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> CHT temps, individual cylinder differences?
falcor75
post Apr 12 2018, 10:50 PM
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For those of you that are running 4 CHT sensors under the plugs, what differences do you see between the cylinders?

Whats your typical temps for each cylinder with:

A: Engine warmed up sitting at idle for a minute or two.

B: Engine warmed up, cruising at 50-55 mph in fifth gear.
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Porschef
post Apr 13 2018, 04:19 AM
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era vulgaris
post Apr 13 2018, 06:38 AM
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I don't own the car anymore, but on my old 75 with the 2270 I had a 4 channel digital CHT. This is going from memory so don't take these numbers as gospel, but I would see warmed up temps in this area:

1) 315
2) 300
3) 325
4) 315

That's not exact, but that type of ballpark. 2 is coolest, 3 is hottest, and 1 and 4 are about the same.
Cruising between 3k and 4k rpm in gears 1-4, temps remained pretty stable. They'd go up a few degrees while accelerating or climbing a hill, and then level off again while cruising or idling.

Also, below approx 60mph you'd have one set of temps that would hold steady for gears 1-4. Once you pass that 60-ish mph barrier temps start to climb and will level off around 15-20 degrees higher across the board at around 70mph, simply due to air resistance, which is why it's so important to keep the revs up in 5th gear. Take the top off above 60mph and temps go up another 10-15 degrees because you've further increased the car's air resistance.
So please, don't EVER cruise in 5th at 50-55mph. You're doing the engine a major disservice. Drive at that low of an rpm in 5th long enough, and you're virtually guaranteeing to have cracked heads or dropped valves in your future because the cooling fan isn't moving fast enough and your temps will creep up up up. 5th gear should not be used below 3k rpm, which equates to about 70mph.
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VaccaRabite
post Apr 13 2018, 07:23 AM
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QUOTE(era vulgaris @ Apr 13 2018, 08:38 AM) *

So please, don't EVER cruise in 5th at 50-55mph. You're doing the engine a major disservice. Drive at that low of an rpm in 5th long enough, and you're virtually guaranteeing to have cracked heads or dropped valves in your future because the cooling fan isn't moving fast enough and your temps will creep up up up. 5th gear should not be used below 3k rpm, which equates to about 70mph.


This is my experience as well.
I never touch 5th till about 70. Especially climbing the long gradual hills going home from work.

Zach
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falcor75
post Apr 13 2018, 11:50 PM
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Thanks for the replies, hope some more people chime in. I need to use my 4th gear more.

The reason for me asking is that I see a different pattern to my temps.
I havnt driven much this year with all four sensors yet but on my 2256 I see the #1 cylinder the hottest, followed by #2 and then 3 and 4 a few degrees lower and pretty even with eachother. I'll try to get it out soon for an extended drive and report back the temperatures I'm just waiting for my new rear brake pads to arrive.
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era vulgaris
post Apr 14 2018, 07:29 AM
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Dual carbs, or FI? If dual carbs, then your carbs are out of balance. The more open the throttle butterfly is, the higher the head temp will be. Your 1,2 side carb is currently set for a higher idle than your 3,4 side carb. That's why your temps are off from where they should be.
I had that car for 2 years and I saw every possible result of temps during tuning. Your temp relationships are typical for carbs that aren't in sync, either because of tuning or because of a mis-adjusted linkage.
When tuned properly #3 will always be the hottest because it's furthest from the cooling fan, and #2 will always be the coolest because it's closest to the cooling fan.
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MikeM
post Apr 14 2018, 09:10 AM
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This is a great reminder... but I've always wondered about the extra friction and heat caused by running at higher RPM. At what point are you defeating the purpose of running the engine fan faster?
Mike
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Boomingbeetle
post Apr 14 2018, 10:28 AM
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Warm at idle on my 2430 with stock fan/cooling and a small external oil cooler/fan mounted next to transmission under rear trunk. I don’t trust my volt meter.



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Boomingbeetle
post Apr 14 2018, 10:32 AM
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Here it is 10min driving at 3250-3500 rpm in 5th. Maybe 80mph. It is 70 degrees today. If I drive for an hour or so #4 can hit 325 or even 350+ climbing a hill. Oil temp gets to 210. My oil pressure is around 60psi hot under load, 10-15 hot idle. Cold it is 80+

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era vulgaris
post Apr 14 2018, 10:32 AM
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QUOTE(MikeM @ Apr 14 2018, 11:10 AM) *

This is a great reminder... but I've always wondered about the extra friction and heat caused by running at higher RPM. At what point are you defeating the purpose of running the engine fan faster?
Mike


With my 2270 the trade off point was around 4300-4500rpm, where extended running at rpm's higher than that would see a gradual increase in head temp. The most efficient cooling was between 3000 and 4000rpm. At lower speeds (sub 50mph), my car was ok to cruise as low as 2700rpm and not see head temp increase. But above 50mph, it definitely needed to be at or above 3k rpm for extended cruising.

