Great info/reading - Displacement on Demand and more. (LONG)
09-24-2005, 07:09 PM
#1
Moderator
Thread Starter
Join Date: Jul 1999
Location: Tempe, AZ
Posts: 2,184
Likes: 0
Received 0 Likes
on
0 Posts
Car: 92 RS, 02 Tacoma, 2 73 Porsche 914s
Great info/reading - Displacement on Demand and more. (LONG)
interesting reading from another board. cut a bit. all started from a gasoline post and talking about the new gm displacement on demand getting 28mpg in the new impala.
I'm new to the group, but you're on a topic I know something about.
Warning: long boring post to follow: Read only if you want to know more than absoutely necessary about cylinder deactivation.
(I was the Engineering Supervisor for the Delphi Valve Train group when we developed the cylinder deactivation system used by GM.)
The old Cadillac system used an electric rotary actuator on top of the rocker arms. We found a '82 Seville with a V8-6-4 when we started working on the new system in '99, and it was still working fine. Must have been the only one left. Putting electrical connections under the valve covers is generally a bad idea. Someone mentioned the Mercedes. Their V8 and V12 were the first of the 'modern' systems (I think in '99), and was very complicated. Big surprise. It's very tough to switch off the valves in an overhead cam engine. It has a very expensive, high pressure valve asm. You've only got the rockers to do it in, and it's hard to get the right oil circuits to your hydraulic actuators (inside the rockers!). Honda have also done it this way. You need a pivot shaft running down the length of the head so the rockers stay in perfect alignment and for the oil to run in. ($)
The new systems from GM (Displacement on Demand) and Chrysler (Multiple Displacement System) are almost identical. They (we) are doing the switching in the Roller Hydraulic Valve Lifters of pushrod engines. Much cheaper. There's enough space there to add locking pins and when hydraulically unlocked to absorb the cam lift without moving the pushrod. Ford would be doing the same, but they seem to have forgotten how to make pushrod engines, so they are out of the party for now. Chrysler's are made by INA (Germany); GM's by Delphi and Eaton. (Yes, legal wrangling has ensued, but let's not talk about that)
Operationally, it switches off the exhaust first, then the intake of every other cylinder as you go throught the firing order. The lifter has to be on the cam's "base circle" to allow the locking pins to move. That means inside cylinders on one bank and outsides on the other. Hence, the motor stays even firing. The engine mounts are bi-state (!), and are electrically switched to a different natural frequency in sync with the motor switching. It is all done within two engine cycles, and no, you can't feel it. GM's calibrators can't even feel it. They wire up an LED on the dash for reference. There is an electrically actuated hydraulic control valve for each cylinder that fire in sequence driven by the ECM and the cam position sensor. Think high speed: elec signal, solenoid movement, oil pressure buildup, locking pin movement... all in 10 milliseconds, and repeatable over the full range of oil temps. Hint: changing your oil regularly is a good idea.
As to economy, as always, it depends. I'm talking full size trucks and TrailBlazers here. The overall real world average they figure to be 8%. Might not sound too huge, but to a car company, that's a big number. In suburban driving, ~45ish and lot's of light loads, it could be over 20%. On the other hand, I heard the calibration guys say once that about 75mph is where the "road load" power required prevents it from going into deac. So, I doubt the heavier versions of the trucks are deac'g much on the highway. I guess running a 6 or 7 thousand pound truck on 4 cylinders isn't too easy. Our job was to just get them turned off and on, not make it more powerful in 4cyl mode. As mentioned, not it's also in the Impala SS. I didn't think they were doing the Corvette, but maybe so. It's also possible to do a V6, although the useable range of loads is a bit narrower. To even-fire a V6 in 3 cylinder mode, you need to deac one whole bank. And, yes, it's been done on a 4 cylinder by a research firm, but... well, let's see how the V8's are accepted.
Concerns? Oil puddling on top of the valve guides, and then getting sucked in when the cylinder suddenly "re-acts". GM's trucks periodically switch back to 8 cyl even if not required to prevent this. The fuel injectors are off of course, but the spark is still on. No need to add the complexity of switching it on and off.
Sorry for the long post, but engineers never know when to shut up.
Jim N.
'73 2.0
next
Great post, Jim!!!
