Compression measurement

Recently I found this compression value sheet from 2001. The compression of each cylinder is between 12.75 and 13 bar measured with a MotorMeter gauge.

Road wheel power

The G-Tech measures horsepower though the formula:

vehicle speed * acceleration * weight of the vehicle = power at the wheels

The more accurate the vehicle weight is entered, the better the measurement will be. I asked the people from a local grain mill to use their scales and got 1145 kg with driver. The G-Tech deliveres rear wheel horsepower. This horsepower includes the loss of power through the drivetrain which is approximately 15%. Rear wheel horsepower is what most people are interested in because that is what they experience when driving. The use of flywheel horsepower measurement is often used in advertising, but not very realistic when it comes to accelerating the vehicle.


For more information about the G-Tech RR device see here: G-Tech-Home

A run consists of a straight on acceleration from stand-still to maximum rpm in second gear.

This is the result of an actual measurement after some work with MS Excel. The red line is the calculated torque at the driven wheels, derived from acceleration and weight.
The blue line is calculated wheel horsepower. The 1600cc DOHC engine with some modifications produces about 90 hp at the rear wheels. This means approximatily 108 hp at the flywheel.

There may be some uncertainties in this result because this is only one measurement. I have to make several measurements and then calculate mean values. This story will go on ...

Bicycle Speedometer

To get an information about average or maximum speed I included a digital speedometer Sigma BC 1200. For calibration it is necessary to input the exact wheel circumference which is also called wheel size factor. It can be measured on the car or it can be determined by the help of this table:

The sensor I use is a wheel sensor with magnet glued on the inner side of the rim. If a cardan-drive shaft sensor is used, the wheel circumference must be multiplied by 0.2195 to get the wheel size factor.

I calibrated the speedo with a GPS based navigation system. The correct wheel size factor for 195/60 R 15 tires is 1882 mm.

Digital instruments unfortunately are not always allowed in historic rallying and this particular one has not backlight function.

Alfa DOHC 1600cc engine at it's time

Engine power of the Alfa DOHC engine was not so bad - compared to other cars and makes at the beginning of the 1970s. The 1600cc double Weber carbureted engine was at the top of the line. Only fuel injected 4 cylinder engines offered slightly more power.

Engines with 1600 cm³ capacity (single carb., double carb. and fuel injection)

Front suspension

There are not much things to make better at the front suspension of an road going Alfa:

• Bilstein shocks
• Superflex Poly bushing between trailing arm and upper lateral arm
• Lemfoerder forged upper lateral link (# 032.311.003.501) with reinforced inner bushing (taken from lower A-arm)

Values for suspension alignment:

Toe-in: 0° 14' (positve toe-in, 3 mm distance between rims)
Camber: 0° 20' +/- 30'
Max. camber difference between left and right wheel: 0° 40'
Caster angle: 1° 30' +/- 30'
Max. caster angle difference between left and right wheel: 0° 20'
King-pin inclination: 8° 35'

Brake conversion

To upgrade and lighten the front brakes I've chosen a pair of Brembo 2-piston fixed calipers from the Alfa 75 1.8 turbo (1779 cm³, 110 kW) which was in production from Sept. 1986 until Feb. 1992. The calipers use exactly the same 48 mm piston diameter, so that the brake force distribution remains equal. But the area of the pads increased from 140 mm² to 201 mm². This should be ok to prevent excessive wear and fading.


A pair of new brake lines (intermediate tubes) had to be manufactured. M10x1 nut thead thread fits the brake hose (steel hose type, see below) and M10x1 screw thread is used for the saddle thread. The brake force diagramm of the GT junior shows that there is not so much difference between the original brake layout and the Brembo/Alfa 75 design.

Calculated brake force diagramm

New steel-flex brake lines from Dickhaut-Specials were used, too. Remember that the Brembo caliper has M10 x 1. The line length is 38 cm at the front and 40 cm at the rear.

Brake assembly in the car

The calipers are made for wider vented brake discs. so I had to open the caliper and remove two spacers - thats all. Brake disk is Brembo, too, matching the GT 1300/1600 (diameter 267 mm). It would be possible to use vented discs. If you like, have a look at the Alfa Montreal disk or at Audi 90 GTE discs. The brake force according to the german TÜV measurement is 220 daN per wheel.

Alfa GT 1300 junior original Specs

Production Years	1966-1977, earlier model from 1966 on with step-front, from 1971 flush front, later model GT junior 1.6
Chassis #	105.30. LHD and 105.31. RHD
Number and layout of cylinders	4 in-line
Bore and stroke	74 X 75 mm
Displacement	1290 cc
Compression ratio	9:1
Horse Power	90 hp DIN, 103 hp SAE at 6000 rpm
Maximum torque	14 mkg DIN at 3200 rpm
Fuel supply	double Weber 40 DCOE 28 horizontal twin-choke carburetors
Fuel tank capacity	46 litres (reserve 7 litres)
Coolant capacity	7.5 litres
Oil Capacity	6.5 kg
Gear ratios	3.304:1 I, 1.988:1 II, 1.355:1 III, 1:1 IV, 0.860:1 V, 3.01:1 in reverse
Final drive ratio	9/41 = 4.555:1
Wheelbase	2350 mm
Track	front 1320 mm rear 1270 mm
Length	4080 mm
Width	1580 mm
Height	1310 mm
Minimum ground clearance	120 mm
Tires	155 SR 15 or 165 SR 14
Brakes	four-wheel discs, ATE-servo ATE 1-piston fixed caliper, drum in hat hand brake (rear)
Steering	Burman recirculating ball
Turning circle	10.5 m
Electrical system	12 volts, 300 W
Battery	45 Ah
Weight	kerb 1020 kg, loaded 1360 kg, measured weight 1145 kg (with driver & fuel)
Acceleration	0-100 kilometers 12,1 secs

Hanhart Digital Triple Timer

I replaced my old TRF Triple Timer with this Rallye approved digital Hanhart precision instrument. Less number of buttons means more easy to use!


I wounder how long the tiny LR44 batteries will hold the needed voltage. AAA type batteries certainly would be better. Let' see ...

Tripmaster Retrotrip 2

When participating in historic rallying you will need a Tripmaster. Because of the high cost of NOS Halda Tripmasters I preferred the new Brantz Retrotrip 2 from England. It has a speedometer cable sensor and two mechanical counters which can be reset to zero.

Here you can see the gauge mounted on the dashbord next to a DCF77 clock, a mechanical stop watch and a digital triple timer. The home made "Rallye Board" is illuminated and has further conectors for the GTech measurement device and a 12V outlet.

New "old style" 15" alloy wheels

It's not easy to find a set of 15" alloy wheels fitting the Alfa 108 mm bolt-hole circle. European Ford Mondeos or some Peugeot cars have an equivalent spec. These are German manufactured R.O.D. Leichtmetallräder GmbH - Rondell 26 6.5 x 15" wheels on the GT junior. The wheel offset is 25 mm (ET). Tires are 195/60 R15 Bridgestone RE720.


I use 10 mm spacers at the rear axle on each side to trim the vehicle to neutral steering.

Battery in the trunk

The battery moved into the trunk to achieve a better weight distribution. I removed the spare wheel and added a bottle of Tire-Fit. On top of the battery box cover you can see an Anderson connector to connect an external power supply or 12V charger. This kind of plastic box is usually used as a battery box for boats.