I have about 1000 miles on a 140hp engine, rebuilt with full-fin cylinders overbored by 0.100" (2.85L), 9.6:1CR ported heads, and a centermount EFI/Megasquirt system. For ignition I'm using a crank trigger and Ford EDIS module. What I'm finding is that it will only take 29-30 degrees of total timing at WOT before it starts pinging back at me. This is with AFR set to 12.7:1. Maybe this is OK, the GM "stock engine test" report I have suggests it should be less than 1% loss for this amount of ignition retard... Here is what the plugs look like, maybe running a little hot?? Would it be worth trying a cooler plug? BR7HS? For CHT I'm reading the resistance value from the stock sender with my ECU. It will hit 400F (~260 Ohms according to the Lew Rishel chart) on the highway with lower shrouds off.

2C6D006E-B8C6-4488-BDA5-4AD43D1BE583 by kenhenry_06268, on Flickr

Ken Henry, Rochester, NY USA
1965 Corvair Corsa
140 hp, 4 speed

Plug looks fine. If you adjust the AFR to a slightly richer mixture, does the pinging lessen? IS the 12.7 ratio at cruise? Does it automatically richen up when the MAP sensor or TPS indicates that you floored it?

I think a colder plug would be definitely worth trying... 7 or 8 heat range. You also might want to try 11.5-12.1 AFR at your max load. Your compression ratio is higher than stock and if you are using pump gas premium, its well below the 98 octane that GM used for their tests. You may also have to back the timing up a bit more, although I think the real problem is the 400 degrees at freeway speeds. I can help alot with that!!!

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car
Test Start#2 [www.youtube.com]

I can easily try going richer. I have the ratio set to decrease from 14. Seven at Cruz to around 13. Five moderate acceleration and 12.7 WOT. I am using premium, 93 octane usually but sometimes 90. I’m not sure the 400° is totally accurate. It’s based on the computer reading the resistance of the stock sender, which with the stock temperature gauge used to run more like 350 for the same set up. Thanks, will report back!

Ken Henry, Rochester, NY USA
1965 Corvair Corsa
140 hp, 4 speed

It looks like I need to check over my voice to texts more carefully! AFR is 14.7 at cruise, 13.5 at moderate load, and currently 12.7 at heavy load/WOT.

I will try dropping the 12.7 values to 12 and see if I can advance my timing any. It currently increases from 18* BTDC at <1100 rpm to 30* at >3000 rpm (WOT). I'm running a CA Corviars 270 cam that is a few degrees advanced and tight 0.042" squish. Lacking a dyno to determine the true best settings, maybe I'll boldly try bumping the timing to 33* after enrichening the AFR to 12 and see if it pings.

Regarding CHT, I'm thinking about pulling my thermistor and tossing it in the oven to see what the actual resistance is at 400 degrees, for my specific sender. Has anyone measured a few of these to test consistency with the Lew Rishel chart that is floating around? Ken

Ken Henry, Rochester, NY USA
1965 Corvair Corsa
140 hp, 4 speed



Edited 1 time(s). Last edit at 05/15/2022 07:13AM by KenHenry.

>
> Regarding CHT, I'm thinking about pulling my thermistor and tossing it in the oven to see what the actual resistance is at 400 degrees, for my specific sender. Has anyone measured a few of these to test consistency with the Lew Rishel chart that is floating around? Ken


The stock gauge is likely a bigger source of inconsistency than the thermistor is, especially a 50+ year old one. They tend to read lower temperatures than reality as they age, and they dont compensate for their own temperature.

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car
Test Start#2 [www.youtube.com]

Heres an old thread I found about thermister accuracy

[corvaircenter.com]

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car
Test Start#2 [www.youtube.com]

Thanks Kevin! I stumbled across an old post by Jim Simpson, PM'd him, and he was kind enough to point me to some fantastic articles on the subject in the May, June, and July/Aug 2016 issues of the Corsa Communique. I have not read them in detail yet, but they appear to have tested a decent sample of used and NOS thermistors (13?). For most units:

Temp(F) R(Ohm)
100 3k
200 650
300 300
400 90

For comparison the Lew Rishel chart shows 3k, 1k, 450, and 250 Ohms for these same temperatures. I guess the good news is that my actual CHT is "probably" lower than what the ECU was reading out... Ken

Ken Henry, Rochester, NY USA
1965 Corvair Corsa
140 hp, 4 speed

First off, the spark plug looks fine yes but it also looks to be running a little hot. The deposits on the ceramic give that away.

Second, Dale DeWald - upnorthvairs - did a scientific test on new, aftermarket and used thermistors with a report on ohm readings. I made the aluminum slug for the test where several could go in at one time.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

Thanks Ken. Here are Dale & Jim's results published in the June 2016 Communique. My thermistor decreases from 4.8k Ohms "cold" (85 degree day) to 250 Ohms full warm. So the CHT is probably around 300, unless I have a flaky one like the Berkman thermistor in the chart

Ken Henry, Rochester, NY USA
1965 Corvair Corsa
140 hp, 4 speed

Its pretty hard to point an IR gun to the factory thermistor location, but easy to aim it at the snap action one on the the passenger side. You could shoot that and compare it to your gauge

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa