For those that are curious as to where to measure here is a visual to help you.. :) Jamie / Lakeside

Keep in mind I believe you will need 1.25 to 1.5" more width than your existing manifolds (not risers). If it close the inner manifolds can be shaved a little over 1/8th but not quite 1/4".. Please take in to consideration the center lift if your boat is equipped.. :)

91 or 93 premium? 87 or 89 octane going to be a little less HP gain?

Actually unless they have changed things, Or my memory is lax, it should not make much of any difference. Lower octane fuel burns faster thus the knocking in higher compression engines. The higher octane burns slightly slower & a bit more controlled whick is what aids it in reducing knocking & heat.. ;) Jamie

True Tubular Style Header System from Lightning & Hardin Marine
 

All true high performance applications wether its Mercury, Ilmor, Chief, or Teague for example; ALL use a true tubular style header for maximum performance. That is why at CP Performance we offer 496 headers from Lightning and Hardin Marine.

VISIT THIS POST FOR OSO DISCOUNT PRICE

Will the Lightning headers work with Corsa diverters?

thanks bill.

That's right, you did ask the same question on their other post. Now if we could get them to answer that and what their performance gains were so we could compare them with these others.

Seems that no one has done as much research in to this as Dana has though.

Without the baseline dyno figures, the dyno sheets with the headers don't mean a whole lot. For instance, what was the air-fuel ratio on the stock engine compared to the one with the headers and pressure regulator? What were the horsepower gains, if any, at various rpm's? What happens when mufflers are added? What happens when the test is run with a wet exhaust?

Now if you want to buy headers for the bling factor, then no doubt you should do it. There is probably nothing more impressive to add to an engine. If you have an engine with a high overlap cam, and dry exhaust, then you should have them. With a stock engine, with a low overlap cam, wet exhaust, and perhaps muffers, I haven't seen any real supporting data for $3K to $4K headers. I need to see a few tests (for repeatability) at baseline, and with headers added.

Michael

496 exhaust testing
 

I thought i would chime in here because we at Raylar ran all the Dana Exhaust dyno tests and I can assure you we tested both the 496mag and the 496Ho engines for baseline output before we installed the Dana header manifold system on the motors. In both cases the stock untouched motors made within about 5-10 horsepower of their Mercury ratings. after the Dana sytem was installed the engines made between 42 and 48HP more than the baseline tests with a significant increase in torque numbers, also as expected.
Its important to realize that even though the dyno sheets show we were using premium 91 octane fuel the specific gravity measurments of the fuel being used indicated it was closer to 89 octane in reality. why, I am not sure, but our highly oxygenated (alcohol laced) fuel here in Southern California tends to be that way. Its also important to remember that HIGHER OCTANE FUEL DOES NOT MAKE MORE HORSEPOWER! It is simply used to control possible knock in higher performance engines.
If a given engine has higher compression and aggressive timing it may need a higher octane fuel to prevent knock and engine damage from knock. Its the higher compression and timing that add the power not the fuels octane. 496's with their moderate compression ratios and the conservative timing in the Mercury ECM, most fuels of 87octane seem to be adequate to prevent knock, even with our 525HP kits and good exhausts.
Hope this information clarifies a few questions here.

Regards,
Ray @ Raylar

[QUOTE=Michael1;2042673]Without the baseline dyno figures, the dyno sheets with the headers don't mean a whole lot. For instance, what was the air-fuel ratio on the stock engine compared to the one with the headers and pressure regulator? What were the horsepower gains, if any, at various rpm's? What happens when mufflers are added? What happens when the test is run with a wet exhaust?

To re-clarify, the dyno sheets do NOT reflect the engine with the pressure regulator installed, thus the high exhaust temperatures. The air/fuel ratio stock vs. after exhaust install is irrelevant. The bottom line is, look at the dyno sheets, the 496 HO got lean with the exhaust added. Something has to be done to correct that. I think it would be agreed by many, that there is no way Mercury sends their engines down the road with 14.00 air/fuel #'s. The dyno sheet reflects the engine with NO fuel modifications.

The engines do not make near the horsepower or torque stock as they do once our exhaust is installed. As backed up by a non-biased opinion, our systems really work.

Adding mufflers or water would affect the outcome. But it would affect it both ways, it would affect the stock engine just as it would the modified exhaust version. If someone is losing 20HP because of a set of mufflers in their boat, they should look at another muffler brand. I can't regulate what people have in their boat. I can show you what the engines make for hosepower and torque after our exhaust was installed. If anyone is looking for deeper information on what Mercury claims their engines put out, you'll have to call Mercury.

I can assure you, you'll find out exactly what I've already disclosed, the stock engines will make slighly more HP than the stock rating. (by slighly I mean like 5-8 HP difference). On the other hand a 496HO was just dyno'd stock and it only made 417HP. It can go either way. Such is life with a production engine.