5spd GT

A331 kit uses DIFFERENT pistons, connecting rods, and crank.

A 331 needs a new crankshaft, new rods, and new pistons to account for the different geometry over stock. It utilizes a 4.030" bore, 3.25" stroke, 5.315" or 5.400" rod, and either a 1.250" or 1.175" compression height piston. A 327 has all the same attributes but keeps the factory 4.00" bore.

A 302 has a 1.608" pistons, 5.090" rods, and 3.0" crankshaft. A 306 has been bored/honed .030".

If he has the bottomend without the heads on, you can put the #1 piston at TDC. This should put the #4 piston at BDC. Measure the #4 piston, from the top of the piston to the top of the deck height. It should measure 3.25". That would be a 331.

If it measures just 3.00", then it is the 302/306.

Do not think that boring it out .030" is going to give you any measureable power.

You could have it dynoed, but there is only a 24 cubic inch difference. I have seen 331s dyno 270 rwhp, and I have seen 302/306s dyno 400 rwhp It depends on a lot of factors.

Want more information on the differences?

Last of all, ask to see his stock crank, rods, and pistons from the 302. Because not one bit of it can be used for the 331

67mustang302

302's can also have 5.7" rods and 1.0" c/h pistons too.

You could try looking for the old crank/rods, or ask him where they are. If he shows you a 302 crank laying around then it's safe to assume it's a stroker. Unless you guys just happen to have 302 cranks laying around.

w8less

exactly i would ask where the stock parts are.

5spd GT

If you want to look at it that way, you could have a 5.6" rod and a 1.1" C/H piston, or a 5.5"/1.2"/5.4"/1.3"...etc, etc. There is a plethora of options.

Trust me, this guy under question is not going to think like that

Having a 1 inch tall compression height piston is likely to guarantee a couple things:

- Less piston ringland thickness (can you say crack?)
- Wrist pin boss will intersect the oil ringland

But for some racers, they could care less. They want the lightest piston possible.

F5GTS331

hey peckerhead you coulda asked me this and i coulda told you what these guys are telling you i have purchased a 331 kit and know what all went into my machining to be able to tell you wether or not you dad had put one together. no offense but i know how tight your dad is and he wouldn't have even spent the 800 bucks on the stroker kit i couldn't believe he bought the cobra stuff for it to begin with plus you know he only bought one rod to fix the one that was bent in that motor and i rode in raymonds car which we know is a 331 before the blower and it would smoke whitey cuz i've rode in it as well it's not slow by no means but it can't be a stroker or something ain't right

03sixbanger

listen here dipsh!t i didnt know how good raymonds was without the blower and i didnt know nothing about the internals of this car....and maybe i woulda asked you but you had to run off and get married!!!!!!!!

tooslow5.0

WTF??????[&:]

F5GTS331

don't get vulgar on me sixbagner and no thats not a mistype don't make me come over a spank you lol but anyways its not like we didn't still talk anyways now did we? so don't throw the marriage thing in my face you'll be in that situation one day and you'll understand

03sixbanger

wont you just come over here and try big boy?? and you can help finish the sixxer too .......oh waiti screwed yours up too.....

F5GTS331

lol we is just having some spitty luck with ours cars lately