It is indeed.....it does exist!!
as he quotes or "adapts" from Mr V in the article ( which is more concerned with exhaust valve dammage) "some engines were designed that way....."
and so it is with the 2cv, apparently you can see that fuel stand off when the motor is on a dyno thats why the panckake filters dont work as well as the big tall green ones.
and you still have to go a long way with jets and filters and 2:1 exhausts to make it work better than a standard one.
As iv always said (i live at the top of a long steep hill and Ive driven some buckets in my day) a faulty, split or missing exhaust( before the crossbox) and the car struggles up the hill. Ok so its a function of the carb and the jetting and the cam. (Incidently a poor exhust and there is MORE fuel consumption not less which suggests there is more to this than simply the inlet charge passing the venturi twice) But still it produces less power!-it needs the back pressure the system has.
Thats how it was set up.OK so a 2cv engine "theoretically" doesnt need it, but on standard inlets and heads and cam and carb and jet etc.
Any hoo back to the graphs...not all they apper to be in the above context.
Black line is Maurices own exhaust and he retains a crossbox and torpedo and long tailpipe...why? clearly there is some benifit other than just silencing. or why not just have 2 BIG bore pipes with cherrybombs?
Red is a standard "gutted"system which has more torque lower down(in comparison) which kinda goes with what most have been saying here.
Maurices exhaust has a peakier low torque and amuch fuller second half .. a function of beter breathing suiting the engine ?
All totally irrelevant to a normal car if you look at the spec of the engine that little lot was bolted to!!
"
Engine :
710 cubic, 8: 1 compression ratio, 7,5mm/288° camshaft, manifold with Weber carb and air filter coming from Visa engine. No indication that the sand prefilter was in use. Custom flywheel with high inertia and low weight(??)!"
None of this shows the plotting for the standard engine and exhaust? and so to most of us these graphs are just a wet dream.
The customer for that engine reported that it did not rev to 5K on a standard exhaust!
my tired old 9:1 on standard heads,barrels and cam will happily rev beyond 6K and has spent days(literaly) sitting at 5.5K(120KPH IIRC). I dont know whats going on with my crossbox but the engine loves it, Ive put on a gutted one and a brand spanking new one and always gone back to this old one.
None of the above is a criticism of STP, more an endorsment of the standard engine Maurice has quite a reputation, has built some hairy engines and some real grunters he appers to know his stuff and most of his work seems to be based around his cams.
Maurice also has quite a reputation for
always being right and everyone else is graded into 3 types of potential customer, 2 sets of fools and those that stump up the cash to do it his way.
But anyone can cut and paste stuff off the tinternet and show graphs ...but to understand them ......well thats something else.
Whats your take on it all then?
Intrested to hear from any with experience of trying to tune a M28 engine or any other Injun for that matter!
Sean
:doh: i wasnt going to fall in to the cliche of putting my name to it!
is that me a "bullshitter" now!
