Upper RPM Limit TAFC/TAD

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by TOL, Oct 24, 2018.

  1. TOL

    TOL Active Member

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    What really defines the upper RPM limit of current blown alcohol TAFC and TAD engines these days, and roughly what are those limits at now?

    Valvetrain? Reciprocating assembly? Increasing parasitic losses versus decreasing power gains? Part attrition (which ones)?

    Something else?....

    Just curious what people's various thoughts and experiences were.

    Thanks.
     
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    Last edited: Oct 24, 2018
  2. MaineAlkyFan

    MaineAlkyFan Active Member

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    The size of your wallet & how much qualified crew help you have.

    Chris Saulnier - Team Tigges
    Mechanic Falls, Maine
     
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  3. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    Primarily valvetrain and to a lesser degree stroke. Now some teams are running 65 mm cams and really beefed up rockers, lifters and pushrods. Hollow stem valves are becoming more commonplace.

    Now that the valve train will live above 10600-11000, camshafts and cylinder heads are being developed to make more power upstairs.

    Obviously this all comes at a cost to the wallet because the margin of error starts to decrease dramatically with rpm. It obviously takes life span off parts.

    I run close to 50 lbs of boost in my Top Dragster customers to run big speed but they are low compression motors that shift at 8500 and cross at 9000. They go 40-50 runs on rods, I drop the pan every 20-25 runs. Turning 9800-10000 in TAFC trim (leaning on it) we changed the same rods at 17-20 runs. Nowdays turning a 4.150 stroke 10,200-10,500 you replace rods at 12-15 runs.
     
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  4. BEDNAR1320

    BEDNAR1320 Member

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    Will, " low compression", how low?
     
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  5. TOL

    TOL Active Member

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    Will how high do the 3.750" stroke guys spin typically, and are they faring better in terms of rod life?
     
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  6. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    10:1
     
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  7. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    It's certainly easier on the rods. Depending on who you ask the front runners are 10500 to 11000+. Ask anyone who has tried to hit a shift point up there, it doesn't take much of a delay to turn a 10,500 target to 11000 real quick.

    The difference in boost and the abuse they take from running that much boost on the edge keeps the rod life pretty close, 10-12 runs usually.
     
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  8. TOL

    TOL Active Member

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    Thanks Will.

    I'd like to throw out a question to the whole group here. Maybe it's a dumb question, but here goes........

    In these instances where people are trying to run up to let's say 11,000 on a regular basis with blown meth, I am assuming they are replacing the rods out of an abundance of caution after 10-12 runs just to be on the safe side. I totally get that, because the alternative is expensive.

    Assuming that everything is totally perfect inside the engine, and assuming that a rod failure were to occur due to these high RPM issues, then:

    1) What clues can be looked at or measured on a rod just prior to failure, to predict a potential for failure? Is it a gradual onset of symptoms type deal, or is it just a sudden unexpected failure out of the blue avoided only by replacing rods at a fixed number of runs whether they show evidence or not type deal?

    2) In the case of a rod failure scenario as described above, has anyone done a deep dive into what the failure mechanism actually was? What failed first? Why/how? Bolts? Main cap? Beam to big end? Again, assuming that the focus is purely on the rod itself, and that everything else was perfect and can be ignored.

    Just sort of curious from a forensic engineering point of view about this. Any thoughts or insights would be much appreciated.
     
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    Last edited: Oct 25, 2018
  9. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    Typically the rod seems to take a beating on both sides, depending on the rpm range, and if we are talking about the upper rpm limits, the teams are probably leaning on them.

    The little end starts getting oversized. I haven't sent a rod back in for a check up in a while, but what Brian at GRP has told me is they will get a bulge in the cap showing a crack in the thinnest point between the bolt boss and the journal.

    I sent a Top Dragster rod back for 'forensic' analysis after 43 runs. He said it had some hairline cracks developing but had not formed the bulge. He had to cut the cap in half to really look for this. He said 40-50 was a good point to remove them in that application.

    From a cashflow stand point, buying a new set of rods sucks because it's $1200 out of your pocket. From an amortization standpoint the risk does not really meet the reward.
     
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  10. TOL

    TOL Active Member

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    Thanks Will.

    That is quite useful and interesting information. So if I understand correct, the hairline cracks on your 43 run rod were in/on/within the main cap structure, near the bolt head of the nearest main cap bolt? Any particular side, or both? I am assuming an aluminum cap like the rod material?

    Anyone run tool steel rod main caps bolted to AL rod bodies? Kind of like the older Pauter rods?

    Interesting stuff.......
     
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    Last edited: Oct 26, 2018
  11. MaineAlkyFan

    MaineAlkyFan Active Member

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    Another thing we keep an eye on is the bearing pins on the cap side. They can start to get loose or get rolled edges.

    Chris Saulnier - Team Tigges
    Mechanic Falls, Maine
     
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  12. rb0804

    rb0804 Member

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    There is a guy in Virginia that makes aluminum rods with steel caps. I believe you know him as he has a couple, three too many camshafts in his top sportsman car. He told me that aluminum rods flex at the parting line and it stresses the bolt and bolt holes and eventually they will break. He also told me that he has a go no go gauge that he uses to check the rod bolt holes and without the steel cap at x amount of runs (I forget the amount) the go no go gauge will fall into the bolt hole if the rod had an aluminum cap on it. With the steel cap on it, the go no go gauge still fits into the hole snugly like it was new. Now he uses these on top sportsman stuff and isn’t seeing the abuse of a TAD/TAFC, but if I had a disposable budget like some of the Alcohol guys, I’d have a set in an engine to see if they are worth anything.
     
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  13. kosky racing

    kosky racing Comp Eliminator

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  14. kosky racing

    kosky racing Comp Eliminator

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    The RPMs of the alky cars do not like the added weight of a steel cap
     
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  15. Mike Canter

    Mike Canter Top Dragster

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    Also steel and aluminum expand at different rates so that would be a real problem
     
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  16. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    This was my thoughts on what the parting line expansion difference would do to the bore of the big end.
     
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  17. TOL

    TOL Active Member

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    Steel caps with aluminum rods (Bi-Metal rods as they are called.....) have been used for decades in many engines all over the world with great success, over many thousands of miles, and heat cycles, and high RPM excursions (motorcycle). The physical science is not new in this regard.

    Pauter used to make them for big inch applications. Patrick currently makes them for same. I'd like to see an FEA analysis of one in the application we are talking about. On my to-do list.

    I'm not saying that this the appropriate answer, just one answer out of many possibilities.

    Why did they do Bi-Metal rods in the past? : 1) Space constraints at the time. 2) Failures of the big end AL cap at elevated RPM.

    More food for thought.
     
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    Last edited: Oct 28, 2018
  18. MaineAlkyFan

    MaineAlkyFan Active Member

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    Just some quick math, the differential between coefficients of expansion of aluminum & steel is .0000058in/in per degree F. If we assume 70°F ambient & 400°F big end rod temperature after a run with a 3" bolt-bolt spacing, that is an .00057" differential.

    That seems like quite a bit.

    Chris Saulnier - Team Tigges
    Mechanic Falls, Maine
     
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  19. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    400 degrees seems pretty high. If there was that kind of temp, you would think the head temp thermo couple would read at least 250+ at the end of a run or shortly after. The hottest journal would probably be 7-8 due to radiated heat from clutch/converter. I don't think a Top Alky clutch gets much over 400 with all the friction it endures.
     
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  20. rb0804

    rb0804 Member

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    Who’s gonna be the first to try a set of these?
     

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