Nickleby4

Newby question. I have an S2000 engine in Rally car running a dry sump setup, so I can run whatever pressure I like on an external regulator. Currently I'm set to ~ 85psi.

Except.

When the VTEC cuts in (@ ~6500rpm) the oil pressure dips to ~ 60Psi.

Anybody out there able to tell me what a standard car does under the same conditions? I'm really looking for the following

Pressure before Vtec (5800rpm?)
Pressure after Vtec (6600rpm?)
Pressure before rev limit (8500rpm?)

Thanks in advance.

PS. This is one of 3 teething problems I'm working on at the minute - you'll see other posts.

chris_barry

I've been there, done that on a F20C powered clubman ( http://www.speedracersportscars.com.au/PRBS2K.htm )

The problems you have is that your pump it not big enough to supply the volume needed during vtec operation. The VTEC rocker assembly is like a huge oil leak back to the sump and if your pump cannot keep up the volume the pressure drops off.

I started with a 1" pressure stage and ended up with a 1.875 which will maintain 75psi under vtec. Pump is a Razor using 7 lobe gears. A gyrotor style pump is more efficient so would not need as big a stage.

This introduced another problem. The inbuilt pressure relief valve in the pump could not cope with the humungous volume off vtec or with cold oil. I disabled the pumps internal pressure relief valve and fitted a Peterson external pressure regulator. Oil pressure has been perfect since.

When I had the problem I measured the amount of oil the factory pump can move per minute at 9000rpm and its staggering.

Nickleby4

Thanks Chris.

You are only telling me what I alread knew I guess. 1. These Hondas need a massive oil pump, and 2. don't trust a salesman!

For info there's another guy on the internet, running one of the Lotus 7 clones, thats seen the exact same thing issue. Certainly I'm now finding it with my dry sump setup in an Escort (which is a little constrained for space around the pump and the engine mount).

I was wondering what a standard car does and it's clear nobody knows. Also clear that I need to fix it before I get the oil hot in competition. Useful to know that I need to think carefully about the bypass circuit to avoid overpressure at low speed. I'm wondering if I just switch in the VTEC as permanent it could be a fix (I can runn my idle speed anywhere - I'm going to need a new ECU and it's not a road car). Time to go take the pump off and pull it apart for a bigger pressure stage.

Not the best news, but sincerely thanks again for taking the time to post a sensible answer - many don't.

INDYMAC

I find the oil pressure requirement for VTEC operation to be interesting. My theory about 30 and 40 wt engine oils recommended by Honda to have some correlation might have some merit.

spets

According to the service manual, at idle on a warm engine, the oil pressure is supposed to be 35psi minimum. At 3,000 rpm, the oil pressure is supposed to be 85psi minimum.

Unfortunately the manual doesn't state VTEC pressures.

SpitfireS

Well..... maybe not generalize because of the fun in your first post.
I remember a post from a reputable member (Slows2k) reporting 125 psi (*) max @ 5000 rpm in an OEM S2000 (apart from the extra oil pressure sensor)
IOW, the bypass starts to open below VTEC.
From 5k to VTEC the pump just dumps more oil (through the bypass), when VTEC engages the pressure probably drops and closes the bypass allowing the extra oil to enter the engine to keep the VTEC pins where they should be.
When the revs climb even higher this increased flow creates higher pressure again as the oil pump is a positive displacement pump.
Its a well designed combination of pump, bypass pressure and I think bypass valve area to get rid of the oil.
Especially if the 125 psi during VTEC is a result of the oil pump (maybe without bypass?) and the VTEC "leak", if you know what I mean.
30 weight oils will have the advantage to create less pressure so the bypass will open at a higher pump rpm, and that means more oil volume through the engine.
So I would avoid running "racing" oils in the 50 and 60 weight range.
(*) IIRC with a 30 weight oil and at operating temp (last bit = obviously)


You know as well as I do that the OEM 40 weight recommendation, or better the 5W-40, has everything to do with cold starts.
As there is a direct link to outside temps and the 5W in the owners manual.
Most likely because 5W-30 were not that good in 1999.

Its 2013








edit: make things a bit more clear... hopefully.

INDYMAC

I'd like to find a good SAE 30 to try!

Nickleby4

Oh no. I'm going to say something bad again! I'm attacking the myth of oil specs...

So. Some feedback as a result of a fair bit of research, a bit of physical experimentation, and a shed load of spending. The problem on my dry sumped engine was the size of the feed pipe. Easy with hindsight, and very expensive in time and money. Suffice to say I'm on dash 16 now (an actual 19mm minimum bode size), which gave me an extra 30Psi of oil pressure everywhere above idle (for the same pressure setting point - I've wound the nut out a full turn on the pressure regulator to get back to 85Psi). Lucky for me I found a clever b*gger, who gave me a big - very big) spread sheet to calculate flow vs. pressure in any given pipe - belive me it is not linear, and is to do with 3 or 4 Phd level fluids dynamics theories.

1. Oil specs. All of the "high quality" oil suppliers (that I researched) published a technical data sheet with the minimum of wwwing.
2. SAE specs. These are a scale - again not linear. I.e a 5W20 is not half a 10W40 - they just fit 2 different scales.
3. SAE specs don't make a scooby of difference to flow vs. pressure! That's the bad bit I'm guessing.
- The first part (I.e the 5W in 5W30 is all about very cold climates. If you are planning to start your car at -30C (C not F - I'm in the UK I have to look up Farenheit - sorry) then you may need to pay attention. In the UK I do not. -17C is the coldest I've ever known here.
- The second part (I.e. the 30 as above) is about the hot operating flow rates. In my model I just cannot show any detectable difference between a cheap 5W30 and a top end 10W60. Backed up with physical measurements I couldn't measure any difference either.

I'm now happily running 10W60 millers motorsport oil. Obviously I'm dry sumped, so it's maybe different with a wet sump. My decision point was £100 an oil change (plus the same to flush a big system). That said I'd never run cheap oil (in anything I wasn't willing to throw away. I'm alos concious some very clever people chose the Honda spec, so my advice would always be to take thirs for yur stock (ish) motors.

Thers been a lot of help on here - which I'm grateful for - thought I should feedback my findings.