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I would have liked to start a fresh thread for this but my 30 days of being a noobie aren't up yet.
Long story short I'm building a 24 Hours of Lemons Racecar. If you're not sure what that is I'll leave a link below and you can check out our VBlog build.
My question is how are Transmission temps on the Stock RX8? I'm not talking 30-minute track sessions I'm talking 8 hours a day swapping driver every 1.5 -> 2 hours. If its an issue I can repurpose the AC radiator for trans cooling if need be. Can't get too fancy with the $500 car limit but I can maybe rig up something.
I've also heard that the diff fluid can boil on some peoples track days? If that's true that might be more of a concern for us. Any input would be great guys.
Great to hear of a lemons car in the works. Depends how serious you want to get, but for endurance racing I would go with a transmission cooler if that is an option. My experience with a mostly stock drive train in a track/race car is that diff temps are not as much of an issue, although the back cover on the s2 diff (which I have) has bigger fins for cooling so you may want to look into that (plus the s2 diff has a shorter ratio which will help on track).
Start with engine cooling though... my engine is mostly stock, and needs a BIG radiator. You may need to get creative to keep it looking in budget. (possibly a stock s2 radiator with the battery relocated and ducting out of the hood).
So kinda 1 for 1 on Trans VS Diff. Not dismissing ether but I am super limited on budget. It's possible maybe someone would be willing to trade diffs if they don't track and prefer better MPG's .provided that the trans gears are the same ratio.
I am actually trying very hard not to cheat, but I'm still in the process of pulling the engine so who knows how bad it will be. Its -1 lap for every $10 you're over...
The S2 radiator is a great Idea, it would be a cheap option and we could possibly sell the S1 rad to mitigate the cost. You read my mind about cutting the hood to duct air out. Also since its, a race car we will be running no thermostat so hopefully that will help us as well.
I don't need it to be fast, just bulletproof as people are donating on a per lap basis so we got to turn a lot of laps. I would hate to do all this work and we only raise $150 for St Judes because we did 15 laps and the diff broke.
We are planning on some track days at Road Atlanta so I maybe run some sensors to monitor temps and get an idea.
I have temp data from a lot of hard track days.... and the diff is for sure an issue for me. I have seen over 300 degree oil temps in the diff.... way over a few times. I do have a clutch type LSD and not the stock LSD..... but the tranny temps have always been below 250 degrees. The problem is by the time you get a pump and a cooler and all the plumbing....even if you pickup used stuff it's still costly for a lemons car.
The good thing is the diff is pretty bulletproof so if you change the oil after every race it will help
Just for a good laugh.... I had to replace my pump once when I forgot to turn it on. I came back into the pits and turned it on and promptly melted the pump head. I think the pump is rated for 350 deg....and it melted very fast. That was a wake up for me.... after that I added the pumps for both the tranny and the diff to the ECU to monitor and turn on the pumps automatically instead of relying on me to remember. I had them on full time for a while... but when I run the electric water pump to cool the car after shutdown they were on as well... and it tended to kill the battery a little too quick
I have temp data from a lot of hard track days.... and the diff is for sure an issue for me. I have seen over 300 degree oil temps in the diff.... way over a few times. I do have a clutch type LSD and not the stock LSD..... but the tranny temps have always been below 250 degrees. The problem is by the time you get a pump and a cooler and all the plumbing....even if you pickup used stuff it's still costly for a lemons car.
The good thing is the diff is pretty bulletproof so if you change the oil after every race it will help
Just for a good laugh.... I had to replace my pump once when I forgot to turn it on. I came back into the pits and turned it on and promptly melted the pump head. I think the pump is rated for 350 deg....and it melted very fast. That was a wake up for me.... after that I added the pumps for both the tranny and the diff to the ECU to monitor and turn on the pumps automatically instead of relying on me to remember. I had them on full time for a while... but when I run the electric water pump to cool the car after shutdown they were on as well... and it tended to kill the battery a little too quick
Good data, thanks for sharing. I must admit I have not measured my diff temps, but I do have >100 hours on a stock s2 diff and it is holding up just fine. I use a good fully synthetic oil (amsoil in my case), but I don't change it all that often. I'd like to say every 20hrs, but it's actually longer than that. I did send one set of oil off for analysis after a long change and it came back fine. I'm assuming stock power, stock LSD and the s2 housing are the difference here. Or it could be that ignorance is bliss in my case!
On the other hand, transmissions don't seem to hold up as well for me. I had an s2 with ~65k street miles and that held up to quite a few hours and still worked when I retired the car, but it was popping out of 3rd by then and no amount of adjustment seemed to help. I then switched to an s1 with >130k miles and the synchros went pretty quick, but it may not have been in great shape to start. I'm now on what was a new s2 via mazdaspeed motorsports. Even when new, I could feel it got harder to shift after 10-15 min of hard driving, and it has started popping out of 3rd with about 35 hours on it. I have yet to try adjusting this one.
