thos

Hi all,
I've got a Westfield (Lotus 7 type car), running a F20C, RED Dry Sump, lightweight flywheel and a DTA S80 ECU. The car is mainly used for sprint and time attack type competitive events, and having only finished building the car earlier this year, I'm still ironing out a few little issues. The engine is a second-hand, 50k miles on it, and is stock bar the items mentioned above.

My main problem seems to be some hesitation around VTEC engagement after 5-6 laps of track work. I understand this to be caused by oil temps rising, oil thinning and resulting drop in oil pressure, but I'm struggling to get to grips and address the problem.

The dry sump is from Race Engine Design (RED) and has a Pace CD2000 oil pump. I've followed their setup advice and have adjusted for 80psi at 8000rpm at 80degs C of oil temp. I've removed the standard oil/water cooler and instead have a 25row 235mm wide air/oil cooler, mounted up in front of the water radiator, and also run an oil thermostat to help it warm up. The oil is Millers CFS 10w/40 and is their competition spec oil.

The oil temps are around 110-120C (230-250F) when the problem generally starts, and from the data logger pressure is around the 5bar (73 psi) mark. I seem to be at the max pressure adjustment on the dry sump pump.

The ECU engages VTEC based on rpm and throttle position, we've played with both of these settings and have checked all the wiring etc, and the problem doesnt appear to be ECU or electrically related. It appears to be sending signal ok, just engine struggling to respond.

So, I'm looking for help on the below:
1) What oil pressure do I need to maintain to satisfy the VTEC engagements?
2) What oil temperatures should I be maintaining?
3) Any other areas I should be looking at to help troubleshoot this problem?

Thanks,
Tom

chris_barry

Tom,

I went through this may years ago. see www.speedracersportscars.com.au

With a factory ECU you need approx 65psi oil pressure to trip the min oil pressure for VTEC sensor. Most aftermarket ECU's ignore this sensor and do not switch off VTEC under low oil pressure. If yours does look at your logs of the input to see if its the problem. With a stock ECU its like you are hitting a rev limiter.

I found the only way to fix this was to run a larger pump stage. I use a gear pump and started with a 1.0" pressure stage, then upsized to a 1.875" stage. This caused hassles with too much oil pressure when cold/off vtec so I installed a Peterson external regulator.

I run a 10w60 castrol edge oil with oil temps in the 125-130 C range. At these temperatures a 10w60 oil is thinning out to 40w oil viscosity at the normal 80-90C oil temps.

My oil cooler is a huge thing almost half the size of the radiator core.

I've set my oil regulator at 85psi and it never gets below 80psi during race rpm.

If your car is just getting sluggish it could also be heat soak in the engine bay. I found that I needed to have a cold air box so I didnt get any hot air from behind the radiator. As soon as the air temps rise the stock ECU starts pulling timing due to detonation. I still get this for around 1/2 lap if I come in to bleed down tyres, when I head back out on the track the car feels doughy till the engine bay temps drop and the ECU puts timing back in.

wadzii

Most s2000 engines I have built see around 90-95psi max oil pressure with the stock pump. You might want to try increasing the pressure a bit. The passages to the head/vtec system are very small, 80 at the main oil galley does not mean you have 80 at the head.

I'd try a different oil before I started changing parts

thos

Thanks for the speedy replies guys.

ECU doesnt have oil pressure input, so it doesnt know whats going on there, and the VTEC control is simple in it anyway, it doesnt allow for oil pressure in that decision.

I've got the air filter sticking out of the bonnet for cool air, intake temps are 25-30C, in ambient 18-20C conditions, and stay pretty static.
Water temps start to climb in-line with the oil, but still well behaved. ECU compensations not really a factor from looking at it.

Oil cooler is pretty big on mine now too, I think it's starting to impact on water cooling slightly, but overall still keeps the engine cooler overall.

I need to talk to Pace and RED and see what can be done with the pump. I'll make a note of that pressure regulator in case I need to go down that route.

Heavier oil sounds like sensible next step anyway.

What volume of oil do you run in your dry sump tank? Is it worth considering bigger tank? It was pointed out by someone in the paddock over the weekend, than some ducting/cooling to my tank might also help matters, as it currently sits in passenger footwell in stagnant air.

Also, where is best point to measure oil temps - at the moment I've taking a reading from the oil filter so it's oil going into the engine. (Oil gets cooled on return feed back to the tank).

Thanks,
Tom

chris_barry

Oil cooler on the return is best, the oil is hottest and not at a high pressure ( trying to split open the cooler).

I measure oil temps in my tank. There isn't a lot of ventilation in the engine bay of my car due to the honeycomb floor.

I have 6 litres in the tank. I also allow a little bit of air into the rocker cover to assist with drawing oil down to the pan.

The vtec assembly in the head is like one giant oil leak when VTEC is engaged, when your oil thins out the flow requirements to maintain pressure is immense. From memory the stock pump is capable of pumping over 100 litres/minute at 9000rpm.

thos

What way have you got the breathers?

Here's my engine bay, I run the front breather back to the sump tank, and have the middle one sealed off.

thos

Had a chat with RED now about the oil pump, currently it's spec'd for 12.5l/1000rpm/min, so 112.5litres per min at 9000rpm. This is with a 1" rotor, and Pace do a 1.1" rotor for 13.5l/1000rpm/min and 1.4" for 15.3l/1000rpm/min. So I've got options there at least.

He reckons 120C is still too hot. Recommends 10w60 and cause of problem is heat.

I can go bigger again on oil cooler and the heavier oil, so sounds like that is the way to go ....

wadzii

You can monitor the vtec pressure switch with the ecu.. when the switch turns on then the vtec system is pressureized. it normally takes a small amount of time for the switch to come on after the solenoid has engaged, i'd look to see if there is a large time difference between the 2 events when the oil is cool and when the oil is hot.

thos

My ECU doesnt have the VTEC pressure switch though, and I've blanked this off. The main oil pressure sender is going into my dash display and data logger.

It's an interesting point though - I was looking at logging the VTEC solenoid feed to see when it's supposed to engage, but I couldnt figure out how to check if it had or not - so is the second pressure feed, on the VTEC line? Is it only pressurised when VTEC is engaged?

wadzii

the pressure switch is basically a hobbs switch.. it comes on when it see's a certain amount of pressure. The OEM ecu uses that switch to know when to change from the low cam maps to the high cam maps.

the ecu turns on the vtec soleniod, then waits till the pressure switch turns on to change maps.