Groden aluminum rod stretch

[Grocerius Maximus]

Anybody have any practical experience with how much stretch Groden rods go through? Trying to decide on where to set the piston to cylinder head quench distance. We usually set it at .035" to .040" for steel rods, but with the aluminum rod and looser piston to bore clearance i'm a bit nervous. Do you think adding .010" will be safe? I don't want to go too far because then we start to see detonation at the intake valve edge of the piston.

6.125" rod, 400g piston/pin, 88mm stroke, 10,000 max RPM, turbo drag race application, approx. 1100 crank HP 4 cylinder app.

[learner]

I have never run a combination like that before. I would think .055"-.060".
Just for my information, what is the rod weight? If you don't mind.

[shawn]

You might check the rod length. Most of those are built with that .010 in them.The 6.125 rod will probably measure 6.115.
Shawn

[Grocerius Maximus]

You might check the rod length. Most of those are built with that .010 in them.The 6.125 rod will probably measure 6.115.
Shawn

Yes they are under length about ten thou.

[Grocerius Maximus]

Just for my information, what is the rod weight? If you don't mind.

These are 1.771" crank journal, .827" pin, 1.125" big end width, somewhere in the 450g neighborhood, I didn't get too concerned about weighing them because of the neutral balance crank and the fact they have been used with success before. No sense reinventing the wheel.


I disliked the bearing tang grooves being full circle cut and using a pin in the cap, the pin is located different on every rod and makes fitting bearings a royal pain in the ass. Build a fixture and it only fits one cap well. Grrrr.

[shawn]

I would think that the turbo would help soften the extension of the rod on the exhaust stroke,because it's using those gases to drive the turbo.The rod gets stretched the worst on a n/a application there.So using this logic, i wouldn't think that you would need anymore quench then what you would normally run.I know that with a piston that light, .040 should be enough. Have you asked groden what they recommned?

Shawn

[Torquemonster]

well I can tell you that in the 494 Mopar Indy Wedge Pro Mod I sponsored we ran an alloy rod as tight as 0.0425" - shifted at 9500rpm and ran 6 sec/200mph.... however it did touch - not hard enough to damage - but enough we raised the clearance.

But we ran 4.36" bore and 4.15" stroke with heavier pistons and a 7.125" rod.... you could probably run 42.5 thou - but 45 should be safe. These are clearances for pushing the limits - most will advise 55 thou plus and most should run at least 55 thou in your application

[Grocerius Maximus]

Thanks all for the advice.

Had to deliver the engine last saturday, it was set at .050", we'll see how it goes.

[Grocerius Maximus]

Well, so far things are looking good, went from 125 to 128+ MPH in the 1/8th with a .15 worse 60 ft and 3 degrees less timing on the only run last night on a poorly prepped track. Was running rich and less timing working on the new combo. Looks like we went in the right direction, went from 165 to 167+ up top w/o using the 2nd stage of nitrous.

[Adger Smith]

I think of it as Thermal expansion. Heat the rod to the operating temp of the oil & see how much it grows.

[la360]

What did you think of the quality of the Groden's overall??? I am looking at replacing my old BME rods. A comp eliminator racer I know of is running them, just haven't had a chance to ask him myself, he is on the road all the time.
AL....