In a 32 minute race last weekend my trans (series 2) got up to 255. Diff has a cooler and stayed around 210. Engine oil never got above160 so I may need to get a thermostat.
In a 32 minute race last weekend my trans (series 2) got up to 255. Diff has a cooler and stayed around 210. Engine oil never got above160 so I may need to get a thermostat.
AC
what was the ambient temp?
i was at Mid ohio last week, and forgot to turn on the diff cooler, at the end of the 20 minutes session, i saw the diff temp gauge pegged out at 280, so not sure what the exact peak temp was on that run. ambient temp was around 45. it stays around 200 when the cooler is on. im running OSG diff and 5.1 FD.
i was at Mid ohio last week, and forgot to turn on the diff cooler, at the end of the 20 minutes session, i saw the diff temp gauge pegged out at 280, so not sure what the exact peak temp was on that run. ambient temp was around 45. it stays around 200 when the cooler is on. im running OSG diff and 5.1 FD.
I would think it was likely north of 350 degrees if it gets as hot as mine. That's why I recommend a diff cooler before the tranny cooler.
It's really a testament to how durable diffs are....
When I first installed my cooler I thought that I had wired it wrong. The fan is triggered by a 180 deg thermostat. When I came into the pits after a cool down lap it was always off. So I thought that I had wired it wrong.... turned out until I heated the sensor up with a heat gun to test it it was just cooling below the threshold for the fan to come on before I got back to the pits. Because of my paranoia I had unwrapped and untied all of the wire thinking I had to rewire it. That was a wasted few hours as I had to remove my rear bumper to get at all of it 😐
When I first installed my cooler I thought that I had wired it wrong. The fan is triggered by a 180 deg thermostat. When I came into the pits after a cool down lap it was always off. So I thought that I had wired it wrong.... turned out until I heated the sensor up with a heat gun to test it it was just cooling below the threshold for the fan to come on before I got back to the pits. Because of my paranoia I had unwrapped and untied all of the wire thinking I had to rewire it. That was a wasted few hours as I had to remove my rear bumper to get at all of it 😐
i was at Mid ohio last week, and forgot to turn on the diff cooler, at the end of the 20 minutes session, i saw the diff temp gauge pegged out at 280, so not sure what the exact peak temp was on that run. ambient temp was around 45. it stays around 200 when the cooler is on. im running OSG diff and 5.1 FD.
@Brettus Yea I'm aware but never done it, actually going to do it this week. Anyone have a link or video on how to do it? And thanks for bring it up, its a very good point.
There’s a bypass passage/hole between the radiator inlet and outlet sides of the t-stat housing. The t-stat closes off that passage when the coolant heats up. Otherwise when it’s cool the bypass is open allowing coolant coming out of the engine go back into the water pump rather than to the radiator.
When you pull the t-stat out you can look in and see that passage. So if you pull the t-stat but don’t block off the passage the system isn’t going to work properly because the bypass passage would be wide open. You might consider drilling holes in the t-stat plate first to increase coolant flow when hot.
The other idea is to pull the t-stat and block the passage, but have an external passage plumbed with valve that you divert coolant until it warms up then force everything to the radiator.
I sometimes wonder if the t-stat closes off the bypass passage fully myself. If the passage is blocked and no t-stat, but the coolant doesn’t warm up that’s a pretty good indicator that the coolant system is fine, but only if the bypass is fully sealed.
However, it could possibly also mean that even when wide open the t-stat is restricting flow too much. Common in racing to have round plates that mimic the t-stat with different center hole sizes and experiment to find the correct size that limits flow to provide the correct coolant temp range.
So maybe drilling holes or cutting openings in the outer t-stat plate might play out if tried first rather than go the full motorhead route.
The guys I bought my RX8 from had several transmission and clutch failures. It was used as an endurance racer and I bought it to rent to drivers for DE days and to endurance race on my team. I followed the car and it always had a problem. Now after getting a fresh engine from a known good builder and finally putting a 5spd in it the car finally finished it's first race.
After the race I finally realized a few things...1. The trans is a great box, but the ratios are really wide for an engine with not much torque and drivers who aren't familiar with rotaries. 2. The original owners had no gauges in the car and without the undertray paneling the engines were probably cooking themselves and eating side seals as I saw coolant temps that were too high and oil temps that were really high even for a piston engine.
So, now my plan is to return the car back to a 6 spd as I now have a spare S1 box and hope it holds together. The original owners would have issues with the trans jumping out of 5th and the OEM TO Bearing melting as well as the stock clutch.
There used to be some fixes for some of that; upgraded machined parts to replace cast or plastic pieces swapped with aluminum pieces, etc., but I don’t know who in your area might know about or be able to offer them. Ultimately the only real fix is a partial or full aftermarket gear-set
04-10-2019, 12:00 PM
