JowettTalk

Dear all
We are in the process of applying for a historic technical passport for NYM 283 prior to hopefully racing at Classic Le Mans next year and the FIA are querying our present exhaust set up which I presume must deviate somewhat from the original? (I don't know what the original system should be....!). Apparently Peter Dixon designed this system back in the 1980s but he thinks Jowett my have used something similar in the past? Has anyone come across anything like this previously as the FIA need some sort of evidence before they sign us off.

Never seen this 4 to 1 setup on a Jupiter before - normally the Jupiter runs 2 to 1 manifolds - then from the offside there is a link pipe that comes round the front of the car just under the front pully - then links to a Y section in the exhaust more or less immediately after the exhaust has picked up the output from the nearside manifold - from this point to the rear its just a single pipe system - I cant see the system that you currently have with 4 exhaust sections running directly under the sump pan doing the oil temperature any favours at all - the oil cant be far off a frying temperature immediately after a race in warm / hot conditions - I shall try to scan a picture of the standard set up later and post it to this thread - Chris

IIRC, Sparrow has this on the R1 and it is also not so different from the Gane's racer. It will be a massive improvement over the stock system.

In that case if you can prove it's on the R1 which already carries race credentials then it should be easy for you prove the case on yours - I can take a look at Richards next Monday when his car is out on circuit

Many thanks for the replies chaps.
We are planning on bringing our car to Curborough on Monday so hopefully we can continue the discussion then!

Scott.
It would be interesting to see the quantitative difference by doing some dyno runs with it and with the stock version.

I did some tuning of the intake track by removing the stock air cleaner and making a pair of hyperbolic horns. The removal of the air cleaner gave about 5 bhp at the top end and the horn perhaps another 2 bhp. I replaced the horns with a Fram (allegedly full flow) foam filter for non-race use. No doubt some fluid dynamics calculations could reveal the ideal tuned pipe length for peak power, but would be complicated by the balance pipe.

On the Javelin I found that at 75mph the carburation was severely affected by a standing wave in the stock airbox. I replaced with a pair of paper filters. This was with the DelLorto carbs so may not occur with the Zeniths which struggled to give enough at those revs.

The mantra of a racing sytem is "equal length" on the primaries, while the stock system is as unequal as possible! The heads have the same two unequal size ports (bad) and then each port sees a different flow dynamic due to the collector system. #4 has to push past everything. The exhaust note is proof of the limits of the system.

It was great to meet so many of you on Monday at Curborough.
Very many thanks for all the help and advice.
I think the consensus is that we will fit a stock exhaust for the benefit of the HTP and try and do a dyno run with the 2 different exhausts and see what the difference is.
Potentially then we can revert back to our original setup and take the stock exhaust with us to Classic Le Mans just in case we get rumbled!
Thus if anyone has a stock exhaust that they would like to be rid of then please let me know!
On a separate topic - now that I've been shown how damn good the brakes are I'm hoping to wear through the brake shoes rather more quickly than I have been. Any recommendations as to the best place to pick up brake shoes?

Jowett Car Spares.

It is of course worth considering tuning both the induction side of the engine as well as the exhaust side. On the induction side, the distance from throttle plate to combustion chamber for the Javelin/Jupiter is remarkably short relative to most other cars, and this may account for why the peak of the torque curve is at a higher speed than is typical.

On the exhaust side, "the length of the primary pipe from piston crown to the junction box [where the pipes come together] at the time of EVO (Exhaust Valve Opening) determines the tuned length and the corresponding engine speed at which the optimum extractor effect is obtained". Of course, optimizing both the induction and exhaust pipe lengths for maximum horsepower may make the engine rather peaky and down on low-end torque, whereas having different pipe lengths for the different cylinders will likely give you a lower but broader torque curve which would be preferable for normal everyday driving.

Philip

Quick update on this guys!
We swopped the exhaust over and I'm pleased to say that the HTP has now been granted.
Am now in the process of putting in the application for Classic Le Mans net year.
We are off to Birmingham Friday week to put the car on the same rolling road that Julian Crossley uses for his Javelin so that we can then compare notes and bhp!

All good stuff - Keep us informed / updated has to how you get on - Chris

Assuming that you are happy to do so, it would be helpful to the Jowett community if you could post the resulting data plot of engine speed vs torque or horsepower. We can then plot that against the original factory performance to see what progress has been made over the decades.

Philip