Direct Injection Technology
Race Director
Joined: Jun 2001
Posts: 10,084
Likes: 3,056
From: CA
Even the new LT1 is WAY lower than it should be. To me 11.5:1 is a joke. If you can run 11:1 in a LS7 with port injection. A DI on PREMIUM should be able to run 13:1+ no issue. GM kept it low so idiots can run 87 in the thing and not kill it. Waste of technology, IMHO. Granted they have MANY factors to consider, but the potential is there. They should use it.
Just because you keep raising the compression ratio, doesn't mean you are going to get anything out of it. You can still be octane constrained. You can end up with a mis-shapen combustion chamber, which could raise emissions, shroud valves (lower volumetric efficiency), slow flame travel, and increase detonation.
Michael
Instructor
Joined: Mar 2007
Posts: 109
Likes: 34
From: Los Angeles CA
It may eventually come into the aftermarket, however, its is complex and VERY costly. As noted the block, heads,etc...all have to be setup for it.
Injectors, low pressure pump, cam driven high pressure pump (typically), hard lines,etc...all are needed.
You an run much higher compression ratios and get stellar air/fuel mixtures.
I don't see it taking off because of cost constraints in the aftermarket.
Most OEM application are more focus on fuel economy and emissions. Nissan for example has a 1.6 Turbo DI in the Juke. Makes 188HP stock. However, there is a lot of untapped potential in the engine, but the compression ratio is quite low at 9.5 to 1. Tune conservatively so it lives, gives good gas mileage, good drive-ability, and emissions.
Even the new LT1 is WAY lower than it should be. To me 11.5:1 is a joke. If you can run 11:1 in a LS7 with port injection. A DI on PREMIUM should be able to run 13:1+ no issue. GM kept it low so idiots can run 87 in the thing and not kill it. Waste of technology, IMHO. Granted they have MANY factors to consider, but the potential is there. They should use it.
If the aftermarket is going to do DI, its going to hack PCM's and tune it to work better for POWER over OEM concerns. All of this is IMO.
Injectors, low pressure pump, cam driven high pressure pump (typically), hard lines,etc...all are needed.
You an run much higher compression ratios and get stellar air/fuel mixtures.
I don't see it taking off because of cost constraints in the aftermarket.
Most OEM application are more focus on fuel economy and emissions. Nissan for example has a 1.6 Turbo DI in the Juke. Makes 188HP stock. However, there is a lot of untapped potential in the engine, but the compression ratio is quite low at 9.5 to 1. Tune conservatively so it lives, gives good gas mileage, good drive-ability, and emissions.
Even the new LT1 is WAY lower than it should be. To me 11.5:1 is a joke. If you can run 11:1 in a LS7 with port injection. A DI on PREMIUM should be able to run 13:1+ no issue. GM kept it low so idiots can run 87 in the thing and not kill it. Waste of technology, IMHO. Granted they have MANY factors to consider, but the potential is there. They should use it.
If the aftermarket is going to do DI, its going to hack PCM's and tune it to work better for POWER over OEM concerns. All of this is IMO.
DFI (on DOHC engines) gains you about 10% power for the displacement and fuel consumption, but with lots of labor and cost. Just skip it and funnel your money into a different power adder. GM's estimate 450 hp is only a 5% advantage over current. That may be due to them being conservative, or limitations of cam-in-block 2v design.
Instructor
Joined: Mar 2007
Posts: 109
Likes: 34
From: Los Angeles CA
What in the world could you possibly be basing this on? Are you an OEM direct injected engine developer?
Just because you keep raising the compression ratio, doesn't mean you are going to get anything out of it. You can still be octane constrained. You can end up with a mis-shapen combustion chamber, which could raise emissions, shroud valves (lower volumetric efficiency), slow flame travel, and increase detonation.
Michael
Just because you keep raising the compression ratio, doesn't mean you are going to get anything out of it. You can still be octane constrained. You can end up with a mis-shapen combustion chamber, which could raise emissions, shroud valves (lower volumetric efficiency), slow flame travel, and increase detonation.
Michael
DFI makes it's power gain and increases in fuel mileage by going to higher compression ratios.
Every point increase in compression ratio increases thermal efficiency by something like 4%. When you increase thermal efficiency, you get more power for the amount of fuel used.
