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#26 |
Registered User
Join Date: Jan 2013
Location: Eastern TN
Posts: 1,921
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Re: Brand new fan clutch - overheats at idle?
Sounds like you got it fixed. If you need to get the radiator fixed check out Beach Radiator in Virginia Beach. A really nice guy owns the place and the work is top notch. Avoid the place on Military Highway that has a good rep with the old timers. The quality went down hill and you can actually see them working on radiators at the car wash next door because they rented out their shop! Two attempts to fix a radiator there only resulted in a bigger leak. Beach radiator fixed it right up.
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#27 | |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Brand new fan clutch - overheats at idle?
Quote:
I bring it up not (only) to brag but because there shouldn't BE any vacuum advance at idle.
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#28 | |
Simple? What's simple?
![]() Join Date: Apr 2007
Location: Southeast CT
Posts: 1,472
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Re: Brand new fan clutch - overheats at idle?
Quote:
This gets into a whole other topic I was researching last night. My truck is non-emissions (No A.I.R.), so as I understood it I should be using manifold vacuum for the distributor, not ported. Thus, I have full vacuum at idle (which is why you set initial with the module disconnected). I read a superbly good write-up by a GM ignition engineer who helped design the systems and why they did what they did. That makes the most sense to me, since you only want to retard timing under high load (low vacuum) scenarios, and idle is about as low load as it gets. It definitely idles a lot more smoothly with the manifold vacuum.
__________________
CURRENT '50 GMC 100 shortbed Gen IV 4.8 LS - 4L65E (Secret truck, Shhh!!!) Build '63 Buick Wildcat Coupe 401ci Nailhead (Very much in pieces) Photos '66 Impala SS convertible 327-QJet-glide (4 speed swap one of these days...) Photos '69 CST/10 4x4 SWB Stepper 350 2bbl - NV4500/NP241C (Broken Truck!) '72 Sierra Grande 2WD LWB fleetside 350-TH350 Refresh '99 K2500 Silverado RCLB 5.7 Vortec - NV4500/NP241C (Daily) '99 K2500 Suburban 7.4 Vortec - NV4500/NP246 (still working out the bugs) SOLD '71 Custom/10 2WD LWB fleetside - '72 GMC K/3500 Dually (Sold to redryder) |
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#29 | |
Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
Posts: 1,642
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Re: Brand new fan clutch - overheats at idle?
Quote:
Obviously I don't know your engine combination or your local emissions law, and none of what I've said disputes anything you said about how your vehicle runs and responds but I know for certain it will cause your CO readings to increase at idle if you use the same base timing specs with the pod dis-connected, due to incomplete combustion. The idle mixture screws will allow you to set the engine to idle smooth with either set-up in most cases, unless the engine has been modified to the point the carb needs modified. Last edited by mechanicalman; 09-24-2014 at 02:45 PM. Reason: error |
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#30 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Brand new fan clutch - overheats at idle?
There were in fact attempts at combating emissions by using full manifold vacuum for timing control, but I'm pretty sure those didn't come along until the late 70s or early 80s.
Unless there's something really special about that motor, and a lack of Air Injection isn't it (all mine lack it too), I don't think this is the case. Remember vacuum advance advances the timing under light load. Your initial timing is appropriate for idle, but once you start adding load at low volumetric efficiency you need more lead time to get it to burn. If you used manifold vacuum you'd have whackadoo idle timing and then less as you tipped in load, which is the opposite of what you want. Where's mechanicalman when you need him? He can likely back me up on this (again, unless there's something weird about the post-70 trucks).
__________________
1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#31 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Brand new fan clutch - overheats at idle?
Never mind, we posted at the same time! I call the vacuum port he refers to as the transfer slot (the transition between idle and drive circuits) but otherwise what he wrote sounds right to me!
__________________
1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#32 | |
Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
Posts: 1,642
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Re: Brand new fan clutch - overheats at idle?
Quote:
Weird that only the bottom half of the rad gets hot. Are you sure it's not plugged and needs to be boiled out? Maybe it's been like that a long time, but didn't matter until the clutch fan relied on it for temp sensing. Unless you had a fancy two-pass radiator I can't picture a scenario in which a factory rad wouldn't heat evenly. In fact it should be hotter at the top and cooler at the bottom by whatever temp drop (maybe 30-60 degrees) that your rad can manage". Spot on, Dave. Who would have known he was running manifold vacuum? And, I didn't pick up on the radiator being cooler at the bottom, yeah that didn't make sense unless it was low on coolant. |
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#33 | |
Simple? What's simple?
![]() Join Date: Apr 2007
Location: Southeast CT
Posts: 1,472
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Re: Brand new fan clutch - overheats at idle?
In the interest of learning and education, here's the information I read last night (borrowed from the HotRodders.com forum):
Quote:
Again, not meaning to be arguementitive, just trying to understand what's at play here, what is correct, and why - we all know the internet is full of mis-information so it's best to be sure!
