As you may know, my Dad and I are pretty competent at building engines for racing, but we've hit a problem that has us both baffled... Perhaps somoene here can come up with a solution???

The engine in my race car has been good and powerful, but for the last couple of races we've had fluctuating water temperatures at the end of a race and slightly lower than normal oil pressure. So we took the engine out to investigate, found nothing wrong, and rebuilt it (with new bearings and gaskets as a matter of course).

Back in the car, and now the engine is idling with lower than 'normal' pressure at idle (50psi when stone cold, 25psi when a bit warmer... Can't get oil temperature in the workshop though, so can't get it to the 100°C+ we see on track), when it used to be more like 80psi/40psi.

But!

If I rev it - only to about 3500rpm - then the oil pressure goes up to 150psi!!!!!!!!!!!

So, what could be wrong that gives LOW pressure at idle, and excessively HIGH when gently revving?

We've taken the engine out, and removed main bearing caps - bearings look fine, as do thrusts. We've checked the oil pump (a twin scavenge, single pressure gear type pump on a dry sump system) and the pressure relief valve. We've checked all the oilways are clear (by blowing through them). We've checked the oil filter, and it isn't blocked or seized. We've drained the oil and it looks clean and nice. We've put a mechanical gauge on the back of the head (the electronic pressure reading is taken at the pump, and we know from experience there is a 12psi pressure drop between pump and head) and verified the pressure readings with a known good gauge. We've checked the head gasket is on the right way around.

Whenever we think of a plausible cause, it could only result in either low OR high pressure, but not both...

I'm stumped!!! Help please

Last time I encountered a problem like this is was a loosely torqued sump plug, but, I'm pretty sure you would of checked that in the beginning.

:twocents:

No sump plug! It's a dry sump...

I think we've found it though. A small insert in the pressure relief valve that should be pressed in had come adrift and possibly on the 'wonk'. As such it would probably allowed some oil to get passes (lower pressure at cold idle), and had the effect of increasing the preload (and hence the opening pressure) of the valve part - silly pressures when revved. On the plus side, it shows we have a good pump if it can provide 150psi!!!!!!!!!!!!!!!

It's the only thing we've found engine back together now. Will refit it to the gearbox after dinner, and back onto the tub tomorrow, then run it again.

Fingers very firmly crossed!!!!

Well I was just two centing, but it turns out it was somethin else that was loose hehe, I never did know how a dry sump worked, is it similar to a two stroke motor (IE : putting engine oil in with the fuel) ?

Not really.

The dry sump means the sump is very very shallow, and just collects the oil thrown off the crank. This is them sucked out of the sump and sent to an external tank - in our case the tank is part of the bellhousing. Often there are multiple pumps (in parallel, driven by a common shaft) to get as much oil and air out of the crankcase.

Another pump takes the oil from the tank and feeds it under pressure into the oilways.

The advantages are lower installation height (CoG), and more power (less air and oil to move around in the engine), but at the expense of more cost and complexity.

A road car has a single pump that picks up oil from the sump (which is also the oil tank) AND delivers oil under pressure. We have three pumps in a single assembly (twin scavenge and one pressure).

But yes, it was a loose bit. At least we've triple checked he rest of the engine.

The aim now is to get pole, fastest lap and a win on both Sunday and Monday, ideally with a new lap record. The current record is 44.1 seconds, but I did a 43.6 in testing on old tyres earlier in the year...

Thanks for the explaination, and good luck

an other advantage of a "dry" sump is that it's a lot less susceptable to surge as the oil is forced from side to side / front to rear by cornering forces etc.

in a normal "wet" sump there's a danger the oil pickup will at ttimes be out of the oil resulting in a drop in oil preasure / feed, whilst this can be limited with sump baffling a "dry" sump eliminates this by only having a scavanger pump to fill the external tank which which then has it's feed pump to supply the engine. in effect it's the same as some fuel injected cars that have a fuel accumulator in the system to prevent the fuel pump running dry under cornering etc when the fuel level is low.

also in a "dry" sump the oil capacity can be a lot higher than a "wet" system which can be important for endurance events or for engines that have a high oil consumpion, plus this larger oil quantity allows for better control of oil temperature and the fact that the oil system is seprated from the engine allows easier instillation of filters / pumps/ coolers etc.

Also I understand another advantage to a dry sump is because the oil is effectively detatched from the engine block, it doesn't change tempreature as much and helps keep the motor cool?

Our bulk oil temperature (i.e the temperature in the tank) gets to about 130°C at the end of a race, which means it's around 150°C as it leaves the bearings.

Apparently this is nothing to worry about, but it seems bloody hot to me. Adding an oil cooler didn't make much difference as the oil going through it had too much air mixed in with it to enable decent heat transfer... Putting the cooling in the feed pipe FROM the tank isn't feasible sadly, but it would no doubt be better.

Might even remove the cooler to save weight and improve weight distribution (slightly) if I'm 100% certain modern synthetics can cope with such high temperatures. Bearing in mind the oil is changed quite frequently - every 3 or 4 races (or even more frequently occasionally).

might be worth giving your oil company a call tris, most of them have someone who can advise on motorsports use.

You would think so!

However, I challenge you to phone Millers, Agip, Mobil1 etc and get through to anyone who knows ANYTHING about oil!!!!