I hadn't read how the cylinders are being deactivated.
So, you still have pumping loses, correct? ... which would explain the 8% improvement
next
This followup will be short, I promise.
Reduction in "pumping losses" is why Deac improves economy. By pumping losses I mean the work required to pull down on intake against the restriction of the throttle blade. When in 4 cyl mode, a deac engine has it's throttle blade further open than it would in 8 cyl mode at the same speed-load point. Think: working harder on the remaining four cylinders. Further open means air flows in easier, i.e. less losses.
If you mean the frictional losses of the piston going up and down with both valves closed all the time, yes of course that is an unavoidable loss of efficiency, but it's not that bad, cuz the work required to compress the air is recovered when it expands. You only lose the friction, which isn't terrible with a warm engine and the low tension rings they use now-a-days.
Saab's Variable Compression engine is no doubt still around, and still in development. (Did you hear about the one that sparked from the plug to the top of the piston? Those Swedes!) These things take years. I've also seen one from FEV, a Euro engine design company in their Detroit office. It's a steep uphill challenge: added complexity means lower reliability, and more variables means tougher to meet emissions reg's, which is the hardest aspect of designing an engine. And when a new engine line costs many hundreds of millions, they tend to be a conservative bunch. Believe me. Very conservative. On the other hand, engines are now extremely reliable when you think about it.
OK, not short, but let's call this one medium. See you around. Good questions.
Jim N
'73 2.0
next
Jim N,
I have a dumb question which I ask because I don't feel like thinking right now and because, well, I'm dumb. What would be the problem of just shutting off the injectors for particular cylinders and leaving the valvetrain operating normally? Wouldn't there still be a gain in economy?
Oh, and isn't part of the increased efficiency due to the fact that the remaining cylinders are operating with a greater charge density? I was under the impression that a denser charge burns more efficiently.
Andrew
next
First, Eric- I agree completely. We could cut the oil consumption of cars and light trucks in half with today's technology. i.e. Double fuel economy. No sweat. But we can't do it while driving Tahoe's, Durango, Expeditions, and Land Bruisers... For me, step one is diesel. Instant 30% improvement with no sacrifice or downside for Joe American. Europe is now 50%+, US is <1%. I can tell you diesels are finally coming to the States. The fuel will be 30ppm sulfer I think in '06 or was it '07. That allows the diesel catalysts to live. Get ready for a gradual 20 year roll-in to reach 40 or 50% penetration. I don't know anything special about fuel cells, but I'm optimistic they will eventually make them economical. They've only scratched the surface compared to the millions and millions of man-hours invested in getting IC engines to work well.
Andrew- good guestion. You're making think, which has it's pro's and con's most days. Wish I could draw you a P-V Diagram. (Pressure vs Volume as a four stroke completes one cycle) Pulling the connectors on four injectors would certainly make things worse. The throttle blade would be open a bit more, as on a deac engine, but the non-firing cylinders would be wasting more energy pulling air in against the manifold vacuum and then pushing it out against the exhaust back pressure. It's a loser in both directions. These losses would be worse than the slight gain in the firing cylinders.
If you've heard it said that an engine is just a big air pump- well, that may be true but it's sure an inefficient one cuz the first thing you come to is a nearly closed off throttle valve. At highway cruise it's only open 10%. 90% blocked off, which is proven by the huge vacuum in the manifold. My 914 pulled 14.5psi vacuum at idle when I tested it this fall. That's a measure of how inefficient a motor is, not the opposite. One of the reasons diesels are more efficient is because they don't need a throttle valve, so there's no vacuum in the manifold. i.e., it's very easy for the pistions to suck in the next gulp of air. So, controlling a gas engine by throttling the air (both at the throttle valve and at the intake valves- don't forget) is inherently worse than controlling a diesel by the amount of fuel injected.
Charge density helps but it's not more efficient, it just has more air and fuel cuz it's denser. That's why intercoolers help. Cool air is denser (more) air, to which it's easy to add a smidge of extra fuel, and so get more power. Remember, you need to stay very close to the optimal 14.7:1 ratio. Burn rate and burn completion is mostly due to fuel atomization (droplet size), and local air/fuel ratio (how homogenious is it in there really?) and the degree of turbulence created by the intake velocity and direction and the shape of the upwardly rushing piston against the chamber shape.
