So I have been playing with adding resistance to the cht to bump my mixture. Messing with the mps was not getting me to where I wanted to be I wanted something a little more global. Anyway, bought a 10 dollar Bluetooth relay. Set it up so one channel was clean the other had 50ohms resistance in it. As I am driving I can switch back and forth and watch the results on the cht and AFR. 50 is really working well (this is all in addition to my 250ohm found on 73s). Now I have added another 20 ohms to the alternate so the relay will switch between 50 and 70. It ain't pretty but it's only for troubleshooting.

Click to view attachment
Click to view attachment

And yes, I couldn't find my electrical tape and covered the resistor with painters tape...

I'm struggling with the same issues. I have a 270ohm and a 50 ohm in mine right now and I'm tweaking the MPS to get the AFR readings where I need them. I circle a few blocks in the neighborhood and I can tell pretty quick if I'm heading in the right direction. I have an AFR guage installed and an O2 sensor in the exhaust.

I'm running a new rebuilt 2056 with a webcam 73.

Today I went and reset the timing... and my engine seems to have lost some power and zip. I'm going to go back and reset my timing in the morning. I'm also running a 123 Distributor. It's been a struggle. After everything gets good and warmed up.... I go lean. The resistors have helped....but I'm not totally confident I'm there yet. I'm even more concerned about what happens in really hot weather.

Is anybody running one of these things?

https://www.ebay.com/itm/274663091106?itmme...vQAAOSw3PlgEuEF

And how does that work?

That actually looks kosher. Just a pot adding resistance to the cht circuit.


On the timing front I have found in my 2056 with stock cam etc that 8 degrees advance was all I could add temp wise, advance disconnected. The engine wants 9. It just sounds, responds, everything better at 9 maybe even 10. Temps wouldn't allow it. I have the advance disconnected. Sadly I think the 123 dizzy doesn't have the finesse of the original retard advance analog fight the original dizzy had. I think it probably throws too much in and it makes the lean fight harder. So I am waiting till I feel good with my mix, then will add it back in later to see what effect it has.

I may just end up with a rich switch for long climbs.

I would also add that I tend to use hot highway 72 mph as my standard. That is where I see the issues. Around town I see benefits but there is never any concern about damage at less than 50.

Been A/B testing increased resistance today. I am up to 100 + the 250 and it looks pretty good. I could probably go just a hair more but the plugs are looking pretty good where I am. And I have put the advance back on. Seems to be fine now with the added fuel.

Hot, same Steady rpm?
How is the fuel pressure at 72 mph steady speed?

I got a 2.4 to perform and behave, so it can be done with djet.

Rich

I put a boroscope on my fuel pressure gauge and put it through its paces, all good. 29lbs.

Yeah, my tests are done at 72, then I try it at 60, checking the plugs after immediate shutdowns. I have an AFR but I don't trust it much. It can tell me if I am richer or leaner than before but I don't have much faith in the number it gives me.

I have it set up with a 150 +the 250 for tomorrow. I want to see if I can go a little into the stinky rich range. So far I am not there.

I have found this more useful than tweaking the mps. This seems to behave better across rpms, throttle position , and vacuum level. I think setting the curve in the mps perfectly, richening to taste with the inner screw, then fine tuning with resistance might be the right thing, at least for this engine. I found the inner screw would give me rich spots I didn't want and barely nudged my cruising AFR (17-12inhg).

Sounds so familiar to my 2056. Ran great towards stoichiometric, but too hot. I played a lot with potentiometers too. Then took on the fight against rust. Resealed the engine against oil leaks and while at it reduced the compression ratio to. Hope to be able to report soon.

I went all the way to 200+the 250 today. Played with timing (left the advance hooked up all day), gave it a little more on the inner screw, etc. even took the shield off the fan intake (stole it from a bus motor). I had a brand new O2 sensor I put in today as well. I was running 12.8 to 13 at cruise. Never went over 400, tends to sit at 375 up and down small hills at 72 mph 3200rpm. Cools rapidly on down hill. It was a cool day today though, 45 degrees at the warmest. Oil was great all day till I dropped the timing to 7, then the oil warmed a little. Put it back up to 8.5 and the oil came back down. Didn't change cht much. Extended long hill sat me steady at 394 (fighting a strong wind too). Cht from plug on cylinder 3 of course.

I may just have to suck it up and deal with it. Maybe I went a little higher than the 8.6 I calculated for compression. Probably get to the Dyno next week.

It’s been a while, but I did get a 2.4 to work.
I tried every MPs ever made, ended up back with the proper 914, though I set it up for my engine and tune.
Djet was in more than the 914, and the MPs are all a bit different.
The Volvo p1800 ES MPs was very rich.
I remember using a POT (volume knob) in the CHT circuit while watching an 02 sensor live while driving in different condition's

It was a combination of CHT and mps, raising the FP a bit to get it slightly rich, which was the goal.

