I put a set of new pistons and cylinders from AAperfomance on my 1973 GA 2.0 while I was replacing the oil cooler. Cleaned up the engine and had new valves and guides installed. Added a tangerine oil bypass spring thingy and that was all.
Stock engine, ansa muffler, 123dizzy, not Bluetooth, set on advance and my year dizzy.
Ended up with 8.4:1ish compression.

Runs great. No more cleaning burnt oil off my rear valence.

However, it was running much hotter.

Part of this turns out that I was never getting the spark plug on #3 all the way down with my fishing the dd cht ring through the hole in the tin. That was probably a lot of it. However, now that I am getting good heat measurements I was a little bit startled. Makes me wonder what my temps really were before.

I had left the timing from before and it was running at 350 degrees now just puttering around town.

I did replace my fan with two broken vanes for a 'new one'. Of course it's off a bus motor. No marks. I transferred the TDC mark before install.

Checked my timing, it was easily in the 40s. I posted before about adding timing and it cooling off in another thread. That was me being stupid. I was retarding the timing. It has been so long since I messed with the timing on this car I forgot which way it rotated.

Anyway, I can only assume I must have knocked it while working on the motor or the bad rings, valve guides, and dirty heads/pistons might have been fine with that kind of advance. Oil temps were always pretty low. No damage on the pistons or the old valves to indicate detonation.

So that brings me to the topic. I got methodical with it. I double checked my tdc mark and checked the timing. This morning it was about 34 btdc (me mucking with it earlier this week, no gun used). At 34 I couldn't cruise on the highway at Seventy without hitting 370 and nearing 400 on any slight rise. Temps in the 70s. Last night driving home, air temp in the low 60s, 60mph, still skirting 370 on the flats. Never any pinging.

This morning I changed the oil (500 miles since the new rings) I tried again, same temperatures. Came home and set the timing to 27. I can't imagine you could could think that is better than +-2 considering the marks, the methods, and the human involved. For what I am getting at, it actually doesn't matter.

Took it for the drive I always take, through town for a mile, then on the interstate for 4 miles and then through county roads (55) back to the house. About 15 miles total. At 27 degrees advance in the timing the car was still intolerably warm. Same as before. Tried it without the vacuum advance, same result Air temps in the high 60s.

Bumped the timing up to 30 (again +- 2, it's me and my timing gun). Took it for the exact same drive. Ever so slightly cooler cht but still too hot. Removed the vacuum advance and tried again. Same temps. Oil temps have been the same all throughout. The needle hangs just the left of the T on my gauge. I would say that has been far more predictable than before I replaced the cooler and the pistons and cylinders. Before it would run much cooler but under stress jump up faster. Now it's pretty much rock steady. The tangerine oil valve? The oil cooler without leaks? Hard to know.

I tried 27, I tried 30, so I tried 28/29. Wow. Temps have been climbing all day, now the air temp is 88 degrees. In town it went from 330 to 308. Climbing to 320 when getting aggressive but dropping quickly. Took it out on the highway and it was doing 60 at 345 degrees. Hard driving would bring it up to 370 but it would come back down rapidly. I did a 600 foot in 1/2 mile hill climb on a twisty road going full on, redlining 3rd so I was running mostly in fourth, 383 was the max temp but it rapidly fell as I lifted for a corner and when I got to the top it was sitting at 350, dropping to 265 rapidly as I started descending into town (we have hills and twisty roads in abundance).

In conclusion, the crazy thing to me at the moment is how sensitive this thing is to just a couple degrees of timing and that less advance, by only a degree or two, was not a safe place, and just giving it a little more was also not a good place to be. It doesn't really matter what the actual timing is (only the gods know what that is), it's just that there is a very specific spot this engine needs to be in.

Final note: during the last bits of tuning I noticed little change in performance. AFR didn't really change much throughout. It runs a little leaner than I like at feathering throttle cruise (no matter what the timing or advance) but as soon as you put load on it, it is in good places between high 11 and low 12. We have days of 90s coming so it will be interesting to see how it does.

Whew.

P.s. always 93 octane Ethanol goodness.

Great way to do it. Repeatable, methodical. Following this as you know my situation which is different than yours as I now know (thanks to you an others) that i have a bad distributer can.

When I get a 123 in there, I'll be doing exactly what you just did - repeatable track.

Yep. A few degrees of timing makes a big difference. Leaner is hotter as well. What’s the condition of the cylinder fins? Are the engine bay seals in position on the tins? Bottom tin pieces in place? What’s the (numerical) oil temp? Is it possible your CHT readings are off?

