[Revalot]

It's on YouTube a direction injection LT is worth 65hp vs if the same car had port injection alone, half port, and half direct injection/16 injectors I believe you still lose 35 hp, port only I believe you lose almost 65hp, might gain a couple of hp. I could be off some on specs, somebody post a video of BTR test. So if I add a 2650 and maybe a better cam, but most 6 speeds with a good cam will loose some toque on the bottom, I just wonder if a 2650 could pull 750 rear wheel and about the same amount of boost. Man when you sit back for a few years you really let everyone experiment and then find this best combination for the $, and looks like for a decent hp jump, you dont need port injection. The test is called BTR Port vs Direct injection. Imagine a LS7 with direct injection 570 at the crank, I know the heads would haft to be different.

[KingLT1]

That is on NA applications that is not limited by fuel system. On Boost applications it's a different ball game. Yes these cars do need port injection for supplemental fueling because the DI system cannot keep up with builds pushing 1100whp+ on full E85. Why do you think GM made the LT5 dual injection and also why Ford went dual injection on the Coyote.

The caveat with direct injection is that the window to inject fuel is very small vs port injection. So you need huge injectors that only can use 30% of their capability vs port can use 80-90% of the injector. The problem with really large injectors is the idle quality suffers due to really low injector pulse widths. So, there is a point where it makes more sense to add a secondary port injection system to only activate under boost that way you can use a smaller DI injectors for better drivability.

The good news is that you don't need either a 2650 nor Port Injection for 750whp. If you have been paying attention over the years, you would see that a Ported blower, 38% lobe cam, and low side would get you 750whp on E60 all day.

[Revalot]

O yes I've been watching what works and what doesn't, A ported throttle body on a LT4 can over heat (= timing pulled in the ecm) the air after a couple of pulls due to the 1740 being smaller and thinner, and the same car that threw that big number up with the throttle body gets a beat down by even a stock car after a few runs. The 38% fuel lobe is a winner, I just like to keep that low end toque, I do like a good cam, so it's more positive than negative. E60, E85 meth, you can keep all that, gas mileage is not that important to me, but we know it suffers big time, I rather pull up to a gas station here in Texas pump 93 octane and be on my way, I don't want to mix gas and all that head ache, I did the airplane gas with my carburetor motorcycles back and the day, just to find out lower octane gas burns faster from the pump and you go faster, Now VP m109 this or MR12 etc,etc, what few don't pay attention to is after every weekend race on some fuels you haft to flush your oil, the contaminants from the fuel breaks down seals/O-rings etc.
A 2650 if a person can afford it is what the LT4 really needs, you don't have to worry about heat, no timing being pulled, so back to back to back pulls can be made, Hell I imagine you could road race a 2650 magnuson and the car would run cooler than a bone stock factory car, performance is great, performance and longevity is better.

If I was talking about 1000 hp motor of course port injection would be included, but the LT4 definitely deserves a couple more hp and can totally be reliable, that's my point. Thank you for all your wisdom, I was just trying to inform everyone about BTR video and information. Thanks

[Evansa22]

Originally Posted by KingLT1

That is on NA applications that is not limited by fuel system. On Boost applications it's a different ball game. Yes these cars do need port injection for supplemental fueling because the DI system cannot keep up with builds pushing 1100whp+ on full E85. Why do you think GM made the LT5 dual injection and also why Ford went dual injection on the Coyote.

The caveat with direct injection is that the window to inject fuel is very small vs port injection. So you need huge injectors that only can use 30% of their capability vs port can use 80-90% of the injector. The problem with really large injectors is the idle quality suffers due to really low injector pulse widths. So, there is a point where it makes more sense to add a secondary port injection system to only activate under boost that way you can use a smaller DI injectors for better drivability.

The good news is that you don't need either a 2650 nor Port Injection for 750whp. If you have been paying attention over the years, you would see that a Ported blower, 38% lobe cam, and low side would get you 750whp on E60 all day.

Is it possible to lower rail pressure at idle, but open up the pulse width? Better atomization? As apposed to a quick little burst of a lot of fuel with the bigger injectors.

