Intentionally overfill my STI 6 speed?

[altitude7200]

I was told by the previous owner of my 818R that my STI 6-speed transmission, the one with the internal oil pump and the external link pipe, should be over filled intentionally for track use.
I can't seem to find any information on this though. Does anyone have any insight? What's the best fluid to use? Thanks

[Rob T]

I have been tracking my car with a six speed for a couple of years. Mine is still in the original Factory Five orientation (down angle, not like Gator did). It does have a built in pump. I run just under 3 qts of OEM subaru gear oil. I figured this out the first time I changed it after I got the car back from Wayne Presley, who installed the transmission for me. This is the amount that drains when I remove the plug. The fluid does get hot on the track (just over 200F) and I have a trans cooler installed in the pump circuit. At most, I run 6 track days a year, 18 or so sessions, for a grand total of about 325 track miles. Both the trans fluid and the engine oil get changed every year. In the motor I run Red Line race 50 (15w50) which was recommended by the engine builder. It has very high ZDDP content and is not street legal. I am no expert. This is what I am doing.

[Hobby Racer]

That depends a lot on the angle it is installed at. Sgt. Gator posted some good information about it here.

Gator's 81R build thread, on page #6 (https://thefactoryfiveforum.com/showthread.php?26054-Gator-s-818R&p=417204&viewfull=1#post417204)

Unfortunately the picture linked in the post is no longer available on the web, but the text descriptions do a good job of explaining it.

The problem is that the pump is located toward the back and may not get sufficient oil supply when the transmission is tilted forward. This can lead to oil starve / excessive heat and possibly bearing failure. So the prevailing thought is that overfilling the trans will raise the oil level so as not to starve the pump.

A better, but more complicated, solution is to level the transmission angle like I and other have done.

Frame mods for the 6 speed install (https://thefactoryfiveforum.com/showthread.php?23199-John-s-EZ36R-H6-818R-Build&p=391561&viewfull=1#post391561)

And

Major Frame Mods Done (https://thefactoryfiveforum.com/showthread.php?44235-John-s-JDM-Honda-K24A-818R-Rebuild&p=519791&viewfull=1#post519791)

[driveslikejehu]

These guys have more experience so def consider their thoughts. I've only got a few track days on mine. I have everything stock (STi), with the addition of a trans oil temp sensor, and Sube recommended fluid.
The 6-spd pump picks up oil from a pan/strainer so not sure what over-filling does other than add to the available volume for cooling or drain back?

[altitude7200]

Without draining mine, is there a way to tell on the stick?

[Hobby Racer]

Without draining mine, is there a way to tell on the stick?

Not really since Factory Five altered the angle the transmission sits, the dip stick is not accurate. Best to drain and fill with a know quantity and place a mark on your dipstick for the new "Full".

[Bicyclops]

Overfilling will flood the differential to the point of causing frothing of the oil. Frothed oil neither lubricates or cools well. Modifying the frame to lower the rear of the transmission is complicated by interference of the intercooler with the rear crossbar. I handled that with an air/water intercooler. This is something FFR blew in the original design. Rather than correct it (and other oversights) in later shipments, they chose to discontinue the 818. A pity. It appears that the thinking was to tuck the back of the tranny up into the rear fender perhaps for ground clearance. I haven't scraped my lowered transmission mount bolts. The front end is what scrapes. I took the opportunity to weld a tow loop to my lowered trans mount and I don't think it looks wrong having it show ahead of and below the fender. That's another thing they didn't design in - front or rear tow points.
211886
I reinforced the radiator support and used the WRX tow loop into a couple of nuts.

211887
I lowered the back of the transmission about 2 3/4"

Ed

[driveslikejehu]

I looked thru some old posts but didn't quickly find it; dose anybody know what the transmission angle is installed in a Sube? I'm assuming using the flattish top of the trans is a good enough reference line? I'd like to recreate the stock angle and compare with my build to confirm the dipstick point.
211888

[Hobby Racer]

I looked thru some old posts but didn't quickly find it; dose anybody know what the transmission angle is installed in a Sube? I'm assuming using the flattish top of the trans is a good enough reference line? I'd like to recreate the stock angle and compare with my build to confirm the dipstick point.
211888

If you read thru Gator's post I referenced he states "... 5.3-5.9 degrees tail down slope from Subaru (5mt, 6mt, auto)..."

