Loki: I think the popping and noises you hear are more a factor of the design of the exhaust system rather that any lean at engine braking.
The only way i can think to describe what i mean is the newest technology on modern cars actually cuts off the fuel completely when coasting is happening. It turns the injectors off and leaves no fuel going into the cylinders when your say... going down a hill or something!! It causes no harm to the bores or valves or anything as there is no heat pbeing produced that needs to be cooled by the fuel, and the bores are still being lubed by the oil down bottom...
During engine braking the only fuel that could be coming in is from the carbies idle circuit and that wouldnt be enough to worry about. Yes it would be lean, but again its more vaccum than anything as no air OR fuel is being admitted to the engine past those butterflies! THe only time a lean condition is a problem is under massive load and power output when everything is running humungously hot. The vaccum created under engine braking woudlnt allow any piston or bore damage due to lean-engine braking condition.
That's how i understand it anyhow, and i'd be happy to be corrected if i'm wrong.
I understand where you mean keeping on light throttle to maintain speed will cost fuel, but that doesnt correlate with neutral idle coasting either, If your maintaining a speed your burning fuel! And again as i suggested a propperly tuned carby and ignition system would minimise your costs in these easy-running conditions!
Cheers mate, and thanks for the good way of putting your thoughts across.
Neutral Coasting + auto
Started by
_Loki_
, Jul 10 2006 12:04 AM
51 replies to this topic
#26
Tiny
-
- Administrators
-
- 10,018 posts
Oh My, Don't you post alot
- Name:Tiny
- Location:Sydney
- Joined: 04-February 07
Posted 11 July 2006 - 04:41 PM
#27
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 11 July 2006 - 07:06 PM
I believe the point I've made is very relevant to the thread.....well, it was originally just whether damage could be done to the gearbox......and I'll state it again perhaps more clearly:if we were talking new cars then i'd agree with you.
if i'm driving an auto i prefer the little engine braking the old g'boxes give.
i belive it gives you that little more control ova the car.
and devils the reason i'm having a go at you is cause your arguing with everyone based on new car specs which i fell is irelivant to this thread.
cheers tom
If its standard practice in new cars to provide auto gearboxes that basically coast in neutral when one lifts there foot off the accelerator there can be little credence in claiming that it would be dangerous to be coasting in neutral in an older car, authorities would have banned them(the new cars) because the driver doesn't have as much control. I feel this word 'control' is bandied around a little too, "I prefer to have more control over the care etc", why not say i just prefer to have the car slow down a bit when I lift my foot off the accelerator......that's the only difference. I personally prefer this as well when im driving the car through heavy traffic or mountain country, but frequently use the coast in neutral when it is appropriate.
Re the idle circuit.....Im definitely not an expert here(dont hesitate to correct me...Im sure there is someone here who lives and breathes carbys), but my understanding is this. In a fixed venturi carby the idle jet is below the throttle opening. The volume of fuel that gets drawn from this jet depends on the amount of air getting past the throttle when it is closed, it cant totally block of the intake, there is no independent air supply for the idle jet.
If the motor spins faster more air will be drawn past the closed throttle, taking more fuel from the idle jet with it. If this didnt happen, the mixture at idle would vary widely depending on the actual load on the engine. Also idle speed is generally set by controlling the opening on the main throttle valve, hence an engine idling slower will use less fuel.....whether it is slowed by closing of the throttle or extra load placed on it by the transmission etc.
I have no idea on how much extra fuel this would drag through when on engine overun at 3000rpm etc, perhaps the idle jet having a fixed limit .
Edited by devilsadvocate, 11 July 2006 - 07:16 PM.
#28
_mike_nofx_
_mike_nofx_
-
- Guests
Posted 11 July 2006 - 07:28 PM
I would say neutral downhill would use no less fuel.
Sure the engine is turning over faster, but no more fuel is going in, its being PUSHED. Just like if you were to turn the engine completely off, but leave it in, say 5th in a manual and coast downhill. Yeah the engines turning over, but is it using fuel?
It also saves on brake pads! Plus no lost brakes down steep hills. neutraling down hill will require frequent braking. (Dont tell me you found the 'perfect' downhill which keeps your speed at a constant 100-110km/h)
Also, if i coast in neutral downhill, and around a corner, it feels a lot more likely to understeer, and it just feels less stuck to the road for some reason.
