I am running a 1/2 bridge with a 4 ITB setup. After 2 years of working out the Mapping, what a freakin chore setting up 4 throats with no common manifold vacuum, we finally ran our first races with it this past weekend.

What I am experiencing is that the car flat out flew at a smaller track (ran easily with a Z06 Vette) and in morning warm up (was able to draft up and pass a 300 hp CCTCC BMW). In the first race I started to pick up some detonation/ light rattling in long hard pulls in 3rd and 4th above 8500 rpm. It didn't do it in morning practice only in the first race and only in 2 places on track. As well the power fell off terribly. We pulled the timing back 2 degrees and went out for the second race and it detonated worse and at a lower rpm, 7500 rpm.

What we have been able to figure out is that the intakes are sucking really really hot air and it is causing detonation. As my present setup just has the intakes pulling air from the engine compartment we put the Intake Air Sensor on the front face of the strut tower. In the morning session it was reading about 110 degrees F and the car ran okay. Ambient air was about 50 degrees. In the first race the Intake Air Sensor was reading around 160 degrees F as the ambient air was up to around 65 degrees. For the final race the ambient had gone up to over 75 degrees F and the sensor reading was over 195 degrees.

I spoke to a couple of other racers and they say that they never read higher than 100 degrees F or ambient and that the intake air temps alone could cause the detonation. Keep in mind that the actual air the ITB's were breathing was probably hotter than that as the intake bells are about 6 inches from the turn of the headers.

I think that this is the cause and will build some heat shielding between the header and the intakes and build an airbox to pull only outside air in like it used to be. If this is the cause of the detonation, I just wonder why it didn't do this with the Holley and the air cleaner set up I ran previously.

Other details, timing set at 17 degrees BTDC at all rpm ranges. Max rpm hit was 9500 rpm (was pulling hugely strong at that in second gear). Air Fuels targetting 12.5:1 and pretty successfully after a lot of work. 450 primary, 550 secondary injectors, 190 lph pump. Air fuels in the 8,000 and above are in the 11.5 to 12.0 to 1 range.

Am I on the right track? Comments from you guys that run in 120 degree ambient would be a big help. The picture thats attached shows the physical location of everything. Things have been tidied up a bunch from then and it looks pretty sanitary now, LOL.

Eric Nummelin

 

i think you're right, lowering the air temps would be step one...

what spark plugs are you running? maybe those should be colder? mazda wanted the cold plugs in NA motors too...

 

Good idea as I am running stock plugs right now. I think I will do a plug read and see whats up. Great clue.

Eric

 

Yeah try all 9's in there Eric.

I doubt the 190F (I hope thats F! ) air is helping things, an airbox/heatsheild will likely do wonders.

Also does your MS have an air temp correction map?

 

Yes it does, but we haven't been touching it yet because we are running such conservative timing. After going over to the Improved Touring site I am more and more leaning towards the extremely high air temps and the plugs as being the culprits. Now just need to build a proper airbox and seal it from the header heat and go to all 9's.

Its off-topic, but I am still wet sanding the Cougar. Freakin have to do it by hand as my dual action won't touch the orange peel. Grrrrrrrrrr.

Eric

 

that's a nice set-up! are you running a 4-port or 6-port?

 

Scroll down. This should help.

http://www.extrudabody.com/Products/Accessories.html

 

The engine is a bit of a mish mash. I am running S5 TII housings, S4 TII end plates with a mix of aggressive primaries and conservative secondaries with a bridge, so I guess its a 4 Port. The exhaust is a Racing Beat Race Port. The rotors are S5 NA rotors. The whole keg was put together by Joe at RPM here in Canada and it has been one tough mule to live through all the issues we have had getting it set up to run.

Eric

 

Are you SURE the air going into the engine is the same as what the IAT is reading?

If the engine's getting 80 degree air and the IAT is reporting 180, to throw some numbers out there, then the ECU is probably going to be underfuelling the engine. A lot.

My air filter is stuck on the end of my throttle body so it is pulling underhood air, the IAT is in the filter's elbow, and the only time the IAT reads significantly higher than ambient is on a hot soak. And then the air temps come down within an 1/8 mile of driving.

BTW - My cooling issues have gone from issues to non-issues. I can't GET the engine to run higher than 180 degrees. The solution - I unbolted the hood latch and mounted it one bolt hole higher. This will only work on 1st-gens

 

FYI I tried that about 4 years ago a,d saw a drop in underhood temps and coolant temps, but the car drove differently. So i did a yarn test on it and turned out my speculations were correct. at any speed above 30 mph the lifted hood was acting as a cowle induction because of the high pressure area at the front of the windshield and it was sucking additional air into the engine bay, now this helps evacuate the hot under hood air, but it's all going under the car. Above 80MPH it was causing significant lift around 100mph it was straight scary. So i put my hood down. Now i have a vent inthe hood right infront of the engine after the radiator and hot ait gets out there in a perfect low pressure zone.
https://www.rx7club.com/1st-gen-general-discussion-207/vented-hood-843760/

 

Actually its the other way around. The IAT Sensor is reading 90 degree air because it is mounted further away from the inlet throats. The Inlets are breathing 180 to 200 degree air. So if anything its running rich. The Air Fuels are all reading rich, but I'm not going to change anything until we get the proper airbox and intake on the car.

Thanks for the idea on underhood air release though, I'm going to look into it again.

Eric

 

I misread what you wrote, then.

As far as the hood is concerned... I didn't notice the car driving any differently at the track for those few seconds of over highway speed, but I did note that at 65-ish MPH, the windshield washers are completely useless. The airflow causes the stream to blow straight sideways.

YMMV, of course. I remember that my SA would actually lift the corners of the hood over 70mph. My '85 would lift the hood 4 inches if you unlatched it. This car does not. Maybe it has something to do with the giant air dam under the hood (EFI 13B) versus the carbureted 12As in the other two cars.