993TT - Undertray on or off?
Discussion
On - smooth airflow under the car, additional cooling hardly an issue in Europe. Keep the road crap thrown up by the car off the engine.
I have heard of one 993tt that had been obviously been run without the tray by someone that lived up a dirt track. The mud caked onto the turbos rusted through the casings - not the normal reason to have to replace your turbos.
I have heard of one 993tt that had been obviously been run without the tray by someone that lived up a dirt track. The mud caked onto the turbos rusted through the casings - not the normal reason to have to replace your turbos.
Well I guess you'd spot oil leaks earlier?!
How much of a "cooling" effect is there when removed?
I ask because when I had a Turbo MX-5 (not that I'm comparing them of course!), the undertray was an often discussed issue - most folks with forced induction left it off because trimming it to accomodate the intercooler pipes was a chore. However, one usually found that the cars ran *hotter* with the undertray removed and yes, this was counter-intuitive. Seems the tray directed air coming inbound through the mouth of the car all around the engine rather than back out the bottom. This was fairly easy to see via the aftermarket ECU datalogging used to control the turbo setups. I altered mine to accomodate the IC piping and refitted it. I noted a measurable (albeit small) drop in both coolant and intake air temperatures with it in place. Keeping all the crap off the underside of the block was an added bonus as well as having reduced bonnet-lift at high speeds. Obviously the 911's engine being where it is is an entirely different setup against an MX-5 but things aren't always what they seem.
Mine's staying on my 993 if only to help keep the crud out...;-)
How much of a "cooling" effect is there when removed?
I ask because when I had a Turbo MX-5 (not that I'm comparing them of course!), the undertray was an often discussed issue - most folks with forced induction left it off because trimming it to accomodate the intercooler pipes was a chore. However, one usually found that the cars ran *hotter* with the undertray removed and yes, this was counter-intuitive. Seems the tray directed air coming inbound through the mouth of the car all around the engine rather than back out the bottom. This was fairly easy to see via the aftermarket ECU datalogging used to control the turbo setups. I altered mine to accomodate the IC piping and refitted it. I noted a measurable (albeit small) drop in both coolant and intake air temperatures with it in place. Keeping all the crap off the underside of the block was an added bonus as well as having reduced bonnet-lift at high speeds. Obviously the 911's engine being where it is is an entirely different setup against an MX-5 but things aren't always what they seem.
Mine's staying on my 993 if only to help keep the crud out...;-)
Interesting point,the factory did not fit one on my gt2,and i dont run one on my rs,it runs much cooler.
Also 964 and 993 wear more on the exaust valves,guides etc than other earlier type 911. Mainly down to heat.
Also a 964 rs caught fire one day at pembrey circuit,oil on the engine tray ignited!
Also 964 and 993 wear more on the exaust valves,guides etc than other earlier type 911. Mainly down to heat.
Also a 964 rs caught fire one day at pembrey circuit,oil on the engine tray ignited!
phelix said:
I think general consensus is that it's mostly to reduce noise and smoother airflow is secondary.
You might be right, but note that the workshop manual recommends a test drive without the undertray in place after a major service, so any leaks or problems can be seen more easily. Underenath this recommendation they write in big bold letters not to exceed 95 mph without the undertray in place.
This implies to me that all their aerodynamic work was done with the undertray attached, though this does not mean that the car is necessarily less stable without it - they were probably just covering their asses!
Gassing Station | Porsche General | Top of Page | What's New | My Stuff