Can someone help me identify what the item I have circled in red below is on this Quadrajet Intake Manifold? Is it a choke of some kind? I am pretty sure when my dad and I have this engine in my first car, the item was never really hooked up to anything and I now want to know if I need to even have it on the intake manifold and/or if I need to buy a new one since this one has seen better days.



Thanks,
Jason

 

That is called a divorced heat choke spring. Typically used on Holley and Quadrajet carbs. Replacements available from many places. Bob

 

Thanks so much.

JP

 

Just so I understand fully. I imagine that this choke would have to attach to the carb somehow.

Correct?

 

There's a rod that goes from the spring to the carb and a stamped steel cover that goes over the spring. The rods are unique to just about every application and year. Divorced chokes were used on Corvettes from 66-74. From the spreadbore design of your intake manifold and the look of the choke, I think it's a 70-74 350 intake, so the rod the choke would use is likely the following one.

https://www.corvettecentral.com/c3-6...d%26count%3d18

This is the cover for the 70-74 divorced choke.

https://www.corvettecentral.com/c3-6...r%26count%3d27

 

If you plan to use that intake manifold, consider blocking the two ports that allow exhaust gas under the carb base. I used Dorman freeze plugs and a little epoxy to seal it up. I think the plugs were 3/8". There is also a set of three gaskets, one of which is made of aluminum that goes between the carb and the manifold. Good luck. Jerry

 

Thanks. I was just reading about divorced heat choke springs and I read where it said to make sure you do not block off the two ports that allow exhaust gas under the carb base as those gases are used to heat up the divorced heat choke spring.

I am also trying to decide if I want to use this Quadrajet intake and Holley carb on my 58 Corvette and the 66 327 engine I have going into it. I would appreciate people's feedback. I have 2 Holley carbs that I could put on this engine; Holley 6210 Quadrajet (650 CFM) and a Holley 3310C Classic Carb (750 CFM). I am leaning towards using the Holley 3310C and that would require a new intake manifold.

Anyone have any thoughts or what would you do? I would also love to have any recommendations for an intake manifold to use with the Holley 3310C Classic Carb.

I looked up the Holley 6210 Quadrajet car and Holley discontinued it, so my thinking is it may be better to go with a carb that is not discontinued.

I appreciate everyone's opinion and suggestions,.

Thanks,
Jason

 

I am also going to go into my garage attic and my dad's old storage shed to see what other intake manifolds he had. I am 99% sure he didn't have the original motor for the 58 Corvette.

 

The intake and carburetor must match for the best performance. They did make an adapter to bolt a Holley to the spread bore Quadrajet intake, but the performance was horrible due to the flow.
The older 4 bbl intakes were for the early carters with the smaller throttle bores. If you use a modern 600 cfm Holley or Edelbrock AFB on them, you need a 1/2 inch spacer to make them work. Thus, your best match for the Holley is a post 65 GM intake or an aftermarket intake. However, they still used a Rochester with a different bore and spacing after 65. Just be sure to measure the throttle bore and bolt spacing of the carburetor you want to use and compare it to the specifications of the intake.

 

My Chevelle has a divorced choke like this. It works fine.

The hot gas passge under the carb was also intended to warm up the carb, not just operate the choke, quickly., But you have to consider that modern fuels are different. We have many more complaints here these days about fuel percolation from a too hot carb than we do about slow warm up. Given that you are in Texas, it's likely the benefits of blocking the exhaust crossover passage will outweigh any downsides. You can always adjust the choke, too.

 

There is a very important distinction between the exhaust crossover passage (which is important for proper operation of the divorced choke) and the "hot slot" that runs under the primary bowl of the carb.

The crossover path through the intake manifold is placed under the carburetor and works in conjunction with the heat riser valve attached to the passenger side exhaust manifold. The entry and exit ports for the crossover path are in the heads. This passage is intended to warm the carburetor on cold starts. The crossover passage was a feature of all carbureted Corvette engines. To operate the divorced choke, the crossover passage is very important.

