speedygonzalez

[QUOTE=speedreeder;2002561]Is the only reason people say that most of the "manifold type" headers won't fit a 496 is because of the short riser or ?? I installed a 496 in a '96 Baja 240, closed cooled and put on regular EMI Thunder headers. It is on it's third year now with no problems!
Now that you say that, the only thing that I remember is that the o2 sensor can not be installed without drilling and welding a nut for it but again I am not sure, I gues I have to do some more research.

James

About Mercury and Illmore" can't be wrong", CMI builds a nice product, but they do have limitations and they can and do leak

- I see where McDonalds has sold billions and billions of hamburgers, but that does not mean the food is good for you -

MarkDonzi

I've had two sets of CMI headers crack/leak on stock 525's. From reading this thread, it sounds very common. This is on a pleasure boat, not racing. Do you guys pull the headers and check them on a regular basis? Do you drain them after every use?

Any info would be appreciated, first boat with headers and they are driving me nuts, not to mention $$$.

Thanks, Mark

BGIII

Many CMI exhaust systems that I have seen have no where near equal length 32" runners. They are mearly a tube style "manifold". That is a pretty bold statement saying a 32" equal length runner KE manifold can't keep up with a header.

Isn't Mercury Racing the same group of people that chose the valve springs for the original HP500's and the Gil exhaust with the low risers for the same engine?

speedygonzalez

If you look at kieths web site his chart claims to out perform all tube headershttp://www.keitheickert.com/products/Exhaust/ke-exhaust.htm

bcarpman

Not sure I have a whole lot to add here (no experiece with the Ke's), but it seems like a lot of people are having some problems with the definition of a header, and I have some experience with custom headers, having hand fabricated more than a few sets.

The only things that matter are runner length and diameter as well as how tight the bends are. It doesn't matter what the header is made of! Stock low performance manifolds are bad because they have no runner length and dump into a log that is very bad for both flow and reversion. Then the exhaust passes through a horribly tight riser that cuts flow further.

If the KE's are a good design and the correct length FOR YOUR PARTICULAR ENGINE then they will easily perform as well as hand fabricated SS headers. However the KE's are only one length/diameter so they would reguire a complete retooling to work well on a custom racing engine.

Race teams with any real $$$ spend a great deal of time on trial and error, getting exhaust to tune properly. If they could do this easily without hyper expensive tooling changes and end up with the same performance, but better reliability I'm sure they would.

Personaly, if I were building a recreational big dollar big block and didn't KNOW what would work best with my particular application, I'd certainly go with the KE's if they were more reliable.

PS. I like the comments regarding "bling" factor and how much Mercury Racing pays for the CMI's. Marine exhaust (along with most go fast stuff) seems to be priced on the 1000% markup theory as apposed to the 100% markup that exists in auto hotrodding. I'm guessing MR pays a couple hundred for them and CMI still makes a profit.

PPS. Extrude hone processes are worthless on anything other than the worst castings. The material the process removes ends up being directionaly incorrect (ie. takes off material where it should actually leave it).

speedreeder

[QUOTE=speedygonzalez;2003019]HEY speedy, Forgot to say I was running a MarinePower 496 not a Mercury.

Coolerman

Here is a cutaway pic of when I made the headers. They are all 31 to 32 inches in length with a 4 into 2 into 1 collector.
Typically it performed like any good 2 X 32 header with frequently a little extra torque around 3600 to 4400 rpm because the 4-2-1 collectors which typically broaden the torque band. The runners actually have an oval profile with an area equal to a 2" round header. Currently we are using them on 1250 HP motors.
Dennis

articfriends

Keep in mind for anyone considering keith eickerts in a procharged or similar mounted supercharger,there is not enough clearence to bolt the blower on due to the fwd bend of the casting,Smitty

rexone

As a manufacturer of many stainless parts including a lot of 316L tube products (not headers) I can tell you with confidence you are way off base on your cost estimate. You can't even purchase the material for a set of headers for that amount of $ much less the labor to bend, weld, polish, R&D, equip cost, etc etc etc... Not saying Merc isn't high priced, they are. But no where near that level of markup exists in any of this stuff.