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  • #1

    Connecting rod question

    I am considering upping the jetting on the TNT kit for another 25 horse to the wheels, hoping to reach a 125 mph trap......

    I am wondering if I am flirting with disaster though. I am not exactly sure what rods I have as the car was purchased with the storker kit. When I did the rebuild, the machinist said it looked like a SCAT crank. Anyways, the rods appear to be stock, but I am wondering if that is likely. The pistons are keith black hypereutectics. Is it possible the stock rods could have been used?......or would the stroker kit have come with a better rod? In any case, I dont think they are anything special.......

    Assuming that it is not a forged rod, am I flirting with the "line" now? COuld I add some more juice to this thing?
    96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
    11.6 @ 123mph (1.6 60' - getting there )
    Tags: None
  • #2
    I've seen 2 cases documented of failure of a stock PM rod. Both cases were probably running about 600 flywheelHP, counting the juice. Sounds like you might be getting near the limit if they are stock PM rods. If they are stock and not PM (PM's strated in early/mid 94???) they are probably rated 50-75HP lower.

    A "basic" forged rod would probably have a higher HP capacity, able to handle the 600HP without failure.

    Just thinking out loud.....
    Fred

    381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

    Comment

    • #3
      You could always just pull the oil pan and look to see what's in there. I would have to agree that you are pushing the limit if they are in fact the PM rods. I would hope that whoever did the scat crank also did a set of aftermarket rods.

      Did the machinist say whether the crank was cast or forged? That might help to determine the actual "goal" of whoever previously built the shortblock. If the rods turn out to be upgraded, your weak point will still be the hypereutectic's. The Swain coating might help a little, but they will still be on the edge with the power you will make on a 150 shot.

      Comment

      • #4
        It's usually RPMs that kill rods & rod bolts, so keep that in mind.

        Comment

        • #5
          Scat rods can usually be identified from the bottom by their unique rod cap design. They have a rectangular shaped reinforcement on the bottom of the rod cap.

          Comment

          • #6
            Originally posted by fastTA
            Scat rods can usually be identified from the bottom by their unique rod cap design. They have a rectangular shaped reinforcement on the bottom of the rod cap.

            That looks like my rod........but then again, that looks a lot like a stock rod too! I should have asked this question when I had my motor apart. So is that a forged rod?

            The crank was cast......so the previous builder was not looking to built a 9 second car or anything.....

            So, you think the Keith Blacks are my weak point? Cracking? Swain virtually guaranteed them against melting.....he did do the job for me for free, so I wouldnt hold him to it!
            96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
            11.6 @ 123mph (1.6 60' - getting there )

            Comment

            • #7
              Originally posted by Injuneer
              I've seen 2 cases documented of failure of a stock PM rod. Both cases were probably running about 600 flywheelHP, counting the juice. Sounds like you might be getting near the limit if they are stock PM rods. If they are stock and not PM (PM's strated in early/mid 94???) they are probably rated 50-75HP lower.

              A "basic" forged rod would probably have a higher HP capacity, able to handle the 600HP without failure.

              Just thinking out loud.....
              Well, I am making 460 something at the wheels on the mustang dyno......so I figured 525 or 550 at the crank? So, another 25 wheel horse would put me close to that 600 HP mark......Hmmmmmm......
              96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
              11.6 @ 123mph (1.6 60' - getting there )

              Comment

              • #8
                It seems like all the kits I am researching come with connecting rods. I searched "SCAT connecting rod LT1 383" and found this kit. Maybe this is the one that was purchased for my car? Its the only one ive found that comes with a SCAT crank and keith black pistons. It seems like the rods should be upgraded from stock.

                So, if I have the PM rods, 600 HP is probably the "line".......what about these SCAT rods?.....and Kevin mentions the KB pistons......if this is the kit I have, what do you guys think a safe HP level would be (assuming the A/F ratios are nice and safely rich).

                http://www.strokermotor.com/RALT1383.htm
                96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
                11.6 @ 123mph (1.6 60' - getting there )

                Comment

                • #9
                  What size rear tire are you using?

                  Comment

                  • #10
                    Originally posted by N20LT4Bird
                    It seems like all the kits I am researching come with connecting rods. I searched "SCAT connecting rod LT1 383" and found this kit. Maybe this is the one that was purchased for my car? Its the only one ive found that comes with a SCAT crank and keith black pistons. It seems like the rods should be upgraded from stock.

