some more insite on this.

That's my understanding as well; if you only boat in warm weather it isn't an issue. In my case we actually do go out in cool weather sometimes, was in the high 30's to low 40's last Sunday when we got on the water.

What is a turulator??
 

No, thats correct, turbulators are there to collect condensation and burn it off when the engine is restarted.

A boat slipped or stored over water, especially around salt water where the condensation can build up and drip down onto the stock iron head valves and such that are steel and not stainless.

This type of condensation buildup can rust exhaust valves, intake valves, valve faces, valve seats and cylinder walls and quickly damage an engine with compression loss, sticking valves and such.

If your boat is a trailer queen that gets flushed after every use and is stored dry then the turbulators can usually go with no real problems from condensation.

Best Regards,
Ray @ Raylar

I have been reading this thread and the tubulator rings are located under the riser. you can remove the riser ,remove the rings and reinstall with new gaskets. This is similar to gutting a catalytic converter.

So do I really need them? I boat only during summer months...May thru Sep.....boat is stored on hoist.....inland fresh water. I have been debating the new CMI's but would I expect to possibly see some damage?

If it were my boat and it sat on a lift over the water for a few months or so, fresh or salt, and it had stock iron heads I would leave the turbulators in.
Get our Raylar aluminum heads with our special valves, seats and guides and you won't need turbulators at all!
You'll also have a lot more power!
Put CMI's on a Merc 496 with captains call, silent choice etc, or drop type s-tubes to clear intergrated transoms and I can just about guaranty stock iron head valve and cylinder water and rust damage.

Best Regards,
Ray @ Raylar

Thanks for your input Ray! You may have saved me a lot of trouble down the road....and a good down payment on a Raylar package if I still have this boat when the warranty runs out. :ernaehrung004:

I hope BOBL does take a set of turbulators and cuts them back and then dynos the motor. If shaving them back to roughly the half way point helps produce positive results and yet still provides some protection against condensation, this would be a nice solution. I guess we'll have to wait and see.