Super quick starting LS?
Joined: Nov 2001
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From: Schiller Park, ILL Member: #317
I assume this would be different with an electric fuel pump? I've never used a carb with anything but a mechanical pump, which obviously requires engine revolution to build pressure. When an e-pump is used with a carb, I imagine the bowls are filled immediately during "key-on" (unless operated separately with a switch)? Of course, the accelerator pump would still need manual operation prior to cranking if you want the engine to start (cold).
It could probably be possible to start a bit faster than shown in the video but, for all the reasons already mentioned, it will never fire as quick as a carb'ed + distributor setup that's up to temp and running well.
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From: Nebraska, The Good Life
Correct, but I'm not entirely sure this is a "downside". That extra cranking to fill the fuel bowl(s) is normally enough to circulate oil into places that haven't seen any in quite some time if the engine has been sitting for weeks/months, so I don't really see this as a problem - especially for a non-daily driver (which is likely the case if the car ever sits that long in the first place).
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From: Nebraska, The Good Life
This is funny. You see it sitting on the dyno? It was tuned. If you like, skip forward to about 1:12 where it was started again with a few more tweaks to the tune (now with exhaust and not open headers), same thing, it cranks a bit before it starts. Always has. My 04/LS1 does the same thing, even cranks just a little longer than the LS2 does. Same thing when they were stock, same thing after they were tuned.
Joined: Apr 2006
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From: Grand Rapids, Michigan
Funny you say that... I have a buddy who years ago had a 406 small block in a mud truck that needed a shot of nitrous to start, and let me tell you, it started QUICK! This engine also had 6" AND 5.7" rods due to it being pieced together from a couple blown up engines... The crazy things we did back then 
Funny you say that... I have a buddy who years ago had a 406 small block in a mud truck that needed a shot of nitrous to start, and let me tell you, it started QUICK! This engine also had 6" AND 5.7" rods due to it being pieced together from a couple blown up engines... The crazy things we did back then
Joined: Apr 2006
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From: Grand Rapids, Michigan
I know how nitrous functions, lol. All I know is what I saw... crank crank crank, a few sputters, hit the button and zoom, came to life. Maybe it was the fuel side helping out. Still was funny to watch.
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With my 02 (factory LS1), if it heard my keys jingling, it would practically start, lol... half crank was all it needed, but after I dropped the engine, to do a rear main, and some freshen ups, now the first turn of the key acts like a primer and then the second fires it up. I miss the quick start 
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Y'all DONT KNOW DO YA?
The reason you hear FOUR compression strokes when you crank a MODERN V8 EFI ENGINE is because you have a CAM SENSOR and CRANK POSITION SENSOR, the first FULL REVOLUTION of the engine there is NO FUEL COMING OUT OF YOUR INJECTORS while the computer counts hits and maps the position of where the engine parts are relative to each other. THEN it gives you fuel on the FIFTH compression stroke. It has to do this because as we all know the cam spins half as fast as the crank so it needs a full rotation of the crank to determine where everything is.
An old engine with a carburetor and distributor would have fuel and spark on the FIRST COMPRESSION STROKE, only needs to turn half turn or less to start.
If you had one of the cams with 4 notches on its position sensor, technically you can get it to fire a hair sooner on the starter, but that's something I have no personal experience with.
One thing to know is that if you have a heavy flywheel or a big automatic transmission torque converter bolted onto your engine, that can slow the cranking. I swapped my old mustang to a light clutch and it cranks a lot faster, but still needs a full revolution of the engine to fire.
The reason you hear FOUR compression strokes when you crank a MODERN V8 EFI ENGINE is because you have a CAM SENSOR and CRANK POSITION SENSOR, the first FULL REVOLUTION of the engine there is NO FUEL COMING OUT OF YOUR INJECTORS while the computer counts hits and maps the position of where the engine parts are relative to each other. THEN it gives you fuel on the FIFTH compression stroke. It has to do this because as we all know the cam spins half as fast as the crank so it needs a full rotation of the crank to determine where everything is.
