Lower coolant temps DO provide more HP!
Thread Starter
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Lower coolant temps DO provide more HP!
Today at Raceway Park, in 95+deg F temps my hood was stuck for a while and we were doing round-robin time shots (not many racers in the heat).
When I arrived at the track coolant temp was about 170deg F and I made a time shot down the strip.
As my coolant temp rose to a little over 200deg F my trap speed dropped and ET rose.
After a few time shots I got the hood open, which allowed the engine to cool a little between passes, coolant temps came down to 170deg F while trap speed rose and ET dropped.
These passes occurred during the late afternoon while temps hovered in the mid 90s and RH and baro were constant.
The obvious conclusion: lower coolant temp DOES produce more HP.
When I arrived at the track coolant temp was about 170deg F and I made a time shot down the strip.
As my coolant temp rose to a little over 200deg F my trap speed dropped and ET rose.
After a few time shots I got the hood open, which allowed the engine to cool a little between passes, coolant temps came down to 170deg F while trap speed rose and ET dropped.
These passes occurred during the late afternoon while temps hovered in the mid 90s and RH and baro were constant.
The obvious conclusion: lower coolant temp DOES produce more HP.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Glad to hear you ran well, hot kills ET's!
However, cooler temps do not help. What lower temps DO provide is a cooler intake manifold.
Do the same test, this time icing down the intake. You will really be stunned what happens to ET's.
However, cooler temps do not help. What lower temps DO provide is a cooler intake manifold.
Do the same test, this time icing down the intake. You will really be stunned what happens to ET's.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Well put Bogus, the 160 thermos were designed to get the last drop of hp, unfortunately it comes at a cost-engine longevity diminishes.Soooo,if you're looking for 1-2 hp, go 160,if you're looking for longevity 180. Another thing-160's really weren't meant for everyday driving.Don't want to start anything-those in doubt should go to http://performanceunlimited.com/illu...ermostats.html
Race Director
Joined: Sep 2001
Posts: 14,680
Likes: 752
From: NEwhere Ohio
Likely whats going on here, in addition to cooler, denser air, is spark advance.
From what I understand, the reason why your car feels so fast when you first get into it on a 50F fall day vs. after driving around for an hour in 90F heat is because of timing.
As coolant temp increases, spark timing advance decreases. Its a table in the PCM. coolant temp vs. spark advance.
Ive always wondered how much safety margin there is in that we can bypass.....
From what I understand, the reason why your car feels so fast when you first get into it on a 50F fall day vs. after driving around for an hour in 90F heat is because of timing.
As coolant temp increases, spark timing advance decreases. Its a table in the PCM. coolant temp vs. spark advance.
Ive always wondered how much safety margin there is in that we can bypass.....
Thread Starter
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Indeed the trap speed increases of several MPH were in excess of what I would calculate from air temp changes (resulting from lower coolant temps) alone.
So, indeed there seems to be something else going on that caused the increase in power. But my point is that, had I been running the stock T-stat performance would have stayed on the low side; whereas, with the 160deg T-stat, performance increased markedly with the drop in coolant temps.
So, indeed there seems to be something else going on that caused the increase in power. But my point is that, had I been running the stock T-stat performance would have stayed on the low side; whereas, with the 160deg T-stat, performance increased markedly with the drop in coolant temps.
Race Director
Joined: Jul 2004
Posts: 16,795
Likes: 62
From: Lake Havasu City, AZ
The thermostat only controls the temperature at which the coolant flows through the radiator to be cooled. The actual operating temperature will be governed by the cooling efficiency of the radiator. (ie. its heat transfer capability)
This cooling efficiency is affected by the fluid in the rad, as well as the size, composition and the condition of the radiator. The condition of the radiator considers both air flow though the cooling fins and deposits on the internal surfaces that inhibit heat exchange. The air flow is impacted by air coming through the intake passing freely over the fins and the operation of the fans....
So even though a 160 degree stat opens earlier operating temperatures will usually still be in the 180 to 200 degree range in summer driving conditions..
This cooling efficiency is affected by the fluid in the rad, as well as the size, composition and the condition of the radiator. The condition of the radiator considers both air flow though the cooling fins and deposits on the internal surfaces that inhibit heat exchange. The air flow is impacted by air coming through the intake passing freely over the fins and the operation of the fans....
So even though a 160 degree stat opens earlier operating temperatures will usually still be in the 180 to 200 degree range in summer driving conditions..
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
I have never denied that cooler temps could make more power. What's good for the track and good for street use and longevity are two different things. I use a garden sprayer to wet down the outside of my radiator and my manual fan switch, between rounds, to get my temps down to the 160-170 range as I leave the starting line. However, the constant, indiscriminate, use of a 160 stat gives little, if any, increase in every day performance. Delayed or never reached warm ups, cause additional, albeit gradual, wear and tear on the engine. A 160 stat isn't for those that don't know EXACTLY what they're doing, and why.
RACE ON!!!
RACE ON!!!
Last edited by CFI-EFI; Aug 31, 2004 at 11:21 AM.
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Melting Slicks
Joined: Jan 2000
Posts: 3,418
Likes: 1
From: NW Chicago Suburbs
My 96 makes more HP/Trap speed and a lower ET when the coolant temp is below 170*F. When the coolant temp exceeds 180*F, the PCM starts enriching the A/F ratio, goes as low as 11:1 when ECT exceeds 190*F. The PCM is protecting against detenation by enriching the A/F ratio, killing HP. Not sure if the L98 or early LT1 has this "feature" but all the 94-96 C4s have it.
Eric
Eric
