Single Overhead Camshaft V8s

[LTC8K6]

That's a good engine but it's a little weird. That's the only SOHC engine I know that uses three valves per cylinder instead of 2.

Ford has a few of those, and didn't Honda use a SOHC with 4V V6's?

 

[ElFenix]

The only way a fuel injection system gets flooded is if the pressure regulator, injectors, or temperature sensor are faulty. You cannot build up excess fuel while starting, as the fuel is either ignited or pumped out the exhaust valve with each cycle of the cylinder. This isn't anything like a carb where you can pump the accelerator and keep shooting fuel into the intake manifold with or without cranking and regardless of actual air flow or RPM. Note that with fuel injection even if you pump the throttle while cranking, there is also a corresponding increase in air flow with each opening of the throttle and the computer will match it with the correct amount of fuel always.

my nissan 2.5L i4 would flood all the time. only happened after driving a very short distance. such as, if i backed it out of the garage and put it in the driveway. my workaround was to drive it around the block once. i guess it ran rich when cold and would have fuel left in the cylinder when turned off. it also had trouble starting the first time you cranked it. if you disengaged the key and then cranked it again it would always start immediately. local stealership never could find the problem.

 

[Raduque]

On cars with carburetors I would assume that its giving it fuel as soon as air starts getting sucked into the engine but on modern fuel injected cars I'm not sure if the car delays providing fuel until the engine reaches a certain rpm. Does anyone here know?

In my experience, carburated cars start faster than fuel injected cars. Every carbed car I've driven always started almost as soon as the key was turned, while every injected car seems to crank for 2-3 seconds before it starts. The only exception to this that I found was my old Accord - it took about a half-second between turning the key to "start" for the engine to actually be running on it's own.

 

[JeffreyLebowski]

Yes, but if the valves aren't operating when the car is turned off how can the gas/air be released into the combustion chamber?

I guess that's what the battery is for? But if the battery turns the engine, again, how does the proper ratio of gas/air enter the combustion chamber to move the pistons?

That's what the starter motor is for. It engages the flywheel, which is connected to the crank, which is connected to the connecting rods, which are connected to the pistons. the crank is also connected to a gear, which has a chain or belt that connects to the cam shafts. turning the starter turns everything else.

 

[exdeath]

In my experience, carburated cars start faster than fuel injected cars. Every carbed car I've driven always started almost as soon as the key was turned, while every injected car seems to crank for 2-3 seconds before it starts. The only exception to this that I found was my old Accord - it took about a half-second between turning the key to "start" for the engine to actually be running on it's own.

That is by design. A modern fuel injection car won't start the fuel pump/injectors until there is a steady oil pressure when cranking.

 

[exdeath]

my nissan 2.5L i4 would flood all the time. only happened after driving a very short distance. such as, if i backed it out of the garage and put it in the driveway. my workaround was to drive it around the block once. i guess it ran rich when cold and would have fuel left in the cylinder when turned off. it also had trouble starting the first time you cranked it. if you disengaged the key and then cranked it again it would always start immediately. local stealership never could find the problem.

Classically, flooding with a carb setup is large amounts of liquid fuel pooled up in a wet intake manifold, and is very hard, or at least time consuming, to flush out.

Fuel injection systems not only inject the proper amount of fuel at all times, they use dry intakes, with the fuel injected directly into the intake ports, meaning there is very little chance/place for fuel to pool up and collect. Even then, fuel injection has a parameter called "wall film compensation" or "tau" for the amount of fuel estimated to collect on the port walls in liquid form at various temperatures. Any "flooding" of a fuel injection system will just cycle out in a couple of cranks and you'll hardly even notice it.

Not quite the same thing as flooding a carb'ed engine where the intake manifold was completely wet in liquid fuel (shot in with each pump of the throttle regardless of cranking) and it could take anywhere from 5-15 minutes to clear it up.

 

[JulesMaximus]

That is by design. A modern fuel injection car won't start the fuel pump/injectors until there is a steady oil pressure when cranking.

My Mustangs always used to run the fuel pump before starting. You could hear it when you turned the ignition on. The fuel system pressurizes as soon as you turn on the ignition, maybe the injectors don't spray for one or two revolutions of the crank by design but the fuel system is always pressurized.

 

[LTC8K6]

The last 2 FI cars I have owned before this one both started before I could release the key. A simple bump of the starter would start them.

 

[SparkyJJO]

In my experience, carburated cars start faster than fuel injected cars. Every carbed car I've driven always started almost as soon as the key was turned, while every injected car seems to crank for 2-3 seconds before it starts. The only exception to this that I found was my old Accord - it took about a half-second between turning the key to "start" for the engine to actually be running on it's own.

Interesting. My 98 Camaro just takes a quick flick of the key and it starts right up. Probably fires within a half second.

Well, it does now anyway. I had a bad fuel pressure regulator at one point that made it take a few seconds of cranking for it to sputter to life

 

[JulesMaximus]

My motorcycle is fuel injected and starts at the slightest press of the start switch...and it has a relatively crude fuel injection system. It's like, press-bam and the engine is running.

 

[exdeath]

My Mustangs always used to run the fuel pump before starting. You could hear it when you turned the ignition on. The fuel system pressurizes as soon as you turn on the ignition, maybe the injectors don't spray for one or two revolutions of the crank by design but the fuel system is always pressurized.

