Tibbstoy2

iTrader: (1)

I need to get 2 sets of headers for my AT - just did the measuring, I'm pretty much set on getting some new CMI sport tubes with thru hull tails. I attached a picture of my current engine compartment.

The sport tube height in the down-turned bravo style will work great with my current engine compartment configuration... but... I would rather my collectors exit straighter. I am well aware that there is a straighter version being sold by CMI - If you've seen the costs, about $1400 per set more to go straight/custom - all I would need is a little less mandrel bend in the upper tubes to make this happen. Why such a price increase when all of these sets are "custom to the application" anyway. What gets me is that the "Bravo" stock manifolds exit almost exactly the same as the sport tubes - except they can go straight out the back.

I'm planning to modify the straight thru hull tailpipes to go from the down-turned bravo to exit more straight out of the boat - not afraid to do some cutting and welding on the pipes. This won't require a major direction change according to the pictures - I definitely would have a quick turn up, and then down the majority of the tail pipe length for water to exit.

Has anyone ever done this in the past? Would CMI work with me on this minor change to save a TON of cost and to have to mess with my tail pipes so much? I may be cheap, but I can do a lot to the boat with the extra $3000

Tibbstoy2

iTrader: (1)

Pantera28-650HP - Thanks for the input!

My exhaust exits well above the waterline... I do not plan to change to the current port locations. That's my problem: Please see the picture attached...

Using the peak height of the Bravo Sport tube version (which peaks, then turns down several inches), it drops down too quickly, my exhaust currently would nearly straight back from the current tail location if the angle of the collector exited horizontally...

If the exit were straight (assuming the header collector height is nearly the same - 23.5" crank CL to peak of header) I can easily exit straight, then put 2 miter cuts on the tails to come out at the right point (all downhill). My question is basically, what would add the $1300 (at the typical 20% off rate) to soften the angle of the normal bravo sport tubes? Basically, any angle removed would help, I can take up the rest with the tailpipes - as needed.

To reduce reversion possibilities - I'm going to use the thru hull style with water entering the exhaust stream at the tip outside the boat. If I do end up going with the bravo style... I would need to put a quick jog up (first 6" after collector) then go down from there to the outer tip - that way any water mixing at the tip that may get sucked back up would need to go uphill. If that would not work... I'd need to go dry (really don't want that).

Any input on this would be much appreciated!! Thanks!

Tibbstoy2

iTrader: (1)

The picture shown shows my exhaust exit... really isn't affected by the water line. Are there other considerations I'm not thinking of?

I'm building a new engine that is the same as the one coming from my other boat... NA 540's with cams that can cause issues. I've run exhaust that is dry to the tip before... the new boat has a much higher exhaust exit, will not be an issue when backing up as before.

Tibbstoy2

iTrader: (1)

I'll get the exact tailpipe tip to crank CL measurement today.

I guess my question for now is: does CMI pro-rate the cost based on how custom you go with the big block sport tube straight back/taller style? From my initial look - all I need is a straighter outlet than the typical bravo... which from a manufacturing standpoint shouldn't be much.

Tibbstoy2

iTrader: (1)

OK - I measured the crank CL to CL of exhaust exit at the transom (inside) - 18.375" This should be within 1/8" accuracy.

If the peak of the sport tubes (bravo style) is at 23.5" - then this drops down a little at the point of attachment (maybe 3-4" from the picture) -

Using my 18.375" measurement plus half a 4.5" OD tailpipe (2.25") gets me 20.625" to the top of the tailpipe at the exit just inside the transom.. In other words, I'll have a nearly upward angle, even if the collector exited horizontally. See the picture attached below. I used a scale to make sure things were close.

So... moving forward, looks like a bravo style is not what I need. I'll need straight exiting exhaust. If I was to go truly custom - I can go a few inches taller in my engine compartment to increase the angle - but if possible, would like to save cost with a less radical change to the bravo style, possible?

Thanks much!

Ateco

I'll measure the straight set we have on the shelf, it seems like they will work for you, if so, I'll get pricing from CMI for a matching set. I too suggest shopping around, maybe someone else has another straight set on the shelf

Kirk

1983corsa31

ateco
do you have any new or used 4 inch cmi tails for a trs setup? the distance from the cmi header tube to the inside of the transom is 10 inches. i currently have rope seal headers that i want to convert to flange and gasket seal style.
chris 218-391-6226

AIR TIME

with all the leaks with cmi's thats the last route I would take, a friend has been testing a twin turbo motor he built useing split top cmi's, the inner welds let go at a pokerrun at the lunch stop. filled this motor with water blew the starter a part. he should look at stainless marine 4 1/2'' or 5'' exhaust or hurricane headers from hardin marine ,my exhaust comes out high also, I have the ones with the sway in them with a straight collector. 5'' dry tails with a bun to unscrew and run a pipe to let water mix at the end , also they can put a drain out side bottom of tail. you should call BILL at Diamond marine 302 521 0123 , I have found him to have the best prices on OSO for all my parts over the last 2 years.I also have a friend who has had leaks with his cmi tube tops. I have not heard about any leaks on here with the hardin headers they have 3 styles.I would look at hurricanes or sm.

Michael1

I've heard about leaks with CMI's, but in reality you are taking your chances putting turbos on any header designed for a naturally aspirated engine. They are not designed or tested for that much pressure and heat.

Michael