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Engine roars up to 1.5 rpm on cold start, is this normal?
 

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It’s to heat up the cats quickly and it settles down shortly after. All new vehicles do it.
 

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Yes. Normal. As far back as I can recall back at least to my '96 Mustang, upon engine start the engine RPMs "zoom" up to about 1.5K then drop to a faster than normal idle speed for a while. With some cars the fast idle drops to normal idle speed when the secondary air injection system shuts down and the engine controller is able to go into closed loop mode.

The engine speed initially goes up to help ensure the gear oil pump primes and to get oil flowing to the engine ASAP. Gear pumps are not very efficient at slow speeds and the engine starter probably only cranks the engine to around 75 RPMs. It only takes one cylinder going through a good intake/power stroke to get the engine running. (Any one who has kick started a motorcycle engine and I kick started a number of different engines from a 90cc dirt bike to a 1000cc Harley Davidson Sportster) knows it just takes one good crank to get the engine running.)

Additionally the higher RPMs help ensure the residual oil in the bearings forms a hydrodynamic bearing (a wedge of oil) that prevents metal to metal contact. This residual oil suffices until the oil from the gear pump arrives.

Normal but important. Generally I let the engine idle until the RPMs drop. This is a sign -- as I touched upon above -- the engine controller is in closed loop mode and is able to more precisely fuel the engine.
 

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Yes. Normal. As far back as I can recall back at least to my '96 Mustang, upon engine start the engine RPMs "zoom" up to about 1.5K then drop to a faster than normal idle speed for a while. With some cars the fast idle drops to normal idle speed when the secondary air injection system shuts down and the engine controller is able to go into closed loop mode.

The engine speed initially goes up to help ensure the gear oil pump primes and to get oil flowing to the engine ASAP. Gear pumps are not very efficient at slow speeds and the engine starter probably only cranks the engine to around 75 RPMs. It only takes one cylinder going through a good intake/power stroke to get the engine running. (Any one who has kick started a motorcycle engine and I kick started a number of different engines from a 90cc dirt bike to a 1000cc Harley Davidson Sportster) knows it just takes one good crank to get the engine running.)

Additionally the higher RPMs help ensure the residual oil in the bearings forms a hydrodynamic bearing (a wedge of oil) that prevents metal to metal contact. This residual oil suffices until the oil from the gear pump arrives.

Normal but important. Generally I let the engine idle until the RPMs drop. This is a sign -- as I touched upon above -- the engine controller is in closed loop mode and is able to more precisely fuel the engine.
When I first fire mine up, I don't touch the gas pedal or move the car at all until it settles back down to a normal idle.

I'm gonna let the computer take care of all the important startup stuff as designed.
 

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That's pretty much what I do, unless the engine is warm. My timer as to how long I wait is when the RPMs fall back down to near normal idle speed.

My experience with my cars has been that waiting the seconds until the RPMs fall the engine is just a bit more tractable probably because the engine controller is in closed loop mode and fueling is more precise. Doesn't take long and gives me time to fasten my seat belt and run through a mental checklist to make sure I have everything and last but not least to make sure the engine is running ok.
 

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It’s to heat up the cats quickly and it settles down shortly after. All new vehicles do it.
To some extent but the converters are heated up mainly because the engine controller supplies excess fuel and the air injection system injects air into the exhaust to provide the air needed for the rich exhaust mixture to burn in the exhaust and this supplies extra eat to get the converters hot quicker.

Don't hear this so much -- in fact I don't think I've ever heard it -- with my HC or JCW but with my 996 Turbo I'd hear faint backfires from the exhaust system during when the RPMs were elevated.

The converters heat up pretty quick as do the O2 sensors. Occasionally I'd monitor the OBD status with my OBD2 reader and concurrent with the RPMs dropping the secondary air status would switch from downstream to atmosphere (essentially it would shut off) and the OBD status would switch from open loop to closed loop mode. This was an indication the O2 sensors at least were up to temperature. The converters were probably up to temperature too as the #2 sensor readings were as I expected them to be, signaling no excess oxygen in the exhaust from the converters. A sure sign this oxygen was being consumed in the converters.
 

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This is why so many exhaust videos are "cold start" videos

A Guy
 

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To some extent but the converters are heated up mainly because the engine controller supplies excess fuel and the air injection system injects air into the exhaust to provide the air needed for the rich exhaust mixture to burn in the exhaust and this supplies extra eat to get the converters hot quicker.

Don't hear this so much -- in fact I don't think I've ever heard it -- with my HC or JCW but with my 996 Turbo I'd hear faint backfires from the exhaust system during when the RPMs were elevated.

The converters heat up pretty quick as do the O2 sensors. Occasionally I'd monitor the OBD status with my OBD2 reader and concurrent with the RPMs dropping the secondary air status would switch from downstream to atmosphere (essentially it would shut off) and the OBD status would switch from open loop to closed loop mode. This was an indication the O2 sensors at least were up to temperature. The converters were probably up to temperature too as the #2 sensor readings were as I expected them to be, signaling no excess oxygen in the exhaust from the converters. A sure sign this oxygen was being consumed in the converters.
Its the only reason I’ve been given as an answer to this question and the same answer I’ve seen in any forum when the subject arose.
 

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The initial run up in RPMs is for the oil pump and the formation of the hydrodynamic bearings I mentioned. The prolonged higher than normal idle does help the converters/sensors warm up quicker. Didn't mean to imply it didn't play a role. But the warm up is not all just idle speed. It is in combination with the extra fuel and extra air that is injected into the exhaust by the secondary air injection system.
 

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I can confirm that my neighbors are not a fan of this feature when I leave at 5am every morning.
 

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I can confirm that my neighbors are not a fan of this feature when I leave at 5am every morning.
I hear ya! And so do my neighbors! I leave for work at 6am and its still dark and calm out. Everyone of my neighbors know when I left for work. Sometimes I forgot to close my cut outs from the night before and I can't close them fast enough.!!
 
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Know what you mean. Every time I start my Hellcat I cringe as the initial run up and exhaust sound is loud. My car is parked nose first into my assigned carport and the back of the car points right at some apartments just across the driveway from the carport.

A mitigating factor is I seldom start the engine early as I do not leave for work until 9am or even a bit later.

But for the sake of remaining on good terms with the other residents most of the time shortly after engine start I shift into reverse which tends to drop RPMs and quiets the exhaust considerably.

I park it at this carport as it is the furthest from my apartment so I'm less likely to drive the Hellcat stopping off instead at the JCW which is parked closer to my apartment in my 2nd assigned car port.

But the JCW car port has the back of the car pointed away from apartments with nothing behind the JCW but a large lawn that is part of a church's property. I could switch cars and carports but then the Hellcat would be handier.
 

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The reality of the loud start ups in the morning............my neighbor has told me that he loves my car and wishes he had one.:grin2:
 
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