At the point of detonation, decreasing intake charge temperature by 8-10 degrees F is like adding 1 octane point to your fuel. DFI takes liquid gasoline and atomizes it in the combustion chamber. That is roughly equivalent to evaporative cooling (like you sweating or a swamp cooler) and causes cylinder temperatures to drop, which allows for higher compression ratios without detonation.
Audi, Porsche, Lamborghini and Ferarri run 12.5:1 with DFI, but with DOHC 4V systems. It may be that 2V designs and large piston bores wont tolerate the higher CR. That would be a question better answered by the engineers.
Last edited by Phimosis; Jan 7, 2013 at 12:59 AM.
Instructor
Joined: Mar 2007
Posts: 109
Likes: 34
From: Los Angeles CA
from a GM press release:
Compared to the Gen 4 engine, the Gen 5’s cylinder block casting is all-new, but based on the same basic architecture. It was refined and modified to accommodate the mounting of the engine-driven direct injection high-pressure fuel pump. It also incorporates new engine mount attachments, new knock sensor locations, improved sealing and oil-spray piston cooling.
Tech Contributor
Joined: Oct 1999
Posts: 41,058
Likes: 9,822
From: Charlotte, NC (formerly Endicott, NY)
Bill
Burning Brakes
Joined: Jul 2011
Posts: 1,168
Likes: 2
From: Saint Johns Florida
Please google compression ratio vs thermal efficiency. It will explain better than I can:
DFI makes it's power gain and increases in fuel mileage by going to higher compression ratios.
Every point increase in compression ratio increases thermal efficiency by something like 4%. When you increase thermal efficiency, you get more power for the amount of fuel used.
At the point of detonation, decreasing intake charge temperature by 8-10 degrees F is like adding 1 octane point to your fuel. DFI takes liquid gasoline and atomizes it in the combustion chamber. That is roughly equivalent to evaporative cooling (like you sweating or a swamp cooler) and causes cylinder temperatures to drop, which allows for higher compression ratios without detonation.
Audi, Porsche, Lamborghini and Ferarri run 12.5:1 with DFI, but with DOHC 4V systems. It may be that 2V designs and large piston bores wont tolerate the higher CR. That would be a question better answered by the engineers.
DFI makes it's power gain and increases in fuel mileage by going to higher compression ratios.
Every point increase in compression ratio increases thermal efficiency by something like 4%. When you increase thermal efficiency, you get more power for the amount of fuel used.
At the point of detonation, decreasing intake charge temperature by 8-10 degrees F is like adding 1 octane point to your fuel. DFI takes liquid gasoline and atomizes it in the combustion chamber. That is roughly equivalent to evaporative cooling (like you sweating or a swamp cooler) and causes cylinder temperatures to drop, which allows for higher compression ratios without detonation.
Audi, Porsche, Lamborghini and Ferarri run 12.5:1 with DFI, but with DOHC 4V systems. It may be that 2V designs and large piston bores wont tolerate the higher CR. That would be a question better answered by the engineers.
saying a car has 12.5:1 static compression ratio with DFI, is a useful as saying a car has a 4.6l engine. Without saying how many cylinders or how much HP at what RPM all we know is the size. General a bigger engine has more potential, that doesn't mean it is being utilized.
Last edited by hig4s; Jan 8, 2013 at 01:48 PM.
Instructor
Joined: Jan 2010
Posts: 203
Likes: 2
I had Mazda's version , called DISI, in my 2007 Mazdaspeed 6, which was a 4 cyl, turbo 274Hp, 280 torque. It was/is a great car.
The main problem with DI, the fuel being directly injected into the cylinder, means you get no fuel cleaning effect on the intake valve and intake tracts. The result is they get gummed up. Almost every MS-6 owner used SeaFoam a couple of times a year to clean out the intake tract and clean the intake valves; or like me they used an alcohol/water injection system right after the intercooler that did an excellent job of both power boosting by allowing more turbo boost, and also did a good job of cleaning the intake tract.
Why did they get gummed up? Because the PCV dumped the nasties back in the intake tract upstream of the intake valves. So all the nasty crankcase blow by gets put in the intake tract with no gasoline cleaning effect to get rid of it.
