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Afr
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Author:  '67 Dart 270 [ Sat Oct 19, 2013 6:22 pm ]
Post subject:  Afr
My new slant is running a bit hot. It's definitely not the cooling system (I have a triple core V8 radiator), and it is all clean, fresh rebuild, all flushed, no clogs, fresh coolant, etc. The timing is correct, it was a bit too advanced, but I have it now at 5 deg BTDC and that seemed to cool it down a little.

I'm thinking it's my AFR. I tuned it to 14.5, but, although nearly stoichiometric, I think maybe it's lean for my engine. I've read that for most naturally aspirated engines, people generally run between 12 and 13ish AFR to make sure it runs a bit cooler.

The engine runs great, lots of power at low, mid- and high speeds, idles smoothly, but it's a lot hotter than before the rebuild. I'll get some temperature readings as soon as my digital IR thermometer gets here from Summit. I have a 180 degree thermostat, it's working fine, I tested it before I put it back in the engine. I'm running a 14 psi radiator cap.

Does anyone have experience with temperature lowering with richer mixtures? I don't want to run too rich of course, but I think it will lower my temperature. It's not overheating, but the temp gauge is definitely running hotter than before the rebuild and boy is the engine compartment hot after just a short drive. The temp gauge needle used to sit at the "E" of TEMP before the rebuild, now it's between the "M" and the "P", closer to the "P."

I have a mild cam, the head has been milled a couple of times, but I haven't checked the compression. The plugs are burning cleanly. I don't notice any particular color of the plugs, they seem really clean, not brown or any deposits that I can see. I'm running 45 thousands gap, Pertronix 60k volt coil.

Thoughts? I just need to know if running AFR at between 12-13 is bad for the engine. If not, I'll try it and see if the temperature lowers at richer mix.

thanks all,

BG
Author:  DusterIdiot [ Sat Oct 19, 2013 7:37 pm ]
Post subject:  Yep...
Quote:
Thoughts? I just need to know if running AFR at between 12-13 is bad for the engine. If not, I'll try it and see if the temperature lowers at richer mix.
That's typically a race cheat to richen the mix 1) for more power, but also 2) to have the excess fuel remove heat from the cylinders (it works but is not good on the environment..LOL...this is one of a couple reasons for the EGR in the 70's with more advance and unleaded fuels: to cool the combusion chamber with spent exhaust rather than using a slightly richer mix to combat ping ). If the plugs have no color or deposits after a lot of miles (500 after rebuild), it may need a little more fuel. Hopefully you opted for hardened exhaust seats as lean mixes for extended periods on the old style seats can cause problems. Typically on carbed cars they like to be slightly rich since they are sloppy in anticipating changing load and road conditions (but not overly rich where you have a black cloud out the back and the smell of gas in your garage/driveway).

2 cents,

-D.Idiot
Author:  '67 Dart 270 [ Sat Oct 19, 2013 7:47 pm ]
Post subject:  Afr
Thanks, I've only put about 50 miles on it after break in, so if it is lean, I hopefully haven't hurt anything yet. I've been giving it kid glove care, as I did all the work starting from the rebuilt long block. No leaks! Except that little drip where the speedo cable goes in the tranny (I'll get to that one).

I'll go a bit richer, say down to 13 and see if it cools it down any. My IR thermo just came in the mail, so I can take some readings before and after.

Don't want to hurt the environment, but I figure a little more carbon, a little less immediate global warming from the hotter engine...it's a wash.

bg
Author:  ceej [ Sat Oct 19, 2013 8:09 pm ]
Post subject: 
At what power setting are you seeing this 14.5:1 ?

With only fifty miles on it, with an honest to god rebuild, slightly elevated temperatures are to be expected. There are a bunch of parts in there that need to get used to being in close proximity to each other. Metal will be removed, and variations will relieve themselves. It all depends on how tight you built it.

Leave it alone until you get a couple hundred on it, unless you have obvious signs of overheating. Running rich can result in fuel wash down if you take it too far. Without oil on surfaces, you will have premature wear.

2¢

CJ
Author:  kxracer728 [ Sat Oct 19, 2013 8:41 pm ]
Post subject: 
I don't think if you are actually running a lean mixture it is causing the temperature rise! I've ran my truck with a lean mixture where the plugs are snow white and the temperature gauge never ran much hotter than the 180 degree thermostat...

