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  1. #1
    jetpilot785's Avatar
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    Maximum safe boost numbers for 91-93 oct pump fuel

    I did a search on here and didn't really have any luck. I would like to know who is running higher boost engines on pump fuel and has it been safe and reliable. I am in the process of increasing boost to either an ET15.5 or ET18 and i was wondering who is running those wheels or similar boost numbers between 16-20#'s of boost safely on pump fuel. I have no problem upgrading internals like I did on my last engine but I guess what I am after is what are the maximum realistic numbers that are safe on pump fuel without too much fear of detonation. I am looking for a realiable rec boat setup and not a "well if you don't hold it for more than 8 seconds at wot, it should be ok" type setup. I ride in the northeast where the air temps range from 60-90* and water temps are usually between 60-75* when and where I ride. I realize air and water temps will affect that as well so it would be nice to know what everyone has been running for boost numbers safely on pump fuel along with their normal operating conditions. I would love to run the ET18 but don't want to get into the race fuel thing but I also hear alot of people run the ET18 on pump fuel with no issues so I am digging around trying to find out what the limitations on pump fuel with max boost vs operating conditions. Thanks for any input!!


  2. #2
    Leendert's Avatar
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    Also depends on amount of timing you will be running. So what amount of timing will you be running?

  3. #3
    jetpilot785's Avatar
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    Quote Originally Posted by Leendert View Post
    Also depends on amount of timing you will be running. So what amount of timing will you be running?
    I don't know the exact timing numbers as i am running an R3 reflash now but I was thinking of doing the R&D 725cc injectors and R8 reflash with the ET18 if I went that way. Not sure what the timing in that reflash is either.

  4. #4
    Too many variables to consider.plus i dont think many of us are actually logging knock but if we had to put a number id say over 17 and 8800rpm you start to roll the dice a bit.how long you hold it for and your tune up in the ski will all have an impact on what could be considered reliable for your kind of riding.

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    hdlefler's Avatar
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    Quote Originally Posted by jetpilot785 View Post
    I did a search on here and didn't really have any luck. I would like to know who is running higher boost engines on pump fuel and has it been safe and reliable. I am in the process of increasing boost to either an ET15.5 or ET18 and i was wondering who is running those wheels or similar boost numbers between 16-20#'s of boost safely on pump fuel. I have no problem upgrading internals like I did on my last engine but I guess what I am after is what are the maximum realistic numbers that are safe on pump fuel without too much fear of detonation. I am looking for a realiable rec boat setup and not a "well if you don't hold it for more than 8 seconds at wot, it should be ok" type setup. I ride in the northeast where the air temps range from 60-90* and water temps are usually between 60-75* when and where I ride. I realize air and water temps will affect that as well so it would be nice to know what everyone has been running for boost numbers safely on pump fuel along with their normal operating conditions. I would love to run the ET18 but don't want to get into the race fuel thing but I also hear alot of people run the ET18 on pump fuel with no issues so I am digging around trying to find out what the limitations on pump fuel with max boost vs operating conditions. Thanks for any input!!


    Hello JetPilot-
    I have the 15.5 and I'm seeing 18-19 [email protected] 8760 (currently with weather conditions) running 93 octane and no issues what so ever. AFR's are in 12.1 range at this point. I do not go crazy with it riding and consider my riding as recreational.

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  7. #6
    jetpilot785's Avatar
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    Quote Originally Posted by FXSlowKroozer View Post
    Too many variables to consider.plus i dont think many of us are actually logging knock but if we had to put a number id say over 17 and 8800rpm you start to roll the dice a bit.how long you hold it for and your tune up in the ski will all have an impact on what could be considered reliable for your kind of riding.
    Very understandable brother. I will be trying to keep the rpms in the 8500-8700 rpm range at wot which puts the ET18 around 18lbs at 8500 and around 19lbs. at 8700. I'm not the type that holds the throttle wot all the time. I'm more of a 7800-8200 rpm cruising type at 2/3-3/4 throttle position with an occasional wot burst but I always hated holding it at 100% when 65-75% throttle position gives me 90% of my top speed. I don't feel the need to introduce all that extra air and fuel for little gain when making long pulls down the river or across the lake. I have had way too many burn downs of snowmobile engines on lakes in Canada from holding it wot way too long when I could of held it at 3/4 throttle and gone almost as fast and kept the engine alive on a long pull so that habit I got into of not running full bore all over has carried over to the skis. I just want to see what other guys are having good luck with as far as setup on pump gas.