Time to put the cookie-munchers to bed.
Jim N.
'73 2.0
next
Jim,
Makes sense. If an engine had individual drive-by-wire throttles, would it be simpler to switch those out (closed) rather than the valves? And what if there were similar butterfly or other type of valves on the exhaust side. Wouldn't it be less complex than deactivating the valvetrain? Or if not less complex, would it work? I think it wouldn't work as well since the butterfly valves woudn't seal as well as a closed cylinder-head valve. I am just curious whether you think it would work at all since that would seem to address the pumping loss issues you mention. Don't think that I was thinking of trying it..... .....this year... ...
I do still think that (maybe?) a fuller cylinder will burn more efficiently. It is harder to ignite and sustain ignition in a partially filled cylinder compared to a more fully filled one. I don't know the exact mechanism(s), but the pressure developed before and after ignition, heat generated by combustion and heat rate lost to cylinder walls etc affect ease of starting/sustaining combustion and also energy output/efficiency. Some of these factors would be affected by the amount of cylinder filling, wouldn't they?
Also, a car will get better mileage with higher gearing. Which of these factors are significant: 1) less frictional loss due to engine turning fewer revs over a given distance2) less pumping loss due to higher throttle opening 3) increased efficiency due to greater cylinder filling 4) any thing I didn't mention.
Is that too many questions? (oops, that was another one)
Andrew
next
We call them ETC's: Electronic Throttle Control, and no, that won't work. For one, you can't put an ETC into a 500deg C exhaust stream. Well, you could, but it wouldn't live long. Why do you think this would work better? Doing it in the valvetrain is the closest to the combustion chamber we're trying to control and by far the most mechanically simple (engineers would say, "elegant") solution. There's no need to think up anything else.
Individual throttles implies you're using individual intake runners. Very expensive and won't fit for a V type engine. V engines like plenum's and a single throttle cuz it helps even out the flow balance to the cylinders, fits better, and of course is lots cheaper. Racing engines may have seperate runners, but keep in mind they are optimized around a very narrow rpm band.
Cylinder filling: I don't think you caught what I wrote before. You need to seperate the idea of quality of combustion from the amount of mixture in there. To have acceptable emissions, you need to keep the mixture at 14.7 to 1 air/fuel ratio. Period. After that, the AMOUNT of 14.7:1 mixture we get in there is the thing that directly controls the torque that cylinder makes. At Wide Open Throttle (WOT), less restriction to air flowing in, more mixture in the cylinder, max torque. At idle, tons of restriction past the throttle, little mixture inside, low torque. In both cases, the mixture is always 14.7 to 1. It takes a while to digest that fact. So, things like the ease of initiating the burn, and the combustion 'efficiency' are the same in both cases. The power generated is drastically different of course, so the heat loss to the wall is different, sure, but the efficiency is the same. Engines are most efficient at WOT not because they burn better, but because they don't waste work pulling air past the nearly closed throttle at low loads.
Answer to paragraph #3: Number 1 and 2 are both good, although I think number 1 is the easiest and likely the larger improvement, at least for big V8's. With a 914 engine pushing the car at 70 mph, you can't be lowering the revs too much can you? But, when Chevy was trying to avoid the gas guzzler tax on the Vette inspite of increasing hp to 400 (and now 500!), they went to gearing that left it turning what, 1600 at 70? Something like that. IF you have the torque, that's the easiest way to go. By now, I hope you agree that Number 3, increased filling, is simply a method to increase torque, not improve efficiency, BUT, you can use your increased torque to drive taller gearing, and THAT is option Number 1, the best option. So, 3 is just an enabler for 1. Got it?
Now, since you're such an inquisitive guy, here's my advice I hope you take on board: Go to a used book store (or probably Amazon) and buy a copy of "Internal Combustion Engines and Air Pollution" by Obert. That's the one used in most engineering schools and is the all time classic. Every engine designer in the country has a copy in his office. Read the whole thing. It's actually not that hard to read. I'm sure you will get a ton out of it.
Jim N.
next
Jim N,
Check out BMW's N73 6.0L V 12. They are the only gas engine I have seen that has direct injection in the actual cylinder like a diesel. This engine also has Valvetronic which is something else to check out.
