If you already own the 750DP, bolt it on and don't look back! The carb will always tell you if it is too big, by the way it can't be tuned, or is hard to tune for low-speed operation
I have run that bad boy on my 367 with a 230*, a 223*, and a 249* cam. With a 3.55,a 4.88 and a 2.76 and just about everything in between but always with about a 8.5 or better DCr. I also tried an AVS, a TQ,a 600 and a 750 vacuum secondary carb. I like the 750DP best, and it's been on there now since about 2004,so 10 years, and it's staying on there. Fuel consumption be hanged.
I agree with rumble as to timing. I ran a less initial (14*), cuz with 3.55s and a 2.66 low, things get a little jumpy down at 600rpm. To compensate. I ran a 22* Vcan, bringing it in as fast as she'll take it. I have since, switched to a 3.09low gear. I left the timing alone cuz it's just soo sweet, to idle around at 600.
Yeah so don't look back!
Oh wait 6000? That 230* cam probably peaks around 5600. With a stick shift split of 72% she will probably want to be shifted at 6400/6500. Outshifting at say 6500, the tranny will pull the rpm down to 72% or 4680 going into the next gear, making a powerband of 6500 less 4680=1820rpm. Splitting that up the middle is 910 rpm and 4680+910=5590 pretty much bang on. So you will need a new chip.
Your current starter gear is 2.66x3.91=10.4. I run a starter of 10.97, and would not like less with my 230* cam, well maybe a little less, say 10% or 9.87 as a minimum city gear.This would be 3.73s for you. With 3.55s there will be a fair bit of clutch slipping required to get moving, and no chance of any parade action. The minimum rpm with that 230* and a sharp tune might be 650 which translates to 5.54 mph; at which time things will get rather jumpy and you are gonna have to pedal it. I would just leave the 3.91s in there for a minimum roadspeed of 5mph.
I would,however slow down on the hi-way. 55mph with 3.91s and 27s is about 2672rpm,(as opposed to 3157@65). Then I would start feeding her timing until she complained about it (probably somewhere north of 55*). And then I would start pulling fuel out of the low-speed circuit. Pretty soon you will see way better than 6 or 7. Ima thinkin she's got double that in her,under steady-state 55;unless the compression is in the basement. Then you are screwed. To make numbers at 2672rpm, you are gonna need compression.Lots of it.
But 3157 will drink gas no matter what you do.
So if hi-way economy matters to you, And your Dcr is sour,go down 1 cam size and put in 3.23s.Or even the 3.55s if you already own them. .3.55s will bring your Rs down to 2867@65, but more importantly the next smaller cam at say 223*@050 will be waaaay more fuel-thrifty. And the new starter gear of 3.55x2.66=9.44. While being a little tall, the smaller cam with the increased Dcr,is way more street-friendly and will easily pull it. The 223 cam will keep pulling down to 500 with sharp tune, and that makes the minimum speed 4.26mph, but the jumpiness will be gone.The new hiway speed of 65@2867rpm is much more fuel economy friendly. I see mid to high teens easily enough, with just a good tune. I don't think the DP will go there tho. The low speed circuit in those is too hard to access. So on this cam I would install a carb with metering rods and get the matching kit.
With this smaller cam, and supposing the increase in DCr is favorable,and with the gear changes, I see a slight loss of performance. Well OK more than a slight loss.; a significant loss. But who cares! You already have more power in the first two gears than the tires can handle! It's like shooting a deer did with a 303 or a 22; how dead does the deer need to be to stay dead?
Now if you were a drag-racer the loss would be felt all right. But as a streeter,you have more targets to hit. And sometimes you have to give a little to get a little.
Anyway, I have driven a multitude of combos in my 68 FormulaS-clone, and my favorite was this exact combo; the 223* cam, a TQ carb, and 3.55s. I however added a 3.09 low gear, and a GV o/d to bring the Rs down to 2236@65. I'm not gonna tell you you can get mileage in the hi 20s. And I won't say the 3-gear run to 106 was particularly fast, but it was in the 12s with a 2.2 60ft. In my quest this was waaaay more than I had hoped for.And a 12second street car with mileage in the 20s is a thing of beauty!
Oh yeah I loved to stomp it at 35mph, in second, with the 3.55s, to light up the 295s. Yeah I know this is not particularly incredible, but it made me giggle every time I did it! And I remember those times fondly.
My current combo is much like yours; a 230* cam, a 750DP, an A833 and 3.55s. Yeah it has more power at the top. And I managed to perk up the bottom with the 3.09low gear, and I can still lite 'em up at 35. But I sure miss the long summer cruises I used to go on, endlessly passing the filling stations..........
I took a little and lost a lot.
