tuning a 396 BB
11-22-2007, 08:37 AM
#1
tuning a 396 BB I just bought a 64 NOva with a 10 pt cage,396(.030 over 402) with a th350 and 4800 stall. This car is super lite with fiberglass front cap, doors, trunk lid with lexxan windows .
The engine is supposed to be 11/1 compression with stock 69 model heads that are ported. The guy was running C12 race fuel and the motor has a stumble just above 2500 rpms . I changed the squirters around on the carb as it had 32 front and 28 rear. that helped alot but when the back starts to come in it gets a stumble. I plan to put a 28 in the back as well and then look at timing.
I have been racing my trans am so long that I have got out of the tuning side of carb cars. What is a good base line timing fully advanced to start with ? I will be going to av gas as it is cheaper and local. the engine should work better with the less octane too.
THE carb is a 780 Holley . The cam is a solid lift and all he new was .551 lift. I dont know what to set valve lash at or anything. what is a good all around figure to start with on that? .020 seem safe?
The engine is supposed to be 11/1 compression with stock 69 model heads that are ported. The guy was running C12 race fuel and the motor has a stumble just above 2500 rpms . I changed the squirters around on the carb as it had 32 front and 28 rear. that helped alot but when the back starts to come in it gets a stumble. I plan to put a 28 in the back as well and then look at timing.
I have been racing my trans am so long that I have got out of the tuning side of carb cars. What is a good base line timing fully advanced to start with ? I will be going to av gas as it is cheaper and local. the engine should work better with the less octane too.
THE carb is a 780 Holley . The cam is a solid lift and all he new was .551 lift. I dont know what to set valve lash at or anything. what is a good all around figure to start with on that? .020 seem safe?
11-22-2007, 10:20 AM
#2
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Is it a solid roller or is it a solid flat-tappet? The only true value for lash is what comes from the manufacturer. Do you know who made the cam? Because they could help find out the exact cam. If not, I would start around .030 and work tighter from there. I'd rather have it to loose to start with and have to adjust a few more times. Check the lash now and see what it is, and work from there.
When you say the motor has a stumble, does it stumble and then turn on and go? It's possible the cam is just not happy down low. When I punch my solid rollered 468 below about 2500 rpm, it stumbles and then takes off. It's all in the power zone of the cam. Does it bog, like it's getting to much fuel or just stumble a bit?
Another few stupid things that have helped me with stumbles in the past are: Check the airfilter. A dirty/clogged one caused a bog on my old 454. Also, have you pulled any of the plugs? How do they look? They may need replacing, and when the extra fuel of the secondaries come in they aren't firing 100%.
Chris
When you say the motor has a stumble, does it stumble and then turn on and go? It's possible the cam is just not happy down low. When I punch my solid rollered 468 below about 2500 rpm, it stumbles and then takes off. It's all in the power zone of the cam. Does it bog, like it's getting to much fuel or just stumble a bit?
Another few stupid things that have helped me with stumbles in the past are: Check the airfilter. A dirty/clogged one caused a bog on my old 454. Also, have you pulled any of the plugs? How do they look? They may need replacing, and when the extra fuel of the secondaries come in they aren't firing 100%.
Chris
11-23-2007, 07:23 AM
#3
its supposed to be a solid flat tappet. I am going to pull the intake due to a oil leak on the back of it . Then I will check to see for sure as it is a very quiet valve train right now. I dont want to try to lash them to find out it is a hydraulic cam.
I just want to base line tune the car before I go to the track with it as the guy I bought it from put this motor in to a rolling chasis that he bought. I bought the whole thing from him with a trailer for a deal that I could not pass up even with out a motor or trans.
I am going to go into the carb to make sure it is in good working shape and then put it back on . I did find yesterday that the squirter that I put in the front is bad. It just dumps fuel in when you give it gas. I am going to replace it and then check to see what jets are in it.
It must be on the fat side as you dont even have to give it gas to crank on a cold morning with out a choke. it cranks up pretty easy.
Once I get all the stumble issues fixxed , I am going to put a bung in the exhaust and fine tune it on the wide band.
This is going to be different coming from my ls1 tuning by sitting in the car
I just want to base line tune the car before I go to the track with it as the guy I bought it from put this motor in to a rolling chasis that he bought. I bought the whole thing from him with a trailer for a deal that I could not pass up even with out a motor or trans.
I am going to go into the carb to make sure it is in good working shape and then put it back on . I did find yesterday that the squirter that I put in the front is bad. It just dumps fuel in when you give it gas. I am going to replace it and then check to see what jets are in it.
It must be on the fat side as you dont even have to give it gas to crank on a cold morning with out a choke. it cranks up pretty easy.
Once I get all the stumble issues fixxed , I am going to put a bung in the exhaust and fine tune it on the wide band.
This is going to be different coming from my ls1 tuning by sitting in the car
11-27-2007, 09:50 AM
#4
Soaking carburator in b12 , it was awfull looking from old fuel sitting in it. any one know about what rpm the old 396 engines liked to be run to? the guy said it easily turned 7200 but I find that hard to believe as heavy as parts are in the big blocks. I doubt its got light weight parts in it .
