Gert Frost

Hello edinmass, I managed to send you a pm.. regards Gert

I still have the Carter 3873s I bought from you - but I dont know if it is easy to use this - as I have ethe cast iron manifold for the 340hp on my 409.

hello edinmass, I would very much take your offer to try to get help from your contact, but I was not able to send you a pm - I have not yet posted enough items to be able to send you a message. Would you be able to send a message to me, please?

Thanks Frank, I have tried with some contact cleaner I had, but maybe it does not “vapourize” enough - I had a har time determine, where it came out. When I tried to block the hole and block the two inlet holes in the secondary channel, and then blew compressed air into the screw-hole, I did not feel any air in the primary channel, but some air in the secondary channel - but I suspect that I did not block the inlet completely. I like your idea to determine air flow, but in practice I find it a bit challenging - I may have to try 3 or 4 strategies before I get it right. 😊

Thanks Jon 👍, I have bought it as a “Rochester 4GC Low Silhouette”, part number 7025124 - but there was no tag on it. I hoped, that as long it was a “Low Silhouette”-4GC, it would be the correct one. Do you know what gasket would be the correct one for the adjustable air bleed system version?

Yes, I'm aware of that - but then the air has to flow to the primary channel - as depicted in the figure with red - and this is the problem.. I can not see how the air flows from the vents you point to, and to the primary channel. It seems, that the only "exit" for the air is the hole underneath the throttle body, and this hole is blocked by the gasket. I CAN see, that the air adjustment screw can modify how much of the air that flows past the adjustment screw, ie. out through the hole, if there had been access.

Hello Joe, and thanks for your reply! I'm not convinced that you are right - this is a picture of the upper side of the throttle body, I have put a red circle around the air-inlet from the secondary valves. This would be where the gasket you have put in my picture lies. this is same picture, but with the gasket mounted.. I can not see any other way for the air to flow other than through the hole, that comes out underneath. I'm trying to follow the advice from Frank below, and try to block the holes and put air/solvent through the air idle screw hole, to see if I can determine where the air-flow should go to reach beneath the primary valves as depicted in the manual - but it a bit difficult - if only I had some smoke to send through, that would have been easier to follow. Anyway, when I blow air from my compressor and block the hole described above and the holes in the picture in this post, I would expect to "feel" air somewhere in the primary part - but that is not obvious to me, I think.

Dear all, I have have been struggling with getting the Rochester 4GC Low Silhouette to idle properly on my 1965 Impala 409cui. I have found the "Delco Rochester 4GC Service Manual", and I can see in this, that the carburetor I got has the "Idle Air By-Pass System", that allows for setting the idle RPM from the "Adjustable Air Screw" on the back-left side of the carburetor : This would allow for air to flow around the closed throttle valves : I can see that I have this adjustment screw : but when I look underneath, I cannot see how the air should flow from the air-channel into the space under the closed throttle valves: I have out a red circle around the hole where the air should come through, but as you can see, there is no "path" for the air to get to the primary part of the carburetor. As a matter of fact, as far as I can see, the hole is being blocked by the gasket: as there is no path for the air from the hole, either in the gasket nor in the bottom part of the carburetor. Has the bottom part been "machined" so the air-flow-path has been cut away, or can anyone help me understand what is going on here? Would there be anyone out there who could provide a picture of how the bottom cast-iron-part of the carburetor that mounts onto the manifold looks like originally? Thanks in advance! kind regards Gert

Hello Mark, Thanks for your question - the answer is - "it's complicated".. or maybe not really. My car is a 1965 Impala SS. It was born a 6 cylinder with powerglide, but somewhere along the way someone has put a 340hp 409cui in it, and fitted with an Edelbrock carburetor, HEI distributor, and a TH700R4. I order to get the car approved "by the book" in Denmark, I have to configure the engine in such a way, that it resembles something that Chevrolet has described in its documentation. The straight forward method is to get a Rochester 4GC low silhouette, that fits my engine and manifold - but it is rare. I'm in the process of trying to find this, this would make my car a bit more "original" - even though it really is'nt anyway (original, that is). Another way is to get a Carter 3783s, which in Chevrolet papers replaces the 3499, which in turn is clearly documented by Chevrolet for the 409. The amount of HP is not important in this approval-process. The Carter is easier to find, but then I learned that it needed another manifold - I'm new to Chevrolet, so my knowledge builds for every obstacle I encounter.. 🙂 When I found what type of manifold, I learned that the cylinder head is also different. I guess that the manifold is within reach, but I doubt that I will replace the cylinder heads any time soon, so I now wonder if the Carter 3783s with the appropriate manifold will be able to run on my 340hp engine and 340hp cylinder heads. I can see that the intake valve is smaller (2.06) on my as opposed to the 400hp (2.19). I just need the car to run and respect the emission- and noise-limits in order to get approved. Once approved, I have all the time in the world to get it to run properly in the configuration I want. I hope this answers your question. kind regards

Hello Jon, that makes a lot of sense - I believe you’re completely right.. 👍 Does the Carter 3783s have this vacuum-port?

Hello, can anyone clarify if there is any problem with using either of the manifolds 3814678 or 3844463 with the Carter AFB? 348-409.com writes this, but I’m unsure how to interpret it: ”Intake# 3844463 Carb used: 4 bbl Carter AFB Year used: 1965 Model: Passenger car Engine: 409 Horsepower: 400 Notes: This intake was used on all early 1963 400hp engines with the power brake option only. All early non power brake cars recieved #3814678 intake. Im mid year of '63, production swithched over and used this intake for all 400hp 409 application up to the end in 1965. ” thanks

Hello, I’m searching for a good condition Intake Manifold part number 3844463 for 400hp 409cui engine. thanks

Hello, I have a 1965 Impala with a 409 engine with TH700R4, an Edelbrock 1406 3110 carburetor and HEI distributor. I had it dyno’ed, and the result was an estimated 207 hp at the crank (corrected for loss in driveline). As it is rated at 340 (I’m aware that the 340 and tje 207 is not “completely” comparable), I tried to measure the cylinder pressure - it came out consistently with 125psi/9bar on all cylinders. I have no knowledge of the internals of the Edelbrock - but does anyone in here have a possible explanation for the missing power?

Hello, I'm searching for a Rochester 4GC "Low Silhouette" for P/G-option, with GM partnumber 7025124 in good condition for my 1965 Impala with 409 cui. Can anyone help? kind regards