Wondering if upgrades like lightened flywheel, clutch, driveshaft, wheels etc. make a difference in wheel horsepower? Does the game differentiate between BHP and WHP? Or do these upgrades just lighten the car overall?
Tbh it kind of seems like the latter, but of course I’m not really sure.
Yeah, it’s the latter I’m pretty sure. If you look at the HP numbers they don’t change with any “lightweight” engine parts (Flywheel). Their system is just too simplified for that.
It doesn’t simulate a change in HP, but it does change the gearshifts, because a lighter Flywheel makes the load changes easier or something. So don’t treat the flywheel as just a weight reduction, it can make the car much more stable when shifting in long corners while acceleration or trail braking.
In meta tunning flywheel and clutch is just dead upgrade, cost too much and u gain too little, and if u use race transmission, your shift time gets reduced to minimum (around 30ms) and u don’t even need to use clutch anymore with m/c, making flywheel and clutch useless.
Using race transmission is meta in new motorsport.
Driveshaft and wheels just make your car weight less, like weight reduction upgrade, quite good way to fill up missing pi. This game does not simulate unsprung weight at all.
There are a ton of “upgrades” that don’t make any sense when compared to IRL performance. Upgrades like flywheel and clutch reduce drivetrain loss like the OP mentioned, which in turn should allow the engine to rev more freely and as an end result have more HP on tap at the wheels.
It’s all bogus in the end. Rev limiters are set at random spots in the rev range (sometimes up to 2k beyond redline), no valve float, Cam specs are non-existent (only 3 options, sometimes less). Torque is meaningless, it’s all about HP and revs.
I could go on and on…lol.
I am honestly interested to hear what you have to say so please do!
Essentially if I’m understanding you correctly - it’s really as though the upgrade system is superficial at best - because although they provide some ‘bonuses’ to the cars handling or performance - it does not seem to be as the result of a comprehensive and detailed simulation correctly having part influence the simulation’s outcomes - but rather they just bump some invisible stats?
Yep, but Forza isn’t the only one that has issues like this. One of the longstanding modders for Assetto Corsa proved the same point about torque being meaningless by making 2 versions of the same mod, 1 with proper torque numbers, 1 with absolutely 0 torque. The 2 versions drove exactly the same.
My belief is that in FM, since there is no valve float (when you go beyond the rev capability of an engine), if they didn’t impose the imaginary rev limiters, the cars would continue to rev infinitely to oblivion.
The way tuning is so broken, meta tunes (as stated before) completely ignore proper physics. Sway bar settings, springs, dampers all set to unrealistic (and sometimes unknown) numbers. Sway bars don’t even have a “rating” like ft/lbs of torque or tension numbers. It’s just 0-40. 0-40 what? If you set your springs to proper weighting (not including unsprung weight, which we can’t figure out) your car will feel out of sorts, almost undersprung (for lack of a better term).
The addition of the “anti” metrics (dive and squat) go against the other settings. Springs and dampers are supposed to do those things.
I’ve only ever played 1 racing game that took car building seriously, and it was supposed to be a NFS title (until they yanked the NFS part out of it). Motor City Online. A full parts catalog with actual licensed parts (Edelbrok, Crane Cams, Holley carbs, Hooker headers, etc. If you got your compression ratio too high and added a blower, it caused damage. Thousands of parts to choose from. Nothing has come close to building a car and racing it like that game.
Nail on the head. To take a line from “Romancing The Stone”, “Nothing is as it seems”.
“With carrpg, we want you to learn what your upgrades do” 
I would have expected the “most advanced racing game to date” with its “built from the ground up” ugprade system to not simulate any of this, and in the replies we got our confirmation. Making a brand new Upgrade System clearly wasn’t “worth it”.
Yeah that’s the one thing I notice with a lighter flywheel is it really stabilizes gear changes mid-turn with RWD cars, which it should. Without it you have to lift the throttle to shift if you don’t want the rear end to slide.
There’s a bunch of other things in Forza that aren’t simulated or not done justice. I was also hoping “built from the ground up” would mean big advancements in the physics engine, but as far as we know it was only old physics running faster and more contact points. Not any radical changes to upgrade parts, tuning (same old numbers, plus geometry tuning which is so-so), or physics simulation stuff like making air brakes work… The game is built from the ground up only if you count the ground as being “2005”.
