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Thread: School me on 90mm bore issues

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    School me on 90mm bore issues

    Currently running an 86.5mm un-sleeved block which fingers crossed lasts another race season without failure. I am investing in another block but this time sleeved, for not a lot of extra cost figure we might as well go 88 or possibly 90mm bore to bump capacity out to 2.2 litres. Use my existing crank & carillo rods so figure a piston change & sleeved block & back in business! I have read about 90mm head gasket failures & I think the combustion chambers need to be opened up to match the head gasket footprint for detonation reasons I think. We are very much on a budget with all work done typically done in house with my Mechanic brother in law. What haven't we considered & what is required for a reliable 88 or 90mm bore engine that will see track abuse? Any recommendations on a proven source to purchase a sleeved block from? I'm nervous about dealing with a company that doesn't know what they are doing with the 4B11.

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    Evo X Harlot UT_EvoX's Avatar
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    Head gasket failure will always be an issue on a high HP 90mm block. The bigger issue is phantom knock.

    Stick to 86-87 mm even on sleeves.

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    The only 'proper' way to increase displacement is with a stroker crank. Overbore will not make any noticeable difference.

    It doesn't make sense to me to go with a 90mm bore on a sleeve, if you ever have to rebuild it you will need new sleeves again. The largest I would go is 88 at most. But as UT stated, it's best to go 86-87. I went back and forth for a while, and finally decided on a 86mm. Easier to find pistons off the shelf, potential to be rebuilt several times on same sleeve, and has the most amount of meat.

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    Trackstar, If you do everything right from the beginning.... would you ever have to rebuild the engine???

    And for the 90mm headgasket issues.... i assume people have already tried the metal to metal contact to seal the cylinders? Essentially, its a sharp or radiused edge being heavily torqued on a flat surface to form a metal seal. I don't know anything about headgaskets or engine building so i'm not sure what is normally done or what has been tried.
    Last edited by HispanicPanic; 06-10-2018 at 09:25 AM.
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    Considering everything is done right, which even the best shops make mistakes. But even the best built motor will eventually need to be rebuild, especially when making big power. And it's not only the motor that's that play, you can have a solid motor and something causes you to go lean and there goes your motor.

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    2.2lt is 2.2lt right? How does 2.2lt of stroker provide more performance over 2.2lt of overbore? Curious as to why say AMS go overbore when other company's go stroker. When would you choose one over the other?

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    Well, one perspective is if your RPM or TQ limited. If your TQ limited, you'd make more power by hitting target TQ and revving to the moon, which is what an overbore can do. But if you're RPM limited, then a stroker is going to be your best bet because you can crank the boost and make infinity TQ till you hit your RPM limit.
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    Is big horsepower for our platform what, 700 and up?

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    Senior Member Mnemuth's Avatar
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    I have the AMS 2.2 and haven't had problems with it for 5 years. I run 24-26 lbs of boost, so perhaps that is one reason why.

    I don't daily drive it either.
    The finger cannot point at itself.

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    Quote Originally Posted by Mnemuth View Post
    I have the AMS 2.2 and haven't had problems with it for 5 years. I run 24-26 lbs of boost, so perhaps that is one reason why.

    I don't daily drive it either.

    2.2 stroker or overbore?

    On my last motor I tried 88mm with the standard stroke and I honestly couldn't tell any difference vs a standard 86mm bore other then the knock detection frequency change.

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    Quote Originally Posted by Mnemuth View Post
    I have the AMS 2.2 and haven't had problems with it for 5 years. I run 24-26 lbs of boost, so perhaps that is one reason why.

    I don't daily drive it either.
    I’m at about 10k miles on my 2.2 overbore over 3 years. No issues yet, 610/523 @29psi.

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    Quote Originally Posted by Black E View Post
    Quote Originally Posted by Mnemuth View Post
    I have the AMS 2.2 and haven't had problems with it for 5 years. I run 24-26 lbs of boost, so perhaps that is one reason why.

    I don't daily drive it either.

    2.2 stroker or overbore?

    On my last motor I tried 88mm with the standard stroke and I honestly couldn't tell any difference vs a standard 86mm bore other then the knock detection frequency change.
    Crap. If you take a 200cc motor bike for a drive the performance is pretty awesome, an extra 200cc pushing the weight of an evo in theory should make for noticeable differences. Theory versus real world I guess.

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    Quote Originally Posted by HispanicPanic View Post
    Well, one perspective is if your RPM or TQ limited. If your TQ limited, you'd make more power by hitting target TQ and revving to the moon, which is what an overbore can do. But if you're RPM limited, then a stroker is going to be your best bet because you can crank the boost and make infinity TQ till you hit your RPM limit.
    Ok so an the 4b11 starts having oiling issues at 8,500 & the SST starts freaking out at 8,500 rpm. Ok so if you were running to a redline of 8,500 which benefits more, stroker or overbore?

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    Quote Originally Posted by 4B11T View Post
    Quote Originally Posted by HispanicPanic View Post
    Well, one perspective is if your RPM or TQ limited. If your TQ limited, you'd make more power by hitting target TQ and revving to the moon, which is what an overbore can do. But if you're RPM limited, then a stroker is going to be your best bet because you can crank the boost and make infinity TQ till you hit your RPM limit.
    Ok so an the 4b11 starts having oiling issues at 8,500 & the SST starts freaking out at 8,500 rpm. Ok so if you were running to a redline of 8,500 which benefits more, stroker or overbore?
    Well i'm not an engine builder so i can't speak from experience. I'm only talking theoreticals. The oiling system does have issues past 8,500 but i'm not aware of any SST issues revving past 8,500. I figured the SST was good to rev to whatever the hell you can push . BUT, if you're limited to the stock oiling system and a 8,500 RPM limit, then the stroking would likely do you better. I'm pretty sure people have been pushing stroked 4b11's to 8500 without a problem.


