As Rick said.
I spoke with Tony Parella about 6 months ago and Mark I's could be bored to 306 but not stroked. Sean, boring to 4.125 only gets you to 321ci, I don't think this is commonly done. Also, if you want to rev reliably you can't stroke a 302 to the nth degree without hurting reliability. 3.4" on the stroke is probably too much
Wondered when SVRA would restrict so much they limited participation...
I agree 3.4 stroke is too much, I was just giving the options on a 302, a 3.4 gets you a long stroke 347 or a 363 if you bre it. A 3.25 a 331 or 347(with bore) You run in to all types of issues with a 3.4, particularily if you want to rev, and if that is the case IMHO just go for a 351/427.
On a 3.25 if you are very careful you can still run 5.4 rods and keep very good rod ratios, but you need the right block with longer than stock bores(in the bottom) and special pistons and rings. On a 3.0 stroke its easy peasy.
Of course any type of 347 or 363 can be built with off the shelf stuff and make 500 or near 500hp, sacrificing longevity and smoothness at revs, but they still last 15k miles in near track conditions., just burinign oil and wearing the bores quickly. For the price you can probably afford to replace the mtors every 10 miles.
There is more to the whole thing than just bore and stroke though, although for a "crate" motor its about bore and stroke.
Go custom and the type of crank you use (weight ritational mass) is it internaly balanced and to what degree. Rod length and weight, piston type, rings, it all adds up. Then there are the heads, how well optimised are they, type of valve springs and valves. Are you going to spend the better part of a day breaking the motor in on a dyno, is it going to be tuned on dyno, fuel and ignition mapped. When the motor is in the car, will you tune again on a chassis dyno.
As to the bore, a 4.125 is "standard" if you start with a boss or dart block. In fact there is enough meat on these blocks that you can still bore safetly past 4.125, but you start at 4.125 leaving room for 1 rebore. Its also why the boss and dart blocks weight 30-40 lbs more than a normal 302. These are blocks designed for near 1000hp when using boost, so twist far less and are over strong when bored and at 5-600 hp.
Are you starting with a 1970's tech 302 block or a 2k tech 302 block. Are you starting with 60's tech heads(gurney) 2000 tech heads for example (afr 185 or 205 or twisted) or 2014 tech heads Afr 195. Go solid roller lifter instead of hydralics, custom grind cam, custom carb, sacrifice some power and smoothness below 3k revs(still strong, but not a 1000rpms up stoplight grand prix motor) How much effort is being put into maximising all the componants, port matching carb intake etc. In other words a motor optimised for between 3-7.2k thta can spin to 8 comfortably.
Every little thing adds, 5hp here 20 there. Build a 302 like a factory crate motor and you get good power and variances. Build it like a nascar team builds their motors and yeah you can find 50+ more hp for double the cost, and it can be still be a street motor (with the right heads and cam). All of which makes many say why bother, just go for a more powerful, more reliable, less maintance intesive, less costly 351/427, and for street use they are absolutely right.
Most crate motors 302 or 351 are optimised for the Cobra crowd, that is where the volume is. These are almost primarily street cars, spending the bulk of their time dealing with stoplights and cruising, with occasional high speed blasts. Other motors are more for mustang drag cars, once again another priority.
Considder all those distributor failures a few years back on the 351/427's. A single part driving the oil pump and distrbutor on a power montser never contemplated. Yes the solution now is billet distrinutor shafts. I would say best practice is also to go dry sump. But you dont need dry sump in a street driven or mildly track driven car.
You also dont need or want all the compromises in a track style motor for a car primariy on the street that may have to deal with traffic. Is it a street mtor that can go on track, 351/427 or a track motor "detuned" so it can go on street (worked 302).
If you read what the mustang guys have to say(and mustang guys use lots of SBF fords in all manner od spec), they invariable go for a 351 based motor, because its more power more torque more reliable for less money.
In a drag mustang the extra hood height required and weight of a 351 is worth it. Those that drive on street and do a 302 to 351 swap find they need to change springs and shocks to cope with the extra front end weight. For pure power the 302 is seen as a lesser choice. 302's go in mustangs where stock hood height and froint end weight or class is a requirement.
There are whole bibles out there on SBF fords. Most dont deal with road track cars but there is a lot to learn, and circle track guys use a similar spec to what we want. There are also a lot of FFR cars built and a lot that go to the track. You can speak to various builders and get their thoughts, in the end you assimilate as much info as possible, and rely on a builders experience, at elast that si what I did, in a few months I will know the results and give feedback.
As to cost, for a bit more than say a good 351/427 with 8 stack costs, I am building a 302 based motor with carb. The whole shebang will probably weigh 100-125 lbs less. Lack the low end torque, be good above 3k, be really strong from 5k up peak in the low 7s and be able to rev to 8 with little drop off. Its also going to need valves lashed every 2 k miles.
