Doubling power: need for gearbox oil cooling?
Discussion
I'm in the middle of converting my [road-going & occasional track use] MT RWD car from 215 ish bhp to 400-450 bhp whilst reducing the airflow from the engine bay over the gearbox. I considered the need for cooling the gearbox oil to preserve gearbox life and decided that I'd be OK on the road but was unsure for track days. Does anyone have any knowledge or experience here?
I had 3 options in mind:
1. Do nothing
2. Put in a cooling system during the conversion.
3. Suck it and see by designing a cooling system, leave space for it to be fitted later if needed, and monitor gearbox oil temperature (say by fitting an oil temperature sensor with a switchable input to the engine oil pressure gauge I'm fitting).
Some details:
Mazda RX8 with single-turbo 13B REW engine from RX7 FD generating 350-400 rwhp
Intercooler and half of radiator airflow to be ducted out of bonnet.
Retaining 6-speed gearbox in first instance, with the intention of fitting a 5-speed gearbox if/when the 6-speed goes bang.
I had 3 options in mind:
1. Do nothing
2. Put in a cooling system during the conversion.
3. Suck it and see by designing a cooling system, leave space for it to be fitted later if needed, and monitor gearbox oil temperature (say by fitting an oil temperature sensor with a switchable input to the engine oil pressure gauge I'm fitting).
Some details:
Mazda RX8 with single-turbo 13B REW engine from RX7 FD generating 350-400 rwhp
Intercooler and half of radiator airflow to be ducted out of bonnet.
Retaining 6-speed gearbox in first instance, with the intention of fitting a 5-speed gearbox if/when the 6-speed goes bang.
Stevie, thanks. I'm in the middle of the conversion, probably 3 months away from completion, and have no info yet.
BTW I have no information from other cars as AFAIK I'm the only one going this route of the 13B REW, exhausting intercooler and radiator air flows through the bonnet and retaining the original gearbox. Most turbo RX8s retain the 13B MSP Renesis engine and are limited to 300 bhp, if that, by the engine's relative fragility when turbocharged. Fast track or race RX8s in the US change the gearbox but the options there are out of my price range. There is a track-only 13B REW RX8 here in the UK, the owner has had his hands full with pressing issues/problems and I don't think he's done enough running to help out.
BTW I have no information from other cars as AFAIK I'm the only one going this route of the 13B REW, exhausting intercooler and radiator air flows through the bonnet and retaining the original gearbox. Most turbo RX8s retain the 13B MSP Renesis engine and are limited to 300 bhp, if that, by the engine's relative fragility when turbocharged. Fast track or race RX8s in the US change the gearbox but the options there are out of my price range. There is a track-only 13B REW RX8 here in the UK, the owner has had his hands full with pressing issues/problems and I don't think he's done enough running to help out.
I've had issues for years with my Saab b234 running 450+hp and torque wrecking gearboxes despite sympathetic use and quality oil usually issues with synchro assembly's . Measuring case temp after a 20min session the block would be at 85c and the box at 110 , added a £50 spur gear transfer pump drawing oil from what was the drain plug and putting it back via what was the fillet plug and a 10 row foot wide cooler plus cheap temp guage has brought oil temp down to 80c and the pump system has added an extra litre and a bit to the capacity .
Done 4 track days so far which is double what a non cooled box would last before something failed and the oil is still clear with a tiny shimmer of brass in it .
I had the box built by competition trans services with a few new bearings and the first thing he said was add a pump and cooler if you want it to last ,
I've no idea on the maths but 350kw of power must create some serious heat in the box with 2 or 3 litres of oil to cope with it I'm not surprised the oil gets cooked
Done 4 track days so far which is double what a non cooled box would last before something failed and the oil is still clear with a tiny shimmer of brass in it .
I had the box built by competition trans services with a few new bearings and the first thing he said was add a pump and cooler if you want it to last ,
I've no idea on the maths but 350kw of power must create some serious heat in the box with 2 or 3 litres of oil to cope with it I'm not surprised the oil gets cooked
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