  8. #7
    jetpilot785's Avatar
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    Quote Originally Posted by hdlefler View Post
    Quote Originally Posted by jetpilot785 View Post
    I did a search on here and didn't really have any luck. I would like to know who is running higher boost engines on pump fuel and has it been safe and reliable. I am in the process of increasing boost to either an ET15.5 or ET18 and i was wondering who is running those wheels or similar boost numbers between 16-20#'s of boost safely on pump fuel. I have no problem upgrading internals like I did on my last engine but I guess what I am after is what are the maximum realistic numbers that are safe on pump fuel without too much fear of detonation. I am looking for a realiable rec boat setup and not a "well if you don't hold it for more than 8 seconds at wot, it should be ok" type setup. I ride in the northeast where the air temps range from 60-90* and water temps are usually between 60-75* when and where I ride. I realize air and water temps will affect that as well so it would be nice to know what everyone has been running for boost numbers safely on pump fuel along with their normal operating conditions. I would love to run the ET18 but don't want to get into the race fuel thing but I also hear alot of people run the ET18 on pump fuel with no issues so I am digging around trying to find out what the limitations on pump fuel with max boost vs operating conditions. Thanks for any input!!


    Hello JetPilot-
    I have the 15.5 and I'm seeing 18-19 [email protected] 8760 (currently with weather conditions) running 93 octane and no issues what so ever. AFR's are in 12.1 range at this point. I do not go crazy with it riding and consider my riding as recreational.
    I hear that is a pretty good wheel. Do you have any surge issues with that wheel? I heard rumors it had a surge around the 5000-6000 rpm range and the ET18 does not surge at all.

  9. #8
    hdlefler's Avatar
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    Quote Originally Posted by jetpilot785 View Post
    Quote Originally Posted by hdlefler View Post
    Quote Originally Posted by jetpilot785 View Post
    I did a search on here and didn't really have any luck. I would like to know who is running higher boost engines on pump fuel and has it been safe and reliable. I am in the process of increasing boost to either an ET15.5 or ET18 and i was wondering who is running those wheels or similar boost numbers between 16-20#'s of boost safely on pump fuel. I have no problem upgrading internals like I did on my last engine but I guess what I am after is what are the maximum realistic numbers that are safe on pump fuel without too much fear of detonation. I am looking for a realiable rec boat setup and not a "well if you don't hold it for more than 8 seconds at wot, it should be ok" type setup. I ride in the northeast where the air temps range from 60-90* and water temps are usually between 60-75* when and where I ride. I realize air and water temps will affect that as well so it would be nice to know what everyone has been running for boost numbers safely on pump fuel along with their normal operating conditions. I would love to run the ET18 but don't want to get into the race fuel thing but I also hear alot of people run the ET18 on pump fuel with no issues so I am digging around trying to find out what the limitations on pump fuel with max boost vs operating conditions. Thanks for any input!!


    Hello JetPilot-
    I have the 15.5 and I'm seeing 18-19 [email protected] 8760 (currently with weather conditions) running 93 octane and no issues what so ever. AFR's are in 12.1 range at this point. I do not go crazy with it riding and consider my riding as recreational.
    I hear that is a pretty good wheel. Do you have any surge issues with that wheel? I heard rumors it had a surge around the 5000-6000 rpm range and the ET18 does not surge at all.

    I really like the wheel a lot. Yes the 18 lb wheel pulls harder but considering all I have is retainers, my limit is 8700-8900 rpm with stock rods and pistons. I saw what 20-21 lbs. of boost can do to a stock motor and I do not want to risk it. A far as surge, it has a little flutter but it does not bother me at all. It does not shake or feel its not balanced. For a recreational ski its all I need.Going riding this Sunday and will enjoy it with a pitcher of beer and some chicken wings.

  10. #9
    h2jim's Avatar
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    I'm running the R3 with the 15.5 wheel. I run 91 in the summer and mix it with 94 in the spring and fall. Rpms around 8700 and afrs 11.9. Not sure if our gas up here is much different than yours.

