![]() The trouble is ultimate can mean different things to different people. What is the 'ultimate' SOHC engine, using a mix and match of stock components is a question I'm asked very often. These engines are amazingly strong and capable of a reliable 8000rpm in the longer stroke options and up to 10,000rpm for the short stroke options. I'm hoping it gives some of the uninitiated readers a glimpse into my love of Lampredi's work, and also my reasons to build heavily modified engines based on a 40+ year old design, that some would term term ancient and obsolete. So what does all of this have to do with building a performance SOHC engine, well not much and also lots. It only lasted through to the mid 1980's before it underwent major design changes (reverse flow) and then ceased to be produced altogether before that decade ended, a lifespan of just 25 years when it was completely redesigned as the 16 valve engine. Not many mass produced engines can boast that, certainly not Fiat's twin cam. The sohc engine in a form that is true to it's original 1116cc's was still a current production engine in Eastern Europe as late as 2009, albeit with only Euro 1 emissions compliance, that's a production run of over 40 years. ![]() (58.125hp/litre) The SOHC was also massively over-engineered in it's bottom end, it uses the very same con-rod bolt hardware as it's 1608 counterpart as well as the same sized main and big-end journals. 62.5hp/litre) with much larger inlet ports / valves and far higher valve area / displacement ratio, the 'inferior' SOHC with it's non cross flow design holds it's own to produce a healthy 75Hp in stock trim from 1290cc's. When you consider that around the same time the 125 special was making 100hp from 1608c, (approx. In standard form the SOHC eclipses it's 'big brother' the Fiat twin cam. I'm certainly not reinventing the wheel with any of this, achieving a good result is possible by always choosing best practice, understanding some basic tuning theory and following Aurelio's lead. Most home tuners want a few tips on how to do the fairly basic task of assembling an engine and while they're at it, improve a few things and get a bit more power out of it in the process. I figure what people want to know about is what 'works' when you mix and match some of the standard components. However, this sort of engine build is well beyond the scope of this discussion as I'm not writing about a multi valve, dry sump, mechanical fuel injected, 12000rpm, $30,000 engine that everyone drools over but no one is ever going to build. Many tuners also developed cross flow DOHC 16 valve cylinder heads to fit atop the standard block for various racing classes and Hp went even higher. Aurelio was a very clever man and he intimately understood the relationship between the moving piston and the column of air that follows it, he did after all design some of Ferrari's finest Formula 1 engines of the 50's and 60's, and he used all the lessons learned from that time with Ferrari when he joined Fiat and designed the gem we know as the SOHC ( Single Over Head Cam)ĭuring the early '70's the SOHC became the engine of choice for many of Italy's finest tuning houses and some managed to develop quite extraordinary power in the engines 8 valve form, topping 100hp/l with mechanical fuel injection. Notwithstanding it's 'inferior' design non cross-flow cylinder head the SOHC engine can be made to top the magical 100hp/l figure, which is certainly a benchmark for engines of this era. Despite having very humble origins as a power-plant for the 1969 front drive revolution Fiat 128, in my opinion the SOHC is quite a spectacular engine and Aurelio Lampredi's finest mass produced work.
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