Just turn your engine completely off for those 5kms downhill. (Watch for steering lock)
Thats my $2 (Cents are so 1990)
Sure the engine is turning over faster, but no more fuel is going in, its being PUSHED. Just like if you were to turn the engine completely off, but leave it in, say 5th in a manual and coast downhill. Yeah the engines turning over, but is it using fuel?
It also saves on brake pads! Plus no lost brakes down steep hills. neutraling down hill will require frequent braking. (Dont tell me you found the 'perfect' downhill which keeps your speed at a constant 100-110km/h)
Also, if i coast in neutral downhill, and around a corner, it feels a lot more likely to understeer, and it just feels less stuck to the road for some reason.
Just turn your engine completely off for those 5kms downhill. (Watch for steering lock)
Thats my $2 (Cents are so 1990)
#29
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 11 July 2006 - 08:04 PM
I think we have all heard the stories of how cars towed in gear manage to empty their petrol tanks.......possibly a myth? , but would also think that more fuel has to be sucked from the main venturi when the motor spins faster, the closed throttle still allowing more air to be drawn into the motor.
Tiny, Im not sure that manifold vacuum has a significant retardation effect, it would be mainly the compression stroke.
Tiny, Im not sure that manifold vacuum has a significant retardation effect, it would be mainly the compression stroke.
#31
Tiny
-
- Administrators
-
- 10,018 posts
Oh My, Don't you post alot
- Name:Tiny
- Location:Sydney
- Joined: 04-February 07
Posted 11 July 2006 - 09:48 PM
Compression stoke is definitely what causes the braking however the intake stroke would cause a pretty large vaccum in the intake.. Not the cause of the braking, but not enough to draw anythign more than the idle fuel circuit and air bypass can feed.
If the butterflies are closed than no more air could POSSIBLY be going in otherwise the engine would produce more power and therefore increase in speed ( or loose engine braking...)
Anyway.. We're getting pretty far off topic here.. I've given myopinion and backed it up with my reasoning so i think i'll leave it at that!
Cheers!
If the butterflies are closed than no more air could POSSIBLY be going in otherwise the engine would produce more power and therefore increase in speed ( or loose engine braking...)
Anyway.. We're getting pretty far off topic here.. I've given myopinion and backed it up with my reasoning so i think i'll leave it at that!
Cheers!
#32
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 11 July 2006 - 10:20 PM
If you have secondary butterflies perhaps they can be completely closed, but for a single barrel carby the main throttle or butterfly restricts(not stops)air from entering the motor, otherwise it wouldnt be able to idle.If the butterflies are closed than no more air could POSSIBLY be going in otherwise the engine would produce more power and therefore increase in speed ( or loose engine braking...)
Ive actually cut the fuel while under engine braking and it does make quite a bit of difference to the effect, hard to say whether its due to just the absence of the idle power or the extra fuel(by my reckoning) that would be sucked through the throttle.
#33
rodomo
-
- Members
-
- 18,042 posts
To advertise here, call 13TORANA
- Name:R - O - B Dammit!
- Location:Way out west of Melbourne Awstraylya
- Joined: 10-December 05
Posted 12 July 2006 - 12:05 AM
Points to ponder:
Air speed through the venturi is what is required to draw fuel from the discharge nozzle. Little air speed with butterfies closed.
Vacuum + compression = little pressure.
Air speed through the venturi is what is required to draw fuel from the discharge nozzle. Little air speed with butterfies closed.
Vacuum + compression = little pressure.
Edited by rodomo, 12 July 2006 - 12:06 AM.
#34
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 12 July 2006 - 02:24 AM
Not sure what this is referring to?compression in the cylinders?Vacuum + compression = little pressure
Yes there is "little" air flow when the butterflies are closed, but wont that little amount be proportionally bigger as the motor spins faster?
#35
TerrA LX
-
- Members
-
- 14,241 posts
Fulcrum Fixture
- Location:Sid 'n' knee
- Joined: 31-May 06
Posted 12 July 2006 - 05:33 AM
with the throttle closed on a carb, the idle passage takes over. this is a seperate system to the main which mixes its own air/fuel. this passage has a take off hole above the butterfly and travels internally thru the carb then exites below the butterfly. this idle passage contains a mixture screw that you use to enrichen or lean out your idle. if the butterflys were open past the transfer slot then the main metering of the carb would take over, and you will not be able to adjust the idle vie the mixture screw.
so in closing the vehicle would have to use less fuel if the throttle was closed.
shifting to neutral would also use less fuel if you had to otherwise open the throttle to maintain speed.
if this is good for the Th350, well i really dont know enough about auto's, whish i did tho, i reon it's a licence to print money.
my head hurts.
this thread is dead.
i'm going to bed.
so in closing the vehicle would have to use less fuel if the throttle was closed.
shifting to neutral would also use less fuel if you had to otherwise open the throttle to maintain speed.
if this is good for the Th350, well i really dont know enough about auto's, whish i did tho, i reon it's a licence to print money.
my head hurts.
this thread is dead.
i'm going to bed.
