HOHN

OK fellas, I was playing around with my spreadsheet.

Consider a stock HO truck:
BSFC: .400
HP: 245 (crank) @2700 rpm
Intake manifold temp @ boost: 130ºF
A/F ratio: 23.5:1
Peak Boost: ~20.5 psi

Some of these number, like A/F ratio I had to interpolate to get (based on stock specs).

However check this out:

If intake temp (in the hat) goes up from 130 to 200, it takes 24.6psi of boost to get the same mass of air into the engine as you had at 20.5psi of boost with 130º temps.

When you kick up the HP to 500, the difference in required boost from 130 to 200 goes from 57 to 65psi.

What if I rig up a water sprayer system on my intercooler and I can actually get intake temps down to ambient or lower?

Let's say we drop from 130º to 85º in the hat with our stock 245hp engine. Now we only need 17.8psi of boost to deliver the same amount of O2 as when we had 20.5 at hotter intake temps.


What happens when I push my turbo way off the map and intake temps soar? Let's say output is 375º (pretty reasonable guess): If you had 38psi of cool (130º) boost, that hot 375º boost would have to be OVER 60psi to deliver the same amount of oxygen.


What does this tell me?

1) You can never have too much intercooler. At least at long as you have enough heat for efficient combustion.
2) I NEED TO INSTALL AN INTAKE TEMP GUAGE!!
3) You can't make meaningful comparisons between turbos without knowing intake temps. Who cares if a turbo makes 40psi? You CANNOT know how much air you're actually getting to the engine without knowing both pressure AND temp.

Maybe I can "tee" the boost port on my intake hat and get temp readings there?

I'd love to go to a SPA dual guage, but that's expensive, and I honestly don't feel like yanking off my gauge pillar for the billionth time.

Anyway, I'm just thinking out loud here.

Maybe rigging up a small Shurflo pump with a spraybar towards the intercooler woulb be worthwhile? Water injection-- but outside the engine!


Justin

Bart Timothy

About 5 or 6 years ago over on the TDR there were a few threads talking about intake air temps and what effect they had on performance. They have always stuck in my mind.

One conclusion was that the best performance for intercooled diesel engines is achieved when ambient temps are between 45 and 75 degrees F. It has something to do with ignition temperatures.

In another thread someone reported dyno test results where the intercooler was sprayed with liquid nitorgen vs. ambient air temps. No power gains were shown. Maybe the liquid nitrogen was a little too cold.

I've never seen any tests where the intercooler was sprayed with water.

BBA

Wow ok it seems like there was TONS of thought put into this. IN a way it strikes me as like oh wow yea that seems like great info! THe the other part of the time im like ok this is way to much for me or should it be . Really though pretty interesting

Ph4tty

It can't hurt. I've heard the turbo neons come stock with these. I still think you love your hx35 too much and just are looking for ways to keep it =P All kidding aside this might be a fun thing to test when you get back home.

Wouldn't you think this might not show as much of a difference on a single dyno pull as it would towing or racing?

HOHN

ABSOLUTELY. This is one of those things were a single dyno run most likely will not tell the tale.

Unless, of course, it's a sophisticated variable load dyno like the Superflow I ran on in Greeley, CO. That thing could simulate any load you wished.

Once you get some heat saturation in the engine, you'd really start to see how important those intake temps are.

Towing of course would be the proof of concept, as imo that's really the ultimate test for almost any add-on.

All the more reason that I simply MUST install a temp gauge in my intake hat.

I would expect that a guage like this would show a pretty rapid increase with boost levels, then it would level off once you reached peak boost. However, heat soak would set in and you'd see a steady but slow climb to some undefined maximum.

jh

RowJ

Just to add an unscientific observation along these same lines.

I always wondered if the first pass at the drag strip wasn't my greatest opportunity for best times, for some of the reasons you mention... primarily heat soak. But it has never works out that way.... even when making fairly rapid back to back runs?