My 2056 runs about 280 - 310 CHT on regular roads, and up to as high as 375 for short stretches climbing the mountains. Oil temps usually get to 210 unless going up steep grades. Then it can get as high as 240 till I hit the downslope and then cools off quickly.

Running stock DJet with mps optimized for 2056. Ham heads. Raby cam

I think that raby cam is the ticket. My engine is perfectly clean, all tin good and painted black, all seals good. Oil temps according to the charts for a 73 gauge and sender would be below 220 I believe. Need to check the figures again. Engine still runs 'cool'. No boiling gas (original location for the pump). Engine is easy to work on even after a hard run.



At 'the glen' with my tired old motor my oil temps still didn't climb much more than to the m.

Absolutely possible my cht gauge isn't accurate, I don't want to pull it and check at this point though. Hard to get into that perfect position where you don't have to vandalize your heads....

Edit: so according to our favorite diagram, regardless of the sender I am parked in a good spot... Feels like 215 to me.


Click to view attachment

With my engine, there’s def a correlation between CHT and oil temps. Though the oil temp is less responsive. When my CHT is at 375, oil is at 240. Albeit I only see those temps for brief pulls up steep grades.

Are you keeping your RPMs above 3K and staying out of 5th gear up hills?

For the run up the hill it was all 4th, but my highway measures are all in 5th. I did notice that moving to fourth when it was off on the timing didn't help. Perhaps it would have held it at 400 better than 5th but it wouldn't bring it down. When racing I would definitely see the oil temps moving but that was the old motor. They do move but now they seem to be better modulated? Did you add tangerine racings oil valve to your build? I can't remember from the videos.

Took it out on the interstate this morning before the temps got out of control. air temp was 70 degrees. 70 mph holds nicely at 364, moving between 354 and 368 with gentle rises and falls (for this area that is maybe a 75 foot alt change across a 1/2 mile). On a good hill at 70 it climbed up to 375. The same temp and route yesterday at 27 or 30 btdc I would have been into the 370s cruising and hitting 405 on that hill.

Oil temps raised quite slowly (I suspect on my way "out" the thermostat still had the flaps closed as well, on the way back everything was up to temp, and that is where the big hill is). Flaps closed would mean higher head temps than normal anyway. As soon as I got back into town off the ramp the car was nice and cool again and held 304-307 through town.

Here are my gauges after I got off the highway waiting at the light (that's a 310 on the cht).

Click to view attachment

350-380, 390 pretty common for stock motors under load especially if they are on the lean side. Bumping up displacement without changing anything else is likely to only make that worse. Being a new build may be causing slightly higher temps as well, they might come down slightly as everything breaks in, but as you have already assumed the stock cam is probably causing most of your issues.

I have tangerines adjustable mps setup so I am keeping up on the lean issues. My next big operation will be the raby cam and a complete bottom end freshen up for sure. Doubt I will go for a stroker but I will definitely balance what I have.

Wow. This is good stuff. IIRC, the factory setting was to be 27° Looks like you have it dialed in to what the engine wants

And yeah, looks like summer’s going out with a bang

What is your AFR at cruising speed?

That's a tough one. Any throttle at all, let's say a 1/2 inch pressed and it is between 13 and 14 (20 to 15 inhg). Cruising lightly around 30 it's often around 13 but if you bring the throttle back to less than the just a little touch and it becomes rather unpredictable. Sometimes it will go to 12 sometimes it will go to 15. None of this is under load of course and considering the position I don't know how much you can trust the afr under those conditions.

Now at any kind of load it goes plenty rich so I think I am safe there.

At 70, feathering the throttle to hold speed in fifth (3100 rpm) it goes leaner. Sometimes 14.5 sometimes 15.5 this is at 11-8ish inhg . Again this is with the throttle barely cracked open Any kind of real dip into the throttle gives an immediate richening from the tps squirts but then settles back to 12-14 depending on how much you are goosing it. Light acceleration it's leaner heavy acceleration its richer. The feathering throttle leanness is all between 11 And 9ish inhg on the vacuum gauge. Maybe an Inch of travel in the pedal at 70. Try my Hardest tuning that mps and it just doesn't get that spot any richer. Since there is almost no load, and the engines running reasonably cool now, I think that leanness is fine. If it were doing that under any kind of load I would be much more worried. I am wondering if perhaps the tps is not perfectly adjusted though. I wonder if the ecu thinks it is still idling?