Recommended 4bbl carb for stock 318
Well this carb turned out to be a 600CFM with VS's, but I understand the differences better now between double pump and VS's, and why VS is recommended for mild street driving, and I see why double pump is best on throttle control for power
I defiantly understand the physics, I just never really thought about it until you pointed it out, which was a good thing. As I said I planed on changing the rear gears at some point, but never really considered the effect of the torque converter stall speeds. And I assume 1800TC is the same as saying 1800 ftlb stall speed, but I can see the change to a different gear and stall speed having a better affect on power performance. And if I do use this carb I can upgrade something else, gears, cam, TC, but now I'm not sure what to go with first? Gears or cam?
I'm not sure what you are saying here, only hiway tractors, and such, make 1800ftlbs
An 1800TC is rated to stall at 1800rpm with a given amount of input torque. Stall-speed is what the the engine revs to at zero mph when you floor it.
Your engine has a torque curve that starts at the stall rpm and ends when you shift. It varies from a low number at low-rpm to peak at a higher rpm when the engine reaches peak efficiency, and then begins to decline on it's way to the shift rpm.
One cam-size is an increase of about 7* at .050.
Each increase in cam-size will move the power-peak up about 200 rpm
Beginning with a stock teener cam of 240*adv , and for street, ending around a 276*adv, that makes about a 6 size range for a street-teener. Therefore,
Peak efficiency usually falls in the range of 1200 to 1400 rpm centered somewhere around 3800, and depends principally on the cam for a given sized engine. Peak power usually falls about 1500 rpm later, but depends on more factors. The shift rpm is kindof dictated by the transmission ratio splits, but sometimes other factors reduce that.
Put simply; if you move the power peak up 200 rpm, you will lose a minimum of half that at the bottom,probably more.The 268 cam is about 4 sizes bigger than stock, moving the power peak up about 800 rpm, and going soft at least 400 rpm sooner. The factory 1800TC while not particularly soft for a DD, for performance is already 400 to 600rpm short of where it should be. So that make your new TC requirement for the 268* cam,to be about; 1800+600+400=2800rpm.
I got my first 2800 in about 1980, for a 225 in a 69 Barracuda. That TC has been with me ever since, going from one engine to the next,in almost every DD,ever since.It's got a great little "hit". At that time it was called a "Dirt-Jerker 2800". You need one.lol The company I worked for at that time, made those.