The "hot slot" under the primary of the carb was a short-lived experiment that failed, according to John Hinckley (RIP). John said the hot slot was an attempt to provide additional heat to the carb for cold starts, beyond the heat provided by the traditional crossover passage. The hot slot caused numerous carburetor fires and was discontinued after just a few years. John recommended blocking the hot slot for all cars that had it. Blocking the hot slot has no effect on the operation of the traditional crossover path and the traditional divorced choke.

With today's gas that has a lower boiling point than gas from the 1960s, it is even more important to block the hot slot to prevent percolation when the hot engine is shut down, which can lead to vapor lock when re-starting the engine is attempted. Attached is a photo of how I blocked the hot slot on my '67:

 

These cars were daily drivers in all 50 states, driven year round. Thus, the heat riser valve and the heat passages under the divorced choke and heat for the carburetor made the engine drivable in freezing weather. Most owners of these cars today no longer drive them in freezing weather or even weather below 50 degrees F. I wired the heat riser open, plugged the passages under the carburetor and blocked the heat passages on both heads on R66 with the stock 3367 Holley. The choke still operates as designed, but may open just a bit slower. That is not a problem as the choke pull-off opens the choke.
Any racer will tell you the engine produces more power when the air and fuel charge are cool.
As far as Holley or Quadrajet, that is a personal preference and I don't offer an opinion. If you are just cruising on the street, either a stock cast iron or aftermarket duel plane intake will work just fine in most cases. Some aftermarket intakes are designed to perform at or above the normal range of an engine driven on the street - about 2,500 rpm. I don't recommend a single plane intake for street use, although I have used them for street / strip cars.
For the what it is worth - maybe $.02 which today is nothing.
Ron

 

Thanks everyone for the info. That is a lot of info to take in lol.

 

You can get a block off plate.

https://www.summitracing.com/parts/e...hoC2ucQAvD_BwE

 

I'm not sure what that Edelbrock part accomplishes, but I think it only fits certain Edelbrock intakes.

The part that the OP circled in the post #1 photo is the thermostatic spring for a "divorced choke" that operates the choke. It is heated by a passage (not visible in the photo) on the underside of the intake that connects to two ports in the heads. Exhaust gasses flow through this passage from the passenger side to the driver side, deep under the carb, to warm the carb and help with cold weather operation. This system was used for many years and it works fine, but the choke plate on the carburetor requires some linkage to connect to the thermostatic spring. An alternate solution is to use a carb that has an electric choke.

The "hot-slot" that is visible in the post #1 photo is not the passage described above. The hot-slot was a short-lived GM experiment to provide additional carb warming in conjunction with the existing the passage that runs deep under the carb. Reportedly the hot-slot caused several carb fires and was discontinued.

The main point that I'm trying to get across is that the passage (not visible in the photo) that runs directly under the thermostatic spring and the carb works fine and helps the choke respond faster to warm up from a cold start. The hot-slot is a completely separate passage that turned out to be a bad idea. Blocking the hot slot has no effect on the main passage that runs under the thermostatic spring and the center of the carb. It is common practice these days to plug the hot slot.

If desired, I can take some photos that show the main exhaust crossover passage that is not visible in the post #1 photo.

 

If he does not need to use it. I plugged it off one for my son's corvette. Also, plugged the water port in the middle too since not needed.

 

So the hot slots that we are talking about are what I have circled in the below photo, correct? And I am thinking if I need to plug those, I would have to run a tap through them to make threads and if I did that I would have to remove the manifold to make sure no metal shavings got into the engine.




One other question about my intake manifold. I am assuming the item that I have circled in the picture was used to pug items in to access the engine's vacuum. Does that sound correct? So if I don't have anything to plug into it, I could just plug that hole.

 

You can instal a plug in the H/S holes similar to a freeze plug but sized correctly .
The vacuum fitting can be replaced with the correct sized threaded plug .
Are you trying to build a correct engine for your car ?
Is it the original engine ?

 

for the hot slot holes I don't understand why people want to plug them but if you do use freeze style plugs that are interference fit, if you don't have power brakes, AC, auto trans, K19 then a standard NPT pipe plug is all you need

 

Engine is not original to the car. Car is a 58 Corvette and I think the 327 engine was out of a late 60's Corvette maybe. Not trying to build a correct engine for the car.