View Single Post
Old 06-19-2017, 01:24 PM   #271 (permalink)
Lurking Eco-wall-o-texter
Join Date: Dec 2015
Location: MPLS, MN area
Posts: 128
Thanks: 0
Thanked 65 Times in 45 Posts
VW cooling: maintain pressure differential, avoid chrome.


VW cooling systems, you want to learn about them? Google up "Bob Hoover Sermons" (you are looking for Bob Hoover's "Sermons" files - and not the preacher nor the noted aviator) and anything you can find about "HVX mods" that he did for airplane power plant usage of VW engines. Oh, and his "Tulz" files are good, too - tools he made himself/figured out how to use properly, etc. There's a pdf of most of his "Sermons" around on the 'net, but you can find more by searching around. Huh, his blog is still around: Bob Hoover's Blog He's sadly passed on, but I learned *so much* about VW engines from his posts. Most of what he writes is based on bus usage, plus his airplane stuff. He wanted more power out of the VW engine for climbing up to altitude, so he basically taught himself thermodynamics while reverse-engineering the VW cooling system. His findings: with stock cooling fin area, you can dissipate the waste heat from 40hp continuously so long as the cooling tin is properly set up. Any more hp than that must be intermittent, and the heat goes into heating up the metal and the oil, and then you need to run lower power for a while to dissipate the buildup.

Also very good at story telling for his trips/adventures, and how to build and maintain yourself a good reliable engine (he'd get 100k out of a set of jugs, 200k out of the crankcase/heads).

Cooling basics (and apologies if you know this already): Cooling system depends on a pressure differential between the engine bay and the underside/rear of the vehicle. There's a rubber gasket around the engine tin that seals the engine bay from the underside of the vehicle. What you need to do is make sure that air can get into the engine bay in sufficient quantity, and that it can exit out the bottom, and that the hot air does not get sucked back in. You can create positive pressure in the bay, or negative pressure underneath. Avoid negative pressure in the bay. *Avoid chrome valvecovers and pushrod tubes* (the engine you show has them - avoid!) - it traps heat inside the engine, and both were apparently fitted for artic usage for that very reason. Use stock "accordion" style pushrod covers - they are part of the cooling system. Make sure all of the engine tin is in place - Bob has a lot of notes about bits that are often missing, etc. Paint the fins with a thin coat of flat black for best heat rejection. Beware stroker engines - they spread out the cylinder heads and need properly reworked cooling tin to cool properly - involves cutting the shroud pretty high up around the fan (Type 1) to make sure the "slug" of coolest, densest air from the fan hits the right spot on the cylinder heads.

I really cannot recommend Bob's work too much. Hands down the most informed, readable technical resource for VW aircooled engines I've ever read. Some ranting here and there about "what the cool magazines have that's all wrong" but written in an entertaining style. He even has some mixed praise for John Muir (of "How to keep your Volkswagen Alive, a Manual of Step-by-Step Procedures for the Compleat Idiot" fame) - mostly in the form of only knocking on the few things the guy got wrong and some bad advice in the book. Muir's book is beautiful, too - still my go-to for "how to understand a car".

Sounds like you're gearing up for an interesting project! Have fun!

  Reply With Quote
The Following 2 Users Say Thank You to cajunfj40 For This Useful Post:
ChopStix (06-21-2017), freebeard (06-19-2017)