92rslt1

I was wondering is a loose motor or tight motor better for high performance? I think a loose would be because there more room for oil between the bearing. but then again theres more room for slop. hmm

93LT1355

looser clearences are better for performance

blackztpi

lol. you want your clearances as tight as possible for longevity. if you get them perfect and even all around, you will hold perfect oil pressure from new to 150,000 miles. looser clearances usually allow for more beating of the bearings, as it's more possible for the parts to actually move around in the bearings. if a stockish setup is revved to high, the crank can actually float off the bearing surface inbeteen shifts when there is no load on the crank.
in a general statement, you are correct, though. nhra uses clearances you wouldn't believe for less friction, but since you are probably not going to make it a 1/4 mile car only, you want to run the tightest clearances possible. typically a forged motor will have more clearance, but those clearances tighten once it's warm. forged expands more cast parts. a typical forged piston might see .005" piston to wall clearance, and a typical cast piston might see .0035" p to w clearance.
so, if you run forged, follow torque specs of a forged setup, but don't go setting huge clearances in anything for the sake of a little horsepower.

93LT1355

Most definatly, when I rebuilt my engine I took the time to measure out all the clearences to the specs given to me by my machine shop so I could build a strong motor that lasted. I was speaking in generality that looser clearences would give more horsepower because of less friction, but I would never advice putting an engine together loose to try to gain something. I would build to last.

92rslt1

just what i thought. i agree to. but what weight oil are they using 20=50w? so you have more chance of spinning a main on a loose engine?

"White Knight"

Do you plan on rebuilding your motor a lot?

92rslt1

nope. just wondering

93turbo5oh

most of the stock eliminator guys are running 0w10 redline race oil. their is an optimal clearence range for main/rod bearing. for oil flow rate at .015" clearence is approx 1/3 gal/min. at .020" that goes up to about 1/2 gal/min. at .025" it goes up to approx. 1 gal/min.

as far as bearing temp rise, at .030" you are looking at approx. a 5 degree rise, at .025" about 8 degrees, at .020 approx 10 degrees, at .015 about 18 degrees, at approx .010 it jumps to 38 degrees.

relative load capacity is much higher at .020 then .015". .025 is down a little from .020" but is still a lot higher then .015. .030 has about the same load capacity as .018" which are both still lower then .025".

set your main and rod clearances between .020-.025" and your engine will live a long and happy life.

unTAmedLS1

mines setup loose but not super loose and thats for the juice

SStrokerAce

Good post...

As you can see guys a more is not better. The temps, oil and application all play a big part in it.

Bret

OldSStroker

If you are talking bearing-to-journal clearances, didn't you misplace the decimal point by one place? Shouldn't the numbers be .0015; .0018; .0025; .0030 ?

93turbo5oh

it was late, i worked a 14 hours and i was tired. what can i say?

slimdawson

Do you mean bearing clearance only? What about rings? Are you gong to spray?

93turbo5oh

piston to wall clearences are going to depend not only on if its going to have a poweradder or not, but will also vary greatly depending on the alloy of the piston. we look for 2-3% leakdown when hot. the stock eliminator guys basically build a wornout shortblock with exceptional ring seal.

92rslt1

so the tighter the hotter the more chance of spinning mains? or am i understanding it backwards.