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1981 242 16v Turbo SCCA RallyCross Project

RallyRat

RallyRat

New member
Joined
Oct 19, 2015
Location
Denver, CO
I've been racing my first car, a 1968 144, for 15 years. Despite all of my efforts to kill the 144 being unsuccessful so far, I bought an already stripped 242 from a friend to replace it.

My 144 has been the top 2wd RallyCross car in Colorado for the past 2 years thanks to a lot of driving experience and consistent finishes (not so much its performance). My goal with this car is to make something faster and see what's possible. Most mods are geared toward reliability, more power, and weight reduction at the front of the car without going too crazy on the budget. It should be a fun drift car too! :)

Mods, completed or planned:
B230 block with upgraded rods and pistons
Stock b234 head with a little bit of port work
Megasquirt 3:
-fully sequential
-throttle bypass anti lag
-coil per plug
Precision T&E ball bearing turbo
T5 transmission (-260 tag # for now)
Low inertia clutch etc:
-Tilton OT-II 7.25" cerametalic single plate racing clutch (5.6lb)
-Late model b230 flex plate (1 piece stamped with welded ring gear, 4lb)
-Custom 4140 button flywheel (4.5lb)
-Tilton hydraulic release bearing
-~25lb weight savings over a stock dog dish set up, with 2.5 to 3 times less moment of inertia
Floor mount Tilton clutch/brake pedal box with dual brake master cylinders
Bilstein HD shocks, stock springs cut to keep roughly stock ride height
Welded diff
Hydraulic hand brake
Stock power steering rack with hydraulics removed
Electric power steering on the column (from early 2000s GM light suv)
Custom steering column
RX-7 Turbo 2 front brakes
Electric water pump for effective cooling between runs (and more power)
Radiator probably from a Volvo 850, something with a big fan and full shroud

Pics:
https://drive.google.com/drive/u/0/folders/0B8HwFfdJFYaCeXA0bnNPb0VTS2s

-Will
 
Hi Will,

Great project so far...nice pictures...you build bike frames for a living or hobby?
I have a set of Mazda calipers with uninstalled rebuild kits if you have not bought yours yet.
 
Stiggy, all the Tilton stuff is pretty straight forward, well documented, and looks to be pretty well made. Also nice that you can interchange parts.

Rada, this is my first time using Google Drive for sharing photos. Anyone else have any ideas?

Dammit, I'm the machinist for da Vinci Designs. We build high end tandems.

Added pics of welding the diff (12/24).
 
Last edited:
Ah, cool - we've got a couple of tandems on order at the moment, working on an eddy-current brake (really a drag brake) for one of them, which is proving to be a tough one!
 
Update (3/24):

Added some pics of the cooling package. Im in the process of converting the radiator to double pass with a water cooled engine oil heat exchanger built into the right side end tank. The intercooler is shrouded in parallel with the radiator between the frame rails, basically a V-mount configuration. Either one or two 14" fans will be mounted just behind the grill to feed cooling air into both.
 
Machine work looks top notch. Nice work.

A few questions:

1: why are the ribs on the back of the flywheel not axisymmetric?
2: do you really want to tie the oil temperature to the water temperature? The oil will heat up faster but once at temp you might be sacrificing heat rejection capability vs having an air to oil heat exchanger.
3: bilstein HD dampers with cut springs seem out of place on this car considering the time and expense of the engine and drive line.
 
Alex Buchka said:
Machine work looks top notch. Nice work.

A few questions:

1: why are the ribs on the back of the flywheel not axisymmetric?
2: do you really want to tie the oil temperature to the water temperature? The oil will heat up faster but once at temp you might be sacrificing heat rejection capability vs having an air to oil heat exchanger.
3: bilstein HD dampers with cut springs seem out of place on this car considering the time and expense of the engine and drive line.
Click to expand...

I agree with #3 especially, but from just the few pics you posted, I'm sure you have something planned. Maybe you just want to get it rolling and build suspension from there.
 
Alex Buchka said:
Machine work looks top notch. Nice work.

A few questions:

1: why are the ribs on the back of the flywheel not axisymmetric?
2: do you really want to tie the oil temperature to the water temperature? The oil will heat up faster but once at temp you might be sacrificing heat rejection capability vs having an air to oil heat exchanger.
3: bilstein HD dampers with cut springs seem out of place on this car considering the time and expense of the engine and drive line.
Click to expand...

Right on, thanks!

1: Simply because it's an 8 bolt crank and 6 bolt clutch. The predicted stresses were a little bit lower by lining up the ribs around the crank bolts with the ribs that stiffen the clutch mountings. It was actually still pretty easy to model it that way, I could design and simulate just one quarter, then mirror it horizontally and vertically.

2: Water flows from the engine, through the first half of the radiator, through the oil cooler, through the second half of the radiator, then the electric pump and back to the engine. It's kind of an ideal spot because the oil cooler still sees water that is cooler than the engine, and some of the heat added to the water can be dissipated before returning to the engine. I'm still using the stock oil thermostat so no need to worry about over cooling. Plus, I got the heat exchanger for free! :)

3: Yeah, stiffer springs are probably in order at some point. Keeping full travel as well as the cost kind of ruled out most coil over stuff. I know the Bilsteins can handle anything I'll be using this car for, it just comes down to valving. I have their "take apart" circle track shocks in the back, still have to figure out how to open up (and put back together!) the HD front inserts to stiffen the valving. I'm putting new HDs in my 940, so I'll be able to expriment on HDs I take off of that (they are pretty close to the valving I want in the 242 as well). I kind of like excessive body roll for drifting anyway. lol
 
The engine is mounted in the car. It turns out the Mustang driveshaft I got from the junk yard is the correct length! The tunnel just needed some massaging from an air hammer to clear the 3.5" shaft. I used a Spicer 2-2-239 flange yoke and 1310/1330 adapter u joint to connect to the rear end.

I added some pics and a new folder to the Google Drive.

You can also follow the build on Facebook:
https://www.facebook.com/SubieSnacksRallyeTeam/
and Instagram @volvoracernumber5
 
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