Forza Touring Car - 2017 A Class Mercedes Huge Turbo Lab Error

In preparation for the next league event I’ve been recently trying out the touring Cars for next week. Bought them all and been tested each of them at different circuits to see which one suits me the best. Driving the 2017 Mercedes A Class #33 touring car on paper looks to be a good car, however the turbo lag is absolutely stupendous. It takes ages for the boost to build up an by the time it has yore changing gear or having to let off the throttle for the next corner. I can’t help but think this is an error that needs to be patched as there’s no way the engine would take this long to boost, especially when it shares the same engine that’s in the Audi S3 Touring car as well.

I do wonder if this issue/bug would be rectified before the leagues kick off in full swing next week.

Take a look at the power curves in the upgrade menu, if it’s bugged there then it’s bugged in the game.

Forza doesn’t simulate turbolag


Drive the Speedsource Mazda.

It does though, it as if the car has huge amount of turbo lag, you go try the car, put the telemetry on and watch how long it takes for it to achieve full boost of 36.7psi. It takes ages! Far too long as if there’s something wrong with the physics of the engine.

The engine curve in the upgrade menu does portray how it feels in the game too, stupid though really as there’s no way the car should react like that.

Forza 100% simulates turbo lag. You notice it a lot in certain cars. Or at least I do.

placebo, it’s just the torque curve that’s different… no turbo lag at all.

That’s not a placebo effect, the power and torque curve of a forced induction engine doesn’t start to build in power till the turbo starts to “spool”/build boost pressure. The delay in game is the exact same thing. Not feeling instant power, but a slower build up of power and torque. Just go look at any dyno reading of a turbo car. There is no significant movement in the curves till the pressure starts to build.

I haven’t driven the A class, but from the OP is sounds like the torque and HP curves are building way too late. It’s acting as if it has a diesel turbo on it (Large).

you can not see turbo lag on your traditional dyno graph.
fact of the matter is when you’re off throttle at 6k rpm and you gas it you don’t instantly get the torque that the graph shows, the turbo first has to spool up hence “lag”… as in the time between you mashing the throttle and the turbo actually working on maximum boost.

whilst in forza there is no such thing, as soon as you floor it you get 100% power displayed on the torque curve at those rpm’s at an instant, without the delay… aka “lag” .

So like i said, the torquecurve is different opposed to NA cars as turbo’s require higher rpm’s to reach their maximum boost (as it should), but the lag isn’t actually simulated.

You haven’t taken my advice of driving the Speedsource Mazda, it seems.

Easily noticeable in that car because the power band is extremely narrow, being a diesel. You have no power below 3000 rpm then WHOOSH!, it hits you with all it’s got. And what will make it behave is, in fact, keeping that turbo spooling. Behavior similar to certain cars in Project CARS (Lotus 98T for example), and in that game the turbo is modeled.

I find this Mazda undrivable without TCS because of the horrible lag, but then LMP2 allows you to use TCS anyway so it feels more proper with TCS activated.

Your example of 6000 rpm isn’t valid because you won’t have nearly as much lag, as the engine is running fast enough for the turbo to spool quickly.

I have noticed turbo lag in other cars, such as Nissan GT-R GT500 and even the Renault R.S.17.

Sounds exactly like driving a Porsche 930 or any turbocharged car from the 1980’s.

^This simply isn’t true. Go look at telemetry. If everyone is arguing against you and these are long term Forza fanatics, then you are wrong. It’s as simple as that.

Edit: If this is still being argued tomorrow then I’ll do a telemetry video showing the time between throttle and spool, but I’m 100% sure on this. There’s is zero doubt in my mind.


And the telemetry shows and instant 100% torque at any given boost level…

The engine will always generate torque, I don’t get your point. Even without spool, it generates torque.

You can compare the Ferrari and the McLaren in Formula 90s division. Ferrari is 3.5L V12 and smoother power delivery than McLaren’s 1.5L V6 twin turbo.

Sooooo many people in this thread are mistaking boost threshold for turbo lag

Boost Threshold - the rpm at which the engine (at full throttle) begins to build boost pressure via the turbo

Turbo lag - the delay in boost response to a change in throttle opening WHEN the engine is above the boost threshold.

Imagine puttering along at very low speed in a high gear, say 50km/h in 6th, doing 1500rpm. You mash the pedal, but the engine takes forever to build speed until you hit 3500rpm and boost begins to build - this is NOT TURBO LAG. There simply isn’t enough exhaust flow at low rpm, even at full throttle, to spin the turbo any meaningful amount and compress the incoming air.

Now imagine you are on the freeway doing 100km/h and you spot a chance to overtake a slow truck ahead - you drop back to fourth, revs go to 4000rpm (with very little throttle) and you then mash the loud pedal. There is a delay as boost builds to what it should be for 4000rpm at WOT, and then you scream past the truck - THIS IS TURBO LAG. You are doing enough revs to generate boost, you are full throttle, the turbo should be producing boost, but it isn’t because it is slow to react to the sudden change in demand.

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There seems to be some match between the sound of the turbo spooling and the moment the car begins accelerating, but I have only tested this with modern cars which have little lag.

Either way input lag turbo lag, the A Class BTCC car is fudged an needs remedying. If anything it probably has a mixture of turbo and input lag! haha

It has a V6 sound but NGTC is capped to L4…

I hate these “liberties” devs take with sounds sometimes.

Sorry for the bump, but the sound issue is now fixed, the car sounds like a 4-cylinder. I noticed it needs to be driven like a VTEC indeed.

These touring cars all have weird torque curves and I doubt they’re realistic. The BMW 125i’s curve is suspiciously similar to that of the “1.6L I4 - Turbo Rally” engine swap, which was originally taken from a Ford Fiesta.

The A45’s “lag” becomes more manageable if you add an engine upgrade, but then you break the limits of the division… Since you can fit 275mm tires all around, my guess is they did this for balancing and ended up killing the car in the process.