Heat Soak

[Omni]

Good Afternoon
With Carlisle 2023 in the rear view mirror, looking to improve on the drive-ability of the 'Party Barge' ('65 Newport 383).
This year I installed an AFB (3644S) that was rebuilt by Woodruff. While acceleration was better I was disappointed in the overall mileage. the 1000 mile round trip averaged 11.5. Average turnpike speed (both years) of 75 mph.
Last year with the BBD (2BBL) overall mileage was 14.1. Car is filled with 89 octane. I would rate the highway cruising as equal between the 2 and 4 BBL.
Anyway, the issue I would like to remedy is the heat soak. Anyone have thoughts on blocking the cross-over passages under the manifold? I am using the stock well-type choke so I understand that it will take longer to warm up. I am also looking at employing a phenolic type spacer (1/4") under the carb. Hood clearance would not be a problem. The only 'tweaks' I see are longer studs and a lengthening of the choke rod.
Thanks to all who respond.
Omni

 

[Fireflite56]

I agree with the two options you are looking at - Fel-Pro makes a "performance" valley pan with bock-offs for the heat crossover. My girlfriend did this on her car and it helped with hot starting. Non-ethanol gas will also make it less likely to have vapor lock issues. You also could add in the factory-style aluminum-wrapped insulation between the intake and the valley to prevent heat soak.

 

[Boydsdodge]

Are you using the thick carb base gasket now?

 

[Omni]

Good Evening
Thanks for the replies. I am using the stock insulation pad between the valley pan and the intake (although it it a little worse for wear). The carb mounting gasket now in use is a thin one.

 

[CBODY67]

I've been wondering if the under-manifold "insulator" really insulates that much as the main heat path is from the cyl heads, not ambient underhood heat. In order to get away from that insulator, it would be necessary to use the aluminum plate to cover the valley and use separate side gaskets, as one of the alleged reasons for that insulator is to dampen harmonics in the valley pan gasket to prevent it from splitting over time.

Having had out '66 Newport 383 since 7100 miles, hot restarts have always been an issue in the summer. Using the recommended 1/3-1/2 open throttle setting when starting seemed to work best for us. All with the OEM Stromberg WWC 2bbl. Even when we had "real" gas with lead.

With a 2.76 rear axle ratio, I would have suspected cruise fuel economy would have been closer to 15.5mpg (at those cruising speeds), unless you were going uphill all of the way back. Might need some stiffer springs under the power pistons to delay "power enrichment" to a lower manifold vac level. Might need to install a vac gauge to check vac levels and then check the no-load air fuel ratio of the current rod/jet combination.

I know many in here like the blocked heat to the heat crossover in the intake. That might work well in an area with moderately-cool winters and work better with an aluminum intake (which will heat sooner from the cyl head heat migrating into it), UNLESS the carb has an electric choke. Even with the stock set-up, it can be tweaked to get the choke off sooner and not significantly harm cold-start performance, from my experiences in our winters down here. Additionally, you might need to move the choke thermostat coil 1 notch leaner than the stock spec as they tend to tighten with age.

One other thing to look for on the carb are the idle air bleeds on the venturi cluster. If hard deposits have closed them down, ever slightly, that can tend to richen the mixture over the stock calibration. Cleaner soaks will not remove them, so they have to be removed mechanically with small twist drills. On the bottom side of the venturi cluster, the small tubes are the idle feed tubes. Same thing can happen there, too! Except that when in those tubes, it restricts fuel flow to the venturis and the car will not idle, no way, no how, once it comes off of fast idle. Been there, done that on a BBD.

DO use the thick carb base gasket. You can lengthen the choke rod a bit. Make sure it just closes at an ambient (engine, underhood, carb, air) temp of about 65 degrees F. Then that the choke pull-off adjustment will then pull it back open the needed amount. Also, get hard bolts or "black" carb studs of the correct length.

On the ignition, try to aim more toward a dwell of 32 rather than 30. Plug gap more toward .040" than .035". Both will "trick" the coil into building more voltage before it fires the plugs. Plugs with a cut-back ground electrode can help some too.

Many thoughts,
CBODY67

 

[Omni]

Thank you CBODY67
Opening up the carb (2BBL) will probably happen this winter. I have been in contact with Mikes Carb Parts to figure out the jets and needles for a 3850S. What I have is a Delco rebuilt. I can only guess that, as a rebuilt, is has whatever parts that fit in it. I would be ecstatic if I could get 15.5.
The spark plugs are light tan so the jetting should be right. (May not have to change the needles/jets) Will try re-gapping the plugs and playing with the dwell. Will also investigate the stiffer spring under the power piston. It is difficult to get an accurate dwell with the meter that I have as the needle tends to 'bounce' around.
Thanks again for the input.

Omni

 

[CBODY67]

Thanks for the information. If the dwell meter needle moves, then the lobes on the breaker cam probably have some wear on them (i.e., visible depressions of the peaks). Try to set the point gap with a dial indicator and you'll see it quickly as you check each lobe.

The jets and such are listed in the FSM.

The issues with heat soak have been around for at least 55 years, with no "magic bullets" revealed. Just one of the little quirks which made Chryslers Chryslers, back then. Not sure quite why GM cars are not subject to the same things, but they seem not to be. E10 gas seems to have made things worse, though.

Still, IF the carb is percolating-out fuel into the plenum, it's going to evaporate quickly, with the resultant vapor being easier to fire-off IF there is a strong enough and good enough spark, I would suspect.

