There’s are several different topics here, so this could go all over.

The DI comparison was used to point out the closer you get the CC the better. Elevated pressures in DI are mainly to overcome CC pressures. I’m not saying the pressure doesn’t help, but you don’t need 2000+ psi to atomize a fuel mixture. More precise delivery of the fuel directly in to the CC (maximum cooling) at a more opportune moment in the combustion cycle is the main advantage.

I agree, charge cooling does occur under a carb. Your theory of this being beneficial because it “provides more time for the charge to cool” is what I don’t agree with. If your theory was true, why don’t we see “competent” FI guys mounting all their injectors upstream of the TB? Wouldn’t this maximize the “charge cooling”? This has been done. Regardless of the ice deposits forming on the charge piping, it performed poorly when compared to standard FI placement.

With forced induction temps, fuel is flashing/evaporating before it ever hits the CC. This is a complete waste of energy. (though it will make the intake feel cold) Ideally you want fuel that has not changed states entering the CC to provide maximum cooling. The longer the path to the to the CC the more potential cooling energy is wasted.

Most importantly, you can’t control individual cylinder AFR’s as accurately with a carb. Anytime you distribute fuel pre-runner, each cylinders fuel charge will vary. More controlled fuel distribution per cylinder was the main reason for the switch to FI. Control over individual cylinder AFR will almost always lead to more power in a Carb VS FI “shootout”.

That comparison is laughable. They needed to retain the carbs and use them as throttle bodies. Then install/fabricate injector bungs on the same intake for a like comparison.

 

Not sure I'd agree with the injector placement.

Anything I've read or people I've spoken to who have tested, upstream injectors almost always improve performance at higher engine loads.

Some even run 2 injectors, and switch from close mounted to upstream only at higher loads because they perform better there.

 

Still curious on air distribution with relation to AFR and cylinder balance with a single plane compared to front feeder. EFI on both, none of the toilet bowl stuff.

 

Travis Quillen and the Butler Performance guys tested it and disagree. They switched back to a standard placement inj setup after disappointing numbers in pre-TB injection testing. (methanol setup)

This was on their record setting 2800hp 482 Pontiac. Lots of controversial stuff on that engine. 2.5" collectors/charge pipe, 91mm TB, low compression...etc..

 

This is from On the dyno's Holley Hi-Ram carb/fi test. They claim they have used blow through carbs with great success. Fitment on ours would be a challange and frankly I wouldnt want to give up the benefits of fuel injection but the results speak for themselves. If its a waste someone needs to go on there and correct them.

http://onthedyno.com/GM-LS-motor/art...hi-ram-468-ls/

CONCLUSION & TECH TIPS:
How is it that simple carburetors make more power than precise EFI tuning, especially when you can optimize the air/fuel ratio at every rpm on the EFI motor? The answer is easy-carbs are cool-or more specifically the charge cooling offered by carburetors. The majority of the credit for the change in power on this can be attributed to the charge cooling offered by the introduction of fuel higher in the intake (as opposed to directly into the cylinder head). Cooler air offers more oxygen molecules to burn-hence more power. To better illustrate this, we could run the test again using the carbs as throttle bodies and hook up the injectors to supply the fuel. This way there is no other change (like the single throttle body and slightly different lid). Testing on blow-through forced-induction applications, we have seen a simple carb drops inlet temps by over 130 degrees (they work well as intercoolers).

 

I’d like to see his degree in thermodynamics. (Not claiming I have one!) Anyone can write an article, that doesn’t make it true. (Including me!)

We all know a carb cools the A/F charge in the intake, no argument there. For his statement to have any merit he would need to measure CC temperature differences.

I'd also like to know how they measured the actual air charge temp drop under the carb without saturating a temperature probe of some sort? This is no different than the alky injection kit guys claiming impossible charge temperatures by spraying methanol on a temperature bulb.

Lastly a carb does not work as well as an intercooler, he needs a swift kick in the nuts for even writing that. That last statement alone discredits anything the guy wrote IMO.

 

You didn't say that earlier when you was pointing out my misconception about fuel cooling the intake charge. The test was conducted with the same Hi-ram configurations in both Hotrod shootouts.

 

I wouldnt give up the intercooler either. It is interesting though.

 

I didnt say pre TB injection, I doubt that would ever yield optimal results. I said injectors ran at a distance from the intake valve, but still either in or pointing directly into the runner.

Pre TB injection opens up a whole world of changes especially if the intake manifold was not designed with fuel flow in mind

 

Pretty dumbe they used the EFI grind cam for the carb setups. We run a different LSA from EFI, 108-110, rarely wild you see a 111. Clearly not fair for a real comparison.

