So you think a car from 1964 will have equal power, economy, interior room, and safety as a car today? Interesting.

I'd really like to see a back to back test of lighter oils vs heavy to see just how much power/ mile per gallon difference we are talking. If you ask me I don't really think there has been much if any improvement over what we had 50 years ago. Everything built today is lighter and over-driven.

I remember the Honda bearing thing . And I remember some impressive research done on the bearing clearance science by I believe Carrilloon bearing surface temp in relation to clearance ,if memory serves me correct on BBC going +or minus the 002 had negative results

The benefit from the Honda bearings besides being tough , was there were several color coded sizings within that range they would put you exactly where you wanted to be on every journal

Sorry guys can only type a paragraph before the phone spaze but the gurus I have sponged from on most builds go square clean and exact at specs for journal size 0.0000 taper ect

Not a thinking matter. I know. Fuel economy didnt suffer until the 70's when smog devices started showing up and the knocked all the compression out of the motors.

First off, I don't know the EXACT clearances that the NASCAR engine builders use so I will have to check on that. I do know that there average operating temperature is way above what a drag race engine SHOULD see and in this case I can see the clearances tightening up a little but due to component expansion but I don't think its whole lot. I will have to call some of my engine building friends over there and ask. I also see why there oils wont/don't/cant make power in a drag racing engine. We have tested all there high dollar oils that where specially formulated for them. Some costing in the $30.00 a quart range. They all failed miserably in the power department. There oils are formulated for extreme temps above 200+F and have additive packages to withstand stresses for extended periods of time. Anyone who takes a Drag racing engine over 140F at launch needs to have there head examined! (personal opinion)

The main and rod diameters we use are stock BBC and SBC and the Pro Stock engines have a 1.880rod journal a little over .625" wide and a 283 SBC main about .750" wide. Total bearing surface area in a P/S engine is about 20% less than a stock SBC.
If your looking at some preconceived clearance derived from the bearing diameter and surface area your missing the point. You cant scale the clearances up and down from a simple equation based on surface area and bearing speed. Don't take me wrong here, you must take into account the bearings surface speed and area but they are not the major factor in determining clearance. Factors yes, primary factor, no. You need to consider Internal component deflection and distortion when determining bearing clearance as well. We still routinely hone rods oval. Wider at the parting line than top to bottom. Why, because the rods distort under dynamic conditions and the parting line pulls in and wipes the bearing. When the bearing parting line touches the journal, BOOM out the side of the block it goes. We have had to oval Titanium rods .0075 at the parting line in order to make them live! Titanium has a very high modulus of elasticity in comparison to steal so the deflection and contortions of the rods big end had to be compensated for.


Why people think that there is something in having tight clearances is something I just don't understand?????
What possible benefit could you derive from shrinking the clearance down that last little .001 close to where the bearing seizes?????
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Darin Morgan
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Darin Morgan
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Joined: 02 Nov 2004
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Location: New Carlisle
Posted: Sat Mar 04, 2006 10:01 pm Post subject: Re: help with switching to 0-30w oil

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seth wrote:
when switching from a 20-50w to a 0-30w oil do you need to tighten up the clearances. I have tried 0-30w oils in the past with limited sucess. if i run .001" per inch of dia. as my oil clearance do i need to tighten that up and how much as a rule.

amsoil racing oil 20-50w and switched to their 0-30w bearing life has been shortend drastically.

as of now i'm not sold on the 0-30w


If your having bearing problems with 05-30W synthetic oils your problems are not with the oil as much as they are the clearances and the machine work. Bearing misalignment or worse yet, to tight a clearance will hurt you every time. A good line honed main and properly trued and honed rod housing bores seem like a given but they seldom are. They need to be addressed, checked out and honed by a professional that knows what he is doing. You need to have .003 on the rods and .0035 on the mains or your playing with fire. We run .003+ on the rods at all times never less than that, ever. We run .0035 to .00375 on the mains and never less than that, ever. On engines with higher loads the clearances go up never down. Pin bores can have up to .00225 for clearance on some engines with high vacuum in the crank case and good oil control in the pan. The better the oil control and vacuum in the pan, the less oil the wrist pins get! We run 0055 (not a misprint) weight and it about the thickness of water. we run .0035 on the rods and upwards to.004 on the mains in the PS engines and the mains last all year long. Our 1300 horsepower Super Series engines have .003 rods and .0035 mains and run for 600 runs down the track! The record so far is 675 runs by Scotty Richardson.

(1) Get a good, professional machinist to line hone the mains and hone the rods properly.
(2) Make sure you have proper oiling. If your pressure fluctuates during the run,, you have problems.
(3) .003 rods and .0035 mains for clearance
(4) Use a good synthetic 05-30w oil like Mobil-1 or Castrol syntec
(5) In my personal opinion you need to stop using any oil from Amsoil. That is not a racing oil even if they say it is.
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Darin Morgan

We talking just engines, a certain part or parts of engines, or complete 50's / 60's vehicle vs complete 2010's vehicle ?

BTW: Always love the Darin Morgan info. He's one of my fav's to study and thus of course quote.

Doesn't he mean that Ti has a lower modulus of elasticity than steel?