BOB HOOVER'S FREE HORSEPOWER / VW ENGINE
FREE HORSEPOWER:
Bob Hoover was a pilot, technical writer, avid outdoorsman and family man. He has given the VW community valuable information on engine builds. Making cool running, having long service life and free horsepower all explained in his blog post.
The following is an excerpt from his blog:
FRIDAY, NOVEMBER 24, 2006
VW - Free Horsepower
(written about 1995)
A subscriber of this list recently took me to task for my repeated use of the expression ‘properly assembled engine,’ insisting that some ‘shade tree mechanic from California’ could not possibly improve on Volkswagen’s own methods and their millions of engine’s-worth of experience.
He failed to consider the fact that I build just one engine at a time. And where VW specifies an acceptable range of tolerance in their parts, a necessity for high-volume production, I don’t have that particular burden. When setting crankshaft end-play, for example, I dress the thrust-face of the #1 bearing until I achieve a clearance of .0025 exactly. This takes as long as it takes, from a few minutes to a day or more if I have to track down another set of bearings. And I didn’t learn this out of books, I learned it from VW mechanics; guys who took considerable pride in being able to improve on a ‘factory job’.
What remarkable improvement in horsepower or longevity results from assembling an engine to better than factory spec? In the case of crankshaft end-play, I doubt if there’s any at all but the truth is, I don’t really care. I know that if all the shims are dead flat, the flywheel and crank are true and the thrust surface of the bearing brought to truth with dye and judicious flatting, I get a nicer fit that holds spec longer. (The wear limit here is .006; you can check it without dismantling your engine by taking the measurement from the pulley-end of the crank. It’s a quick check on the general state of health of the lower end.) No quotas. No time clocks. When it’s right, the engine tells me so. And I derive great satisfaction from that. This applies to fitting the rods, adjusting ring-gap -- to everything involved in ‘proper’ assembly of an engine. And you can do it too.
Chances are, if you’ve never built an engine before, you won’t do any worse a job of it than Volkswagen and may do even better, which is why I think everyone should build their own engines. But most of you don’t. A lot of you are satisfied with a short-block from a reputable manufacturer. And that can be a costly mistake.
Back when the Volkswagen engine was designed, the importance of balancing, both dynamic and volumetric, was not well understood; by modern standards the VW balancing specs are quite crude. The best proof of this is to compare the output of a properly assembled engine against one assembled to stock specs. The difference is never less than a 5% increase in horsepower and often as much as 10% when careful attention is given to proper balance. This shows up as improved efficiency, with the balanced engine requiring less fuel for the same output, and producing less heat. The balanced engine also lasts longer.
To properly (there’s that word again!) balance an engine the clutch pressure plate, flywheel, crankshaft (with the cam gear installed), and fan pulley are balanced as a unit. This cannot be done with a short-block without dismantling the engine. In effect, each time you elect to use a short-block you are accepting the fact the engine will not be as efficient as it could be. Another burden I escape by building one engine at a time is that I can do as many pre-assemblies as I feel are necessary; VW puts each engine together once, as does all of the high-volume after-market engine builders I know of.
Continue the rest of Bob's blog...
A subscriber of this list recently took me to task for my repeated use of the expression ‘properly assembled engine,’ insisting that some ‘shade tree mechanic from California’ could not possibly improve on Volkswagen’s own methods and their millions of engine’s-worth of experience.
He failed to consider the fact that I build just one engine at a time. And where VW specifies an acceptable range of tolerance in their parts, a necessity for high-volume production, I don’t have that particular burden. When setting crankshaft end-play, for example, I dress the thrust-face of the #1 bearing until I achieve a clearance of .0025 exactly. This takes as long as it takes, from a few minutes to a day or more if I have to track down another set of bearings. And I didn’t learn this out of books, I learned it from VW mechanics; guys who took considerable pride in being able to improve on a ‘factory job’.
What remarkable improvement in horsepower or longevity results from assembling an engine to better than factory spec? In the case of crankshaft end-play, I doubt if there’s any at all but the truth is, I don’t really care. I know that if all the shims are dead flat, the flywheel and crank are true and the thrust surface of the bearing brought to truth with dye and judicious flatting, I get a nicer fit that holds spec longer. (The wear limit here is .006; you can check it without dismantling your engine by taking the measurement from the pulley-end of the crank. It’s a quick check on the general state of health of the lower end.) No quotas. No time clocks. When it’s right, the engine tells me so. And I derive great satisfaction from that. This applies to fitting the rods, adjusting ring-gap -- to everything involved in ‘proper’ assembly of an engine. And you can do it too.
Chances are, if you’ve never built an engine before, you won’t do any worse a job of it than Volkswagen and may do even better, which is why I think everyone should build their own engines. But most of you don’t. A lot of you are satisfied with a short-block from a reputable manufacturer. And that can be a costly mistake.
Back when the Volkswagen engine was designed, the importance of balancing, both dynamic and volumetric, was not well understood; by modern standards the VW balancing specs are quite crude. The best proof of this is to compare the output of a properly assembled engine against one assembled to stock specs. The difference is never less than a 5% increase in horsepower and often as much as 10% when careful attention is given to proper balance. This shows up as improved efficiency, with the balanced engine requiring less fuel for the same output, and producing less heat. The balanced engine also lasts longer.
To properly (there’s that word again!) balance an engine the clutch pressure plate, flywheel, crankshaft (with the cam gear installed), and fan pulley are balanced as a unit. This cannot be done with a short-block without dismantling the engine. In effect, each time you elect to use a short-block you are accepting the fact the engine will not be as efficient as it could be. Another burden I escape by building one engine at a time is that I can do as many pre-assemblies as I feel are necessary; VW puts each engine together once, as does all of the high-volume after-market engine builders I know of.
Continue the rest of Bob's blog...