This was….2004, and it was a race/autox toy, and still is out there racking up the miles with no drama.

It took me a while, but once set it was done.


Rich

Yeah, the only place where I have an issue is 5th gear interstate travel. Racing it stays nice and cool. I may just have to make some kind of fudge for that and stop worrying about it.

I took my personal engine to 2.6, back to carbs and a better camshaft.
I’m changing to ITB and EFI, with fully tunable settings….because it’s time

Yeah, since I just did a quick top end build the cam wasn't an option. When I go deeper next time I will definitely upgrade the cam, that is probably what is causing most of my problems at cruise. I have heard they run hotter than they should due to the exhaust timing I think.

djet needs a certain camshaft...though you can go slightly more aggressive.

I will warn you...once you change the camshaft...$$$$ must follow.
Its a big costly decision...

Or...enjoy it as it is, which is cheaper and competitive against others in the same class.

Rich

I think I would just go with that web cam or whatever I always see people putting into djets. Nothing fancy or high revving (mine already likes to blow right past the redline).

I added something new today. Leaving the resistance in my cht lead at 400ish. Will season to taste with the inner screw. However, now I have set up my little bluetooth switch to turn on and off a vacuum valve (EGR thingy from a Mazda) that allows ported vacuum to the distributor. Now, while cruising I can see what kind of effect the vacuum advance is having. Although I can see my vacuum on the gauge, it doesn't absolutely tell me if the advance is operating or not. Now I have to wait for it to warm up a little.

I also took this little snow interruption to actually install the bushing in the firewall for my shift linkage. I can't wait to try it. There was nothing there. When I pulled the motor I didn't even realize there was supposed to be a bushing there.

Click to view attachment

Cold day but I did feel temps were better without the advance. I am running a couple degrees advanced already (car just really likes it there) so perhaps it was just too much. Running really, really good though. Dyno is my next stop.

Oh my! The plug looks great! Maybe this explains why Porsche didn't just tune the 2.0 in 73 with only the MPS and instead added the washer and the extra resistance when they still used the 1.7 computer. Just tuning the mps alone maybe won't get you there.

Click to view attachment

I like the creativity

On L-jet crap I'll added variable ratio potentiometers on both the CTS (your CHT) and IAT circuits.

Big changes with CTS and small adjustments with IAT.

I'd adjust till a bit on the rich side and then lean out with small adjustments with the airflow meter spring tension.

With patients and practice I could dial in a L-jet powered 280Z pretty close...

I know you're D-jet and it's different.

Don't know if you're even using an IAT but it works the same way...

Used to buy the little puppies at Radio Shack for less than $5!

I miss radio shack... What a loss to all tinkerers.

I think the same thing everytime I drive By the Weed Grass healthfood place where the RS used to be.

You are somehow tuning the vacuum advance and monitoring that?
Please explain more…..

Rich

No, I have a 123, old school, no Bluetooth. I was just turning it on and off remotely while driving by blocking the ported vacuum to the dizzy. I was then watching cruise vacuum level, AFR, and cylinder head temps.

hey there , am following your testing on ths and curious about your results, because i have a similar issue and similar set up. my rebuild is also using a similar cam, d-jet, a 123ignition distributor, and also the motor seems to really run well with more advance and the 93 octane. i think i am at 30 degrees advance at 3400rpm(set using stock recommended method.) and wondered well if i back off to the stock advance in timing, this would probably help head temps but if i remember when i put that in a couple years ago, it hurt performance but didnthelp head temps that much. I run no vac or retard hoses on the dizzy, i could never get a good proper rpm at idle set up like that.

i also have a bored out throttle body bored to 50mm, stock air cleaner.
compression is 9.5, these are new heads new P&C's, etc, SSHE and SS muffler from Ben.
i bumped my fuel pressure up to 32, it likes that, and my A/F readings are really good, but still on highway cruising at 75mph i am at about 3400-3500 rpm i think and get great milage and the A/F says 13.5,oil temps perfect but head temps will go slowly up and get up around 330-350 and if i am pusshing up a hill or something then they go up more,
I added a rheostat to my CHT and settled to around 1000 ohms, - all temps are fine otherwise, and i felt like maybe this is due tojust not enough airflow over the #3 head,
i wonder if they have this issue with the set up they are developing at PMB for this same motor configuration.
BTW if i cruise in 4th gear at about 3400rpm head temps drop to just under 300, that isa bout 60-65mph give or take, so why? less heat production?

i like to take longer drives but cant cruise on the interstate witough watching my head temps and worrying about seeing that read out of the AFR being around 340-350.

