Carb recommendation

[Right hand drive]

[Tonys Toy]

Thanks for all the suggestions. Investigated them but thinking of assembling a carb with some of the metering blocks and the 850 base plate w/ 1.750" throttle plates and fuel bowls I have. Thought I would go with a Proform main body -the 750cfm to "create" a 820-830 cfm carb. Are there any issues with the Proform main bodies that a person needs to be aware of? I believe it would be necessary to open up the bottom of the venturi to match the throttle plate. Am I correct? Any casting or fitment problems? I do have an AFR gauge to help with tweaking it.
Hoping to possibly to hear from someone who may have done this conversion... maybe Mark or Tuner if he is still around.
TIA.





















proform main do

[rgalajda]

What part of the country do you live that does not require a choke for a street car?

Cam - SFT w/264*/264*@.050" & .600" lift I & E on a 108*.
Is this 108 degree Lobe Separation Angle?

[Right hand drive]

[Tonys Toy]

Yes the cam is on a 108* lobe separation angle.
Didn't realize the Proform 850 main body had the smaller venturi. Good info.
Thank you for that advice.

[Tonys Toy]

Missed the inquiry about location. Sorry. Northeast, PA is where I am. Car is used from late April/ May until late Oct / early Nov.

[rgalajda]

[1969Camaro]

The only double pumper used from the factory is the 4296 on the ZL1 and later 69 L88 vette

[Right hand drive]

I agree vacuum secondaries are overlooked a bit too often. But I also think there are two schools of thought or criteria that have to be accepted when choosing between vac sec and mech sec for a performance oriented vehicle driven by an enthusiast (most of us I dare say). There is one of of looking for what is the most ‘correct’ style to use given the application or the other school of how we want our cars to feel and drive to suit our own driving preferences and idiosyncrasies. Either camp could potentially select either carb secondary style. I am the later but can respect the former as I too have had everyday driven carbed cars that I wanted to perform their best for the intended purpose and snubbed mechanical secondaries for those cars. The way I like my performance oriented car to drive is served best by a mechanical secondary carburetor. This is mostly because I can feel when they are about to open due to slightly more resistance under the right foot. I can do all of my cruising around town and driving from town to town for car meets on the primaries only, 0 to 100km/h and only get in to the secondaries by choice. Mileage is not a factor. This would be due to torque output, gearing and car weight but it challenges the “vacuum secondaries are better on the street” argument if the driver has control of secondary engagement with the mechanical secondaries and chooses not to open them. Primaries v primaries on both styles should be identical. Personally I would find vac sec for my car and how I want to drive it boring as I like the feeling of engaging the secondaries by choice and it’s not for hooning or breaking traction that I do it. I would agree that a miss applied mechanical secondary for the street is where the engines low speed torque production is low enough that the engine demands the secondaries be opened regularly to gain or maintain speed. Let the vac sec regulate when and how much the secondaries open in that instance. But again, the enthusiast might have a penchant for opening the secondaries himself despite there being a better option. I’m not saying a vacuum secondary is wrong for Tonys Toy, it may be the more correct choice than a mech sec overall. But looking at the cam spec for his big block and the months of the year he gets out cruising as indicators as a pastime car the mechanical secondary may be considered more enjoyable for the intended purpose of Tonys Toy and how he likes to put the power down. Only he can answer that. I know of people that have automatic gearboxes with ratchet shifters and prefer to change gears manually all the time on the street. What the...? It’s an automatic, just put it in ‘D’ and the gearbox takes care of the changes for you! But that’s how they enjoy driving their carbed V8’s our cruising the streets.

[Tonys Toy]

Regarding use of a choke mechanism, typically when you start a vehicle with a choke the accelerator pedal is pumped several times providing fuel in the manifold and setting the choke. The choke then stays in various closed positions until fully warmed and open. I believe there is just as much excess fuel washing the bores. My 383 SBC starts great with no choke, pump 3 times hit the starter, fires off and I keep it at a high idle - 1500 RPM for 90 seconds. No problems.

RHD, your are spot on relative to driving style. I subscribe to having control of the secondaries - at my discretion when to tickle them.
This SS is an excellent minimal restoration car. Engine is not original but has a correct date code. My original SS was ordered in Oct. 1968 and I took delivery on Dec. 17, 1968. Original L78,M21 4 speed with posi 4.10 axle. Had a 780cfm vac secondary carb. It was driven year round so the choke was left intact. This latest SS is a fair weather toy so no choke needed for me.

Thanks for all the suggestions and comments.