Baja Motors -


more than just a VW motor


This is not an article on how to build a motor. I strongly recommend the first-time motor builder make use of a Guru to show 'em how it's done.

Instead, this is about what it takes to build a baja motor. Not to be confused with the average VW engine. Reliability is always a factor, but when you're 20 miles into the boonies, it's a matter of survival!

Furthermore, all these magazine articles show turbocharged 2500cc motors in rails. That's real nice, but few rails are actually daily drivers, and many bajas are. So reality check comes into play.

Here's a quick reference for a lengthy article.

Engine Size

Components Needed

Special Tools Needed

Trick Stuff

Heads


Engine Size

Two factors to consider when deciding which baja motor to build are: power and reliability. Nothing new. But keep in mind there's no wreckers where you're going, so many of those street motors you read about aren't the same application. Drag strip motors are real good in the top end, but I doubt they'd be much at hill-climbing. Turbos, well it's a complicated subject, but the bottom line is that engine life will be decreased and there's another level of complexity to deal with when you're far away from pavement.

Engine size is determined by the bore and stroke. Again, nothing new. However, the complicating factors here are the cylinder wall thickness and compression. VW motors in general have to deal with a lot of heat, which is carried away by the cooling fins and the motor oil. As your motor generates heat, the cylinders and heads reach tempratures approaching 600 degrees F! Big time! The scientist can tell you how the coefficient of expansion of various metals causes your cylinders to increase in diameter by some small amount when at running temprature. So this cylinder heats and cools again and again, and if it's not strong enough, it eventually weakens, cracks, wears funny, or does other bad things.

A "stroker motor" is a motor with a different crankshaft, so the stroke, or distance the piston travels, is larger than the stock 69mm. Every intake stroke sucks in more air/fuel mix, and every compression stroke smashes it a little bit harder than stock. The end result is higher compression. This can be compensated for by having the head opened up some, or by using shims under the cylinder to increase the deck height (the space between piston and head). So the increased amount of air/fuel has a bigger space to get smashed into, and compression is still in a manageable range.

The dilemma here is: More compression makes for bigger bangs, and more power. More compression generates more heat. How much bang / heat can your motor take? Add in the complicating factor that high compression motors need some really good fuel to burn clean. Otherwise there's detonation (fuel ignites at the wrong time) which causes MAJOR heat problems. If your baja's a daily driver, you probably don't plan on dumping trick fuel into it constantly, and maybe you aren't even too hip on buying premium gas all the time. I do say, all the time... compression can't be adjusted without pulling the heads.

Let's hope you have a good Guru working on your motor, and they can determine what's acceptable for you. If you drive like a maniac all the time, your requirement is stiffer than for someone who drives like a maniac only periodically. If you're running decent mountain roads, you keep up better speed and have better cooling than the person bumping over trees and stumps all day. It's hard to nail down.

However, here's some basic facts to help you out.

Cylinder wall thickness: There's some magic numbers in piston size you ought to know about. The following CC numbers are based on 69mm stroke.

Most motors larger than 1915 cc have stroker cranks on one of these cylinder sizes.

So, the theory goes like this: since I'm in central Arizona, and it often hits 120 degrees in the desert, I gotta be careful about that motor heat. I've seen several (literally, almost 7) 1835cc motors seize due to heat factors - big bang, little cylinder wall to transmit that heat away and stand up to the abuse. So my choices are 1776 or 1915cc. 1915 has thinner cylinder walls than 1776, while it still has a bigger bang and more heat - still an option, but not the most reliable option.

So, now that you know this info, let me toss out this gem: Appletree Automotive, one of Michigans' reknown VW parts businesses, has granted permission to link to Appletree Automotive's engine calculator tool! Much thanks to the good guys at Appletree. When you're done with the calculator, be sure to check their web page at http://www.appletreeauto.com.

Components needed to build your baja motor

Following is a rough list of what's needed to build a baja motor.

Special Tools needed

Above and beyond your usual collection of tools, here's some specialty items for building VW motors. Most of 'em you can't build without.

Trick Stuff

OK, now that the basic list is assembled, let's talk about some of the trick stuff.

Heads

VW cylinder heads are an arcane science all of their own. You can spend several hundred dollars on heads alone, and I'm sure they're worth it, but what do you really need for a baja?

All I can suggest is that you talk to several head experts. Some will say that flow is paramount - thus, bigger valves, ported so much that they need to weld in some areas for strength to compensate, would be their answer. Others say that big valves reduce low-end torque and response, since the swirl of incoming charge is critical at lower intake velocities. Some say that VW spent a fortune on head engineering, but no one says that Gene Berg was wrong. One baja fanatic tells the story of the big-valve heads he put on his 1776cc baja motor, then swapped out for stock heads he'd purchased for his wife's VW. Make Up Your Own Mind.

Some general info is globally accepted, however.


As always, this SandLizrd knows there's more to be said!