    Also, i think the 90mm bore engines only have issues once you approach 40 psi, no?
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    Senior Member Mnemuth's Avatar
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    Quote Originally Posted by Black E View Post
    Quote Originally Posted by Mnemuth View Post
    I have the AMS 2.2 and haven't had problems with it for 5 years. I run 24-26 lbs of boost, so perhaps that is one reason why.

    I don't daily drive it either.

    2.2 stroker or overbore?

    On my last motor I tried 88mm with the standard stroke and I honestly couldn't tell any difference vs a standard 86mm bore other then the knock detection frequency change.
    Overbore. It seems like everything ends up that way, once I reach the scene.
    The finger cannot point at itself.

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    I have an 89mm overbore and had nothing but issues for some time. The combo that seems to be working for me now is a copper o-ringed head and I switched from H11 head studs to ARP 625+. I went through 2 head gaskets with the H11s and no o-ring with peak boost, on a cool day, cresting 30 psi. Now I'm holding steady 32 psi with no signs of issues. I am however dealing with phantom knock which is a whole other can of worms.

    If I had the decision, I would stay at 86mm without hesitation.
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    Quote Originally Posted by 4B11T View Post
    Quote Originally Posted by Black E View Post
    Quote Originally Posted by Mnemuth View Post
    I have the AMS 2.2 and haven't had problems with it for 5 years. I run 24-26 lbs of boost, so perhaps that is one reason why.

    I don't daily drive it either.

    2.2 stroker or overbore?

    On my last motor I tried 88mm with the standard stroke and I honestly couldn't tell any difference vs a standard 86mm bore other then the knock detection frequency change.
    Crap. If you take a 200cc motor bike for a drive the performance is pretty awesome, an extra 200cc pushing the weight of an evo in theory should make for noticeable differences. Theory versus real world I guess.
    What bike are you overboring 200cc? lol Even on a hyabusa you'll get up to mid 100cc increase.

    And you're talking about a bike that weights 200-500lbs to a 3200+ lbs car...yea that margin gets significantly reduced

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    Ok what I'm hearing is been there done that, don't waste your money, stick with standard bore. Will get sleeved block done in 86.5mm to drop in all my existing parts. Thanks guy's.

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    Quote Originally Posted by HispanicPanic View Post
    Trackstar, If you do everything right from the beginning.... would you ever have to rebuild the engine???
    Everything wears out eventually. Doing it "right" just means there are fewer "unexpected" early failures. It certainly doesn't mean the engine will last forever.

    Even unlimited budget F1 and NASCAR engines wear out and die.
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    Now I know this is like saying how long is a piece of string, what would one consider engine rebuild intervals to be (bearings, rings, crack testing etc) on 500 + WHP engines? Am I expecting too much with say 3,000 miles of WOT track abuse or say 10,000 miles or street racing before rebuild intervals? I'm talking about preventative maintenance, not shit it just blew up & needs rebuild.

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    Evo X Harlot UT_EvoX's Avatar
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    Quote Originally Posted by 4B11T View Post
    Now I know this is like saying how long is a piece of string, what would one consider engine rebuild intervals to be (bearings, rings, crack testing etc) on 500 + WHP engines? Am I expecting too much with say 3,000 miles of WOT track abuse or say 10,000 miles or street racing before rebuild intervals? I'm talking about preventative maintenance, not shit it just blew up & needs rebuild.
    Experience tells me bearings are usually the weak point in built engines. OEM bearings tend to hold up better long-term.

    Built engines really tend to top out at 40-50K miles of mixed street / drag strip driving with regular WOT in regard to bearings. I'd always swap rod bearings before you hit 40K miles on a built engine unless OEM bearings were used.

    Everything else holds up fine at a sane power level. Pistons, piston rings, cylinder walls, etc. I've never really seen issues involving those components.
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    another data point for you...
    MAP 2.5L short block (i think they discontinued it shortly after i got it)... so 90mm bore, and 97mm stroke (4b12 crank).
    motor has done 35k (kms), tuned for 26psi, mostly daily driven, done a skidpan day, regularily hit full boost and redline (8k)

    no real problems except for phantom knock...

    BUT I havn't driven it in 6 months because it needs a new HG (and some other bits).

    if I had to do it over again, I probably would have gone with stock bore (or maybe 88), just to get some more meat for the gasket to seal properly...

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    Quote Originally Posted by tephra View Post
    another data point for you...
    MAP 2.5L short block (i think they discontinued it shortly after i got it)... so 90mm bore, and 97mm stroke (4b12 crank).
    motor has done 35k (kms), tuned for 26psi, mostly daily driven, done a skidpan day, regularily hit full boost and redline (8k)

    no real problems except for phantom knock...

    BUT I havn't driven it in 6 months because it needs a new HG (and some other bits).

    if I had to do it over again, I probably would have gone with stock bore (or maybe 88), just to get some more meat for the gasket to seal properly...
    I think that is the key, if you want to run a bored out motor, just keeping the boost low, will allow everything to be ok, only when trying to push 40psi does it look like you run into trouble

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    Evo X Harlot UT_EvoX's Avatar
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    The big issue is a lot of people push these overbore 4B11T's into detonation and don't know it because factory ECM knock detection has to be disabled basically on a 90 mm engine.

    On E85 you'll keep making power by adding timing advance even with a bit of knock.

    Couple that knock with 35-40 psi boost and you've got a whole lot of cylinder pressure to hold in.

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