307 question!

Is it possible for one to put more stroke into a 307. Would a 350 or even a 400 crank work in a 307? The 307 only has 1/8" less bore then a 350 and I assume it shares the same deck height and main journal diameter as the 350.

There was a guy on here that mad some kind of wierd stroke using a 307.. I dont know how he did it, but it came out to be a 331? stroker motor. I'm pretty sure its possible, but have no idea how to go about doing it.

Rob

Yeah I calculated it out and if you were to put a 350 crank into a 307 it would come out to 331 about and if you were to put in a 400 crank it would come out to 353. I was just wondering if the cranks would physically fit into the 307.

the 350 crank will fit no problem. the 400 will have to have its main journals turned down to 350 specs. or you could get a 383 stroker crank that will bolt right in to give you that 353cid V8

How much of a power difference would the 1/8inch less bore then a 350s cause? Would the smaller bore just overly shroud 2.02/1.6 valves from aftermarket heads?

well what you get into there is the relation of bore on intake charge velocities and bore/stroke ratios and such. the simple explenation is that the smaller bore longer stroke creates high low rpm port velocities makeing good low end power, but as rpms increase, piston speed increases quite substantially which is hard on the rotating assembly, and also moves too fast to make proper use of the intake charge. so top end power is reduced. the small bore blocks are pretty much for truck engines.

disclaimer - this is a generalization, of course small bore blocks can be made into performance engines, but for the general description, they are truck engines.

I was just curious. I know that the 4.6 liter Ford is a strange engine. The thing is put into a car and is seen as a performance engine and yet has smaller bore then a 305! The engine prior to 05 was only a 2 valve per cylinder engine. The 307 only has 1/8inch less bore which is the same difference in bore as a 350 from a 400. That little 3.6" bore pushes the new GT, that weighs over 3500 pounds, well into the 13s. The 307 has a 3.875" bore and would be 3.905" with a .030" overbore. I asked about the heads because I know putting a set of 350 heads onto a 305 would actually kill power. I was curious if the 307 would suffer the same as a 305?

as far as the 4.6, it was made using small engine design, while the 305 and 307 were made along the same lines as the 350 and such, it would be hard to explain in short order, but it does make a difference.

as far as 350 heads on a 307 yes it would lower compression the same as if you bolted them on a 305

Well I wasn't reffering to a loss in compression I was reffering to overly shrouding the valves. I have read that it is not a good idea to swap 350 heads onto a 305 cause the small bore shrouds the valves and kills power.

not nessesarily, the heads off a 350 have 1.94/1.5 valves, which fit just fine in the 305 and 307 bores, the shrouding you are talking about is when you try to run 2.02/1.6 valves in the small bores. the loss of power is due to the increase in combustion chamber size. going from the 305 chamber of 52cc to the 350 chamber of 64 or even 72cc's will drop compression to somewhere around 7:1 which will drop a helluva lot of power.

note those numbers are all out of my ass, but illustrate the point. i can do the calculations if anyone really wants me to.

I have read in CHP that when you want to boost the power out of a 305 putting on a set or 350 heads with the larger valves will actually kill power because of the shrouding of the valves. I know it is a problem with the 305 but the 307 has a much larger bore then the 305 and I was wondering if it suffered the same prob as it's newer version the 305.

one could always dome the piston the increase the compression. But you cant unshroud the valves from the cylinder bore.

yeah you can run domed pistons, but they interfear with flamefront propegation.

True. But I really wasnt reffering to the comp ratio. I was reffering to the valve shrouding problem. One could alway go out and buy a set of aftermarket heads with a 58cc chamber then you would not have to worry about the comp ratio and domed pistons.