What that car taught me is that ideal driving/cruising for max cooling is done between 3k and 4k rpm, and ideal shift point is around 4500 rpm. This is of course, for your normal slogging along type driving. For the fun stuff, as long as you don't spend too much time above 4500 rpm, you're ok!
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falcor75
post Apr 14 2018, 12:26 PM
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I've got itbs and FI.

I've measured my airflow on the cylinders at idle and #1 does draws the most air, then #3 and #4 are slightly below and #2 the least. The problem is that I have no way of adjusting the individual cylinders, only have idle air between the banks to adjust on at idle. And once the throttle butterflies is opened the idle air really doesnt matter much.

In the FI system I have the options of adjusting the fuel and timing of individual cylinders but I've left those options unused for now.
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era vulgaris
post Apr 14 2018, 02:41 PM
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QUOTE(falcor75 @ Apr 14 2018, 02:26 PM) *

I've got itbs and FI.

I've measured my airflow on the cylinders at idle and #1 does draws the most air, then #3 and #4 are slightly below and #2 the least. The problem is that I have no way of adjusting the individual cylinders, only have idle air between the banks to adjust on at idle. And once the throttle butterflies is opened the idle air really doesnt matter much.

In the FI system I have the options of adjusting the fuel and timing of individual cylinders but I've left those options unused for now.


Ah, programming EFI is beyond my experience. But the ITB's should still be connected with a linkage similar to dual carbs, right?
I'm curious if you disconnect the linkage, do the airflow numbers change at all?

Re-connecting the linkage was always the trickiest part of tuning for me. It was easy to tune the individual carbs when they were unlinked, but connecting the linkage and making sure that it didn't ruin the tune was always a really fiddly job. And I always relied on my 4 channel head temp gauge to know when I had it set right.

I don't know what linkage you have, but it's possible that it's pulling the 1,2 side open more than the other side.
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Elliot Cannon
post Apr 14 2018, 03:46 PM
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Coming home from Rt. 66 a number of years ago, I was driving up a very VERY long up hill stretch west of needles into about a 50 mph wind. The throttle wouldn't answer to accelerate and when I looked at the head temp. it was way over 400 degrees. Way over! I pulled over, let it cool, drove from then on in 4th gear and about 60-65 mph. The engine temp. cooled down nicely, to the usual 325-350 and stayed that way till I got on the other side of the mountain and then resumed in 5th gear. I should mention that when I stopped and pulled over to let it cool, I almost couldn't open the door to get out, the wind was so strong.

When the cyl. head temps go up, drop a gear, the higher rpm's mean the engine is working less hard and the fan speed also increases. Thanks to Joe Sharp for the advice. (IMG:style_emoticons/default/pray.gif) (IMG:style_emoticons/default/smoke.gif) (IMG:style_emoticons/default/driving.gif)
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Boomingbeetle
post Apr 14 2018, 04:30 PM
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Sorry for the sideways pictures, they are not rotated like that on my phone (IMG:style_emoticons/default/confused24.gif)

Mine does not cool down above 4000rpms. I have to drop speed and reduce load on the motor if it starts climbing. It hasn’t gotten that hot in a while though, I had a problem of crud in my tank and fuel lines and my main jets would sometimes clog (running lean would increase temp). Since replacing all the lines and having the tank flushed and coated I haven’t had that issue or temps above 325 yet, although the season is getting warmer now...
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worn
post Apr 14 2018, 05:33 PM
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QUOTE(Elliot Cannon @ Apr 14 2018, 01:46 PM) *

Coming home from Rt. 66 a number of years ago, I was driving up a very VERY long up hill stretch west of needles into about a 50 mph wind. The throttle wouldn't answer to accelerate and when I looked at the head temp. it was way over 400 degrees. Way over! I pulled over, let it cool, drove from then on in 4th gear and about 60-65 mph. The engine temp. cooled down nicely, to the usual 325-350 and stayed that way till I got on the other side of the mountain and then resumed in 5th gear. I should mention that when I stopped and pulled over to let it cool, I almost couldn't open the door to get out, the wind was so strong.

When the cyl. head temps go up, drop a gear, the higher rpm's mean the engine is working less hard and the fan speed also increases. Thanks to Joe Sharp for the advice. (IMG:style_emoticons/default/pray.gif) (IMG:style_emoticons/default/smoke.gif) (IMG:style_emoticons/default/driving.gif)

I built a 2056 with too much compression and a non-stock cam. Rebuilt the manifold pressure sensor and have to run richer than I want to in order to keep below 400.
My experience with fourth gear hasn’t been positive. Louder, but not much cooler. Excellent motivation for a six
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Mark Henry
post Apr 14 2018, 07:08 PM
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QUOTE(Vacca Rabite @ Apr 13 2018, 09:23 AM) *

QUOTE(era vulgaris @ Apr 13 2018, 08:38 AM) *

So please, don't EVER cruise in 5th at 50-55mph. You're doing the engine a major disservice. Drive at that low of an rpm in 5th long enough, and you're virtually guaranteeing to have cracked heads or dropped valves in your future because the cooling fan isn't moving fast enough and your temps will creep up up up. 5th gear should not be used below 3k rpm, which equates to about 70mph.


