Exhaust Pipe Clearance?

Can anyone tell me if there is a minimum clearance requirement between an exhaust pipe and a heat shield, and between the heat shield and structure or a component, specifically a gas tank? I have a newly installed performance exhaust system that the heat shield is riding on the exhaust pipe and there is very little clearance (maybe .16”) between the gas tank and the heat shield. Also, with the reduced clearance between the gas tank and heat shield, should there be a concern for a hot spot on the tank? THANKS!

 

[GregLocock]

Yes there is, but it has to be determined by experience with that vehicle. 16 mm might be a bit too close, given that exhausts move by 20 mm when they heat up, and can shake around by 10 mm or so when the car is moving.

Some heat shields are happy to be wrapped closely around the puipe, others use the air gap.

Is the tank plastic or metal? is the heatshield insulating or reflective? Do you care if the pipe clonks the tank?

I don't know of a regulatory limit , but I can imagine scrutineers or inspection mechanics raising an eyebrow.


Cheers

Greg Locock

 

[crewchief]

The gas tank is plastic and the heat shield is sheet metal (reflective). There are loud vibrations at specific RPMs with the heat shield riding on the pipe…I prefer some gap. Should I be concerned of this having an impact on the plastic gas tank, i.e. melting? THANKS

 

[GregLocock]

It wouldn't be acceptable to an OEM, and I don't think contact would be acceptable for a custom system.

It probably won't melt your tank, what it will do is heat the fuel more, which is very bad for evaporative emissions.



Cheers

Greg Locock

 

[JayMaechtlen]

it may also make a difference which part of the tank?

very low, where it is "always" cooled by the liquid, might be a tiny bit safer- higher up, no cooling of the plastic...

Are those tanks thermoplastic? I'd imagine not, but what temp are they typically rated for?

Crewchief said 0.16 inch - that's about 4mm !!!!!

I'd vote for another 1/2 inch or so.

do you carry a REALLY BIG fire extinguisher?

Jay

 

[GregLocock]

Ow, I misread that as 16 mm. 0.16 inch is 4 mm which is too close for all the reasons I gave before. Cheers

Greg Locock

 

[crewchief]

I took a closer look (and pics), the heat shield is riding hard on my gas tank and I have .031 inch clearance between the pipe and the heat shield. Per Greg's expantion rates, as the car is moving and heated up, all three (the tank, shield, and pipe) can be riding or sandwiched? It's riding on the lower part of the tank and I'm not sure of the temp rating, I'm to talk to the manufacturer tomorrow. The dealer that installed it is saying the manufacturer is aware of this and all is safe. THANKS

 

[carnage]

if I was going to make a metal heat shield to put under a fuel tank would i want as high or as low of thermal conductivity as possible?

 

[NickB]

I would think you'd want a low thermal conductivity, and high reflectivity. Reflect what it can, and resist the rest.

 

[GregLocock]

Nick's right, we use some fibre sheet covered in 1.2 mm aluminium normally. Shiny side to the pipe, obviously.

Cheers

Greg Locock

 

[evelrod]

Back to basics. Often it is not possible to have proper clearance on performance type exhaust systems, race cars in particular. On a street system ??? I find it rather foolish to put a HOT pipe next to ANYTHING, much less a PLASTIC fuel tank!!! Having said that, and if you still cannot get the proper clearance, at least use one of the proprietary exhaust pipe wraps. I use it on the exhaust headers of most of my race cars. It really cuts down on transmitted heat and improves performance (?) to a degree.

If this is still not to your liking, do as Jay reccommends. Better yet, install a BIG AFFF fire system. I have had one of these plastic tanks on a truck catch fire from a broken exhaust---IT AIN'T MUCH FUN, BOYS!



Rod

 

[NickB]

Rod- I've actually been thinking about putting a fire extinguisher in my car. Not for the appearance (like so many hondas i see driving around), but in fear it might actually catch fire or blow up one day

Greg- Another interesting combo i've seen if the exhaust manifold heat shields on the mitsubishi 4g63 turbo engine. They have two layers of stamped steel with a layer of a slightly fibrous gypsum board material i sandwiched in between, and riveted together. The stuff in the middle tends to crumble when you cut the shield to make room for bigger turbos and external wastegates Any idea what it is?

 

[ivymike]

Nick, I've carried a fire extinguisher in my Honda for quite some time - just in front of the driver's seat, where I can reach down and grab it. I also have two safety flares in the same location. The reason for putting the extinguisher there was not for fear that I'd catch fire, but so that I could easily access it in case someone else caught fire.

Rod- sounds like you've melted, burned, exploded, or otherwise destroyed a sample of every type of mechanical device known to man... how is it that you've still got all your limbs and a pulse? I push my luck pretty far at times, but I don't think it'd carry me nearly as far as yours seems to have taken you!

 

[NickB]

ivymike- I should have been a little more clear, i was referring to all the 'all show, no go' cars i see running around town with the extinguisher on the passenger side A-pillar where they couldn't even reach it in a hurry if they had to. That, and they're too small to be of any real use anyways.

Nick

 

[JayMaechtlen]

dunno- a lot of those little cars, you can reach the passenger-side A-piller while you're still belted in!

Jay

 

[evelrod]

Isaac, it's a combination of several things---old age, agressive personality, love of things 'fast', 'good' luck, etc. (I broke 11 transmissions in my 40 Ford/265SBC in 7 months + couple of clutches) Didn't say I was overly smart, did I? About that same time(1960) I had 35 traffic tickets for speed contests etc. Pre-computer Texas. You would find yourself in jail these days.
Nick--- I have been carrying fire extinguishers in my cars since the first fire (my brother-in-law's Ford/Olds, c.1959). If you attend car shows you will find that ALL are required to have them. My Mini is an extreme case with the AFFF system but, it will eventually be raced in vintage races.

As to the plastic fuel tank fire---I did not even know it was on fire until someone flagged me down on the Pomona Freeway!!! The spare tire was also on fire and no one could get close enough to me to tell me. I was on my way home and in the "zone". The 20 lb. extinguisher I had in the tool box saved the day.


Rod