Posted By: 69 GTX
Commpression - 02/19/11 06:04 AM
I have tryed to figure out how to use those online CR formulas with no luck, can someone give me a figure on my CR with these componets,440 bored 30 over 4.350, stock deck height using stock length H beam rods,6.768 with Ross 99501 dome pistons,2v/v relieves,comp dist 1.273,dome height 0.640, piston head volume -50cc, comp height 2.065, dome volume -14cc.On top is a set of stock Stealth Heads with a .040 head gasket,also cam is Comp 284H with Crane 1/6 roller rockers with a lift of 541 in and 544 ex intake opens at 36 BTDC and closes 68 ABDC, EX opens 82 BBDC and closes 34 ATDC, Duration @.50 In 240, Ex 246,Valve timing 0.006 Lobe center 110,intake centerline 106 Thanks very much for any info, Rodger
Posted By: JohnRR
Re: Commpression - 02/19/11 06:52 AM
Some of your things do not compute , first off there is no H beam rod that is STOCK length , all except for a manely which is not available anymore, are 6.760 .
Then your piston volumes, -50 and a dome of -14 ???? A dome with a NEGATIVE volume is a DISH
Compression distance of 1.273 but a compression height of 2.065 ????
No wonder you can't figure out your compression ratio
edit ... i goofed the rod length , damm dyslexia
Posted By: Dodgem
Re: Commpression - 02/19/11 04:04 PM
Posted By: Dodgem
Re: Commpression - 02/19/11 04:11 PM
So you have a 2.065 compression height piston with a 14 cc dome and stealth heads in a + .030 440 with a .040 gasket.
You compression will be about 12.5 to 1
Stroke 3.75
deck 0 deck
Dome - 14 cc
Head 83 cc average
gasket .040 average about 10 CC
Displaces 913 cc per cylinder
effective volume 83 + 10 - 14 = 79
913 + 79/79 = 12.55 to 1
Posted By: RapidRobert
Re: Commpression - 02/19/11 04:14 PM
Rodger get the correct specs & plug em in & see what you really have & head CC's and deck height figures you really need to measure what you actually have as listed specs are not accurate. The KB calculator is simple/accurate for SCR but to add in your cam specs etc for DCR you'd want a diff calculator (not sure which one, maybe Wallace racing ones which have been mentioned on here)
Posted By: Dodgem
Re: Commpression - 02/19/11 06:16 PM
Your dynamic compression ratio is 10.95 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 237.43 PSI.
not knowing where you live I used 1000 feet actual altitude
Why did you go such high compression???
Posted By: Dodgem
Re: Commpression - 02/19/11 06:17 PM
Posted By: Dodgem
Re: Commpression - 02/21/11 05:32 PM
Some of you guys are way to anal!
.008 really blueprint really.
Yes it was a generalization of being within spec.
Short of actual ccing which i doubt you guys have the equipment to do to be exact it does end up ballpark.
Posted By: Dodgem
Re: Commpression - 02/21/11 07:39 PM
well if you go to the low side of tolerances 225 tat 12 to 1 with that cam piston has a 14cc dome
Posted By: Dodgem
Re: Commpression - 02/22/11 07:02 PM
Normally a piston spec includes the valve notch so a -14 cc dome is gross just as a + 14 cc dish would include the valve notches in that number.
http://www.rbracing-rsr.com/comprAdvHD.htmThis calculator uses @.050 numbers on the calculation so a 240 at .050 intake lobe is 240/2 = 120 then the install is 106 so 74 deg remain to bdc you take the remaining 120 deg and subtracted the 74 from it leaving 46 degrees @.050 ABDC boost is 0.
It gives me 225 and 10.5
This calculator has been withing 7 to 8 lb actual average cranking compression on my last three motors and numerous friends motors.
i went through that when I did my low deck stroker,got some of the last Manleys that are a true 6.768 rod as JohnRR said. 