Last edited by tblrklakemo; 03-21-2009 at 09:23 AM.
I would like to know more about these new CMIs. The picture looks a lot like lightnings, one piece with no tails. Anyone have info? CMI web site doesn't have anything.
You seem to be the new CMI spokesman for this new CMI -496 E-top type header release. I am sure the OSO 496 users would like to know how these new headers compare with the older 496 Sporttube offerings from CMI and what REAL horsepower they will provide versus the other headers that have been independently tested here by OSO'ers. We need to know more closely how these headers will price versus the other $2200-$2500 headers manifolds like Dana that performance boaters are using.
You also mention that these headers install in 2.5 hours on 496's, does this include the whole kit with oil filter brackets, hose extensions and mounting plate adaptors required on a stock 496?? CMI needs to stay accurate here with these figures you are quoting and the generalizations being offered by you. We will really appreciate the details.
Just Merc Me:
Notice you are a new OSO poster so I will ask just a few questions and offer a few comments on your question post.
First: A 496Ho engine can not be run at 5300 rpms unless the ECM has been reprogrammed. If it has a reprogrammed ecm, running a stock 496 at 5300 rpms is very dangerous to the engine and will eventually result in valve float and possible engine damage!
If your 22 Donzi is really running 75-76 mph GPS, then you have a really fast 22 and you might be very close to the maximum speed this particular boat is considered safe to run at in all but perfect condtions.
If as I suspect your max rpms per the stock rev-limiter is running at 5100-5150rpm and your real speed may be more like 70-72mph on the high side.
The accuracy of your information is important here if you are really going to make improvements to your boats performance and give good feedback to who ever you work with,header, engine, drive, prop people so they can reall y help you achieve measurable gains and improvements to get "Your Bang for the Buck"
If you really intend to get to 80 mph in your 22 Donzi GT in most normal water condtions you will probably have to do a trio of changes as the added horsepower it takes to add 6-10mph to most high performance boats is that the added horspower will spin more prop after the horsepower is added with engine upgrades and sometimes drive changes are needed also.
As for safety of a 22 footer at 75-80 mph you should automatically consider hydraulic steering or steering assist
to make sure the boat will remain stable at higher speeds and keep you and your passengers safe.
I will throw in my opinion on horsepower available and speed improvements from most of the options available to you:
Prop work and new prop with labbing 1-3 mph possible @$800 - $1000 , you can install
Headers (real headers) exhaust 35-40 horspower increase with 1-3 mph possible. $3000-$6500 installed might need prop rework.
Engine upgrades like a Raylar BCK103 engine kit , 100hp increase with stock exhaust and 135-140 hp increase with headers + 6-10 mph possible with right setup and propping
+$9000 - $9500 installed by shop , but will need prop change.
That kind of lays out a starting point for bang for the buck scenario, but get an accurate starting point with real speeds and rpms.
Hope this helps,
Ray @ Raylar
I will not budge, the tube headers will not change any performance gain by themselves on a stock 496 mag or HO !!!!!!!!!!!!!!!!!!
We have seen too many people buy them and it sounds great then then they run their boats and NO CHANGE in performance, I WOULD LOVE TO BE PROVEN WRONG, PLEASE SOME ONE STEP UP ??????
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