verbeekb
Automotive
- Feb 7, 2002
- 4
Hello,
I've been lurking on this forum for a few weeks, and I love it. I wish I could go back to school
... Anyway .. I love to read up and shape myself into a more knowledgeable and better technician. Of course, everything new I learn is directly translated to a use or application in my own projects. My newest project is a killer horizontally opposed VW/Porsche combination. I found that the block width of their 4 cylinders is the same as their 6 cylinders, and I came up with the idea to build the 4 cylinder using new factory Porsche parts of the 6 cylinder, and use the same geometry to stay within the limits of these parts and reduce the chance of breaking something later on. Reliabillity, power, and high revs are keywords in this project. Whenever I see a calculation or equation pop up here I apply it to my project and compare the data I find with similar engines. I love this stuff ..
Question: Would one prefer a different rod-ratio in a 6 cylinder engine VS a 4 cylinder? I mean ... is the result different in either a 4 or a 6?
The Porsche six has a 76.4mm stroke and a 127mm rod lenght, it makes for a rod-ratio of 1.66. Rather short. I must note that the Porsche bottom end is very very strong and seemingly has no problem with this rod ratio, it is not evident in either crankshaft problems or piston/cylinder wear, these engines occasionally see 7000rpm.
My intitial goal was to exactly copy Porsches geometry into my 4 cylinder. But .. you guys got me thinking (uh-oh!) .. .. I would love a very reliable strong engine to be installed in my 0-miles 2002 -classic- VW bug (not the "New Beetle". I would love a well balanced, light running, high revving engine.
Instead of 76.4strokex127rod, I could go with
71x130 which gives a 1.83 rod ratio. OR 74x128.5 which gives 1.73.
A smaller stroke would give me less displacement, yes, but it would also give me less stress on the crank, and a stronger crank to begin width, higher revs, less flex.. No? Yes?
I am just thinking, maybe going to the max displacement one can get within the confines of a given engine is just not always the way to go...
Bore = 100mm
valves are 48x39
induction is 2x48ida Weber or equivalent throttle bodies.
Compression Ratio, there is a lot of controversy regarding CR in the VW world. The old testament of the VW bible is: Lower CR for todays fuels, combine with big hemi-like combustion chambers and run much advanced timing, into the 35deg btdc region max..
The new testament: BS! Run high CR, and retard timing as necessary, high squench combustion chambers, the increased combustion speed wants initial ignition to be later, so as to have optimum combustion pressure at 15 deg ATDC. Max. ignition advance in the 25 btdc region.
How do I know if the ideal combustion pressure is happening at 15 deg ATDC?? Dyno set timing?
Detonation will kill one of these engines in no time. Does 9:1 in an aircooled engine with 93 fuel sound bad? (Taken into account that the combustion squench area has been pretty much destroyed because of displacement increase and thus requires bigger combustion chambers.. but then is not 'hemi' shape, just the factory squench areas came out about 2mm higher.. is this still a squench area to speak of?)
Is there anyone who wants to hire me to mess with stuff like this all day and pay me for it?? hee hee .. (I'd LOVE too!)
I'd love to babble some about this, I can get you most data you may need. This is not a theory only project, it will be built
Thanks for reading this far,
Brian.
I've been lurking on this forum for a few weeks, and I love it. I wish I could go back to school
... Anyway .. I love to read up and shape myself into a more knowledgeable and better technician. Of course, everything new I learn is directly translated to a use or application in my own projects. My newest project is a killer horizontally opposed VW/Porsche combination. I found that the block width of their 4 cylinders is the same as their 6 cylinders, and I came up with the idea to build the 4 cylinder using new factory Porsche parts of the 6 cylinder, and use the same geometry to stay within the limits of these parts and reduce the chance of breaking something later on. Reliabillity, power, and high revs are keywords in this project. Whenever I see a calculation or equation pop up here I apply it to my project and compare the data I find with similar engines. I love this stuff .. Question: Would one prefer a different rod-ratio in a 6 cylinder engine VS a 4 cylinder? I mean ... is the result different in either a 4 or a 6?
The Porsche six has a 76.4mm stroke and a 127mm rod lenght, it makes for a rod-ratio of 1.66. Rather short. I must note that the Porsche bottom end is very very strong and seemingly has no problem with this rod ratio, it is not evident in either crankshaft problems or piston/cylinder wear, these engines occasionally see 7000rpm.
My intitial goal was to exactly copy Porsches geometry into my 4 cylinder. But .. you guys got me thinking (uh-oh!) ..
.. I would love a very reliable strong engine to be installed in my 0-miles 2002 -classic- VW bug (not the "New Beetle". I would love a well balanced, light running, high revving engine. Instead of 76.4strokex127rod, I could go with
71x130 which gives a 1.83 rod ratio. OR 74x128.5 which gives 1.73.
A smaller stroke would give me less displacement, yes, but it would also give me less stress on the crank, and a stronger crank to begin width, higher revs, less flex.. No? Yes?
I am just thinking, maybe going to the max displacement one can get within the confines of a given engine is just not always the way to go...
Bore = 100mm
valves are 48x39
induction is 2x48ida Weber or equivalent throttle bodies.
Compression Ratio, there is a lot of controversy regarding CR in the VW world. The old testament of the VW bible is: Lower CR for todays fuels, combine with big hemi-like combustion chambers and run much advanced timing, into the 35deg btdc region max..
The new testament: BS! Run high CR, and retard timing as necessary, high squench combustion chambers, the increased combustion speed wants initial ignition to be later, so as to have optimum combustion pressure at 15 deg ATDC. Max. ignition advance in the 25 btdc region.
How do I know if the ideal combustion pressure is happening at 15 deg ATDC?? Dyno set timing?
Detonation will kill one of these engines in no time. Does 9:1 in an aircooled engine with 93 fuel sound bad? (Taken into account that the combustion squench area has been pretty much destroyed because of displacement increase and thus requires bigger combustion chambers.. but then is not 'hemi' shape, just the factory squench areas came out about 2mm higher.. is this still a squench area to speak of?)
Is there anyone who wants to hire me to mess with stuff like this all day and pay me for it?? hee hee .. (I'd LOVE too!)
I'd love to babble some about this, I can get you most data you may need. This is not a theory only project, it will be built
Thanks for reading this far,
Brian.