Anyone with a stock FD (or can remember their FD in stock form) know if removing the stock downpipe, which has the precat (itself a source of heat), is a main cause of the "hot transmission tunnel" ? The reasoning would be that the stock heat shields prevent the cabin from getting too hot, whereas an unwrapped aftermarket downpipe heats up the floor boards.

I don't know if ever been in an FD that didn't get noticeably hot in that area but I don't remember the last time I rode in a truly stock one with all heat shields intact either.

I'm asking because I'm thinking about buying a stock FD and I would want to keep it a "normal" car. And to me there's no way a $40k car in 1993 got hot like that when brand new.

 

These cars actually got pretty hot stock. So much in fact that Mazda installed a temperature sensor in the passenger floorboard and the overheat exhaust system light. That being said, I've never seen one actually go off. Excessive heat in the floorboard is usually attributed to a clogged cat, or missing heat shields on the exhaust and turbo system. Heat wrapping the downpipe and exhaust piping with DEI titanium and installing some heat shielding under the carpet makes a big difference.

 

Totally stock (pre-cat + all heat shields, carpet, and insul) = not hot

Substituting a wrapped DP for the pre-cat and high flow cat for stock cat while retaining all heat shields, carpet and insul = not hot.

Have no data points for any other alternative

 

I have the HKS DP with Jet-Hot 2000 inside and out. No heat issues apparent with that setup.

 

I should add that missing or having a ripped shifter boot or insulation will allow heat from the transmission and exhaust to radiate up as well.

 

Thanks for the replies.

Who did the coating? I would prefer a coating to a wrap.

 

i don't recall the cat changing cabin temps either way, although its been a while. the Rx8 is just as bad...

so plan B might be a JDM downpipe, its wrapped like the precat, but no cat.

 

does the JDM downpipe bolt up to the USDM main cat? I know it has that kink in it for the steering column on RHD cars. I mean I'm sure it flows better than having a cat there though.

 

I have a JDM DP gathering dust. pay shipping and you can have it


when I removed the precat and replaced with a jethot coated and dei wrapped DP I had no more heat than stock.

when I went with a larger DP uncoated and unwrapped the trans tunnel and pass floor get noticeable hotter

 

I would second the Jet-Hot recommendation.

https://www.jet-hot.com/

Their 2000 degree coating is amazing. Big time reduces underhood temps and keeps the heat where it needs to be. The stuff is VERY durable as well, I've done a number of downpipes with it with absolutely no discoloration, flaking, anything.

Matter of fact a buddy totalled his FD and the downpipe took a hard hit in the wreck and dented it. The Jet-Hot didn't come off at all, didn't flake or crack.

Last I remember it was like $120 to have it done. If you want a second bung for a wideband, I would get that welded on first and then just plug the hole up.

Dale

 

Here is another data point. I have a gutted precat. I cut it apart, removed all the innards, ground all the welds smooth on the inside, welded it back together, and reattached all the OEM heat shields. There was no discernible difference in the amount of heat coming up.

 

It has gone up, a tad... I received a quote this week from Jet-Hot @ $240.

 

Thanks.

I found a PFS downpipe, ceramic coated (not sure what coating) in the classifieds. I'll either do that or the JDM downpipe maybe.

 

It will bolt up no problem and it's not really a kink. The top part of the pipe that bolts to the twins has a dip in it to make room for the steering shaft.

 

I'm wondering what difference the stock DP made in underhood temps though.


And arghx, don't sell the DEI wrap short. I stayed with it when the coating wasn't available in my area at the time. It's low tech old-school, and not as cool looking, but it's a quarter of the cost and with the twins not much shows. And with their 'ceramic sealant' it works well. I can pull of the highway and it less than 5 minutes have it up on the lift and grab the DP with my hands. No heat issue to the floors and the sealant keeps it from being itchy to work around. Plenty left to do the inlet and outlet of the main cat too.

 

you know that reminds me, i wrapped my downpipe. no change in cabin temps, and underhood temps did go down. and its less loud

 

my friend had one without the heat shield on it, the pipe is TEENY, it looks like a wet cat...

 

I agree - coating is better, especially if it is inside AND out. Outside only (coating or wrap) can degrade the metal because the heat will be trapped in the metal and the pipe will run hotter.

https://www.google.com/url?sa=t&rct=...48073327,d.eWE

 

I can remember the exact video, but a was researching inconel and I came across a video where the person said that the exhaust(down pipe) of rx7 were made with inconel aloy because of the rotary engine's exhaust high heat.
I though , it was really cool if it's true.

 

I remember when I switched from the stock pre cat to a downpipe I noticed the engine bay was a bit cooler, granted I only noticed the difference after an hour or so of driving no immediate difference. I have a midpipe laying around that i will put in place, ill try and remember to let you guys know if i notice a temperature difference in the cabin.

 

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Replaced the engine and a lot of brittle hoses and wire problems; would like to reduce the heat on the new engine.
Your JDM DP: Fits stock dual turbos, and has air port?

 

I'm super happy with my JDM downpipe. It has No cabin heat problems, looks like stock, no noise, fits a stock turbos US car, probably a slightly less restriction. I have stock main cat. There is no impact on the secondary air injection pipe.

yesterday I drove around in stop and go with the A.C. and did not feel the cabin get hot in the downpipe area.

 

I have an HKS DP that I bought brand-new earlier this year and sent out to SwainTech for their "White Lightning" exhaust coating. I haven't installed it yet because I'm being a colossal ***** about getting underneath my car on jack stands. For some reason I'm feeling my mortality lately. Thinking of getting a QuickJack prior to doing the work.

Anyhow, the coating cost about $85 I think, but then shipping out and back took it up to $140. The HKS downpipe was like $220, new.

 

if the downpipe has never come off the car before (after 20+ years), you will probably break all the studs and have to replace them. Be warned.

 

^This.
Apply a lot of PB and go to church while it soaks because your mother and the Lord's name WILL be taken in vain.