Upgrade Project (Part 3)
01-29-2003, 03:58 PM
#46
Drifting
Join Date: Feb 2002
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Hey Christer,
Are you still driving around without heat shields? My shield on the cat side will go tomorow when I am going to install a by-pass pipe and I am a bit worried! What did you garage have to say about removing and drive without the shields?
Ciao,
Johannes E.
Are you still driving around without heat shields? My shield on the cat side will go tomorow when I am going to install a by-pass pipe and I am a bit worried! What did you garage have to say about removing and drive without the shields?
Ciao,
Johannes E.
01-30-2003, 04:51 AM
#47
Race Car
Thread Starter
Johannes
I spoke to GHL at length about this - they have told me that they have run their system on 964's for a year so far with no report of any ill-effects - and a lot of these cars are track cars apparently. I have told them in writing that I have some reservations about running without heatshields. My mechs, JZ Machtech have had a look and have stated that the HT leads (which are under the heat shields) are not terribly close to the GHL system (not sure how your by-pass compares) so they say it shouldn't be a problem. They did point out that perhaps if the car is stuck in heavy traffic then there would be more heat build-up but impossible to say what the effect would be long-term. I am happy to run with it for now and we will see what happens. If for example, my HT leads go from having a 12 year life to 8 years as a result then I can accept that. If it quarters the life of the leads then I will find another solution. Please note that at least in the UK, HT leads are expensive - around GBP600 plus fitting. At least when I need mine done there will be less labour involved as they don't need to take the heatshields off! <img border="0" title="" alt="[Wink]" src="wink.gif" />
I spoke to GHL at length about this - they have told me that they have run their system on 964's for a year so far with no report of any ill-effects - and a lot of these cars are track cars apparently. I have told them in writing that I have some reservations about running without heatshields. My mechs, JZ Machtech have had a look and have stated that the HT leads (which are under the heat shields) are not terribly close to the GHL system (not sure how your by-pass compares) so they say it shouldn't be a problem. They did point out that perhaps if the car is stuck in heavy traffic then there would be more heat build-up but impossible to say what the effect would be long-term. I am happy to run with it for now and we will see what happens. If for example, my HT leads go from having a 12 year life to 8 years as a result then I can accept that. If it quarters the life of the leads then I will find another solution. Please note that at least in the UK, HT leads are expensive - around GBP600 plus fitting. At least when I need mine done there will be less labour involved as they don't need to take the heatshields off! <img border="0" title="" alt="[Wink]" src="wink.gif" />
01-31-2003, 05:56 AM
#48
Drifting
Join Date: Nov 2001
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964 HT leads are £240 at Type-911 BTW!!
I expect a CAT bypass won't get as hot as a CAT - since the CAT has a 50 deg temp drop across it.
In a bypass pipe, you will get some heat, obviously, but most of the thermal energy will be pumped out through the exhaust outlet.
I expect a CAT bypass won't get as hot as a CAT - since the CAT has a 50 deg temp drop across it.
In a bypass pipe, you will get some heat, obviously, but most of the thermal energy will be pumped out through the exhaust outlet.
01-31-2003, 06:04 AM
#49
Race Car
Thread Starter
John
If only they were self-installing. I guess the £600 includes labour. Not something you want to be doing every year in any case. I will be keeping an eye on those.
If only they were self-installing. I guess the £600 includes labour. Not something you want to be doing every year in any case. I will be keeping an eye on those.
01-31-2003, 02:49 PM
#52
Rennlist Member
Johannes E.,
Which heat shields are you talking about?
The metal shields that bolt directly to cat, or the flat composite shield with padding that is directly next to the valve cover?
If the cat bypass is simply a bolt-in replacement for the cat (unbolt the cat, bolt in the bypass), I don't think you have anything to worry about. The flat composite shield near the valve cover will still be there to protect the spark leads, and I agree with JohnF, the bypass is going to run much cooler than the cat.
Cats get extra hot because they burn stuff (e.g. unburned fuel in the exhaust when the motor is running with a rich mixture dialed in by the DME). Bypass does not burn stuff and therefore should run a lot cooler. Also, the bypass is (I assume) a straight pipe that is much narrower in diameter than the cat it replaces, so there should be a lot of airspace between the bypass pipe and the composite shield.
Which heat shields are you talking about?
The metal shields that bolt directly to cat, or the flat composite shield with padding that is directly next to the valve cover?
If the cat bypass is simply a bolt-in replacement for the cat (unbolt the cat, bolt in the bypass), I don't think you have anything to worry about. The flat composite shield near the valve cover will still be there to protect the spark leads, and I agree with JohnF, the bypass is going to run much cooler than the cat.
Cats get extra hot because they burn stuff (e.g. unburned fuel in the exhaust when the motor is running with a rich mixture dialed in by the DME). Bypass does not burn stuff and therefore should run a lot cooler. Also, the bypass is (I assume) a straight pipe that is much narrower in diameter than the cat it replaces, so there should be a lot of airspace between the bypass pipe and the composite shield.