An old engine with a carburetor and distributor would have fuel and spark on the FIRST COMPRESSION STROKE, only needs to turn half turn or less to start.
If you had one of the cams with 4 notches on its position sensor, technically you can get it to fire a hair sooner on the starter, but that's something I have no personal experience with.
One thing to know is that if you have a heavy flywheel or a big automatic transmission torque converter bolted onto your engine, that can slow the cranking. I swapped my old mustang to a light clutch and it cranks a lot faster, but still needs a full revolution of the engine to fire.
Joined: Nov 2001
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From: Schiller Park, ILL Member: #317
The issue seems to be that some folks just haven't experienced the difference (i.e. limited/no experience with well tuned carb'ed/dist. engines and how quickly they can restart when hot) therefore, to them, an SEFI LS1 is as "quick starting" as it can get.
In other words, one doesn't know what one doesn't know.
In other words, one doesn't know what one doesn't know.
Lol, I actually had to cal out these instant starts at Chrysler. Or moreso the symptom that causes that instant start in older engines. The reason is the availability of fuel vapor waiting in the manifold. As mentioned below, crank sync is needed before injection on modern EFI, but only for start consistency reasons. Customers like being able to expect the same exact start, everywhere, every time. Fuel from a hot carb application (or in my case, a highly active purge system) prior to shutdown allows for fuel to be in cylinder at the first closing of an intake valve after you hit the key for a hot restart. Produces a nice quick start.....sometimes. Too much or too little fuel though, and start consistency is affected, making a customer bring the car to the dealer with a complaint. EFI fixes that by the nature of having controlled fuel delivery, but also by delaying injection until some calibratable condition...typically a desired cranking RPM when warm.
If you're dying for a super fast hot restart with EFI, find a way to keep that evap solenoid open after you shut the engine down. Might have some mixed results though lol
If you're dying for a super fast hot restart with EFI, find a way to keep that evap solenoid open after you shut the engine down. Might have some mixed results though lol
Yes, a previously cranked/warmed up properly tuned carb'd engine will "insta-start" as OP mentioned with a mild bump of the key 🔑. My 72 Vette did with the Lars tuned Q-jet & the current Demon. If the carb'd car's sat for a week or it's cold that initial start won't be an "insta-start" in my experience.
However, running around town making a half dozen stops, it is pretty cool how "intuitive" the good carb car starts...almost like the car responds enthusiastically to your will with a bump rather than a turn & hold key, spin & then crank.
Overall, I much prefer the EFI start experiance overall, especially on colder days if a car has sat for a month...but on a sweer summer day, making a lot of stops and brief trips...there's charm to a good carb'd set up.
However, running around town making a half dozen stops, it is pretty cool how "intuitive" the good carb car starts...almost like the car responds enthusiastically to your will with a bump rather than a turn & hold key, spin & then crank.
Overall, I much prefer the EFI start experiance overall, especially on colder days if a car has sat for a month...but on a sweer summer day, making a lot of stops and brief trips...there's charm to a good carb'd set up.
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From: Nebraska, The Good Life
I assume this is the case too for many if not all other LS vehicles.
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Actually I can't speak for ALL LS vehicles, but on the GTOs you don't have to hold the key until it starts. Just turn the key briefly to START and let go. It will crank by itself until it starts. If it happens to not fire, it will stop cranking by itself after a few seconds of cranking (or you can turn the key off to stop it manually).
I assume this is the case too for many if not all other LS vehicles.
I assume this is the case too for many if not all other LS vehicles.
Joined: Nov 2001
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From: Schiller Park, ILL Member: #317
LS1 F-body can't do an automated crank. The B+ side of the start relay field coil is literally hard-wired to the Start position of the key switch. The relay cannot operate without key switch in Start position.
The BCM (Body Control Module) controls the B- side of the field coil and it can interrupt the starter relay for the security system, but it cannot energize the relay on its own to do an automated crank.
The BCM (Body Control Module) controls the B- side of the field coil and it can interrupt the starter relay for the security system, but it cannot energize the relay on its own to do an automated crank.