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Heat soak and the 5.7 hemi

12813 Views 31 Replies 13 Participants Last post by  MoparR/T
This engine seems really sensitive to heat soak. More so than any other engine I have owned. Maybe my opinion is due to the 0-60 timer we have, whereas all my other cars have not had such a tool/reference point to judge this by, but wow the difference in performance.

When the motor is freshly warmed, I am getting roughly .2x to .3x better 0-60 times vs when it's highly driven/warm/heat soaked. This creates more of a performance difference than any mod I've done. The best mod I've seen for our cars is an engine with about 5 minutes warm up time vs driven all day. It hates heat! I even installed a water/meth injection kit (running 80/20 meth to water, as this has given best results) in an attempt to mitigate the heat soak to no avail. Being able to manage this heat soak seems to be a worthwhile mod for this engine.

As a note, I just installed a srv 392 intake manifold, which is the best mod I have done so far, but 0-60 times range from [email protected] 80 degree ambient temp to a heat soaked 4.9x at same temp.

Any ideas on how to reduce heat soak?
Any thoughts?
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This engine seems really sensitive to heat soak. More so than any other engine I have owned. Maybe my opinion is due to the 0-60 timer we have, whereas all my other cars have not had such a tool/reference point to judge this by, but wow the difference in performance.

When the motor is freshly warmed, I am getting roughly .2x to .3x better 0-60 times vs when it's highly driven/warm/heat soaked. This creates more of a performance difference than any mod I've done. The best mod I've seen for...
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Discussion Starter · #5 ·
Yes I have a home made CAI. Below the factory box, I have a 5in tube coming up from a ram air scoop under the car to the triangle opening at the base of the box with a k&n filter inside. Intake temp is on average 10 degrees above ambient when cruising around town at 30-40 mph. When activated, the injection drops it another 30 degrees. It can be in the mid 80s outside and I'll have intake air in the 50s.

The sensor is about 5" downstream of the nozzle, so the water/meth affects it quickly. However, I question how much air is being displaced when the water/meth evaporates.
 

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Discussion Starter · #8 ·
Funny, people get all bent about air temp. Not really much of an issue, add a blower and intercooler if you want more air.
Yes actually air temp is very important. I would be making more power with straight air at 50+ degrees vs evaporated methanol fuel and air at the same temp. The evaporated fuel is displacing oxygen, as evidenced with a sharp increase in the air/fuel ratio. I'm still playing with this some, but my trinity is freezing up on me preventing me from logging.

I am just amazed how much output drops when the hemi is heat soaked. I wonder if a lot of dyno discrepancies are due to engine heat soak. Next time I dyno, I might test this. Let the car cool for several hours outside the dyno shop, then put it on the rollers freshly warmed and compare it to being heat soaked.
 
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Discussion Starter · #9 ·
Can you post a thread about the 392 intake I'm interested in that mod or can you share where you read about it
I'm not sure if I can post links to other forums on here. Do an internet search for 6.4 srv intake swap cirkit boss. You will pull up a thread elsewhere from JS1977 I think. He posted instructions.

I bought the intake from another member who is putting a supercharger on his car. He had the harness already made up. I bought the intake, harness, intake elbow, msd rpm switch, and cirkit boss. It is an easy mod and probably the best single one so far. The first one I could actually feel. Repaired the low end torque destruction due to the Modern Muscle NA cam.
 

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Discussion Starter · #11 ·
I agree with all the posts about air and coolant temp, i just have to add that not alot of ppl know/realize how important fuel temp is. When your fuel rails are competely heat soaked, and that fuel is being misted at super high temps, your differences in air temp really are mitigated. Gasoline doesnt cool off like water or ethanol does when its vaporized (much lower vapor pressure at same temp) so whenever you atomize fuel into the intake gases, it can actually heat them up if the fuel is boiling hot. Having said that, i don't really know of a way to minimize the effect, other than insulating your fuel rails, or upgrading to a thinner aluminum rail.
I completely forgot about this. I almost bought a cool can for my 400 sbc, but it's not very practical for driving around in the street.

Very good point, this has to be the main reason for hemi heat soak.
 

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Discussion Starter · #28 ·
It seems that around 20 horsepower is lost on my fully heat soaked engine compartment, more with the water/meth off. Right now the mixture reduces the IAT sensor readings from 100-120 degrees after sitting a bit fully heat soaked, down to 59 degrees. Performs a little better than without, but not as good as a freshly warmed engine with a still cool engine bay.
My 0-60 times a roughly 4.70 cool, 4.80 with injection on a hot motor, and 4.90-5.0 hot hot hot on a day in the 70s.

Also, if it's in the 30s, I have gotten 4.50 times.
 

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Discussion Starter · #30 ·
Location is a big factor, then launch technique, heat soak condition, and current weight. On greasy roads I get 4.9-5.0

I was out on a sticky black section of highway this evening and I got a 4.75 with 5/8 tank of gas and case of beer, water, and my 10" sub box in the trunk. Went to my normal spot and got a 4.86. 66 degrees out.

I brake torque up to 1700rpms in sport and using paddle shifters. Let go of brake and put gas pedal down as fast as I can without spinning the tires. Hit up shift paddle at 5,400-5,500 rpms. Got my limiter and limp modes raised to 6,300 rpm with a Eurocharged TCM flash.

Best way I have found for me.
 

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Discussion Starter · #32 ·
I have never been to a track. I want to travel to one in September. I have ran 1/4 times on my trinity. I usually get 13.2x times at 109 or 110. My fastest recently was 13.06 and my record is a 12.91 @ 113. That was the same 37 degree day that I went to my 0-60 spot and got a 4.50.

Went out this morning and got a 4.80 time, drove a mile or two, then I went back and ran a 4.63 0-60. Temp was 66 degrees. Still have 5/8 tank of gas. Shift timing, launch grip is critical.

On some of the most traveled roads around here I probably could not even get a 5.00 second time just because the tires cannot hook up. Spins my 275/40r20 nitto invo tires even with traction control on. Those roads I guess are just too greasy or something.

From what I can tell, the factors in getting the best 0-60 times from the car at any given power level is, from most important to least are:
Practice technique
Ambient temperature
Heat soak amount
Launch grip
Shifting
Weight

I dropped a half second off my times just from figuring out how my car wanted to be launched and shifted. I would have to try it again, but I don't think I can get under 5.0 by letting the car do the shifting and by not power braking.
 
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