Marginal oil pressure- Which turbo to use? Ball bearing or regular journal?
 

This is something I could not find by searching. My motor recently had the bottom end freshend up with new bearing inserts. The main and rod clearances were on the high side of factory spec. Using 10-30 Dino I'm getting a hot idle pressure of 12-15 PSI. Above 3,000 rpm it hits 40 PSI and stays there. I have a mechanical aftermarket Oil pressure gauge that was tested before installation and is accurate.

My question: Which type of turbocharger will least burden my already wimpy oil pressure situation? Would journal type require more pressure than ball bearing? Would the ball bearing need more volume to operate safely?

Basically I'm trying to preserve what little oil pressure I have.

Also, this is all new to me and I don't know if the addition of a turbo would effect oil pressure at all. Am I just worrying about nothing?

Thanks for any insight.

That is just slightly out of spec for oil pressure. Have you tried running a different oil? I use Mobil1 0w40 with good results. Filter choice can also affect oil pressure somewhat.

Ball-bearing turbos generally require less oil pressure than journal-bearing turbos, to the point that they are usually fitted with restrictors on the inlet. In terms of total flow (IOW: the impact that the turbo will have on your oil pressure) I doubt that either type will cause a significant drop. Journal-bearing turbos present a significant restriction to flow all by themselves, so total flow though either one will be fairly small.

Do you have any data on what your oil temperature is? I might recommend that you try fitting an oil cooler to the engine. The water-oil sandwich plate which was stock on all the '94+ cars would be a good choice for the street, as it requires no external plumbing (apart from a couple of water lines) and as a by-product also has the effect of pre-heating the oil when cold.

Thanks Joe,

I don't know what my oil temp is running. What is considered a good operating temp for oil?
Water temp hits 195 F and stays there. I'm going to try 10-40 semi synthetic (as this is the only 10-40 I could find this past weekend). Hopefully it will nudge the pressure up a bit. Will keep an eye out for the Mobil 1 10-40. Was using Dino for the bedding in of the new rings I installed.

Thanks for your insight. I'm glad that I won't have to pay for a ball bearing unit as I'm trying to put together a system as cheap ( er... frugally) as possible.

im willing to bet your gauge just reads low...

"im willing to bet your gauge just reads low..."

Maybe so- I'm not too worried-yet.. I did hook it up to my air tank the gauge agreed with what showed on the compressor. It is an inexpensive gauge

I put my motor into a different shell and it only reads 10-15psi at idle, never see above 60psi on the coldest morning. I blame the gauge.

Thanks for the data- Again not too worried. I'm an older guy used to seeing big numbers on the oil pressure gauge of the old 327's and 402's of my early years.

I'm going to hold off on the semi synthetic oil i bought and feed that to the Taurus.

I should be able to find Mobil 1, 10-40 somewhere!... I'm hoping that the local autozone has some in the back room- I haven't seen any displayed for quite a while.

Wallymart will carry the Mobile 1 full synthetic. I use Mobile 1 5w40 full synthetic. I found that my local Wal-mart has the cheapest prices for the 5qt jug. I always use a Mazda oil filter as well.

Don't know why, but non-oem oil filters often cause lower oil pressure than oem's. Not that it'll fix your problem, because personally I don't think you have even got a problem (my oil press. behaves about the same) but do make sure you use oem filters.

on my old built 1.8l I would see 15psi at idle and it would never get past 50psi when warm. It kinda freaked me out, what I did was go with a thicker oil ( mobil 1 15w50 ). That oil and a k and n oil filter ( yes they have about 3-5psi higher pressure ) netted me about 26psi at idle and 55-60psi when warm over 3000rpm. With the thick oil you gotta let her warm up for a couple minutes, but once warm that oil was perfect for me.

Am I the only one running 5/10 w30? 5 in the winter, 10 in the summer. My oil pressure is about like the op's, I think ill use an oem filter on my next change though, thanks for the advice.

Well thanks for all the responses. What I was worried about was having enough pressure to handle the turbo. Looks like I'm going for higher viscoscity. Just ordered a t25 and a used Bell "upper" down pipe from the Fly'n Miata "Deal of the Day" bin. Got a Bipes, BEGI FPR, and a few more odds an ends. I'm Commited! :vash:

Next step- a Cast Iron manifold. ..... This is starting to cost.

Thanks again!

Lubrication performance isn't really based off of pressure anyways. In bearings its actually the movement of fluid that causes everything to happily float. So with a lower oil pressure your getting more flow somewhere and probably in the clearances you said were wide. By adding viscosity you will increase pressure because flow everywhere goes down, but it will help to make sure all the bearings are atleast getting a fare share of oil. I'd run what the car calls for in viscosity, and not try to inflate up the numbers too much. More then likely everything in the motor is fine. If you raise the viscosity up a bunch you'll end up putting the cam bearings, and other clearances that are much closer to the normal range out of spec in their load bearing/efficiency ranges.