Torej ce kdo fajn obvlada anglescino, pa ce bi pripravljen si malo vec casa uzeti in tole malo prevesti bi mu bil hvalezen!
Saj nekaj kapcam ampak vseeno se pri vsaki drugi besedi zatakne!
SAj ni treba vse, dase nebo kdo ustrasil, ampak tako taglavne stvari!
LP monster_d

Performance Tips

Fiat SOHC Power tips

Yugo Cylinder Head Conversion

One of the things most people look for in their X1/9 or their 128, is a little bit more power. Sure, all of us want more power, but not all of us are willing to compromise streetability, reliability, fuel economy, or the look of the motor. There is a way you can get more power from your carbureted X1/9 or 128 in a weekend, without losing any of these things.

U.S. Spec X1/9's and 128's were delivered with an absurdly low compression ratio, (8.5:1) for emissions reasons, due to a relative lack of sophistication of the Fiat's emission system in the late 1970's. This results in a relatively low power output for the SOHC series of engines, which can easily be improved in a weekend.

The Yugos sold in the States from '86 - '91 all used a variant of the Fiat SOHC motor. Most that were imported used the 1116cc engine, while later cars used a 1301cc engine. There are no differences between the 1116cc and 1301cc Yugo heads. The cylinder heads from the Yugo are a direct swap for any of the carbureted Fiat SOHC motors. The advantage to using the Yugo cylinder head on your Fiat is this: Yugos were delivered with a compression ratio of 9.2:1 on the 1116cc and 1301cc engines. Higher than the Fiat CR, but not too high to create a problem running pump gas. The Yugo head has a smaller combustion chamber than any Fiat head, which provides the increase in compression, without the need for expensive high compression pistons, or expensive machine work. It also retains the non-interference benefit on the 1500 engines.

The application of the Yugo head to a Fiat block will result in the following approximate compression ratios:

Yugo head on (stock) Fiat 1300cc block: 9.5:1

Yugo head on (stock) Fiat 1500cc block: 10:1

Utilizing the Yugo head on your Fiat motor will provide a nice increase in low end torque, peak horsepower, better fuel economy, and no penalties in reliability or the need for complex, custom modifications. It fits right on, uses the same head gasket as your original engine, and looks stock.

Caveats:

There are a few caveats with the Yugo heads. I will try to explain them as best I can, so that you have all the information before you start tearing down your motor.

Fiat engines were delivered with two different sizes of head bolts/studs. All of the 1300 cars used a 12mm bolt/stud combo, the early 1500 blocks used a 12mm bolt/stud combo, and the late (80+) 1500 blocks used a 10mm bolt configuration. These can be identified by the socket size that fits them. A 12mm bolt/stud uses a 19mm socket, and the 10mm bolts use a 17mm socket. Yugos were delivered to the States with two head bolt sizes as well, Yugos from `86-late'87 used the 12mm bolts, and Yugos from 88-91 used the 10mm bolts. So, if you go looking for a Yugo head, try to get one that has the same size boltholes as your block. If you can't find a 12mm head and you need one, any competent machine shop could open up the small boltholes in the later style head for a nominal charge.

Use with fuel injected motors. At this time, I can't recommend the Yugo head conversion for FI cars, as the FI heads have an extra sensor in the cylinder head for the FI computer, and notches in the intake ports for the fuel injectors. Yugo heads do not have a provision for the Bosch FI temperature sensor, or the notches in the intake ports for the injectors. I'm sure the sensor could be added to the Yugo head in the same spot, and the notches could easily be added to the intake ports, but you're on your own here. I haven't done it, yet.

Port sizes. Yugos were only delivered to this country with 1100 and 1300 engines. Thus, the port sizes are optimized for these motors, and not the 1500. Installing the Yugo head on a 1300 engine presents no issues, but installing a stock Yugo head on a 1500 will cause some high RPM restriction. The upside to this, is the fact that it turns the 1500 into a low-end torque monster. If you like to cruise around, and don't rev the engine over 6000 rpm much, there is no problem. If you want to alleviate the high RPM restriction on the 1500, you'll need to do a decent porting job on the Yugo head.

Smog ports. This may be a benefit to some of us, depending on your locale, and emissions laws. Yugo heads have no provisions for EGR or air injection, so if you are required to have these in your area, it may not be a wise modification. The flipside is that the ports were never on the head to start with, so if there are things like that missing, you don't need to plug holes, and it looks stock.

There you have it, the easy way to get some more power out of your Fiat SOHC motor, using the same carburetor, cam, pistons, and manifolds your Fiat came with. I've picked up Yugo heads from salvage yards for less than $25, so find a head, pick up a gasket set, and you can get some more power out of your X1/9 or 128.

I have a Yugo head on my '78 1500 X1/9, and have done the conversion on several other Fiat motors, both 1500 and 1300 with great success. I highly recommend it if you're looking for an inexpensive way to increase your horsepower.