Some inside looks at the GM 8.1L alias Merc 496
 

There have been some past threads about the Merc 496 (GM 8.1L) and how possibly Raylar and myself specifically were wrong about our Raylar information about why the stock intake manifold has problems with its structure in making 525HP or more on the stock or modified 496's especially when re-used on a good flowing head like the Raylar aluminum heads or the new Dart iron replacement head.
I thought to help existing 496 owners and other interested parties understand why I make these statements I would share some pictures and facts in support of the Raylar findings. I have attached just a few pictures of a stock G M 496 intake as it comes on the Merc. 496's and others like Volvo Penta, etc.
First you need to understand that this engine was developed and designed to be a 220HP to 340HP truck and industrial engine with good low rpm torque numbers and it was never originally intended to be a high performance marine engine especially a 500-600HP engine and was only released in a 375HP to 425HP versions with larger camshafts and programming to the standard marine engine marinizers to fill the void of the 454-502 stock GM 330-415HP engines that GTM discontinued in 2000.
As I originally informed those who where claiming that stock intake manifolds could support over 525HP up to 600HP the reason our original inspections and dyno testing could not reach these levels of performance was because the manifold internally had flow restrictions and limitations which kept it from reaching these higher horsepower levels when the manifold was put on top of good flowing cylinder heads with bigger camshafts and higher flowing exhausts.
These attached pictures were taken of a stock 496 intake manifold cleanly sliced into two half sections showing the internal flow path of the incoming air from the throttle body opening down into the in lifter valley passage and up thru the center plenum area whre it then flows into the individual long individual cylinder port runners.
I know some people on OSO think they know this engine and its compnents very well and others do not so I thought it important and informative to show the real item as it is manufactured and installed on all 8.1L -496 stock engines whether they are in a truck, on an industrial version or on any stock marine engine version.
If you look at and study the attached pictures you will see that the manifold has a stock throttle body opening of approximately 3" diameter or 75mm which is approximately 7.5 square inches in area. You can also see in the section pictures that about 7" down the entrance opening under the throttle body opening the passage goes square in shape and necks down to an approximate 2.5" by 2.25" size that yields approximately an opening with an area of 6.0 square inches. This choke point in the manifold is only 80% of the area of the stock throttle body opening and can obviously not flow even the same amount of air flow the stock 75mm throttle body can flow!!
This is why Raylar chose to design a whole new intake manifold that could flow the required air flow to support 525HP to 600HP + when the engine was equipped with good flowing cylinder heads and a relatively mild camshafts that would not revert water in a wet exhaust system with stock exhausts, aftermarket header systems, even those with switchable exhaust systems.
Again just some good factual information and pictures to show why I sometimes make the statements I do about what works with a 496 (8.1L) engine and what I am pretty sure does not even when some are claiming it can.
Thanks for your attention, hope this explains my statements more clearly.

Best Regards,
Ray @ Raylar

Good stuff. Doesn't look like it would flow well at all. Ray, it would be interesting to see one of your manifolds cut open for comparison.

I agree and Carl I would also like to see your 525 intake cut open to compare.

:eek:

Your Intake
 

Carl: I agree with brian... that would be interesting.. Give it a try. There are alot of good welders out there to put it back together

Hey, you have a Raylar intake Mick.......:cuqui:

C'mon Ray, you must have a ruined intake laying around. :)

No, as it turns out i don't have a junk Raylar intake laying around I can cut open for show and tell, however I will take some closeup pictures to show how our 496 manifold is obviously radically different from the throttle body opening to the plenum and intake runners and why it does not have high flow issues.

As for the Raylar version HP525efi manifold I will tell you it has an entirely different top portion of the manifold or plenum which is where the stock Merc manifold gets in trouble when you are trying to feed a 540 inch version of our HP675efi conversion engine with its specially rework heads and other goodies!

You guys want to see it , send us a HP525efi and well send you a 675HP version back and you can photograph it all you like, that is when you're done having a blast running around in your boat with the power of a 675HP 89 pump gas N/A engine that looks pretty much just like a stock HP525efi with just an obviously nicer looking plenum with a nice Raylar HP675 polished plate on top!!

My discount offer still goes for a good first of the new breed demo and magazine photo shoot and results article.

Best Regards,
Ray @ Raylar