stroke or destroke a turbo motor ,bbc?
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stroke or destroke a turbo motor ,bbc?

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    senior member turbo wog's Avatar
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    Default stroke or destroke a turbo motor ,bbc?

    not sure if i should stroke my 476 bbc or destroke it?(or leave it alone )i have a standard stroke motor now & was told that turbo motors like sm. ci motors. i can see if the turbo is not big enough to fill the new cyl. volume , you would get less boost. so on that theory should i destroke the motor for more boost & cram in the longest rods i can fit in there? right now i have rajay turbos with .65 turbine housing

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    Senior Member GT Jets's Avatar
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    If it was me, in the interest of curiosity, I would leave it alone and see what happens, I have heard also that camshaft selection is a larger player in the turbo "game" than CID, but don't know how much theory is built into that..boost is determined buy the speed at which the impeller spins and the size of the impellers and openings, which I guess could be translated into it has to come out before it goes in, meaning the pressure and volume of the exhaust gasses are what ultimately gives you the boost, I would translate that to meaning the exhaust duration should be much larger than the intake, but that's just my opinion, never tried it but should theoretically work...My buddy always uses different rocker ratios from intake to exhaust to enhance this further, has had large successes with big inch turbo power in pull trucks, maybe he's just lucky...

    Would love to see some progress on this project There is nothing like turbos..."The quiet sleeper"

    GT
    GT


    Quote Originally Posted by Quickjet View Post
    Put a 300 on the back of it, Flywheel it and a nosecone. $15,000 later you'll have a 65 mph pile of shit......

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    senior member turbo wog's Avatar
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    do you know what rocker arm ratios he's running & what h.p. range were talking about & who does his engines?

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    GT Jets - Turbo cam grinds have short duration on the exhaust side. This produces velocity. Here is a Comp Cams baseline grind.

    http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=426&sb=2[/URL]

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    Senior Member GT Jets's Avatar
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    Quote Originally Posted by Boost Daddy View Post
    GT Jets - Turbo cam grinds have short duration on the exhaust side. This produces velocity. Here is a Comp Cams baseline grind.

    http://www.compcams.com/Cam_Specs/Ca...?csid=426&sb=2[/url]
    I thought I had it straight in my head, apparently not.... that actually makes perfect sense, keeping the pressure in the cylinder and rapidly releasing it would be more benificial, I had it in the memory banks backwards, thank you for the clarification.
    That and I just had a tooth repaired yesterday afternoon , a little punchy...

    The fact remains that cam choice is of higher importance than bore/stroke right?

    GT
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    Quote Originally Posted by Quickjet View Post
    Put a 300 on the back of it, Flywheel it and a nosecone. $15,000 later you'll have a 65 mph pile of shit......

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    Senior Member GT Jets's Avatar
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    Quote Originally Posted by turbo wog View Post
    do you know what rocker arm ratios he's running & what h.p. range were talking about & who does his engines?

    He called his rocker arm ratio's a secret (I noticed because of two different brands of rocker and different style adjustable pushrods while in his shop). I do know he runs 510 CI and horsepower is always in the 1200-1500 range, he typically turns his motors at 6500 RPM + and they are very short legged (power curve comes in with boost) I don't think they really start working hard until 4500 RPM. I think I have a video around here somewhere, I'll see if I can convert it and put it on Photobucket (it's in VHSC).

    GT
    GT


    Quote Originally Posted by Quickjet View Post
    Put a 300 on the back of it, Flywheel it and a nosecone. $15,000 later you'll have a 65 mph pile of shit......

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    Quote Originally Posted by GT Jets View Post
    I thought I had it straight in my head, apparently not.... that actually makes perfect sense, keeping the pressure in the cylinder and rapidly releasing it would be more benificial, I had it in the memory banks backwards, thank you for the clarification.
    That and I just had a tooth repaired yesterday afternoon , a little punchy...

    The fact remains that cam choice is of higher importance than bore/stroke right?

    GT
    The cam choice is very important. You got it straight.

