Continually Blown Exhaust Couplers

[Racerdude]

My B Mono is blowing the rubber couplers used to connect the header to the pipe. The coupler material is rated up to 500 degrees. It melts the tie wraps holding the coupler on, then the coupler itself ends up with a hole in it.

I don't think the coupler material is bad. I think something else is going on.

Mac .45 motor with a mac pipe (drilled to 1/4") at 10 1/2 inches center of cylinder to the weld.

Any ideas what could be causing this? I could always add water cooling to the header, but I'd really like to know why this is happening.

thanks

Jay

 

[lohring]

I've run that engine in monos and a hydro for years without that problem. Things shouldn't get anywhere near that hot. A good silicone coupler (Prather pink) should be fine. One reason things are getting hot could be that the engine is too lean. Macs really like fuel. The engine needs to be so rich on the stand it will barely run. If this is true, I'm surprised you don't have problems with the engine quitting, or blown plugs. There are couplers for gas engines that will stand the heat of a torch. They are available from Seducer.

Lohring Miller

 

[Shark]

Racerdude,

The Mac 45 will burn hot and I experienced the same conditions as do all the boaters here in so cal who run the Mac 45.

The suggestion to run richer is a "bandaid" fix as the extra fuel is not being burned or ignited but bypassed thru the engine as coolant.

The Prather coupling material which I am very familiar with (more than the others) is only rated to 350 degrees and will blow as well.

The best couplers to handle the heat is the blue couplers which is rated to 500 degrees.

However, for maximum performance, you should cool the header with water instead of fuel. This will maximize the power range of the engine without having to consistently change your remote needle to cool the engine with fuel.

Both my teammate and I use a cooling header that I designed to fix this very problem. We run the same blue coupler for 6 races then change to a new one for the sake of changing to be safe. On the inside, the coupler is still consistent and not plyable from melting.

Coolng an engine with fuel takes power away and wastes fuel. A cooling header will take 100 degrees away from the case at the exhaust and eliminate secondary ignition, which I am sure you have heard just before your coupler blows. Its the secondary ignition that heats up the engine and not the chamber ignition.

Secondary ignition is a popping sound you can hear as the boat passes by. Since changing to a water cooled header, we have never blown a coupler.

Just my opinion based on 4 years of MAC 45 use.

 

[AndyBrown]

Jay,

Does your header telescope inside of the pipe? At 10 1/2" is probably does not. Drill your pipe out to the full diameter of the stinger, .435".

Anything less will hold too much heat in the pipe, especially if you are running the moddifed engine that I just sent to you.

Also, shorten your pipe to 10" and richen the mixture. You will go faster with less pipe/header heat.

Do not under prop it. Try to pull the biggest prop you can. It's best with the MAC 45 to start with a big prop and a rich mixture then work your way smaller if the engine seems over loaded. This is a bit different then I recommend with other engines, but the MAC 45 is a different kind of beast.

Joe Knesek has a very fast speedmaster hull with a MAC 45 that is modded the same as yours. He is pulling an X455/3. I don't think your hull will allow that much prop, but you get the picture.

Shark wrote:

"The Mac 45 will burn hot and I experienced the same conditions as do all the boaters here in so cal who run the Mac 45.

The suggestion to run richer is a "bandaid" fix as the extra fuel is not being burned or ignited but bypassed thru the engine as coolant."

Shark, This is incorrect information. This is only your preception based on the way you personally used your own MAC 45's.

While water cooling the header has merit, there are many boaters racing MAC 45's with great success without water cooled headers.

The MAC 45 can be run at the correct mixture and does not need to be run richer than what would produce optimum power to keep the header temp in a workable range.

It is possible to run the MAC too lean and generate excessive heat because the pipe is too long or the prop load is too light.

When a rich mixture is used with the correct load, the mixture will be burned efficiantly and cooler, producing maximum power.

 

[Roger Hooks Jr.]

Jay,

Does your header telescope inside of the pipe? At 10 1/2" is probably does not. Drill your pipe out to the full diameter of the stinger, .435".

Anything less will hold too much heat in the pipe, especially if you are running the moddifed engine that I just sent to you.

Also, shorten your pipe to 10" and richen the mixture. You will go faster with less pipe/header heat.

