High Perf/ Race Engine, Oil weight ?
 

Getting ready to dump fluids back into everything this weekend, and was wondering, what weight oil are most people running? I ran 10/30 last year thinking the new engine might like the thinner weight, but I'm leaning towards 10/40 this time.

Hi Mike,

Just changed the break-in oil from the new 420SBC and replaced it with 10/30 synthetic. This was what was recommended by the engine builder.

Ken

Whatever it takes to keep the oil pressure up when the engine is at operating temp. I use 20W/50 or 25W/50 racing oil at the track.

sweet launch
Attachment 48177318

I always use 10-30 and my oil pressure hot idling is 50 pounds and goes up from there. My bearing clearances never never exceed .0025

Interesting that some of the big name crank makers do NOT recommend synthetic oil for their products.

Dep

:iagree: I would start with 10/30 and let the psi be your guide.

Dep,
I don't know why I feel compelled to pick on you. It must be either your good nature or a forum disease, but 377? Isn't that a medium block chevy?

Yes...uses 3.75 stroke crank. Impossible to find a 302 crank I can use.
I liked the Cheetah car and engine. At least it isn't a 383 Mopar :D

Dep

Don't mean to sound stupid here(it comes naturally) :lol: BUT, if you increase the weight of the oil, the oil pressure will increase?

SBC Oil Pressure

A common error in building a small block Chevy engine is to use too much oil pressure. As is often the case with choosing camshafts, "More’s rule" occurs. You know- "If More is better then too much is just right!"

Sure, inadequate oil pressure will starve the engine for lubrication and cause premature failure, but conversely excessive oil pressure will cause problems as well.

Oil pumps don't create pressure. It moves oil, but until there is a restriction in the system, pressure can't build.

Bearing clearance, oil viscosity, temperature and the oil pump pressure relief spring all contribute to the observed oil pressure. The oil stays under pressure until it leaves the bearings. Then it whirls around in the tornado like vortex of air around the crankshaft. As the spinning crank smacks this cloud of oil droplets, it loses energy. This energy loss is called "windage".

Modern racing oil pan design has yielded significant horsepower gains by minimizing windage.

A good wet sump system with a scraper and windage tray may pick up 20-30 hp over a stock pan.

A dry sump system can gain as much as 65 hp over a stock type pan on a racing engine.

Another hp loss is the power needed to drive the pump. No mechanical device does work for free. According to Steve Morrison of Milodon a Big Block Chevy pump (5 bolt cover) on a Small Block wastes 12 hp.

Smokey Yunick says the small Block pump(4 bolt cover) uses 10 hp at 7,000 rpm.

He also reports that some Winston Cup engines run 50 psi for qualifying just to extract every last bit of power(Circle Track April '93)

In the late seventies and eighties, Chevrolet reportedly reduced oil pressure to try to squeeze more fuel economy out of 305’s.

Other reported problems are more strain on the drive system, and the speculation that mechanical pulses through the distributor drive increase spark "scatter". (see Melling Link below for comments on this)

I've seen stock oil pump drive shafts fatigue and break from the increased load caused by a HV/HP pump. Look at your stock shaft and imagine it having to endure a 10-12 hp load for 100,000 miles.
How much is enough? The rule of thumb: "10 psi for every 1,000 rpm", was originated more than 25 years ago by Smokey Yunick. Does that mean that because you think your engine will run 7,000 rpm you need 70 psi?

No. Recommendations also depend on application.

Note: All pressures are "hot" (ideal temp is about 220 F)
Street engines 35-45 psi

Street HP 45-55 psi

Racing (only) 60 psi

Pro, turbocharged 70+ psi

In the 1984 Power Manual, Chevrolet recommends 65 – 80 psi for racing applications. This means purpose built, trailered racecars. Bob Mainetti of Canton Racing was quoted in Circle Track (April ’96) as saying: " At 6,500, you want 50 to 60 pounds. At 7,500, 60 pounds is plenty of pressure."

What was thought true in the last century is changing in this one. Gary Penn from GM's Performance Parts division says (CT June '03) "At GM we are big fans of synthetic oil motor oil after break-in. The stuff has really improved over the years and allows you to get by with things you never thought possible." He goes on to say: "...We run only 3 qts of 0W-10 in the motor.... and run it with no oil pressure across the finish line at 7,500 rpm" Gary concludes with: "The advanced quality of the (synthetic) oils on the market means the old rule of thumb that you need 10 pounds of oil pressure per 1,000 rpm is not valid anymore."


