This page was originally our first current projects piece, and showed some pics of a custom air intake system. Since then, the car has been completed, and so we decided to add more pictures, and tell the story.
The original pictures and descriptions are at the bottom of the page.
The owner of this car has a 2nd gen RX-7 built by Mariah motorsports for SCCA's E-Production class. The car is very nicely constructed (Kudos to Mariah for the exceptional workmanship!) and is meticulously maintained and cared for.
It seemed like a good idea to add a lower priced race car to the stable for the sake of cheap seat time (And cheap tires) to run in the local regional events.
So...we started with the following idea. "How fast can we go without spending gobs of money?" After looking over the AZ region rules, we decided to go with the RS class. This class had recently changed, and the new rules were quite interesting. Loosely based on IT prep, there were a few surprise additions, like no minimum weight, no minimum ride height, lexan all around, any porting, and any rear wing!
Wow! Loads of fun! We dusted off John's old PRO7 car, and got started.
The first issue was power. After digging around the shop, we found that we had enough parts to build a fuel injected 13B using a 1989 TII motor, with rotors from a naturally aspirated engine. We decided to use the stock intake manifold and throttle body, and control the stock injectors with a fuel only system from SDS. SDS makes a nice reasonably priced unit with great reliability, and even better customer support. For spark, we used the original distributor for the 12A that was in the car.
The intake ports were very mildly modified, with only 10 degrees duration added, while the exhaust ports were more typical of our higher rpm race engines.
The intake manifold was left stock except for a very little bit of porting in the plenum.
To get cool air to the intake, we fabricated a duct which drew air from in front of the radiator, and that was capped of with a large K&N cone filter.
For the suspension, we kept it simple. Instead of fabricating lots of trick parts, we built just what we had to, and chose off the shelf dampers that had the characteristics we wanted.
At the rear, we fabricated a panhard bar to get the roll center lower, and left the stock longitudinal links in place, rubber bushings and all. We used a Koni rebound adjustable shock, originally intended for circle track use, along with their coil-over kit so that we could easily adjust ride height and spring rate. We also installed a Racing Beat 3/4" adjustable rear sway bar.
At the front, we used a Koni rebound adjustable insert which required fabricating new strut housings. We used this opportunity to extend the bottom of the housing to raise the roll center, and we also offset the mounting points to increase Ackerman geometry. For the tension rods, we used a delrin ball and socket arrangement from G Force Engineering. And finally, an off the shelf 1 1/8" sway bar.
We put all this together with 650lb front springs, 300lb rear springs, and Hoosier 225/45 radials on the existing 13" Panasport wheels.
The new rules allowed for a rear wing, and so we chose the World Challenge Touring Car spec wing. To help reduce lift on the front end (And help cooling) we cut a large exit vent in the hood, and fabricated some aluminum louvers to create a low exit pressure at speed.
The transmission was modified to accept a Miata gearset, and the worn out clutch was replaced with an aluminum flywheel, and "Street/Strip" clutch from Mazdatrix. (You should buy all your goodies there. They stock nearly everything, and treat their customers well.)
We made many other small modifications that are too numerous to list, but with every step, we stuck to our "bang for the buck" approach.
After the car was completed, we went to the chassis dyno to dial it in, and were quite surprised to find that the motor made 210hp@7800 rpm! (240 at the flywheel maybe?) This was about 20 more than I expected, and we were able to make that power without winding the motor to the stratosphere. On the track, we will limit it to about 8200 rpm, and so we expect it to last a long time.
At the track, we found that the little 13" Hoosiers didn't have the grip of the big slicks that we run on Johns EP car, so corner exit requires a bit more finesse. The high speed corners are another story. The combination of the exit vent in the hood, and the rear wing resulted in substantially better grip than the EP car on slicks!
Overall, the car was very well balanced, requiring only a rear sway bar adjustment to make the driver happy. The high speed blow off characteristics of the Koni shocks make the car very driveable over curbs, and tire wear looked good all around.
We've only been out in the car once, but based on what we experienced, and the fact that the power to weight ratios are similar, we expect to go as fast, or faster than the EP car for a fraction of the cost.
Needless to say, we love the new RS rules.
In the future, we will probably add a front splitter, and crank a bit more angle into the rear wing, but other than that, the car is quick, easy to drive, and easy on tires. (Tires that are about $200 cheaper per set!)
Enjoy the pictures.
PY
Here's the completed car in front of John's house.
This picture shows the extreme height of the rear wing. The mounts that came with the wing placed it much lower (To meet class rules) and further back so that it would be in clean air. A quick calculation showed that the extreme rearward offset would result in substantial lift on the front of the car as the force was applied far behind the rear wheels. Since the RS rules did not limit the height, we made new mounts so that we could get it up high into clean air, and further forward to reduce lift at the front.
The strut tower brace was actually meant for a 2nd gen car, but being true to our "bang for the buck" approach, we modified it to fit this car. You can also see the custom thermostat housing built to clear the strut brace. "Hmm...Did we really save any labor here?"
Here's a good shot of the custom cold air intake that was originally shown on this page. We're quite proud of this simple but effective piece. (Yes, we know there's too much blue paint under the hood!)
Here's a shot of the exit vent in the hood. We cut an opening in the fiberglass, and fabricated the louvers from thin aluminum sheet.
At speed, air entering the nose stagnates under the hood, and lifts the nose. By letting this air exit, the pressure under the hood is lessened, and front end grip is increased. This arrangement also increases airflow through the radiator.
Here's a shot of the interior. It's a little rough, but a new steering wheel and fresh paint will not make it faster. This old PRO7 car has really been around. Originally from CA, it eventually made it's way to AZ where it had several owners over the years. It ultimately ended up as a rental before John bought it to keep himself busy while Mariah was crafting his EP car. (Oddly enough, my partner once rented this car years ago to keep his SCCA license current. Small world....)
This shot is a bit better and shows a few of the simple pieces we built for the interior. What you see is the lap timer, SDS injection programmer, and SDS mixture knob. (Try that with a carburetor!)
Original Pictures and text below
This used to be an SCCA Pro7 car, and we will be converting it for the Arizona SCCA region RS class. The engine is made up of street ported TII housings with rotors from a naturally aspirated engine.
Here it is in the chassis after the cold air intake was completed. The engine will now go on the dyno for tuning with the intake intact so that we replicate the in car conditions as closely as possible.
The intake was fabricated from 4" diameter 18ga. mild steel, and tig welded together.
Note that the oil filler tube required relocating, and so the stock piece was modified into the S shape you see here.
We will also be upgrading the suspension, and adding an aftermarket radiator and oil cooler. Those pictures will be added at a later date.
