2000 zx12 stock rod hp rating

[woody8w]

i was woundering wat the hp rating is for stck rods. are carrillo rods necessary? are the stock rods the weak link on these motors or not. im gonna have mine pullin hard and up on the revs so just curious if i dnt need them i wont buy them thanks

[peanut r1]

what kind of hp? whats the set up? are you shooting nitrous? a little more info will help

[cabrazx14]

I sprayed 80 shot on my bike with stock rods and never had a problem.

[woody8w]

no nitrous its just a stock bore motor and gonna be run in dirt car dnt know the hp rating

[peanut r1]

stock rods will be good for that

[woody8w]

ok thanks for the imput

[CompetitionCNC]

Thats a question that i get asked all the time.

It's not really a HP issue. Its a load issue, more specifically a tension load issue.
Rods don't break because they are put under compression loads due to increases in torque output.
Pins might but rod beams and rod bolts don't.

Rods break because either they starve for oil and get hot and break or the tension loads exceed the rods limits or the tension loads exceed the bolts limits.

The heat issue is usually due to lack of oil flow past the bearing to cool the crank and rod. This can be from tight rod bearings, misaligned rod caps, out of round big ends, or simply not enough flow thru the oiling system for many other reasons.
When this type of failure occurs the rods are blued on the big end and usually end up spinning a bearing as a result.

When the rod it self is overloaded in tension the big ends can go oval which can pinch the bearings in and create heat and spin a bearing. Or the beam can simply snap off, or more commonly the bolts strength can be exceeded and the rod caps can walk or even pull away from the rod. When this happens the bearing crush is lost and it comes loose and will likely spin or the bolts will just snap off.

The tension on the rod is highest at TDC during valve overlap not at TDC when firing the cylinder. This is because of the pressure on top of the piston at TDC during firing. This is also when the piston is most likely to contact the head.

This tension load on the rod and bolts is determined by the stroke, the length of the rod and the weight of the piston, pin, and small end of the rod and also most importantly the rpm of the engine.
The g loading on the rod gets crazy at high rpms. As the rpms rise so does the g loading in tension on the rod and bolts.

So, on a stroker engine where the stroke is longer the rod is under more tension at the same rpm vs a stock stroke engine. Or if you rev the engine another, lets just say, 1000 rpms the load is higher.
A stock rod and bolts are designed to handle stock stroke and stock rpms and as long as the rods get proper oil supply they work fine, but increase either the stroke and or the rpms and you may need stronger bolts or rods or both.

When we run our 5mm stroker engines up to 12,200 rpms with peak power at 11,800 rpms you better believe we need and use better rods and bolts.

This is exactly why turbo motors can make 400-500 hp on stock rods. The rods and bolts are not under any more tensional load than a stock engine as long as you don't over rev the engine.

[NCTWINGEE]

Great post Jim!!!