SBC NASCAR rods

[NeilRoshier]

I have noted with some interest that some SBC NASCAR engines use (reputedly) a honda rod journal size of 1.888. What is the particular reason for this? (reduce crank weight etc?)
What is the expected life span of such a set of 'NASCAR' carillo 'H' beam rods from such an engine (curious as there seems to be a range of 'just!?' used engine parts often marketed on the usual forums)

 

[patprimmer]

The two reasons I know of for reduceing bearing diameters are
To reduce the periferal or surface to surface speed of the bearing
To make room for the con rod if the stroke is increased, and the rod ends up hitting the cam, gasket rail or the bottom of the bores.

I don't know the NASCAR rules, but I expect that big strokers are not allowed, so the only reason I can think is to reduce the bearing speeds at the very high rpm used.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patdaly]

Neil, They do it for Recip. weight savings and to reduce bearing speed.
The life would be quite a variable, as a short track race would impose significantly higher loads on the Rod than say a restrictor plate race. As for your concern, I would share the same, unless they were traceable to a major team, and as such, you would pay more.

Unless you are really pushing them though, they should be fine for anything us mere mortals would do. ( after Magnaflux of course )

 

[NeilRoshier]

thank you both for your responses. Patdaly I am perhaps even more 'mere' than most and had thought of using them in a 4cyl race engine with RPM's up to 7500. I would imagine that the 'carr' bolts are usually throw away items given the unknown previous use?

 

[clshore]

Yah, it's a HP thing.
The so-called 'honda journal' saves a few HP, and the reduced recip weight also helps at higer RPM (inertia loads increase as the square of the RPM). Bearing loading is really not so much of a factor, since the PV varies directly as the journal diameter changes. So in theory, diamter matters not at all, only width. But from a practical standpoint, a larger diameter will mean more thermal mass, less unit loading from combustion forces, and also allows more oil to flow into the bearing, significant for cooling (and thus ultimate lifetime).
I've acquired a set of these rods for my 4-banger, as they are about 250 g lighter than stock, with the ability to handle twice the power.
There is also some anecdotal evidence that the stock Honda bearings are more durable and of better quality, (perhaps due to tetraethyl lead coating which yields a 30% higher PV in the same sizes).

As always, YMMV

Carter Shore