dan, i looked at the shop manual at a ford dealer, the clearances are the same. (wish i'd had the opportunity to measure for myself.) i'm guessing the true difference is the intended use/application. the cobra R is marketed as a "racecar," so the oil temps at the end of a long track session might mean the 15w-50 is as thin as a 5w-20 is during light/regular street use.
the clearances are actually tight, compared to what i'm used to seeing. from memory (this is ~4 years ago) both the rods and the mains had .002" as an upper limit, with middle of the range roughly .015".
i actually did not intend to say i think the original poster should use a thick oil, i just wanted to point out the folly in making a blanket statement that modulars require thin oils. (a blanket statement even ford doesn't make, apparently.)
one thing i have noticed about (4V, i never had the opportunity to try this with the 2V) modulars is oil pressure. it's extreme. i put a mechanical gauge on a few i built while on the dyno, and i was shocked. the 100psi gauge is pegged through the upper half of the rev band.
i think they also have some sort of inherent oiling problem, either in the drainback, or maybe the pan/pickup design. during a lot of dyno pulls, i noticed the oil pressure drop all the way to zero, then slam all the way back to the peg, somewhere in the upper rev band. it did not happen consistently, but i noticed it on multiple cars, including ones that were near stock. this pressure loss was less than 1 second long, and so fast that the stock gauge and/or idiot light would never catch it, i never saw it until i used a mechanical gauge.
something else about those engines, the cam bearing bores are almost always out of line. one or more of the cam journals would usually be ultra tight. (i don't know if this plays into ford's recommendation of thin oils, but probably not.) i had a few problems with that when using aftermarket cams and/or mega rpm/hp, so we started to just machine the heads to insert cam bearings and all the problems vanished. (stock the cams ride directly on the aluminum of the head.)
quote:
Originally posted by mf150:
seems like complete BS to me, especially since my pal has a cobra and uses 5w30 (4V DOHC 4.6L).
since you asked nicely, let me backup my "BS" by asking you to google "cobra r 15w-50," you'll find plenty to corroborate my assertion, including mobil's own website.
quote:
Originally posted by mf150:
I'd put my money on 5w30
pay up!
thing is, i don't think any of us have yet seen an engine fail due to using the "incorrect" viscosity. so who's to say what's "incorrect?"
i worked at mti, then helped start houston performance, and built plenty of modulars. i'm definitely familiar with them, tuning them, racing them, and i was doing so since '96. (i'm out of the industry now.) i never saw an oil related failure (except for oil starvation, which might still be some inherent oiling problem as i described earlier, but open-tracked modulars had a habit of blowing up unless the oil system was modified), so i can't tell you anything about what oils work best in them, because they all worked fine to me. i never even saw any oil pump breakages that were widely reported in the high hp cars, so i can't comment on that either.
i see nothing more concrete in your anecdotal evidence, even empirically it's not enough data, especially since we have evidence to the contrary. (that thick oils don't hurt modulars.) but you assert that a 10w30 should be more than enough, and i can't argue against that. ford would argue against that on the cobra R, but we don't have the full story there, i'll concede that.
again, i'm not trying to comment on the use of 15w40 vs 5w20, just trying to bring a saner view to the debate.
thanks.
-michael
