What are the differences between bus heads and Porsche heads? Long story short, I have a 2.0 bus head that needs a new exhaust valve. The diameter i measuring at 38 mm, which is bigger than the 36 mm Porsche size.
Thanks!
Full Version: Bus heads vs. Porsche heads
The two most obvious differences are the intake manifold stud count(914 2.0: 3, Bus 2.0: 4) and the spark plug locations(914 2.0: horizontal, Bus 2.0: vertical).
If you have an old 2.0 Bus head it's hard to say what has been done to it over the last ~50 years. The original Intake valve would have been 37.5mm, and the Exhaust 33mm.
Reference data link: http://web.archive.org/web/20130824065844/...nce/cylhead.htm
If you have an old 2.0 Bus head it's hard to say what has been done to it over the last ~50 years. The original Intake valve would have been 37.5mm, and the Exhaust 33mm.
Reference data link: http://web.archive.org/web/20130824065844/...nce/cylhead.htm
QUOTE(krazykonrad @ May 11 2023, 09:43 AM) 
What are the differences between bus heads and Porsche heads? Long story short, I have a 2.0 bus head that needs a new exhaust valve. The diameter i measuring at 38 mm, which is bigger than the 36 mm Porsche size.
Thanks!
The “Porsche” heads were reconfigured at the factory for better flow and spark plug placement. The heads have 3 studs to attach the intake manifold. Bus motor built for torque not horsepower.
The bus engines were way lower horsepower mostly on the compression ratio. That was achieved primarily with the dish in the piston. However, you need to check and see what the combustion chamber CC is; my guess that it is greater in the bus head.
QUOTE(sportlicherFahrer @ May 11 2023, 10:33 AM)
If you have an old 2.0 Bus head it's hard to say what has been done to it over the last ~50 years. The original Intake valve would have been 37.5mm, and the Exhaust 33mm.
Reference data link: http://web.archive.org/web/20130824065844/...nce/cylhead.htm
^That
Not sure what specifically you are looking for but that link sums it up. There was no single head used for all busses just as there was no single head used for all 914s, so specific differences are going to depend on specifically which two heads you are comparing.
If you have a 38mm exhaust valve though it sounds like what you have already isnt stock anyways so its sort of irrelevant. Just get any headwork/ head replacement done in pairs so they match and dont worry about it.
Originally, the combustion chamber would be different, the spark plug location would be different, the intake studs would be different, the intake and exhaust ports would be different (the later Bus heads even having "square port" exhaust ports!), the valves would be smaller...
If your Bus head has larger valves than a 914 head, it has been modified. Just about any of the above can be changed on a head, though it is cost-prohibitive to do most of them when you can buy a new casting for less.
--DD
If your Bus head has larger valves than a 914 head, it has been modified. Just about any of the above can be changed on a head, though it is cost-prohibitive to do most of them when you can buy a new casting for less.
--DD
Bus heads had smaller combustion chambers than the 2.0 PORSCHE Heads
they were 48cc vs 60cc for the 2.0 heads
they were 48cc vs 60cc for the 2.0 heads
Lots of 2.0 answers here. But I’m sure there had to be differences even with the 1.7 and later 1.8, right?
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here.