Revs falling almost intantly
Discussion
I've just been playing with my Quantum, and remembered when I owned it the first time around it had a non standard engine in it. You could rev it, say to 2k in neutral and the revs would fall back to idle very quickly. It was like a race prepped car, but not quite as severe
There was nothing electronic controlling the revs but it got me thinking about how and why it was happening. In my head the flywheel had been lightened, but I have no proof that's what had been done or whether it was related. I liked the sound and feel though. Anyone know why and how an engine does that? In my Jag, you can rev it to 3k and it falls slowly, like the ECU has a decision on a target idle incase a gear is engaged
There was nothing electronic controlling the revs but it got me thinking about how and why it was happening. In my head the flywheel had been lightened, but I have no proof that's what had been done or whether it was related. I liked the sound and feel though. Anyone know why and how an engine does that? In my Jag, you can rev it to 3k and it falls slowly, like the ECU has a decision on a target idle incase a gear is engaged
I'm lead to believe that on modern cars which don't loose revs quickly its more to do with engine management set up than flywheel weight (although its sort of mimicking having a really heavy flywheel). This is definitely another one of my irritations with modern cars, poor throttle response which spoils the driving experience.
When you change up my V70 goes so far as to briefly hold the revs at the correct level for the next gear, it's a Diesel anyway so lightning shifts aren't the idea but if you do slam it into the next gear for a fast change it seems to accept it's fate with dignity...
Every car I've driven from the last decade or so seems to have some kind of electronic interference in how the revs are managed, mostly seems to be if you accelerate hard in 1st or 2nd gear and then chop the throttle the car continues at about the same speed instead of instantly slowing down, very noticable in a 2.5l Diesel
Every car I've driven from the last decade or so seems to have some kind of electronic interference in how the revs are managed, mostly seems to be if you accelerate hard in 1st or 2nd gear and then chop the throttle the car continues at about the same speed instead of instantly slowing down, very noticable in a 2.5l Diesel
LaurasOtherHalf said:
I remember in my younger & slightly less mechanically sympathetic days I always used to blip the throttle at junctions &traffic lights etc with the clutch just slightly biting, as to my young & simple mind it made my old fords sound much more "race tuned" 
The engine that was in mine that I'm referring to was a Specialised Engines 1900 CVH. Only a single carb (I've had DCNF's on one) but a lairy cam and a 4 branch made up for it a littleI thought that the slow falling of revs on modern engines was part of emissions control? Reduces unburnt fuel passing into the exhaust and cat? Whatever the reason, it massively pisses me off and spoils the enjoyment of brisk up-changes. One of the reasons I have given up on manuals.
AnotherClarkey said:
I thought that the slow falling of revs on modern engines was part of emissions control? Reduces unburnt fuel passing into the exhaust and cat? Whatever the reason, it massively pisses me off and spoils the enjoyment of brisk up-changes. One of the reasons I have given up on manuals.
Not all manuals do this, but pretty much everything with a "drive by wire" throttle seems to. I agree it's massively annoying to have the engine RPM 'hanging on' when you try to go for a fast gearchange.Now sold it, but I fitted my Morgan 4/4 with a 1828 cross flow and twin 45 delortos. This was always a good responder, but when I fitted a lightweight steel flywheel, unbelievably good response. No need to 'blip' it, but it was quite capable of raising and lowering the revs at the lights perhaps four times to most cars one.
My TD5 Defender though was awful, you could floor and release the throttle pedal before the engine woke up to fact you'd done something. Throttle response just wasn't in its book.
My TD5 Defender though was awful, you could floor and release the throttle pedal before the engine woke up to fact you'd done something. Throttle response just wasn't in its book.
There could be several things going on
engine management might be hold the revs up on some modern cars, but there are plenty of cars where i know it certainly doesn't.
lightened flywheel obviously makes a difference, equally lightened rods, pistons and crank etc.
But the think that makes the major difference between a high performance / race engine and something a little less exciting is the ratio between bore and stroke
short strokes mean the pistons do not have to move very far, and the wide bore means they still swallow a lot of air in that short stroke, the result is an engine with less inertia that can rev much more quickly
engine management might be hold the revs up on some modern cars, but there are plenty of cars where i know it certainly doesn't.
lightened flywheel obviously makes a difference, equally lightened rods, pistons and crank etc.
But the think that makes the major difference between a high performance / race engine and something a little less exciting is the ratio between bore and stroke
short strokes mean the pistons do not have to move very far, and the wide bore means they still swallow a lot of air in that short stroke, the result is an engine with less inertia that can rev much more quickly
MarkRSi said:
Try a GT86 or a Megane 265 - in these the throttle seems to directly control the RPM the engine spins at rather than how much fuel is pumped into the engine.
Personally I prefer feeling of a flywheel - a Honda K20 is perfect in this regard IMO.
Traditional throttles have never controlled the amount fuel injected, they open butterflies which have been restricting the airflow, some modern engines bypass the throttle body completely and use the cam to control the airflow, but the pedal is still controlling the airflow.Personally I prefer feeling of a flywheel - a Honda K20 is perfect in this regard IMO.
I don't see how a pedal can ever be used to directly command engine rpm, how would it work?
cruising at say 2k rpm and you put the pedal to about half way, the engine accelerates hard with a lot of throttle to about 4k rpm then stops accelerating all without you moving your foot.
it's the sort of thing i can imagine on a eco car where the ecu calculates the most efficient way for you to accelerate, but on a performance car, no way
Driving an 09 Astra 1.6 Club recently I found by far THE most annoying thing I've ever experianced in a car was the throttle control. It was a naturally aspirated car that had a much slower throttle response than my turbo diesel 
and when the throttle was fully released it didn't react for about three seconds. I got the impression it was trying to keep the ride smooth, was f
king horrible.
and when the throttle was fully released it didn't react for about three seconds. I got the impression it was trying to keep the ride smooth, was fking horrible.ging84 said:
you've obviously never seen how fast the needles can move on nice big racing rev counters, i suggest you watch days of thunder or some drag racing
Days of Thunder, that well known factual documentary 
Drag engines rev very quickly anyway. Any half decent instrument will indicate exactly what speed the engine is doing, not some random value as the needle swings wildly around.
StottyZr said:
Driving an 09 Astra 1.6 Club recently I found by far THE most annoying thing I've ever experianced in a car was the throttle control. It was a naturally aspirated car that had a much slower throttle response than my turbo diesel and when the throttle was fully released it didn't react for about three seconds. I got the impression it was trying to keep the ride smooth, was fking horrible.
How quick were your gearchanges? Sounds defo like something wrong. and when the throttle was fully released it didn't react for about three seconds. I got the impression it was trying to keep the ride smooth, was fking horrible.Gassing Station | General Gassing | Top of Page | What's New | My Stuff