With Forced Inducted motors the clearances are looser than N/A motors and will use more oil due to this, so I use as follows, Remember this is in Texas where is gets pretty hot in the summer.

Summer Heat: 20w50
Fall cooler weather;15w40
In the cold of winter:10w40

It does not get cold enough here to warrant weights of 0w30 or 5w30 oils but if you live in a snowy area this might be the oil of choice in the winter..

 

Lower viscosity oils make more power, that is clear. Most of us "sportsman" racers are less concerned with the last couple of hp out of a combo. That is more for "money" racers in heads up classes where races are often determined by a couple of hundreths of a second. For us, we are most concerned with protecting our investment in the motor. Traditionally, lower viscosity oils were considered to have inferior "film strength" and thus less protection against metal to metal contact when, for example, the crankshaft deflects under WOT/high rpm operation. I am not so sure this is true with modern oils.

However, there is still a role for higher viscosity oil. Some hi-po motors are set up with large bearing clearances, especially on the mains. The idea to to help prevent metal to metal contact due to large amounts of crankshaft deflection. If you use a low viscosity oil in that circumstance, the pump may not be able to move enough to maintain and oil film in the face of the large clearances. Hence the use of higher viscosity oils in that circumstance. As I mentioned in a previous post, blown alcohol motors as well as fuel motors use very thick oil to counteract oil dilution by the fuel secondary to blowby, as well as for bearing protection. The blown alky cars often use straight 50 weight while the fuel guys typically use straight 70 weight.

All this has nothing to do with oil choice for street cars run under widely varying temperature conditions, that's another thing all together. I am pretty conservative when it comes to oil. Since the gains are so small wiuth thinner oils and I have very few spare motors sitting around, I stick what what I know works. For me, it was a big change to 20W-50 Brad Penn semi-synthetic from straight weight Kendall GT1. I only made the change when they reformulated the GT1 and it became "just another oil". The Brad Penn uses the same formula as the old GT1 for the conventional component. Semisynthetic blends (part conventional, part synthetic oil) are supposed to have most of the benefits of each type. We started using the Brad Penn this year and the bearings on our three shop race cars all looked great this year. They are a blown alcohol Hemi car (Brad Penn 50 weight), my NA alcohol BBC car and a centrifugal SC SBF (both using the 20W-50 blend). So, I am going to stick with that. I am using the Brad Penn 10W-30 in my street cars.

Rich

 

I never knew there was such a science or planning to the type of oil and clearances when building a motor - I realized there was some thought put into it of course, but not to the extent of having more or less clearance on the bearings depending on if it's NA or inducted. I always went with the school of thought that I wanted thinner (5W30, I live in Fla) to promote better mileage and power (all my vehicles). But as I read this the gains are obviously minimal when protection is the bottom line.

 

Stockish motors in good condition have tight clearances and 5W-30 ought to be fine in your climate. Don't worry, be happy

Rich

 

OK - I'm in the process of building a fairly mild motor (355, 503 Comp cam, mildly worked heads & intake), and trying to pick up some good tips/info. For every post in this section I'm probably reading 100 threads to every 1 of my posts.

 

Yeah, so I was thinking about my last motor and I should be shot for posting false info. I just looked at my motor build sheet, and my new motor is MUCH tighter...
front to back is:
.0015, .00155, .002, .002, .002.

Rods are all .0015. Yup, Im a tard. Tar and feather me!!!
At least I corrected it, right? hehe.

 

I see it is much much tighter.....

Can anyone answer why? B/C it is a street engine I assume?

If I was rebuilding a stock LT1 for a street eninge is that more along the lines of what to look for?

just curious