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3 hours ago, mender said:

https://www.jstor.org/stable/44730726

 

Just the compression ratio change is worth about 3%:

https://www.musclecardiy.com/cylinder-heads/maximizing-cylinder-head-compression-ratios-power-part-12/ 

 

Also, more oxygen gets through the same intake tract because there's no fuel being induced with the air. 

So for an otherwise very similar engine, DI over port injection is going to have a small advantage in power, and a small advantage in efficiency. 
 

Specific to ChampCar though, where swaps are valued by manufacturer rated HP, is there going to be an advantage to using a DI engine over a port injected engine with identical rated HP? Maybe a small weight savings… maybe the DI engine is 5% smaller on displacement… maybe some efficiency gain due to CR. But likely no power gains to be had because those are already baked into the rated power. Perhaps it’s actually worse to use DI because it’s already been tuned / optimized by the manufacturer to a higher level than the PI engine?

Edited by enginerd
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3 hours ago, enginerd said:

So for an otherwise very similar engine, DI over port injection is going to have a small advantage in power, and a small advantage in efficiency. 
 

Specific to ChampCar though, where swaps are valued by manufacturer rated HP, is there going to be an advantage to using a DI engine over a port injected engine with identical rated HP? Maybe a small weight savings… maybe the DI engine is 5% smaller on displacement… maybe some efficiency gain due to CR. But likely no power gains to be had because those are already baked into the rated power. Perhaps it’s actually worse to use DI because it’s already been tuned / optimized by the manufacturer to a higher level than the PI engine?

For the Toyota 2gr they went from regular to Direct injection and raised the compression also when doing so to help, all which makes more hp. The regular was rated at 268hp and went to 301hp.  Sure, the hp went up with DI and the engine evolution, but if you wanted to use that the hp would be in the swap calculator. The example here was a 2017 avalon vs a 2018 avalon. If the swap calculator works it should not matter.

 

I also wonder about the other variables for DI. The extra mechanical fuel pump and being able to control all the variables for a new DI injection. The extra complexity for the gains might not be worth it for endurance racing, but that is speculation, though more things to go wrong seems like extra items to fail long term.

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8 minutes ago, MR2 Biohazard said:

For the Toyota 2gr they went from regular to Direct injection and raised the compression also when doing so to help, all which makes more hp. The regular was rated at 268hp and went to 301hp.  Sure, the hp went up with DI and the engine evolution, but if you wanted to use that the hp would be in the swap calculator. The example here was a 2017 avalon vs a 2018 avalon. If the swap calculator works it should not matter.

 

I also wonder about the other variables for DI. The extra mechanical fuel pump and being able to control all the variables for a new DI injection. The extra complexity for the gains might not be worth it for endurance racing, but that is speculation, though more things to go wrong seems like extra items to fail long term.

Good point. I drive a car with DI and was strongly cautioned (I can’t remember where, maybe an owners forum) to not run it out of fuel. This car had recalls early on for the HPFP and it’s although it has been improved, is still susceptible to failure especially if run dry, something that happens quite regularly in ChampCar!

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One swap that comes to mind for me as a past owner of 2, is the BRZ FRS, 200 HP from the factory and both DI and PI which is why Subaru decided to go in jointly with Scion/Toyota to build them. They got the use of Toyota fuel injection technology that way. Also they get great Fuel mileage and have 12.5 compression stock. 

 

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45 minutes ago, Timothy G. Elliott said:

One swap that comes to mind for me as a past owner of 2, is the BRZ FRS, 200 HP from the factory and both DI and PI which is why Subaru decided to go in jointly with Scion/Toyota to build them. They got the use of Toyota fuel injection technology that way. Also they get great Fuel mileage and have 12.5 compression stock. 

 

What would that go into being a boxer engine? An older subaru? Again, it is rated at 200hp, put it in the swap calculator and good to go. 

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5 hours ago, enginerd said:

So for an otherwise very similar engine, DI over port injection is going to have a small advantage in power, and a small advantage in efficiency. 
 

Specific to ChampCar though, where swaps are valued by manufacturer rated HP, is there going to be an advantage to using a DI engine over a port injected engine with identical rated HP? Maybe a small weight savings… maybe the DI engine is 5% smaller on displacement… maybe some efficiency gain due to CR. But likely no power gains to be had because those are already baked into the rated power. Perhaps it’s actually worse to use DI because it’s already been tuned / optimized by the manufacturer to a higher level than the PI engine?

DI engines adapt well to boost...

Edited by mender
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1 hour ago, MR2 Biohazard said:

What would that go into being a boxer engine? An older subaru? Again, it is rated at 200hp, put it in the swap calculator and good to go. 

 

So you are saying all 200 hp engines are created equal?  Nice try.

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35 minutes ago, Rodger Coan-Burningham said:

 

So you are saying all 200 hp engines are created equal?  Nice try.

Please School me.  If a 2.0L 200hp and 200tq engine is regular injection vs a 1.8L 200hp and 200tq due to DI and higher compression.  How would they perform different for us?

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1 hour ago, MR2 Biohazard said:

What would that go into being a boxer engine? An older subaru? Again, it is rated at 200hp, put it in the swap calculator and good to go. 

