Thermostat - to use or not to use

[Garys1969RR]

I have a 451 with 12.5 to 1 C/R. Mainly strip, and some limited street use. I have removed the thermostat as it was getting pretty warm last summer in all the heat. That helped it run alot cooler. And it helps when cooling the engine at the water towers after a run down the 1/4 mile. But I heard that I should be using at least a 160 degree thermostat, to get the engine up to operating temp more quickly. We know that a cool motor produces more horse power, and is less susceptible to pre-ignition. What are your thoughts on this, and are you using a thermostat in your high compression engine? Thanks.

 

[RustyRatRod]

You need to run a thermostat.

 

[Meep-Meep]

I agree. Run a T-stat or at least an orifice to allow the engine to get to run temp quickly. If just making 1/4 mile passes with predicted run and shut down intervals an orifice might do it, but a PROPERLY rated T-stat is much easier. For street I'd run 180 but for track maybe 160 to keep the intake cool. I even put a T-stat in my boat and it runs about 160 all the time. And I have absolutely no issues related to the modern crap gas and carburetors. In fact it runs so well that if it rained enough to flood the streets I'd commute in it.

 

[64 Post]

Side question: Is your stated net effective CR adjusted for altitude?

 

[RustyRatRod]

Compression ratio will be the same regardless of altitude.

 

[Garys1969RR]

I am at 5280 feet. (Denver). C/R based on 14cc domes, .017 deck clearance, .020 head gasket, 906 heads @ 88cc. After checking the calculator, comes to 12.1 to 1. But will be putting on 915 heads next week, which at 80 cc makes it 13.3 to 1 C/R. And I have been using 100 Sunoco fuel.

 

[64 Post]

Compression ratio will be the same regardless of altitude.

But cylinder pressure won’t; net effective 12.5 compression @ sea level is 10.0 or less in Denver.

So when building an engine for altitude, it is in one’s best interest to increase mechanical compression at least 25% to make up for D/A.

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I am at 5280 feet. (Denver). C/R based on 14cc domes, .017 deck clearance, .020 head gasket, 906 heads @ 88cc. After checking the calculator, comes to 12.1 to 1. But will be putting on 915 heads next week, which at 80 cc makes it 13.3 to 1 C/R. And I have been using 100 Sunoco fuel.

Plug your cam timing events into the calculator and see what your cylinder pressure is.

 

[RustyRatRod]

But cylinder pressure won’t; net effective 12.5 compression @ sea level is 10.0 or less in Denver.

So when building an engine for altitude, it is in one’s best interest to increase mechanical compression at least 25% to make up for D/A.

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Plug your cam timing events into the calculator and see what your cylinder pressure is.

I got that, but that's not what you implied. ;)

 

[theman440]

You need to run a thermostat.

X2

 

[64 Post]

I got that, but that's not what you implied. ;)

ok, I ficks it... :tongueflap::icon_razz:

 

[67 B-body]

I use a restrictor....

 

[snakeoil24]

thermostat is a must, add an air bleed also in the thermostat housing if you really want good results. A small pet cock drilled in the housing to make sure all air is burped from the top of motor. Just like farting.

 

[Garys1969RR]

Thanks 64, was wondering how much the altitude affected C/R. So what would 13.3 to 1 at sea level be equivalent to in Denver? Thanks

 

[RustyRatRod]

I digress once more. Compression RATIO is not effected. Net or gross. 13:1 is 13:1 on top of mount Everest or on the bottom of the ocean, in the marianas trench, or even on the moon. The only thing that's affected is the air density. Compression ratio is a comparison of the cylinder's volume from BDC to TDC. That volume can be anything for the sake of math. It can be air fuel mixture. It can be air. It can be the vacuum of space. It can be a cylinder full of dodo. 13:1 will BE 13:1 regardless of any other variables, because compression ratio is a product of the physical parts of an engine. Whether that engine is in Denver, or Macon, Georgia makes zero difference in the RATIO. What's affected is the air fuel ratio and the cylinder pressure, because the air is less dense at altitude, but the actual compression ratio remains completely unchanged. Gary, if you want an idea, just take a compression test and see where the cylinder pressure is. That will give you a ballpark idea of your engine.

