Effect of an oil cooler on combustion temprature
 

I have a Heads and Cam LSx with about 11.1:1 static compression. It is tuned very mildly regarding timing, about 18 degrees total, and needs about 93 octane to run without knocking under heavy load and hotter ambient tempratures. I was thinking maybe an oil cooler would help the situation (more timing or lower octane fuel) by lowering the combustion chamber temperatures. :huh: I'm I thinking correctly? Can cooling the oil make much of a difference in combustion chamber temps?

I doubt it will help that much but it would be easy to test. Add the cooler and then run the tank near empty. The add a couple gallons of 87 and see. If it pings under load just fill the rest of the tank with 91.

1) The real issue is that you need a tune. Lowering the oil temps if they are not unreasonably high is a band aid.

2) I think you already have one, but if you don't I would go for a 160F thermostat.

3) What spark plugs are you running? This can make a big difference. I like the old school autolights. I will stay away from any platinum shit. The stay hotter which helps them last alot longer, but they are way more likely to detonate.

4) As a referance point for a similar motor: Normal friving oil temperature is about 200-215F, When I'm road racing oil the oil will get to 255F. With the new synthetic oils thier breakdown limits are so high that you would have other major failures before that point.

Go get a tune;)

I have a tune. It took a full day from a reputable tuner. He said I might have higher compression than advertised. With 91 octane, 18 degrees total timing is all he could do before it got ugly. I run Torco (about 1 quart to 15 galoons for a net of about 93 octane, I can explain if you want). With that it's safe, but there's probably A LOT on the table with tuning and higher octane. The Vette my motor was originally in gat 432 to the wheels with mid length headers and the ls1 intake. I have an ls6 intake, a different TB, stock manifolds and of course the C3 IRS, and the best I've gotten is 391. My Dyno chart was reviewed by a serious F-Body guy who said there was a little on the table in the way of low end torque with the same octane, but it was otherwise already idealized.

HOWEVER
I'm running a stock temp thermostat. I don't recall what that is, but it's not 160. And I'm running Iridium plugs

MY GUESS
Since I'm running a fairly high compression motor with retarded timing, there's a bit on the table. The main problem is heat causing pre-detonation thus requiring retarded timing. If I can lower some of the temps and up the timing, I can get some "free" power.

18 total timing or 18 degrees at idle???

I run 34 total degrees at 2,500 rpm with 11 to 1 compression.

I have 15 degrees timing at idle.

There has to be something wrong for it to detonate with a tune. Regardless of your compression ratio, when you tune a car it was not detonating at that point so the question then becomes what have you changed. I'm assuming that the throttle body and the manifolds were changed out prior to your tune.

Have you inspected the spark plugs?? I would start there to see if any/all of them have any fouling, carbon build up, or signs of detonation. If someone had an engine scanner they could determine which cylinders were having pre-ignition and see what fault codes were showing. I had a differential pressure sensor go out on my mustang which made the EGR valve fail open which ultimately cost me a motor in hte mustang. Alot of times a code scanner is the easiest way to get down to the root cause.

To be clear, it does not detonate with my tune, we just had to retard the timing and adjust the A/F curve to not detonate. My tune will run ok on 91, but will ping on warmer days in the summer. With one quart of torco (very roughly 93 octane) I have no problems in any weather with any driving "style".

In other words, the tune I have is very conservative in order to protect the motor. This is not a new problem. There is power to be had with just a tune, if I fix other variables. Higher octane is the easy one, but I don't want to run race fuel everywhere. A quart of Torco per tank is fine, but that's my limit. That's why I thought things like an oil cooler, which might lower combustion temps might help. Also headers, which will lower cylinder back pressure might help. Then I can go back and get a new tune with the improved dynamics and pick up some cheap power. :bigthumbsup:

18 degrees total as I recall. The tuner was surprised that's all he could put in and wondered if the motor might actually be higher comp than advertised.

The vette the motor was in before had a lot of different variables than I do. Including

cold air intake
Aftermarket TB
LS1 intake
Headers and different exhaust
Ran 50/50 91 octane and 100 octane (I think)
aggressive tune
432WHP in a C5

I have
hot air intake
ported truck tb
LS6 intake
stock manifolds and custom dual cat back
Run 91 octane with 1 quart of Torco
conservative tune
391WHP in a C3

Did you use the Torco when you had the car originally tuned?

No.

The original tune was on 91. With that final conservative tune it wouldn't detonate, but would ping on hotter days and/or heavier loads. With the Torco it is totally fine. It's just that with such retarded timing on a high compression motor, power is being left on the table. I'm just trying to tap that power without going to a race fuel mix if possible. The other "easy" solution is to use a cometic gasket and drop the compression, then go for an agressive tune on 91. :huh: But if I can keep my higher compression and go for the agressive tune on 91 + a little torco, that'd be cool. Right now, I have a conservative tune on 91 (and I run torco for safety).

The things I can think of doing to make it more agressivel tunable w/o using race fuel mix are:
- oil cooler (reducing combution chamber temps)
- find a way to get cooler air, if not cold
- headers (reducing cylinder backpressure?)
- cooler thermostat? I have heard lots of mixed opinions on this surrounding thermodynamics. I tend to understand the arguments against running a cooler thermostat and keeping the stock one instead.
- plugs? I'm running iridium plugs. Would a more standard plug be better for some reason, like be cooler when not firing?

Slam dunk solutions
- Race fuel mix (pretty opposed)
- Cometic gasket dropping compression (prefer not to)