Engine internal part strength

[racetek82]

I'm rebuilding a 91 7MGTE, and I'm considering dropping in some aftermarket internal parts. I thinking about going with a set of Probe pistons, ARP head studs, rod bolts, and main studs. I also have a Cometic MHG.

The thing I'm on the fence about is the rods. I'm looking at a long term goal of 500-600whp, would a set of shotpeened stock rods hold up, or would a set of Eagle rods be a better investment? I'm not sure if I can afford to get the rods too, but if it makes a big difference, I guess I can try to scrape up the cost difference. Any input to reassure myself would be much appreciated.

[IJ.]

5>600 I'd get new rods.

[Doward]

Eagles would be a great investment.

[Zumtizzle]

X3 For Eagle.
But i love the Pauters if you have the money.

I'm Taking a Risk with stock rods, i'm just gonna have 400ish HP. I maybe going 2JZ if i granade a 7M. But it's never let me down before.

Peening the Rods is a waste. Magna Fluxing is worth doing IMO.
http://www.supramania.com/forums/showthread.php?t=67054

[Newkid]

Well I done some research and read that the stock bottom end would be good for 500rwhp. That its all up to the tune

[jdub]

500 HP is at the top of what I would run on stock rods and that leaves little margin for error. I'm with IJ...get new rods if you plan on pushing those kind of numbers.

[racetek82]

Okay, Eagle rods it is. Now, any opinions so far on the Probe pistons? The price isn't too far off from just getting JE pistons, so is it worth going cheaper with the Probe pistons? Any money I can save will go toward other deserving mods.

[Nick M]

Engines 101. The rod is the first thing to go.

[IwantMKIII]

Engines 101. The rod is the first thing to go.


unless you melt the piston :icon_bigg


BTW. Stock internals are proven at 500whp on a good tune. In fact on a very good tune, someone just did 750WHP with no breaks. I Pm's him awhile back and he's been running 500whp reliably for some time now with many 600+whp track and dyno runs and a few 700+ dyno runs

[jdub]

And Mike Malloy threw a stock rod at ~540 HP...doing 70 mph on the interstate.
My 7M passed away today (http://www.supramania.com/forums/showthread.php?t=32197)

The stock rods are good, but only as good as the weakest link. The problem is you don't know which of the six it is ;)
The guy you know is lucky.

[IwantMKIII]

And Mike Malloy threw a stock rod at ~540 HP...doing 70 mph on the interstate.
My 7M passed away today (http://www.supramania.com/forums/showthread.php?t=32197)

The stock rods are good, but only as good as the weakest link. The problem is you don't know which of the six it is ;)
The guy you know is lucky.

In regaurds to this, do yourself a favor and have your rods magnafluxed and possibly see which of rods IS the weakest. It can't see internally weak points but will tell you whether yours rods are tip top or will break sometime soon with inceased power.

[jdub]

In regaurds to this, do yourself a favor and have your rods magnafluxed and possibly see which of rods IS the weakest. It can't see internally weak points but will tell you whether yours rods are tip top or will break sometime soon with inceased power.


LOL...I did myself a favor and purchased Pauter rods ;)

Like I said, the stock rods are good, but the alloys used are for conventional automotive mass produced rods to keeps cost down. If the rods have internal stress fractures or voids from impurities, magnaflux will not show it. If you're going to spend the $$$ on a 550 HP build, why go cheap on the rods?

Another thing to have done is have stock rods properly stress relieved (shot peened). I still would not use them over a 500 HP goal.

[IwantMKIII]

LOL...I did myself a favor and purchased Pauter rods ;)

Like I said, the stock rods are good, but the alloys used are for conventional automotive mass produced rods to keeps cost down. If the rods have internal stress fractures or voids from impurities, magnaflux will not show it. If you're going to spend the $$$ on a 550 HP build, why go cheap on the rods?

Another thing to have done is have the rods properly stress relieved (shot preened).

you answered your own question :icon_bigg

FTR. Mine were magnafluxed, we will see how they do when a bigger turbo rolls around lol. That is when my engine is in a non-crisped car.

I've heard shot peened rods are even stronger than the other aftermarket ones, ever heard of this?

