Building and tuning cars in FM3 (for beginners): C Class RWD

Posted: July 12, 2010 in Best Forza-ing

Sorry guys, RRoD and crazy work schedules have kept me from this thread. I had a car mostly done for the C class RWD section, but I’d forgotten how I got there so I started again

In case you missed it, here’s Part 1 in my building and tuning in FM3 series to get you up to speed.

Anyway, here’s the C class RWD section you’ve (probably not) been waiting for…

C Class RWD online tune

Since I began tuning this car, the C class RWD hoppers have gone the way of the dodo, but the regular C class hopper is still there and this can still be useful.

To the track!

First we need to choose a car and a home track. If you have Live! head over to multiplayer in career mode and choose ‘private race’. I’m going to make Sedona Full (fwd) my home track and just because I like the look of it– the ’82 Porsche 930T as my car from the stock dealer. The 930T starts at C360, but has nearly 300hp and over 300 ft/lbs of torque so it should handle the long straights of Sedona’s troval well out of the box. I set the max AI to 7, their difficulty to hard and the laps to 10. This may seem excessive, but 10 laps should cover the car from the dealer and quite a few parts when/if we decide to make a purchase. Remember to have a pad of paper and a writing utensil to write down your lap time(s) and to make notes on the car’s handling after your race is done.

’82 Porsche 930T
Class: C360, Power: 298hp/304tq, Weight: 2866lbs (39% front)
SPD: 5.7, HND: 5.0, ACC: 5.2, LAU: 5.4, BRK: 4.9

We can sit here and bang our head against the wall trying to figure out if these numbers are good, or we can simply take it to the track and find out. Since I’m already in a private race I’ll do the latter…

Sedona full is a troval, or a track connected with or using part of, an oval circuit. With Sedona you end up using most of the oval section along with most of the road course section making it tricky to tune for. Do you tune high speed for the oval sections and straights? Or do you tune for handling to make your time on the frequent decreasing radius corners on the club section? The answer? Power. Lots of it, then deal with the consequences with some tuning later. This, is not easy without analyzing.

The oval is all on-camber corners, coming into and out of the oval is another matter entirely. The aforementioned corners either rise to a crest, or fall down one so braking and throttle control are paramount. In the club section the tricky corners are of a decreasing radius, meaning that they get tighter as you go through them; also making braking and throttle control a necessity. With our chosen car being rear engined and 28 years old we’ll have to be mindful of this when we set this beast loose.

930T stock notes
-Numb front end (can’t feel the front traction easily)
-Too much dive under braking
-Sloppy cornering (holds too much yaw)
+Lots of torque (pulls hard from 4k RPM)
+Geared well (only 4 gears but still decent)
+Excellent on corner exit

Best lap: 2:33.762 (made $54,400 in 10 laps for first)

Evaluation time. Let’s look at our negatives first. The numb front end comes from the car being rear engined and having very little weight over the front wheels. This can be remedied a bit by shifting some weight forward, either through lighter engine parts to lighten the rear or swapping in an AWD system to add weight to the front with driveline parts. Since this is a RWD project, I’ll stick with the first option. The dive under braking can be improved with a suspension upgrade. Sloppy cornering can be improved with lower profile tires, anti-roll bars and suspension upgrades or a combination thereof.

From our positive points, having lots of torque means we don’t have to spend PI on a new trans as the stock, 4-gear set works just fine for our needs (130 mph in 3rd). Our third point, great on corner exit means we have a good amount of grip to the rear on acceleration. It’s only hurt by holding too much yaw from the corner’s apex causing oversteer.

Upgrade notes:
-POWER!!! (lighten the rear)
-Buy a Porsche 930T first!

To the garage!

Okay, now it’s time to head to the upgrade shop and see what’s available. First check out the swaps section to see if there’s anything cool. Here we see that there are three swap categories to choose from, engine, drivetrain and aspiration. Available engine swaps include the 997 GT-3, the 959’s TT mill and the 997 Turbo all of which bump us out of class (B or A) so no go there. The lone drivetrain swap is an AWD conversion which drops PI 21 points but adds 200lbs but shifts almost all the weight forward… Since this is pretty much cheating (imo), and we’re making a RWD car it’s a no on this one. The final swap is a twin turbo setup adding 30hp and 30tq, but also adding 35lbs to the rear of the car and adding 29 PI, so no here too.

Looking in the engine section we see that there’s no cooling option, that’s because the 930T is air cooled. The intake starts at street and the fuel system starts at sport so we could upgrade the intake (it drops rear weight) but we should probably leave the fuel system alone. All else is stock. Again this is simply to make a decision to begin with, you will rarely get the perfect build on the first try so this will probably be changed after further testing.

Keeping this in mind, let’s get this beast to C425!

