SL/R129: Acceleration Characteristics
Thread Starter
MBWorld Fanatic!
Joined: Jul 2003
Posts: 1,181
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From: Abbotsford, BC, Canada
1999 SL 500 & 2011 E 550 4Matic
Acceleration Characteristics
It is so much fun getting to be familiar with the R129 capabilities.
Has anyone noticed:
1) The car seems to accelerate harder from a stop when turning a 90 degree corner. As if the engine management system recognizes the need to avoid crossing / merging with moving traffic situations and allows extra power through.
2) There is a sticky point at 90% gas peddal travel. If you press hard enough to pass that point it is like the afterburners are ignighted. Even from a standing start ... so it is not just a down shift.
I know this is not my imagination, because when I do engage this extra power with my wife in the car, she screams louder at me.
3) Extra power when the air temp is very cool. Say 45 degrees ... it is noticable. Under hard acceleration there is extra air in the pistons (due to increased air dencity) kind of like an intercooler effect.
Has anyone noticed:
1) The car seems to accelerate harder from a stop when turning a 90 degree corner. As if the engine management system recognizes the need to avoid crossing / merging with moving traffic situations and allows extra power through.
2) There is a sticky point at 90% gas peddal travel. If you press hard enough to pass that point it is like the afterburners are ignighted. Even from a standing start ... so it is not just a down shift.
I know this is not my imagination, because when I do engage this extra power with my wife in the car, she screams louder at me.
3) Extra power when the air temp is very cool. Say 45 degrees ... it is noticable. Under hard acceleration there is extra air in the pistons (due to increased air dencity) kind of like an intercooler effect.
MBWorld Fanatic!
Joined: May 2004
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From: California
2014 C250 sport
1) the engine management isn't that smart, wish it were
2)if you floor the gas pedal all the way where it pushes what feels like a button, it's called kickdown and it engages the lowest gear possible for fastest acceleration. when you say you feel it from a stop,you're just feeling what full throttle feels like, the kickdown button doesn't give any extra power.
3)true, cool air is easier on the engine than hot
2)if you floor the gas pedal all the way where it pushes what feels like a button, it's called kickdown and it engages the lowest gear possible for fastest acceleration. when you say you feel it from a stop,you're just feeling what full throttle feels like, the kickdown button doesn't give any extra power.
3)true, cool air is easier on the engine than hot
Newbie
Joined: Feb 2005
Posts: 14
Likes: 0
From: Illinois
190E, SL500, Alfa Romeo 164L
Yeah, it is fun. I've found the 129 SL takes quite a while to get to know, but that's part of the charm and half the fun. Here are my comments -
1 - my guess is that it just seems like you're accelerating faster because of the dynamics of turning. But, if you're noticing the extra push during more rolling type stops or corners, the adaptive transmission may also be kicking to a sportier shift pattern than you're used to.
2 - are you sure you don't have the transmission in W? In older 4-speed SL's (I think 1995 and earlier), they always started from a stop in 2nd gear unless you pushed the pedal all the way to the floor and triggered the kickdown button that ackbro described. This also may happen if you have the tranny in W ("winter" or "wet") on a later 129. In that mode, the car will start off in 2nd unless you floor the pedal. In that case, I believe the kickback button should drop it back down to 1st for emergency acceleration power.
3 - yep. But I do suggest making sure your engine and its juices are at a nice operating temperature before really opening the throttle up.
Hope you continue to enjoy your car!
1 - my guess is that it just seems like you're accelerating faster because of the dynamics of turning. But, if you're noticing the extra push during more rolling type stops or corners, the adaptive transmission may also be kicking to a sportier shift pattern than you're used to.
2 - are you sure you don't have the transmission in W? In older 4-speed SL's (I think 1995 and earlier), they always started from a stop in 2nd gear unless you pushed the pedal all the way to the floor and triggered the kickdown button that ackbro described. This also may happen if you have the tranny in W ("winter" or "wet") on a later 129. In that mode, the car will start off in 2nd unless you floor the pedal. In that case, I believe the kickback button should drop it back down to 1st for emergency acceleration power.
3 - yep. But I do suggest making sure your engine and its juices are at a nice operating temperature before really opening the throttle up.
Hope you continue to enjoy your car!