[Rennat]

hasnt it been said that OEM rods are shot peened? lol

and theres no way that an OEM rod can be stronger than a aftermarket rod due to the metallurgyof the aftermarket rods, there a completely different procedure to make them, which is why we buy them.

and isnt the weakest point of the OEM rod the oil hole on the lower half of the rod too?


and when you can buy nearly ready to go eagles from suprarich for $400 shipped, you'll never use OEM rods again. lol

[IwantMKIII]

hasnt it been said that OEM rods are shot peened? lol

and theres no way that an OEM rod can be stronger than a aftermarket rod due to the metallurgyof the aftermarket rods, there a completely different procedure to make them, which is why we buy them.

and isnt the weakest point of the OEM rod the oil hole on the lower half of the rod too?


and when you can buy nearly ready to go eagles from suprarich for $400 shipped, you'll never use OEM rods again. lol

I have no idea what their composite is vs. aftermarket....just one of those things you hear along the way and are very skeptical of but still think..."well...maybe"

[racetek82]

No need to debate, Probe pistons and Eagle rods it is.....that's some good pricing on the Eagle rods...I might have to PM SupraRich now...=)

[IJ.]

mmm Pauter roddly goodness :D

[jdub]

you answered your own question :icon_bigg

FTR. Mine were magnafluxed, we will see how they do when a bigger turbo rolls around lol. That is when my engine is in a non-crisped car.

I've heard shot peened rods are even stronger than the other aftermarket ones, ever heard of this?



Shop peening is primarily to increase fatigue life. It works through a mechanical plastic deformation of the metal surface...think of each shot as a tiny hammer. It's very important that the correct size and hardness shot is used at the correct velocity for the specific part to induce the desired residual compressive stress to the metal surface. Shot peen does have an effect on the internal tensile stress, but this is less of a problem since cracks tend to originate at the surface.

Shot peening does help to strengthen the part, but the same factors apply to the stock rod alloy and the chance of internal defects.
There's no way I would risk the investment in my motor pushing 500-600 HP on stock rods.

BTW - I/we were discussing the OP's goal of hitting 500-600 HP on his motor. I'm not the one with a question ;)


mmm Pauter roddly goodness :D

They are nice! I had the oil channels cut on the crank end...I didn't do the EDM direct oiling for the piston pin. CP pistons have a double forced pin oilers for the wrist pins...would have been severe over kill ;)

[Rennat]

No need to debate, Probe pistons and Eagle rods it is.....that's some good pricing on the Eagle rods...I might have to PM SupraRich now...=)


its what im gonna be running... just wish i would have gotten the tops of my pistons ceramic coated... would have been a nice little extra feature.


i dont plan on going over 500hp though, so im not worried.

[IwantMKIII]

Thanks for the explanation Jdub, but i'm completely aware of how and why shot peening works. Again, i simply did not and do not know the difference in materials used on stock rods vs. aftermarket and how they are cast/forged (whichever applies). I guess logic should have answered my own question, i just never really sat down and thought about it, just kind of threw it out there.

[bigboost7m]

Okay, Eagle rods it is. Now, any opinions so far on the Probe pistons? The price isn't too far off from just getting JE pistons, so is it worth going cheaper with the Probe pistons? Any money I can save will go toward other deserving mods.


My personal experiences have been anything but good with Probe pistons. I've never built a 7M with probe pisotns, but I have built quite a few "budget" minded builds on V8's with probe pistons. Each one had a really awkward skirt profile; the wear pattern was never the same on any of the pistons. And I know for dam sure the machining was done correctly, it was all done on CNC machines at my old job (Livernois Motorsports). Each set of pistons typically had +/- .0006":aigo: difference between the 8, and they were all measured at the recommended measure point (.400" from the bottom of the skirt). And also, each set of pistons had pin oiler grooves, but they were 180deg apart from each other (9 and 3 o'clock position), the proper place for them would be closer together, near the 11 and 1 o'clock positions, that would intern lead to excessive wear on the pin boss bore.

But then again, none were on a 7m though. I think what usually is true for one is true for all. If it was me, I would go with the JE's, no question about it.

[Adjuster]

The 7M rods are forged, and they are shot peened stock.

The weak link on the stock ones is the cheap ass bolts, and then the oil squirter hole at the shoulder of the rod...

I've seen stock ones fail there, and at the bolts..

HP wise, if your going to spend the money on the motor, why go cheap on the rods?

Pauter makes the nicest 7M rods.. :) This is why I have them on my stroke'd 7M.. Of course, they are really made for a 327 SBC, but hey, the design is the same, only the 327 has 2" mains and slightly larger pin bores than the 7M... (You'll need custom pistons with custom pin heights and much more.)

The Pauters make my engine resistant to abuse, at least so far. ;)