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    Quote Originally Posted by turbo wog View Post
    not sure if i should stroke my 476 bbc or destroke it?(or leave it alone )i have a standard stroke motor now & was told that turbo motors like sm. ci motors. i can see if the turbo is not big enough to fill the new cyl. volume , you would get less boost. so on that theory should i destroke the motor for more boost & cram in the longest rods i can fit in there? right now i have rajay turbos with .65 turbine housing
    leave it alone and get bigger turbos. hass828 is doin 120gps in his heavy stealth with a 468 and lil rayjay turbos he's goin bigger turbos soon too.

    Dare to be different, if it turns out great you can claim you planned it that way.

    Jetboatperformance.com

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    just read you ar is .65, that's your issue, your turbos are spooling up to fast in the rpm and coming outta peak on the topend. you need bigger turbos with a 1.1 ar or something close, even a 1.32 ar would be alotttt better than your current deals.

    Dare to be different, if it turns out great you can claim you planned it that way.

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    senior member turbo wog's Avatar
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    i tried the 1.0 or 1.3, i can't remember, but i thought it went faster all the way around with the .65 . i better do some note reading on that day again. although i think i have been loosing the motor since laborday or prior. i know i hydro locked the motor & pulled all the plugs out on labor day & couldn't turn the motor over it was jammed . it finally, bearly moved( with the plugs out ) so maybey i should retest some things again when i get the motor back in .

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    senior member turbo wog's Avatar
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    does anybody have a map of the rajay turbos with different a/r ratios, or any at all?

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    Quote Originally Posted by turbo wog View Post
    i tried the 1.0 or 1.3, i can't remember, but i thought it went faster all the way around with the .65 . i better do some note reading on that day again. although i think i have been loosing the motor since laborday or prior. i know i hydro locked the motor & pulled all the plugs out on labor day & couldn't turn the motor over it was jammed . it finally, bearly moved( with the plugs out ) so maybey i should retest some things again when i get the motor back in .
    think of it this way, you're peaking boost way low instead of leaning against the impellor with peak boost at efficiency. we're building a 496 twin turbo blow thru motor for my uncle and using 1.32a/r on it to lean up against a big impellor(aa-cut), the boost should be at peak efficiency on the 1.32 ar turbos from 6-7krpms, right where we need it. with a .65 ar , and the same motor, we'd peak boost from 3500-4500rpms and any rpms above that, is just excessive backpressure and heating up the compressors.sure boost may increase, but it isn't really boost you're seeing increase, its the heat expanding the air charge volume , and it turn, psi raises since the intake tract doesn't get any bigger.

    been doin alot of research and reading(i even bought a 200 page book) to try and totally understand compressor maps /ar's/ compressor housing sizes etc.. and what i see would be the easiest thing to overlook and cause yourself hp loss is the wrong a/r. a small turbo with a bigger a/r will still do the job, but do it in a higher rpm range and not make alot of boost doin it, although its efficient boost, not heated boost with to much backpressure in the exhaust.

    most guys who run nos will tell ya it doesn't help their mph much. well i've never had that issue and the reason why i the way i set up my pumps. i want my power leaning against the impellor instead of runnin past its peak or not turning it hard enough. same thing applies with boosted motors, lay that tq up against a big impellor so its usefull

    put a backpressure gauge on it, that'll tell ya alot!

    Dare to be different, if it turns out great you can claim you planned it that way.

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    steelcomp was here
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    Shoot for a rod ratio as long as you can, near 1.7 as possible. De stroking will allow longer rod...don't worry about losing displacement, you;re making that up with boost. The dynamic advantages of a longer rod will far outweigh losing a few inches.
    JMO
    If God is your co-pilot, change seats!
    Acts 2:38, the perfect answer to the perfect question.

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    Senior Member howler439's Avatar
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    My little blower deal runs a 1.782 r to str ratio. Always acts like a big guy. but is just a little fella. 6.700 oliver 3.760 crank 4.320 bore. Good or bad its been a lot of fun using an odd combo. It loves to spin. Next time I'm going to put one of the bigger inch fellas together. Jim

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