CMIs on 496 HO-Myth or Real?

[CRC]

Speed increase claims that is. I have seen claims from retailers in Powerboat mag that a swap to CMIs will get you anywhere from 2 to 7 mph. The latest claim being in the Feb '10 issue stating that the owner of a 26 Baja Outlaw can expect 4-7 mph with just the headers and a prop change. That is not going to happen! I fell for this ploy and dropped $4,600 for a set of CMIs to put on my 496 HO in my 2005 Donzi 22 Classic. I saw ZERO top speed increase! I have seen dyno results on paper but I have also seen others post that they too saw NO speed increase. Maybe we can get folks who upgraded their 496 HOs w/CMIs to post their actual results (or lack of results).
Remember, actual results, not paper results.

[Wardey]

The HP is true.....I know the guy that did the test for CMI. Speed is a determining factor. You can dump all the HP in the World to your boat but if it is not set up correctly you will see no terrific gains in MPH.

[HaxbySpeed]

I did the sport tubes and a k&n on a customers 496HO in a 22Donz and picked up 2-3mph..

[MOBILEMERCMAN]

Some boats don't respond to increases in power as much as others. Generally the boats with the drives in the basement respond less. Boats set up with less drag { higher drive heights } are the ones with the notable increases IMO.

[CRC]

The HP is true.....I know the guy that did the test for CMI. Speed is a determining factor. You can dump all the HP in the World to your boat but if it is not set up correctly you will see no terrific gains in MPH.

Wardey, my boat was/is set up correctly. My engine had the all aluminum exhaust which flows really well. I just don't think the CMIs really do much on an otherwise stock 496. It was almost 5k down the drain for me and I cringe every time I see these claims because that Baja owner will NOT see 4-7 more mph from headers and a prop! Now the switch to the 525 which added 100 hp gave me over 10 mph.

Mobilemercman, I already had the Imco shorty on the boat.

[Pismo10]

90% marketing.

[Ratickle]

Speed increase claims that is. I have seen claims from retailers in Powerboat mag that a swap to CMIs will get you anywhere from 2 to 7 mph. The latest claim being in the Feb '10 issue stating that the owner of a 26 Baja Outlaw can expect 4-7 mph with just the headers and a prop change. That is not going to happen! I fell for this ploy and dropped $4,600 for a set of CMIs to put on my 496 HO in my 2005 Donzi 22 Classic. I saw ZERO top speed increase! I have seen dyno results on paper but I have also seen others post that they too saw NO speed increase. Maybe we can get folks who upgraded their 496 HOs w/CMIs to post their actual results (or lack of results).
Remember, actual results, not paper results.

Teague wrote it. Send him an email asking the same questions. I don't know of anytime they've made claims of something they did not have first-hand knowledge of.

[MILD THUNDER]

From some things i have read, the stock merc 496 aluminum exhaust flowed pretty good for a stock merc setup. Way better than the cast iron stuff from the 80's and 90's. Im sure their are some gains to be had, but not enough to see dramatic speed increases on a 496 HO just by bolting some headers on.

Now, if you were to run a stock merc manifold on say a 525, or 600, you would see a huge improvement because the bigger HP engines with with more aggressive cams, heads, etc can move more air thru.

Its like my buddies old 454's. They started out as 370HP mercs. Then they upgraded to larger cams, roller rockers, bumped compression, but left stock cast iron manifolds on. I keep telling him his next best bet would be upgrading exhaust. In his case, upgrading cams and other internal mods should be complimented by adding a free flowing exhaust.

[CRC]

Teague wrote it. Send him an email asking the same questions. I don't know of anytime they've made claims of something they did not have first-hand knowledge of.

I did that a while back and didn't get an answer. I respect Bob Teague and won't bother him any more.

