Excessive Oil Pressureon Rb30e

[Nickandm]

G'day people I'm new here but have been using alot of the info from here whilst building my Rb30 and nutting out the problems you always end up with.

I'll fill you in with some background info, the car is a 73 Datsun 240Z, motor is an Rb30E out of a VL with all new standard gear except for a ported cyl head and N1 oil pump.

Most of you will have read enough after hearing the oil pump is an N1 as I too read disturbing things about these after I purchased it.

The reason for going N1 was because I want to fit twin turbos later on to make an Rb30E+TT and thought the N1 would be a good match being high volume and high pressure.

The problem is on first start up the oil pressure went straight off the stock 240Z oil pressure gauge which goes to 140psi, now I didn't like it much but let the engine warm up to see if the pressure would drop as the oil thinned, It did drop to about 50psi at idle but as soon as revved above 2000rpm it's back off the scale (over 140psi).

After playing with a thinner oil (nulon 10w40 which gave 30psi at idle when warm and off scale at 3000rpm) and installing a mechanical workshop gauge straight into the pressure sender hole with the same results I thought it was time to pull the oil pressure relief valve out to have a look, the oil relief piston (valve) slid out beautifully so it couldn't have been jammed shut.

I did notice the spring was very long and stiff (insert joke here) so I ordered genuine nissan spring, piston, and nut.

Once I received the new bits I installed them, added some penrite run in oil and started it, oil pressure sat on 90psi for about 5 mins, then slowly dropped off to around 25psi at idle once warm, I gave it a few good revs and pressure wouldn't go over 90psi, I thought perfect....but no.

After about 10 mins when revved oil pressure slowly crept back up and then went off the scale again, then every time it was revved about 3000rpm pressure was off the scale.

So now I'm stumped, why would it creep back up? why did it maintain the 30psi at idle and 90psi at revs for only 10 mins? Is the pump just putting out too much oil and even the relief valve fully open can't bypass enough?

Any ideas welcome no matter how out there they are.

This is a fresh engine with only the runs I have detailed, no mods to oil passages, no restrictors, it does have a modified oil pickup for rear sump but basically just stock with an N1 oil pump.

Sorry about the novel, better than getting asked heaps of questions though.

Cheers.

Nick

[Nickandm]

No ideas from anyone?

[Nickandm]

The latest plan is to take I little bit of size out of the piston incase it's expanding once the oil warms up and getting stuck in the bore, will update again once this is done and engine has been run again to see if theres any change.

[moo_r32]

there is a posibility that that as the rb30 doesnt have oil squirters under the pistons it creates too much pressure? if u think how much flow 6 oil sqirters would use like in a rb20-25 and 26... just a possibility???

all the rb25/30's iv biult have had more oil pressure than realy needed but if u put an rb30 standard pump on a rb30 it works perfect as with putting a 25 pump on a 25 and likewise with a 26...

just an idea that iv come up with from my expereance..

let me know what u think?

mark