Oil pressure fluctuations with tight bearing clearances

[Truckedup]

That makes sense to me. The particular issue is this: giving the car a straight line hit sees the pressure drop a little then pick up and stabilize at the relief valve pressure. I'm pretty certain it's not surge related cause I'm not pulling big g's . The engine ran for years without issue until rebuild. The only difference with this build is the bearing clearances are on the tight side. 2" main journal. 1.4 thou clearance vs 2 thou before.

Ok, so you mean like hitting the engine wide open after a turn? It could be a simple as a momentary slight drop in pressure when the oil pressure relief valve opens fully, the pressure goes back up when the pump catches up so to speak as the relieve valve closes a bit....If this isn't normal then you'll have to investigate...

[AC sports]

That's what it's doing but it wasn't before the build.
The only 2 differences in the engine are the tighter bearing clearances in this build and the oil pickup strainer. Originally the strainer was a 4" mesh. Now I put a jam jar lid over the mesh and cut out a smaller 2" circle in the lid to stop the pump sucking air from the edges on turns. It's not actually a jam jar lid but similar. It's from a later model version of this car.
It's a simple enough operation to take the sump off and resort to the original setup....but just nice to understand what's going on and why.

[Truckedup]

Most of the high performance pick ups I see are small rectangular boxes with coarse screen..I do know that screen mesh size can affect air flow on bike carburetors...You may have created a bottleneck with the smaller diameter and same size mesh...I suppose the only way to know is too pull the pan and change it....

[AC sports]

I actually installed the mesh and pickup from a later model, hence my confusion as to why the fluctuations if the later models had it and it worked fine.

[Kevin Johnson]

Fiat has a very large assortment of pans and pickups.

If you are using the same pump in the picture that I posted last year, it appears that the suction opening is offset to the front of the engine. With your circular baffle that would create a transient localized starvation area under heavy forward acceleration. A vortex would likely travel up the forward wall of the circular baffle.

Auto-Oil-Pump-for-FIAT-FIAT-132.jpg

20170329_143547.jpg

20170329_142523.jpg

[AC sports]

Hi Kevin.
This is a different engine I'm working on. No modified baffles like my previous post ( which is where your pix are from) This is an 1800 sump without the circular baffle in the base of the sump. Basically a standard windage tray across the top. I left it as such because after running it in I'm installing an accusump.
Indeed I took the gauze and jam lid with hole as in your pic, and installed it on the original oil pump.
BTW interesting to see the Chinese are making them now!
The one I have is NOS out of Italy. Lucky me!

[Kevin Johnson]

Longitudinal or transverse installation (e.g., Scorpion, Monte Carlo)?

[Belgian1979]

If it's the bearing clearance using a thinner oil should solve most if not all of it.

[AC sports]

It's in a north south RWD application. A 124 coupe to be precise.
10w40 synthetic is the plan if it ever gets run in.
Right now it's on 15w40 mineral .
I'm still concerned about the tight main bearing clearances though @ 1.4".

[Truckedup]

That's a 5 main bearing 4 cylinder with a rigid block and crank?

[Kevin Johnson]

It's in a north south RWD application. A 124 coupe to be precise.
10w40 synthetic is the plan if it ever gets run in.
Right now it's on 15w40 mineral .
I'm still concerned about the tight main bearing clearances though @ 1.4".

This general pan with baffle?

late 1800 pan.jpg

[Kevin Johnson]

That's a 5 main bearing 4 cylinder with a rigid block and crank?

Yes.

[AC sports]

Yes and yes.

[Kevin Johnson]

Yes and yes.

Since the hole is offset, indicate where it sits on the pic below. Also, when you transferred the cover and screening over to the pickup did you make sure that the screening is well proud of the inner surface of the cover? Otherwise the flow cannot reach the additional open area and would be restricted and possibly cause cavitation at high pump rpms.

4433914.jpg

[Kevin Johnson]

When you exit the turn is the car in understeer, neutral or oversteer?