One could make it go into anything for enough time and money, granted they are RWD, but are set up to be 4x4, or could be changed to FWD with the right trans... Just another interesting possible swap. More then I can afford..Lol. and to be rediculous, add an Edelbrock Supercharger to bring HP to 300. Would be nice!

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30 minutes ago, MR2 Biohazard said:

Please School me.  If a 2.0L 200hp and 200tq engine is regular injection vs a 1.8L 200hp and 200tq due to DI and higher compression.  How would they perform different for us?


As Roger Waters would say you don’t need no education.  The calculator only uses hp as the input for the swap.  Torque, weight, efficiency are not considered. 

Edited by Rodger Coan-Burningham
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1 minute ago, Rodger Coan-Burningham said:


As Roger Waters would say, you don’t need no education.  The calculator only uses hp as the input for the swap.  Torque, weight, efficiency are not considered. 

I am aware of that. My thought is HP is HP so the calculator will work. HP goes up so does TQ so our series the hp calculator works as it should.  The exception that can be is a diesel, but the weight offsets the gain there. The DI might be lighter, but I can not imagine enough to worry about. On the 2GR it weighs 366lbs regular and 359lbs for the DI model. I am not seeing how 7lbs really matters. Efficiency is fine, but that is mianly for the mid range and low range tq. When at WOT the HP will equal fuel usuage so 200hp should be very close, if not the same, as 200 DI hp.

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The advantage of DI engines is not that they can make more HP at wide open throttle, they are equal or even worse in some cases to a really good port injection engine. The big advantage is being able to run really lean in low load conditions which are almost never seen in racing.

 

With direct injection, wide range variable cam timing, EGR, and boost, the modern engines can switch into and out of high power mode and super lean cruise mode where they are running close to Miller cycle.

 

A cautionary example of what these engines can and can’t do is when Ford put the original 2.0L EcoBoost engine in the Explorer. The available power that engine had vs the weight it had to carry around meant that the engine was forced to run in high power boost mode much of the time and the fuel milage was dismal. The upgrade program was called the FE or fuel economy upgrade, featured a new cylinder head, turbo and some other bits and was worlds better.

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7 minutes ago, mhr650 said:

The advantage of DI engines is not that they can make more HP at wide open throttle, they are equal or even worse in some cases to a really good port injection engine.

Interesting. So the DI engine might actually be worse for us in endurance racing. Then I guess there is really no worry about the swap issues then. Good to know.

 

Thinking about this also, when endurance racing and the engine being at WOT and higher rpms the engine bay will get hotter, causing the intake charge to be hotter, usually, and the engine intake manifold to be hotter. I wonder if the cooling effect of a port injection engine might be better at cooling the intake charge vs the direct injection model. So in reality and real world testing the port injection engine might be superior while the DI engine might win on the dyno. just pondering out loud on that idea as I have never worked on or own a DI engine or plan to.

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1 hour ago, Rodger Coan-Burningham said:

As Roger Waters would say you don’t need no education.  The calculator only uses hp as the input for the swap.  Torque, weight, efficiency are not considered. 

In addition to those factors, I think the biggest flaw is engines which respond very well to porting / tuning / etc. and those which don’t. Some engines will lay down WHP numbers exceeding their rating after simple 0 pt changes and others fall short. The ones that do are the only ones you want to swap.

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49 minutes ago, MR2 Biohazard said:

Interesting. So the DI engine might actually be worse for us in endurance racing. Then I guess there is really no worry about the swap issues then. Good to know.

 

Thinking about this also, when endurance racing and the engine being at WOT and higher rpms the engine bay will get hotter, causing the intake charge to be hotter, usually, and the engine intake manifold to be hotter. I wonder if the cooling effect of a port injection engine might be better at cooling the intake charge vs the direct injection model. So in reality and real world testing the port injection engine might be superior while the DI engine might win on the dyno. just pondering out loud on that idea as I have never worked on or own a DI engine or plan to.

The DI engine will make more power because you can have a higher CR with less detonation.  So you can't really compare them directly like you are trying to do.

 

The cooling effect on the intake would be nothing. Most port injection engines have the injectors so close to the valves, the fuel is only present for a fraction of a second anyway.

 

The DI engine has better airflow and thus more oxygen to burn as there is no fuel in the air, or on the walls of the intake.

It can also better control fuel flow (when getting on or off the throttle for example) and save fuel and have better throttle response. This may be small, but its still an improvement.

 

The only real downsides to DI, are the extra weight, a bit more complexity and possibly dirty valves.  The dirty incoming air has oil droplets (from the crankcase) and other contaminates in it. This will stick to the valves. A port injection engine will have fuel spraying the backsides of the valves down and washing them. A DI engine will not. This can hurt airflow if not cleaned.

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Just now, Team Infiniti said:

Realistically, I don’t see problems with a track dedicated DI engine in regards to valve build up, a racing PCV system would eliminate any incoming oil.

I agree. It is an issue with the DI systems in general.  The issue would be if you get that engine from a street vehicle, it may have alot of buildup already. 

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1 hour ago, petawawarace said:

I agree. It is an issue with the DI systems in general.  The issue would be if you get that engine from a street vehicle, it may have alot of buildup already. 

Which is why the Toyubaru's use both systems!

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