Bus heads vs. Porsche heads, What are the differences? |
|
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG.
This site is not affiliated with Porsche in any way. Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners. |
|
Bus heads vs. Porsche heads, What are the differences? |
krazykonrad |
May 11 2023, 11:43 AM
Post
#1
|
Senior Member Group: Members Posts: 1,126 Joined: 21-February 06 From: Canton, GA Member No.: 5,610 |
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! |
sportlicherFahrer |
May 11 2023, 12:33 PM
Post
#2
|
Nothing to see here. Group: Members Posts: 1,079 Joined: 18-April 05 From: Tacoma, WA Member No.: 3,945 Region Association: Pacific Northwest |
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 |
mgphoto |
May 11 2023, 12:34 PM
Post
#3
|
"If there is a mistake it will find me" Group: Members Posts: 1,339 Joined: 1-April 09 From: Los Angeles, CA Member No.: 10,225 Region Association: Southern California |
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. |
davep |
May 11 2023, 01:23 PM
Post
#4
|
914 Historian Group: Benefactors Posts: 5,144 Joined: 13-October 03 From: Burford, ON, N0E 1A0 Member No.: 1,244 Region Association: Canada |
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.
|
JamesM |
May 11 2023, 01:37 PM
Post
#5
|
Senior Member Group: Members Posts: 1,900 Joined: 6-April 06 From: Kearns, UT Member No.: 5,834 Region Association: Intermountain Region |
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. |
Dave_Darling |
May 12 2023, 12:14 AM
Post
#6
|
914 Idiot Group: Members Posts: 14,986 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
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 |
barefoot |
May 13 2023, 06:05 AM
Post
#7
|
Senior Member Group: Members Posts: 1,276 Joined: 19-March 13 From: Charleston SC Member No.: 15,673 Region Association: South East States |
Bus heads had smaller combustion chambers than the 2.0 PORSCHE Heads
they were 48cc vs 60cc for the 2.0 heads |
Van B |
May 14 2023, 09:30 AM
Post
#8
|
Senior Member Group: Members Posts: 1,589 Joined: 20-October 21 From: Maryland Member No.: 26,011 Region Association: None |
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?
|
Lo-Fi Version | Time is now: 20th May 2024 - 04:38 PM |
All rights reserved 914World.com © since 2002 |
914World.com is the fastest growing online 914 community! We have it all, classifieds, events, forums, vendors, parts, autocross, racing, technical articles, events calendar, newsletter, restoration, gallery, archives, history and more for your Porsche 914 ... |