 

[Garys1969RR]

Yea, Rusty, I agree. With the 906 heads on the motor now, gauge pressures are 190 to 205 PSI, last time I checked. I think what 64 is saying, is that total cylinder pressure is going to be higher at sea level or even 2500 feet, than at 5280. Thus, (hopefully) more horse power. Thats probably why the oil companies serve us 91 octane premium in Denver, while most of the country is getting 93 octane premium.

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In other words, higher cylinder pressures generally require a higher octane fuel to avoid pre ignition.

 

[Meep-Meep]

Rusty is dead on and knows his doodoo, but the key word is EFFECTIVE. I have no experience with high altitude tuning but can see how the loss of atmospheric pressure can be detrimental to performance. One solution is to put a lung on it.

 

[RustyRatRod]

Exactly. That's why you see the professionals....especially funny car and top fuel having tuning problems at altitude. The pro stockers...not so much, because those cars are not pushing the envelope so hard......but you can bet they have to tune as well. I'm no expert, so I cannot say exactly what the difference would be........I would GUESS with less air density, there would be less cylinder pressure like 64post is talkin about. It certainly makes sense. But sometimes when somethin makes sense, it's entirely wrong, too. Anyway Gary, whatever compression difference bein at altitude makes, rest assured, you ain't gonna run that beeotch on 87. LOL

Maybe IQ52 will see this and chime in. He lives in Utah so maybe he's got some altitude opinion.

 

[Meep-Meep]

Yea, Rusty, I agree. With the 906 heads on the motor now, gauge pressures are 190 to 205 PSI, last time I checked. I think what 64 is saying, is that total cylinder pressure is going to be higher at sea level or even 2500 feet, than at 5280. Thus, (hopefully) more horse power. Thats probably why the oil companies serve us 91 octane premium in Denver, while most of the country is getting 93 octane premium.

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In other words, higher cylinder pressures generally require a higher octane fuel to avoid pre ignition.

So you are pumping 190-205 PSI at 5280 ft? I'm doing that at sea level with my small cam 440 and 10.1:1 CR. The difference between seal level and 5280 is the atmospheric pressure, and that basically means there are fewer molecules of ATM gases per liter or CU FT. Your RATIO of a weaker ATM pressure on the way into the cylinder vs. being compressed in the cylinder is the same (Rusty's point). What changes is the amount of O2 molecules to mix with fuel, so with fewer O2 molecules you need fewer gasoline molecules to maintain proper mixture. The end result must be less energy released because you have less of everything. I believe what 64 post is referring to is bumping the compression as a way to compensate for the less energy released by the weaker mixture - sort of a band aid. I still say put a lung on it. Turbo EFI.

 

[64 Post]

Let me see if I can hit the fine points.

First, I lived in Denver from ’95-’10. I’ve had a TT Supra (still suffered altitude loss despite popular belief that turbos are immune from altitude loss), a Hayabusa, assorted late models and old n/a cars.

Second, no argument with Rusty on the compression part. Mechanical compression = mechanical compression; hence my correction to “net effective.” In Denver most guys know what you mean when you say "compression loss" even though it’s not correct. Bad habit, I guess.

Third, and it’s strictly my opinion, is matching cylinder pressure with intended engine use and fuel octane so as not to leave any power on the table is the name of the game at altitude. When I pre-planned a build in Denver, I generally added 20% to mechanical compression and then fine tuned cylinder pressure with cam timing (I spec'ed my own grinds). I also checked the DCR. You’ll never get all the power back but it’s the best one can do short of TC/SC. Most of the summer months D/A runs from 6,000ft. − 8,000 ft. or higher; I’ve seen 11,000 at Bandimere. I know quite a few old timers that do not believe in my methodology but they’ll wonder why their magazine combo doesn’t run right.

Generally, 180-185 psi cranking comp. is about max for 93 pump at sea level.

I’ve used this site for years... http://www.wallaceracing.com/Calculators.htm

This ( http://www.wallaceracing.com/dynamic-cr.php ) has an input for altitude adjustment so you can see what happens. Run the calcs three times changing only the altitude numbers to 6K, 8K and 10K.

 

[Cranky]

Also, don't run your engine too cold. Heat is energy so don't go for the belief that running cold increases horsepower. Also, your oil was designed to work best at full operating temps.