                    So, if I have the PM rods, 600 HP is probably the "line".......what about these SCAT rods?.....and Kevin mentions the KB pistons......if this is the kit I have, what do you guys think a safe HP level would be (assuming the A/F ratios are nice and safely rich).

                    http://www.strokermotor.com/RALT1383.htm
                    I seem to remember seeing a few kits with a Scat crank and rods and KB Hypers as a kit. Probably have a marketing relationship.

                    Your Swain coating will help to keep heat out of the piston, but the real weakness of a Hypereutectic is in the ring lands and wrist pin location above the skirt. Nitrous can produce some pretty violent spikes in BME pressures which can wreak havoc on the upper ring land (compression ring). Of course, a dead on tune will help to minimize pre-ignition and/or detonation which will greatly help in preserving the life span of your motor.

                    Aside from the piston, I would really try to find out what rod is really in there. Another thing I would look at is whether they press fit the wrist pins or bushed them for a full floating pin. Connecting rods that are designed for pressed pins have a smaller end diameter that is actually smaller than the wrist pin diameter. The process of installing a press fit wrist pin usually involves heating up the rods then inserting the pin. Then you allow the rod to cool and the contraction will hold the pin in place while being pressed. If they're made for full floating they have a bushing in the end that is honed about .001" bigger than the diameter of the wrist pin so it can rotate in the small end of the rod. Full floaters also have an oiling hole drilled into the top of them to allow oil to get down onto the wrist pin and allow it to stay lubricated. If it is a full float pin you should be able to see the spiro-locks.

                    Full float pins if installed correctly will handle additional n20 much better than a press fit wrist pin. So find out which rods are in fact in there and then you will have no doubts. If they are 4340 full floaters, then spray away!

                    Comment

                    • #11
                      Originally posted by Joe 1320
                      What size rear tire are you using?
                      26X11.5X15 why?
                      96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
                      11.6 @ 123mph (1.6 60' - getting there )

                      Comment

                      • #12
                        Originally posted by fastTA
                        I seem to remember seeing a few kits with a Scat crank and rods and KB Hypers as a kit. Probably have a marketing relationship.

                        Your Swain coating will help to keep heat out of the piston, but the real weakness of a Hypereutectic is in the ring lands and wrist pin location above the skirt. Nitrous can produce some pretty violent spikes in BME pressures which can wreak havoc on the upper ring land (compression ring). Of course, a dead on tune will help to minimize pre-ignition and/or detonation which will greatly help in preserving the life span of your motor.

                        Aside from the piston, I would really try to find out what rod is really in there. Another thing I would look at is whether they press fit the wrist pins or bushed them for a full floating pin. Connecting rods that are designed for pressed pins have a smaller end diameter that is actually smaller than the wrist pin diameter. The process of installing a press fit wrist pin usually involves heating up the rods then inserting the pin. Then you allow the rod to cool and the contraction will hold the pin in place while being pressed. If they're made for full floating they have a bushing in the end that is honed about .001" bigger than the diameter of the wrist pin so it can rotate in the small end of the rod. Full floaters also have an oiling hole drilled into the top of them to allow oil to get down onto the wrist pin and allow it to stay lubricated. If it is a full float pin you should be able to see the spiro-locks.

                        Full float pins if installed correctly will handle additional n20 much better than a press fit wrist pin. So find out which rods are in fact in there and then you will have no doubts. If they are 4340 full floaters, then spray away!
                        I do know they are full floaters, because i remember fighting with the damn spiro-locks when I took them apart to bring the pistons to Swain......other than that, I guess I gotta pull the pan if I wanna spray more, which is gonna suck.....I really wish I checked on the rods when i had it apart....
                        96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
                        11.6 @ 123mph (1.6 60' - getting there )

                        Comment

                        • #13
                          Originally posted by N20LT4Bird
                          26X11.5X15 why?
                          if you can step up to a 28" tire, you should see a 2 mph increase in trap speed without a loss in ET.

                          Comment

                          • #14
                            28's might be a tight fit in the wheel well......but thats not a bad idea......I would probably reduce the torque on the launch for a little less slippage too.
                            96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
                            11.6 @ 123mph (1.6 60' - getting there )

                            Comment

                            • #15
                              Originally posted by N20LT4Bird
                              I do know they are full floaters, because i remember fighting with the damn spiro-locks when I took them apart to bring the pistons to Swain......other than that, I guess I gotta pull the pan if I wanna spray more, which is gonna suck.....I really wish I checked on the rods when i had it apart....
                              That's good they are at least floaters. I know it sucks pulling the pan with a stock k-member but at least you will know what is in there.

                              Get one of your students to pull the pan for you!

                              Comment

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