The main problem with DI, the fuel being directly injected into the cylinder, means you get no fuel cleaning effect on the intake valve and intake tracts. The result is they get gummed up. Almost every MS-6 owner used SeaFoam a couple of times a year to clean out the intake tract and clean the intake valves; or like me they used an alcohol/water injection system right after the intercooler that did an excellent job of both power boosting by allowing more turbo boost, and also did a good job of cleaning the intake tract.
Why did they get gummed up? Because the PCV dumped the nasties back in the intake tract upstream of the intake valves. So all the nasty crankcase blow by gets put in the intake tract with no gasoline cleaning effect to get rid of it.
Last edited by Sgt.Gator; Jan 8, 2013 at 02:11 PM.
Team Owner
Joined: Sep 1999
Posts: 41,732
Likes: 1,718
From: Springfield MO
it needs a cam driven fuel pump to generate 2,000 psi. They probably also have new starter mounts to alllow start/stop generator/starter motors.
from a GM press release:
Compared to the Gen 4 engine, the Gen 5’s cylinder block casting is all-new, but based on the same basic architecture. It was refined and modified to accommodate the mounting of the engine-driven direct injection high-pressure fuel pump. It also incorporates new engine mount attachments, new knock sensor locations, improved sealing and oil-spray piston cooling.
from a GM press release:
Compared to the Gen 4 engine, the Gen 5’s cylinder block casting is all-new, but based on the same basic architecture. It was refined and modified to accommodate the mounting of the engine-driven direct injection high-pressure fuel pump. It also incorporates new engine mount attachments, new knock sensor locations, improved sealing and oil-spray piston cooling.
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Verdad Gallardo
Team Owner
Joined: Sep 1999
Posts: 41,732
Likes: 1,718
From: Springfield MO
Please google compression ratio vs thermal efficiency. It will explain better than I can:
DFI makes it's power gain and increases in fuel mileage by going to higher compression ratios.
Every point increase in compression ratio increases thermal efficiency by something like 4%. When you increase thermal efficiency, you get more power for the amount of fuel used.
At the point of detonation, decreasing intake charge temperature by 8-10 degrees F is like adding 1 octane point to your fuel. DFI takes liquid gasoline and atomizes it in the combustion chamber. That is roughly equivalent to evaporative cooling (like you sweating or a swamp cooler) and causes cylinder temperatures to drop, which allows for higher compression ratios without detonation.
Audi, Porsche, Lamborghini and Ferarri run 12.5:1 with DFI, but with DOHC 4V systems. It may be that 2V designs and large piston bores wont tolerate the higher CR. That would be a question better answered by the engineers.
DFI makes it's power gain and increases in fuel mileage by going to higher compression ratios.
Every point increase in compression ratio increases thermal efficiency by something like 4%. When you increase thermal efficiency, you get more power for the amount of fuel used.
At the point of detonation, decreasing intake charge temperature by 8-10 degrees F is like adding 1 octane point to your fuel. DFI takes liquid gasoline and atomizes it in the combustion chamber. That is roughly equivalent to evaporative cooling (like you sweating or a swamp cooler) and causes cylinder temperatures to drop, which allows for higher compression ratios without detonation.
Audi, Porsche, Lamborghini and Ferarri run 12.5:1 with DFI, but with DOHC 4V systems. It may be that 2V designs and large piston bores wont tolerate the higher CR. That would be a question better answered by the engineers.
Burning Brakes
Joined: Jul 2011
Posts: 1,168
Likes: 2
From: Saint Johns Florida
I had Mazda's version , called DISI, in my 2007 Mazdaspeed 6, which was a 4 cyl, turbo 274Hp, 280 torque. It was/is a great car.
The main problem with DI, the fuel being directly injected into the cylinder, means you get no fuel cleaning effect on the intake valve and intake tracts. The result is they get gummed up. Almost every MS-6 owner used SeaFoam a couple of times a year to clean out the intake tract and clean the intake valves; or like me they used an alcohol/water injection system right after the intercooler that did an excellent job of both power boosting by allowing more turbo boost, and also did a good job of cleaning the intake tract.
Why did they get gummed up? Because the PCV dumped the nasties back in the intake tract upstream of the intake valves. So all the nasty crankcase blow by gets put in the intake tract with no gasoline cleaning effect to get rid of it.