[Raylar]

Bob Teague is CMI's biggest dealer, what the hell you think he is going to say!
As for 4-7 mph in a Baja with CMI's on a stock 496HO, NO WAY!
I've dynoed almost every header made on stock and our Raylar built 496's and I can tell you unequivocally that CMI Sport tubes make between 35-40HP more on a stock 496 than the stock Mercury 496 exhaust and the new CMI Sport tubes do about 20-25HP.
I know about that 50-60Hp dyno test originally done by CMI and I've never seen anybody in the industry re-create that result on a calibrated dyno, running the SAE standard with full accessories and water in the exhaust! You can confirm this with Bob at Full Throttle, he's also done a lot of header dyno testing and the results we have both seen in boats and on the dyno are about the same and pretty consistant. Bob, will also confirm with his propshaft dyno that water in the headers takes away about 15-20HP all by itself as we have seen in wet tests.
As Mild thunder has said if we were comparing Merc's older MPI and log manifolds the increase would be larger and when you go up to 500HP plus on the 496's you also se a slightly bigger increase in power, about 10-15HP more due to the better breathing required. Lets face it there are no realy cheap 40-100HP increase upgrades for any bbc engine especially the 496 family. We oughta know, we've only done hundreds of them!

Best Regards,
Ray @ Raylar

[jet]

how's the old saying go ....THERE"S NO FREE LUNCH

[Ratickle]

As for 4-7 mph in a Baja with CMI's on a stock 496HO, NO WAY!

I've dynoed almost every header made on stock and our Raylar built 496's and I can tell you unequivocally that CMI Sport tubes make between 35-40HP more on a stock 496 than the stock Mercury 496 exhaust and the new CMI Sport tubes do about 20-25HP.

Hey Ray,

What would you expect to see speed increase wise on that Baja with 35-40 HP more like your tests showed?

And what else would you think you'd have to change to get the 60HP they discussed?

[Ted]

Ray, from your tests, do you recall the torque numbers from the different headers? Do they change significantly, or at all? Because, as you know, a header is designed to get more flow which equals in most cases less backpressure. And some engines need backpressure to develop torque, so headers can cause you to lose torque. Which could slow down a boat or at least keep it the same, all other things being equal.

[CRC]

Ray, I always appreciate your input. I'm aware of the CMI hp results on paper. If I had added 35-40 hp to my otherwise stock 496 HO I think I should have seen a gain in top speed. I didn't. When I search this topic on other forums I find others who also saw no noticable increase in hp. Some people report an increase of 1 or 2 mph. Yes, it is Bob Teague making the claims and, yes, he sells CMIs. Like I said, I respect Bob and will continue to do business with his company but I don't like the way he is pushing the CMI Sport Tube headers with these outrageous claims. Now I wonder if these letters are entirely made up? The latest Teague On Tech letter writer is the owner of a 2009 Baja 26 Outlaw, 496 HO, Bravo One, 26p 4-blade. He is asking about "bolt-on power upgrades" for "more on the top-end". Bob Teague replies: "We have found that the CMI 496 Sport Tubes provide the greatest power increase of all the bolt-on exhaust systems. All things being equal, I would expect a 4-7 mph increase in top speed for your boat with this upgrade. You may have to go up a pitch in propeller.....".

My boat responded well to the Imco shorty, BBlades Bravo1 and, of course, the new 525! The headers did nothing to my boat except bling up the engine room. I took a big loss when I sold the 496 with the CMIs.

I'm just wondering what others opinions and real life experiences are on this. Dyno charts be damned!

Ted, good point. A loss of torque could off-set the hp increase and CMI pushers would not be too quick to report a loss of torque!

[Madpoodle]

A WIDE variety of boats here in SoFla will dispute the CMI claims..

They are damn purty though, but chrome don't get you home..

[Ratickle]

They are damn purty though, but chrome don't get you home..

Now you tell me......

[Biggus]

From my own experience, to gain speed on a straight bottom single engine boat it takes 20 hp/mph. It would most likely take a 140 hp increase to gain the 7 mph claimed.

[GB]

90% marketing.

Yeap, 90% ++++++

[JupiterSunsation]

Some boats don't respond to increases in power as much as others. Generally the boats with the drives in the basement respond less. Boats set up with less drag { higher drive heights } are the ones with the notable increases IMO.

I know a guy that had a 288 Sunsation and got 1 mph increase but then was selling the boat, took off the exhaust and still had the 1 mph.....go figure

[CRC]

From my own experience, to gain speed on a straight bottom single engine boat it takes 20 hp/mph. It would most likely take a 140 hp increase to gain the 7 mph claimed.

OK so I'm not the only one disapointed in the CMIs. Funny how adding only " 100 hp" with the 525 gave me a solid 10 mph increase from about 75+ to 85+. Maybe they are sandbagging on the rating!