The Road to Drag Week 2014 - July 27

[Cyclone03]

Plus with the throttle blades too far open now the IAC will do nothing to lower the idle speed.

Depending on the LocTite used MEK has been known to soften it.

[900HP]

Jay, on the oil leak, is it possible you have a fitting or line that has a leak and it's migrating down the oil pan rail to the rear?  Just a thought because I know it was dry on the dyno so I've been thinking about what could have been changed/removed/reinstalled from the dyno to the car.

[jayb]

I've been thinking about that too, Mark, and checked a couple of areas up top last night, but they were dry.  I'm going to try to do a better job of that tonight, as well as checking all the dry sump fittings to make sure there is no issue with those.  The leak has got me scratching my head, that's for sure, but one thing that I did do after the engine was off the dyno was tighten up the oil pan bolts, and I'm wondering if somehow I squished the oil pan gasket out of shape when I did that.  Seems unlikely, but that's the only real change that I can think of...

[turbohunter]

Still curious how negative pressure would affect oil as far as leaking out of the block.
Does it affect it at all?
Since I've never run a pump I have no idea.

[cdmbill2]

Last time I had this issue with a leaf after install it was a mechanical oil pressure line that goes to a gauge in the dash with a union at the firewall. It leaked on the back of the motor which drove me nuts as it doesn't push oil out with the vacuum pump normally.

[900HP]

Still curious how negative pressure would affect oil as far as leaking out of the block.
Does it affect it at all?
Since I've never run a pump I have no idea.

I have multiple engines with vacuum pumps/vacuum systems on them.  One would think that if you are pulling a vacuum in the crankcase that it would not be possible to leak oil out but that is not true.  I had a BBC that leaked oil on the right side, it took forever to find, there was a pin-hole in one of the fabricated valve cover welds.  The engine had 10-12" of vacuum (wet sump) yet still leaked out the pin hole.  I also had a front seal leak on a circle track SBC even with 10" vacuum. 

The interesting thing is that if it can leak oil out it can definitely leak air in so by fixing the leaks you should see more vacuum.    The other thing to consider is that if it can leak air in it can also leak dirt in.  This isn't a big concern on a drag race car but it can become a big concern on a car that is driven in dusty conditions.  It doesn't take much dirt to ruin bearings.

The biggest advantage to running negative pressure in the crankcase is that it allows us to run ultra-low tension oil rings and still maintain ring seal.  This reduces parasitic losses.  You can't run 5-8lb tension oil rings (at least for very long) without having vacuum in the crankcase as they won't seal.  It is absolutely imperative that you keep oil out of the combustion chamber so you can see how important vacuum becomes. 

I did a test once with a methanol motor.  We were making dyno pulls with VP M1 and no top-end lube.  We added the recommended 1oz of top-end lube per gallon of gas (or maybe it was 1oz per 5 gallons I don't remember now) and the engine immediately LOST 10 HP!!!!  We removed the fuel with the oil in it and the power came right back.  We then used VP's top-end lube which is lead based, not oil based, and power remained the same. 

This should show you how important oil control is.  If you are pulling spark plugs on your engine and the threads have oil on them you still have some work to do on the oil control.  Adding a vacuum system will help greatly with this, as will the right ring package, the right cylinder wall finish, round cylinder walls, etc.  Another thing to consider is bay to bay breathing.  If you have an engine with poor bay to bay (meaning air can not move around freely in the crankcase) this can hurt ring seal as well.  Vacuum systems will help with this issue some as well but I personally don't think you can have too many crankcase vents (internal of course) to connect the heads, valley, and lower crankcase together.  The easier it is for air to move around in the crankcase the easier it is for the rings to remain sealed.

These are my thoughts on the issues anyway.

[turbohunter]

Thanks Mark.
Hadn't thought about the crank case side of the rings.
I only had the simple view of containing combustion.
Really am enjoying learning this stuff.

[900HP]

Thanks Mark.
Hadn't thought about the crank case side of the rings.
I only had the simple view of containing combustion.
Really am enjoying learning this stuff.

remember that if you can build pressure under the rings (for whatever reason) that pressure can un-seat the rings.  Ring seal is #1 as far as getting the most power and best drivability and least oil consumption from a combination.  You will find it's very common to gap the top ring tighter than the 2nd ring.  This goes against the tradition of gapping the top ring wider (the theory here is it's hotter so it expands more and needs more gap so it doesn't touch).  The reason for this is because IF some combustion pressure leaks by the top ring, you do not want it to be able to build pressure between the top ring and the 2nd ring causing the top ring to unseat.  I almost always gap my 2nd ring .004" wider than the top ring to make sure no pressure builds between the rings.