Yours was (96 was it?) a conventional return system where the pump runs all the time completely out of control of any electronics loop. Later cars use returnless designs where the pump is pulse width modulated by the main computer. No injection = no change in rail pressure = no signal to pump either. Also most cars will prime the fuel system by turning the pump on, then off, in anticipation of upcoming use, but that doesn't mean it will start it again once you start cranking

Depends on the design of the system really, there are a million different EFI systems. Even with Ford/Mustang, each generation of EEC varies. Pretty sure the EEC-V on my car doesn't start fuel injection until there is oil pressure and a stable RPM signal from the crank/cam sensor. Some systems go so far as to also require a minimum airflow from the MAF otherwise it starts in limp mode, if at all.

At any rate, it's a possible reason for perceived delay starting a EFI car. Personally it's all over the board for me in any car. Sometimes it starts up instantly (and grinds the starter the moment you touch the key) as if a cylinder is already TDC, sometimes it takes cranking for 1-2 seconds.

 

[Pulsar]

That's a good engine but it's a little weird. That's the only SOHC engine I know that uses three valves per cylinder instead of 2.

Hardly wierd.... it's merely balancing what the engine needs in terms of air flow with what it costs to make it and the total area of the top of the piston.

4 Valves utilize dual OVC for each head. 3V's do not. So you get a ton of the benefit for far less price.

It's why the engine also made Ward's 10 best a number of years. That plus it's big brother the 5.4L 3V are sweet engines. I've having trouble placing which 4.6L is though, because that one has the front of the intake cut in half and it's easiest to tell from the intake throttlebody. I'd GUESS though that it's a mustang, because it appears that it should be dual-butterfly valve, and the mustang was the only 4.6L 3V with a dual valve.

Interesting fact: those cam covers are magnesium.

 

[JJ650]

http://news.google.com/newspapers?n...TkzAAAAIBAJ&sjid=HBQLAAAAIBAJ&pg=3012,1357638

haha Charleston's Postless Courier. Awful paper.

 

[LTC8K6]

Did anyone other than Honda make SOHC 4V engines?

 

[DivideBYZero]

Did anyone other than Honda make SOHC 4V engines?

The VW 24v VR6 is a SOHC 4 valve.

 

[angry hampster]

The VW 24v VR6 is a SOHC 4 valve.

Well, yes and no. It's only got one head so that's kind of a copout.

 

[LTC8K6]

One head + 2 cams = DOHC imo...

 

[Howard]

That's a good engine but it's a little weird. That's the only SOHC engine I know that uses three valves per cylinder instead of 2.

MB made a couple of them.

http://en.wikipedia.org/wiki/List_of_Mercedes-Benz_engines

 

[LordMorpheus]

Hardly wierd.... it's merely balancing what the engine needs in terms of air flow with what it costs to make it and the total area of the top of the piston.

4 Valves utilize dual OVC for each head. 3V's do not. So you get a ton of the benefit for far less price.

It's why the engine also made Ward's 10 best a number of years. That plus it's big brother the 5.4L 3V are sweet engines. I've having trouble placing which 4.6L is though, because that one has the front of the intake cut in half and it's easiest to tell from the intake throttlebody. I'd GUESS though that it's a mustang, because it appears that it should be dual-butterfly valve, and the mustang was the only 4.6L 3V with a dual valve.

Interesting fact: those cam covers are magnesium.

I know it's a good engine, I'm not saying it isn't - hell, I even like the older 2V version. I'm just pointing out that it's not representative of SOHC V8s.

 

[ElFenix]

Classically, flooding with a carb setup is large amounts of liquid fuel pooled up in a wet intake manifold, and is very hard, or at least time consuming, to flush out.

Fuel injection systems not only inject the proper amount of fuel at all times, they use dry intakes, with the fuel injected directly into the intake ports, meaning there is very little chance/place for fuel to pool up and collect. Even then, fuel injection has a parameter called "wall film compensation" or "tau" for the amount of fuel estimated to collect on the port walls in liquid form at various temperatures. Any "flooding" of a fuel injection system will just cycle out in a couple of cranks and you'll hardly even notice it.

well maybe that's why it required cranking twice so often

Not quite the same thing as flooding a carb'ed engine where the intake manifold was completely wet in liquid fuel (shot in with each pump of the throttle regardless of cranking) and it could take anywhere from 5-15 minutes to clear it up.

it could take five minutes of intermittent cranking with the accelerator floored and regular cranking to clear it out.

 

[PlasmaBomb]

One head + 2 cams = DOHC imo...

http://en.wikipedia.org/wiki/VR6_engine

According to the DOHC = cam for intake and cam for exhaust, it's a DOHC engine...

 

[LTC8K6]

well maybe that's why it required cranking twice so often



it could take five minutes of intermittent cranking with the accelerator floored and regular cranking to clear it out.

Dealer couldn't find the problem? Sounds like some lazy mechanics.

 

[DivideBYZero]

Well, yes and no. It's only got one head so that's kind of a copout.

Yeah, I know, I was going to state it was a DOHC of sorts, but I wasn't in the mood to argue with people. I had one.

 

[Raduque]

At any rate, it's a possible reason for perceived delay starting a EFI car. Personally it's all over the board for me in any car. Sometimes it starts up instantly (and grinds the starter the moment you touch the key) as if a cylinder is already TDC, sometimes it takes cranking for 1-2 seconds.

My latest car, 98 Altima, is very consistent. When cold it cranks for 3 seconds, every time, till it starts. When warm, it starts, to paraphrase "before I can release the key".

My dad's Solstice and my mom's Eclipse both crank for about 2 seconds, whether cold or warm, but my truck would always start on count of "1" after turning the key.

 

[ElFenix]

Dealer couldn't find the problem? Sounds like some lazy mechanics.

"we can't replicate your issue."

the service salesm... er, adviser, was standing right next to it as i started it and it did it. i shot him a dirty look and he shrugged at me.