CMI Headers/496 HO
 

Looking to purchase and needing some feedback. What kind of HP gains and sound over stock? Advertised seeing a 55 Hp gain? Worth the money or not?

Re: CMI Headers/496 HO
 

We recently installed a set of CMI Headers onto a 35 Outlaw, twin 496. Fairly straightforward installation, but still a pretty big job. We had a few issues with some fitment (due to keeping the Quick and Quiet diverters), but CMI was great about getting us the parts and help we needed.

When finished, the motors looked great, and ran noticeably better.

Did we get a 50+hp gain? Hard to say, but I doubt it. The boat is noticeably quicker, but top speed is no more than 1 or 2 mph higher.

Is this a worthwhile modification? Yes. The cool factor is way up there - sound and looks are a lot of boating, and these have both to the max.

-David
THUNDER MARINE
727-501-3183

Re: CMI Headers/496 HO
 

Thanks David!

Looking to install in a 28' Advantage Victory. I have been told they are worth the sound and HP gain of a 525 at fraction of the cost?

Re: CMI Headers/496 HO
 

Did you take any pics of the final product?

Re: CMI Headers/496 HO
 

Great sound and looks, and some moderate HP gains have been reported. Do a search; there are several threads. Fred at www.trickmarine.net has sold a lot of sets to OSO members. He can give you a rundown of feedback he has been given.

Your 496HO is making 425HP+/-. The 525EFI is making at least 525HP, and many are dynoed out of the box at 535-540. If you get your CMI headers installed, you MIGHT get up to 470ish HP out of your 496HO. A 35HP gain is more realistic with a little aged 496HO.

The older 500EFI was rated at 512HP at the crankshaft and 470 at the propshaft. Expect your typical Bravo1(any) drive to eat 25-50HP, so you can figure out your propshaft HP. Adding headers to a 496 does not make a blue motor, but it should net you some gains. (Although there are a few folks that I know whom have upgraded, who have not gained anything.)

Its also worth doing a search on "Raylar". He has forgotten more info on the 496 motors than most of us know. He has a lot of products to give the 496 some pep.

Also, this section is for asking questions about how the forum works, and issues. Your question is of a technical nature; and belongs in the Technical area of the Forum found here:

http://www.offshoreonly.com/forums/f...splay.php?f=20

Re: CMI Headers/496 HO
 

The average speed increase reported back to me has been in the 3 to 4 mph range. The majority of the sets sold have been without the Corsa kit.

Re: CMI Headers/496 HO
 

I put a set on my miserable old tub that are only the e tops, not the kit you are looking at. I did the prop and bottom paint at the same time and made 11 MPH!!! I personally think that it is the best money you can spend. I would buy these things before petrol. They are so good its actually not worth going boating without them. You can run a better cam and do all sorts of up grades you cant do without the CMI headers. The look is worth the money alone. Only my opinion though. Jas

Re: CMI Headers/496 HO
 

Before you do anything pull your "turbulator plates" out (between the manifold, risor). It is good for 10-15 hp. Raylar will verify that for you.
Do a search on this forum for 496 exhaust manifolds and you will find a thread were Ray talks about porting work on the stock manifolds which are actually made by Gill. In a nut shell he says they are not bad for a stock manifold and with some porting work he can really wake them up. I think it also states that he has made up to 550 hp on the stockers with the porting work in conjuction with his kits. If you check out his web page you'll see several of his motors are running the stock manifold only with the paint removed and then polished. They look pretty good. Between the turbulator plates and the porting you could easily see the same 35 hp gain at a fraction of the cost.

Re: CMI Headers/496 HO
 

The 496 Kit is a very reasonably priced upgrade for the increase in performance and of course the "Bling" factor!!

We have several sets in stock for immediate delivery.

Let us know if we can help.

Kirk

Re: CMI Headers/496 HO
 

I can't find the thread which details how to port the 496 exhausts...anyone have the link?

Re: CMI Headers/496 HO
 

Get a hold of Ray or search for "Raylar" and u will find it.

Re: CMI Headers/496 HO
 

I'm a little old fashion. How about some proof that removing the turbulators and porting will produce the same results as a set of CMI headers.

Anyone can say anything on a forum. Show me some sie by side dyno tests proving your claims. :rolleyes: If you can do that, I'll gladly recommend my customers just modify their stock exhaust.;)

Re: CMI Headers/496 HO
 

How about somebody show me the actual (not magazine article) dyno for a claimed 55 hp gain by simply bolting on CMIs?

Although CMIs are a fine piece. They are a little overkill for a stock 496. If your gonna go big then CMI's all the way!!!

If you follow some of Rays threads on the 496 you'll see the biggest restriction to air flow is actually the stock intake manifold not the stock exhaust manifolds.

Raylar has tested their porting work on a flowbench and I'm sure he can back his claims with dyno sheets along with removing the turbulators.

I'm not trying to starv yor sales, but the man asked the question if they were worth the money or not? Just letting him know there are other options out there if money is an issue :D

Re: CMI Headers/496 HO
 

Only 9 posts on this site and you start your last post with "I know a guy" ???????

Re: CMI Headers/496 HO
 

By having the tubulators removed & porting the stock manifolds you can pick up some power because you are fine tuning them. The headers will still be the best option though because they will scavenge & help pull the exhaust out rather than let it just flow out a little better. :) Jamie / Lakeside

fyi: If you remove the turbulators (which are are not so much there to stop reversion as they are to help prevent corrostion)you run the risk of allowing condensation to leak down onto the valves causing corrosion or rust..

Re: CMI Headers/496 HO
 

Raylar has about 6 different stages or options for 496s. Perhaps the guy you know only paid for 5mph.

Re: CMI Headers/496 HO
 

Just to clear the air here a little (PUN)! Removing the turbulators on a stock 496HO yields about 10HP and yes we didi dyno pulls to confirm it. We have never recommended porting the stock Mercruiser manifolds on stock 496's because the benefits would be nominal. Stock 496's don't breathe well enough at WOT to take real advantage of big exhaust only changes. Also the stock valves in the stock 496's are steel and they rust easily when exposed to a lot of moisture, especially in salt water, sans the reason for turbulator plates to cook off this condensation. We do give some clean up porting tricks on the manifolds to our kit purchasers that do help the motor because after the kit install ,it benefits from exhaust side deep breathing and we use stainless nitirided valves that don't rust. We saw about 10-15HP at WOT on these mods. If you really want to see a Raylar HO525 or a HO600 deep breathe then install a good set of headers like the CMI's and yould see overall numbers around 560-570 HP and 625-630 HP on the HO600. Yes we dynoed those to confirm. Our Raylar/LaveyCraft race boat has our HO525 engine with 496/CMI's and I can only say that it outruns the same hull with a HP525 blue motor. It will be running this weekend in the OSS/OPA races at Lake Mead outside Las Vegas. There should be some surprised looks when the weekends over!

Re: CMI Headers/496 HO
 

After talking with Ray personally on this issue. He cleared alot of my questions up and the reason for my post deleation. I spoke out of turn which happens when you don't hear it from the horses mouth so to speak. Ray has a great product which I intend to look into putting on my setup....