Re: cranking psi question?
[Re: dusturbd340W5]
#300482
04/26/09 09:18 PM
04/26/09 09:18 PM
|
Joined: Jan 2006
Posts: 132 Kingman, Az
Scojodak
member
|
member
Joined: Jan 2006
Posts: 132
Kingman, Az
|
Quote:
cams will change cranking compression based on the different duration
I was "generally speaking"...
Last edited by ScojoDak; 04/26/09 09:20 PM.
Dakota for life!
|
|
|
Re: cranking psi question?
[Re: BIG-MIKE-500 ci]
#300485
04/26/09 10:08 PM
04/26/09 10:08 PM
|
Joined: Aug 2003
Posts: 8,716 Baltimore/Denver
64Post
master
|
master
Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
|
One should solve for dynamic compression vs cranking pressure or static compression. There are still other variables to consider as well such as quench. By using online calculators such as the one below, you can change intake closing points to get the dynamic compression where you want it, then spec/order a cam. http://www.wallaceracing.com/dynamic-cr.php
Last edited by 64Post; 04/26/09 10:12 PM.
|
|
|
Re: cranking psi question?
[Re: BIG-MIKE-500 ci]
#300487
04/27/09 12:24 AM
04/27/09 12:24 AM
|
Joined: Jan 2006
Posts: 132 Kingman, Az
Scojodak
member
|
member
Joined: Jan 2006
Posts: 132
Kingman, Az
|
Quote:
Now lets see; Yes, "generally speaking" changing the cam "will" affect cranking pressure. If the closing event of one cam is say, 13 degrees & the new is 9 degrees, both @ 050 approx,after bottom dead center then you will have more cranking pressure on the cam with the smaller degrees. Even just advancing a cam on the ajusting slots of 4 degrees can give significant increase in pressure. I have a programne download from comp cams that has a calculator for cranking pressure; haven't used it for a long time, but when you load all the specs of cylinder & combustion chamber in, plus stroke & bore, it gives the effective cranking pressure to the opening event of your intake valve. cheers, Mike.
I've been schooled. Thanks
Dakota for life!
|
|
|
Re: cranking psi question?
[Re: Scojodak]
#300488
04/27/09 12:59 AM
04/27/09 12:59 AM
|
Joined: Feb 2004
Posts: 4,501 Gainesville,FL
goldmember
master
|
master
Joined: Feb 2004
Posts: 4,501
Gainesville,FL
|
Quote: --------------------------------------------------------------------------------
Now lets see; Yes, "generally speaking" changing the cam "will" affect cranking pressure. If the closing event of one cam is say, 13 degrees & the new is 9 degrees, both @ 050 approx,after bottom dead center then you will have more cranking pressure on the cam with the smaller degrees. Even just advancing a cam on the ajusting slots of 4 degrees can give significant increase in pressure. I have a programne download from comp cams that has a calculator for cranking pressure; haven't used it for a long time, but when you load all the specs of cylinder & combustion chamber in, plus stroke & bore, it gives the effective cranking pressure to the opening event of your intake valve. cheers, Mike. Your correct and if your swapping the same camlobe familys pretty easy to get a pattern,the problem is the .050 duration is has little bearing on the seat duration,most calculators are pretty general therefore gigo.
|
|
|
Re: cranking psi question?
[Re: yellowscamp]
#300489
04/27/09 11:32 AM
04/27/09 11:32 AM
|
Joined: Sep 2008
Posts: 34 Sydney, Australia
B-STUNG
member
|
member
Joined: Sep 2008
Posts: 34
Sydney, Australia
|
There is quite an interesting article that analyses cam timing vs. compression, at the following url: http://victorylibrary.com/mopar/cam-tech-c.htmYou can download an excel spreadsheet that estimates cylinder pressure. With my 541ci RB, using that spreadsheet and associated formula's, my measured cranking compression is actually within a few PSI of the predicted value. For a given engine, the key determining factor to cranking compression is static compression and the intake valve closing point ABDC. You need to use the advertised value (not the value at 50'), as compression cannot start until the valve is fully closed. Ive taken the liberty of inputing some values into the spreadsheet for your 340. Based on the calculations, if all 3 cams are installed on the same ICL then: XE268 calculated to be 154psi XE262 calculated to be 158psi. Remember, this is only a theoretical calculation, and your results may vary, as there are numerous real world factors that are not taken into account. I would be interested to see how well the spreadsheet calculations match up to other users known engine parameters vs. predicted values.
|
|
|
|
|