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CURRENT '50 GMC 100 shortbed Gen IV 4.8 LS - 4L65E (Secret truck, Shhh!!!) Build '63 Buick Wildcat Coupe 401ci Nailhead (Very much in pieces) Photos '66 Impala SS convertible 327-QJet-glide (4 speed swap one of these days...) Photos '69 CST/10 4x4 SWB Stepper 350 2bbl - NV4500/NP241C (Broken Truck!) '72 Sierra Grande 2WD LWB fleetside 350-TH350 Refresh '99 K2500 Silverado RCLB 5.7 Vortec - NV4500/NP241C (Daily) '99 K2500 Suburban 7.4 Vortec - NV4500/NP246 (still working out the bugs) SOLD '71 Custom/10 2WD LWB fleetside - '72 GMC K/3500 Dually (Sold to redryder) Last edited by JJorgensen52; 09-24-2014 at 03:10 PM. Reason: forgot to write the last bit |
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#34 | |
Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
Posts: 1,642
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Re: Brand new fan clutch - overheats at idle?
Quote:
So, "when the throttle blades open and ported becomes equal to manifold", six of one and half a dozen of the other, it's all the same then. I'm not trying to be argumentative either, and I used to make the same assumption. BTW, very good link I saved it on my favorites. Thanks. Last edited by mechanicalman; 09-24-2014 at 03:33 PM. Reason: minor clarification |
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#35 | |
Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
Posts: 1,642
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Re: Brand new fan clutch - overheats at idle?
Quote:
This I know to be "internet mis-information". No distributor from the factory ever had near that much centrifugal advance. Yes, ported vacuum was initiated for the purpose of heating up the exhaust and lowering the emissions on both AIR and non-AIR engines along with the low base timing specs. And yes, you want as much advance as you NEED at idle without making it crank slowly if emissions are not on your list of to-do. But you don't need manifold vacuum to do it, you simply set the base timing for as much as you can without cranking hard (I run 15 degrees base with ported vacuum and still barely pass Arizona emissions without changing the settings). I have a true 8.7:1 compression ratio (flat-top pistons with 80cc combustion chambers), my mechanical advance curve is correct (after much fuss) and I get 37 degrees total timing (15 base plus 22 mechanical) and 54 cruise advance (15 base plus 22 mechanical plus 17 vacuum). Stock HEI (I did replace the shaft with a GM part don't remember the number) with aftermarket pod and advance springs, my vacuum pod is adjustable and is just barely all in at cruise, I'm running a 373 gear without overdrive, headers, and I get 12 MPG city and 15 MPG highway at 65 MPH. I know, I need an overdrive. No excuses. "For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts". This too is untrue, and conceited at best. This too is just someone talking on the internet, not straight from the pages of a GM engineer, unless it's the engineer that got fired for printing things that were untrue. Yet I admit a lot of the stuff he said is true, but not all of it. And, I'm just someone talking on the internet LOL. You never know who to believe, and really, trial and error and your own satisfaction and happiness is all there is. Good luck and stay safe. Last edited by mechanicalman; 09-24-2014 at 04:27 PM. |
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#36 | |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Brand new fan clutch - overheats at idle?
Quote:
At idle, the transfer slot is above the mostly-closed throttle blades so there is no ported vacuum but lots of manifold vacuum (because the blades are closed). As you tip into the throttle, this uncovers the transfer slot and you start to get vacuum there. Manifold vacuum drops just as a function of the blades now reducing restriction as they open. Once both are open, unless its a carb design that routes one to a venturi, they are exposed to the same conditions and hence, as he says, six of one half dozen of the other. But as you read in the article above vacuum advance is for part throttle. At WOT it's zero. At idle its zero. Only during part throttle does it do anything. A frequent mistake I see made is for people, particularly with older higher compression engines, to experience pinging under part load. They then back off the total timing, thinking its a function of high compression. What they actually could do is change the vacuum curve (some are adjustable with an allen key, otherwise replace) to bring in less part throttle advance. After all, that's where it was detonating. But the approach of backing off mechanical timing hurts the engine's performance at every RPM.
__________________
1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#37 | |
Simple? What's simple?
![]() Join Date: Apr 2007
Location: Southeast CT
Posts: 1,472
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Re: Brand new fan clutch - overheats at idle?
Quote:
I'm beginning to wonder about my balancer. As far as the ported vs. manifold - my thought (perhaps incorrect) was that as soon as I uncover the transfer slot (so small throttle increment), I now am seeing port = manifold, and since my throttle percentage is still low, my advance would jump right up. It makes good sense that if I go from idle to WOT that the vacuum advance never has a chance to get involved. There only appears to be one ported vacuum location available on my 2GV, and it's currently hooked to the charcoal can. I presume that's where I should be getting my timing vacuum? The vacuum fitting on the rear of the carb base, closest to (and I had assumed, for) the distributor is manifold vacuum. Thanks for the info folks!
