case and head vents, do I need to run a breather box? Options

[DNHunt]

Len, my observations about higher and more rapidly rising head temps are with the same tune before I plugged the head vents. I run SDS injection and tune with a WBO2 and EGT so, I can get my tune close. I feel my tune is safe and if anything is conservative on the fuel side. The timing is the same as we set on Jake's dyno. With my gearing and tire combination 75 actual is about 3800 rpms. 3800 rpms fails at the high end of an rpm range that requires less fuel than engine speeds above and below. I've seen that on every engine TypeIV I've tuned. That kind of dip in the fuel table is always the toughest to tune in my opinion. I always feel like it is a compromise and I have found in order to give the engine what it wants above and below this speed this portion ends up a bit rich. The linear nature of SDS tuning is both and advantage and a disadvantage in this case since one cannot tune each individual load vs rpm cell. The advantage is it is simple, the disadvantage is one has to accept a bit of compromise.

It may be that the engine is asking for a tweak in the timing since EGTs are the highest at this engine speed. Very light load (overrun to slightly cracked throttle) will heat up the exhaust.

I will admit that the head temp change is an observation and I didn't quantified it. I put it out there just because I thought it was interesting. It's certainly not a huge change and I wouldn't even worry about it except I'll be doing a lot of climbing with a lot of weight again for WCR and it's in the back of my mind that I better pay attention to head temps. If worse comes to worse I'll pull over and cool it down, richen the mixture or slow down.

As far as the 390 head temp last year, I am able to say that was with an AFR of 12.5 because I could use the SDS tuning knob to adjust it on the fly. I don't remember having to do that however. Again, the timing table was the one from Jake's engine dyno. Temps came down quickly after we crested the summit and I rarely see head temps over 325. Up here in the PNW the biggest challenge is to get the engine hot.

[Jake Raby]

Dave, which CHT gauge are you running again?
Yet again, your first hand experience is greatly valued. I appreciate your analytical overviews and your situational awareness- thats how you learn.

What you are experiencing tuning wise with the engine is the difficulty that we always see with perfect tuning at peak torque- the point of highest efficiency with every engine I have experienced. This difficulty exists whether you have carbs or EFI, a standard dizzy or direct fire. It is always the point where the engine is more twitchy with EGT and CHT and where lots of things occur in a very narrow RPM range. Due to this at that point its near impossible to tune the engine perfectly based on the feedback from the vital signs of the engine.

The gearing of the 914 and most popular tire sizes are partly responsible for this. The dip in the fuel curve is also a point where EGT spikes and CHT spikes if the engine is held under load for long enough.

[ChrisFoley]

I have always run valve cover vents and a single tower vent on my FP race engines - since 1997. I have never experienced any oil pressure related issues.
My breather systems have always incorporated a self draining feature, so loss of oil volume has not been a concern. With 3 National race wins and 3 Regional titles under my belt I must be doing something right. (IMG:style_emoticons/default/dry.gif)

If the oil temp increases above the desired operating temperature as a result of spending more time in the rocker box it stands to reason that increasing the oil cooling capacity is an appropriate solution, rather than trying to prevent the oil from absorbing more heat. Obviously the oil is taking heat from the heads which is a good thing. I can understand not seeing evidence of the oil cooling effect from reading CHTs under the spark plugs. Those sensors react very quickly to load induced combustion chamber temps but aren't necessarily indicative of overall head temp. CHT readings fall very quickly as soon as one backs off the throttle.

Oil is intentionally used to cool the pistons, so why shouldn't it be used to cool the heads as well?
If loss of oil pressure is a concern from some of the oil being away from the pickup during cornering at AX or track then increase the oil level. The total volume of oil that can be held inside a rocker box is no more than a pint.

[charliew]

I'm still stuck on the thought that oil is usable after being in a 360f enviorment. That alone should change the viscosity so much that oil pressure would really fall off. I bet the characteristics of the air cooled head and it's propensity to get hot are very hard to tune on the lean side to make the most power but still be safe.

[Jake Raby]

Chris,
Thanks for your input. I had wondered if you ever ran into this issue through your experiences.

The issues we ran into did nothing more than prove that we needed to investigate more deeply and try a few things that have proven to defy what we had previously thought completely.

Yet again, there is no general blanket statement about which is best for every engine, application and arrangement. Had we not experienced what we did with the race engine and had I not experienced what I have with street cars I'd have the exact same opinion that Murray and others have had who have been the opposition in this thread. I tend to be a student of the engine.