Air hose from exhaust to intake?

[Eddo Rogue]

I thought colder air (and fuel) made more hp? Is this only true once the engine is warm?

 

[Dirtman]

I thought colder air (and fuel) made more hp? Is this only true once the engine is warm?

What good is more HP for the first 60 seconds the engine is started? It's only supplying warm air at startup for a minute or two then closes and let's cold air in.

 

[scotts90ranger]

I thought colder air (and fuel) made more hp? Is this only true once the engine is warm?

In short, yes... cold fuel doesn't atomize well (stays liquid like mentioned earlier) and when really cold until the engine warms up the pistons and cylinder walls aren't up to temp so the compression isn't where it would be either. For carburetors they have a few things going on that this helps, a lot of intake manifold designs had an area for fuel to pool in the middle of the intake manifold so it could vaporize on the hot manifold if it was liquid...

There's a happy medium in there, cold air is always good but cold fuel doesn't atomize at low speed (idle), high speed there's enough turbulence to make things happen (I'm guessing, but it makes sense). There's a lot of things that make more sense on carbureted engines but do some for fuel injected engines so they stick around. There's also a lot of general engine things that are used and just labeled emissions related... like adding fuel when at high speed high load, technically the exhaust valves start getting toward their melting temperature and get close to tuliping so on a gasoline engine you add more fuel and it cools the exhaust down. Technically this temperature conveniently coincides with the catalyst temperature getting hot so it is now called "catalyst protection" and is therefore an emissions related function. And there kids is why you add fuel and decrease the AFR at high engine speeds and loads, you would actually make more power running leaner but that would get melty (to be technical...)

 

[RonD]

Cooler air is heavier, i.e. "hot air rises" because its lighter than the cooler air around it, its how a hot air balloon works, the warmer air inside the balloon "floats" in the cooler air outside

Air/fuel mixes are WEIGHT RATIOS, not volume
Gasoline has a ratio of 14.7 to 1
14.7 POUNDS of air to 1 POUND of gasoline, this is why fuel injectors are rated in POUNDS per HOUR flow rate
So with cooler/heavier air you can add more fuel, and if you can add more fuel then you can release more energy/power on each power stroke
So better HP, its why engines are "peppier" in the winter with the cooler air
But..............higher elevations have lighter air, less air pressure, so even though its Colder air, in say Denver, it still Weighs less so less power can be released

Startup and Choking
A spark plug can't ignite liquid gasoline
A spark plug can only ignite gasoline Vapor, the stuff you smell from gasoline
Cold gasoline has less Vapor, less smell
You need a minimum of 30% Vapor in a cylinder to get a good ignition, good explosion

A Choke plate in a carburetor restricts the air flow into the top of the carb, since an engine generates the same vacuum when cranking or running the restriction causes more gasoline to be sucked out of the Jets and into the cylinders
If the cold gasoline had vapor at 20% then sucking in 1.5 times the gasoline would get you to 30% and a good startup, the colder it is outside the colder the gasoline would be and the less Vapor it would have, so the more the Choke Plate closed, and more fuel was sucked in to get the needed 30% Vapor

The Engine Computers do this with fuel injected engines based on ECT sensor(engine coolant temp), and IAT(ACT) sensor(Air temp)
Computer adds more fuel(opens injector longer) to get more Vapor on cold start
This extra fuel added can cause carbon build up and really is a waste of fuel, so the faster the engine/gasoline can be warmed up the better

And the pre-heated air raises the Vapor level in the gasoline as it leaves the Jets or injectors so less Choke can be used until no Choke is required

 

[Chapap]

In short, yes... cold fuel doesn't atomize well (stays liquid like mentioned earlier) and when really cold until the engine warms up the pistons and cylinder walls aren't up to temp so the compression isn't where it would be either. For carburetors they have a few things going on that this helps, a lot of intake manifold designs had an area for fuel to pool in the middle of the intake manifold so it could vaporize on the hot manifold if it was liquid...