  11. #10
    jetpilot785's Avatar
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    [QUOTE=hdlefler;2473894]
    Quote Originally Posted by jetpilot785 View Post
    Quote Originally Posted by hdlefler View Post
    Quote Originally Posted by jetpilot785 View Post
    I did a search on here and didn't really have any luck. I would like to know who is running higher boost engines on pump fuel and has it been safe and reliable. I am in the process of increasing boost to either an ET15.5 or ET18 and i was wondering who is running those wheels or similar boost numbers between 16-20#'s of boost safely on pump fuel. I have no problem upgrading internals like I did on my last engine but I guess what I am after is what are the maximum realistic numbers that are safe on pump fuel without too much fear of detonation. I am looking for a realiable rec boat setup and not a "well if you don't hold it for more than 8 seconds at wot, it should be ok" type setup. I ride in the northeast where the air temps range from 60-90* and water temps are usually between 60-75* when and where I ride. I realize air and water temps will affect that as well so it would be nice to know what everyone has been running for boost numbers safely on pump fuel along with their normal operating conditions. I would love to run the ET18 but don't want to get into the race fuel thing but I also hear alot of people run the ET18 on pump fuel with no issues so I am digging around trying to find out what the limitations on pump fuel with max boost vs operating conditions. Thanks for any input!!


    Hello JetPilot-
    I have the 15.5 and I'm seeing 18-19 [email protected] 8760 (currently with weather conditions) running 93 octane and no issues what so ever. AFR's are in 12.1 range at this point. I do not go crazy with it riding and consider my riding as recreational.%5”Å1#QUOTE]

    I hear that is a pretty good wheel. Do you have any surge issues with that wheel? I heard rumors it had a surge around the 5000-6000 rpm range and the ET18 does not surge at all.

    I really like the wheel a lot. Yes the 18 lb wheel pulls harder but considering all I have is retainers, my limit is 8700-8900 rpm with stock rods and pistons. I saw what 20-21 lbs. of boost can do to a stock motor and I do not want to risk it. A far as surge, it has a little flutter but it does not bother me at all. It does not shake or feel its not balanced. For a recreational ski its all I need.Going riding this Sunday and will enjoy it with a pitcher of beer and some chicken wings.
    LOL, enjoy that thing with some beer and wings. Thanks for the input about the surge. I am also running the R&D watercooled housing with the anti-surge port in it so maybe that will help with the "flutter" as you describe. As far as internals, I don't mind doing it up if the ET18 is that much stronger and better. I saw some brand new Molnar rods on ebay for $385 shipped and their are several sets of these things I guess. They look identical to the K1 rods I bought from Ross a couple years ago and also look like the Carillo rods for 3x's the money. The Molnar's came out around the same time the K1's stopped being produced so I don't know if they were bought out and are the same product or what but they look decent for the money. I also saw a set of weisco pistons for around $480 shipped for the set of 4 with rings, pins, clips etc. I'm not sure how good they are in the 1.8l yami engine but I always had great luck with weisco's in my sled and 2 smoker ski engine years ago. I didn't think for under $850 shipped for full forged internals was a bad deal unless they are both garbage for some reason.

    I have also thought about trying E85 either straight or as a mix to slow the burn down on the higher boost of 18+ pounds. I talked with Art earlier and he said the 15.5 will be fine on pump gas up in this region all season and the 18 would be iffy in the spring and fall but fine during the summer months of mid june to around mid september. He is located in Toronto which is only 2 hours north of me so he shed some light on the fuels needed to run these wheels safely and he highly recommended internal upgrades with the 18 but he also said he knows a bunch of guys who run the 18 with stock internals and pump gas all season with no issue but he didn't really mention where these guys run them like that so thats another reason why i am asking these questions. I want to know if it's a "cover my ass" type thing as most companies will do to either push product or be conservative or is it all legit and every one above the mason dixon line has to run race fuel or a mix of race/pump fuel with the ET18 lol. One thing Art did say with the Et15.5 was that all is needed is a RRFPR and stock injectors should be ok but I have heard repeatedly that the stock injectors are maxxed out around 14 pounds and around 8500 rpm. i tried that experiment with a C5/R3 with RC2 cam setup a couple years ago and it didn't seem to like the stock injectors so thats why I am going with the 725's and the R8 reflash which is tuned to those injectors and will work well with either wheel. I'm not doing the stock injector thing again with anything over a C3 wheel again.

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