static compression for street turbo

I was thinking like 8.5:1 for static before my cam and turbo is taken into account..
and 12.5:1 dynamic afterwards

As for off boost performance; do you think 8.5 will be puttin around, or adequate?

what's the lowest you've gone on a street motor?

using a dynamic compression calculator...only taking into account cam opening/closing, rod length, and dimensions physically machined to 9:1.... im getting 5.84:1 and an effective stroke of 2.3 inches (30% less than actual dimensions)

Im running KG-10

--did I pick a cam that's letting too much charge blow out my engines' a** until higher RPM?


-- will 8.5:1 be comfortable? Will the non-destructive koolaid man make a visit every time I hit the gas... "heyyyyy *BOOOOOSTIIINN*" skkkrrrrrrrrrr----rrrrt *CRUNCH*

thanks and happy 4th. Dont blow your dick off.

edit: I've spent the morning reading, and these are the two most useful pages i've found. https://www.researchgate.net/post/H...ion_engines_achieve_higher_thermal_efficiency
http://www.eng-tips.com/viewthread.cfm?qid=90282
and http://physics.stackexchange.com/qu...ombustion-engines-more-efficient-on-cold-days

so I think actually a compression closer to 9.0 or 9.5 would be for the best. if 50% of my power came on from 2700 to 3200 it doesnt take a genius to think about what the wheels are going to want to do, and very quickly....

also, the higher compression ratio will benefit power production from efficiency alone.--- as anecdotal evidence always leads to... "low end is better with higher CR"...."shes a torque beast with that high CR"... I guess I finally understand where it comes from from a thermodynamic point of view...

Just my .02 worth. The B230FT in my wagon was built to a 9.0:1 spec and I f'ing LOVE it for a daily. Nice easy off-boost power, handles boost like a champ as long as the tune is solid.

My engine build in progress, shooting for 9.2:1 static with IPD turn cam, big intercooler and water injection. Up to 15psi with E10. I'm hoping to achieve a very fat torque curve low mid.

it definitely sounds like the way to go.... I was worried i would drop out of my pressure ratio range on the turbo.... but anything from 8-15 psi is pretty much golden for me at like 1.7 to 2.3.

so ill prob end up with 9.25.. I decided to compare against my old BMW... it only had 8.5 and it had plenty of get up and go; it was 30% larger.. but still. lol the car weighed as much more atleast.

so uhh yeah.. that's that lol

i want to do water injection, and a 50 or 75 shot of nitrous... but together it's like an additional 1000 bucks.

Comparing cr on a volvo to a bmw is like....well no comparison at all. Based on your cam selection I'd guess you are talking about an 8v b230ft. They were 8.7:1 from the factory so not sure why you'd drop it unless you're running alot more boost. Plus a badly done 8.5:1 motor could run alot worse and take less boost than a well done 10:1 engine. Are you touching the combustion chambers? How about the block, tightening up the squish? Flat pistons or dished? Adding nitrous...I hope you've got a strong late block, and transmission, and rear end...
Good you've done lots of reading, keep reading so you don't blow something up.

Isn't this on the pushrod motor?

I'm guessing that this is the b18/b20. Personally I like the higher compression, low-ish boost for that off idle grunt. Currently I'm running like 9.5:1 on my b20, boost at ~15psi, idle advance at about 20* and WOT/15psi/5500rpm is like ~12-15* (but this area is going to need some dyno tuning) no det yet, but temps have been pretty low for testing and AFR's holding pretty steady at ~12