Measuring compression ratio

[J_PEPIN87]

I'm finally putting together my 427bb, i already have the heads torqued down and going to start putting everything else on it.the problem i have is that i have no idea what my compression ratio is i'm just guessing.can someone please explain to me what i have to measure and the formula.also my machinist gave me a gasket set but it looks cheap to me and i cant find what the head gasket thickness is. The part number of the gaskets is 260-1009 is on summit wat yall think about them?thanks in advance

[Hottrucks]

your going to need this info

head CC's
bore size
stroke
piston type...dome ,flat, vavle cut
was it decked and how much??

here something your not going to reget...SCRAP THOSE GASKETS..use nothing but felpro...and they come in dif thickness's so you can adjust your comp# .... a little....to what you want...keep in mind what your going to do and if you plan on running premeum fuel ALL THE TIME

[J_PEPIN87]

Well the block is .030 over,the stroke is standard 427 which i believe is shorter than 454, the pistons are trw dome tops part#l2239nf-30.how do i measure the heads the deck height?

[swb85]

You can't measure the deck height with the heads already installed. You need a straight edge and feeler gauges (poor man's method) or a dial indicator and magnetic base to measure how far the piston is below the deck at TDC. If the block hasn't been decked, they usually measure .020-.025" in the hole.....but guessing isn't knowing.

[J_PEPIN87]

Originally Posted by swb85

you can't measure the deck height with the heads already installed. You need a straight edge and feeler gauges (poor man's method) or a dial indicator and magnetic base to measure how far the piston is below the deck at tdc. If the block hasn't been decked, they usually measure .020-.025" in the hole.....but guessing isn't knowing.

the block has been decked, can you explain to me exactly the poor mans method for the deck height.what about the heads how do i find ccs?the heads have been milled a little

[Hottrucks]

ok here goes and your not going to like it but I would swao the head gasket anyway

for deck height pull the head ( your going to need to in order to find out the cc of you head)...I am now worried about valve to piston clearance how much cam are you running??....with a straight edge across the top of the piston hole at TDC use a feeler guage to measure the clearance...unless your piston is above the block then your going to need a mag mount dial indicator..( we'll worry about that if needed later...)

to measure your head get a piece of hard plastic (plexi stuff 1/4" thick) and drill a small hole in it.....place the plate over one cylinder use grease to seal it to the head around where the head gasket seals...I use a big cc needle ( you can pick them up cheap @ the drug store) fill the needle with water and start adding what ever amount of water you add is the CC of you head.....

what worries me is a valve meeting the piston this can be checked with a piece of playdo out of the kids toy box cover the piston wth a bit of oil same as the head/valves this will stop it from sticking cover the valve area with a good piece of playdo...reassemble the head to block and torque down drop in a coulpe rocker and push rod...gently rotate the motor so both valves open and close..take it apart be easy so as not to disturb you guage ( playdo ) once apart I use a sharp exacto to cut the playdo across the vavle indent and check the clearance

I can break it down more if you decide to do it

[J_PEPIN87]

Ok is not as hard as i thought it would be.today i'll be taking one of the heads off and measuring deck height, i cant remember if the piston comes out of the hole or not.is a good size dome on it though.ima go buy one of those cc needles too after work and i'll get back with yall.wats the formula though?do you just multiply or divide or wat?

[Hottrucks]

try this

http://www.rbracing-rsr.com/compstaticcalc.html

[J_PEPIN87]

Well I took one of my heads off and it turns out that my pistons do come out of the hole. How do I measure deck height with this type of pistons?

[BossHogg69]

the best way to check with domes is with a dial indicator and mag base. you'll have to check the piston on the flat part of the crown, not the dome. Check at both the top of the piston and the bottom and average the two numbers to account for piston rock. Bring the piston to true TDC with the dial indicator, zero the dial and the slide it over the the edge of the block and check the measurement.

[J_PEPIN87]

Oh ok got it.now i have to see wher i can find one of those dial indicators.

[Hottrucks]

I resent you a pm but this is going to change things..I came up with 8.03:1

[BossHogg69]

Originally Posted by J_PEPIN87

Oh ok got it.now i have to see wher i can find one of those dial indicators.

Harbor Freight has 'em on sale right now, the mag base and dial indicator is less than $25 together. let me know if you need more pics or info. hth

[djracer]

What heads do you have?

[J_PEPIN87]

I have the 049 oval ports