John
next
Yes, it's an amazing engine. Not the first though.
DIG was intro'd by Mitsubishi about 10 years ago, although it wasn't new then. The '55 Mercedes SLR had mechanical DIG.
The Valvetronic system came out on BMW's European 318 in about '99. They have been gradually increased the volume of manufacture.
Jim N.
I'm new to the group, but you're on a topic I know something about.
Warning: long boring post to follow: Read only if you want to know more than absoutely necessary about cylinder deactivation.
(I was the Engineering Supervisor for the Delphi Valve Train group when we developed the cylinder deactivation system used by GM.)
The old Cadillac system used an electric rotary actuator on top of the rocker arms. We found a '82 Seville with a V8-6-4 when we started working on the new system in '99, and it was still working fine. Must have been the only one left. Putting electrical connections under the valve covers is generally a bad idea. Someone mentioned the Mercedes. Their V8 and V12 were the first of the 'modern' systems (I think in '99), and was very complicated. Big surprise. It's very tough to switch off the valves in an overhead cam engine. It has a very expensive, high pressure valve asm. You've only got the rockers to do it in, and it's hard to get the right oil circuits to your hydraulic actuators (inside the rockers!). Honda have also done it this way. You need a pivot shaft running down the length of the head so the rockers stay in perfect alignment and for the oil to run in. ($)
The new systems from GM (Displacement on Demand) and Chrysler (Multiple Displacement System) are almost identical. They (we) are doing the switching in the Roller Hydraulic Valve Lifters of pushrod engines. Much cheaper. There's enough space there to add locking pins and when hydraulically unlocked to absorb the cam lift without moving the pushrod. Ford would be doing the same, but they seem to have forgotten how to make pushrod engines, so they are out of the party for now. Chrysler's are made by INA (Germany); GM's by Delphi and Eaton. (Yes, legal wrangling has ensued, but let's not talk about that)
Operationally, it switches off the exhaust first, then the intake of every other cylinder as you go throught the firing order. The lifter has to be on the cam's "base circle" to allow the locking pins to move. That means inside cylinders on one bank and outsides on the other. Hence, the motor stays even firing. The engine mounts are bi-state (!), and are electrically switched to a different natural frequency in sync with the motor switching. It is all done within two engine cycles, and no, you can't feel it. GM's calibrators can't even feel it. They wire up an LED on the dash for reference. There is an electrically actuated hydraulic control valve for each cylinder that fire in sequence driven by the ECM and the cam position sensor. Think high speed: elec signal, solenoid movement, oil pressure buildup, locking pin movement... all in 10 milliseconds, and repeatable over the full range of oil temps. Hint: changing your oil regularly is a good idea.
As to economy, as always, it depends. I'm talking full size trucks and TrailBlazers here. The overall real world average they figure to be 8%. Might not sound too huge, but to a car company, that's a big number. In suburban driving, ~45ish and lot's of light loads, it could be over 20%. On the other hand, I heard the calibration guys say once that about 75mph is where the "road load" power required prevents it from going into deac. So, I doubt the heavier versions of the trucks are deac'g much on the highway. I guess running a 6 or 7 thousand pound truck on 4 cylinders isn't too easy. Our job was to just get them turned off and on, not make it more powerful in 4cyl mode. As mentioned, not it's also in the Impala SS. I didn't think they were doing the Corvette, but maybe so. It's also possible to do a V6, although the useable range of loads is a bit narrower. To even-fire a V6 in 3 cylinder mode, you need to deac one whole bank. And, yes, it's been done on a 4 cylinder by a research firm, but... well, let's see how the V8's are accepted.
Concerns? Oil puddling on top of the valve guides, and then getting sucked in when the cylinder suddenly "re-acts". GM's trucks periodically switch back to 8 cyl even if not required to prevent this. The fuel injectors are off of course, but the spark is still on. No need to add the complexity of switching it on and off.
Sorry for the long post, but engineers never know when to shut up.
Jim N.
'73 2.0
next
Great post, Jim!!!
I hadn't read how the cylinders are being deactivated.
So, you still have pumping loses, correct? ... which would explain the 8% improvement
next
This followup will be short, I promise.
