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Old 01-20-2012, 05:33 PM
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Is this SBC 350 set-up right?

I recently purchased this rebuilt SBC 350 engine and was wondering if it was set-up right. According to cast number 3970014 this is a 69-77 2 bolt main. I was told when I purchased it that the rotating assembly was balanced. It is Bored .030 over, has Competition roller tip rockers and push rods. Has a Crane 294 hydraulic cam, lobe separation 106, gross lift 502, rpm range 3200-6600. Double roller chain. Weiand action plus intake, rebuilt 600 Holly vacuum secondary carb. The heads are stamped 3927186 which are 1970 and the double hump camel which is also stamped on the heads. They are 64cc chamber with screw in studs, double springs, and have been upgraded to 2.055 intake valves. Stock Hei ignition. Engine runs strong and sounds great. It has great oil pressure 60 psi cold and 40 when hot at idle, which is about 1000 rpm. This is the main problem it will not idle well under 1000 rpm it is like the engine wants to stall. Maybe it has too much cam or not enough carb??? Any ideas would be greatly appreciated. Jeff
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Old 01-20-2012, 06:48 PM
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That cam needs around a 4000 stall. I'm not sure if your running it on the street or not but it's way too much cam for a street machine. Going by its specs it's likely to get it to idle correctly you'll have to drill the butterflies of the carb. But I will ask what is the base spark timing set at?
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Old 01-21-2012, 05:05 AM
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Lock out the distributor mechanical advance curve.
Set the locked timing at 36deg BTDC.

Carb power valve 3.5 or 4.5"
Carb jetting 66-68 pri 73-77 sec

Get a 10" 3500+ stall converter and 4.10+ gears.

Now it will idle clean in gear and go like hell.

Do not drill the carb throttles.
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Old 01-21-2012, 08:34 AM
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Quote:
Originally Posted by hammer-time
I recently purchased this rebuilt SBC 350 engine and was wondering if it was set-up right. According to cast number 3970014 this is a 69-77 2 bolt main. I was told when I purchased it that the rotating assembly was balanced. It is Bored .030 over, has Competition roller tip rockers and push rods. Has a Crane 294 hydraulic cam, lobe separation 106, gross lift 502, rpm range 3200-6600. Double roller chain. Weiand action plus intake, rebuilt 600 Holly vacuum secondary carb. The heads are stamped 3927186 which are 1970 and the double hump camel which is also stamped on the heads. They are 64cc chamber with screw in studs, double springs, and have been upgraded to 2.055 intake valves. Stock Hei ignition. Engine runs strong and sounds great. It has great oil pressure 60 psi cold and 40 when hot at idle, which is about 1000 rpm. This is the main problem it will not idle well under 1000 rpm it is like the engine wants to stall. Maybe it has too much cam or not enough carb??? Any ideas would be greatly appreciated. Jeff
Your problem is a common one w/cams having a relatively high duration @ 0.050" lift- in your case 238 degrees- AND using a stock HEI distributor.

The cure is in the distributor for the most part. Start by adding enough initial advance to allow the primary throttle blades to be closed enough to keep the engine from drawing too much idle fuel from the transition slot. That will give you a lower idle, cleaner exhaust (no more eye watering exhaust) and will hopefully give control of the idle mixture back to the idle mixture screws.

This means starting out w/about 18 degrees of initial timing and modifying the distributor to limit the mechanical advance supplied by the weights and springs inside the distributor to 18-20 degrees. This will have the total timing at 36-38 degrees total, about right for those heads. This is a starting point. You may need to add initial and remove mechanical advance (to keep the total to 36-38 degrees) until you get it perfect. Depending on the vehicle and how you use it, the gas quality, etc. you will want to have all the timing in by no later than 3000 RPM, sooner if you can providing there's NO detonation under load!

You didn't mention CR but that cam is going to want at least 10.5:1 and a tight quench/squish distance for the best results. The carb is definitely on the small side for this combo, and I'd expect the idle circuitry to be inadequate as delivered.

This engine will want a lot of gear especially if in a heavy vehicle, stall (if AT) needs to be at least 3500 RPM. Power brakes are going to be a problem most likely, due to the relatively low vacuum this cam will make, and it'll be a gas hog. Stay w/a dual plane high rise intake and be sure to give it all the initial timing it wants to get the idle under control.

If you choose to use a vacuum advance, it'll need to be an adjustable unit supplying about 10 degrees added timing under light throttle cruise conditions and in this case you should try to run it off ported vacuum unless the vehicle is light, has a lot of gear and you have a loose torque converter. Only then should you consider using manifold vacuum.

Grind #H-238/3347-6; P/N 110651
Power range- 3200-6600 RPM
Duration @ 0.050" in/ex- 238/238 degrees
Advertised duration in/ex- 294/294 degrees
LSA- 106 degrees
Lift in/ex- .502"/.502"
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Old 01-21-2012, 03:40 PM
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That holley carb will not have enough of a idle circuit for that big of a cam. You can still use that carb but you will need to be able to change the idle feed restrictions and the best way to do that without buying a new carb is getting the standard quick fuel billet metering block part 34-8 for the primary side and the billet metering plate part 34-2 for the rear which excepts jets on it or the secondary billet metering block part 34-66 for the secondary side.

They both have the options to change out the idle feed restriction bleeds for the idle feed circuit with out having to drill holes and such. It will also allow you to tune your carb way more then you can with the standard holley metering block and the plate that is in the rear already. It will cost less then a hundred to get both of those.

I once had a milder 222-230@50 hydraulic roller cam with a holley 600 carb like yours and it took a little time to get it to tune well with even that smaller size and with your cam it will take a lot more. That's the thing with big cams you will have to really fine tune your carburetor for the idle wise side of things if its not normal for a particular application.

Also as stated above you will have to get your timing all setup as well as a stall. I have very similar problems like you did before and it turned out I did not have enough stall and going to a smaller cam better matched with my setup really made a difference.

Get a bigger stall and get your timing all fixed first before you really mess with fine tuning your carb as that will make a difference with the above suggestions.
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