Senior Member
Joined: Mar 2004
Posts: 290
Likes: 3
from a stop, it seems to me that it accelerates quicker when I'm half throttling the car, then when I am flooring it 
I dunno, that's just me maybe, it really feels like it pulls harder, half throttle impresses me and gets me tingly more than flooring it.
I dunno, that's just me maybe, it really feels like it pulls harder, half throttle impresses me and gets me tingly more than flooring it.
Thread Starter
MBWorld Fanatic!
Joined: Jul 2003
Posts: 1,181
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From: Abbotsford, BC, Canada
1999 SL 500 & 2011 E 550 4Matic
Originally Posted by MeAndMySL
Yeah, it is fun. I've found the 129 SL takes quite a while to get to know,
1 - my guess is that it just seems like you're accelerating faster because of the dynamics of turning.
2 - are you sure you don't have the transmission in W?
3 - yep. But I do suggest making sure your engine and its juices are at a nice operating temperature before really opening the throttle up.
Hope you continue to enjoy your car!
1 - my guess is that it just seems like you're accelerating faster because of the dynamics of turning.
2 - are you sure you don't have the transmission in W?
3 - yep. But I do suggest making sure your engine and its juices are at a nice operating temperature before really opening the throttle up.
Hope you continue to enjoy your car!
From a stop, when passing, full throttel to very high speeds etc. Just to make sure the systems are on their toes!
1 - Yes probably just my imagination and a bit of lateral G-force thrown in.
2 - No way. I have driven in that mode in the wet. It's fun ... but must make sure to turn back to "S" when the pavement is dry.
3 - I never goose it without the engine temp being over 80 degrees operating temperature.
Thread Starter
MBWorld Fanatic!
Joined: Jul 2003
Posts: 1,181
Likes: 75
From: Abbotsford, BC, Canada
1999 SL 500 & 2011 E 550 4Matic
Originally Posted by agentMurdoc
from a stop, it seems to me that it accelerates quicker when I'm half throttling the car, then when I am flooring it
I dunno, that's just me maybe, it really feels like it pulls harder, half throttle impresses me and gets me tingly more than flooring it.
I dunno, that's just me maybe, it really feels like it pulls harder, half throttle impresses me and gets me tingly more than flooring it.
However I think the previous owners never really pressed the car to it's limits. Now that I have been heavy footed for a good part of my miles, the car is a bit more predictable.
It used to rev and search for a gear when mashing the accelerator at about 45 mph. Now it just kicks down and goes.
I think this has to do with the addaptive transmission not having been pushed through it's paces enough.
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Joined: Jul 2002
Posts: 2,447
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From: UK
SL55 AMG
The reason the engine performs better when it's cold is because the density of colder air is higher than that of warmer air. That means than when air is sucked into the engine, a greater mass of air is available to mix with fuel and burn and the greater the power.
A performance indicator of an engine is the volumetric efficiency - if you have a 5 litre engine, how much air actually makes it in to engine; it's less than 5 litres (taking all the cylinders into account). The reason it's not 100% is because the descending piston creates a partial vacuum so only a limited amount of air makes it in there. That's the whole point of turbo and supercharging - to force the air into the engine rather than rely on the engine to suck it in.
Volumetric efficiency is all to do with manifold and filter design and also the circumference and number of inlet valves. The area the air flows through approximates to a slit around the circumference of the valve, so the longer this dimension, the better it is. It also explains why, when you have 3 valves per cylinder, as in the current MB V8s, you have 2 inlet and 1 outlet valves. For gas leaving the engine, the air is pushed out which is more efficient than sucking fresh air in.
A performance indicator of an engine is the volumetric efficiency - if you have a 5 litre engine, how much air actually makes it in to engine; it's less than 5 litres (taking all the cylinders into account). The reason it's not 100% is because the descending piston creates a partial vacuum so only a limited amount of air makes it in there. That's the whole point of turbo and supercharging - to force the air into the engine rather than rely on the engine to suck it in.
Volumetric efficiency is all to do with manifold and filter design and also the circumference and number of inlet valves. The area the air flows through approximates to a slit around the circumference of the valve, so the longer this dimension, the better it is. It also explains why, when you have 3 valves per cylinder, as in the current MB V8s, you have 2 inlet and 1 outlet valves. For gas leaving the engine, the air is pushed out which is more efficient than sucking fresh air in.
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