Have you pulled a plug to look at the plug color? If it's a tannish brown than your pretty much right on! Escpecially since your saying it runs and performs good

I know with my truck! If i go too lean i can tell in the performance (won't pull and excellerate as well...same things goes for if it's too rich)

I think your engine running hotter is caused by something else since your saying
Quote:
The engine runs great, lots of power at low, mid- and high speeds, idles smoothly, but it's a lot hotter than before the rebuild.
If the engine were not performing well than you could have an AFR issue! But based on my more amatuer experience, compared too a lot of the elders who have been fiddling around with these engines for ages! Just teasing :D i think you need to start looking elsewhere if the motor is running hot...

You might think about getting a numeric gauge to see what temperature your actually running...in my truck it runs at 82 degrees celsius which is 179.6 fahrenheit with the cooling fans on whether i'm rich or lean...

I use a electric dual cooling fan setup off a 2000 nissan maxima. The radiator i'm using is aluminum and designed for the 8 cylinder 318 motor

Image
Author:  DusterIdiot [ Sat Oct 19, 2013 10:01 pm ]
Post subject:  x2
Quote:
With only fifty miles on it, with an honest to god rebuild, slightly elevated temperatures are to be expected. There are a bunch of parts in there that need to get used to being in close proximity to each other. Metal will be removed, and variations will relieve themselves. It all depends on how tight you built it.
Definitely, only 50 miles...it needs to get some drivetime in so everything can wear in correctly. If you built it to the tight side of the spec it will be hot for a while.
Quote:
I don't think if you are actually running a lean mixture it is causing the temperature rise!
Very lean but operating can cause overheating, and all sorts of fun things inside the engine (including melting the seat material if not hardened, burning the piston tops, etc...)

One of summer hyperpak tuning sessions allowed me to run for one drive a set of #48 jets in the Holley I had...the O2 sensors dropped off the lean side, the engine lacked a little power, and the temp gauge was at the 3/4 mark and climbing by the time I got back to the driveway (normally the gauge read 1/2 with a 180 thermostat)...went back to #51's and all was well again.

He may need to also be mindful that he may not have deposits on his plugs at 50 miles, he might have to take a drive out of town and back to get 200 miles on it and check again at that time.

-D.Idiot
Author:  ValiantBoyWonder [ Sat Oct 19, 2013 10:41 pm ]
Post subject: 
Run a 16psi radiator cap. It will cool it down some.
Author:  wjajr [ Sun Oct 20, 2013 7:07 am ]
Post subject: 
I tend to agree with above, engine needs to be broken in. I think after 500 or 600 miles you will see temperatures settling down as rings begin to wear in thus sealing better.
Author:  '67 Dart 270 [ Mon Oct 21, 2013 5:29 pm ]
Post subject:  Thanks so much!
I did enrich the AFR to 12.5 just to see if the temp went down, and it did somewhat. BUT, I will take your comments on the new engine running hotter to heart and put the AFR back to spec. There was no issue with performance at spec AFR.

My (champion) radiator cap has an "11" stamped on it, maybe it's an 11 psi cap, anyhow it's not overheating, no coolant loss. The temp gauge holds steady, just higher than before.

It was amazing though, the IR thermometer showed the downpipes about 100 degrees cooler with the AFR at 13 vs 14.7. So there is definitely a difference. I don't want to risk washdown, so I'll put the AFR back up to spec and drive her for a few hundred miles and see if the temp drops down "naturally." Strangely, the downpipe from the front Dutra dual reads a lot hotter than the rear down pipe from the modified stock manifold. This was consistent at both AFR settings (spec or enriched). First I figured the front downpipe does have more bends, although no tight bends, so there may just be more heat buildup due to those bends. So, I shot the IR thermo at the straight portions vs the bends and the bends are hotter. Still, I took readings at each pipe just past where they bolt to their respective cast iron manifolds and the pipe for the rear three is cooler than the pipe for the front three. BUT, the castings themselves read at about the same temperature though, which was very strange. Could be the flow velocity through the pipes makes a difference, should be pretty close, my pipes have only 45 (135) degree or larger bends, nothing even close to 90 degree bends. Maybe that IR thermometer is acting squirrelly. It's accuracy depends on the emissivity of the material, but for my readings the pipes are the same material/color...go figure. Anyway it's a fun toy...laser beam and all...

Thanks all, I'll let you know what she's doing after I've put a few hundred miles or so on her.
Author:  MitchB [ Mon Oct 21, 2013 7:33 pm ]
Post subject: 
Spark is going to have a much greater impact on engine coolant temp than AFR. For a variety of reasons, late timing generates a lot of heat. Can you describe your vehicle: specifically compression ratio, camshaft and your distributor setup - initial timing, vacuum advance and max spark @ RPM.

Thanks

Mitch
Author:  '67 Dart 270 [ Fri Oct 25, 2013 4:18 pm ]
Post subject:  engine did cool down after a few hundred miles...
thanks all...
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