I just checked the bore size on my spare motor.. It's 4.004 is that std ? They range from 4.003 to 4.005 The block looks really good... I want to do a 306 CU IN short block....
So when you take the block into the machine shop just confirm to them you would like it cut 30 over (4.030) and you will have your 306 ............. The selection for pistons for 30 over is really good!
So much so that unless you pay close attention to the pin height of the new pistons, you're liable to end up with a sub par compression ratio. Pin heights range from 1.585 to 1.620 for 302 flat topped pistons. That .035 can play hell with the comp ratio in a small displacement engine such as a 302. So it pays to do your homework before pulling the trigger on a piston order. Just food for thought here.
That is an awesome point! Catalogs are very good at listing parts that fit inside the motor but you need to read the fine print for the specifications and know what is right for your build. I try to consult with the engine shop, telling them what I want to end up with, and for the most part I follow what they say will work best .......
Thanks for the advice, I will ask about the right parts... I want to end up with 10:1 compression and I want to try a set of E street heads with 202/160 valves... They are a budget head $935.00 for a pair... My cam is a Crain 284H w/512 lift and 112 ° separation....
Not to rain on anyone's parade, but every part the magazines try, end up to be impressive. Find someone who you know to be knowledgable and ask them. Just me, but for a (street) 302 build, I'd stick to 1.94 valved heads.
In my younger years I wanted more compression and ended up with going over .030 THEN I was told I didn't gain much . I had a machine shop bore and install these http://www.summitracing.com/parts/TRW-L2305F30/ . I wish I had the knowledge to find out what my compression is.. So I will know when I get the car running again. So with those pistons I have does that mean I have a 306?
A .030 overbore gives a 306, & .040 yields 308... A .060 will produce a 311 but it's probably not safe to go that much on most blocks... Ford only recommends .030 but there are a bunch of 308s out there... A buddy blew one up(crank broke no fault of pistons/block) but it had over 1700 drag strip passes... Since those pistons have a 7.4cc dish & valve relief volume, that would likely cut compression approx one point...
I have stock heads. They have been worked on but nothing changed as far as the size of the bowls <-? .. Can't remember what it's called.. The valves and springs have been changed. Port and polish by me so not professional.
You have to take into account, head gasket thickness and gasket bore plus deck hight and valve overlap too if you want to know real compression. A lot of science to it all, and a good machinist will get you set up right ...........
I did all that in my calculations. 9.5 ccs for the head gasket, 8.5 for the piston top volume along with the valve reliefs and area above the top ring. He's got a zero deck with those pistons with a deck height of 8.20" If he's got a mid 70's block, that only adds 4 ccs to the equation.
Chamber volumes over the years ranged from 53.5 ccs to 70 ccs for small block heads. It depends on which heads he's got.
