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Discussion Starter #1
Alright guys I need your help. I have a sbf 408 with 14-1 comp. N/A. Best of 9.92 so far. I have been running open headers and the carb is a proform 950 with 82 primary and 86 secondary jets. C12 fuel. Today I put on a dual 3" exhaust with bullet mufflers that exit in front of the rear wheels. Class I want to run requires mufflers. The car is running very lean since the exhaust was put on. Is there a general rule of thumb as to how much jetting I should add? Any input would be greatly appreciated.
 

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Discussion Starter #4
Well, took it out and it is popping under load. Made a couple changes up in jets and got a little better, but now i have them at 86/90 and still has a lean pop. I am thinking that the 3" exhaust combined with the length of pipe is too restrictive for a 14-1 motor. Motor is making right around 700 hp. What do you guys think?
 

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Well, took it out and it is popping under load. Made a couple changes up in jets and got a little better, but now i have them at 86/90 and still has a lean pop. I am thinking that the 3" exhaust combined with the length of pipe is too restrictive for a 14-1 motor. Motor is making right around 700 hp. What do you guys think?
It may have been lean to start with and you just didn't notice with open headers. I run 93s all the way around on my 950 in the summer and 94s in the spring and fall.
 

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Discussion Starter #7
You might have a point. We ended up taking the exhaust off and car runs great. Will be buying some 3.5 or 4" mufflers with turndowns this week. Thanks everyone.
 

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A restrictive exhaust will cause it to run rich, not lean. I will say a 950hp is too small for a healthy 408 inch engine with that much compression. You can also tell by the amount of jet it starts needing to run the number..A larger carb wil flow more fuel, not needing as much jet. Even our street 408's with 11.1 use a 1,000 hp when a 4150 is used. If you slow up that much with an exhaust, then the exhaust is too restrictive. It may have just been too lean to start like previously mentioned.
 

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Discussion Starter #9
Well, I am running a 408 with AFR 205's that flow 345/250. Engine is 14 to 1 comp. Camshaft is .673 lift solid roller. Super victor with 950 Proform carb. I went a 9.92 @ 135 last week in my 88 coupe that weighs 2850 with me in it. Do you guys think that I need a bigger carb. Thanks again for all the help.
 

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Discussion Starter #11
I am going to see if any of my buddies have a larger carb that I could try. Do you guys think that a 950 might be a little small for the engine? I have noticed that the car seems to stop pulling at about the 1000 ft. mark. I was thinking that the 4.56 gears might be a little too steep and the engine is running out of rpm's. This is a new combination so I guess this is part of the game!
 

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Similar car to yours local. Same cubes, heads, less comp., not sure on cam. He runs a ProSystem 1000HP and 4.10 gear with a C4 and 28.5x10.5 tire. It typically runs 6.teens in the 1/8th.
 

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Discussion Starter #15
Made a few calls and have decided to try a 1050 from a buddies car. Not quite sure if we will get out this weekend, but I will keep you guys posted as to what happens. I really appreciate all the help.
 

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My freinds PUMP GAS 410 in a 3100lb car goes 9.70's in decent weather, R head, c-4, 4.10 gear, demon 950, goes 60's in mineshaft conditions. Goes through the traps around 7200
 

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Discussion Starter #17
I am thinking that with a bigger carb and rear gear change, this car should run alot better. been 9.92 @ 135 all motor so far and running out of rpm at about 1000 ft.
 
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