It is also best to get rid of the antiquated 1/16"-1/16"-3/16" ring packs and go with a more modern, thinner pack like a 1.2mm/1.2mm/3mm because the thinner rings actually seal better and today's materials are so good they last longer as well.  There are a number of benefits to using thinner ring packs, especially at higher rpm.  Almost all of the O.E. (I say almost because I don't know all of the engines from all of the manufacturers) are using thin rings now.  The reason they do is due to emissions and oil consumption requirements but the end result is the thinner rings seal better. 

[900HP]

Jay, I'm sorry if I derailed your thread

[turbohunter]

My fault Jay sorry.
I'm in sponge mode and your oil leak got me thinking.

[jayb]

Jay, I'm sorry if I derailed your thread

Sheesh guys, don't worry about that!  All part of the learning experience.  FWIW I follow exactly the same procedures as you do, Mark, with respect to ring gaps; I always gap the second ring .004" looser than the top ring.  I have also gone to .043/.043/3mm ring packs on most of my engines.  I had never thought about how air moving around in the crankcase could affect ring seal, and I'm thinking that the SOHC should be pretty good there because there are no lifters in the lifter bores; they are wide open.  On the other hand, my dry sump pan is relatively tight up to the bottom of the reciprocating assembly, which probably doesn't help any.

By the way, last night I checked all around the top of the engine at the back, and no sign of leakage anywhere; she's bone dry up there.  It's either the pan gasket, the rear main, or one of the plugs at the back of the block popped.  I've had the cam plug in the back come out before, so that one is held in place with a strap.  If one of the pipe plugs in the back of the block came loose, or was never tightened, that could cause it, but I think I would have seen that on the dyno.  And pipe plugs don't just come loose for no reason, at least not in my experience.

Mark, when you do a dry sump motor do you reverse the rear main seal?  I did that on this engine, and had second thoughts about it, but it is indeed in there backwards.  I know of at least one well respected engine builder who does that, and one who prefers not to.  Any thoughts?

[900HP]

Jay, I'm sorry if I derailed your thread

 I always gap the second ring .004" looser than the top ring.  I have also gone to .043/.043/3mm ring packs on most of my engines. 

This is the same thing I do, Jay.  .004 wider/looser on the 2nd ring

Mark, when you do a dry sump motor do you reverse the rear main seal?  I did that on this engine, and had second thoughts about it, but it is indeed in there backwards.  I know of at least one well respected engine builder who does that, and one who prefers not to.  Any thoughts?

I use special vacuum seals from Signal Motorsports Technologies, I get them from CV Products.  If they don't have an FE size for you (probably not) I would use a good Viton seal but install it normal, I've not had good luck installing them backwards.  I know a lot of people do it but it has never worked for me. 

That being said, I haven't done a pure dry sump deal with lots of vacuum either.  All of my vacuum pump motors are wet sump so I limit vacuum to 10-12".  After that, oil pressure drops.  At 10-12" a normal Viton rear main seal holds up just fine and you can pull plenty of vacuum with it. 

I think I would have to re-visit it if I was pulling 18" or more of vacuum.

[900HP]

I should add that on our Engine Master's Pontiac motor, we were pulling a measured 8.9" of crankcase vacuum with a pan-evac set-up.  Vacuum pumps and dry-sumps are not legal for the competition.  To get that kind of vacuum out of a pan-evac the motor does need to seal up well.  This engine has a Viton rear main seal installed in the normal position. 

[cdmbill2]

900 HP: Peterson advised me to go with a -16 oil pick up line with their wide-vac external wet/sump two stage vacuum pump deal. So far so good.

Do you run a larger than normal pick up line with your motors?

[900HP]

900 HP: Peterson advised me to go with a -16 oil pick up line with their wide-vac external wet/sump two stage vacuum pump deal. So far so good.

Do you run a larger than normal pick up line with your motors?

I haven't ever tried that to be honest with you.  -12 seems to work fine.  I don't see where -16 would hurt though.