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2011 Chump Car Build

Old 03-15-11, 04:01 PM
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2011 Chump Car Build

Here's a bit of a blog covering the build up on our 2011 Chump car build for the Race City event in Calgary. After many years sitting, the old car will roll again.
We're trying the old circle track trick of cutting the roof off to do the cage. We'll see how it goes back on.

http://www.4kruzn.com/wordpress/?page_id=109

-Trent
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Old 03-15-11, 04:53 PM
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This should be interesting. You Canadians and your rust.
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Old 04-02-11, 10:21 AM
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please keep updates going. Are you going to just use the parts from the three cars? Or are you adding actual performance parts too?
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Old 04-04-11, 03:17 PM
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Trying to stay under the $500 cost cap we'll likely use stock parts for the majority. Our first goal is a good handling car which can hang together for the 14 hours. Fast comes third.

-Trent
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Old 04-25-11, 08:33 PM
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Bump!
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Old 04-26-11, 04:38 PM
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Well, we just did a work-bee on the car and it fired up for the first time. We seem to have transplanted the wiring harness correctly.
I also managed to weld the roof back on with only minimal warping, so a little bondo and it should look just fine (the 20/20 rule applies, 20 feet away, 20 mph).
The big changes were the cutting of the stock springs, which didn't drop the car near as much as we expected. We cut 2 1/2" off the springs and the car still looks too high. I guess when you chop almost 800 lbs out of a car you need to worry about the stock spring rates. We'll likely let it sit for a bit and then take a little more out of the springs at a later date if it doesn't settle to where we want it. Other things were the installation of a whisper quiet exhaust to keep us under the 92 DB limit. All said, the car should be good to go for some test and tune action to sort out the handling.

-Trent
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Old 04-29-11, 01:36 PM
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Another evening of work.
I chopped the stock springs about 2.5" (the Falken Azenis 615K's in 215/45/16 are very short, so the car can be very low.

-Trent
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Old 05-04-11, 08:28 AM
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Nice!

I used to live in Ft. Mcmurray, I know how harsh and cold those winters can be,

the running joke, everywhere else in the world cars rust from the top down.. in Canada they rust from the bottom up
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Old 05-04-11, 03:57 PM
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Trent, just slightly off topic. I have run 4 lug hubs for years and lived with the single piston brake setup that came with my car. It looks like the GXL 4 bolt rotors would work on my "Pig" and allow me to go to a 4 piston setup with a larger rotor. What year GXL RX7 rotor am I looking for? This setup would allow me to keep my 6 sets of 4 lug wheels.

I honestly can't believe that I go as fast as I do with a stock single piston caliper and small rotor, but I am at the limits as I melt the seals out and crack rotors every 1 Hour long race. I am glad that I race mostly at Mosport where you only really use the brakes 1 time a lap.

Eric
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Old 05-09-11, 12:21 PM
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We're using a five bolt car for the chump car.
We have however, re-drilled the five bolt rotors with four holes and used them on the 4 bolt hubs, along with the TII brake calipers. It wasn't that hard to do and allowed us to keep using the four bolt wheels we had built up. Just take the tII rotor to a local machinist and get the four holes drilled with the correct spacing. Stock TII calipers will bolt right up.

-Trent
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Old 05-09-11, 12:28 PM
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Car runs well

We managed to get out to Stratotech ( local go-kart track) for some laps. The car works pretty good. It has an initially unnerving snap turn in on turn initiation, but a few laps in you get used to it. (An alignment would help) the chopped and bent springs work quite well and the car is quite good through the corners. The power isn't what I'm used to (the turbo FC really kills it) but it is a predictable and stable race car.
Less than two weeks to the main event. Time to start building up our pile of spares.

-Trent
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Old 05-26-11, 04:44 PM
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Chump Car update

Well, the event is over and the car worked well, other than fueling and the blown oil cooler line.
We managed a second place on the first 7 hour enduro and finished off the podium in the second due to the oil line and a driver penalty for hitting a cone in the car merge zone.
Here's the details on the car. We were one of the faster cars out there and put in some very fast laps.

Here's Conroy's breakdown on the car:

the #20 bandit... (From Smokey and the Bandit fame)

S5 1988 mazda rx7 factory rated 160hp, AIV = 375.00 125.00 in go fast parts allowed.

old header which failed at end of race. 50.00 (pacesetter)
k+n filter 15,00
strut bar 40.00
misc steel for fab work 20.00

with header and k+n i would assume around 140rwhp. car is super stripped aka very light. weight is close to 2100lbs.

that power to weight is a hard to beat combo.

stock springs when cut 2.5" off will increase in rate by about 20%. Good condition factory shocks will still handle that for spring rate but not much more. If you were watching close you would have noticed alot of other cars out there bouncing alot... that was because they put way too stiff springs without the shocks to back them up. our car ran stock cut springs and stock replacement shocks.

swaybars are essentially springs. shorten the arm and increase the spring rate... this is simple physics. we redrilled some new holes in the stock bars and changed the rate of the factory bar.

dont forget the rules say you cant spend money on the car, but you can spend money on a couple drill bits.

the diff is stock 4:10 ratio, we went with 1.2" shorter than stock tires to keep tham light and increase the effective gear ratio to a 4:28-1 in adition to the height the shorter tires were 3 lbs lighter per tire than the taller ones. also the factory diffs have a 20-25% locking posi system. it was decent although it did slip some out there. by feathering the throttle under some of the corners we were able to keep the inside wheel from spinning "most" of the time.

the fuel system on the rx7 is also better than most give it credit for. factory 70 litre tank!!! it would also alow us to run it down to about 6 litres from empty before making us stop. allan ran 1:50 flat out sunday morning!!! we had to fill 63 litres! but this also allows for a 3 stop stratagy over 7 hrs of racing.

alignment, i am shocked at how many teams dont do it. the camber and the alignment is SOOOO important. The rx7 rear susp cambers in huge when lowered. no mods are required to get nearly perfect camber on the rear. the front is another story so we fabbed up some ball joint spacers from flat bar and drilled some holes and bolted in some camber. we were running 3.4 front and 2.75 rear. in adition the factory car runs ridiculously high offset wheels. aka terrible for racing. we ran 16x8 +30 wheels front and 16x9 +24 rear. this and the balljoint spacers gave us 5" increased track front and 4" rear. wider is better.
Attached Thumbnails 2011 Chump Car Build-chumpcar-build.jpg  
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Old 05-26-11, 08:48 PM
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awesome write up.i have a 88 rx7 im taking to sebring for the 14hr race.we have about the same setup but we have a fully rebuilt motor and stainless oil cooler lines i have learned my leason about stock oil cooler lines.we also have lowering springs instead of cut springs they only cost us 160.00 bucks so that with our header we will probly get about 5-10 penlty laps but over 14 hrs i think the racingbeat header and springs will make up for it
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Old 06-01-11, 08:24 AM
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At the Calgary event a number of cars had springs. You could clearly see the cars bounce through the corners. Given the limitation to stock shocks, I'd advise against running stronger springs based on what I saw. Our car was complemented for looking flat and smooth. We built it based on the old Herb Adams concept of soft springs and a strong swaybar setup. The car was a great mix, able to stay quite flat in the corners, yet able to handle the rough sections in a composed manner.

-Trent
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