Question Regarding CMIs w/Q&Q

[Carl C]

Last fall I installed CMIs on my 496 using the Q&Q kit. In the kit is an inner sleeve that, in my case, almost completely blocks the Y pipe. Through prop works fine at idle but at speed creates so much back pressure that it overpowers the butterfly solonoids and opens the exhaust. I think I'm lucky that the back pressure didn't force water into my engine since it had nowhere to go untill the butterfly was forced open. I plan to remove the inner sleeves and cut holes in them to line up with the down pipe. Why are they made this way? Are the pipes longer on most boats so that this doesn't happen? Has anyone else here had this problem? Will my fix cause any problems or performance loss? I will talk to the tech guys at CMI also but am looking for real life experience and opinions here. Thanks.:confused::confused::confused::confused:

[BigGrizzly]

I never saw that inner befor mine doesn't have them.

[Carl C]

I never saw that inner befor mine doesn't have them. Its slightly triangular shaped. Its one piece with the adapter and water inlet. I guess I'll e-mail CMI the pic I made; Maybe I got the wrong part?

[mjw930]

The inner sleeve is there to prevent reversion my putting the mixing point of air and water as far away from the exhaust port as possible.

It will be interesting to see what CMI says. My guess is their system is not intended to be used through the prop above 3000 RPM.

How far from the butterfly valve is the inner pipe? Did you by chance get the one for the Corsa system when you really needed the one for the internal sound choice system?

[Carl C]

The inner sleeve is there to prevent reversion my putting the mixing point of air and water as far away from the exhaust port as possible.

It will be interesting to see what CMI says. My guess is their system is not intended to be used through the prop above 3000 RPM.

How far from the butterfly valve is the inner pipe? Did you by chance get the one for the Corsa system when you really needed the one for the internal sound choice system? No good above 3,000 rpm is not acceptable to me. The butterfly is far enough down to not hit the sleeve, I forgot to put it in my drawing. I got the papers out and it does say "496 Corsa kit" is that the problem?

[mjw930]

No good above 3,000 rpm is not acceptable to me. The butterfly is far enough down to not hit the sleeve, I forgot to put it in my drawing. I got the papers out and it does say "496 Corsa kit" is that the problem?

I'm pretty sure that's your problem.

CMI makes a separate Y pipe to convert factory switchable systems. Page 18 of their catalog : http://www.custommarine.com/pdf_docs/CMI_CATALOG_2007-03-20.pdf

[Carl C]

[quote=mjw930;439878]I'm pretty sure that's your problem.

CMI makes a separate Y pipe to convert factory switchable systems. Page 18 of their catalog : http://www.custommarine.com/pdf_docs/CMI_CATALOG_2007-03-20.pdf[/quote About 1/4 down pg 18 is a "CMI 496 Sport tube performance package, Corsa adapter version" part #13008. That's what I got and they said it would work on my Q&Q which is made by Corsa. They didn't say anything about only working at put-put speed. Something isn't right and BigGrizzly's don't have them.:confused::confused:

[mjw930]

You're probably going to need to take a picture of what you have and forward it to them vs. your drawing.

Someone got their signals crossed.

[SilverBack]

Carl....Good luck man...you know how I feel now..I have been getting that kind of news alot lately. Oh well you need this or I forgot to tell you that you are going to need this and that too. It sucks!!

I talked to IMCO when I was still thinking that I could keep my Corsa Captain Call and they were talking about haveing to cut this brand new riser and modify that...all I could think is that sounded so nice to cut into a brand new $1,000 + riser. Now it looks like I can't even have my Q+Q. They have taken it out of the boat. I am detuning the engine and paying more to do it.

Did the CMI's help your performance much. I know they don't give those things away!

Anyway..Good Luck!!!

[blueliner]

when i bought my cmi's i had to order the one designed to be used with the corsa q&q system. if i remember, it was like 500 bucks more for that option, but i'm not positive.

[Carl C]

Did the CMI's help your performance much. I know they don't give those things away!