Lots of other variables involved, but I have seen guys make 4-5 passes back to back... without loosing ET or top end?? I don't like to do this because tranny temps get toasty (200*+), but I have on two occasions. With no apparent loss in performance?

This observation in no way negates what you are saying, Justin.... but perhaps, it does speak well for the Dodge set up from the factory?

RJ

Ben

Hohn,

The pump and spraybar is something I have thought about for a while except in a different application.

The radiator on liquid cooled 4wheelers. Anytime you go on a long dusty ride the rad gets packed with dust, loses cooling ability, and the temp light will come on.

I thought of rigging up the same setup to spray the backside of the rad to cool it down. You would have to install a temp guage and flip the switch when you see the temp climb.

Never went past thought stage, mainly due to my mechanical declination and my wheeler is oil cooled.

I like your way of thinking tho. Makes sense to me. My truck always runs better in fall, late winter/early spring. Hazy, hot, and humid doesn't cut it. I had to take the Smarty off of kung fu to keep the egts and smoke in check. The forementioned seasons dont have an issue. Dead of winter is too cold imo. -40 to 0.


Keep us posted and throw some pics up of your temp guage setup.

HOHN

I agree with your post. It's quite possible the heat soak isn't much of an issue with our trucks. We've all heard that "diesels like to run hot", and while I don't have proof at all and it flies against my first bluch reasoning, it could entirely be true.

After all, a hotter engine burns the fuel more completely, and loses less of that heat to the coolant. That's more heat to push down the piston.

Also, a hotter engine preserves more of the heat energy that drives the turbo.

Not to mention that hotter oil is thinner oil.

There are plenty of reasons why heat soak might not be an issue, because there are lots of good things that tend to balance out the negatives we associate with heat soak.

jh

Big Blue24

Hohn, whey don't you tap into the built in stock intake air temp sensor. The Juice/Att reads it but I don't know how well it reflects the actual air temp. I'm sure it experiences lots of heat soak being mounted right on the block.

I've noticed that at highway speed, intake air temp usually levels off around 35* above ambient air temp. If I pull a big pass with boost sitting 10 - 15 psi, it will raise about 5*. It also seems that when it is 100* plus, it sits about 40* higher than ambient air temp at cruising speeds. I am at higher elevation than most so who knows what affect that has on my numbers. In my opinion, the stock HX 35 spools too slow for my liking. High temps and high altitude kill spool up. Truck feels different when I drive to see my parents in Wash at 2200' compared to my 5000' here.

HOHN

Bingo. I want a temp sensor that tells me what temps are as they come out of the CAC, or close to it. The intake hat is as close to the engine as I'd be willing to consider.

Considering the MAP location, I can't imagine that being accurate since it's down inside the engine. Well, it IS accurate in the sense that it tells you what the temp of the air going into the cylinders actually is.

But I don't want to know that. All that really tells me is that the engine gets hot enough to warm things well above ambient. It tells me nothing about turbo performance or intercooler efficiency.


So the purpose of me installing a temp gauge wouldn't be necessarily to measure the temp of air going into the engine (and hence, account for engine heating)-- rather, I'd be looking to install it as a tuning tool, something to indicate temps as they exit the CAC....

Justin

NoSeeUm

I have spread sheeted this problem six ways to Sunday, but probably not nearly as advanced in thinking as your spread sheet. I typically just use an efficientcy number for intercooling and typically that number is/was 73%. My goal was the same as yours, make a smaller turbo perform bigger.

Seems the biggest (easiest) improvements to IAT come with increased compressor efficientcy. It is my belief that lowering EGT's comes down something not ussually talked about. I like to call it "excess air". This excess air is that air not reacted in the combustion reaction, but simply is present to absorb heat. The total energy of combustion is spread out over more molecules so the temperature is less. The temperature change for compression is greater, but the net effect is lower EGT's.

Water sprays would be very effective at lowering intercooler outlet temps if you could find a way to keep the outside heat transfer surfaces clean.

