mpcv2000

iTrader: (1)

- Cylinder bore : 4.040"
- Stroke : 3.75"
- Head Gasket : 0.039"
- Chamber : 56cc
- Piston : -5cc
- Deck : -0.016"

I have 230 PSI of compression right now and with the numbers I have up here I end up with 12.97 : 1

Does it sound about right ?

I got my motor back in October and almost every week I ask the builder what is my compression ratio and I'm unable to get a answer , he must know since he is the one who suggested me to use a Fel-Pro 0.039" head gasket.

I have very bad service with these guys

jaycenk

iTrader: (1)

Not exactly Some of that will get you close but there is more to the actual CR ratio than that but then again dynamic maters more than static.
IDK

mpcv2000

iTrader: (1)

What is missing for me to figure out the compression ratio ?
Static , Dynamic , which one is the one we all use ?

Like GM say the LT1 has 10.4:1 in stock form , is it static or dynamic ?

...

quik95lt1

iTrader: (7)

ok.....let me shed some light here.........your compression with those dimensions is.....11.80:1....thats based on the felpro 1074 gasket which im assuming he used its a .039 compressed thickness wit a 4.125 bore.......

thats a healthy amount of compreesion

now............for that whole dynamic vs. static thing........

static compression is the calculated compression ratio based off of volume only.....the total volume of cylinder space vs. the compression volume this is the number we all use and see liike a stock lt1 being 10.4:1 SCR (Static Compression Ratio)

dynamic compression is the determined amount of compression based off of intake and exhaust valve timing........personally dynamic compression is a joke.....alot of guys on here say its soooo important but its not......dynamic compression calculations do not take into account the actual air flow and volumetric efficency of the motor...........i can tell you now to ignore alot of what you hear on dynamic compression......seems these internet people love to talk dynamic compression....
if we tested our motors while they weren't spinning then dynamic compression would be a good useful tool..........but last time i checked my motor mad more power at 7500 than it did at 0


perfect example........my current 386ci has a SCR of 14.1:1 and my DCR is down in the mid 9's.....however my new setup will hopefully make around the 700fwhp mark.....DCR is a discussion topic only IMO.....

hope this helps!!!

mpcv2000

iTrader: (1)

I'm 0.040" over so I'll guess my piston size is 4.040 ?

Sorry for all the newbie question but I cannot get that information from the builder.....

quik95lt1

iTrader: (7)

no prob......well it matter what u bought.....usually the pistons are a bit smaller and you end up with a 4.040 bore.....for isntance im 40 over as well my pistons were 4.0396 and my bore was 4.040.....now i just honed block on a rebuild so my new bore dimensions are 4.045.......i had to do a little trickery with the pistons to make em fit right


but yea chances are your pistons are designed for a 4.040 bore and are around the 4.0396 mark......depending on the material and the required piston to wall clearance desired from the manufacturer of the piston....

quik95lt1

iTrader: (7)

its also kind of odd that your builder wont give u the info........

mpcv2000

iTrader: (1)

Ok my piston average 4.0367" so does it affect the 11.8 ratio you gave me a few post back ?

Thanks for your help.

mpcv2000

iTrader: (1)

Please don't remind me..

quik95lt1

iTrader: (7)

yea it may be like .03 lower if that.......that small bore change is negligible.......

quik95lt1

iTrader: (7)

makes sense depending on what your piston material is that seems right.....that gives you a piston to wall of .0033......your bore may be a hair over 4.040

mpcv2000

iTrader: (1)

Wow... He just emailed the numbers..
I think this morning he felt I wasn't too happy about his service.

So here's the final result :

jaycenk

iTrader: (1)

That looks better. Yea the whole dynamic isn't just an internet fad. When I built mine my builder told me to pay more attention to dynamic rather than static but thankfully I would not let the static thing go so Lloyd Elloit cut the heads to 52cc to help me out on the static since the builder ordered a -16cc piston and then Lloyd gave me a cam to complement everything. Runs good now. lol

mpcv2000

iTrader: (1)

So 12:1 will be OK if I have a good tune and run 91 or more Octane

quik95lt1

iTrader: (7)

apparently he decked the block a little down to a .010 but yea that makes sense...........91 is gonna be close 93 would make it happier........for the best power result race gas will be ur friend.........

jaycenk

iTrader: (1)

Is it a street car or race?

fex77k

iTrader: (2)

What is the rod size and the pin height without those numbers its a wild guess. How much PTV do you have cause there isn't going to be much with that block being decked and running a thinner gasket.

mpcv2000

iTrader: (1)

Just sunny day car...




....too technical for me.

quik95lt1

iTrader: (7)

he will have plenty....assuming the piston is .010 down the hole like he said that tells you your height immediately......and the gasket is not that thin at all.......depending on his LSA he should be able to fit quite a bit of lift...espically with -5cc valve reliefs......

check out my case .........
my piston is .008 down the bore
i have a 60 cc chamber with BIG *** valves
a .027 gasket
a 7.5 CC dome piston
and .703/.711 lift

and i clear just fine......its tight but i clear............he will be plenty fine for PTV clearance

mpcv2000

iTrader: (1)

My motor is already running and I have a baby emission camshaft in it : 223/230 .565/.565 112 LSA .
I'm using LE2 heads with specification :
( copy & paste from my built thread ) Fully Ported heads milled 0.030" with 0.56cc chamber, casting 10128374.
Manley 2.00/1.56 6000 series valves.
PAC 1218 bee hive springs (145 lbs seat and 340 lbs open)
Steel retainers and locks.
205 cc intake port flow about 275/190 CFM.