I got to looking my uninstalled the TC Motorsports baffle and it annoyed me the way the OP Relief Valve (OPRV)interferes with any attempt to baffle the right side of the oil pan. A couple guys at e30tech.com experimented with removing the OPRV and plugging it’s port. They unsurprisingly had high cold oil pressure but the case for higher hot oil pressure was mixed.
Pics of the TCMotorsports baffle here: http://www.spece30.com/forum/46-oiling-system/66226-poor-mans-tc-baffle-project
My perception is that the OPRV’s spring limits OP to around 70psi with cold oil and with hot oil the pressure limit is a matter of the flow resistance of the oil system. Tight tolerances everywhere means high pressure. Once loose tolerance and hot OP suffers.
The OPRV can also be a failure point. One of my engines a couple yrs ago had low OP and Chuck Baader fixed it by replacing or fixing my OPRV.
I’m told that the E30 M3 does not have an OPRV. That needs to be confirmed tho.
The oil pump also has a pressure relief valve. I think the purpose of that valve is to protect the oil filter, not set cold old pressure for the whole system.
OPRV plug. A common oil pan bolt in 20mm x 1.5 available at your local autparts store.
OPRV in place.
DIY baffle that really does seal the right side, as opposed to leaking around the OPRV.