Here's my problem.........spun a rod bearing and ruined my crank. I have a well seasoned naturally aspirated crank........std/std and very nice with no cracks. So, do I look for an unknown (mabey abused) turbo crank just to get the rolled fillets on the rods, or do I use the NA crank??? I'm going to run a combo in the neighbourhood of 430fwhp. Also does anyone make a drop-in replacement crank that doesn't need balancing????
Who runs a NA Crank???
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I have a std/std one from a 4.1 block-unabused-should just need a cleaning up-low mileage motor-$50. plus shipping-figure $45. if you want it-$95. or $100. paypal- several people using these into the 11s possibly 10s without problems-i have a na crank in one of my motors.
84BuickGNYorkPA
Daily Driving Buick V-6 Turbo's 1979 - Present
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Banning is the president of MAGNA, he was in the 10's with his.
Chuck
Chuck
Well i had one in my engine, and the engine was redone. Anyway if you have your engine done by any machine shop they are going to use a NA crank in. It will hold up under stock HP. But i put a 4340 in from fullthrottlespeed $359, but its got to be balance.
texasturbo
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Dude, don't use an NA crank for that kind of horsepower.... That is just playing with expensive fire....
No one has proven the rolled radius cranks are stronger than the non rolled ones. Imo they both will flex the same under the same loading. Which will put the same stress on the bottom end. The stock rods are more of a problem than the crank under high cylinder pressures. There is not a lot of sense in pushing a stock bottom end past 125 mph anyway.
texasturbo
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Wrong....... Buick Motorsports division proved the rolled fillet crank was superior to the non-rolled fillet cranks. Back in the early 80's using "OSCAR", onsite computer aided research, and various testing at the engine plant. I remember seeing a number of articles on this particular subject, but it has been awhile..
"Detonation, will be the NA cranks nightmare" or some kind of wording like that in one of the articles....
Come on guys. $360 or so for a decent forged crank that just needs to be balanced... Why play around...........
More likely to drive over an NA crank than the forged one don't ya think....
"Detonation, will be the NA cranks nightmare" or some kind of wording like that in one of the articles....
Come on guys. $360 or so for a decent forged crank that just needs to be balanced... Why play around...........
More likely to drive over an NA crank than the forged one don't ya think....
usetaboost
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DOesn't the 4.1 motors have turbo cranks?? Always thought they did
texasturbo
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A 4.1 should have a rolled fillet crank, but I have seen some without one. Either someone else got into the motor before you or it came that way from Buick. The latter of the 2 seems wrong, but I have pulled a know unmolested 4.1 out of a car only to find a NA crank installed....It happens.......
Wrong. Heres my quote "Detonation will break any engine". A rolled fillet crank, forged crank, or steel crank wont prevent it. These cranks were never intended to be pushed as far as we have taken them (even with no detonation). The BMS book states that the rolled fillet crank shouldnt be used over 400hp. Its been over 800 hp repeatedly in the last year. Ive seen them break in 11 second cars that were detonated. Theres a lot more involved in just balancing a forged crank for one of these also. Id like to think that we would drive over a NA crank before a rolled one but there is no evidence to prove it.
I've attached a scan of what the Free Spirit book has to say about the reasons for the rolled fillets. I always thought (and the Free Spirit book pretty much confirms that) is that the fillets are more of a reliability thing. You might only be able to lay down 1 low 11 pass on the NA crank for every 2 or 3 similar passes on the turbo crank for example. Not that you can't get away with it for a while, just that the turbo crank will hold up better after repeated floggings.
John
John
MajorBoost
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N/A Crank
I know for a FACT my buddy broke a N/A crank in half, didn't know it was a a N/A crank until he took the motor apart! Don't use them if it can be help sometimes it's just not in the budget to but new parts. But I will say " If you think it's expensive to pay to have a turbo motor built right, try paying for it twice"
I know for a FACT my buddy broke a N/A crank in half, didn't know it was a a N/A crank until he took the motor apart! Don't use them if it can be help sometimes it's just not in the budget to but new parts. But I will say " If you think it's expensive to pay to have a turbo motor built right, try paying for it twice"
texasturbo
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Do you feel better now BISON...
J-B Racing
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You can run it. Won't make a diifference if you haven't changed the set up and blame detonation....
sixgun86gn
six offender
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I ran a NA crank for 3 years in a motor and went plenty fast,hundreds of runs. Still runs in another car. Made 440 HP on pump 93 and 17#,pushed it 25# at the track.
BTW,I haven't seen a broken NA crank yet...but I have seen several broken "turbo" cranks,FWIW.
BTW,I haven't seen a broken NA crank yet...but I have seen several broken "turbo" cranks,FWIW.
I think every stock crank ive seen that was broke was between the 5 and 6 rod journal. Makes sense since this area has the least amount of mass and has to transfer the loading of cylinders 1-5 through it under positive load.
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