Phil

I would love to hear how PMB handles it but I suspect with a good cam grind most of this goes away. At least that is what I have heard. I have the stock cam.
djet, original 2.0 heads, 96mm piston/sleaves, 123 non-bluetooth dizzy. Mine is a little warmer than yours. Mathematically I was shooting for 8.5 compression but I suspect I am closer to 9. I suspect the combustion chamber was a little smaller than my measurements (oil and clay both).

And yes, a couple degrees advanced is where it likes it, and the impact of reducing the advance is quite a performance hit (I will have hard data on that once I get to the Dyno) with little effect on temps at cruise. Right now I am at 8.5-9 (at 950rpm) so about 30 at 3400 (how accurate can we possibly be?). Idle for me is very good though, not sure why that would vary much, I do notice idle is terrible at 7 (at 950rpm), inconsistent, engine rpm dropping too low frequently etc but a soft landing would idle ok. That is with tuning the ecu and idle control etc.

Apparently around 330-350 is where these heads like to be if I remember correctly, so anything around there doesn't bother me. It's when it climbs past 380 that I get a little nervous, and mine will do that in 5th cruising at 72 on a pretty relaxed incline if given enough time. Town driving 280-300 depending on ambient temps. Oil is nice and cool (180-200). Even 60 in 5th (which I know many people don't do) is getting there near 360 at level cruise over long periods. I took it through the twisty's yesterday pushing it real hard and the engine never got over 314. My son was asking me why they just didn't make the fan go faster on the highway, so we had a discussion about physics....

Also, the seating of the ring on that 3rd plug really matters on what temperature you get on the gauge.

interesting, we're not far off of each other, my cam is same grind as LN cam for a 2056, and i also do start to push temps up toward 370 at times, and it does like to cruise at about 80 smooth and stil under 4000rpm it runs so good i woud just dive that fast if temps didnt go over 350 but they do. and like you pushing hard in themountains and twisties, or A/X run and no temp issue then. or even idling its fine. and idling,and oil temps are no issue at all, but maybe the oil needs to be pullling more heat from the motor. my A/F is about 13 on idle, 13.2-13.7 at cruise and 12-12.5 on WOT , so i think those numbers are pretty good. it was cooler yesterday abou 60 degrees and driving home from porsche club cruise out to an airport for a cuise in and fly in event, i took more back roads but during the 70 mile trip i only spent about 30 miles on the interstate, andduring that time i was seeing 330-360 depending on my speed which was between 68-75. Motor now has about 6k miles since the build.

btw what PMB is doing is using holly terminator x as the ECU, running 40psi for fuel pressure and GM injectors, either in with stock d-jet set up or using ITB's from Jenvey
. i have to ask Eric how thats working with regard to motor head temps. thats what they are putting on their motors from 2056 up to the 2.4's they are buiding.

That is probably what any sane person would do bumping the power like this. I just emailed the Dyno, hopefully I can get in soon, it will be interesting to see what kind of change I see. Sadly I didn't do a cruise pull before the rebuild but I have all the numbers for the WOT pull pre 2056.

Sooooo.... Got to the Dyno yesterday (Easter miracle). Some kind of rf interference caused his equipment to malfunction (474 foot pounds of torque?). However, we were able to work on the mix. I am now back to nothing but the 250 ohm resistance that the car originally had from the factory. I was so rich his equipment didn't go that low. We did some cruise at speed tests on the Dyno and made sure my AFR was healthy under all conditions.

That smoothed out the curves, and we bumped it to 29 degrees at 3400, which improved the imaginary numbers over 3k quite a bit.

He suggested experimenting with higher octane. I put some octane booster in it today and it seemed to make a significant difference at cruise. I am keeping my fat switch though, I have an extra 100ohm resistor I can activate at will. That richens it nearly a whole point. Just in case.

Anyone ever notice if the Dakota digital cht is sensitive to voltage? My regulator was misbehaving (14+ volts). Replaced it today with an adjustable solid state. Have not driven it yet however.

The Dakota unit seems to be unaffected by what is usually slightly lower voltage in my car, it typically runs at just under 13V

If you really want to improve the shifting, spring for the Tangerine firewall bushing. I’m sure you got a big improvement with the factory style bushing, but Chris’ product really made a major difference

Could it have been your car with its old school unsuppressed ignition system?

Did the problem only exist then your car was runnning?

Yes, only when running, but I had it on his dyno a couple years ago before the 123ignition dizzy. It is a pertronix coil at the moment. I was suspecting the failing voltage regulator and now I wonder if the super cheap chinese bluetooth radio I installed might have been the culprit. Although that would have made a mess of things with the ignition on engine not running, which wasn't the case.