Placing evaporative cooler media / nozzles upstream of the intercooler? Placing evaporative cooler media / nozzles inside the cold air in path? With those ideas you can only knock the temperature down to wet bulb, but on a hot dry day that can be close to 40F below ambient. The second option would likely increase Hp as a direct effect as well.

Spraying water directly on the intercooler fins you could go below wet bulb, but I think you would need to devise a pre-filter to keep the dust minimized. Maybe a house furnace ventilation type filter?

Jim

HOHN

My concern with spraying anything on the outside is cementing the CAC closed. You'd have to use distilled water, because the impurities in tap water will build up on the surface the water evaporates from, and in no time your CAC is essentially no longer working.

That's why I like your evap cooler idea. That way you don't have to spray the CAC directly and ruin it with mineral buildup-- rather you can let the crud build up in a disposable evap cooler media, and let the CAC enjoy the benefits of cooler air.

Water or water/methanol injection into the engine is a proven way to lower EGTs.

I agree with the "excess air" theory you mention. But air has relatively little mass. That means it's not very effective at absorbing heat, especially compared to water or water/meth.

Moreover, it's hard to isolate the effect of "excess air" from the heat absorption aspect, because surplus air shows up as lower EGTs anyway-- no only from heat absorption, but from burning the fuel faster and more completely in an environment with more available oxygen.

Personally, I think compressor efficiency doesn't tell the whole story. I think that the turbine section gets to a choke point where not matter who efficient or good the compressor is, the turbine just can't flow enough to not choke the flow coming out of the engine.

Take the turbo off your truck and just visualize 50-60psi pressurization in those little inlets and how they'd escape the positively tiny turbine section of a stock turbo. Definitely designed for quick, early spool for emissions, not for power or EGT control!

jmo

NoSeeUm

I am thinking to test this out you might try just finding a piece of evap media about the right size, dip it in a bucket, slide it in front of your IC, and then see how it works until it dries out. That would be simple and easy.

When I mentioned compressor efficientcy, I believe I really meant turbine - compressor efficientcy.

I also did quite a bit of number crunching to determine the Hp loading of a tight turbine case (Hx35). Basically considering net engine back pressure or a Drive Pressure Ratio > 1 and trying to calculate the Hp loss due to the greater pumping losses. Eventually I could calculate the Hp loss, but I could never come up with a direct calculation for the EGT increase for a given DPR > 1 as compared to DPR's = 1 or DPR's < 1. My thinking was that if I could some how correlate that Hp loss into added fueled burned (heat) and compute the EGT rise doing a Hp to heat balance calculation.

End the end, coming up with EGT rise calculation was just way beyond me and my High School math skills.

I do know that for the Hx35 the DPR quickly gets to around 2 at around 30 - 35 psi of boost with the DPR staying close to 1 only until about 10 psi of boost. Looking at the Hx35 map, 20 psi boost is also its sweet spot so it is a very good compromise. At 20 psi (from bad memory) the Hx35 is likely running about 30 psi of drive or so.

So I came to the conclusion, as I think you have, that with the Hx35 no matter how much you cool IAT when the Hx35 is running up near the top of its map, that your EGT issues will still likely be the result of a high DPR. It seemed very difficult for me to make the Hx35 into a bigger turbo by just CAC efficientcy increases alone. The material costs to make this happen seemed more expensive (plus R&D trial and error $$$ losses) than just going with a bigger (in my case twin) turbo set up and enjoy more EGT worry free driving.

Jim

Hammer

Justin..
I have had two trucks in recent years utilizing spraybars on their intercoolers and one even sprayed both of his turbo compressor housings also.I also had one which was spraying the intercooler with CO2.The trucks all were above what we would normally see for numbers but the owners of the one from MD,which was a street puller,said the gains really are seen at the big end of a pull where temps go off the chart.The CO2 truck was good but not worth my time as I felt that once the fan was turned on the air blew it into the engine compartment killing his big end number.The owner of that truck told me it was a trick the nacho wagon tuner rides use for that extra ump.....Andy