Some people here gonna hate, call me names, they get tired of hearing from the same person all the time. i dont care. Today im gonna provide some data that those people wouldnt try to, or dont even know how to try….

72F - 1993 corvette #2.
Forged 383 6spd, 80 lb/hr inj (overkill), 185F coolant temp, 215F oil temp.
9.5:1 compression
214/218 , 114 LSA cam, .575ish lift

Was down to 5 gallons 93 octane and mixed in 8 gallons 87 octane.

did some WOT up thru 5100 rpm, uphill WOT on ramps, coast downs, highway pulls WOT lugging it in 5th or 6th uphills, and 1st gear only WOT sprints

had zero knock (see data).
will repeat experiment in warmer weather and with additional 87 octane to further knock down the octane to 87

 

Question from a amateur. Does your engine have antiknock sensors that will cause the ECM to retard timing if it detects a knock?

 

Why are people flaming you? No disrespect to the engine, but 9.5:1 compression is not that high, and totally acceptable with 87 octane. Is there something that suggests otherwise?

I've got an Olds 455 big block with 11.25:1 compression... something like that would need 89 or higher octane.


I'm willing to bet there are more people pissed about this though, "185F coolant temp" ... that you're running a lower temperature thermostat.

I'm on another car forum where I swapped out the 195 for a 180-degree thermostat, and everyone swore I was starting World War 11. They insisted that everything was specifically designed for 195-degree thermostat, it wouldn't run well, and my engine would explode. It's an Iron Duke, which has been around since the mid-1970s, and based on an engine design from the late 60s. I basically mentioned that in the early 1970s, cars literally came with 180-degree thermostats... I.E., they were DESIGNED for 180-degree thermostats. That GM started putting 195-degree thermostats in them later, had more to do with trying to improve emissions standards with crappy charcoal pellet cats and garbage smog pumps. Then you get the people who say the car's ECM is programmed to expect 195 degrees... not really. It references a fuel map that takes all of those values in closed loop to properly provide fuel metering. So, it can operate just fine with the 180-degree thermostat. When you start going with 160-degree thermostats, you do kind of need an ECM reflash or prom burn.

Anyway, people stopped losing their mind once I reminded them that the original versions of the motor came with 180-degree thermostats (just like our small block Chevys).

 

Diz has... a... "following".

 

Yeah, as far as I know... all Corvettes have a knock sensor. My 1984 Corvette (which has lower compression, 9.0:1), has a knock sensor located on the lower passenger side of the engine block, just below the exhaust manifold.

 

Oh good night . A lower thermostat simply changes the lowest engine temperature, that's it. Conditions such as city stop/go in warm weather with stock setup still gets to the same 210F+. All your little low thermo is doing is increasing the possible temperature map.

Start adding a higher cooling capacity blah blah blah, well, it's your car.

 

i run 87 all day long in my 89 TPI, and every other toi ive had.

maybe LT is diff?

 

I live in Florida. None of my cars run up to 210 degrees+. Is this normal for your cars where you live, and why are you allowing it to do so? You should be adjusting your coolant / water mixture to compensate for the temperature / region that you live in.

My daughter's 85 Fiero 2m4 SE runs at a consistent 180-185 degrees on the temperature gauge, confirmed by a thermal gage. The only place it's hotter is by the exhaust ports.
My 2006 Pontiac Solstice GXP Turbo runs between 190-195 degrees (has a 185 degree thermostat). When I really, really get on it and it hits 13+lbs of boost, it hits 200 after I slow down.

Same with all the other cars that I have that are old enough for me to mess with. The new cars just have the stock thermostat.

Really, it depends on the car. The C4 doesn't really have much excess cooling capacity. Cooling hoses are short, basic radiator, and what fits in the block and heater core. The Fiero for example, has cooling lines that run up and down the length of the car, and then again for the heater core. It has a much smaller radiator, but identical coolant capacity (14+ quarts), plus more cooling surface area. There is really no benefit to having a car run so hot, except for slight exhaust / catalyst efficiency. In all of my hobby cars, I wrap the exhaust manifolds in header wrap and / or get them ceramic coated. I'll even run the header wrap all the way up to the catalytic converter to both retain the heat for the cat, and deflect it from the car. Does the job much better.

But like I said... people get so offended by things like this. Haha...

 

Yes, most new cars have knock sensors which can retard timing, lower boost pressure, etc., to prevent further knocking, (pre ignition). Notice I said to prevent further knocking. This is a fact that most overlook. If a knock sensor detects knocking, that is past tense, some amount of knocking has already occurred. And at 4 or 5 thousand RPM that could be multiple times. I had rather spend a bit more on higher octane fuel to help eliminate knock than to have it occur at all.

 

My '90 didn't care for the lower octane blends. It didn't run nearly as well as it does on the 93. It was very noticeable, too.

And, just to add, I believe it's the same 9.5:1 compression ratio.

 

My 90 said premium only or reccomended, my 87 just says unleaded isn't it the same L98 engine and requires the same octane ?

also it ( the 87) drives around 185 coolant temp unless stopped, is it supposed to have a 195 t stat. Friday i'm taking an hour each way highway shakedown drive on a full tank of 93 octane and will be able to report running temps (on highway shouldn't it operate at whatever t stat is in it)

 

That's just the temp it will reach before opening up.

180 degre thermostat will open up fully at 180 degrees.

A 195 degree thermostat will open up fully at 195 degrees.

That's all that means.

The reason for 195 degree thermostat was, I believe to help out with emissions.