Couple of questions following track day

[Rooney1000]

Hi all

Was at Snetterton today in my 3.5s, great day and weather behaved. Probably the last track day of the year for me :-(

Do have a couple of questions though, really am not technical or knowledgeable when it comes to cars so wondering if anyone has any thoughts on the below.

Firstly, when going out for a session the first few laps the car feels rapid everywhere but then I dont know, it just feels like it loses a touch of power. I did several trials today on the long back straight and on my first 2 or 3 laps I can hit about 130, right at the top end of 5th, before I need to brake for the corners. However, 5 or 6 laps into the same session and I can only get to about 120, coming off the prior bend to the straight at the same speed and really pushing but it feels like it has lost a tiny bit of top end. Is that normal ? Is that something all cars would suffer from ? As I say, no idea myself !

Second point, same as above, no issue for the first 2 or 3 laps but then afterwards I noticed that coming off a bend and accelerating, the car has about a second delay to really get going. It accelerates but literally takes a second, maybe slightly more, and then suddenly it accelerates like it should. This happens most of the time in 3rd but I can get it to do the same in 4th. Now it is always as I come out of a bend, so my head is telling me maybe the fuel moving around in the tank but then it doesn't do it for the first few laps. I always make sure I am out with a full tank as well so cant believe 2 laps can make that much difference.

As I say, not technical so hope above makes some kind of sense !!

Thanks all
(car is a standard 2018 supercharged car, no cat as existing cat fell apart so running original cat tube but completely hollow)

[speedmachine]

I recignise what you’re saying from my sc 3.5.
Unfortunately the jackson racing supercharger kit creates a lót of heat and after some laps in it will geat soak big time and hot air doesnt want to compress so nice and thus you’ll loose some pony’s.

The 3.5R has the chargecooler and this not only allows for more power, it also is more consistent because the air entering the engine keeps cooler

I’m afraid no real solution other than upgrading to a 3.5R, which is no punishments apart from the cost

[plip1953]

What you describe in terms of the reduced top speed is similar to the experience with Atom 4, and is largely due to coolant temps going sky high (often well over 100degC). My understanding is that 3.5s don't suffer high coolant temps (better/more airflow to the radiator) but worth keeping an eye on. The other main reason that the ecu will dull the power is if manifold intake temps get too high, which I think is what speedmachine is describing. But the lagged throttle response sounds to me like it could be something different, especially as one of the key attributes of a supercharger setup is instant throttle response.

[Yorkshire]

The loss of power is the air temp increasing as others have said there is no way round this. The delay coming out of corners could be your losing V-Tec have you a baffled sump? Have you checked your oil level?
If the V-Tec loses oil pressure momentarily it doesn't work properly.
If you speak to the factory they may be better to advise but i always made sure my oil was slightly over the full mark.

[speedmachine]

Yes,5-10mm above max mark on track

[John Scherrer]

I'm with Yorkshire on this - possibly not got the Baffled Sump option or oil level too low.

[Rooney1000]

Yes, car does not have a baffled sump. Will check oil level again.

Why would it not do it for the first few laps though, only on lap 3+ ? This is even on second / third sessions so oil already warm I guess ?

[Rooney1000]

Oh and check oil hot or cold ? Just checked it cold and just above minimum but warm engine and oil seems lighter in colour so hard to tell but looks like it coats up to max level !

[Yorkshire]

I always do mine cold whether this is what you should do i'm not sure.

[plip1953]

The loss of power is the air temp increasing as others have said there is no way round this. The delay coming out of corners could be your losing V-Tec have you a baffled sump? Have you checked your oil level?
If the V-Tec loses oil pressure momentarily it doesn't work properly.
If you speak to the factory they may be better to advise but i always made sure my oil was slightly over the full mark.

Just to be clear Stuart - the 3.5 doesn't suffer high coolant temps, but it prone to high intake temps? Do you know at what temp power starts getting pulled? Is it by retarding timing or limiting boost?

[speedmachine]

The loss of power is the air temp increasing as others have said there is no way round this. The delay coming out of corners could be your losing V-Tec have you a baffled sump? Have you checked your oil level?
If the V-Tec loses oil pressure momentarily it doesn't work properly.
If you speak to the factory they may be better to advise but i always made sure my oil was slightly over the full mark.

Just to be clear Stuart - the 3.5 doesn't suffer high coolant temps, but it prone to high intake temps? Do you know at what temp power starts getting pulled? Is it by retarding timing or limiting boost?

Just by to hot air which cant be depressed as much as cold air.

[Yorkshire]

As above its just the hot air that reduces the power i was always told every 10 degree increase is 3% power so without a charge cooler of any description my guess is on a jackson supercharger intake will rise at least 50 degrees so 15% less power hence 310hp becomes 263hp. On my 3.5R all tuned with even larger charge cooler and water meths i struggled to stop 30 degree increases.

[autobackup]

There is also air density to consider - cold air is considerably more dense than warm air.

One of the downsides of a supercharger is that it compresses the incoming air which raises the inlet manifold air temperature markedly which is why on a standard supercharged Atom the air is only compressed to 7.5psi - to get 350bhp the 3.5R pressure is raised to 11psi raising the charge temperature to circa 180°C, which far too hot and could cause pre-detonation hence the need for a charge cooler!

So if the OAT is high to start and then once the engine, oil and s/c itself get too hot it all becomes a downward spiral in terms of absolute power as the fuel/air charge itself becomes degraded once that happens the only solution is a few cooling laps - driving on the public roads achieves this naturally due to the traffic ebb and flow but on track it's a completely different environment so temperatures have to be 'managed' carefully.

For those running a standard s/c Atom on track, given that the climate seems to be changing ever more rapidly, it may we worth considering adding a charge cooler but keeping the s/c pressure and the bhp the same which would be a reasonably cost effective option!