Downshifts with no engine drag

[USAFS4]

Does anyone know how to make the engine rev so freely, that on downshifts there is no engine drag, no deceleration after having engaged the clutch in the lower gear? Not with rev matching/heel & toe. I experienced this behavior once in a used car I test drove, and am fairly certain the car was modified somehow (no blower) to produce this effect. The car certainly also accelerated faster than any stock car I’ve driven. And yet the car didn’t feel more torquey like mine does after adding JHM intake spacers. The car was still easier to pull away from a stop though, even with the fast reving nature, unlike a stock car that I find it difficult to pull away in between creeping away and practically launching the car (hence adding the spacers).

In case someone here once owned the car or knew it, the car was Mugello Blue with black interior, and found at a dealer in Rockville MD around 2015/16.

I’m hoping to build my car to do the same after completing a deflap during an upcoming carbon clean. I’m told you can’t program rev matching into these cars ecus. So the car in question must have had some combination of tune with maybe a lightened fly wheel, and it’s been suggested possibly a different crank pulley. Car’s exhaust didn’t sound very different from stock and I don’t remember seeing a non stock intake.

Any thoughts on how to get this behavior is appreciated. Thanks

Ps. I thought I remember ad literature or maybe a review stating the car would exhibit this non-drag behavior on downshifts because of the engine design, and my car on sport mode seems to have less drag, but not to the extent the car doesn’t decelerate.

[MugelloB7RS4]

Do you mean engine braking? Thats due to the gearing in the gearbox. If you downshift without bringing the rpm's up to the proper level and release the clutch, the engine and transmission need to sync up and equalize speeds. If the engine is too high, it will bog down, if the engine isn't high enough, the rpm's will jump up. Is this what you mean by "downshifts with no engine drag". The only way to get by that is to be more precise on downshifts. Find the proper rpm to match gearbox and engine and you won't notice it.

Some newer vehicles have auto rev matching. Is that what you mean by this other used car? What kind of car is it?

[CrickiKaze]

Not what he means, stated that in the OP...

I've been trying to think of how one would do what the OP is describing and the only thing I can think of initially is that the TB is open at a specific percentage to not induce vacuum and reduce the effects of engine braking.... but even then I'm not sure.

[MugelloB7RS4]

Not what he means, stated that in the OP...

I've been trying to think of how one would do what the OP is describing and the only thing I can think of initially is that the TB is open at a specific percentage to not induce vacuum and reduce the effects of engine braking.... but even then I'm not sure.

So when you push the clutch pedal in, the car continues to rev?

[ginch]

Im confused!!

[S3NICK]

If you want easier downshift blips, a lightweight flywheel would accomplish that. If you want more driveline stability during shifts, get a rear differential mount (Apikol). However, less aggressive engine braking while in gear would likely be the result of a heavier (more inertia) flywheel which would align more with a stock flywheel. Can you clarify?

[CrickiKaze]

So when you push the clutch pedal in, the car continues to rev?

No, similar to removing some pressure of the pedal enough to slow down while still applying pressure until the engine rpm comes down till it "meet/marry" with the reduced throttle position.....crap example as it happens quickly enough to not notice.

Best example I can recall was when I was driving a rental with a CVT trans, full throttle close at what ever speed and I was still coasting at a faster rate versus a tradition auto trans or manual trans. Only other thing I can think of is when you are pressing the throttle and then no response for acceleration, kind of a limbo as the throttle is open so air if flowing through the motor unrestricted. Again crap explanation but the best I can come up with for what he is describing that doesn't quite explain what he is asking...

[USAFS4]

So when you push the clutch pedal in, the car continues to rev?

No, forget about throttle inputs. Let’s say you take your foot off gas, then press clutch to floor, engine would start to drop revs, then let clutch out and at clutch engagement, without touching the throttle, the engine immediately jumps up in revs to match the drive train with little noticeable drag.

Now let’s say you maintain the exact same amount of throttle Input pre downshifts as when you let clutch petal out, the engine again would jump up in revs so that now in the lower gear it still matches the drivetrain… so no discernible deceleration occurs.

Neither of these two scenarios is heel & toe. The car seems magically do this on its own. Maybe you could say the car had a mechanical version of rev matching, so instead of a computer calculating the needed throttle blip to match drive train to engine revs and doing it for you, there essentially is no need cause the engine will just freely jump up in rpm, to the rpm that you would have been at if in the lower gear at the given speed to begin with.

[USAFS4]

Not what he means, stated that in the OP...

I've been trying to think of how one would do what the OP is describing and the only thing I can think of initially is that the TB is open at a specific percentage to not induce vacuum and reduce the effects of engine braking.... but even then I'm not sure.

Ok. This is the right track (though I’m not a mechanic by any means). So what tune and/or mechanical changes would be needed to produce the effect?

[USAFS4]

If you want easier downshift blips, a lightweight flywheel would accomplish that. If you want more driveline stability during shifts, get a rear differential mount (Apikol). However, less aggressive engine braking while in gear would likely be the result of a heavier (more inertia) flywheel which would align more with a stock flywheel. Can you clarify?

So “engine braking” is what I’m talking about, however the seemingly lack there of. So your suggestion of a heavier flywheel doesn’t seem to explain the speed and ease the engine had jumping up in revs, and then having no engine braking. Don’t think more mass would spin up easier?

[USAFS4]

Another thought about how our cars had F1 piston speeds, the first production cars (non-race) to do this. It would seem race cars would benefit greatly from a design to prevent engine braking on downshifts. Every tenth, hundredths, matters in motorsport so having no deceleration and/or no power interruption would be very beneficial. Even with dual clutches the behavior would still be beneficial. So I’m surprised that I can’t find out how it is done.

Maybe the car had a non off the shelf tune (Apr, JHM, Jackal, etc.).

[USAFS4]

Some things I found about reducing engine braking….

“You could reduce it potentially by not using over run fuel cut off (so that the engine is still actually running). If you have drive by wire throttle then you could very slightly increase the throttle targets at the rpm range you're noticing this issue - This would be when the accelerator pedal position is zero. Obviously modifying the dbw targets needs to be done carefully as the engine power may not reduce sufficiently if your targets are too high. I'd make changes of 0.2-0.5% maximum while testing this.”

“What is your ignition timing on overrun? This can affect the amount of engine braking you are feeling.”

[USAFS4]

Found this discussion about engine braking…. https://www.locostusa.com/forums/vie...hp?f=4&t=19989

It’s technical and talks about many things such as “throttle cracking.” So instead of going down a rabbit hole of which the content I’m too ignorant about to really understand, is there a tuner I should turn to? Will any of the big names fiddle with this stuff, APR, JHM, Jackal, etc? Or should I look for a tuning shop? I’ve always bought off the shelf tunes and have no idea about how to find a “tuner”. I can’t afford to blow up my engine so it’s difficult to consider trusting a tuner over buying something a whole bunch of people have already with little complaints reported.

[koolade9]

LWFW

[USAFS4]

LWFW

We’ll that would certainly be the easiest thing to start with.