Cooling your AeroVee Heads
Posted: Mon Sep 27, 2021 12:30 am
Head cooling is THE limiting factor in longevity of your engine. PARTICULARLY the area around the exhaust valves. While the oil can and does carry away a lot of heat from the heads, you need airflow through the fins to carry off more of it, or else your exhaust valve clearance goes away, until you run out of adjuster threads, the head snaps off inside the cylinder or the valves or seats burn and you lose compression.
Leaving aside leaks in baffling for a moment there are two big issues I see with AeroVee installations.
1. No "heat deflectors" plugging the gap in between the heads. See here for a discussion of that https://bobhooversblog.blogspot.com/2006/12/vw-head-baffles.html. I'll post later about how I dealt with this on my heads.
2. Lack of air passage around the exhaust valves. I'm going to elaborate on that here.
This is what a bare VW cylinder head should look like (from Bob "Veeduber" Hoovers Blog):
http://bp1.blogger.com/_JU6RC7jJfRc/Rq8HjOwE0lI/AAAAAAAAAt8/R_4vb8FG88w/s1600-h/blog_head.jpg
And take a look at this head comparison for "Dune Buggies and Hot VWs" http://www.cfiamerica.com/images/pdf/Ho ... _Heads.pdf
Now look at your heads. You can see by the comparison that not all heads are shot full of holes around the exhaust port like the stockers. Some are cast solid - which you can get away with on a drag strip running nitromethane.
It's easier to fix this on a bare head, but at least on the forward cylinders, it can be done on an assembled engine, with 6 inch aircraft drills, chainsaw files, and patience. Veeduber talks about using a pneumatic riffler or a jig saw or hand saw. http://bobhooversblog.blogspot.com/2007 ... s-101.html
Once I figure out how to post pictures, I'll show you my work in progress.
Leaving aside leaks in baffling for a moment there are two big issues I see with AeroVee installations.
1. No "heat deflectors" plugging the gap in between the heads. See here for a discussion of that https://bobhooversblog.blogspot.com/2006/12/vw-head-baffles.html. I'll post later about how I dealt with this on my heads.
2. Lack of air passage around the exhaust valves. I'm going to elaborate on that here.
This is what a bare VW cylinder head should look like (from Bob "Veeduber" Hoovers Blog):
http://bp1.blogger.com/_JU6RC7jJfRc/Rq8HjOwE0lI/AAAAAAAAAt8/R_4vb8FG88w/s1600-h/blog_head.jpg
And take a look at this head comparison for "Dune Buggies and Hot VWs" http://www.cfiamerica.com/images/pdf/Ho ... _Heads.pdf
Now look at your heads. You can see by the comparison that not all heads are shot full of holes around the exhaust port like the stockers. Some are cast solid - which you can get away with on a drag strip running nitromethane.
It's easier to fix this on a bare head, but at least on the forward cylinders, it can be done on an assembled engine, with 6 inch aircraft drills, chainsaw files, and patience. Veeduber talks about using a pneumatic riffler or a jig saw or hand saw. http://bobhooversblog.blogspot.com/2007 ... s-101.html
Once I figure out how to post pictures, I'll show you my work in progress.