shorte stroke to lower compo
Turbo Mini Forums

Rite then i need some advise on my new engine build?
i am bulding a new turbo engine (on a budget) i have a set of 7cc omegas 73.5 and they are the short pin to crown hight ones as used in long stroke moters, on S rods and a race head that has 21cc chambers. so my plan was to have a std crank offset ground to s big ends to give me the chamber volume i need above the pistons. so can i do this with out it causing any problems and any idear to do the maths.
also i am hopeing to run 10psi+

having pistons sat down from the deck is bad practice in any engine (I'm assuming that's what you're trying to achieve????)

yes that what i was plannind is this a big no no or an option. is there a reson for this

plannind!! i ment planning

The lack of what is known as "squish" I believe promotes detonation.....not what you want!

This has been written about in depth before, have a look back or search for "squish".....

As Tom says!

Squish is vital for det control!

Alex

AlexF

Offset grinding and budget are a bit of conflict...

Is your engine currently in one piece or do you only have pile of parts ? If you have a std block and crank, the shorter omegas will sit about 1-1,5 mm below the deck at TDC. This gives you roughly 5-7 cc extra volume.

So, with 7cc in pistons, 5 cc min in cylinder, 3 cc in head gasket and 21 cc in head gives a compressed volume of 36 cc. Swept volume is 345 cc and the resulting CR is (345+36) / 36 = 10,6:1

Like earlier stated having a piston in the bore is not the best possible option. But I would forget the offsetting altogether, it is not cheap, you also have to narrow the rod big ends plus if something would break later one you need to source non std parts. If you are determined to use the pistons, swap the rods to A+ items, use normal A+ crank and live with the pistons down the bore. Have the head modified or if it is not possible have a new head cut with bigger chambers.

Jukka

Metro turbo weekend driver,Mini turbo in the making again!

Looking at your original post Mike, have you considered selling your Omegas and race head to someone building a NA motor and then using the money to buy stuff more suited to a turbo motor? As I think you should be able to get a good price for the parts you have?

thanks for all of your input. It has been some help to me. hopefully when i get the engine done i shall tell you all how i got on with my build. but like every think some people will agre with what i do and some will not!! but thats life. hopefull i should get some good usable power out of it.