Throttle body placement on Jaguar XJ13 V12

[Wes.Coleman]

First of all, the XJ13 is a beautiful car . What really caught my eye, though, is the placement of the throttle bodies and intake trumpets on the engine! Usually, they are located inside the vee (like these on the 330 P3. Clearly between both sets of valve covers), but the ones on the Jaguar appear to be either between the valve covers, or on the outside of both sets; placing them either on top, or on the extreme outside of the vee. What would be the purpose/advantage of this? Possibly a lower center of gravity? Surely, if they wanted a lower COG, they would just go with a flat-12 instead of a V12. It just struck me as strange.

If I'm wrong, please correct me. I'm running on 4.4 hours of sleep for the last three days (three exams in two days ) so I may just be hallucinating.

[Wouter Melissen]

The problem with twin-cam V-engines with a 60-degree angle is that space is limited inside the V. That's why Ferrari switched to a 65-degree angle for various engines from the late 1950s. Another solution is to install the carbs / fuel injection between the camshafts. It has been done on more engines than this one.

Here is the P4 engine with that second setup:
http://www.ultimatecarpage.com/pic.p...=14&carnum=708

[Wes.Coleman]

Originally Posted by Wouter Melissen

The problem with twin-cam V-engines with a 60-degree angle is that space is limited inside the V. That's why Ferrari switched to a 65-degree angle for various engines from the late 1950s. Another solution is to install the carbs / fuel injection between the camshafts. It has been done on more engines than this one.

Here is the P4 engine with that second setup:
http://www.ultimatecarpage.com/pic.p...=14&carnum=708

I picked the 330 p3 as an example because they are from the same year, and would have similar levels of technology, and they also have the same V-angle. What I forgot, is that the XR13's engine was a full liter bigger and the bore of each cylinder was a full 10mm larger. That meant that the camshafts had to be further apart on the Jag's V12 than the Ferrari's V12, limiting the space inside the V, just like you said (though, it was more a combination of the V-angle and the bore, rather than just the V-angle).

I'm wondering if the discrepancy between these two displacements was one of the reasons the XJ13 was never raced; i.e. the maximum displacement for V12's or fuel injected engines in the 1966 Le Mans was 4.0 liters, and the XJ13 was excluded from competition. Things like that happen, like to the BMW M1. Before it could be fully homologated, the rules changed and made it ineligible to compete. Once again, that is just speculation, but it would make sense; Le Mans and Le Mans Series' usually have strict rules on displacement and homologation.

[Wouter Melissen]

Displacement was not limited to 4 litres; Enzo Ferrari just wanted to race engines with the same displacement as his road cars. The XJ13 could have raced in 1966 and 1967, but not in 1968 when a three litre displacement limit was introduced.