jackson

There's another thread about this stuff ... but it's been locked ... probably because of a pissing match.

So, someone wants to put a GMPP 3.8" stroke crank in a dart shp block. Someone else thinks it's not a good idea because of limited piston choices.

Well, piston choice w/ 3.8 ain't a problem in that app ... so the new shp block has 9.025" deck height ... it'll be fine with common 6" rods & common 1.125" cd pistons ... it'll end up with a zero-deck ... and shp has a fresh deck ... so that & a typical composite gasket should work out quite well for a street car. I did similar with an early seventies GM production block (it had smooth & level stock decks) with a scat 3.8" crank ... instant zero-deck.

But what they're both missing is how the GMPP 3.8" crank ain't a good match for shp block anyway. The "why not?" is straight forward & anyone who advises should know why/why not.

SHP block has a 2 piece rear main seal counterbore ... it's intended for use w/ 2 pc rms crank.

GMPP 3.8" crank has a 1 piece rear main seal journal ... it's intended for use w/ 1 pc rms block. Combo won't work without an adapter ($).

Scat & others did offer both cast & forged 2 pc rms shelf-stock cranks in 3.8" stroke; chances are they're still available. 4.125" bore & 3.8" stroke makes 406".

gerry72

Just my $.02, but I look at the return on investment and the most direct, easiest solution. If I can just drop in a 3.75 crank without any consideration of other parts or modifications/alterations -all off the shelf, common parts- then is it worth the extra 6ci to go with a 3.80 crank?

A 3.80 can be done but it's not a direction I would go unless I was building an engine to class rules.

jackson

What works for one fellow ain't for everyone. The 3.8 crank I bought cost same $ as 3.75 ... block had good decks at 9.025 ... any 383 or 406 piston-rod combo works but makes stock deck a zero-deck with no special work. I agree w/ you ... other than to meet rules, I probably would Not pay extra for a custom crank for just 5-6 more ci. However, in my example I built 3.8 motor for same $ as 3.75. So yes, in my example where off the shelf common parts were used, it was worth it for me.

billla

I just never got that far, Jackson It's always tough to sort out all the random stuff in a thread early on.

I'm kinda surprised that the tolerance stack got you .000 deck out of the box, but I have to admit that I never considered that combo.