Merc 7.4 454 Headers
 

I am looking for a sset of lightning headers for my Baja. It has the Merc 7.4 454 and I want to cam it and carb it but I was told by a very knowledgable fella at CP Performance that I need to start with the exhaust. I would like to have a set of the polished stainless but I will settle with the satin finish or the black, and they don't even have to be lightnings I have just heard good things about them. If someone has some advice on someother headers that's cool too. This is my first hight performance boat so I don't know all the little in's and out's, so I am open to good advice. Thanks alot. you can reach me at [email protected]

Welcome to OSO! The 7.4 in a Hammer is a fun little package to drive, and maybe the fastest platform out there for that engine? Sorry I can't help on the header issue, but if you need anything else, let me know.

XT

You may want to consider Stainless Marine brand exhaust manifolds over headers. Unless you plan on building something over 550-600hp headers are going to be a waste of money. You'll never see the performance gains over high performance manifolds, and headers cost double.

If you just want a mild cam/intake/carb setup you may want to look into the Mercury Racing 496 exhaust. It is a good exhaust for up to about 450hp, and its relatively inexpensive. You can pick up a really nice used set of cast iron manifolds with stainless steel risers for $450-550, or a set of aluminum castings of the same for $550-650. That's a heck of a lot better than $1,750+ for after market marine manifolds, and TONS better than $3950+ for marine headers.

- Will

You may want to consider Stainless Marine brand exhaust manifolds over headers.
+1

EMI Thunder, IMCO, Stainless Marine exhaust manifolds will all work very good on engines up to 550HP.

If you want a little bling get stainless steel riser/tails for whatever manifolds you purchase. Also if you upgrade in the future with heads and more cam, the stainless steel riser/tails prevent water reversion.

On a 7.4 with stock heads, even with cam and carb upgrade, headers will not give any additional power over good manifolds. They become very expensive bling!

i had dana marine exhaust on my hammer and was able to spin a non-labbed 25p mirage plus right at 4600 rpm which gained me about 2-3 mph, 68 mph on garmin etrex gps

496 to 454
 

Hmmm...funny thing..I was recently at the Toronto boat and spoke to the engine rep at Merc. You see, I have a set of 7.4 mercs in my 302 and was lookin at changing manifolds. So many people have been telling me that the 496 manifolds works great and bolt right on. Well..according to Merc..NOPE...the rep said he gets this alot and if I tried I would quickly learn that I would have to redrill/tap my head as the bolt pattern is different. Soooo...right from the horses mouth?

He is wrong.. Sort of.....

However, The bolt diameter is a little different on the 496 manifolds and the placement is just ever so slightly different. BUT if you were to drill out the 496 manifolds mounting holes to allow the usage of the larger diameter bolts used on the 454/502 they will bolt on. ;)

Here is a pic with them on one of my clients 454's..

Jamie / Lakeside

thanks
 

Wow! Finally....someone who actually tried it...did it...done it..been there and got the dang pic!...Jamie..I really appreciate your reply! So ...now the next question...any benefits to puttin on the 496 manifolds vrs the original vrs a set from GLM?
Believe it or not but my 302 Baja will run 70mph with a set of stock 385hp 454's. Top speed to date is 71.3 on GPS...go figure...most people dont believe me..but I dont really care..hell I wouldnt believe it if I hadnt seen it myself!..lol So you can understand my doubt in 'messin' with my motors...if it aint broke dont fix it!...but my stock manifolds are startn to rot.

Thanks Again Jamie...
Gerry

Gerry,

Dont want to say it.....but told ya so.

The 496 is under rated for its power potential, and can be ported for even better power gains!!!;)

No problem :)