Very little, but I may SC my motor in a couple years and they will definately be needed then. If I do I will pull the motor and do the whole job right.


when i bought my cmi's i had to order the one designed to be used with the corsa q&q system. if i remember, it was like 500 bucks more for that option, but i'm not positive. Blueliner, I was hoping you would see this since I knew you just put on CMIs too. Your set-up is just like mine. Do you have this problem? Can you use your Q&Q at high speed? I will contact CMI today or tomorrow:crossfing:.

[Carl C]

Well there doesn't seem to be a lot of input on this. I posted it on Speedwake also and got even fewer responses even though a lot more people read it there. Anyway, I just got off the phone with CMI and the scoop is that there are many versions of the Corsa exhaust systems and that my original idea of cutting the holes in the sleeves is the proper fix.:propeller: Also the CMI technician said he had never seen a stock aluminum exh on a 496 HO. Mine came with a lightweight, freeflowing all alum exh. I guess I spent 5 big ones on bling but it was worth it.

[mjw930]

In that case I would simple angle cut the inner sleeve at a 30 degree angle pointing down. The 30 degree angle will open up a larger cross section than the 90 end cut now or even a 45 degree slash cut.

[mjw930]

Kind of like this.

[Carl C]

Kind of like this. That's a good idea and I'll decide what to do when I get it apart. That would be easier to do because I could use a cut-off wheel.

[Carl C]

Just thought I'd post an update on this. This week I modified the inserts as shown in pic. These inserts had small holes (about 2" dia) that didn't even align with the down pipes. This mod should provide plenty of breathing for high speed use of Q&Q.:crossfing: I used an air grinder with cut-off wheel. I reassembled it with my new cool silicone hose. If the weather cooperates I'll get her out next week.

[Carl C]

I got out today for the first run of the season and the problem is still there but not as bad. Quiet mode is good up to 4,000 rpm and then the butterflys blow open and it takes a good amount of pressure to overpower the solonoids. The fix I did in the previous post eliminated the bottleneck. Could this be due to an increase in water going into the exhaust with the CMIs. Do people ever restrict this water flow? Can you guys with headers on BBCs run at high speed in quiet mode? WTF?????:(

[BigGrizzly]

I can run wfo with them closed but choose not to because the back pressure isn't good for my blower motor.

[Carl C]

Randy, you stated earlier that you didn't have the inserts I have but with the mod I made I don't see how that can be the problem. Lower exhaust seems clear and butterfly flappers in down pipes look like new. There is no feeling of power loss before exhaust blows open. Water pressure is over 20 at speed. Lots of water is going through exhaust and pipes stay cool to the touch. Any clues there. I need to fix this to be a good neighbor.:confused::confused:

[BigGrizzly]

I have the air pressure system not electric. I have no flappers in my lower pipes just in the tips. My pipes do have a anti reversion ring at the collector, but that is it. It almost sounds like they are not like mine in any shape or form. Mine look just like the ones in the book. There is about 200 hundred hp difference between you and me, and mine don't blow open, I wish they did, because I have almost tosted mine by leaving them closed at wfo!

[Carl C]

The next step I'm contemplating is taking it back apart and just cutting off the inserts as shown in this drawing. Does anyone have any thoughts before I do this? I think the water may be blasting the plates open since it is being directed right in front of them. Everybody seems stumped by this. I've got it on Speedwake too.

[yeller]

Do they open at higher rpms only since the CMI's? Just curious.

[Carl C]

Do they open at higher rpms only since the CMI's? Just curious. Yes. Since I seem to be the only one with this problem I plan to e-mail my drawings and ideas to CMI for their opinion. They thought that opening up the inserts would fix the problem and so did I. Someone on Speedwake felt that maybe the system is tied into the engine sensors and they could be opening electrically due to some input. I don't know, and both sides don't seem to open at exactly the same time. I'll figure out something hopefully before I get any more "love letters" on Lake Oakland!:doh: