Anatomy of the "Baby Six" HiFlo ST Sport Engine - Pt 1

For example, in a stock small six engine the "achilles heal" is the cam belt. If it fails (i.e. teeth rip off), the engine can literally be destroyed. On our 85mm pistons we have machined in very deep valve pockets so that, if the cam belt does fail, the valves cannot impact the piston (they'll just reside in the pocket) and your investment in our engine is saved.

With our modified head gasket we're able to reduce head cracking problems by increasing water flow to the area most prone to cracking - the #5 cam journal. Special socket head bolts are used to hold down the head gasket.

Now for performance, first our Hi Flo ST Sport Head was added. This head is ported for a 19% flow increase, has our Surface Turbulence treatment and uses a 325i cam. For the ETA engine owners, we can provide a computer chip ($200 extra) that increases the rev limit to 6000 rpm.

The result is a good balance of torque and horsepower with the bottom end torque characteristics of the "e" engine and the top end horsepower revving of the "i" engine. Using the "e" head, this engine puts out 185 HP and 195 HP with the "i" head.

We've offered ported cylinder heads for "Baby" Sixes since the winter of 1986. Despite this, the complete engine proved time consuming to develop due to four major weaknesses:

1. Cam Belt and Rod Problems
These have been reduced or eliminated by redesigning the piston. The high silicon content forged piston with semi slipper skirt design and deep valve reliefs, is about 18% lighter than a stock piston to reduce the load on the connecting rods and crankshaft. The valve reliefs (eyebrow cuts) are deep enough to accommodate up to 11 mm of lift without the valve hitting the piston. Should your cam belt fail, the piston won't bend the valves. (See Picture)

2. Connecting Rod Failures
Our pistons have lightweight low tension rings with a three piece oil ring design. We chose Alusil (high silicon content aluminum) pistons because of their ability to run at tight cylinder wall clearance.

3. Head Cracking Solutions
To correct head cracking problems caused by the restricted water flow at the #5 cam bearing journal, we modify the head gasket to push more water coolant up into this area. To further reduce the possibility of head cracking, we avoid using a head with a casting date older than 5 years.

4. Failing Head Bolts
The factory head bolts will often be stress cracked. These 12.9 grade bolts (comparable to a grade 8 USA bolt) have straight cut shanks. BMW has superseded this bolt to a Torx head bolt that is threaded about 1/3 the length of the bolt. This threaded area is used to produce bolt stretch. When the ETA head heats up, these bolts offer very little give so occasionally, they'll break. We use a special 8 mm socket head bolt (Mercedes style) with a cut down shank similar to the four and six cylinder head bolts. This type of head bolt gives with head expansion, instead of fighting it. The valve cover needs to be clearanced for these special socket head bolts.

Summation:
Our HiFlo ST Head is ported for a 19% flow increase and given Surface Turbulence for efficiency. When this head with an early 323i or 325i cam is combined with our newly developed 2.8 liter bottom end (short block) the result is ONE DYNAMITE ENGINE!
We've raised the rpm limit in the computer to 5800. The engine puts out 185 horsepower and has a strong usable power band from 3200 - 5800 rpm.

We also recommend a rear gear change of either a 3.25:1 or 3.45:1.