#36
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 12 July 2006 - 07:46 AM
Excellent ^, my "basic" idea of a carby didnt go this far. So where is the idle air passage that bypasses the throttle on a basic strommy.......I dont have one to look at.....
The only other thing that puzzles me is that the idle stop solenoid on a basic strommy controls the throttle valve, the throttle valve is partially open when the engine is at idle, if the throttle valve is fully closed then the engine dies instantly indicating it is relying on air going past the throttle at idle.
The only other thing that puzzles me is that the idle stop solenoid on a basic strommy controls the throttle valve, the throttle valve is partially open when the engine is at idle, if the throttle valve is fully closed then the engine dies instantly indicating it is relying on air going past the throttle at idle.
#37
_Lostit_
_Lostit_
-
- Guests
Posted 12 July 2006 - 08:44 AM
Not sure you worried about damaging the auto or just trying to save on juice?
Damaging a auto ? i guess probadly not but the car companies didnt spent millions of dollars , researching for someone to put a auto into neutral coasting along /shurg.
As for saving money coasting, well sell the old technology and buy a modern small car, it will most probadly go faster, more comfort , and get better fuel economy even when you cruiise in neutral ) .One of the guys at work has one of those VW Disesl turbo shit he gets 800km per tank in the city and bloody that has some go in it.
Lostit
Damaging a auto ? i guess probadly not but the car companies didnt spent millions of dollars , researching for someone to put a auto into neutral coasting along /shurg.
As for saving money coasting, well sell the old technology and buy a modern small car, it will most probadly go faster, more comfort , and get better fuel economy even when you cruiise in neutral ) .One of the guys at work has one of those VW Disesl turbo shit he gets 800km per tank in the city and bloody that has some go in it.
Lostit
#38
TerrA LX
-
- Members
-
- 14,241 posts
Fulcrum Fixture
- Location:Sid 'n' knee
- Joined: 31-May 06
Posted 12 July 2006 - 01:46 PM
^^ there is no puzzle, either the main system is functioning or the throttle is closed and the idle system is supplying fuel. slightly open will not create enough vaccume to engage the main system so the idle system will still function.
idle system is located on the fuel bowl side to collect fuel.
solenoid opens the butterfly just like you would fast idle a car with your foot on the accelerator pedal (idle system no longer functioning).
i still missed the point, is it bad for the auto or not.
idle system is located on the fuel bowl side to collect fuel.
solenoid opens the butterfly just like you would fast idle a car with your foot on the accelerator pedal (idle system no longer functioning).
i still missed the point, is it bad for the auto or not.
Edited by ALX76, 12 July 2006 - 01:50 PM.
#39
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 12 July 2006 - 02:58 PM
Sorry, I still dont get it. On a basic holden strommy completely closing the throttle will stop the motor ...that will happen, does that mean there is no separate idle air supply circuit?^^ there is no puzzle, either the main system is functioning or the throttle is closed and the idle system is supplying fuel. slightly open will not create enough vaccume to engage the main system so the idle system will still function.
#40
rodomo
-
- Members
-
- 18,042 posts
To advertise here, call 13TORANA
- Name:R - O - B Dammit!
- Location:Way out west of Melbourne Awstraylya
- Joined: 10-December 05
Posted 12 July 2006 - 06:47 PM
You are correct. Closing the butterfly will stop the engine (provided there are no other vacuum leaks). What the UC 202 has is a base idle screw and an idle solenoid to control idle. The base idle screws main function is ensure the butterfly doesn't jam shut. On earlier Holdens it was the idle adjustment. With the idle solenoid, this was introduced to avoid running on due to leaner mixtures and resulting higher idle. The solenoid is activated by the ignition and turns off with the ignition. If you look down the throat of the carby and hold the rpm at about 2000 you will see fuel coming from the discharge nozzle which is feeding from the main jet. If you snap the throttle shut against the idle solenoid, you will see this discharge stop instantly but the motor will still idle. The fuel is now being delivered below the butterfly from the idle discharge port, adjacent to the mixture screw.Sorry, I still dont get it. On a basic holden strommy completely closing the throttle will stop the motor ...that will happen, does that mean there is no separate idle air supply circuit?^^ there is no puzzle, either the main system is functioning or the throttle is closed and the idle system is supplying fuel. slightly open will not create enough vaccume to engage the main system so the idle system will still function.
