Straight eight and 7 cylinder engines?
Straight eight engines have slowly vanished from the automotive scene in the 50s. Now I understand that with the then current material technology and bigger displacement engines the demands made on a relatively long crankshaft and the overall length of the engine made designers switch to a V configuration. As I am not an engineer (and had no luck in searching on the net for clues), I'd like to know whether there are other reasons for not choosing such a configuration. Specifically, what I'd find very intertesting would be a straight eight made as a combination of two motorcycle 4 cylinder engines, which are reasonably small in displacement and short lengthwise, meaning that the mentioned two problems could be overcome.
Additionally, I came across 7 cylinder engines being used to propell underwater torpedoes (Saab Underwater T2000). They do not seem to be radial (from my understanding) and use something called axial valves. Anyone know more about it?
Additionally, I am interested in some decent literature on the subject. Browsing through Amazon does yield results, but most books are in the 200 US$ plus bracket, and that is used. :( Any suggestions welcome :)
Straight eight and 7 cylinder engines?
The application would clearly be RWD :)
It would still mean a shorter engine than most inline 6s or even fives, so that could be handled. As for crankshaft vibration, given that it too should be shorter (and that the inline sixes of say BMW are very smooth), I guess it's possible? :confused:
There is also a question of balance (which partially influences vibration) IIRC, with a straight or boxer 6 being perfectly balanced, with the next great configuration being a V12. Correct me on this one, it's been a long time :) How does an inline 8 do here compared to a V8?
Coming back to the maritime 7 cylinder. What makes various odd cylinder numbers impractical for automotive use, then, vibration? Is it not really possible to build them in a way to rev to 6 or 7000 rpm in that configuration (V7 for instance)?
Thanks for the prompt answer and help :)
Straight eight and 7 cylinder engines?
I do agree that with the same displacement (especially if your bore would be similar) the I8 would be longer than the I6. On the other hand, a 1.2-2.0 litre I8 will probably be shorter than an automotiv I6 of say 2.5 - 3.0 litres. It's not a totally fair comparison, but on the other hand a motorcycle derived engine will rev significantly higher and allow you a comparable if not superior power output even with such a power discrepancy. Of the two V8 motorcycle derived engines that I know off, the Powertec unit (a combination of 2 1300ccm Hayabusa units) gives off 361hp from 2.6 litres, only because it is limited to "only" 10500rpm (the engine could take more but it is not necessary), the Drysdale unit (own block with Yamaha FZR 400 heads) gives in the region of 160hp from 750ccm. Both comfortably more than per litre than the 3.0 litre from BMW, which gives up to 265 hp or the 3.2 in the M3 with 343hp.
And imagine being the only manufacturer offering a 7 or 9 cylinder car :D
Straight eight and 7 cylinder engines?
Firing order probably does have something to do with there not being 7 or 9 cylinder engines out but as there are some for marine applications, it shouldn't be impossible :confused:
I imagine that the compactness is of vital importance for racing, as it gives you more possibilities to get the weight distribution and aerodynamics right. On the other hand, if you want to have a retro looking roadster or in fact a replica of some 30s machinery, the length of the I8 would be less of a problem (on the other hand it is narrow, not exactly a disadvantage either).
If you want to be different, you should count on occupying a very small niche and stick to it, without grandiose plans in the back of your head. Plus different, in order to be accepted, should not be worse and quite possibly needs to be better. And Robin Reliant cannot exactly boast of uniquely practical or other appealing characteristics? ;)