scr vs dcr know what the differance is

[grumpyvette]

the guys on this site need to understand the differance between static and dynamic compression ratios, and thats understandable as its a difficult concept to grasp at first

but you need to understand it before selecting a combos components

 

the differance between STATIC COMPRESSION RATIO AND DYNAMIC COMPRESSION RATIO is where the piston is in the cylinder when the valves close and the piston can accually start compressing the REMAINING VOLUUM IN THE CYLINDER VS the STATIC COMPRESSION THAT ASSUMES THE PISTON STARTS COMPRESSING THE INSTANT IT LEAVES BOTTOM DEAD CENTER AND STARTS UPWARD ON THE COMPRESSION STROKE!

 

let me try and explain, the short version is that the PISTON COMPRESSES NOTHING untill BOTH VALVES ARE CLOSED, .......thats the only compression ratio that matters,.... since its the only compression ratio the engine ever sees.

 

static compression is simply the differance between the cylinder volume at BOTTOM DEAD CENTER(BDC) and its compressed volume at TOP DEAD CENTER (TDC), into the combustion chambers,... dynamic compression takes into account that on the pistons upward compression stroke the valves have not yet closed and nothing gets compressed by the piston untill they do, that of course depends on the cam and rockers, pistons and connecting rods, the cylinder voluum, the rod/stroke ratio, ETC.,used, in the combo, and the rpm levels to some extent BTW, ALUMINUM HEADS can usually operate at a higher dynamic compression simply because ALUMINUM releases heat to the coolant much faster than iron, its the lower heat levels that remain in the cylinder that help prevent detonation..when you increase the dynamic compression the heat levels in the heads combustion chamber rise , the differance in the RATE heat leaves the cylinder allows a slightly higher dynamic compression level from aluminum before the same HEAT levels are REACHED & MAINTAINED in the combustion chambers

 

heres a calculator for static cpr, which you need to figure first

 

http://www.newcovenant.com/speedcrafter/calculators/compressionratio.htm

 

let me point out a few things

first look at this chart

 

http://www.iskycams.com/ART/techinfo/ncrank1.pdf

 

then lets assume your 350 sbc engine has a static compression ratio of 11:1 but youve installed this cam

 

http://dab7.cranecams.com/SpecCard/DisplayCatalogCard.asp?PN=114681&B1=Display+Card

 

looking at the cam specs we see that the effective stroke is not the 3.48" that the static compression ratio is measured from ,at BDC, BUT from about 2.6 inches from tdc where the valves close as the piston moves upward, so your true working compression is closer to 8.1:1 NOT 11:1

 

heres a longer more detailed explanation and access to the software to figure dynamic cpr with the cam your useing in your engine

 

http://cochise.uia.net/pkelley2/DynamicCR.html

 

http://www.diamondracing.net/cocalc.htm

 

 

 

keep in mind that you can easilly run a stattic compressio of 11:1 with aluminum heads if you keep the cam timing in a range so that the DYNAMIC COMPRESSION is CLOSE TO 8:1

take the time to understand the concept,it VERY IMPORTANT

 

read this

 

http://www.diamondracing.net/cocalc.htm

 

 

 

http://victorylibrary.com/mopar/cam-tech.htm

 

http://victorylibrary.com/mopar/otto-c.htm

 

http://victorylibrary.com/mopar/cam-tech-c.htm

 

http://kb-silvolite.com/article.php?acti...3117842f4eb4c49

 

http://victorylibrary.com/mopar/rod-tech-c.htm

 

http://victorylibrary.com/mopar/piston_position-c.htm

 

http://www.iskycams.com/techtips.html#2003

 

http://victorylibrary.com/mopar/rod-tech.htm

 

http://www.zhome.com/ZCMnL/PICS/detonation/detonation.html

 

http://www.chevytalk.org/threads/showfla...true#Post397334

 

if cams are a mystery please take the time to read these, it will get you a good start

 

http://www.newcovenant.com/speedcrafter/tech/camshaft/1.htm

(read LESSONs 1-8)

 

 

http://www.wighat.com/fcr3/confusion.htm

 

http://www.chevyhiperformance.com/techarticles/95298/

 

http://www.idavette.net/hib/camcon.htm

 

http://www.centuryperformance.com/valveadjustment.htm

 

http://www.totalengineairflow.com/tech/valvelashing.htm

 

http://www.chevytalk.com/tech/engine/Cam_Selection.html

 

http://www.chevytalk.com/tech/101/Cam_Theory.html

 

http://www.babcox.com/editorial/ar/ar119736.htm

 

 

 

http://www.symuli.com/vw/camp1.html

 

http://www.symuli.com/vw/camp2.html

 

http://home.wxs.nl/~meine119/tech/camqa.html

 

http://www.chevytalk.org/threads/showfla...true#Post200511

 

http://www.crower.com/misc/valve_timing_chart.html

 

http://www.speedomotive.com/Building%20Tips.htm

 

]

 

http://chevyhiperformance.com/techarticles/94138/

 

http://www.aera.org/Members/EngineTech/engine.htm

 

http://www.zhome.com/ZCMnL/PICS/detonation/detonation.html

[tannji]

Damn, Grumpy strikes again.... lol. You should put some serious thought into writing a book, dude. you would seel quite a few copies right here, I am thinking, lol.

[Psykovertible]

i second that grumpy. I would be willing to pay 20-50 bucks depending on how many areas of engine concepts convered.

 

you could even turn it into profit and a hybrid fund raiser.

[WickedWild]

I think he would make a great online engine designer. Pick the right parts with p/n and set the machineing specs for the builder. Grumpies online engine building, I'd like a Grumpy Block.

[boodlefoof]

Very true!

 

Also a good rule of thumb is that for a pump-gas iron-headed engine you want a maximum DCR of around 8:1 while for an aluminum headed engine 8.5:1 is doable.

 

Pump gas compatibility is attainable with higher DCRs, but it requires more attention to quench and the combustion process.

[Guest zfan]

I remember Grumpy talking about DCR a couple of years ago and have paid close, strict attention to my DCR numbers. As we speak I am building a 383 with 8.0 DCR for my 240Z. Its an 10.8 to 1 motor with plenty of Roller cam with a little degreeing and plenty of lift.

 

Thanks for the motor educating Grumpy!

 

Mike

[BillZ260]

I think he would make a great online engine designer. Pick the right parts with p/n and set the machineing specs for the builder. Grumpies online engine building, I'd like a Grumpy Block.

 

My thoughts for some time now! I think someone needs to put this together! Serious. Maybe I shoudl start another thread....

 

Grumpy, thanks for explaining the Difference, helped me alot!