With the vacuum question, under deceleration the engine creates high vacuum.
What I was getting at if there is already a partial vacuum in the cylinder and you compress it, you end up with less compression at "those" revs. than you would at idle.
I had a mate with a 202 that he had run low on oil to many times. It developed a miss and on compression test we found no compression on No.3. The fault was worn cam lobes and dished lifter bases to the point that the valves no longer opened. It was creating vacuum on the down stroke and returning virually to atmospheric pressure on the up stroke resulting in near 0 compression reading. He has no money (the reason it never had any oil in it)so we just replaced the 2 lifters and it ran on 6 again.
#41
TerrA LX
-
- Members
-
- 14,241 posts
Fulcrum Fixture
- Location:Sid 'n' knee
- Joined: 31-May 06
Posted 12 July 2006 - 07:00 PM
i think i may have been a little misleading on the idle thing, i am not talking any speciffic carb here, just the principal, fuel is usually fed at idle thru a seperate system to the main. the butterfly opening (around 40thou) and its adjustment screw is used as a means of idle speed adjustment. if this adjustment is taken out too far then the idle system becomes redundant and the main system starts to feed.
hows that gear box going? wouldn't coasting down hill overspeed the servo or something?
hows that gear box going? wouldn't coasting down hill overspeed the servo or something?
#42
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 12 July 2006 - 07:02 PM
Thanks Rodomo for your reply. As I understand it the main difference between an emission control strommy is that the idle solenoid will close the throttle completely on shutdown and that the mixture screws were meant to be tamper proof.....other than that they are the same beast.
You havent quite gone as far as to say whether there is an air feed independent of the main throttle for the idle circuit, but you describe it as basic in that the throttle controls the idle........so reading between the lines are you saying that what alx76 describes:
You havent quite gone as far as to say whether there is an air feed independent of the main throttle for the idle circuit, but you describe it as basic in that the throttle controls the idle........so reading between the lines are you saying that what alx76 describes:
is not part of a basic holden strommy?with the throttle closed on a carb, the idle passage takes over. this is a seperate system to the main which mixes its own air/fuel.
#43
TerrA LX
-
- Members
-
- 14,241 posts
Fulcrum Fixture
- Location:Sid 'n' knee
- Joined: 31-May 06
Posted 12 July 2006 - 07:22 PM
^ this may be correct as i believe strommies take fuel from the main needle jet and are even more so dependant on throttle position and mixture screw position, get these wrong and you suffer increased fuel consumption and or stumble on off idle accelleration.
the principal is still the same.
the principal is still the same.
Edited by ALX76, 12 July 2006 - 07:22 PM.
#44
rodomo
-
- Members
-
- 18,042 posts
To advertise here, call 13TORANA
- Name:R - O - B Dammit!
- Location:Way out west of Melbourne Awstraylya
- Joined: 10-December 05
Posted 13 July 2006 - 12:39 AM
No the idle solenoid only shuts the idle speed down to the base idle screw setting which is like the old idle screw near where the cable fits on. This base idle screw is set at around 450-500 rpm. The mixture screws were plugged from the factory but are by no means "tamper proof" and quite often adjusted to compensate for poor idle quality due to incorrect timing, vacuum leaks, worn valve guides etc. If the butterfy is shut off, fuel won't be drawn from the idle discharge at the mixture screw as it needs air by-passing the near closed butterfly acting as a venturi to draw the fuel. ALX76 is correct as the idle mixture effects the main jet "trimming" to a degree.
Edited by rodomo, 13 July 2006 - 12:42 AM.
#45
rodomo
-
- Members
-
- 18,042 posts
To advertise here, call 13TORANA
- Name:R - O - B Dammit!
