Hi guys
Iwas flipping through my GMPP catalog when I noticed that the specs given for the 305 block (PN 10066098) gave the cylinder bore range as 3.76" to 3.84". Is this a typo??

3.84" bore+3.8" stroke= 351 cid!!!

 

305 stroke = 350 stroke = 3.48"

305 bore = 3.736"

305 bore + .060" = 3.796"; mighty close to 3.8", but also mighty close to water. I can't imagine getting a 305 to go to 3.84", as that would be a + .104" overbore. Won't happen with a production car block. However, if this is some block that's specifically built for racing in a class that requires a 3.736" original bore, then maybe it will. I don't know. Still seems kind of stupid to buy a brand-new 305 block, and spend money to bore it about halfway out to a stock 350, when you can buy a used 350 block for a tiny fraction of that cost, if you're not rules-limited.

350 bore = 4.000"

Nowhere in any of that do I see a 3.8" stroke. Maybe I'm missing something.

 

The lastest info here says 3.74" bore. Can't imagine anyone buying one of these though. Incidently the GMPP HT383 has a 3.80" stroke.

 

Granted, it does; that doesn't have anything to do with a 305 though.

 

I guess it's a typo, then.
oh well
As far as the 3.8 in. stroke is concered, I was thinking about using it in my 305. If I combined that with a 6 in rod, how much would I displace??

 

A 6" rod won't change the displacement at all. All that will do is change the angularity of the rod when it swings around, and it will hold the piston near TDC for a bit longer.

 

So.... you're thinking about buying a new 305 block with a 2-piece rear main seal, and boring it out to its maximum overbore; and then buying a relatively high-$$$$ 3.8" stroke crank with 1-piece rear main seal; and putting those 2 things together somehow with some sort of a rear main seal adapter and custom pistons, to make something with displacement near a 350?

You realize of course that by doing that you bring along the worst of both worlds: you'll have the small bore of the 305, which will create the small-bore valve shrouding problems and all that; and the long stroke, which will create inertial losses.

Have you compared the cost of doing that to buying a junk 350? or even a new 350 block & crank? I think you'll find that there's no benefit to it whatsoever, and that you'll be spending more money - ALOT more - to get less results. In fact, I'd be very surprised if you could get just that crank by itself, for less than you could buy a whole 350 core for; let alone the custom pistons and all that.

 

Yea, starting anything new with a 305 block isn't worth it... you can get a 350 block for the same or less cost, all the machine work costs the same, and typically, parts for a 350 block, like pistons, are actually cheaper than the same thing for a 305 block.

A 350 will also make alot more power than the 305 will, and with a 3.8" stroke, you have a 396ci sbc (assuming .030 bore on 350)

Get yourself a 350 block and work from there, you'll save money and make more power. All around, you'll be happier.

 

3.77" bore (3.74"+.030) X 3.80" stroke yields 339 cu.in.
4.030 bore X 3.80" stroke yeilds 388 cu. in

That 3.80 stroke crank is a one of a kind used only in the GMPP HT383 & 383 shortblock. Try to properly fit it in a 305 block would be expensive since the crank alone is $1100. If you really want to go with the GMPP stuff take a look at the ZZ4 shortblock or the 383 shortblock & use some good aftermarket heads. However there are much cheaper ways to go. There are tons of 350s waiting to be rebuilt in salvage yards.

 

I already have a .03" over 350 block, I'm getting a 383 kit for it some time next year, when I get some more money
I wasn't planning to buy a new 305 block, that was just morbid curiosity. I had no idea the GMPP 3.8 in. crank was THAT expensive!!
my current plans are to throw the 355 into my 86 Z28
and to bore my 305 .06" over and throw it, along with some fastburn heads & a ZZ4 cam into an engine-less 86 IROC
I figure boring out the 305 will allow me to use the fastburn heads with a minimum of valve shrouding. If it doesn't work, I can still throw them on the 355!!

 

THe GMPP 3.80" crank is mde by Cola that's why its is expensive. Its a good one, but more of a race crank.

 

wow thats one pricey crank.. for that kinda money i'd buy a 350 block, have it machined, and buy a stroker kit and build me a bullet-proof short block and probably have a little bit of money left over to put towards a set of heads..