396/375 holley 4053 jetting

[Rick68]

Would you use the same 72/76 jetting on a 396/375 as the 302?

[ko-lek-tor]

My book says, #70 & #76, prim. & sec. respectively, regardless if Man or Auto. trans. A lot of variables with today's fuels, altitude, moisture in the air, etc...One usually has to go 3 sizes at a time in jetting to see measurable differences, so if that is the jetting you have, try it out first before changing out the jets.

[X33RS]

The factory jetting for the 302 is 68/76.  However they do respond to 72's in the front.  If you want to get fancy move the driver side up to 74/78, it's worth a few ponies on the dyno.

This is all considering sea level conditions like Kolektor mentioned.    I believe Kolektor is right on the L78's,  70's in the front are stock.  They also respond to stagger jetting.

Do you have a wideband?    We have drastic elevation changes around here so I find it to be an excellent tuning tool.

[cook_dw]

FYI the 4053 & 4346 used the same jetting regardless if it was on an L78 or Z..  If it required different jetting then it would have had a different part number.  The 3910 since there was no mandated smog requirements used a slightly fatter primary jet.  So to answer the OP.  It really depends on your setup, elevation etc as to what jets, power valve, squirter and sec diaphragm spring you need to run..   

[Rick68]

My 396 is basically stock with a slightly lumpier cam.I am still running exhaust manifolds and a factory style  exhaust system

[cook_dw]

Then do as ko-lek-tor advised and start with what you have and start tuning or you can just leave it with those jets and live with whatever the outcome is.  More than likely itll be fine if you are just gonna cruise around in it or on and off a trailer..  FYI there is no magical answer to your question.  If you are wanting performance or economy then tuning is the only way.  If you are wanting it to start and run so you can drive it around then just stick with either the stock setup of the carb or something close.

[Steve Shauger]

The L78 I just got back is basically stock with manifolds and transverse exhaust. I'm not sure what cam so it's somewhat of a mystery motor. The car has original carb 4346 and it had a flat spot as I accelerated. This seemed odd because when I sold the car it ran fine (12 years ago). I changed the power valve in case it wasn't opening, but no change. The car felt lean so I changed the primary jets from 68's to 72's and she runs perfect now.

[Rick68]

Steve , I just seen your old triple black COPO up here in Canada at the Ontario Camaro Nationals in Oakville Ontario.I cannot remember the gentlemanwho bought it but he has quite the collection.He said he had 5 COPOS,a ZL-1 and a Yenko.

[cook_dw]

http://www.hotrod.com/how-to/engine/ccrp-0807-holley-carburetors-basics-guide/

[Steve Shauger]

Steve , I just seen your old triple black COPO up here in Canada at the Ontario Camaro Nationals in Oakville Ontario.I cannot remember the gentlemanwho bought it but he has quite the collection.He said he had 5 COPOS,a ZL-1 and a Yenko.

Yes, Tim S. has quite a collection which includes three RS COPO's, RAIV 69 TA & GTO Judge, ZL1, L89 Corvette and a half dozen other cars. In 8 years it had only been driven 3.8 miles. The first day he got it he put 60 miles on it. I'm still keeping a few concours cars but I rather have just drivers and survivors.

[Steve Shauger]

http://www.hotrod.com/how-to/engine/ccrp-0807-holley-carburetors-basics-guide/

Thanks Darrell. The last point was helpful regarding the Idle Transfer Slot and throttle position. I knew the trick of drilling a hole in the throttle plate but never knew the reason was the throttle plate position to the idle transfer slot. I just thought the whole provided more air to lean out the idle mixture. I knew the trick worked, but not the dynamics behind it.

[cook_dw]

Also another tip is if you are running a certain style setup that requires more of the throttle blades to be open in order to idle but you get past the point of the idle circuit (too much of the transition slot exposed) and into the primary circuit where is starts to pull fuel through the booster and venturi then back the idle adjustment screw back down and on the pass side of the carb you will notice a bracket on the secondary shaft that rests on the base plate.  Using feeler gauges; put them between the base plate and secondary throttle shaft bracket and slowly rise your idle this way.  Once you are happy with that setting you can pull the carb off and flip it upside down and you will see a flat head screw on the underside of the base plate that you can adjust the secondary blades to that same thickness as your feeler gauges.  Im sure many already know this trick but it seemed to be a pretty common problem for novice carb tuners when I worked there..


This photo is especially helpful for most visual people to understand how the fuel is introduced and how it is suppose to work.






Here is another article on how the circuits of the carb work.

http://www.superchevy.com/how-to/83118-carburetor-basics/

[L78 steve]

I found 72/76 combo works best on a stock L78 or 302 with manifolds and correct exhaust.
76/76 on a cammed car with flow master and header set-up.

[jdv69z]

I found 72/76 combo works best on a stock L78 or 302 with manifolds and correct exhaust.
76/76 on a cammed car with flow master and header set-up.

Works well on my 302!

[cook_dw]

calibrated buttometers?