Do not under prop it. Try to pull the biggest prop you can. It's best with the MAC 45 to start with a big prop and a rich mixture then work your way smaller if the engine seems over loaded. This is a bit different then I recommend with other engines, but the MAC 45 is a different kind of beast.

Joe Knesek has a very fast speedmaster hull with a MAC 45 that is modded the same as yours. He is pulling an X455/3. I don't think your hull will allow that much prop, but you get the picture.

Shark wrote:

"The Mac 45 will burn hot and I experienced the same conditions as do all the boaters here in so cal who run the Mac 45.

The suggestion to run richer is a "bandaid" fix as the extra fuel is not being burned or ignited but bypassed thru the engine as coolant."

Shark, This is incorrect information. This is only your preception based on the way you personally used your own MAC 45's.

While water cooling the header has merit, there are many boaters racing MAC 45's with great success without water cooled headers.

The MAC 45 can be run at the correct mixture and does not need to be run richer than what would produce optimum power to keep the header temp in a workable range.

It is possible to run the MAC too lean and generate excessive heat because the pipe is too long or the prop load is too light.

When a rich mixture is used with the correct load, the mixture will be burned efficiantly and cooler, producing maximum power.

I run a Mac 45 in my mono with closed cowl and I do not have that problem either. I can't remember where the pipe is but I know it is shorter than longer and I pull a 245 prather prop with 4.7 pitch if not more... I know that is where we starte before we started cupping it more. We just reached the point where we might have to start backing off a little... but still not so much heat that it is burning off the tie wraps.

 

[Don Ferrette]

The MAC 45 can be run at the correct mixture and does not need to be run richer than what would produce optimum power to keep the header temp in a workable range.

It is possible to run the MAC too lean and generate excessive heat because the pipe is too long or the prop load is too light.

When a rich mixture is used with the correct load, the mixture will be burned efficiantly and cooler, producing maximum power.

Absolutely. My SGX with MAC45 & .435" drilled parabolic @ 9.5" & 1655 prop runs consistent low 80's in true heat race trim, faster if I want to tweak the needle tight. BTW- same coupler has been on there from beginning. B)

 

[Shark]

(post edited by author)

Peace.

 

[[email protected]]

I never had any problems with the blue tubing. Another thing you can do instead of using zip ties would be to use wire.

 

[Don Ferrette]

Deleted for the sake of the board. B)

 

[Shark]

(post edited by author)

Peace.

 

[topfuel443]

Yet another productive thread....

These things are becoming all to common.

~James

 

[AFIRacing]

Thank You James u took the words right out of my mouth

Steve H.

 

[Don Ferrette]

Again deleted for the good of the board.

 

[Shark]

(post edited by author)

Peace.

 

[mark w.]

hey racerdude, i hope your happy with what you caused!just kidding man,i dont think i'll comment on the problem,guess i'm scaaared of what might come out of it.you'll get it fixed soon.

mark B)

 

[Roxyflash]

Need to delete this thread maybe a pair of boxing gloves are in order!

 

[Mike Larson]

( Smiley inserted here, to ease tensions) Hey Rey (?) Mike Hughes sells a super coupler material Im surprised no one offered.... ( he's on here somewhere) Ive got it on a hot Picco 45 and its 2 years and goin strong........ The stuff is some kinda black material that will not burn out.... give him a try.... its pricey, but darn worth it...... Man, thats a nice boat! Mail me as to brand, etc will ya? Regardless of who's boat can beat whose again, I picked up a little more beginner tuning info that I will put to use....thanks, Mike

 

[Shark]

Ok, you got it, I will Pm you the details.

 

[Racerdude]

Thanks to all who responded!

Thanks Mark! Nice to hear from you! I've left you a couple of messages, but I'll keep trying!

Now, as far as all of the advice given, I appreciate all of it. Rey, Will, and Dave ALL have great running boats, and are good competitors, and good people. I've never seen Don or Andy run personally, but I have no doubt that you are both amazingly awesome to watch! You have both helped me far beyond what I could have imagined, and are good people as well! Every one who responded had something to add, and I appreciate each of those who responded.

I just hope I can actually compete on ANY of your levels sometime soon.

Thanks again -

Jay

P.S. Keep it positive - we all enjoy the competition.

 

[dwb2620]

What size drill bit comes out to .435?

Thanks,

David