All You CHT Gauge Drivers Report Here

Moderators: Sluggo, Amskeptic

Post Reply
User avatar
asiab3
IAC Addict!
Location: San Diego, CA
Contact:
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Sun Mar 16, 2014 8:07 pm

The drawings are immensely helpful. I come from a line of non-mechanics, so I have trouble instinctively noticing details like that during installations and general work. I honestly had to ask around during installation to see if I should keep the crush washer or not. Thank you.

I thought I saw a few washers under the needle valve but I'll check it, experiment, and report back.
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

User avatar
asiab3
IAC Addict!
Location: San Diego, CA
Contact:
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Sun Mar 16, 2014 8:33 pm

Well now. This is:
A) exactly as I pulled it out.
B) disgusting.

Image

(I mean the sender ring. I personally think the plug looks too lean, but I'm going to give it more time with the new main jet and repositioned sender terminal.)


EDIT: I flattened the ring and gave it a nice correct bend as per your illustration. Only got to putt around town then drive 10 miles on flat freeway tonight, but temps showed about 10* cooler all around. I'm eager for tomorrow's 100 mile stint to see how it fares on an extended highway trip.
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Mon Mar 17, 2014 3:59 pm

asiab3 wrote:Well now. This is:
A) exactly as I pulled it out.
B) disgusting.

I personally think the plug looks too lean,
Can't make conclusions with that plug. If there is a leak, then the leak affects the look of the plug.
You can only read the plug *after* you have a certified seal. I think you might find better temps.
I look forward to your new readings.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

User avatar
asiab3
IAC Addict!
Location: San Diego, CA
Contact:
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Mon Mar 17, 2014 9:44 pm

I reset the plug wire and drove the other night no problem. But when I trekked south today I had trouble keeping it below 400.

Last week you asked about which boot leaked in Phoenix, and it was the left. (My exhaust travels right to left through the heat risers, unlike the stock exhaust I have that goes left to right.) A month before that the right boot tore open. Today I made new boots using a stepped Gates Barricade intake hoses from some '97 Japanese import.

I also checked the ring terminal and it didn't look like it seated properly. So I completely flattened it and gave it a nice clean bend a few mm farther from the plug. That cleared the socket much nicer and installation was easier.

I'm extremely happy to report a lead foot run up a few freeway hills had me no higher than:

357* the first loop, and 361* when I did the loop backwards to make sure there wasn't a wind factor.

I really pushed the bus, holding true 65 everywhere I could except for the steepest hill where I dropped to 60. I'm still timed at 24* hoses off and 27* with vacuum advance. I don't mind the way it performs like this, is it bad to keep these timing settings? I'm going up north next week, and I was planning on taking the sedan if the bus continued to feel hot, but I'd really like to hit the grapevine and the coast with my new findings.
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Tue Mar 18, 2014 5:55 pm

asiab3 wrote: when I trekked south today I had trouble keeping it below 400.

I completely flattened it and gave it a nice clean bend a few mm farther from the plug. That cleared the socket much nicer and installation was easier.

I'm extremely happy to report a lead foot run up a few freeway hills had me no higher than:
357* the first loop, and 361* when I did the loop backwards to make sure there wasn't a wind factor.
I really pushed the bus, holding true 65 everywhere I could except for the steepest hill where I dropped to 60.

I'm still timed at 24* hoses off and 27* with vacuum advance. I don't mind the way it performs like this, is it bad to keep these timing settings? I'd really like to hit the grapevine and the coast with my new findings.
So which is the most recent finding?
a) "when I trekked south today I had trouble keeping it below 400."
or
b) "no higher than 357* the first loop, and 361* when I did the loop backwards"

Bring your timing up towards 28 in small increments if you have (b)
Vacuum advance is supposed to give you closer to 37* (Type 4s take a full 40), but you do understand that it does not go up to full vacuum just because you revved the engine? It hits maximum vacuum only when you first release the throttle at high engine rpm, that is the vacuum spike that most closely approximates throttle overrun.
ColinSoWhatIsItAorB?
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

User avatar
asiab3
IAC Addict!
Location: San Diego, CA
Contact:
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Tue Mar 18, 2014 9:36 pm

Amskeptic wrote:
So which is the most recent finding?
a) "when I trekked south today I had trouble keeping it below 400."
or
b) "no higher than 357* the first loop, and 361* when I did the loop backwards"
Apologies if I was vague- the morning drive was troublesome, temps hung around 400 at 50-55mph with a headwind. Adding a little throttle quickly rose the temps. I just drove slow for that trip. When I got home, I allowed the engine to cool off then replaced the DP boots AND adjusted the CHT sender ring. Then I tested again and found the much lower readings. I am ashamed for science, since I got hasty and made two big changes at once. I'll never know which (or both?) of those things caused the apparent leak that has troubled me for this long.

