Where do you get shot peening done?

[method]

as far as im aware shot peening dont make the rod any stronger it de-Stresses it thus giving you pretty much a new rod. which makes sense to me but i fail to see how heating something up and hitting it with hammer makes it stronger.

however i may be completely wrong

Shot peening puts the surface into stress, it doesnt relax it of stress!

The reason for shot peening is as DeeCee said, to prevent fatigue faliure.
You should get them polished too, this will minimize any fine cracks or inconstancies where cracks can form.

And bashing metal with a hammer makes it stronger, when metals yield they become stronger.
Heating it up will relieve the metal of the stresses caused by yielding it though...

[Caveman]

yea i know that but he doesnt think theyre any good!

do you know what sort of % stronger it makes the rod?

30-40% according to my local auto machinist

haha your machinist must be on drugs

shot peening DOES NOT increase the strength of a rod! There may be the slightest increase due to the residual stress generated but they will be neglible. Put two samples in a uniaxial tensile test, one shot peened and the other plain cast. They will fail exactly the same.

shot peening does not change any of the material properties. Method was half right when he said the material is still stressed. It relieves any residule tensile stress but instead introduces residual compressive stresses in the surface.

The main roll of shot peening is resisting crack growth. This increases the life of the rod under cyclic loading.

Anyone feel free to correct me if ive said anything wrong.

[no_8wire]

thats how I understood it...
doesnt make it any "stronger" just cause lots of little stress points, so any stress is distributed more rather than focus on one weak point etc..

I have explained my self crap...never mind

[bluemaumau]

ah i see. he didnt recommend that, he just said i should look at bigger rods

cheers dylan

[strx7]

when he said 30-40% i think he's talking in terms of abuse/punishment, we are talking stressed race motors not mildly tampered with street motors. for sure nothing can outright strengthen something by that %

if comparing what power people have made on std rods, then compare it to what people have made with peened rods its definatley worth doing in terms of gains per $$ spent.

[KinLoud]

can anyone give me some info as to typical weight difference between a factory rod and a forged one. any engine, just as a comparision.

All conrods that I know of are forged! Cast ones wouldn't be able to handle the revs!
I presume what you are talking about is factory vs aftermarket rods?

Weights of aftermarket vs factory rods
4age silvertop rods with rodbolts/nuts
- approx 510g

4age aftermarket rods no bolts/nuts - 357g (refer to tech faq viewtopic.php?t=58213)
4age ARP bolts/nuts - 31g each = 62g per rod
Total rod + bolts/nuts - 419g

Can't find the reference at the moment but from memory the main reason for shot peening rods is to regain the fatigue resistance after the rods have been balanced and polished. Balancing and polishing removes some of the tough outer "skin" that results from forging. This "tough outer skin" resists fatigue cracking.

Top fuel dragsters use aluminium rods! Some will only withstand 100,000 cycles before cracking! (about 14 minutes at 7000rpm!) But they are lighter than steel rods so the engine will accelerate better. They basically rebuild the engines after each run so the poor fatigue life of the rod doesn't matter!

Ken
Ham
021 408 863