There's a happy medium in there, cold air is always good but cold fuel doesn't atomize at low speed (idle), high speed there's enough turbulence to make things happen (I'm guessing, but it makes sense). There's a lot of things that make more sense on carbureted engines but do some for fuel injected engines so they stick around. There's also a lot of general engine things that are used and just labeled emissions related... like adding fuel when at high speed high load, technically the exhaust valves start getting toward their melting temperature and get close to tuliping so on a gasoline engine you add more fuel and it cools the exhaust down. Technically this temperature conveniently coincides with the catalyst temperature getting hot so it is now called "catalyst protection" and is therefore an emissions related function. And there kids is why you add fuel and decrease the AFR at high engine speeds and loads, you would actually make more power running leaner but that would get melty (to be technical...)

Huh didn’t know that was a thing. I’d imagine that “high speed and load” is not just 80 mph. Add EGR to that too?

 

[scotts90ranger]

High speed as in high engine speed not vehicle, normally starts coming in over 3000rpm as a rule of thumb (+/- on different engines and varies on load too so it gets complicated). Yes, EGR is added to the mix there too, cooler combustion means less NOx production, so if you add in some inert gas (exhaust gas is already burnt so no oxygen or fuel in it in theory, just CO, CO2, H2O and NOx mostly in no particular order) there's less fire so less heat and less NOx. I don't use EGR at work so I don't know how much or how it comes in and don't take this as saying that EGR is killing power on everything, I'm pretty sure it's just used at the transition of where extra fuel is added so they can keep it in closed loop for longer, I don't think it kills that much power...

 

[dirtymike]

And that is your physics lesson for today. Ill UN tape it RonD and see if I notice a difference. Thanks Dirty

 

[dirtymike]

Sit a glass of ice water on the valve this morning for a few minutes and it opened up. Did the same ole hesitation for a few a moments and cleared up. Having a problem with losing power going up hill. I do believe the fuel injectors are clogged with rust from the fuel manifold again. This will be the third time since i did the top end. Limp it till winter i guess. Dirty.

 

[Eddo Rogue]

Sit a glass of ice water on the valve this morning for a few minutes and it opened up. Did the same ole hesitation for a few a moments and cleared up. Having a problem with losing power going up hill. I do believe the fuel injectors are clogged with rust from the fuel manifold again. This will be the third time since i did the top end. Limp it till winter i guess. Dirty.

I found some replacement injectors fairly cheap in rock auto. I went middle of the road price wise and got the Bosch. Have about 500 miles on em and seem fine. I kept my originals to send out and have professionally cleaned. Figured I have 2 sets and rotate em out for cleanings.

 

[RonD]

Engine will start to ping/knock under load if its running low on fuel
So if you don't hear that then its not a fuel issue

But..............I think 1987 2.9l had EGR valve and a Knock sensor, and the knock sensor could be detecting ping/knock and advancing the spark timing causing the drop in power
So it is a low fuel issue, lol, or low EGR flow
Its one of those chicken and egg things

Start with vacuum gauge to see overall engine condition, one of the better tools for diagnostics on "pumps"
And that's all any gasoline engine is, a self powered air pump
I like these tests: https://www.gregsengine.com/using-a-vacuum-gauge.html

 

[dirtymike]

I did a vacuum test at full farm up but cant post the vid, says its to large. Ill try to shrink it down. Guess i need to tape to my wiper and do a road test. With it plugged in its runs as if there was a plug there, right? Dirty

 

[dirtymike]

Got no pinging yet.

 

[RonD]

I did a vacuum test at full farm up but cant post the vid, says its to large. Ill try to shrink it down. Guess i need to tape to my wiper and do a road test. With it plugged in its runs as if there was a plug there, right? Dirty

Didn't understand a word of this, lol

Don't need/want a video, just numbers

 

[Chapap]

I did my injectors recently. Was hoping to get a new fuel rail if it was cheap, but couldn’t find any. Guess that’s a junk yard thing if needed?

 

[dirtymike]

(Vacuum Test) It runs around 19 to 20 idle, Initial throttle it drops to 15 and recovers quick to a steady 20 to 21. WOT drops to 0 for a second and recovers to 21. Needle bounces a little at 2k rpm.