Talk to me about the stock con rods

1231 Views 8 Replies 6 Participants Last post by Section 8, Jan 14, 2002

Section 8

Discussion Starter · Jan 9, 2002

What are the limits of the stock con rods? Is it just the RPM limitation, or is there a HP/boost limit (talking more or less daily driver HP levels)? What is the RPM limit? If you are taking the block apart already, is it something that you should just blow $700.00 on and get it over with?

Apparently Adam Bloom did really well with a completely stock botom end. That project is actually the reason behind this corner cutting question.......

Greg

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Pipercub

· #2 · Jan 9, 2002

The stock conrods are pretty good and have held up well at 300HP. I would put 300HP as the max I would be willing to go as a daily driver on stock internals. Remember that is almost double. The weak point on the rods is the area just below the wristpin that secures it in the piston. There is pleanty of material there for normal and above normal use, to a point. But above 300 you are stressing it too much and need something thicker.

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AaronB

· #3 · Jan 9, 2002

My theory was that breaking a piston is bad enough, but a rod through the block, is quite a bit worse...

So I did both when it was opened (the first time)

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scoobyrs25

· #4 · Jan 12, 2002

Has anyone seen aluminum rods for us yet?

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yamarocket630

· #5 · Jan 12, 2002

you wouldn't want aluminum rods, they would be nowhere near strong enough.

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Hndatch627

· #6 · Jan 12, 2002

yamarocket630 said:
you wouldn't want aluminum rods, they would be nowhere near strong enough.

actually forged alumnium rods are awesome...they stretch though which is why they are built .010" undersized to begin. I would trust a forged alumnium rod over a factory cast steel rod ANYDAY! Only one problem with alumnium rods, most you'll have to do some machine work to the block to make the rod caps clear. I am planning on running Forged Steel rods(trying to find a phase II bottom end) so that way i am WELL withing a saftey margin. Anywho...the factory rods will hold about 300 HP don't push to close to that though.

jeremy

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yamarocket630

· #7 · Jan 13, 2002

Hndatch627 said:
actually forged alumnium rods are awesome...they stretch though which is why they are built .010" undersized to begin. I would trust a forged alumnium rod over a factory cast steel rod ANYDAY! Only one problem with alumnium rods, most you'll have to do some machine work to the block to make the rod caps clear. I am planning on running Forged Steel rods(trying to find a phase II bottom end) so that way i am WELL withing a saftey margin. Anywho...the factory rods will hold about 300 HP don't push to close to that though.

jeremy

Oh, yeah, I din't think of forged AL... I stand corrected

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Section 8

Discussion Starter · #8 · Jan 14, 2002

You could probably have AL rods made by someone who makes AL rods for other applicatins. I don't feel that it is as complicated making rods as compared to pistons, so being the first to have someone make them for you will not be much of a risk (the wrong pistons are usually replaced for free anyway, so the only risk is time, BUT you do need to know better to see something wrong with them). I can't, the engine builder most likely would.

I have decided that it would be best to replace the rods, especially since I am mucking around inside of the block already, and leaving room for improvment isn't a bad idea.

The advantage to AL rods is the reduction of mass, since they have to be much "beefier" than the comparable chromoly version, how much mass is usually saved? I have heard that the advantages of such luxeries as aluminum rods and titanium wrist pins are only really benificial when reving over 7-8000 RPM. Anybody car to comment on this?

What about the elastic nature of AL, if your builder knows what he is doing, is there any disadvantages concerning this? Longevity, not suitable for turbo applications ect? Anybody care to comment on price? I am going to search a bit, but I am completely unfamilure (except for hearsay) about AL rods. So it would be nice to know if I sould keep walking if I find something.

Greg

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Section 8

Discussion Starter · #9 · Jan 14, 2002

Alright, more garbage from the internet:

Aluminium connecting rods compress slightly (ignition stroke) and stretch slightly (top of exhaust stroke) and reduce the voilent impact placed upon the crank. This reduces the vibrations to the cam (tranmitted via the cam drive gears) oil pump, distributor and pretty much everything else. Why don't all cars use them? They are physically huge and need too much room to swing around the crankcase, apart from that, all this squeezing and stretching quickly degrades the aluminium and they require changing every 30 to 40 miles of flat out use - a bit expensive on the street!

This was from a dragracing site, with huge V-8's, so they would probably last longer than 30 to 40 miles of flat out use

, but the metal fatigue will eventually catch up with you. Now to find out how long that would be.

Greg

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