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CURRENT '50 GMC 100 shortbed Gen IV 4.8 LS - 4L65E (Secret truck, Shhh!!!) Build '63 Buick Wildcat Coupe 401ci Nailhead (Very much in pieces) Photos '66 Impala SS convertible 327-QJet-glide (4 speed swap one of these days...) Photos '69 CST/10 4x4 SWB Stepper 350 2bbl - NV4500/NP241C (Broken Truck!) '72 Sierra Grande 2WD LWB fleetside 350-TH350 Refresh '99 K2500 Silverado RCLB 5.7 Vortec - NV4500/NP241C (Daily) '99 K2500 Suburban 7.4 Vortec - NV4500/NP246 (still working out the bugs) SOLD '71 Custom/10 2WD LWB fleetside - '72 GMC K/3500 Dually (Sold to redryder) Last edited by JJorgensen52; 09-24-2014 at 08:17 PM. |
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#38 | |
Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
Posts: 1,642
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Re: Brand new fan clutch - overheats at idle?
Quote:
http://repairguide.autozone.com/znet...5280252293.gif |
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#39 | |
Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
Posts: 1,642
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Re: Brand new fan clutch - overheats at idle?
Quote:
Well, I'm not sure that during transition to ported vacuum if the is actually any venturi effect from the pinched airflow, and if there is if it's enough to measure or cause a spike in the ported vacuum vs the manifold vacuum. I think we are all pretty sure once past this point it's all the same, but I'm wondering if the transition is an issue regarding advance operation. Your thoughts? I don't get Hemming Motor News, could not find a link if you have one I'd love to read that article (learning op). |
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#40 | |
Simple? What's simple?
![]() Join Date: Apr 2007
Location: Southeast CT
Posts: 1,472
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Re: Brand new fan clutch - overheats at idle?
Quote:
![]() The labels are hard to read, but the port facing forward from the baseplate is currently to the air cleaner, and the ported vacuum (pointed at camera) to the charcoal can. It appears the charcoal can should be connected at the front port, the air cleaner at the rear port, and that leaves distributor to the ported vacuum. The truck is bone stock 307 2 barrel
__________________
CURRENT '50 GMC 100 shortbed Gen IV 4.8 LS - 4L65E (Secret truck, Shhh!!!) Build '63 Buick Wildcat Coupe 401ci Nailhead (Very much in pieces) Photos '66 Impala SS convertible 327-QJet-glide (4 speed swap one of these days...) Photos '69 CST/10 4x4 SWB Stepper 350 2bbl - NV4500/NP241C (Broken Truck!) '72 Sierra Grande 2WD LWB fleetside 350-TH350 Refresh '99 K2500 Silverado RCLB 5.7 Vortec - NV4500/NP241C (Daily) '99 K2500 Suburban 7.4 Vortec - NV4500/NP246 (still working out the bugs) SOLD '71 Custom/10 2WD LWB fleetside - '72 GMC K/3500 Dually (Sold to redryder) |
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#41 |
Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
Posts: 1,642
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Re: Brand new fan clutch - overheats at idle?
Quote:
But if you want to keep manifold vacuum your set-up might be OK, not sure. I agree you might want to check your balancer, or you might have a carbon build-up lighting the fire early. I know a real good way to clean the carbon out, but on an old engine with questionable valve seats it might end up needing a valve job. The valve seals ever been replaced? |
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#42 |
Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
Posts: 1,642
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Re: Brand new fan clutch - overheats at idle?
Here's a cool link, Jorgie. OK I call you Jorgie?
https://www.google.com/search?q=port...gQsAQ&dpr=0.95 Not sure "transition slot" pertains to ported vacuum, seems to only have to do with idle and part throttle fuel circuit, but always willing to listen to good info from whatever sources. |
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#43 |
Simple? What's simple?
![]() Join Date: Apr 2007
Location: Southeast CT
Posts: 1,472
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Re: Brand new fan clutch - overheats at idle?
Jorgie works for me
![]() So I just got wrapped up rebuilding the carb (I have a separate thread going on that issue), which has improved a few things I was seeing, but: 1. Thermac (I would assume) refers to the thermal air control valve in the air cleaner. 2. TCS clean air tube I'm clueless on, but my carb does not have that port so no worries! 3. I swapped the distributor, Thermac and charcoal lines around so it's now using ported vacuum to the distributor. I just took it out for a quick test drive, and seat of the pants tells me it's happier this way. I've no other way to quantify that. But improvement is good no matter how I came by it!
__________________
CURRENT '50 GMC 100 shortbed Gen IV 4.8 LS - 4L65E (Secret truck, Shhh!!!) Build '63 Buick Wildcat Coupe 401ci Nailhead (Very much in pieces) Photos '66 Impala SS convertible 327-QJet-glide (4 speed swap one of these days...) Photos '69 CST/10 4x4 SWB Stepper 350 2bbl - NV4500/NP241C (Broken Truck!) '72 Sierra Grande 2WD LWB fleetside 350-TH350 Refresh '99 K2500 Silverado RCLB 5.7 Vortec - NV4500/NP241C (Daily) '99 K2500 Suburban 7.4 Vortec - NV4500/NP246 (still working out the bugs) SOLD '71 Custom/10 2WD LWB fleetside - '72 GMC K/3500 Dually (Sold to redryder) |
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#44 | |
Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
Posts: 1,642
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Re: Brand new fan clutch - overheats at idle?
Quote:
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#45 | |
Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
Posts: 1,642
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Re: Brand new fan clutch - overheats at idle?
Quote:
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