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  1. #1

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    Macsboost with Av Gas?

    Is anyone running Macsboost stage II with straight Av-Gas?

  2. #2
    TwoBurgers's Avatar
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    Quote Originally Posted by trxxx250r View Post
    Is anyone running Macsboost stage II with straight Av-Gas?
    I have done it. By avgas you are referring to 100LL - 100 octane light lead blue gas. It's great stuff. When at the Bay the local marina only carries 87 octane, so that does not cut it. That being said, running 100LL I only saw about 1.5 MPH difference (maybe 50 to 100 RPM). I have a portable 14 gal tank that I keep filled with 100LL for all my yard equipment - once treated with Stabil the gas stays good for a very long time. Plus it smells like a GA airport.
    Chris


  3. #3

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    Well thanks, Chris but I wasn't asking about av gas in general and it definitely doesn't make the avg boat go faster. What I was asking was an octane question in a boosted situation like a macsboost 19 lb boost.

    At this point I have used it with the macs stage II and it works very well. So I answered my own question since no one else did.

    I only have 91 in AZ so I mix approx 3:1 av to 91 to get 98 octane to get where I need to be to get the full performance from the macs II. Works great! Hope that answers anyone else's questions.

  4. #4
    TwoBurgers's Avatar
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    Notice what ski's I have. My F-12X runs the 17.5 boost insert. Any more boost with my water temps and heat soak becomes a major issue.
    C

  5. #5

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    I haven't seen that. You hear "heat soak" allot when talking about boosted engines in cars but this is marine where you have a constant flow of relatively cold water flowing thru the IC and no real significant heat in the engine compartment and to top it off, cool lake water running thru the engine (things car guys in hot climates can only wish for). Then the fact that the Macsboost IC is oversized and far superior to the stock unit. I can put my hand on the IC after a hard run and it is not hot. I don't see how heat soak becomes an issue in marine applications if everything is sized properly and running right like the Honda/Macsboost setup. I think and my testing backs it up that octane is the factor that dictates what boost level you can effectively run. Heat has nothing to do with it.

    In the dead of summer here in AZ we are around 110 degrees ambient and 82+ water temp. If I am running my 19 lb. boost tube and 98-100 octane via av-gas or 91 with Boostane octane booster my ski winds up to 6400 - 6450 in about 3 seconds and bounces off 64 MPH. It does it right after I leave the shore or after 15 minutes of hard riding, doesn't matter. So, I'm seeing no "heat soak" issues that I can detect. I can pull the lanyard and wait for the computer to reset then fire back up and take off to see if it runs faster for the first 15-20 seconds to see if it was previously pulling timing and it's no different. It's all good to me. I don't know what people are talking about with this heat soak stuff.

    Now, If I don't have enough octane to run the 19 lb tube or even the 17.5 lb tube it definitely pulls timing and it's noticeable and obvious. Doing the computer reset test really illustrates it while on the lake.

    One other thing. This summer I was really looking forward to fall when air and water would cool off so I could really feel the full potential of my motor and the kit. Well, that was a wasted notion because the last time I went out the water was around 70 and the air was 80 and I felt no appreciable gains. Yeah it was a let down but then again it shows that the Honda and macsboost kit are running very cool and efficient in very hot conditions or I would've seen serious gains when it cooled off.

    Just results that I have personally seen. Maybe others have different results...

  6. #6
    TwoBurgers's Avatar
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    I have run into self defined "heat soak" in two different ways. I have seen much higher RPM in dry cool air of the fall.

    1.) I typically peak at 6390ish RPM in normal lake conditions for me (air and water near 92F). The engine will hit and maintain peak for up to a minute, then drop by 100 to 200 RPM if I keep the engine at WOT. This is typical and consistent for my F-12X.
    2.) Once I had the engine reduce RPM by 800 to 1000 RPM in very warm air and water conditions in a local river (guessing air and water were in the 95F range). Yes, the water felt very warm to swim in. In this situation is was buzzing between some dam markers and felt the engine become noticeably unresponsive. Even after a hard restart (pull the cord), the engine had not cooled down enough, and not being familiar with that response, I took it easy thinking I had damaged something. On the next outing the ski was back to normal. When I wrote about it, Mac of MacsBoost wrote that the ECU was stepping in to save the motor given the heat soak conditions.

    It is worth noting I run 93 octane pump gas with "up to" 10% ethanol, have the 17.5 psi plug in, have Macs IC, weigh 250 lbs, and normally operate at 275 MSL (altitude) - fresh water.

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