Reduction in "pumping losses" is why Deac improves economy. By pumping losses I mean the work required to pull down on intake against the restriction of the throttle blade. When in 4 cyl mode, a deac engine has it's throttle blade further open than it would in 8 cyl mode at the same speed-load point. Think: working harder on the remaining four cylinders. Further open means air flows in easier, i.e. less losses.
If you mean the frictional losses of the piston going up and down with both valves closed all the time, yes of course that is an unavoidable loss of efficiency, but it's not that bad, cuz the work required to compress the air is recovered when it expands. You only lose the friction, which isn't terrible with a warm engine and the low tension rings they use now-a-days.
Saab's Variable Compression engine is no doubt still around, and still in development. (Did you hear about the one that sparked from the plug to the top of the piston? Those Swedes!) These things take years. I've also seen one from FEV, a Euro engine design company in their Detroit office. It's a steep uphill challenge: added complexity means lower reliability, and more variables means tougher to meet emissions reg's, which is the hardest aspect of designing an engine. And when a new engine line costs many hundreds of millions, they tend to be a conservative bunch. Believe me. Very conservative. On the other hand, engines are now extremely reliable when you think about it.
OK, not short, but let's call this one medium. See you around. Good questions.
Jim N
'73 2.0
next
Jim N,
I have a dumb question which I ask because I don't feel like thinking right now and because, well, I'm dumb. What would be the problem of just shutting off the injectors for particular cylinders and leaving the valvetrain operating normally? Wouldn't there still be a gain in economy?
Oh, and isn't part of the increased efficiency due to the fact that the remaining cylinders are operating with a greater charge density? I was under the impression that a denser charge burns more efficiently.
Andrew
next
First, Eric- I agree completely. We could cut the oil consumption of cars and light trucks in half with today's technology. i.e. Double fuel economy. No sweat. But we can't do it while driving Tahoe's, Durango, Expeditions, and Land Bruisers... For me, step one is diesel. Instant 30% improvement with no sacrifice or downside for Joe American. Europe is now 50%+, US is <1%. I can tell you diesels are finally coming to the States. The fuel will be 30ppm sulfer I think in '06 or was it '07. That allows the diesel catalysts to live. Get ready for a gradual 20 year roll-in to reach 40 or 50% penetration. I don't know anything special about fuel cells, but I'm optimistic they will eventually make them economical. They've only scratched the surface compared to the millions and millions of man-hours invested in getting IC engines to work well.
Andrew- good guestion. You're making think, which has it's pro's and con's most days. Wish I could draw you a P-V Diagram. (Pressure vs Volume as a four stroke completes one cycle) Pulling the connectors on four injectors would certainly make things worse. The throttle blade would be open a bit more, as on a deac engine, but the non-firing cylinders would be wasting more energy pulling air in against the manifold vacuum and then pushing it out against the exhaust back pressure. It's a loser in both directions. These losses would be worse than the slight gain in the firing cylinders.
If you've heard it said that an engine is just a big air pump- well, that may be true but it's sure an inefficient one cuz the first thing you come to is a nearly closed off throttle valve. At highway cruise it's only open 10%. 90% blocked off, which is proven by the huge vacuum in the manifold. My 914 pulled 14.5psi vacuum at idle when I tested it this fall. That's a measure of how inefficient a motor is, not the opposite. One of the reasons diesels are more efficient is because they don't need a throttle valve, so there's no vacuum in the manifold. i.e., it's very easy for the pistions to suck in the next gulp of air. So, controlling a gas engine by throttling the air (both at the throttle valve and at the intake valves- don't forget) is inherently worse than controlling a diesel by the amount of fuel injected.
Charge density helps but it's not more efficient, it just has more air and fuel cuz it's denser. That's why intercoolers help. Cool air is denser (more) air, to which it's easy to add a smidge of extra fuel, and so get more power. Remember, you need to stay very close to the optimal 14.7:1 ratio. Burn rate and burn completion is mostly due to fuel atomization (droplet size), and local air/fuel ratio (how homogenious is it in there really?) and the degree of turbulence created by the intake velocity and direction and the shape of the upwardly rushing piston against the chamber shape.
Time to put the cookie-munchers to bed.
Jim N.
