Intercooler heat soak, or clogged Cat?
 

I"m tracking my '93 R1; engine, drive train, turbos, ECU, intake, IC all stock.

I'm running SCCA Club Trials - we get a 30 minute practice session, a 20 minute qualifying session, and a 20 minute race that comes in the afternoon. Ambient temps at the track are usually in the mid 90's by then.

I find I can get in about four laps (1:40 ish seconds) in the morning session before the car just seems to lose power, where I can hit 125 mph at the end of one straight on my first couple of laps I gradually lose power and speed, down to only 100 mph, then by the end of the session I'm only getting to around 85-90. I'm up in the rev range for the entire lap, and the car is working hard. In the next session, I can only get two or three laps before it just feels like the turbos aren't putting out above 5K, and once again I'm barely making speed down the stretch - I give it WOT and there's no noticeable surge, a very slow increase in speed and no punch at all, same thing coming off the corners. It's way beyond turbo lag, there's just no punch.

If I back off for a lap and short shift, I can get some speed again for maybe a lap, or half a lap before she chokes up. At low speeds she pulls like a tractor, but anything above 5k in 3rd or 4th gear after running for awhile is weak. I've done the boost test (3rd gear WOT) and I seem to be getting the right numbers - 10, 6,10 -, but I've only done that on the highway, and not after running hard for a 1/2 hour.

I'm hoping this might be either IC heat soak, or maybe a clogged cat that can't take the heat? Has anyone else had these problems on a long track day?

Yea, it's your (stock) IC. Check this post from Steve Kan:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/hottest-air-water-temp-track-241815/

I can see where the high temps are going to be a problem for me if I continue to race the car. At the bare minimum I'll need a new radiator and IC, and to fabricated some ducting.

The car really is more a street rod than a track candidate; I now know why they didn't have much success in pro road racing when new.

They didn't have much success because there were never that many classes where they could be run. They were kind of a "tweener".

In any case, before you go spending a lot of cash on the radiator and new IC, really work the ducting issue. It seems that a lot of the cooling problems can really be mitigated if you make sure that there are no leaks. and that you are using all of the air that goes in the front.

Question: do the R1's have those two little side plates just inside the main air opening - they sit behind where the driving lights would be mounted on the Touring models? My '94 PEG had them and I kind of wondered why they were there. I removed them a while back.

Last Q: you say "no underhood mods" - do you still have the stock pre-cat?

Good luck,

-b

Yes, R models have those plates as part of the component Mazda refers to as the "Air Guide".

I'm still on the stock i/c and even with well stuffed ducting there is plenty of room for intake heat soak. I only do a couple of informal track days per year but I'm keen on getting a good SMIC when money and opportunity finally come together.

Reno, you could dial down your boost to keep things cooler overall. Yes, you'll lose some power but it might help you be more consistent through the sessions. Less directly, installing a downpipe would help a lot too. The heat from the exhaust manifold and intake temp sensor aren't all that far apart.

Dave

I've still got the stock (original) pre-cat and cat. I can't do a Downpipe in Nevada and still pass smog, they do a visual check and the car barely passes now as is. Yes, I've got the side plates, and the original undertray on the car.

By dial bown boost, you mean change the pill size? I'm thinking I might, might, look into getting a cheap EBay SMIC and try to fab up some duct work for it. I don't think I want to put a lot of money into the car because I probably won't keep it much longer (I've had it 10 years), and I want to keep it as original as possible for resale.

Why don't you keep your stock parts, and then look at something like this:

https://www.rx7club.com/showthread.php?t=771346

When/if you decide to sell it; put the stock parts back on and sell the aftermarket ones separately.

^that is a nice setup and very easy to install/reverse both IC and intake

At 60k your precat is probably a wad of solid junk.

At least you could punch it out or swap for a JDM style with no catalytic element in it. Either way you'll do just fine on a tailpipe check because the precat does nothing to help emissions once the car is fully warmed.

If you want to easily dial down boost, you can unplug your wastegate and precontrol solenoids and reset your ECU when you're done. You'll get a solid 7-8psi. Or remove the pills.

Dave

Agreed. And since the car is not ODB-II, you should easily pass visual with just the main cat in place. The pre-cat has no air feed and no one would realize that it wasn't there. In addition, as Dave pointed out, the precat has very little impact on emissions once you get the car warmed up and you should pass an emissions sniffer test just fine without it.

On the other hand, if you need a replacement precat - give me a call. I have a low mileage one stilling in my garage. You pay shipping. :D

-bill\

PS. Wow, this is my 1000th post. That's kind of disturbing.