Another Radiator Theory Question

[No Rotr]

So I know we have had a few cooling related questions lately but I have yet another one. I need more cooling capacity for my LSX cause its an inefficent motor and runs hot, we all know this. So what would work better.
Option A:
26x19 double pass leaned back like a corvette.
Option B:
26x16 double pass leaned forward

either way it will be ducted to the front bumper and a typical vented hood. The car doesn't have a splitter or undertray right now but will within the next year I think. What are your thoughts?

[Def]

With the vented hood lean it forward if you have the space. The Vette has the radiator leaned back for the super low hood angle and still having space to get the intake up there.

[Matt93SE]

With a 26x16, you shouldn't have to lean it at all. Well not with an S14 anyway. The S13 may be a bit shorter up front.

I measured my S14 the other day and I have 27x17 from the top of the lower support to the top of the upper support. you can probably make it go down another inch or two if you want to cut the factory mounts off at the bottom. any lower and they'll hit the tension rod supports..

[Z28ricer]

Inefficient ?

Or people just using fans meant to cool a 250HP engine, on a 350+ HP engine?

[No Rotr]

Yes inefficent, LSX motors run hot and heat up oil really well. They just do. A 350hp lsx runs hotter than most other 350hp motor given the same radiator.

Would it be worth it to lean a radiator forward just to get an inch or two larger core over a stock sized radiator in the normal upright location?

[Z28ricer]

It would be worth it to use a normal koyo or other quality S chassis radiator that fits, then get fans that provide enough airflow, and properly duct the front side of things so that air goes through the radiator and not around it.

[icantdrift]

It's a bitch to fit the 26x19 in the s13. I had to push the bottom toward the engine and the neck still hit the hood. The 26x16 can sit straight up just fine.

[No Rotr]

I know a 26" rad fits upright just fine, but wouldn't it the air flow better if the radiator was tilted forward? That way the air coming out of the rad can go out the vent in the hood easier instead of flowing out the rad and right into the motor.

[Matt93SE]

You're overthinking things. The air isn't moving that fast by that point.

[CodyAce]

LSX's all run 'hot' comparitivly to import junk, but LSX's love heat...and make better power when hot. I don't see many overheating, even with FI up here...unsure why. Most guys use The big Koyo's with Altima fans for the low speed stuff. If needbe, by not take the Koyo to a shop and have them convert it to dual core?

[Tower240sx]

I agree with Cody GM engineered the LS series to run a hotter thermostat and running temp to help with emissions, so they aren't outside of their comfort zone at 215-230 F

As long as the oil temps stay in check you aren't heating the motor up beyond what it wants to see

[Def]

LSx will run WAY beyond 230 deg F in a bone stock Vette. I've seen guys running 250-265 deg F water temps in C5 Z06s (that's when you don't have mechanical empathy). Nevermind the 300+ deg F oil temps they'll run (which is probably part of the reason I've seen quite a few spin bearings).

IMO, we freak out a bit over water temps that aren't that bad, but I have a feeling overall water flow through the SR/KA isn't all that great. There are probably areas that don't get much flow, so lower temps help compensate for this. I don't have any data for this, it's just my feeling from seeing what happens on my car at various water temps.




BTW - GM ran the LSx hot for emissions AND for fuel efficiency. Going up from 170 to around 210 deg F is good for 3-5% fuel efficiency on the average engine due to less thermal loss to the cylinder walls.

[No Rotr]

My car lives at 235 coolant and 275 oil temps on track on a 70 degree day. Warmer than that and my coolant temps will continue rising. I HATE doing cool down laps, so I wanna fix this rising temp. I'm fine with anything under 235, its over that temp that worries me. I just think if I'm gonna do some hacking up from to get a rad to fit I might as well try to make it move the air in and out better. A 26x19 rad sat in upright in the factory location would be easiest and probably work out. But its winter time and I'm bored so this is what happens haha

[croustibat]

All your hard work will be completely useless, unless you add proper ducting.

A bigger rad will have less flow, if you are not ducting it correctly you could even get worse result than with a thin high flow rad.

Get some aluminium sheets and rivets, duct that properly, vent to your hood, install a fan schroud, maybe a better fan, put back the undertray (i guess you removed it), and you WILL get better result than any bigger rad work.

