Fun with troubleshooting leanness (and 5th gear cruising temps) Options

[emerygt350]

That is pretty much exactly what I am seeing.

[brant]

I agree with wind resistance

Also when you drop into an over drive 5th you drop the fan speed

This is why the factory put a different 5th I believe into the /6 car trans
To not have as much of an over drive ratio in 5th to raise the fan speed and head cooling output


The 356 guys used to drive a gear down to increase cooling to the heads

You could change your gear ratio?
It’s not a heavy load at cruising

Steady state cruising is supposed to be leaner than WOT for gas mileage

[brant]

12-1 at cruising is too much fuel
Washed the oil film more
Increases wear on the motor

WOT should be 12.5:1 to flood the cylinder under that condition as the charge actually cools the head more for load when it’s needed

But not at steady state cruising

And why a pot that changes across the whole range can be detrimental compared to the factory tune that can adjust for conditions and throttle conditions

[emerygt350]

12-1 at cruising is too much fuel
Washed the oil film more
Increases wear on the motor

WOT should be 12.5:1 to flood the cylinder under that condition as the charge actually cools the head more for load when it’s needed

But not at steady state cruising

And why a pot that changes across the whole range can be detrimental compared to the factory tune that can adjust for conditions and throttle conditions

Yeah, 12 is definitely not good at cruise, I was shooting for 13.5. With nothing but MPS mods, it sits at 13.8-9 now at 3200 rpm 72 mph, 12-13inhg. I haven't been able to test my fat switch due to the craptastic weather we are having but from my previous experiments I suspect it will bring me to 13ish. What I am hoping for now is a 'oh jeeze, thats a long climb' switch for the interstate. Out here in upstate ny you can end up climbing 1500 feet over 75 miles with no break as you head west from Elmira. I don't want to be in a position where I am hitting 400 and can't do anything but slow down. No idea if this will actually help that, but it is harmless to try.

[r_towle]

Somewhere out there online is a doc, drawing and pictures of the aero dynamic testing done by a member many years ago….

I’m recalling a set of tests to measure air going into the engine lid, along with temps with and without the rain tray…lots of good tests.

Tray or not makes no difference.

Side vents, like the Boxster, would probably work great.
I recall getting air into the engine lid was actually harder at higher speeds.

Might be worth a hunt to go find old info on 914 aero dynamics

[r_towle]

I’m going to add some custom louvers on the side like a 550 spider.

My goal is a fresh air intake and allow the fan to have all the air dedicated to cooling.

[emerygt350]

That would be interesting, I do have quite the air dam on my car so I am sure that doesn't help. I did put some remote sensing equipment in there a couple years ago, temps in the engine stayed pretty reasonable but things have changed.

[r_towle]

Bottoms of cars have smooth panels now.

The two air flaps on the bottom of the rear firewall are proven to lower temps.

Air dam……no clue if that helps or hurts

[VaccaRabite]

Bottoms of cars have smooth panels now.

The two air flaps on the bottom of the rear firewall are proven to lower temps.

Air dam……no clue if that helps or hurts

Air dam hurts. +10* is what people generally report.

For mine I don't run the rubber lower section of the air dam.

Zach

[r_towle]

I cannot tell from your avatar picture….but it looks like a splitter with possibly a rubber dam below?

If it’s not super hard…take it off and test it

[emerygt350]

Only the splitter, no rubber dam (I was referring to the whole darn thing as the air dam). It is 'attached' so I can't experiment with that, but compared to stock it must be creating some extra resistance.

[era vulgaris]

I’m recalling a set of tests to measure air going into the engine lid, along with temps with and without the rain tray…lots of good tests.

Tray or not makes no difference.

I found this to be the case also. August in North Carolina, generally in the mid 90's with 80-90% humidity. I removed the rain tray and ran two weeks without it just to see if there was any difference. Head and oil temps were exactly the same. Operating temp is operating temp, and has more to do with state of tune as well as whether all the cooling tins are in place.
Over the course of an entire year, through winter and summer, I also saw ambient temps make no difference in head temps, however oil temps were slightly higher in the summer (although not enough to be concerned about) even with a remote oil cooler with thermostatically activated fans.

[brant]

It’s not the resistance that is a problem from a low air dam

It’s the cooling

Under air is required to help evacuate the hot air and increase the temperature fficiency of the stock cooling design

10 degrees was my result also from my own experience with air dams

[emerygt350]

Ahh, yes, I see. I suppose that big oil cooler slot lets some through.... nothing like a regular front of course.