I tend to disagree somewhat, I find this game is doing an okay job in representing what these parts should do.
Camshafts for example completely flatten torque curves and require you to re-gear your car just like you should do IRL. Old games that did not come across the same.
Intakes open up the top end just like performance intakes typically do IRL
Flywheels don’t give you more HP, they make the engine snappy and rev higher. A heavy flywheel will actually help a lower torque car IRL
I find cars get best PI value when matching, sport with sport. Which is very much IRL. A race intake will be better, but without cam and exhaust to match you’ll still be choked.
Some stuff isn’t perfect, but a lot is an improvement on previous games.
I do wish they kept the power curve chart for helping setup gears. It’s a pain now.
I’ve been building performance engines for a living for over 25 years.
Thanks for taking the time to write this out I appreciate the reply.
Thanks for another point of view - it sounds like things might have improved in some areas albeit subtly? - but it’s hard to actually tell because of the values are somewhat arbitrary and a lack of ‘technical feedback’ available as you modify the tune?
Then you know how many cam profiles we SHOULD have, instead of the 3 we have. You also know that lift, duration, lobe separation all play a part in what kind of power an engine should/can have and how it’s delivered. You also know that if you throw a “performance” cam in an engine that has it’s original heads, the performance you “should” gain by the cam can be ruined by the lack of air flow by the stock heads.
It’s been way over simplified, to the point of not mattering what parts are installed.
If you only change your flywheel in a car and run it on a chassis dyno, you will see more HP at the wheels. You have effectively reduced your drivetrain loss. But that’s also part of the problem, where are these numbers coming from? Is it power at the wheels, or engine on a dyno?
I wondered the same thing too. It looks like the game uses the car’s factory rated HP which would be BHP. But what is the game engine itself using? Do the cars put down their rated BHP at the wheels? If so that would make all the cars a bit faster than they are in real life. I suspect that’s probably the case. I don’t know though, I haven’t done any comparisons.
I guess it would matter less with modern vehicles as the testing procedures are more accurate than in years past (though there is still a difference with bhp and wheel hp).
For classic cars, especially muscle cars, Forza uses the advertised numbers from the factory, which were all fudged anyways (to get the insurance companies off their backs). Anyone who had a Ford using a 428 SCJ (not that Forza has any anymore) knew darn well the engine produced more than 335-349 HP (in Shelby trim), yet when Forza had the '68 GT-500KR (FM4), it was rated at 349 HP on the nose. FM4 also had the '69 GT-500 with the same exact engine rated at the lower 335 HP. Which is about 100 HP off from the dyno numbers (car companies would under rev the engine on the dyno and provide those numbers to the insurance companies). Plus those numbers were rated as gross HP, not how dynos work in today’s world.
You have to look at the larger picture, this is all part of the broken PI system that has been in place for a long time (with only minor adjustments). A system that funnels players into engine swaps (many non-sensical ones). A system that repeatedly stifles stock powertrains (pick a muscle car, any one).
Take Pontiac for example, when FH4 got the '68 Firebird, it had the 400 in it. None of the engine swaps available were other Pontiac engines. No 428 or 455. Just the bog standard “LS” swap and the V-10 and V-12. Chevy is the same, '70 454 LS-6 maxed out (N/A) is under 800 HP. When a properly built BB Chevy can produce 1k HP N/A all day. A mild cam would put you at where Forza puts the all in build at.
I think your expectations of the game are too high
Even the IRL they have ruined it. I literally lol everytime I hear somebody say I have a “stage 3” cam.
The game actually does a reasonable job overall. I find best PI setups use similar range parts ie all sport parts.
A lighter flywheel might not give you more power to the wheels, it would have to be holding the engine back. Some engines benefit from the momentum, especially 4 cylinders. Again, parts need to match.
Really going from a 4 speed to 6 speed should steal power, unless the countershaft is lighter, does the 4 cylinder get the same “race” trans as a V8? Too many variables to build into a game and then have them be actually realistic.
Seems you’re just asking too much of a game. Even pros don’t know until they test different parts sometimes. We have an idea based on experience but so many outside factors. Once you add boost it’s a complete different animal.