-SPORT Suspension
I don’t want to complicate the build with variables we really don’t need to change yet. The STREET suspension the car comes with is decent for Sedona already, I just want it slightly stiffer so the dive under braking is reduced.

-RACE anti-roll bars (F&R)
This is how we can tune our over/understeer and they cost 0PI.

-RACE differential
We can use this to tune yaw control under braking and on the throttle.

-Wheels: Gemballa Turbo Sport
Even though the stock wheels are awesome we can’t change the diameter of stock wheels, so I bought these since they’re Porsche friendly. Plus they’re lighter than stock so, yeah…

-Wheels: +1 diameter (F&R) (size 205/50R17, 225/40R17)
Larger diameter wheels means lower profile tires. The shorter sidewalls take up the slop of the stock tires and offer more response.

-RACE Air filter
The race air filter is lighter than stock, thus shifting weight forward. Oh, also much more power

-RACE Exhaust
Same as above.

-STREET compression
Same as above.

-SPORT Intercooler
Adds weight to the rear, but the hp/tq benefit balances that out for minor PI increases.

-SPORT Flywheel
Lightens the rear and brings PI up in small increments to get to 425.

-STREET Clutch
Same as above

-STREET Driveline
Same as above

And the first build is complete, lets take a look.

’82 Porsche 930T (build 1)
Class: C425, Power: 343hp/352tq, Weight: 2785lbs (40% front)
SPD: 6.1, HND: 5.1, ACC: 5.9, LAU: 6.3, BRK: 4.9

Let’s head back to the track to test it out. I recommend driving in free-run so you can rewind and have an easier time getting to a replay for telemetry. You don’t have to run 10 laps, but make sure you get the hang of the car before you quit out, at least 4 or 5 laps to see how the car runs with the tires at temperature. Also remember to make mental notes about how the car is handling, as always.

After your run is over head to the replay and pay special attention to the “traction”, “tire misc” and “heat” tabs. Traction is to see if you’re over-driving the car, like steering too much, too much throttle or brakes, etc… The “tire misc” tab is especially important here as we don’t have an adjustable suspension but we have enough power to get into trouble. What you want to see is the outside tires’ camber (during cornering) should be as close to 0* as possible. A good sign is the “-” flashing mid corner. The “heat” tab lets us know the temperature of each tire’s outer, inner and middle edges. This should be no more than 10* difference across the tire.

Looking at the telemetry I see that the front tires have a little too much pressure in them once warm (about 32.9 psi) and the rears have a bit more (33.5 psi) but the suspension is performing quite well (no bottoming out and the camber is good).

Let’s take a look at the default tune and see what we can do…

’82 Porsche 930T (build 1) default tune
Tires: 30/30
ARB: 28.00/22.78
Diff: 75%/75%

-Understeer at apex
-Slow Turn-in
-Tire psi too high
+Very stable
+Way less sloppy
+Gearing still good

Best time: 2:29.425

Our tires are hitting around 32.9 psi front and 33.5 psi so we can go ahead an drop the front pressure by 0.5 psi and the rear by 1.0 psi so they all heat up to 32-ish psi to maximize grip. I noted that the car understeers at the apex and the “traction” tab shows that the front axle is at fault (front circles go red) so it’s time to make the front anti-roll bar softer. The slow turn-in is probably due to the decel % on the rear differential, so lowering that should be one of the first steps. Decent times are in the mid-low 2:20’s, I’m not sure this build will be able to pull that off, but we’ll see.

The stiff ARB’s and suspension are working together to keep the car stable while the lower profile tires are helping with corner response making for a more reliable handling platform. The gearing still holding up with shorter shift times (from the clutch) and faster revving engine (with the flywheel and driveline) says a lot about this stout 4-speed. 150mph is within reach on the oval.

Time to tweak and run it again…

’82 Porsche 930T (build 1) tune 1
Tires: 29.5/29.0
ARB: 20.00/22.78
Diff: 75%/65%

Best time: 2:28.660 (#1361)

-Turn-in still slow
-Now slippery on exit
+Tire temp/psi good (up to good temp on lap 2)

The turn-in is still slow and now the rear steps out under acceleration on corner exit. This is probably due to our new ARB setup. Since cornering at the apex is only slightly slippery, the issue is in the differential. Both our accel and decel values are too high and our rear ARB could use a little softening. Another spin in the desert, yay!

’82 Porsche 930T (build 1) tune 2
Tires: 29.5/29.0
ARB: 20.00/22.50
Diff: 65%/50%

Best time: 2:28.353 (#1190)

+all seems well to the desert Porsche very possible with practice
-I want 😦

Now we find out that our build won’t support the kind of speed we need for this track. The car handles fine and has gobs of torque but needs to shave a couple of seconds to make a splash with it’s whale tail. Perhaps a more powerful build is necessary? Better brakes, more power and probably less tire and more weight are in order. I guess this is where I leave off…

…I need to rebuild my monster.


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