Two things likely contributing to ignition related RF.

1) Pertronix coil is lower resistance than a Bosch blue coil - therefore generates more RF.
2) 123 dizzy uses electronic switching which is almost instantaneous off/on vs mechanical points switching. This too increases RF.

To reduce RF at the source:
Spiral wound spark plug wires
Resister plugs
Go back to Blue Coil

These are the quick go to solutions.

He could also shield his torque sensor and instrumentation wiring as another option that might help

I have the bosch coil sitting there, I was trouble shooting with the pertronix. I will go back (I like the look of it).

Double check me. Bosch blue should be 3-4 ohms on primary. If I’m not mistaken Pertronix is more like 1.5 or two.

The Bosch I have is the one needed for the 123injection. I checked the pertromix as well to make sure I wouldn't fry the dizzy. I can't remember anymore what the value is but I think they were both the same. I can look after the rain stops.

5th gear interstate travel is always going to run hotter than lower gears below ~65mph. Around roughly 65mph is where air resistance begins to become a factor on the load the engine sees, and the faster you go above 65mph, the more load the air resistance and drag will be putting on the engine.

I used to run a 4 channel digital CHT gauge designed for light aircraft on a 2270 type 4 running dual DRLA40's, tuned to keep AFR in the mid-to-high 12's at cruise (this is where I got the lowest head temps). #3 CHT in gears 1-4 running around town, cruising in the 3k-3.5k rpm range, was low 300's, like 315-320 area. Cruising above 70mph in 5th (same rpm range) with the top on and windows closed was like 350. Windows open it was a little higher due to increased drag. But with the windows down and top off on the interstate it was even higher, like 365-ish area, because with the top off at those speeds the car's aerodynamics basically turn into a parachute that the engine has to fight against. Notably, below 65mph having the top on or off made no difference in head temps because the drag it creates at those lower speeds isn't enough to impact the load on the engine.

As long as head temps keep steady and don't creep upwards continually, then I don't think there's much to be done about this. I took multiple 3+ hour trips on the interstate, and head temps always stayed rock solid steady at the above numbers, and would come back down to the off-highway numbers once off the interstate.

That is pretty much exactly what I am seeing.

I agree with wind resistance

Also when you drop into an over drive 5th you drop the fan speed

This is why the factory put a different 5th I believe into the /6 car trans
To not have as much of an over drive ratio in 5th to raise the fan speed and head cooling output


The 356 guys used to drive a gear down to increase cooling to the heads

You could change your gear ratio?
It’s not a heavy load at cruising

Steady state cruising is supposed to be leaner than WOT for gas mileage

12-1 at cruising is too much fuel
Washed the oil film more
Increases wear on the motor

WOT should be 12.5:1 to flood the cylinder under that condition as the charge actually cools the head more for load when it’s needed

But not at steady state cruising

And why a pot that changes across the whole range can be detrimental compared to the factory tune that can adjust for conditions and throttle conditions

Yeah, 12 is definitely not good at cruise, I was shooting for 13.5. With nothing but MPS mods, it sits at 13.8-9 now at 3200 rpm 72 mph, 12-13inhg. I haven't been able to test my fat switch due to the craptastic weather we are having but from my previous experiments I suspect it will bring me to 13ish. What I am hoping for now is a 'oh jeeze, thats a long climb' switch for the interstate. Out here in upstate ny you can end up climbing 1500 feet over 75 miles with no break as you head west from Elmira. I don't want to be in a position where I am hitting 400 and can't do anything but slow down. No idea if this will actually help that, but it is harmless to try.

Somewhere out there online is a doc, drawing and pictures of the aero dynamic testing done by a member many years ago….

I’m recalling a set of tests to measure air going into the engine lid, along with temps with and without the rain tray…lots of good tests.

Tray or not makes no difference.

Side vents, like the Boxster, would probably work great.
I recall getting air into the engine lid was actually harder at higher speeds.

Might be worth a hunt to go find old info on 914 aero dynamics

I’m going to add some custom louvers on the side like a 550 spider.

My goal is a fresh air intake and allow the fan to have all the air dedicated to cooling.

That would be interesting, I do have quite the air dam on my car so I am sure that doesn't help. I did put some remote sensing equipment in there a couple years ago, temps in the engine stayed pretty reasonable but things have changed.

Bottoms of cars have smooth panels now.

The two air flaps on the bottom of the rear firewall are proven to lower temps.

Air dam……no clue if that helps or hurts

Air dam hurts. +10* is what people generally report.

For mine I don't run the rubber lower section of the air dam.

Zach

I cannot tell from your avatar picture….but it looks like a splitter with possibly a rubber dam below?

If it’s not super hard…take it off and test it