Oil dilution vs comp....with alcohol
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Oil dilution vs comp....with alcohol

  1. #1
    Senior Member Jim W's Avatar
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    Default Oil dilution vs comp....with alcohol

    I am putting together a 509 BBC, blown, injected on alcohol and want to run 11 or 11.5-1.

    My machinist was asking why I want 11 or 11.5-1 and I said, because that's what I have read here on the forums to be the hot set up and it keeps oil dilution down.

    We both pondered that for a while and he spoke first, that he can't (and I can't either) figure why a higher compression helps to cut down on the dilution?

    If the rings are sealing right, why is there a problem with dilution at lower compression????

    I remember years ago watching the World of Outlaws run, after 30 laps they would pull in and the oil was yellow, like calf chit.... This was with SBC and high comp.

    So...... why is the higher compression, helping to keep the oil cleaner???

    Be good, Jim

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    Senior Member wagspe208's Avatar
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    Compression will not keep oil from diluting. Tuneup will dilute oil, or keep it clean. More specific amount of fuel injected/ burned.
    Real world examples in bracket drag boat stuff...with blowers on alky it is usually more difficult to detune the engines. Boost is taken out, then add fuel to slow it down even more. Where the dilution starts (this should seem obvious) is from alcohol literally washing past the rings. Once past the rings..it ends up in the pan.
    My own example. I was running a 8.0 hydro with a two speed. This engine was running 8.0's with -7 ish out of the blower, and still pig fat. I hated the slight amount of blowby. Disassembled, reassembled, re ringed, etc to get it to stop. I broke the two speed one day. Put a tuneup in it I thought would compensate for the softer leave. I went to + 15% in the blower. It sealed up beautifully at about 300 feet out. It also ran a 7.26 et at 171.
    Moral of the story...mixture (then ring seal or lack there of when actually running), not compression dilutes oil.
    Wags

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    Amen. It's the tune up.

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    Senior Member Jim W's Avatar
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    Thanks guys.
    I thought I read a bunch of threads/posts on the old site about 11-1 or 11.5-1 being the ideal comp range if not out for every single HP?

    To get to 11.5-1 with my set up I have to use a JE piston and put it .010 down in the cyl and use a .050 gasket which makes my quench area a bit large. I will give me 11.5-1 though.
    I may be able to mill a bit off the top of the 34cc domes but don't really want to do it.
    Or..... I can go to a SRP piston that will give me 10.6-1???? I don't remember the exact comp ratio but something like that.

    Which piston should I use?

    Be good, Jim

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    I would go JE or something with a full skirt.
    Chris Straub
    Straub Technologies

    3HP is an A$$ Whooping!!! JW

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    Senior Member Hass828's Avatar
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    Quote Originally Posted by Jim W View Post
    Thanks guys.
    I thought I read a bunch of threads/posts on the old site about 11-1 or 11.5-1 being the ideal comp range if not out for every single HP?

    To get to 11.5-1 with my set up I have to use a JE piston and put it .010 down in the cyl and use a .050 gasket which makes my quench area a bit large. I will give me 11.5-1 though.
    I may be able to mill a bit off the top of the 34cc domes but don't really want to do it.
    Or..... I can go to a SRP piston that will give me 10.6-1???? I don't remember the exact comp ratio but something like that.

    Which piston should I use?

    Be good, Jim
    I'm certainly know nothing about blown alky except what I've been told but, as I understand , an alky engine wont start very easily without atleast 11-1 squeeze. Isnt this correct guys ?

  9. #7
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    Well, no. I've run 7.5 to 1 blown alky and no problem starting.

    Jim W: Pm's sent on my combo...piston, etc.
    Last edited by Fiat48; 05-09-2008 at 07:33 AM.

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    Senior Member wagspe208's Avatar
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    10.6 vs 11.5 compression...depends on your budget. 10.6 will be fine depending on how mch power you need to make
    My last BA motor was 11.7... (JE pistons) made tons of power to run 8.0's or 6.0's at 1000' it was a 468 with nice merlin heads (not out of the box) (by the way, this was an old Kurtis hydro..not 501)
    My new BA engine is a 496..it wil be 10.5 to 1...(SRP pistons) still will maKe tons of power (stroke advantage) to run the number
    The SRP and JE are the same forgings. The SRP has more skirt area. The JE has more detail work inside. Also some skirt profiling. Either one will last till the cows come home unless you do something foolish. I had hundreds of passes on the JE pieces. (freshen ups in there)
    Wags
    Oh..did that answer your question, or just give you something to think about?
    Starting...alky egines start like crap at the beginning of the day. Alcohol does not want to vaporize at cooler temperatures. We always prime with gas the first start up of the day. After that (some heat in engine) it starts like anything else. Compression has no factor.

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    Senior Member Jim W's Avatar
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    Well.....I wanted to make the June 6th Lake Anna get together but won't be ready now.
    Cant find a shelf piston with the compression I want and with the ring stack I am looking for and also a piston suitable for blown use.

    Looks like it's going to be a custom piston deal. But I now can use my Crower crank and Crower rods so that saves me a little money for the custom pistons. And it gets me what I looking for all around.

    Thanks for the help guys!! Extra thanks to Fiat who has been helping me for a while on this build.


    Be good, Jim

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    Quote Originally Posted by Jim W View Post
    Well.....I wanted to make the June 6th Lake Anna get together but won't be ready now.
    Cant find a shelf piston with the compression I want and with the ring stack I am looking for and also a piston suitable for blown use.

    Looks like it's going to be a custom piston deal. But I now can use my Crower crank and Crower rods so that saves me a little money for the custom pistons. And it gets me what I looking for all around.

    Thanks for the help guys!! Extra thanks to Fiat who has been helping me for a while on this build.


    Be good, Jim
    get ahold of the guys at arias or ross

  13. #11
    Senior Member Jim W's Avatar
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    Quote Originally Posted by IMPATIENT 1 View Post
    get ahold of the guys at arias or ross
    I was going with Ross already.

    Be good, Jim

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    Senior Member Hass828's Avatar
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    Quote Originally Posted by Fiat48 View Post
    Well, no. I've run 7.5 to 1 blown alky and no problem starting.

    Jim W: Pm's sent on my combo...piston, etc.
    Thanks for the correction, why would you lower the compression on a blown alky engine that much ? As I understand , the more you squeeze alcohol the better it likes it. Is it so that you could run huge boost without finding the mechanical limits of head gaskets and hard parts ?

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    I ran 7.5 to 1 compression only because the motor I started to learn about alcohol with was a blown gas motor. It was an old 496 (4.250 stroke deal) that was pretty much a junker. Many said it would never even start. I ran an 80a gas fuel pump also. Enderle said I would burn it down if I ever got it started. LOL.
    But it ran good. Mid 180's in the 7's in a short wheelbase altered car.
    Today I run a little over 12.1. I still use the 80a pump. Alcohol does like compression. But it is not as picky as one might think.

  16. #14
    Senior Member wagspe208's Avatar
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    Quote Originally Posted by Fiat48 View Post
    I ran an 80a gas fuel pump also. Enderle said I would burn it down if I ever got it started. LOL.
    I still use the 80a pump. Alcohol does like compression. But it is not as picky as one might think.
    Glad to see I am not the only fool doing things that won't work, but magically seem to work just fine.
    Wags
    80a-1 here BTW

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