This is my experience as well.
I never touch 5th till about 70. Especially climbing the long gradual hills going home from work.

Zach

(IMG:style_emoticons/default/agree.gif) Don't lug a T4, 3000 rpm minimum

I only use #3 because I know it's the hottest cylinder.
I aim for just over 300* at 3000-3600 rpm on the flats, pulling a hill 350*.
Much higher and heat soak begins and over 400*+ the alunimum begins to soften.

When you pull hills on the downside the temps should recover to near flat temps.
If the temps are not recovering then you are leaning your AFR too far and/or you're into heat soak issues.
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falcor75
post Apr 15 2018, 01:12 AM
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QUOTE(era vulgaris @ Apr 14 2018, 10:41 PM) *

QUOTE(falcor75 @ Apr 14 2018, 02:26 PM) *

I've got itbs and FI.

I've measured my airflow on the cylinders at idle and #1 does draws the most air, then #3 and #4 are slightly below and #2 the least. The problem is that I have no way of adjusting the individual cylinders, only have idle air between the banks to adjust on at idle. And once the throttle butterflies is opened the idle air really doesnt matter much.

In the FI system I have the options of adjusting the fuel and timing of individual cylinders but I've left those options unused for now.


Ah, programming EFI is beyond my experience. But the ITB's should still be connected with a linkage similar to dual carbs, right?
I'm curious if you disconnect the linkage, do the airflow numbers change at all?

Re-connecting the linkage was always the trickiest part of tuning for me. It was easy to tune the individual carbs when they were unlinked, but connecting the linkage and making sure that it didn't ruin the tune was always a really fiddly job. And I always relied on my 4 channel head temp gauge to know when I had it set right.

I don't know what linkage you have, but it's possible that it's pulling the 1,2 side open more than the other side.


Yeah they're like carbs except for modern fuel injectors that spray underneath the butterflies. I've got Tangerines dual pulley setup with the 1-2 side being the master side where the throttle cable is connected. I'll give it another go to see if I can disconnect the throttle cable and readjust the 1-2 side shaft stop to see if it goes any lower.
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falcor75
post Apr 15 2018, 05:28 AM
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Just spend the last 3 hours fiddling with the thottles.

Started with disconnecting the throttle cable and making sure the 1-2 (master) side was as closed as it would possibly go. Then I hooked up the throttle cable again and made sure there was no slack in the slave cable to the 3-4 side so both sides open simultaneously.

I started the engine and let it warm up for about 10 minutes at different rpms. (the neighbours love me) Then I took out the air gauge and started measuring. To start with
1 drew the most air, followed by 3 and 4 and last 2. By first adjusting the slave cable slightly and then the idle air screws I got cylinder 1,3 and 4 to draw the same amount of air, just below the 6 mark on the scale. CHT temps at idle was then around 110C (320F) for #1 and 125C (257F) for # 3 and #4.

Attached Image
Cylinder 1

Attached Image
Cylinder 2


The odd one out is still #2, when the others draw just below the 6 mark, #2 draws like 4,5-4,8, about a full scale marker lower and the temp is around 95 C or 205F.

What could cause #2 to draw that much less air? air leak between head and manifold, airleak between manifold and throttle body are the only things I can come up with....
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jd74914
post Apr 15 2018, 08:22 PM
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What is your target AFR? Or do you have a screen shot of your map?

That's a pretty big difference in fueling at idle given the airflow differences. Assuming you are at lambda = 1 for cyl. 1 airflows, you'd be at about lamba = 1.3 for cyl. 2 at idle. That's certainly enough fuel to cause some additional cooling and result in those lower temperatures.

You could see lower flows if you have some valve adjust or pushrod length issues (not opening enough) or a flat cam lobe. I'd guess the cam is OK since your motor is pretty new.

Were your injectors all flow mapped or checked? I've seen some new injectors pretty far off the mark. If they haven't been tested it might be interesting to swap them between cylinders and see if the temperature mapping moves.
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Dave_Darling
post Apr 15 2018, 09:25 PM
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QUOTE(jd74914 @ Apr 15 2018, 07:22 PM) *

You could see lower flows if you have some valve adjust or pushrod length issues (not opening enough) or a flat cam lobe. I'd guess the cam is OK since your motor is pretty new.


Another point arguing against a flat cam lobe is that opposite cylinders share cam lobes. So if the left-rear intake had a cam lobe problem, the right-rear intake would have the same problem.

Lifters, of course, are specific to each side.

--DD
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