Been there, done that. Got heating issues, installed 2" thick radiator, still got issues. Ducted a bit on a trackday with 3M tape and Voila ! Temp problem gone.

[Umai Kakudo]

Here is a good radiator and cooling system tech resource from Stewart Components

http://www.stewartcomponents.com/Tech_Tips.htm

Radiators

Thicker radiators do have slightly more airflow resistance than thinner radiators but the difference is minimal. A 4" radiator has only approximately 10% more airflow resistance than a 2" radiator.

In past years, hot rodders and racers would sometimes install a thicker radiator and actually notice decreased cooling. They erroneously came to the conclusion that the air could not flow adequately through the thick radiator, and therefore became fully heat-saturated before exiting the rear of the radiator core. The actual explanation for the decreased cooling was not the air flow, but the coolant flow. The older radiators used the narrow tube design with larger cross section. Coolant must flow through a radiator tube at a velocity adequate to create turbulence.

The turbulence allows the water in the center of the tube to be forced against the outside of the tube, which allows for better thermal transfer between the coolant and the tube surface. The coolant velocity actually decreases, and subsequently its ability to create the required turbulence, in direct relation to the increase in thickness. If the thickness of the core is doubled, the coolant velocity is halved. Modern radiators, using wide tubes and less cross section area, require less velocity to achieve optimum thermal transfer. The older radiators benefited from baffling inside the tanks and forcing the coolant through a serpentine configuration. This increased velocity and thus the required turbulence was restored.

Radiators with a higher number of fins will cool better than a comparable radiator with less fins, assuming it is clean. However, a higher fin count is very difficult to keep clean. Determining the best compromise depends on the actual conditions of operation.

Double pass radiators require 16x more pressure to flow the same volume of coolant through them, as compared to a single pass radiator. Triple pass radiators require 64x more pressure to maintain the same volume. Automotive water pumps are a centrifugal design, not positive displacement, so with a double pass radiator, the pressure is doubled and flow is reduced by approximately 33%. Modern radiator designs, using wide/thin cross sections tubes, seldom benefit from multiple pass configurations. The decrease in flow caused by multiple passes offsets any benefits of a high-flow water pump.

Gross flow radiators are superior to upright radiators because the radiator cap is positioned on the low pressure (suction) side of the system. This prevents the pressure created by a high-flow water pump from forcing coolant past the radiator cap at high RPM. As mentioned in the radiator cap section, an upright radiator should be equipped with radiator cap with the highest pressure rating recommended by the manufacturer. The system will still force coolant past the cap at sustained high RPM.

Of particular interest when selecting a radiator is this bit on radiator caps and configuration

Radiator Cap Location

The radiator cap should always be located at the highest point of the cooling system, and on the low pressure side (after the radiator core).Cross flow radiators mounted higher than the engine are ideal because the cap is on the tank that is connected to the water pump inlet. This configuration offers 3 advantages:

1. The cap is at the highest point of the system, allowing any air to migrate to the area just below the cap. In the event the cap vents due to excessive pressure, the air will escape first.
2. This area has the lowest velocity within the system, allowing air to separate from coolant even at high engine RPM.
3. The cap is located on the low pressure (suction) side of the system, so it is unaffected by the pressure generated by the water pump.

For cooling systems NOT using a cross flow radiator, mounted higher than the engine, you must use a surge tank. A surge tank is typically a 1 quart tank mounted at the highest point of the system, with the radiator cap on top. The bottom of the tank is connected to the inlet side of the water pump with a 1/2" or 3/4" line. A 1/4" to 3/8" "bleed" line from the side of the surge tank is connected to the highest point of the low pressure side of the radiator. The bleed line allows some circulation through the tank while the engine is running. The surge tank is also large enough to allow the air to separate as the coolant flows through it. Air in the system will then migrate to the area just below the radiator cap, again so that it will forced out first if system pressure exceeds the radiator cap's rating.

In street car applications, an upright radiator (top and bottom tanks, with the cap on the top tank) represents a compromise that will work, as long as the car is not operated at sustained high RPM, like those seen in racing.