With enough work and re-calibration you might eventually make a 4300D work (find a stock or super stock racer who has figured it out). The 11:1 CR and 6700 redline makes the torquer OK IF the rest of the driveline matches (ie convertor stall, gear ratio). I would consider finding an early 351C-4V intake (almost square bore with Holley,Carter/Edelbrock bolt pattern). Run it with a 1 inch open spacer, it works amazingly well. If cost is not much of an issue, consider the Blue Thunder intake with the small notch in the plenum divider. With the quality and octane of pump gas the CR is probably going to be a problem. I know everyone has read the engine master articles talking about 11:1 and pump gas. They are pulling on a dyno not driving conditions and they don't care about longevity past three pulls. This is not the real driving world. It is for bragging and advertizing rights. As far as a carb goes a lot depends on the cam specification, how high you are really going to wind it, gear ratio, and convertor stall speed. The 750 suggested by Widowmaker (I think) is the right size. Consider the Holley HP series or the Quick Fuel series series of carburetors. Let us know what you decide to do. Enjoy.
Need cam specs to really be helpful, but most 351C-4V engines will work well with a 750~800 cfm carb. You MUST have a good amount of rear gear to take advantage of the heads. 3.50 at a minimum is what I recommend. You also MUST use a stall converter that matches the camshaft. If you don't know the cam specs, I suggest you find out.
Ditch the spreadbore, take it off and hang it on the wall. You really have much better things to do with your life than trying to tune a 4300. I'd recommend the Torker intake, or as stated, the BT. The Strip[ Dominator is just out there on pricing and not worth the extra $$ unless you're racing. The stock 70-71 M-code intake is very good, but you need to run a spacer or the throttle plates of a 750+ carb hit the intake.
I've had very good luck with the standard 4779/4780 Holley double pump carbs. I can't say anything bad about the HP or the "tuned" carbs, I just don't have a need for them.
I have an edelbrock performer intake with a 1 inch spacer, but it definately dies off around 5400 rpm.
Thanks for all the answer. The guy lost the cam card and he couldn't remember the specs. He said he use to race the engine in St louis and that Roush ported the heads many years ago. Not sure if it was in a mustang.
I may be going with aftermarket carb and intake 750. Thanks MAB
I think you have been provided some very good feedback from the other posters, at least as it pertains to performance enhancements. That having been said, I also believe you might need to take a "deep breath" and try and decide what you really want from the car.
You indicated the motor (ALREADY) has more HP than you wanted (with the modifications that were made prior to your acquisition) and that you would like to maintain the originality as it relates to the spreadbore manifold and carburetor. It sounds like you have a "race" motor that has undergone some detuning efforts but not necessarily to the level that you desire. Is this correct?
If so, it might help us in providing more "spot on" recommendations as to your intake (manifold and/or carburetor) changes or possibly other "detuning" approaches.
Just a thought.
Do the RIGHT thing.
I've been thinking about detuning since I got the engine. I want the car to be sreetable as possible. I don't race but I do kinda like being the first one away from the stoplight. I drive about 50/50
highway and in town. I'm hoping this engine will run on pump gas.
I have stock tires. That may have to change. MAB
I detuned mine, it runs cooler and more predicable. The idle is steady now as well. I gained some vacuum for accessories and the car stoped smelling inside from lack of emmisions equipment.
I went from roasting tires from a standing start with a 2.75:1 gear set, to a slight chirp with a 3.00:1 gear set. I'm glad I did it because the one time I drove in the rain was a slip and slide nightmare.