General What 127 903 engine upgrades have you done?

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General What 127 903 engine upgrades have you done?

Kalgm

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Joined
Jun 5, 2022
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1
Location
Cairo
1- Swap carburetor with injection
2- swap mechanical spark distributer with an electronic one
3- Add Turbo
 

Djaraceandrally

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Joined
Feb 1, 2021
Messages
12
looking for ideas on getting more power out of the 127/112 903 engine and the pit falls
1.Swap out the carb and inlet for a weber DMTR. The carb is quite restrictive.
2. Increase the CR of the engine by skimming the head to bring it up to 9.3-9.5:1 max.
3. Check all other parts are in spec (points, plugs, leads)
4. Change the back box and manifold for something more free flowing than standard (a112 abarth manifold is a good start). Dont increase the bore size, its big enough and it will actually rob you of power.

All other work means the engine has to come out.

After that its cam changes, forged pistons and 8 port heads - expensive
 
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folgore
Joined
Jun 14, 2007
Messages
118
Location
Guildford
1.Swap out the carb and inlet for a weber DMTR. The carb is quite restrictive.
2. Increase the CR of the engine by skimming the head to bring it up to 9.3-9.5:1 max.
3. Check all other parts are in spec (points, plugs, leads)
4. Change the back box and manifold for something more free flowing than standard (a112 abarth manifold is a good start). Dont increase the bore size, its big enough and it will actually rob you of power.

All other work means the engine has to come out.

After that its cam changes, forged pistons and 8 port heads - expensive
Done the carb , the head has 9 to 1 standard. How much to shave off the head ?
 

Djaraceandrally

New member
Joined
Feb 1, 2021
Messages
12
Thats where the fun begins..

IF you know your current engine has never been overbored, you can work it out.

903cc gives a swept volume of 225.75 cc per cylinder. You know that the standard CR is 9:1 and so CR is calculated by 225.75 + X divided by X = 9:1

X is the chamber volume.

Again, assuming that the engine has not been overboard (with all else standard that would increase the CR)

Basic maths shows that the standard CR (9:1) has a volume of 28cc above the piston. Now this includes the head gasket, any space above the top of the piston to the top of the block deck and the valve chamber itself.

To increase the CR, the total volume would be as follows:

27cc would give you 9.3:1
26.5cc would give you 9.5:1

The only way to work out how much to actually take off is to take the head off, clean a chamber, place it level and measure the chamber volume using a pipet or I use a kids Neurofen syringe! Measure it and remove it. Refill with either 1 or 1.5 cc’s less and the measure the distance between the top of the liquid and the face of the head. Thats whats needed to be removed.

Be careful though, too much can put too much load on the stock cast pistons and it can also throw the valve train geometry out. On race engines (not these!) I have use shims to correct the latter. I generally use forged pistons on the former. But these are running much higher CR’s.

A good clean up of the ports (without making them big, just remove the casting marks and dont go for mirror finish, leaving them slightly rough) 3 angle seats, gently improve the short radius on the inlet valves and port match if possible on the inlet and a slight step going into the ex manifold will help.

After this, the ex manifold off a a112 and a free flow back box.

After that it gets expensive!!
 
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