Take care,
CBODY67

 

[Blusmbl]

Depending on how far you want to go with it, I have fire/insulation sleeve on my fuel line from the pump to the carb distribution block, and also have a 1" plastic open spacer between the intake and carb. Between those two, I don't get stumbles/vapor lock when idling for extended durations anymore.

E10 gas is worse than E0, it typically has a higher RVP so it boils at a lower temperature. The absolute worst time for vapor lock is with winter blend fuel on warm spring/early summer days, as the high vol winter fuel has even higher RVP than the summertime E10.

 

[Boydsdodge]

In 1976 Chrysler went with a full time fuel return line from the fuel filter, I have seen a few recent posts on Youtube on this set up to help with fuel boil.
Wix 33040 is a 5/16 filter with return line. This filter does have a reduced orifice, looks like a 3/16 return, but inside it is reduced to control flow..

More Information for WIX 33040

 

[CBODY67]

Vapor separators were used back in about 1971 on some HP B/RB engines, as I recall. An easier add-on that a retuirn-line fuel pump (as GM did). 1973 California-spec Imperials had an electric fuel pump near the tank, in addition to the normal pushrod fuel pump.

CBODY67

 

[Boydsdodge]

Vapor separators were used back in about 1971 on some HP B/RB engines, as I recall. An easier add-on that a retuirn-line fuel pump (as GM did). 1973 California-spec Imperials had an electric fuel pump near the tank, in addition to the normal pushrod fuel pump.

CBODY67

68 440 hp and Hemi had the special black can separator, this filter i posted became regular v8 part in 76 maybe 75. Just thought it may help with OPs problem.

 

[Old Boomer]

I put my fuel filter down by the fuel pump. Puts it in clean air from the fan.

 

[Toolmanmike]

Late to the party. Heat soak or vapor lock? AFB's are prone to heat soak. The fuel bowls are small and are directly over the base and close to the mounting flanges. Think about a Holley where the bowls are quite large and hang out over and away from the main body. If you have heat soak/percolation and hard starting after setting a while, many have added a small electric pump at the tank with a momentary switch to prime the system. That works great after the car sets for a week or more and the fuel evaporates from the bowls.

 

[fury fan]

Anyway, the issue I would like to remedy is the heat soak. Anyone have thoughts on blocking the cross-over passages under the manifold? I am using the stock well-type choke so I understand that it will take longer to warm up. I am also looking at employing a phenolic type spacer (1/4") under the carb. Hood clearance would not be a problem. The only 'tweaks' I see are longer studs and a lengthening of the choke rod.
Thanks to all who respond.
Omni

Blocking the crossover and using a phenolic spacer are related but different.

Blocked crossover keeps the manifold cooler and will affect operation of the OEM divorced choke. (as you mentioned)
It also reduces fuel atomizization as the air/fuel runs thru the manifold.

A phenolic spacer/insulating gasket keeps the carb cooler.
It reduces atomization as well, but it gives the biggest benefit when the engine is off, to reduce the fuel 'cooking off' while the car sits in the parking lot.
There's a thick insulating gasket you could install that @Boydsdodge mentioned. That may work better than phenolic? (I don't know how the heat transfer rates compare)

As you mentioned, you need to review the carb rods/jets first to see if correct.
Installing a thicker gasket is the next-easiest thing to do, followed by insulating sleeving on the fuel line (this helped 1 of my cars a lot), then try the return-type filter.
IF, IF, IF modern gas is sufficiently volatile that it doesn't need the manifold heat for atomization, then maybe the blocked crossover will help.
But otherwise, IMO, blocking the crossover (which holds the choke closed longer) and anything else that decreases atomization will hurt MPG.

 

[Boydsdodge]

Also giving the engine initial timing that it wants helps with running temps.

 

[Gerald Morris]

I'm running a 1966 383 in 110 F heat right now with an Edelbrock Performer 600 cfm with a 1/2" phenolic spacer (Edelbrock), an insulated steel tube fuel line with the fuel filter down low close to the pump as Mopar placed it. I time the engine at 12.5 degrees initial and have had ZERO trouble starting this engine this summer due to heat soak. The same motor burped burning gasoline from the old Stromberg WWC late last August, costing me a coil and some wiring, and I decided to upgrade heads, fuel delivery and such then.

A good phenolic spacer is a SUPERB investment.

 

[USSMOPAR]

What is the underhood temp at the base of the carb after heat soak?
What is the current operating temp?
Thermostat housing temp after heat soak?
Please stop the bs about blocking the crossover - it works! What a bunch of nonsense. Try using a wide band a-f gage instead of old wives tales
Make sure the manifold heat vales is open or better yet removed
Timing? What is the full adv with the vac advance hooked up?
Why is 89 required?
What did you do to reduce vehicle rolling resistance?

 

[CBODY67]

Where can the insulation sleeve tubes/wreap/material be purchased and at what cost?

Just curious,
CBODY67

 

[Blusmbl]

Pegasus sells it at a decent price, same with Amazon, Summit, etc.

Amazon link:
Amazon product ASIN B06WVNXY8W

 

[Gerald Morris]

Where can the insulation sleeve tubes/wreap/material be purchased and at what cost?

Just curious,
CBODY67

Amazon is good. I got this stuff:

Amazon product ASIN B079S1XLM7
I bought a jacket for my starter motor also made by the same folks. Thus far, my PowerMaster starter has done alright, though I still plan to rebuild my factory original one. My motor doesn't NEED to spin to start up. Nudge it with a live ignition and BANG!, it lights right up.