Originally Posted by
pa_sjo
The efficiency difference between say 8:1 and 9:1 is about 3% so you're not really going to gain any 'off-boost driveability' - that's just an old wives tale.
All I will say is if you haven't purchased the parts yet (as it's blatently an internet spec - off the shelf crap from America, where they mainly run superchargers and low boost levels), is have a bit of a think about it. They have drawings over there with JE, CP, Arias etc. for proper low-comp pistons and can sell you those.. From experience, anything over 8:1 isn't going to make a genuine 300bhp on pump fuel - you WILL get unavoidable det before that point and it doesn't matter how much you think you can drown the engine in fuel, it'll still be there!
I'm just trying to save you a lot of money and heartache..
yeah the pistons were from america which if needs be can always be sold on providing i dont split one in half!
EDITED :- oh and i do agree off bost drivability is to an extent an old wives tale but there is some truth behind it.. if the car is that lumpy then off bost its horrible to drive then its off boost drviability is next to zero, higher compression is better off boost but its a balancing act between alot of factors as you will no doubt agree.
Even 1% is an improvement, albit a very small one
and as for drowning it in fuel - as im sure your aware that it's almost as bad as det for the insides of an engine as it will eat the bores and rings rather than the crown of the piston or the head around the valves.
There has tho been good reports in the uk from the exact pistons i am using one fiesta running them in a ZVH (with loads of zoo parts) is running over 300 with nos as well so will just have to wait and see if the gamble pays off.
Like i said its a complete ZT for 2.5k so it aint going to set the world alight in terms of performance or cutting edge developments and if it doesnt make 300bhp then $hit happens and just run it for 18 months and change bit then if i still have it.