Quote:
Originally Posted by na svt
Mod motor clearances are pretty tight compared to the Ford pushrod stuff. A couple of the "high RPM" guys say that oil viscosity play a large role in how the lash adjusters work at high RPMs. I have a feeling the low RPM engines (7k and below) won't see any changes by running a 30w as opposed to a 20w oil.
These are pretty tight:
main bearing oil clearance 0.0001 - 0.0018
rod bearing oil clearance 0.0011 - 0.0027
Aren't the pushrod mains 2-3 thousandths?
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I have seen guys turning 9000-10000RPM with all different viscosity so I don't see it being that much of a factor. There are guys with 10W and guys with 50W and it doesn't seem to affect the adjusters as much as people would have you believe. If you believe you are having adjuster pump up then use the GT adjusters and rockers which are anti pump designs. I remember Cushman making a comment once that he was turning 9500RPM with 15W40 in his 4V.
Those main bearing clearances are for a cold aluminum block probably which sure doesn't keep that spec hot. Every stock modular rod I have ever measured has been dead on at ~0.002" for these motors. Basic rule of thumb is 0.001" for every 1" of diameter, seems to work on every motor from a Honda to a Hemi.
Like I said though, the lighter weight oils you see the differences in the cam bores more than anywhere else. The heads run at like 50% of the oil pressure you see on the gauge and I have measured as low as 5PSI in a modular head. We did a lot of testing with the head pressures when testing the GT rockers and adjusters vs the stock ones and learned a ton.