- Location:Way out west of Melbourne Awstraylya
- Joined: 10-December 05
Posted 13 July 2006 - 12:57 AM
The Varijet uses a separate circuit for idle and has a big screw into the airflow of this circuit to adjust idle speed. It also has a solenoid in the air passage that is ignition operated to shut the passage (thus stopping the airflow) to avoid running on. The circuit runs around the butterfly and the big screw adjusts the airflow in this circuit as well as a smaller idle mixture screw which controls the fuel in this circuit. It is more accurate than the solenoid as it does not act on linkages that can wear. Most EFI applications use the same "air by-pass" type of circuit to adjust idle (and maintain idle using stepper motors) rather than adjust the butterfly and upset throttle position sensor settings
Edited by rodomo, 13 July 2006 - 01:11 AM.
#46
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 13 July 2006 - 07:18 AM
Ok, so I was correct in stating that a basic venturi carby such as the strommy has no separate air feed for idle circuit? and since the throtte valve is always partially open at idle, as the motor spins faster on overrun air more air will be drawn through here drawing more fuel from the idle jet and most likely more fuel from the main venturi as well at 3000rpm etc.
Of more interest to me anyway is the throttle position in relation to affect of compression inside the motor. If max engine braking is desired one should cut the fuel and open the throttle fully?
Of more interest to me anyway is the throttle position in relation to affect of compression inside the motor. If max engine braking is desired one should cut the fuel and open the throttle fully?
Edited by devilsadvocate, 13 July 2006 - 07:23 AM.
#47
Dr Terry
-
- Moderators
-
- 3,325 posts
Technical + Numbers Guru + Moderator
- Location:Eastwood (Sydney) NSW
- Joined: 13-November 05
Posted 13 July 2006 - 10:24 AM
Hi Guys.
rodomo said
" It also has a solenoid in the air passage that is ignition operated to shut the passage (thus stopping the airflow) to avoid running on. "
In a Varajet the solenoid shuts off the idle fuel supply, not the air.
Good point devils !! I've never thought about it that way, but it could be. If the compression is what gives you engine braking, & you do get slightly more air to compress if the throttle is open. You do when you are doing a static compression test, you may get more engine breaking that way. The only problem I can see is that you can do this on an EFI car but not a carby car. If you switch the ignition off on a carby car, & open the throttle on a warm motor, it will 'diesel' or run-on. You will then probably go faster, not slower.
Dr Terry.
rodomo said
" It also has a solenoid in the air passage that is ignition operated to shut the passage (thus stopping the airflow) to avoid running on. "
In a Varajet the solenoid shuts off the idle fuel supply, not the air.
Good point devils !! I've never thought about it that way, but it could be. If the compression is what gives you engine braking, & you do get slightly more air to compress if the throttle is open. You do when you are doing a static compression test, you may get more engine breaking that way. The only problem I can see is that you can do this on an EFI car but not a carby car. If you switch the ignition off on a carby car, & open the throttle on a warm motor, it will 'diesel' or run-on. You will then probably go faster, not slower.
Dr Terry.
#48
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 13 July 2006 - 11:17 AM
Id be cutting the fuel, easy to do with lpg. Will give it a try soon and see how much difference it makes.If you switch the ignition off on a carby car, & open the throttle on a warm motor, it will 'diesel' or run-on. You will then probably go faster, not slower.
#49
Dr Terry
-
- Moderators
-
- 3,325 posts
Technical + Numbers Guru + Moderator
- Location:Eastwood (Sydney) NSW
- Joined: 13-November 05
Posted 13 July 2006 - 03:04 PM
Hi devils.
you said
"Id be cutting the fuel, easy to do with lpg. Will give it a try soon and see how much difference it makes. "
My point precisely, on a carby car if you cut the fuel, say with a solenoid in the line, you still have a carby bowl full of fuel, it will continue to run, so you can't do a nice clean comparison.
Dr Terry.
you said
"Id be cutting the fuel, easy to do with lpg. Will give it a try soon and see how much difference it makes. "
My point precisely, on a carby car if you cut the fuel, say with a solenoid in the line, you still have a carby bowl full of fuel, it will continue to run, so you can't do a nice clean comparison.
Dr Terry.
#50
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 13 July 2006 - 04:22 PM
Yes, agree with above, and yes I meant cutting the fuel, Id be doing that in my car by turning off the solenoid for the lpg, which kills the motor at idle in less than half a sec.
Edited by devilsadvocate, 13 July 2006 - 04:34 PM.
0 user(s) are reading this topic
0 members, 0 guests, 0 anonymous users