'73 2.0
next
Jim,
Makes sense. If an engine had individual drive-by-wire throttles, would it be simpler to switch those out (closed) rather than the valves? And what if there were similar butterfly or other type of valves on the exhaust side. Wouldn't it be less complex than deactivating the valvetrain? Or if not less complex, would it work? I think it wouldn't work as well since the butterfly valves woudn't seal as well as a closed cylinder-head valve. I am just curious whether you think it would work at all since that would seem to address the pumping loss issues you mention. Don't think that I was thinking of trying it..... .....this year... ...
I do still think that (maybe?) a fuller cylinder will burn more efficiently. It is harder to ignite and sustain ignition in a partially filled cylinder compared to a more fully filled one. I don't know the exact mechanism(s), but the pressure developed before and after ignition, heat generated by combustion and heat rate lost to cylinder walls etc affect ease of starting/sustaining combustion and also energy output/efficiency. Some of these factors would be affected by the amount of cylinder filling, wouldn't they?
Also, a car will get better mileage with higher gearing. Which of these factors are significant: 1) less frictional loss due to engine turning fewer revs over a given distance2) less pumping loss due to higher throttle opening 3) increased efficiency due to greater cylinder filling 4) any thing I didn't mention.
Is that too many questions? (oops, that was another one)
Andrew
next
We call them ETC's: Electronic Throttle Control, and no, that won't work. For one, you can't put an ETC into a 500deg C exhaust stream. Well, you could, but it wouldn't live long. Why do you think this would work better? Doing it in the valvetrain is the closest to the combustion chamber we're trying to control and by far the most mechanically simple (engineers would say, "elegant") solution. There's no need to think up anything else.
Individual throttles implies you're using individual intake runners. Very expensive and won't fit for a V type engine. V engines like plenum's and a single throttle cuz it helps even out the flow balance to the cylinders, fits better, and of course is lots cheaper. Racing engines may have seperate runners, but keep in mind they are optimized around a very narrow rpm band.
Cylinder filling: I don't think you caught what I wrote before. You need to seperate the idea of quality of combustion from the amount of mixture in there. To have acceptable emissions, you need to keep the mixture at 14.7 to 1 air/fuel ratio. Period. After that, the AMOUNT of 14.7:1 mixture we get in there is the thing that directly controls the torque that cylinder makes. At Wide Open Throttle (WOT), less restriction to air flowing in, more mixture in the cylinder, max torque. At idle, tons of restriction past the throttle, little mixture inside, low torque. In both cases, the mixture is always 14.7 to 1. It takes a while to digest that fact. So, things like the ease of initiating the burn, and the combustion 'efficiency' are the same in both cases. The power generated is drastically different of course, so the heat loss to the wall is different, sure, but the efficiency is the same. Engines are most efficient at WOT not because they burn better, but because they don't waste work pulling air past the nearly closed throttle at low loads.
Answer to paragraph #3: Number 1 and 2 are both good, although I think number 1 is the easiest and likely the larger improvement, at least for big V8's. With a 914 engine pushing the car at 70 mph, you can't be lowering the revs too much can you? But, when Chevy was trying to avoid the gas guzzler tax on the Vette inspite of increasing hp to 400 (and now 500!), they went to gearing that left it turning what, 1600 at 70? Something like that. IF you have the torque, that's the easiest way to go. By now, I hope you agree that Number 3, increased filling, is simply a method to increase torque, not improve efficiency, BUT, you can use your increased torque to drive taller gearing, and THAT is option Number 1, the best option. So, 3 is just an enabler for 1. Got it?
Now, since you're such an inquisitive guy, here's my advice I hope you take on board: Go to a used book store (or probably Amazon) and buy a copy of "Internal Combustion Engines and Air Pollution" by Obert. That's the one used in most engineering schools and is the all time classic. Every engine designer in the country has a copy in his office. Read the whole thing. It's actually not that hard to read. I'm sure you will get a ton out of it.
Jim N.
next
Jim N,
Check out BMW's N73 6.0L V 12. They are the only gas engine I have seen that has direct injection in the actual cylinder like a diesel. This engine also has Valvetronic which is something else to check out.
John
next
Yes, it's an amazing engine. Not the first though.
DIG was intro'd by Mitsubishi about 10 years ago, although it wasn't new then. The '55 Mercedes SLR had mechanical DIG.
