Compression Raito

[bumblebee03]

I just want to get an Idea of what kinds of compression Ratios people are running with what amounts of boost. Im trying to make a head decision from a 347 I am building. I am considering a 70cc head, which will make my compression 9:1, or should I use a smaller combustion chamber head and run more compression. I will probably be runnning about 8lbs of boost to start.. Im also located at 5000+ feet above sea level... Lee

[blownzoom440]

i have 8.8/1 cr with an open chamber head,pollished.i was at5lbs,soon to be 8 then 14lbs for a 17/1 cr.

[5150 LX]

Mines set up right around 8.5:1, I was running about 13#'s through a little Novi 1000...

[fanglemeister]

I'd stick with 64cc heads and adjust the CR via reverse-dome pistons. Although, the Victor Jr. heads can be had with 70cc chambers, these are not a bad head for boost. If you are planning on single-digit psi, you can "get away with" @ 9.5:1 iron, 10.5:1 aluminum, depending on how much cam you are running to bleed off some cylinder pressure at low rpm. But a low-CR/hi-boost motor will always make more power than hi-cr/low boost motor, because the chambers in the low-cr engine are bigger, they can physically hold more a/f mixture than the smaller hi-cr chambers. The more a/f you cram in there, the more power you make! Really, I'd shoot for mid to high 8s if I was planning on anything over 6psi.

You'll want to avoid big open chambers. Keep some quench area working for you to help avoid detonation. Quench = flat areas of head and piston that are within only .015" to .060" apart at TDC; as the piston approaches TDC this imparts rapid motion within the a/f mixture, helps avoid preignition/detonation.

[blownzoom440]

i have the situation above with large quench if you can even call it that..200 yes that is right .100 chamber,.040 gasket,.060 deck height.i plan on running higher octain for this reason but should come out to 110 oct for 8psi 14/1 cr and c16 for 14psi and 17/1.with a 8.8cr piston.

[fanglemeister]

69, from what I understand, quench height is ideal at .030-.060 and goes downhill above that, basically stops working at .120!!! Me thinks it would behoove you to get rid of some of that extra deck height. ;-) If there's just no way around this situation, you might want to consider pocket-porting your heads and unshrouding the intake valve, so most of the intake flow hugs the outside edge of the intake ports - this will maximize swirl and tumble in the chambers, and gain back some of the missing charge motion.

[blownzoom440]

my heads flow pritty good for iron stuff.280cfm@.600intake/180cfm@.600exh.ya not much i can doo with the quench right now ceptmill.050.i know my stuff is not the best but it is what it is.
look at the swirl pattern on the pistons. http://www.superchargerhelp.com/phot...cat=all&page=4 dont mind the clean one[water leak]

[RSNovi]

10.25:1
20+ psi boost
100 octane

[blownzoom440]

WOW if i had 20psi i would have1200hp.on the real side of the story i havenot had my car running good so i dont know what i will have to run for gas[no intercooler]i'm glad you're doing so well.OH!speeking of 20psi i had to change my cam because i was putting out 20 but the lobe sep [110] only let me have 6lbs so i have a new cam,we will see how it gose.my car is 1000lbs heavier than yours with me in it.

[blownzoom440]

these guys have some good ideas on a lot of subjects.
http://speedtalk.com/forum/viewtopic.php?t=898

[bumblebee03]

Im going with the 70cc head, It will give me 9.4:1 compression. Should be safe there. Can't wait to get this all back together and get it to the track!!!!! Lee

[regattacoupe]

gonna buy a set of Vic jrs.? they're hard to beat for the money.....see the new trick flow heads yet? :shocked: i guess they're supposed to outflow the TEA ported stuff out of the box but i seen where Brian Tooley lives in ohio now so i bet he designed them.

[bumblebee03]

gonna buy a set of Vic jrs.? they're hard to beat for the money.....see the new trick flow heads yet? :shocked: i guess they're supposed to outflow the TEA ported stuff out of the box but i seen where Brian Tooley lives in ohio now so i bet he designed them.

Im getting a "custom" Avenger head from Ford Performance Solutions. It is going to be a 200cc head with 70 cc combustion chambers. Down the road depending on how crazy I want to get with my set up, they can CNC port them to 230cc..... I will let you all know how they work out for me.