 

Perfectly fair intake test on that engine. It wasn't a camshaft test or comparison.

 

I was using the pre TB point to argue the “more time to cool the air” theory.

Spraying the injector directly on the valve is the most popular method because it offers better low rpm performance and cooler combustion. Spraying high up in the runner isn’t done to cool the air charge, it provides better mixing at high rpm. (Like F1 engines that spray directly above the stacks. ) I can’t see the average LS dude with a sub 7k redline gaining much with the injectors placed high in a long runner style intake. Even if they did gain a little “up top” the losses “down low” wouldn’t be worth it IMO. You can also run into reversion issues with “up high” placement that make tuning certain load/RPM bands impossible. Similar to the F1 engines that idle at 7k+ and won’t perform well below 10k.

 

I was chatting to a guy a couple of weeks ago who runs a dual injector setup on his 5cyl Audi engine.

He can easily switch/blend between the inner and outer injectors at any time. When running at higher loads using only the outboard injectors it gained around 40hp on his engine which makes around 550hp vs running all fuel via the inboard.

Not saying all setups will see those sorts of gains, but he was very surprised, and I was too.

 

We grind cams for the engine application, that was not a carb application cam so no, not fair. A fair intake test would be running all 20 with that can and then all 20 with a carb cam. a flow bench test would be meow fair than this.

 

Flow bench would have been pointless.

Clearly some of the bigger intakes would have flowed more air in a test....but that isnt the entire story when trying to make power all across the rpm range which has been very evident on the test results. Most of the big intakes were quite ****.

You could equally say that cam wasnt an ideal cam for ever single intake...why not change cams every time too ? May as well change heads ? or other parts too ?

Because it wasnt a cam test.

 

From everything I've seen on the dyno. Carbs ALWAYS MAKE MORE POWER then FI. I have seen it tested probably 20 times. Changing cams, intakes, and everything you can think of. Now this is on 1000+ hp N/A stuff raced in a All Motor class. The only time the FI comes close is with the injectors placed at the top of the intake. Bar none a CARB WILL MAKE MORE POWER! On N/A stuff.
With that said we will all find out next year when NHRA Pro stock changes to FI next year. Those are the guys with the money to real test it.

 

Glad to see you say that the cam wasnt ideal for every single intake. I see where the different intakes have their places. Thats been my point the whole time. I probly was poor in simplifying that. Clearly the single plane is not suited to that cam but like you said it wasnt a cam test.

Help me out with this. This is not meant to be an argument so please dont take it the wrong way. I have always thought both valves needed to be open at the same time to suck fuel out of a carburetor. Moreso for high rpm power. So narrower lobe seperation, valves are now both open more at the same time, aka overlap. Low end torque would no doubt suffer. But wouldnt it work better in the higher rpms? No doubt this wouldnt be what you wanted in forced induction so please just consider N/A. Earlier we got into overlap didnt matter. I could see where more intake duration would help but why would the overlap be irrelevant? I am certainly no cam guru so please elaborate a little bit more on that please. Everone I know well enough to ask runs a really narrow lsa on their carbs hence that cam didnt seem right. Seems like with a computer controlled fuel injector that doesnt rely on vacuum to pull fuel in would certainly have different needs(cam). I will give it yall from here. I just want to explain where I come from in my thinking.

 

Only the intake valve needs to be open to pull vacuum, and the piston going down the bore is largely the source of that vacuum.

Overlap period....IF the setup is efficient may also add some scavenging effect. Or on the other hand if it is not efficient, may do quite the opposite and allow reversion.

So even there, you cant say the cam is or isnt ideal without factoring in head/valves/exhaust etc

And the injector only injectors fuel. If there is no airflow or intake valve open...that fuel isnt going to go anywhere anyway.

 

Right on. I have always pictured the air traveling through the engine at a much faster rate if both valves were open. I need to change my thinking on that.

 

Overlap is a very very short period compared to the total time the inlet valve is open.

yes overlap can help, but only if the system is efficient, and yes the scavenging effect will improve with rpm/air velocities.

But if you had a restrictive exhaust then chances of that scavenging effect being there is slim, and good chance of overlap hurting things

One of the great things about the LS's and modern engines in general, is their heads flow a lot of air, so people can make great power without using lots of overlap...which in turn makes for a better spread of power too, especially helping the lower end

And lets face it, in most boosted builds we dont want lots of overlap anyway. A blower might get away with it much better than a turbo setup, where often there is more pressure in the exhaust side than the inlet side.

So intake tests with milder cams again are quite relevant to a boosted application.