I'm sure exist, but getting them on a phonelinr is like asking Gollum to leave without a fuss - ain't gonna happen.

Besides, nobody we have managed to speak to wants to put their neck on the line or risk any litigation by telling us something that might not always be true.

So far no problems due to high temps, but that hasn't stopped me worrying. But worrying hasn't slowed me down - pedal to the metal!!!

look at it this way, the faster you go, the sooner the race is over so it can cool down again

Quote from tinvek :

look at it this way, the faster you go, the sooner the race is over so it can cool down again

Good idea!!! I'll try it

Quote from tristancliffe :

Our bulk oil temperature (i.e the temperature in the tank) gets to about 130°C at the end of a race, which means it's around 150°C as it leaves the bearings.

Apparently this is nothing to worry about, but it seems bloody hot to me. Adding an oil cooler didn't make much difference as the oil going through it had too much air mixed in with it to enable decent heat transfer... Putting the cooling in the feed pipe FROM the tank isn't feasible sadly, but it would no doubt be better.

Might even remove the cooler to save weight and improve weight distribution (slightly) if I'm 100% certain modern synthetics can cope with such high temperatures. Bearing in mind the oil is changed quite frequently - every 3 or 4 races (or even more frequently occasionally).

Purely out of interest and not really related to your problem, are you running a more viscous oil because the temperatures are higher than you expected? I suppose you could have been using a 0w oil, but perhaps not advisable if it's at those temperatures? 130+ is pretty toasty

Quote from sinbad :

I suppose you could have been using a 0w oil, but perhaps not advisable if it's at those temperatures? 130+ is pretty toasty

The number before the "W" does not relate to the high temperature viscosity.

A 10W40 oil is very likely to have a lower viscosity above 100 degrees than a 0W40 as the 0W40 has a better viscosity index.

We did used to run a 0W40, but felt that at the high temperatures a 60 grade oil was more appropriate to maintain lubrication, even if it saps a little more power from the engine.

So we now run a 10W60 oil - Agip Racing

only thing i could imagine is the relief valve. i know u said u checked it already but i would replace it just to be sure it isn't that.

Replace it? With what exactly? They aren't a standard road part, and I don't know of another oil pump exactly like it in the world. This isn't a Kwik-Fit job you know...

Anyway, we pretty much fixed it, but in the second race the low oil pressure warning light was flashing a lot - although that might have been due to the low revs I was forced to use at times.

Sunday - Practice - Damp but drying. Had traffic on the last two laps when track was at its fastest, so only managed 3rd on the grid. Up until the last two laps my times were competitive, so annoyed about traffic.

Sunday - Race - Throttle shaft on the throttle bodies broke, leaving me with working throttle on two cylinders and no throttle position sensor data (it is activated by the other two cylinders). Retired with a rough sounding car after one slow lap.

Monday - Practice - fixed throttles with some weld and some bracket fabrication. Pole by half a second. Also half a second faster than the lap record. Hurrah!!!!

Monday - Race - Leaving the assembly area broke 2nd gear. Starting the race broke 1st gear and stalled the engine. So I was last and having to use 3rd gear (which is intended for 70 - 100mph) for the 25mph hairpin. Managed to get to 3rd, and my fastest lap was only 0.3 seconds off the race fastest lap, despite losing 6 tenths of a second in the hairpin alone, plus passing people most (every?) lap.

My main championship rival finished 2nd in race 1 (struggling with a bodged fuel injection system), and retired from race 2 because he'd reconnected his fuel pump incorrectly reverting to carbs between practice and the race. So could have been worse. But not much!!!!!!

Quote from tristancliffe :

Monday - Practice - fixed throttles with some weld and some bracket fabrication. Pole by half a second. Also half a second faster than the lap record. Hurrah!!!!

Monday - Race - Leaving the assembly area broke 2nd gear. Starting the race broke 1st gear and stalled the engine. So I was last and having to use 3rd gear (which is intended for 70 - 100mph) for the 25mph hairpin. Managed to get to 3rd, and my fastest lap was only 0.3 seconds off the race fastest lap, despite losing 6 tenths of a second in the hairpin alone, plus passing people most (every?) lap.

Good goin Tris!

Hardly - the innards of the gearbox aren't pleasant. I'll stick some pictures up at some point!!!!

Just read a snippet in the back of the EDP about you Tristan. Getting locally famous!

Hope things get sorted ready for the next race.

Oooh, I'll go and buy it for the scrapbook. A rubbish mention in Autosport - they think I had a cautious getaway on race 2. I don't call stripping 1st gear, restarting in 3rd and being fortunate that the entire grid yet again avoided running into me particularly cautious!!!! Need to check Motorsport News too.

Anyway - here are some pics of my gearbox and the contents. As I type, the gearbox should be arriving at Silverstone circuit to see if it can be fixed. If not, then it's season over I suspect...

The remains of 2nd gear - it exploded leaving the assembly area!



The layshaft - first gear is totally stripped of teeth. 2nd is missing (the exploded bits above), and even 5th gear (the one closest to the camera) is missing a tooth. Not good!!!

I think that's what first gear looks like in my girlfriend's car.

I'm not sure, but I think transmission fluid probably shouldn't look like gold flake paint... :eek:

I'd be afraid to see what that did to the bearings and any other moving parts in there.

Tristan, do you have any idea why these gears broke ?