Setting SBC oil pressure

Changing the oil pressure relief spring in the pump will adjust the maximum oil pressure. This requires removing the pump cover and carefully driving out the roll pin. Replace the spring, cup and roll pin exactly as removed. Spring pressure ratings are nominal hot pressures. If your bearing clearances are too loose, then your actual pressure will be lower. If you run a thicker viscosity oil then your pressures may be higher, especially when cold.

Most aftermarket high-pressure pumps you buy come with the Z-28 spring (#3848911) that produces 65-70 psi. This is too high for most engines. Not surprisingly, these pumps often come with a lower pressure spring in the box!

I’ve found that the best High Performance oil spring for sbc engines is the factory Corvette L-82 relief spring. The part number is: #10044435

This spring yields about 50-55 psi and is the same spring used in the high performance ZZ4 crate engine.

Cost is about $1 from the dealer and has to be the all time bargain factory HiPo part. While you're there, buy a magnetic drain plug under PN 23011420. This will trap metallic particles generated by normal wear and tear. Clean it off every oil change.

http://www.geocities.com/pcwright77/...lpressure.html

I have one, 3inch stroke large journal like a 350, brand new chevrolet piece I got when they were cleaning house. say please.

Mike - This new oil system on a Motown block is different than a stock block.

I ran oil restrictors drilled out to .110 and I had to use 5W-30. with my tight 383ci it had over 40 at 1200 rpm hot and pegged the meter at 80 at 6000+

Now I'm running the new 5W-50 full syn Castrol in my 427ci

My oil press at @200 degrees is 30 ish at idle and it climbs to 75 or so at over 6000 rpm

Every motor is different. With solid rollers you want at least 30 psi at idle.

use the weight oil you need :)

It's not nice to tease old geezers :nono:
:)

Dep

Wow, this has brought about some good reading, thanks everyone. I believe I had around 35lbs at idle last year with 10/30 so I put that back in and go from there. Thanks :cheers:

Dep, I may be rong here, but me memory wants to say a 302 was nuttin but a 283 crank in a 327 block.....
and if you took a 327 crank in a 283 block it was stroked to 305, that dog engine no one liked....

this is all from dim memory....since I was an old Poncho fan myself....

GENE

Gene: In '68 they changed the 302 to the large 350 size journals. Only 305 I know of was the GM engine they built for the second gen SS Monte Carlo. It was pretty weak. Many guys turned the 283 into a 301. They really screamed but didn't hold togeter very well. GM solved that problem with 4 bolt mains and all forged bottom end. I liked the old Ponchs too. GTO is beyond affordability now. Even clones are going for big $$$$$.

Dep

I use Valvoline VR-1 20/50 in my 383

I just did my second oil change in my recently rebuilt 454. At about 500 miles now.

I switched to the above mentioned oil and my idle pressure went from 15 to 35! I was using Quaker State 10w-30 and using the "Special Oiling" solid lifters from Isky with 0.024 holes in the bottoms to help lube the cam. Supposed to drop the oil pressure though and it did.

When I was using 10w-30 Quaker State in my old 350, my pressure never dropped below 30-35. We'll see if this thicker oil keeps the pressure up.

I use (would recomend) CI-4 rated Diesel Truck 15W-40 for non-cat equipped cars with old school forged pistons and flat tappets. It has better additives than any gasoline duty rated oil. You do not even get that stuff with the synthetics. The old school flat tappet cams and forged piston/bores need it to prevent wear. All that good stuff has been removed over the years because it fouls up the catalytic converters and because the newer engines with cast/hyper pistons and roller cams are less demanding applications. Diesel truck engines do not have catalytic converters and run at much higher compression ratios and more demanding conditions so they require and use better additives. I am not an expert here on this so do your own homework. No marketing hype here, just reasons for the recomendation. Obviously you would not get this info from any oil company retail web site so you wiil need to dig a little deeper to do your own research and decide for your self.

As for pressure, the high pressure relief spring in a stock volume pump works just fine for a streetable car so why improve it? You will not go faster or run any longer either way so why :beatdeadhorse: Sure there are better dry sump systems and fancy oil pans out there but it is difficult to do much better than the windage tray setup and HP pump setup without breaking the bank.

If you regularly road race, you probably need a better pan/system and GM admitted that back in the day. If you have a track bound drag car you might need a little more baffling or capacity especialy if you have opened up the bearing clearances. For those applications it definately makes sense to improve the system.

-Mark.