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Discussion Starter #1
I use a Speedtech 2stage diffuser plate on my SBF and run it by the book but my tune up is a fat. My car seems to run the number but been told i'm leaving alot on the table. Been told to spread the jets for cleaner tune up and better et. I need some advice on this, i'm kind of new to the tuning game, lol. I'm running a 418SBF, Yates C3 heads(flows about 400cfm and been soften), Cam Motion camshaft(780in lift, 114 lobe sep., 1050 dominator carb, 13.5:1 comp., Autolite 3933 but changing to 3932 or NGK 10, C16 fuel, and i run it on 36 degrees total timing
 

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A C3 head on 36 degrees timing? How much spray and how much timing are you pulling?


What is the N/F jetting you have now and at what flowing fuel pressure?


A little more info will help a lot.
 

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pig hunter
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36 on a c3 headed small ford running n.o.s. did you close you eye when you did this??
 

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Well guys to be truthful, i didn't know, i went strictly by what my mechanic suggested. This is a new combo and a huge learning curve for me, so this is why i post so many questions. So if 36 drgrees is to much, what would be a good mark to start at. Z289sec, i run my tune up by Speedtech spec. (squared up, to the fuel pressure, and what ever timing pull it calls for
 

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36 on a c3 headed small ford running n.o.s. did you close you eye when you did this??

No I'm asking him if he is certain that is the static timing....just seems like a lot for a C3 headed motor. Even with the softened chambers.

Then I asked him how much nitrous and how much timing he was pulling off that 36 base, and with what jets and at what flowing fuel pressure. Since he did not include any of that info in his post.
 

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Well guys to be truthful, i didn't know, i went strictly by what my mechanic suggested. This is a new combo and a huge learning curve for me, so this is why i post so many questions. So if 36 drgrees is to much, what would be a good mark to start at. Z289sec, i run my tune up by Speedtech spec. (squared up, to the fuel pressure, and what ever timing pull it calls for

I don't know for sure that is too much base....just most of those combos I have seen seem to be in the 28-32 range on base timing.

If the jets are squared, you can almost surely bet it will be fat. But, you don't want to run off and make a big jet or f.p. change without knowing how much timing is being taken out. Personally, I have always started with far more timing out than what most Mfg's call for. Then, make little steps and check plugs.


See if you can come up with specifics on the jetting , fuel pressure and timing, and I'm sure you will get some answers.
 

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Discussion Starter #7
On my tune up i'm using 65/65 jets(150hp), pulling 6 degrees of timing out, at 5.5lbs of fuel pressure and on 2nd system i'm using 73/73 jets(200hp), pulling 6 degrees of timing out, at 8lbs of fuel pressure.
 

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my C3 headed sbf made the most NA power at 32 degrees on the engine dyno. I run around 16 degrees with both kits on and 24 degrees with 1 kit on.....but I currently have holes in 2 pistons so I may not be the best to get advice from :rolleyes:
 

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pig hunter
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mailman, 32 is where most c3 head are n/a. second kit is WAY TO FAT pull fuel psi down to 5.5 on it. first kit pull 6* second pull 9*-10*. to little timing is way better then to much and slowly walk up on the tune...
 

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Chupa Cabra
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You can run the first stage a little fat(not near as fat as you are now with the jets squared) and use the 2nd stage to help clean up the tune once it comes on down track. I'd be pulling at least 4-6* more total timing out than what you are running now.
 

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I use a Speedtech 2stage diffuser plate on my SBF and run it by the book but my tune up is a fat. My car seems to run the number but been told i'm leaving alot on the table. Been told to spread the jets for cleaner tune up and better et. I need some advice on this, i'm kind of new to the tuning game, lol. I'm running a 418SBF, Yates C3 heads(flows about 400cfm and been soften), Cam Motion camshaft(780in lift, 114 lobe sep., 1050 dominator carb, 13.5:1 comp., Autolite 3933 but changing to 3932 or NGK 10, C16 fuel, and i run it on 36 degrees total timing
Question(s) lol;
Is that a 4.03bore 4.1" stroke?
C3 400cfm needs at least a 2.18" valve...
If heads have been modified (soften) in the chamber and quench is also 0.070" or more then 36 degrees for a nitrous sbf is perfect with a big tuning window... When I say 36 degrees that is before nitrous...
I would tune the first kit with more timing out of it so when the 2 kit comes in you don't need to retard much timing like that the car can hook and go down track if this is a small tire car...
If you want more help you need to give more info on your set up...!
 
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