The Valvetronic system came out on BMW's European 318 in about '99. They have been gradually increased the volume of manufacture.
Jim N.
09-24-2005, 08:27 PM
#2
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,041
Received 395 Likes
on
337 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
I have seen a mid 70s 500 cadillac fitted with the ported 8-6-4 368 heads. A mild RV cam, headers for a GMC FWD motorhome. On top was the original PFI intake. Late model vortec 454 injectors feed it fuel. The throttle body was a BB GM TBI unit minus the injector and injector pods. It was being run by a 730 TPI ecm and harness. In the 10,000 lbs GMC it would run 60 down the highway on 4 cylinders. The cylinder deactivation was run by the TCC output and a relay. The relay cut power to the injectors on that bank and controlled the solenoid. The 6 cylinder mode was eliminated because the cadillac tended to run rough in the 6 cylinder mode.
09-24-2005, 09:59 PM
#3
Moderator
Thread Starter
Join Date: Jul 1999
Location: Tempe, AZ
Posts: 2,184
Likes: 0
Received 0 Likes
on
0 Posts
Car: 92 RS, 02 Tacoma, 2 73 Porsche 914s
as in the above... the gm guy says that cutting just fuel didnt really help efficiency that much because the engine was still working against a closed throttle plate/manifold vacuum...
perhaps thats that why i've seen some caddy tbi units with a selenoid to open the throttle instead of an iac....
perhaps thats that why i've seen some caddy tbi units with a selenoid to open the throttle instead of an iac....
09-25-2005, 10:32 AM
#4
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,041
Received 395 Likes
on
337 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Originally posted by snflupigus
as in the above... the gm guy says that cutting just fuel didnt really help efficiency that much because the engine was still working against a closed throttle plate/manifold vacuum...
perhaps thats that why i've seen some caddy tbi units with a selenoid to open the throttle instead of an iac....
as in the above... the gm guy says that cutting just fuel didnt really help efficiency that much because the engine was still working against a closed throttle plate/manifold vacuum...
perhaps thats that why i've seen some caddy tbi units with a selenoid to open the throttle instead of an iac....
09-25-2005, 02:51 PM
#5
Moderator
Thread Starter
Join Date: Jul 1999
Location: Tempe, AZ
Posts: 2,184
Likes: 0
Received 0 Likes
on
0 Posts
Car: 92 RS, 02 Tacoma, 2 73 Porsche 914s
Andrew- good guestion. You're making think, which has it's pro's and con's most days. Wish I could draw you a P-V Diagram. (Pressure vs Volume as a four stroke completes one cycle) Pulling the connectors on four injectors would certainly make things worse. The throttle blade would be open a bit more, as on a deac engine, but the non-firing cylinders would be wasting more energy pulling air in against the manifold vacuum and then pushing it out against the exhaust back pressure. It's a loser in both directions. These losses would be worse than the slight gain in the firing cylinders.
09-25-2005, 02:54 PM
#6
Moderator
Thread Starter
Join Date: Jul 1999
Location: Tempe, AZ
Posts: 2,184
Likes: 0
Received 0 Likes
on
0 Posts
Car: 92 RS, 02 Tacoma, 2 73 Porsche 914s
And as for the caddy units with the selenoid to control throttle blades vs iac... i at first thought you said the factory simply cut the fuel, and i was confused because i was sure that the v864 did shut off valves. (and it does)... so i have to revert to my previous thought on it...
My thought was that the selenoid was simply over engineering on cadillacs part and is why it wasnt on all tbi cars...
My thought was that the selenoid was simply over engineering on cadillacs part and is why it wasnt on all tbi cars...
02-22-2006, 04:41 AM
#7
Senior Member
Join Date: May 2003
Location: Runnin' from the Reaper
Posts: 663
Likes: 0
Received 1 Like
on
1 Post
Car: 91 B4C/91 RS 305
Engine: L98 and L03
Transmission: 2xTH700R4
Axle/Gears: 3.23 LSD/2.73 Open
thank you so much for posting this. I have been wondering about how this system works since I heard it existed. Now if only i can find a way to do it on my car for free i'll be set.
Trending Topics
Thread
Thread Starter
Forum
Replies
Last Post
Street Lethal
Power Adders
634
04-30-2019 12:14 PM
