Carb Guru Opinions Requested
* Planned engine combo: 408cid, 10:1 compression ratio, EQ Magnum heads with 62cc chamber and 2.02"-dia. intake valves, cam specs 230 in./234 ex. @ .050 w/108 centerline .501 in. lift/.513 ex. lift, Edelbrock RPM Airgap intake, TTI 1.625"x1.75"x3.0" step headers, 3.0" exhaust to the rear bumper
* Trans: 200-4R, manual-shift reverse pattern w/2800 stall lock-up converter, 2.74/1.57/1.00/0.67 spread
* Rear: 8.75 Sure Grip w/4.30:1 gears (2.88:1 gearing equivalent when in OD)
Since we are waiting for the stroker guys to chime in, here's some food for thought
I know it may not count for much, on account of it pertains to a smaller engine , but........
but I run a similar combo in a 367; a lil more compression(10.9) and a lil more lift(549/571), but on a 110. And similar gear ratios with 3.55s,allbeit with a manual trans (3.09-1.92-1.40-1.00-.78od), and with a FinalDrive of 2.77
>What I can tell you is in my combo, fuel economy does not exist. I have run it with 3 different intakes and 4 different carbs,all with similar results. So you might as well strap on the 850 annular discharge carb. I also ran it with a 292/108 Mopar cam, and a 223/230/110 Hughes, and currently with a Hughes 230/237/110.
>So I think I know why this 230/237/110 cam of mine sucks gas, and why yours will be worse. The answer is IMO, in the power extraction duration. For this cam the duration events are;
intake 276, exhaust 286, compression 116,
extraction is 103, with overlap of 61, and compression plus extraction =
219.
By my cruise rpm of 65=2236, the vacuum has just peaked so overlap is not hurting me yet. But check out the meager extraction degrees of 103. When that exhaust comes out the dual 3" turndowns, there is still a lot of energy left in it. Energy that could have been used to propel the vehicle. Since it wasn't used, my theory is that I have to drive a wee bit deeper into the throttle to maintain cruising speed.
>And I'll tell you how I came to that theory; the previous cam from the same manufacturer was a 223/230/110 cam with advertised of 270/276/110. The duration events were;
intake 270,exhaust 276,compression 116,
extraction 111, with overlap of 53, and compression plus extraction of
227*.
>Ok notice the difference in extraction is 8 measly degrees.
With the rest of the engine being exactly the same including the 750DP carb (with slightly leaner MJs of course), this combo made amazing fuel economy; even better with a purpose built 600VS
>If you have a Magnum roller of 230/234/108, then your mileage will be worse for several reasons; starting with the 4inch stroke,the 10/1Scr, and ending with even more meager extraction.
>If you have an LA FTH, it won't be quite as bad because they have faster ramps out of the gate, leaving a larger compression plus extraction total degrees.
You know what the extraction is for an old 318LA? answer 120*
>Some guys might blame the poor fuel economy on the overlap. And typically I would agree........ if you didn't have the overdrive. Cruising with 4.30 might get you 65@~3500 and at that rpm the headers could be yanking a lot intake charge right across the piston and out the still open exhaust; that is what headers do. But at 65=2330, reversion in the intake has barely stopped and the header is not yet yanking, IMO. So, I am reluctant to blame the poor economy on the overlap.
>So workout your compression and extraction degrees and see where your specs compare. If you need help just ask.
