Exige S2 with added supercharger

[johnfishcurtis]

Oh come on, we need to hear it.

[andybond]

I don’t have any drive bys yet.

[thommo]

Enjoying the story . . . keep up the good work

[andybond]

Well,

Part 231 of the Exige.

I am sure you wont need reminding of the previous series of posts where in reverse chronological order where I had a new shiny back box built after I found a knackered back box that caused a loss of power despite putting a komotec manifold on.

So this is the post to bring us upto date

As ever I used the super reliable, friendly and knowledgeable RSTuning.

Here are some pictures of a dirty exige ( it was clean when I left ) on the dyno




With almost no changes we made +15bhp on the last result. However lots and lots of fuel was added. Various things tweaked and a load of advance added to the map ( again! )

This yielded 282.1hp ( its all about the .1 ) and 189.2ftib or in a nutshell more than the car has ever had.

I have below the mapping dyno print.

Red is when the car was first completed to AndySpec with the chargecooler etc ( 268.5 hp )
Green is when the car was last tested after putting on a komotec manifold and baffled me how I lost power - but I know now ( 256 hp )
Pink is the latest dyno with some super smooth lines of torque and hp goodness.



One nagging thing in my mind. .45bar was observed as the boost pressure. Thats a bit lower than I had anticipated. Do I have the 2.9inch pulley that I thought I had?

Tune in soon to find out when I goto Daves@seriouslylotus and have the car serviced, tyres fitted and ask Dave nicely to measure my pulley.

[andybond]

[Fonzey]

Positive update Andy.

I know we've discussed this already, but for the benefit of anyone else reading my car measured 9.5psi of manifold pressure on the dyno with a 2.9" pulley.

[JDS]

Bear in mind that any engine, in simple terms is an air pump. Any forced induction backs up the inlet - creating boost - pressure, depending on how efficient the inlet, combustion chamber, valve overlap/lift/duration, exhaust is. Its even more evident on an SC engine, as the SC is directly related to engine speed.
It's been shown time and again, that everything being equal, the same size pulley, on the exact same engine/map could loose boost pressure, simply by having a less restrictive, bigger, betterer, exhaust, but still gain power/less heat issues. The upside is an even smaller pulley, tweak of map, can generate more power - compressor map/heat dependant!

[andybond]

Bear in mind that any engine, in simple terms is an air pump. Any forced induction backs up the inlet - creating boost - pressure, depending on how efficient the inlet, combustion chamber, valve overlap/lift/duration, exhaust is. Its even more evident on an SC engine, as the SC is directly related to engine speed.
It's been shown time and again, that everything being equal, the same size pulley, on the exact same engine/map could loose boost pressure, simply by having a less restrictive, bigger, betterer, exhaust, but still gain power/less heat issues. The upside is an even smaller pulley, tweak of map, can generate more power - compressor map/heat dependant!

I think we shall be talking theories on restrictions next week @JDS whilst measuring a pulley!

[Fonzey]

It's a good point, you can see it in effect on a log trace as a vvtli engine passes over onto the high lift cam. The sudden reduction in restriction creates a boost drop, which gradually works its way back up again towards the redline.



I've also seen the effects of this the opposite way, I recently talked to somebody (again on an SC 2zz) who went on a dyno, and at the point the cam change should happen the engine felt flat and the MAP reading sky rocketed, up to 13-14psi(!)

It turned out that his catalyst had started breaking up, and so was creating a massive restriction. Under the strain of a dyno, the cat finally gave up and almost entirely folded in on itself. The car would barely rev above 5k after that. As soon as the cat was relieved of its duties, the car went back on the dyno and made a tidy 7 or so psi.

Whether something could be tuned around the cam timing or whatever to influence this appreciably without a difference in cam lobe profile I'm really not sure.

[andybond]

Service time!

New brake fluid
New gearbox fluid
New tyres.