[radz28]

I think if you lower pressure too far, you start losing the atomization and efficiency window of DI. There's a specific window in the combustion chamber-processing where the fuel needs to be injected for full efficiency, and I believe High Side pressure plays a roll in that. There are desirable swirling/tumbling that GM spent millions of modeling on to find the balance. The way the air moves through the intake runner, past the valve, and moves across the combustion chamber and mix with the fuel at the correct time, blah blah blah. If you move DI pressure around in a way that isn't conducive to that balance, you'll push fuel out of the exhaust stroke, or the last part of the intake stroke. I think you have to worry about cam timing and spark timing, to an extent. It's a balancing act. The more you mess with, the further down the rabbit hole you have to go...

[Revalot]

Evansa22, I would run my questioning by BTR, he has a dyno called the spintrone or something like that, he says GM designed the LT is on a nascar's level of technology, But he will answer your questions. It seems like the more you share information, from shops that's doing the time and work to make our sport better every one knows more than the tuning and building shop. I'm sure
on his YouTube channel, people can speculate or tune a car and it's a trial and error process. I have never purchased a part from BTR, but I definitely will even if it's a cam for my LT4, the guy is teaching us light years of information, he mentioned Richard Holder(LS true guru)also, they talk quite a lot, and Richard will tell you what works and wasn't doesn't.

[KingLT1]

Originally Posted by Evansa22

Is it possible to lower rail pressure at idle, but open up the pulse width? Better atomization? As apposed to a quick little burst of a lot of fuel with the bigger injectors.

yes, I have had to do that with +65 injectors, and they work fine. These require lower rail pressure across the board vs LT4 stuff. 2500psi max

LPE supposedly has some +90's coming out...not sure how those will be to tune.

I prefer to fuel the engine DI only, but with the price increases on DI fueling, PI starts to make a lot more sense.

[ZL1Atlanta]

Good info, I'll check that out. Admittedly, we never did the test ourselves, but a couple years ago when planning for port injection, I had multiple reputable people, including TooHighPSI, suggest that I retain my upgraded DI parts versus selling them. All of them said it'll make more power the further we can push DI before needing the PI. Monetarily, that was a bummer because much of the PI cost could be covered by selling my upgraded DI pump and injectors, but I'm also always going for max effort of whatever parts are on the car, so I kept them.

The other bummer is that there is a high likelihood the aftermarket DI parts aren't going to be as reliable as 100% OEM. I'm on my third LPE Big Bore (various reasons for failures) and second set of +30 injectors now.

[KingLT1]

Originally Posted by ZL1Atlanta

Good info, I'll check that out. Admittedly, we never did the test ourselves, but a couple years ago when planning for port injection, I had multiple reputable people, including TooHighPSI, suggest that I retain my upgraded DI parts versus selling them. All of them said it'll make more power the further we can push DI before needing the PI. Monetarily, that was a bummer because much of the PI cost could be covered by selling my upgraded DI pump and injectors, but I'm also always going for max effort of whatever parts are on the car, so I kept them.

The other bummer is that there is a high likelihood the aftermarket DI parts aren't going to be as reliable as 100% OEM. I'm on my third LPE Big Bore (various reasons for failures) and second set of +30 injectors now.

Just curious are you running XDI or FIC injectors?

[ZL1Atlanta]

Originally Posted by KingLT1

Just curious are you running XDI or FIC injectors?

FIC. On the gen 2 now, so fingers crossed. They are down the road from the shop, so testing and swapping is pretty easy. Getting them out sucks obviously.

[KingLT1]

Originally Posted by ZL1Atlanta

FIC. On the gen 2 now, so fingers crossed. They are down the road from the shop, so testing and swapping is pretty easy. Getting them out sucks obviously.

Gotcha...I know some shops/tuners have switched exclusively to XDI. I haven't had any issues with either other than 1 set of FIC would misfire at 2900psi.

[Joshinator99]

Originally Posted by KingLT1

Gotcha...I know some shops/tuners have switched exclusively to XDI. I haven't had any issues with either other than 1 set of FIC would misfire at 2900psi.

The HP Tuners forum posts I’ve read seem to agree that the XDI ones are easier to tune and more reliable than the FIC ones.

[ZL1Atlanta]

Originally Posted by Joshinator99

The HP Tuners forum posts I’ve read seem to agree that the XDI ones are easier to tune and more reliable than the FIC ones.

I've seen that also and will likely switch if I have another issue.

[Joshinator99]

Originally Posted by ZL1Atlanta

I've seen that also and will likely switch if I have another issue.

Have you heard anything about the +90’s that King referenced? What confuses me about those would be what will LPE do on the HPFP side. The +52 and +65 injectors out there pretty much max out their existing Big Bore HPFP.