Work requires me to take the bus often, so I get lots of time to drive and stop to test and repeat. A couple more months on the clock and it will have paid for it's new engine :geek:
Bring your timing up towards 28 in small increments if you have (b)
Vacuum advance is supposed to give you closer to 37* (Type 4s take a full 40), but you do understand that it does not go up to full vacuum just because you revved the engine? It hits maximum vacuum only when you first release the throttle at high engine rpm, that is the vacuum spike that most closely approximates throttle overrun.
ColinSoWhatIsItAorB?
I definitely have B now. I have always understood that vacuum readings work that way, but when I attach a vacuum gauge to the advance (left) port of my German 34/3 I see a steady rise in vacuum along with RPM. I see the spike in let-off with the gauge and with a strobe light, but I also feel like my carb pulls the timing up a little during normal acceleration. I have no way of measuring this under load though. Is that normal?

I measure my amount of vacuum allowed at high RPM let-off, and have it set to about 2-3* right now. Should I increase this gradually as I increment up to 28*?

I'm really happy that I'm making progress in this. And I think my bus will be happier for it as well.
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

User avatar
energyturtle
Getting Hooked!
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by energyturtle » Wed Mar 19, 2014 1:11 pm

I took the bus on her first long drive since the build. 15 min. into the drive Temps rose to 350 F. At highway speed, 55MPH for 20 min, heads temps never rose above 375F. On a 10 mile incline from the valley to the mountains in Gatlinburg I hit 380-390F. She performed very well in my opinion. Are these temps at an acceptable range? VDO gauge.

Scottie

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Sun Mar 23, 2014 10:17 am

energyturtle wrote:I took the bus on her first long drive since the build. 15 min. into the drive Temps rose to 350 F. At highway speed, 55MPH for 20 min, heads temps never rose above 375F. On a 10 mile incline from the valley to the mountains in Gatlinburg I hit 380-390F. She performed very well in my opinion. Are these temps at an acceptable range? VDO gauge.

Scottie
With a VDO, there is much guesswork, but those numbers seem OK. We need to know ambient temps with VDO, because VDO does not compensate the gauge head.

That means if it reads 375* and it is 70* ambient, yer good.
If it reads 375* and it is 40* ambient, the actual CHT temp is closer to 400*.
If it reads 375* and it is 100* ambient, actual CHT is closer to 345*.
See how VDO distorts things in the wrong direction?
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Sun Mar 23, 2014 10:25 am

asiab3 wrote: I measure my amount of vacuum allowed at high RPM let-off, and have it set to about 2-3* right now. Should I increase this gradually as I increment up to 28*?
How do you "set" vacuum to 2-3*?
If maximum advance (no hoses) is 28* and the maximum advance allowed on overrun is let's say 38*, that is 10* total vacuum advance allowed.

So l :cyclopsani: :cyclopsani: k in your Bentley manual at the end of the Engine chapter.
There is a chart of all distributor advances. Ignore the vacuum only distributors which have to do the entire advance (they show a range of 16+* ), and you will see that every VW distributor that has both centrifugal and vacuum advance gives the vacuum advance range as 8* to 11* on top of the centrifugal number!
So, add 28* + 11* and your total advance should be about 38* on overrun.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

User avatar
asiab3
IAC Addict!
Location: San Diego, CA
Contact:
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Sun Mar 23, 2014 10:53 am

Amskeptic wrote:
asiab3 wrote: I measure my amount of vacuum allowed at high RPM let-off, and have it set to about 2-3* right now. Should I increase this gradually as I increment up to 28*?
How do you "set" vacuum to 2-3*?
If maximum advance (no hoses) is 28* and the maximum advance allowed on overrun is let's say 38*, that is 10* total vacuum advance allowed.
I've been working with a Mallory Unilite SVDA for the last two months. I might not have mentioned it before but thought I did. Total mechanical advance, mechanical curve, and total vacuum advance are all programmable. Originally I was working with John @ac.net to get it as close to their Bosch SVDA as possible. Then the CHT debacle lead me to experiment with changing the curves around, and I haven't reset the vacuum advance all the way yet. Still gradually incrementing.

I do notice now that the leak(s) are gone, 28* hoses off gives me slightly cooler temps than 24* hoses off. Do the exhaust temps go up and affect CHTs with that retarded setting?
So l :cyclopsani: :cyclopsani: k in your Bentley manual at the end of the Engine chapter.
There is a chart of all distributor advances. Ignore the vacuum only distributors which have to do the entire advance (they show a range of 16+* ), and you will see that every VW distributor that has both centrifugal and vacuum advance gives the vacuum advance range as 8* to 11* on top of the centrifugal number!
So, add 28* + 11* and your total advance should be about 38* on overrun.
Colin
Checking now :salute:
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Sun Mar 23, 2014 11:02 am

asiab3 wrote: now that the leak(s) are gone, 28* gives me slightly cooler temps than 24*.
Do the exhaust temps go up and affect CHTs with that retarded setting?
Double check that. As you retard the timing, the exhaust system will heat up, but that should not be affecting the spark plug area, not within the narrow parameters you have posted here.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

User avatar
asiab3
IAC Addict!
Location: San Diego, CA
Contact:
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Sun Mar 23, 2014 11:52 am

Amskeptic wrote:
asiab3 wrote: now that the leak(s) are gone, 28* gives me slightly cooler temps than 24*.
Do the exhaust temps go up and affect CHTs with that retarded setting?
Double check that. As you retard the timing, the exhaust system will heat up, but that should not be affecting the spark plug area, not within the narrow parameters you have posted here.
Colin
Perhaps I was not pushing the bus as hard, or there was a tail wind, but I saw 5-10* lower temps when driving the highway yesterday. I will confirm today on a longer drive.

