Bearing clearances for high rpm sbc?

[travis]

For a 355" sbc with a forged crank, rods, and light weight pistons, what kind of rod and main clearances do you like to see? Shift point on this will probably be somewhere around 7500 I'm guessing. Would you run a touch more ring gap than a "normal" street engine? I'm stepping outside of my comfort zone here

[engineguyBill]

.0020" clearance on the rod bearings, .0025" on the mains. Have your crank checked to verify that it is absolutely straight. Use 5W20. 5W30 or 10W30 oil. Minimum .0045" per inch cylinder diameter for the top ring gap and minimum .0050" per inch cylinder bore for the second ring gap.

[S10LS2]

^^^ Eazy peezy,^^^ just like that. The haynes or chilton's got them same specs. Or any car mag of the last 25 years. 5w20 is a good all around advice Especially when no idea what you a buildin. ?? Enlighten us? Up here in the northeast junk circle track classes run close to your rpm, not much effort. I am positive you are guessing rpm along with the guy who is guessing said 5w20 is close to ballpark. When he has no clue on what you are doing. Imo only so do not get upset.

[KnightEngines]

If it's an aftermarket block, good crank & good rods then I'd go with what Bill suggested - though to me that's a bit on the tight side.

I'd likely go for .00275-.003" on the mains & .0025" on the rods.
With a factory block .003-.00325" on the mains - coz they move around more.

[Walter R. Malik]

In my opinion ... Large clearances are usually a band-aid for suspect parts or shoddy machine work, or both.

[rewguy]

Darin Morgan stated awhile back......that he hadn't run less than .003 or .0035 on any clearance, rod or main, in any engine in many many years. I believe that is verbatim. And I have a good feeling he uses NO shoddy parts. And I also have a feeling that he has probably built, or been involved with building more horsepower than everyone on this thread combined. Just something to consider.

[kimosabi]

In my opinion ... Large clearances are usually a band-aid for suspect parts or shoddy machine work, or both.

What would be large clearances to you?

[vortecpro]

.0028/.0022 With a very strait crank.

[vortecpro]

.0028/.0022 With a very strait crank.

[travis]

This is a GM 4 bolt block out of a '70's era truck, GM steel crank, and a new set of Scat 6" rods and Wiseco 2vr lightweight flat tops (replacing a set of cheap CAT rods and L2256 pistons). The block needed a lot of work...things was clearly moving around in there and the guy said he couldn't keep bearings in it. The crank was chewed up pretty bad and had to be ground .030" under. This guys budget was blown at the machine shop with all the work done plus the new rods, pistons, and balancing. He had me come do some measuring on it...I come up with 0.0032 on the mains and 0.0028 on the rods. Seemed loose to me but I dunno...this isn't what I normally build.

[cgarb]

If this is a drag race build...I would use them as is. That's right in the ballpark of what I like to see on clearances for my drag race builds, but I use heavier oil. Depending on the season I use SAE30 and SAE40. Spring and fall 30W summer 40W. I'm probably giving up a few HP I know, but I'm not having any bearing issues and my stuff generally stays together for years. My $.02

[travis]

I forgot to mention...it is a low budget drag car, with a little street driving once in a while.

[RCJ]

.001 X Journal diameter.+.0002,-.0003

[kimosabi]

.0028/.0022 With a very strait crank.

How do you know the crank is straight when running?

[Racerrick]

.001 X Journal diameter.+.0002,-.0003

X2 that formula works so for a sbc 0025 -.0027 mains and .002-0022 is plenty unless its blown or you have weak parts and/or shoddy machining.