Why does the exhaust go round the front?

[ian Howell]

Why does the exhaust go round the front?

TO GET TO THE OTHER SIDE OF COURSE!

From memory the exhaust passages in the heads are swept - not straight. Wouldn't this make the exhaust gases have to 'double back' if the exhaust pipe on the offside went rearwards?

[Forumadmin]

Yes, hence you have to modify heads or have 180 deg bend.

[jowettgeoff]

I've played around quite a lot with various exhaust configurations on my competition Javs and Jups. I've modified the offside ports to flow backwards (by removing metal at the rear of the port and adding metal to the front). In terms of exhaust systems, I've tried 4 into 1, 4 into 2 into 1, and 2 into 1. (the latter by fitting an offside manifold on the nearside, and then reversing the offside manifold). Confused? I was! By far the most successful (in terms of performance), was the 4 into 2 into 1. Each primary pipe had a square flange welded onto it, which matched the exhaust port. The primary and secondary lengths and diameters were calculated to a formula I found in an old tuning book. From memory, internal diameters were 1.25" into 1.375" into 1.5". Primary lengths were 18", secondaries were 24", and the final pipe was whatever remained before the back of the car! The exhaust was fabricated for me by Tony Law of Leeds, a well known rally and race bespoke exhaust manufacturer. Tony confirmed that the dimensions I'd chosen were probably about right. This configuration as fitted to the Javelin was a marked improvement over standard, and the car (BEG) was very successful in competition (despite its dodgy driver!). I had a 4 into 1 on the Jup, using flexible piping, but was less convinced about any improvement - although the car did go very well - so perhaps it worked after all. On BEG at the moment I have the 2 into 1, but I don't believe there's any improvement at all. Incidentally, with all of these systems, the cars sound most un-Jowett-like.
I seem to remember reading that Horace Grimley tried a twin pipe system all the way through (possibly for the R1?), but concluded there was no real performance advantage. Other Jowett racers (Frank Woolley, Mike Smailes and Peter Crosby), have all experimented with different configurations.

G McA.