NVetro

Some background, this is a 383 LT1 built for nitrous...she has Callies dragonslayer 3.75" crank, Callies Compstar 5.7" rods, JE custom 2816 alloy -16 cc nitrous pistons w/ pins and hellfire rings gaped for nitrous, melling high volume/high pressure oil pump w/ steel oil driveshaft (forget the name at the moment). The motor was bored 4.030", I think the stock piston to wall clearence on an lt1 is .0040" (i am not 100% sure on that) JE recommended that I go with .0060-.0070" piston to wall clearence for this application as the pistons will be expanding more and faster becuase of the type of alloy, I had the engine shop go with .0065" The engine builders who built my motor are old school racers and told me i should be running penzoil 20w-50 oil as they have had good luck with it.

Now onto my concern/problem/discussion:

I've been having rather high oil pressure on my new motor. When she is cold, at first start up, the oil pressure is about 70-75psi which is almost burried, granted after awhile she will thin form the heat and the oil pressure will drop to between 45-55 or so but it does take quite some time for that to occur.

I dynoed my car after a 300 or so mile break in, before my last run on the dyno i let her cool down started her up and must have not noticed the higher oil pressure, i let her rip and it must have had so much oil pressure it loosened the oil filter!

1) Do you guys think the thick 20w-50 oil I am running is causing the high pressure issue?

2) Do you think running this thick of an oil is robing me of some HP? My dyno numbers wernt exactly the best, at 407rwhp, still a little rich on a mail order tune.

3) If the oil is the issue and I should drop down to a thinner oil, with the above piston to wall clearance what would be the safe oil to goto 10w-30? 15w-30?



I am going to ask my engine builders regardless, but wanted to hear what you guys thought. Post away :-)

mdacton

piston to wall does not matter so much. I'm running more than that...

What are the bearing clearances?

I would go with 10w-30.....like you said they are old school, times have changed.

NVetro

What berring clearence information should I ask my builder? Just ask him for all the berring clearences?

mdacton

yeah main and rods.....

MachinistOne

Like mdacton said, the piston to wall and piston material type have no bearing on oil type/viscosity. You need to find out what your oil clearances are to determine the oil that needs to be run. By using a specific nitrous piston I assume that you plan on running a 200+ shot, that would dictate setting the oil clearances on the looser side, and a 20w-50 oil would be a good choice, but if your oil clearances are too tight, that will be causing the excessive oil pressure.

Oil pressure did not loosen the oil filter, and 75psi or so is not too high on startup - the 302 in my mustang makes 80+psi cold.

Pennzoil would be at the very bottom of my oil's to run. It's a horrible base stock and leaves a sludgy varnish all over the inside of your motor, not enough detergents in the oil.

Use Brad Penn, Castrol, or Mobil.

NVetro

MachinistOne would 20w-50 be robing horse power as it takes more efford to flow the oil through the motor since its thicker?

I'll find my main and rod clearences today and report back.

NVetro

ok just got off the phone with the shop.....they really couldn't tell me anything in detail. The only record they really keep is the balancing information, piston weight, and how much mallory was added to the crank...But from what it sounds they do a standard clearance on any motor that doens't spin to like 9-10k rpm....so they did pretty much standard clearances, they told me the following:

Clevite H-Series Berrings
Main Bearing Clearances: .003"
Rod Bearing Clearances .003"
Piston to wall Clearance: .0065"

I am assuming these are the stock clearances except for the piston to wall which is a little looser...is a stock lt1 .0025" or .003" I told them the issue I was having with the higher oil pressure and they said i should be fine running a 10w-30...Are these clearances to tight to be running nitrous?????????? I thought they would have put a little more in there, i hope this doesn't limit me now, what do you all think?

MachinistOne

They don't keep and supply a build sheet for every motor = don't get machine work done there anymore.

Them telling you some generic clearance number does you absolutely no good, besides the fact that those clearances are too loose - rod/main(especially the rod). I don't know what JE asks for on those pistons. Stock clearances are significantly tighter at anywhere from .001"-.002" You really should be about .0027" on the mains(.003" thrust)/.0025" max on rods - that's assuming a large shot of nitrous, a good HP street motor should be at about .0025" mains/.002" rods.

High volume pumps are the big waste of HP, if you match your oil weight to the clearances of the motor and the running oil pressure, you will not loose much HP there.

NVetro

I guess they went a little loose on the clearences for main/rod bearings, does this mean my hopes of running nitrous are done? Am I stuck running 20w-50?

At the end of the day what does this really mean? I'm dont know a whole lot about clearences and what is required which is why I had a professional engine/race shop do it.

MachinistOne

No - you will be just fine running nitrous.

If your oil pressure stays too high even when warmed up, you can drop down to a 10w-40 and see how that does. Also important - you need to run a good quality oil, not pennzoil.

NVetro

With my looser clearences is it better to run a thicker oil or thinner oil....what is bad about having the oil pressure at 75psi and running her down the crack or on the dyno?

The oil filter that blew loose was the truck type 2qt filters we run, prob not a good idea to run that extended filter?

What can break with to much oil pressure? I have a arp steel oil pump driveshaft also btw.

rskrause

We run Brad Penn semi-synth 20W-50 in the race cars and very hot street/strip cars except the blown alcohol Hemi, which gets straight 50 weight. Your pressures are as expected with 20W-50. As with any combo, the oil needs to be warm before leaning on it. That said, even though I would use 20W-50 you will probalby be ok with 10W-30.

Loose clearances= heavier oil.

Rich

rskrause

You may want to read this, which I wrote.
http://www.kennedysdynotune.com/Oil%...ure%20Tech.htm

Rich

NVetro

how about like a 15w-30? that is a little thicker then 10w-30 right? just to be safe?

Injuneer

NO!!!!

15W-30 is only "thicker" than 10W-30 on cold startup, meaning it will circulate slower and possibly contribute to cold start engine wear. Once the engine reaches normal operating temperature, they will be IDENTICAL. That's what the "30" means.