[Bicyclops]

He said that he got about 1.6 degrees down and that it was enough to make a huge difference.

Ed

[Dave 53]

My 6 speed was built by Zack at ZF Designs. I have the internal pump with a cooler. He is fully aware of the 818 and it's transmission angle and how I use the car at track days. No disrespect to others, but Zack is a Subaru race car transmission nerd whose opinion on this subject I value the most. He said to just slightly over fill it per the dip stick and change the Motul fluid every 3 oil changes. I have no plans to lower my transmission. So far so good...

[lance corsi]

Overfilling too much may cause case seals leak at stub shaft. Also the extra drag from too much oil could cause heat from churning. Could affect fuel mileage too.

[Dave 53]

Overfilling too much may cause case seals leak at stub shaft. Also the extra drag from too much oil could cause heat from churning. Could affect fuel mileage too.

My definition of "slight overfill" is about 1/8". Never below the dip stick mark.

The time to worry about this transmission angle stuff isn't on the track. There, the car is getting tossed around so much, the fluid is splashing all over the place. On track, oil pressure, fuel starvation and several other track specific things are far bigger issues. Seems the worst case scenario would be a long smooth road decent. We have several of those in California - the SoCal Grape Vine or 80 from Tahoe. No jarring movements to cause the fluid to slosh around and the transmission angle exaggerated by the road grade. I've never heard stories of any car of any sort ever having a transmission problem on these long smooth highway grades.

The vast majority of 818's have not done the transmission lowering mod. Maybe less than 10. Yes, FFR should have lowered the transmission a bit, but it seems to me it's not that big of a deal. How many 818's have actually burned up a transmission that can be attributed to this? Why aren't we all burning up transmissions?

I've got 23,000 miles and 44 track days with both a 5 speed and 6 speed and I can report no issues that could be attributed to the transmission angle. I've had the 5 speed apart 4 times (install an LSD, 2 pinion gears and a 3rd gear) and other than my track induced catastrophic failures, everything else, specifically the gear facing, looked fine - no signs of lubrication / heat issues. Zack at ZF acknowledge the 818 angle thing and I asked if I needed to do the mod. He said no.

I just want to suggest this transmission angle thing might be a bit overblown. Just my opinion. I respect those that went down the transmission angle worm hole and shared their conclusions. It's a fascinating discussion. I get the theory. I recall being a bit freaked out about it when I first started reading about it here, but now, the transmission angle has been removed from my list of things to worry about.

Back to the original question of this thread (plus more)....
Don't worry about the transmission angle
Overfill the dip stick by about 1/8". As noted, too much is bad too.
Motul Gear 300 75W90 for a track car.
I can't find my notes to confirm, but I recall Zack said to keep it under 210 degrees. Easily accomplished with a cooler. This infers that a track car should monitor trans temp.
Change trans fluid every 3 oil changes.

[driveslikejehu]

Just for grins I repeated the test. With 818 "flat"- zero'd for floor angle- I set the trans oil on the full mark (50* air temp here in Chicago). By my gage, trans angle is ~1.8deg. nose down. I jacked up the front about 7deg, so trans shows 5.2deg nose up. Dip stick reads about 1/8" below "L" mark.
So, in an STi the oil would be low but in the 818 there should be plenty of oil to get to the pump. Maybe 1/8" over F would be good as it would approximate the L level in the STi config? The dip stick goes down just by the differential and not down to the pan; so, as others have noted, I wouldn't want to fill much more as the big diff gears could really froth it.
I reached out to the STi community to get some measurements to correlate with eng/trans measurements I took just to confirm stock STi config.
During track days last year- the first when I'm finally getting into it- I saw trans temps peak at ~220, but nominally around 190-200. So far I don't have a trans oil cooler.
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[Hobby Racer]

... I saw trans temps peak at ~220, but nominally around 190-200. So far I don't have a trans oil cooler.


That is amazingly low temps for not having a cooler. I see those same numbers but I have a really good forced air cooler setup.

I do really push it hard though :p

[driveslikejehu]

Yeah, you're probably just a lot faster than me, lol. I only do track days at a fairly small track; 20 min sessions. Invariably you run up on a slower group of cars forcing you to pedal it for a lap or two. Gives temps a chance to moderate.