The main problem with DI, the fuel being directly injected into the cylinder, means you get no fuel cleaning effect on the intake valve and intake tracts. The result is they get gummed up. Almost every MS-6 owner used SeaFoam a couple of times a year to clean out the intake tract and clean the intake valves; or like me they used an alcohol/water injection system right after the intercooler that did an excellent job of both power boosting by allowing more turbo boost, and also did a good job of cleaning the intake tract.
Why did they get gummed up? Because the PCV dumped the nasties back in the intake tract upstream of the intake valves. So all the nasty crankcase blow by gets put in the intake tract with no gasoline cleaning effect to get rid of it.
GM does some creative valve timing on the Cadillac DI V6 to keep any fuel mixture from backing up into the intake and they have no issues with it. Not sure, with more aggressive sport tuning/timing on the Corvette, if there will be any buildup issues on the new LT1.
Le Mans Master
Joined: Oct 2000
Posts: 6,507
Likes: 723
From: Sausalito CA
Interesting discussion.....
The intake track gumming up from the PCV system.
Maybe there will be a service interval and procedure for the C7.
Maybe there is an OEM "catch can" like the aftermarket offers for C6s.
The intake track gumming up from the PCV system.
Maybe there will be a service interval and procedure for the C7.
Maybe there is an OEM "catch can" like the aftermarket offers for C6s.
Pro
Joined: Feb 2003
Posts: 623
Likes: 11
From: Ankeny IA
As far as the power and compression ratio, both are probably compromises. Anyone who has stuck a bigger camshaft in a LSx motor realizes the tremendous amount of power to be gained there. So there isn't a limitation of the OHV setup we're fighting against. It's very likely that a ballpark output needed was determined when taking into account the overall characteristics of the car. Then you factor in fuel efficiency and emissions targets and you arrive where we are now. Compression is where it is because it probably doesn't need to be higher to hit the established goals. And going with a lower number means less chance of an uneducated owner creating warranty claims. I think the idea of utilizing the current motor as a platform for F.I. could also be a good reason for the compression ratio we have.
Burning Brakes
Joined: Feb 2010
Posts: 878
Likes: 61
From: Louisa, Ky
Start/stop tech
it needs a cam driven fuel pump to generate 2,000 psi. They probably also have new starter mounts to alllow start/stop generator/starter motors.
from a GM press release:
Compared to the Gen 4 engine, the Gen 5’s cylinder block casting is all-new, but based on the same basic architecture. It was refined and modified to accommodate the mounting of the engine-driven direct injection high-pressure fuel pump. It also incorporates new engine mount attachments, new knock sensor locations, improved sealing and oil-spray piston cooling.
from a GM press release:
Compared to the Gen 4 engine, the Gen 5’s cylinder block casting is all-new, but based on the same basic architecture. It was refined and modified to accommodate the mounting of the engine-driven direct injection high-pressure fuel pump. It also incorporates new engine mount attachments, new knock sensor locations, improved sealing and oil-spray piston cooling.
Melting Slicks
Joined: Nov 2008
Posts: 2,938
Likes: 65
From: Rochester Hills MI
The 2008+ cobalt ss (LNF) and 2011+ buick regal both came with direct injection.
A lot of guys trying to make big power typically go with the 2005-2007 cobalt ss (LSJ) because there aren't any injectors available for upgrade for the LNF. Tuning the injectors is very limitied due to the massive fuel pressures and extremely small amount of time for the injection window. Once you need more fuel, the only option is an upgraded injector or a higher pressure fuel pump which isn't available. Tuning the DI is also completely different than regular injectors. Some other makes do have higher pressure fuel pumps and upgraded injectors for DI, but it is super costly$$$$$$.
I think that currently, if you are trying to make significantly more power than stock, it is more cost effective to go with an engine that uses standard fuel injection.
It will be interesting to see what aftermarket options there will be on the c7 and how much the stock injectors will be able to handle. Perhaps the people who are trying to make ludacris power will prefer the c6.
A lot of guys trying to make big power typically go with the 2005-2007 cobalt ss (LSJ) because there aren't any injectors available for upgrade for the LNF. Tuning the injectors is very limitied due to the massive fuel pressures and extremely small amount of time for the injection window. Once you need more fuel, the only option is an upgraded injector or a higher pressure fuel pump which isn't available. Tuning the DI is also completely different than regular injectors. Some other makes do have higher pressure fuel pumps and upgraded injectors for DI, but it is super costly$$$$$$.
