Engine tuning and back pressure.

[Vic Vitol]

I am only going on my suspicions as a layman when it comes to the technical aspects of engine workings, but I bought my 280zx last year and only managed to drive it (due to our lack of Summers) for a few weeks before it had to be dry stored for Winter. The car had quite a bit of engine work done at Fourways engineering, which turns out to have been, after a kind member located for me an old edition of the club magazine that featured my new car previously, a high-lift cam, polished ports, and tricked injectors. There may be more engine enhancements I am not aware of, and it has a six branch manifold. When I bought the car the garage that sold it to me had put a standard 280 rear silencer on it. I found in the medium rev range before the power is pushed through at higher revs, that changing gear produces a kind of puff fart noise, rather like a lorry's air brakes. Could this be too much back pressure being released when the clutch is dipped due to engine tuning and the final stage of exhaust being a standard box?

 

[SKiddell]

Could this be too much back pressure being released when the clutch is dipped due to engine tuning and the final stage of exhaust being a standard box?

In a word No

Dont think of back pressure like the fizz in a can of shaken drink, its more a resistance to flow
If you had that kind of "resistance to flow" then your engine wouldnt run at all.

Don't get me wrong, having a stock backbox is probably not the best idea in the worls and you should consider a more "free flowing unit"

look to other areas, like inlet and exhaust manifold leaks, servo leaks, carb standoff etc.

 

[Vic Vitol]

Thanks for your help, I will be getting a stainless exhaust system for the car, hopefully one that frees up a bit of power and still keeps the noise down.I don't think there are inlet/outlet leaks, but I do know the lorry air brake style "puff" fart noise is coming out the rear during clutch dip and gear change.