Re: narrow vacuum limit:
All the dual advance distributors for T4 engines (according to my 1974-published Bentley) allow 7-14* timing or less depending on models, like 205 E, J, F, N, and S. The 205Q shows 2-5* max vacuum range. All the other T1 distributors listed are vacuum only. This is why I went with the narrow range originally.

RobbieStuckIn1974
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Sun Mar 23, 2014 8:56 pm

asiab3 wrote:
Re: narrow vacuum limit:
The 205Q shows 2-5* max vacuum range. This is why I went with the narrow range originally.
RobbieStuckIn1974
Indeed, the 205Q is exactly as you read it.

So we have a 1600 AE engine with dual port heads and a 34Pict3 carburetor.

We know the factory technicians had to, by law, set the idle timing with the hoses on to 5* ATDC as per the decal. Let's do the math.
Wide Range Where All Units Do The Max Spread:

If the retard has a 13* range, we start counting up from 5*After 13 degrees to 7*Before at idle with no retard. Now add 25* max allowable range of the advance and we get 7* + 25* = a total of 32* before we have even plugged in the allowable 2-5* additional vacuum advance. Let's add the max 5* and total advance will be 37* at throttle overrun. That's fine.

Narrow Range Where All Units Do The Minimum Spread:

Now, if we do the factory timing at idle under law 5*ATDC, and our retard unit only has 11* range, then hoses off idle timing will be 6* BTDC. Add a centrifugal advance that can only pull 22* and we are at a max of 28* before we plug in the vacuum advance. Let's say it is good for 2*. Then your max max at overrun is barely 30*.

Remember, the factory guys just followed the directions. Both examples above would have made it out the door. But look at the difference between customer 1 and customer 2.
"My VW's great! Peppy, good mileage!"
"My VW's a bit slow, but they all are, you know?"

What I am saying, is work with the range given the factory's blessing. The factory says 37* BTDC is fine, so don't limit yourself to the mere range of the factory specified vacuum unit! If your centrifugal is a little narrow, fine, stick it at YOUR specified ( I like 26-28*) centrifugal max, and go make the vacuum advance hit 37* and if that means the total vacuum range is now 10*, what the heck.
Practice experiment test record report . . .
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

User avatar
asiab3
IAC Addict!
Location: San Diego, CA
Contact:
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Tue Mar 25, 2014 12:42 am

Ok, I'm getting it, and right now the bus is set pretty close to the second example.

And the bus is getting to be a REAL pleasure to drive again. Just got back from 750 miles in two days, and it was great. Interstate 5 North for a few hours, Grapevine at 75*f ambient, and a few more hours north… Then back down the coast/101.

Main: 130
Air: 75 (changed form 60 because the temps whereon the low side.)
Mech advance: 28*
Vacuum: 4-5*
Average MPG: 18.2 over the whole trip.

Average cruising CHT on flat ground: 360* @ 60-65mph. What interested me, is that on flat ground a push to 65-68mph didn't see a rise in CHT nearly as much as an uphill or headwind shows. Grapevine, full throttle run approached at 65mph showed 409* nearing the top of the hill when it finally wouldn't hold 4th at full throttle and dipped below the torque peak. Never saw another CHT above 390 this trip, and only saw a few 380s under full throttle up two grades between the 5 and the coast. I finally stopped peeping at the gauges constantly on the second half of this trip, and the bus politely reminded me how nice it feels to Just Go.

This week I will shoot for the example #1 and closely monitor the temps and economy. It may take a few more days than usual since I don't have any PLANNED trips for a while. Or is it worth gradually incrementing from example B ( basically where I am now) to example A?
Practice experiment test record report . . .
That IS why I got this distributor, after all. I would much rather find a perfect balance through experimenting, than get lucky with one distributor and not completely understand the system and full potential of this beautiful car.

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Tue Mar 25, 2014 10:55 am

asiab3 wrote: Main: 130
Air: 75 (changed from 60 because the temps were on the low side.)
Centrifugal: 28*
Vacuum: 4-5*
Average MPG: 18.2
Average cruising CHT 360* @ 60-65mph
full throttle approach at 65mph showed 409* nearing the top of the hill when it finally wouldn't hold 4th

bus politely reminded me how nice it feels to Just Go.
I say take a rest and . . . Just Go.
That is the pleasure of Chloe out on the road, to be within Volkswagen's original recipe. I look at all of this marketing gee whiz tom-foolery and heartache and disappointment and rants about how VWs should not be driven on the highway or in the desert, and it makes me want to . . . . you know,
go in circles around the country to share the air-cooled gospel.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

Post Reply