I think that currently, if you are trying to make significantly more power than stock, it is more cost effective to go with an engine that uses standard fuel injection.
It will be interesting to see what aftermarket options there will be on the c7 and how much the stock injectors will be able to handle. Perhaps the people who are trying to make ludacris power will prefer the c6.
Pro
Joined: Feb 2012
Posts: 545
Likes: 85
The C7 has DI for one reason: CAFE.
This single factor accounts for almost all the new C7 drivetrain features and the compromises that came with them.
I agree with prior posters that there are other lower cost and less risky ways than DI to add power. DI required a bunch of sound deadening materials and modifications, a very expensive high-pressure fuel pump, a new complicated PCV system, weight addition that makes the LT1 heavier than the LS3 (acknowledged by GM in the C&D video), and I'm willing to bet increased warranty & recall expenses.
Even more to the point is the AFM (cylinder deactivation) system which requires a very complicated (and bug-prone?) control system, heavier and more complicated lifters on 4 cylinders, 4 solenoid-actuated valves under the valley cover, 4 oil-passage risers cast into the LT1 block, and some extra valves and actuaters in the exhaust system so the C7 won't sound like someone passing gas when running on 4 cylinders.
This single factor accounts for almost all the new C7 drivetrain features and the compromises that came with them.
I agree with prior posters that there are other lower cost and less risky ways than DI to add power. DI required a bunch of sound deadening materials and modifications, a very expensive high-pressure fuel pump, a new complicated PCV system, weight addition that makes the LT1 heavier than the LS3 (acknowledged by GM in the C&D video), and I'm willing to bet increased warranty & recall expenses.
Even more to the point is the AFM (cylinder deactivation) system which requires a very complicated (and bug-prone?) control system, heavier and more complicated lifters on 4 cylinders, 4 solenoid-actuated valves under the valley cover, 4 oil-passage risers cast into the LT1 block, and some extra valves and actuaters in the exhaust system so the C7 won't sound like someone passing gas when running on 4 cylinders.
Burning Brakes
Joined: Feb 2010
Posts: 878
Likes: 61
From: Louisa, Ky
The C7 has DI for one reason: CAFE.
This single factor accounts for almost all the new C7 drivetrain features and the compromises that came with them.
I agree with prior posters that there are other lower cost and less risky ways than DI to add power. DI required a bunch of sound deadening materials and modifications, a very expensive high-pressure fuel pump, a new complicated PCV system, weight addition that makes the LT1 heavier than the LS3 (acknowledged by GM in the C&D video), and I'm willing to bet increased warranty & recall expenses.
Even more to the point is the AFM (cylinder deactivation) system which requires a very complicated (and bug-prone?) control system, heavier and more complicated lifters on 4 cylinders, 4 solenoid-actuated valves under the valley cover, 4 oil-passage risers cast into the LT1 block, and some extra valves and actuaters in the exhaust system so the C7 won't sound like someone passing gas when running on 4 cylinders.
This single factor accounts for almost all the new C7 drivetrain features and the compromises that came with them.
I agree with prior posters that there are other lower cost and less risky ways than DI to add power. DI required a bunch of sound deadening materials and modifications, a very expensive high-pressure fuel pump, a new complicated PCV system, weight addition that makes the LT1 heavier than the LS3 (acknowledged by GM in the C&D video), and I'm willing to bet increased warranty & recall expenses.
Even more to the point is the AFM (cylinder deactivation) system which requires a very complicated (and bug-prone?) control system, heavier and more complicated lifters on 4 cylinders, 4 solenoid-actuated valves under the valley cover, 4 oil-passage risers cast into the LT1 block, and some extra valves and actuaters in the exhaust system so the C7 won't sound like someone passing gas when running on 4 cylinders.
Team Owner
Joined: May 2004
Posts: 31,800
Likes: 2,422
From: DFW/Long Island
There are a lot of carbon problems due to early adopters of DI. My DD is one of them. With no fuel in the intake track and then the compounding problem with our emissions systems (PCV) it has led to a lot of issues. My car needs to have a carbon cleaning every 15000 miles to keep it from throwing a code. I can do it myself but Audi will charge about $1500-2000 for this service.
