[MasterGore]

Yeah yeah yeah, I realize there's a million of these all over the web But this one not only calculates static compression ratio and displacement, but also dynamic compression ratio! I initially coded it to help me figure out where I was going with my own engine building project, and then I thought other Pontiac enthusiasts might get some use out of it too. So here it is:

http://www.projectpontiac.com/ppsite...nt/view/11/43/

Feedback is always welcome, of course.

[MasterGore]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by grandville455:
Here's the #'s
4.19
4.21
98 c.c
.005
.039
6.6
.1
.0028
6.625
290
112
+6 <HR></BLOCKQUOTE>

It was in fact an error in my formula. I was adding the cam advance to the valve closing angle instead of removing it. An advanced cam makes events happen sooner, not later.

I also forgot to double up the advance to convert from cam degrees to crank degrees. I've fixed it and it should give you a more accurate result now.

Adding a field for cam advance was just an afterthought, and I forgot to debug it properly. I'm glad someone spotted this error Based on the corrections, you should have 9.3:1 static CR and 7.46:1 dynamic CR. That makes a whole lot more sense

[BVR421]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by GoreMaster:
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by BVR421:
nice calculator but javacrap is not welcome on a lot of computers <HR></BLOCKQUOTE>

Criticism is good, but only if it comes with explanations. <HR></BLOCKQUOTE>

I have always had generally negative impression of javascript and its uses. thats speaking as an enduser only. often silly uses similiar to flash animations. your calculator certainly doesnt belong in that category.
sorry I have no programming expertise nor math skills and I admire those who do so dont take it personal. I wouldnt presume to recommend any other vehicle than what you have chosen

[pastry_chef]

Lowering dynamic CR by delaying the intake closing point (increasing duration or retarding the intake centerline) can indeed help a little to run higher compression on lower octane.

I believe a dynamic CR of 9:1 is too high for pump gas.

Read this article: http://www.pontiacstreetperformance....mpression.html

[MasterGore]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by BVR421:
projectpontiac.com seems to down or is it my dumb browser? <HR></BLOCKQUOTE>

I was shocked to discover that my domain name expired on November 23rd. It's my own fault, I forgot to renew it. Luckily it was fixed within a day by my hosting company, they have excellent customer service.

[Bud Lyons]

Deader then a hammer!

[shaker455]

I like it!

Thanks for the post

[RPM]

Nice 'cept the dramatic compression is coming up low. Why?

[fiedlerh]

I run a couple of Javascript programs on a couple of corporate website and I haven't had any complaints yet about it not working. I just put up a message like "This feature requires that you have JavaScript enabled in your browser settings."
------------------------
I see you already did that.

[BVR421]

nice calculator but javacrap is not welcome on a lot of computers

[MasterGore]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by DiamondJim:
Is there an easy way to move it so it prints out better? Not complaining, I hope you don't mind my suggestions. -Jim <HR></BLOCKQUOTE>

Constructive criticism is always welcome

But I'm not sure I understand what you mean exactly. Are you referring to physically printing it onto paper? Or the way it lays itself out on the screen? If you're referring to actually printing it onto paper, there's a "Print" link near te top of the page (to the right of the page title) that opens the page up into a new window without any graphics or navigation stuff.

I've also removed the right blue column from just that page to reduce the displayed width a little. It should fit better in all resolutions now.

[Judge not]

It does not work for me either

[Trips4me]

Great job and very interesting reading.. I read the article in Pontiac Street Performance as well and that only raised more questions. I like this calculator and will be using it to do some calulations for my new motor. In the meantime I have a question for the gurus!!

What is the maximum dynamic CR that you can run 93 octane without worry of detonation. I'm thinking that there may not be a "correct" answer to this question due to so many factors but it seems to me there could be a number that would be a good "rule of thumb" that allows one to feel comfortable with the available fuel.

For example... The dynamic CR of my 389 is 6.78:1 and the static is 9.69:1. I mix 105 racing fuel and 93 octane or run straight 100 octane.. am I wasting my time and money??

[DiamondJim]

Here Ya go. Jim Click here

[johnta1]

Read the link 242177P gave above.
The dynamic compression ratio will always be lower than the cr.

It is also dependant upon the cam that is being used. A wilder cam will have a lower DCR than a milder one will have generally. (LSA and duration etc will affect it)

[pastry_chef]

Thanks Frank.
I'm afraid I've confused you a little.

The changes I was suggesting would make the correction on their own (a little second guessing on my behalf)

During correction you made one other change in the initialization, that is:
Old
advance=x.advance.value*2

New
advance=x.advance.value/1

previously you were multiplying advance by two, that is why in ...
ICAx=lsa-(advance/2)
I divided the advance by two.

thus with your additional change it is still off a little.

To know when it is bang on use these inputs and compare manual entry intake closure vs. the triple team of duration, lobe sep, and advance entries. When accurate they will yield the same dynamic compression number.

280 adv duration (crank degrees)
110 lobe seperation (CAM degrees)
4 degrees advance (crank degrees)

VS.
66 deg ABDC intake valve closure.

-------------------------------------
(280/2)=140 duration crank degs either side of lobe centerline.
@ 106 ATDC intake centerline (110 - 4 degs advance) there remains 74 degrees left until BDC
thus 140-74= 66 crank degrees of the lobe will occur ABDC.
--------------------------------------

When a 110 lobe sep cam is straight up (no advance or retard), the intake centerline is 110 crank degrees ATDC, the exhaust centerline is 110 crank degs BTDC.

If we advance 4 crank degrees (most typical) the lobe sep is still 110 but intake centerline becomes 106 ATDC and the exhaust centerline 114 BTDC.
(106 crank degs + 114 crank degs) /2= 110 CAM degrees. - most typical of nearly all CompCams

Lobe seperation has the distinction of being the only spec stated in "cam degrees", at least in common practice.

[Tom Vaught]

Make sure you have inputted the correct CC volume in the program. A lot of 326 heads had mid 50s cc chambers to get the 10.75 compression ratio.

Tom V.

[Formula jg]

Can someone confirm if the 400 Eagle stroker kit with the JE piston set has 9cc valve reliefs? What is the Piston Ring Height for the JE's?

Thanks

[fiedlerh]

Very nice!
So if we put in a negative number for valve reliefs, then we are entering dome cc, right?

It would be nice to fit it on one page to avoid having to scroll down, but that may be hard to do.

It would be interesting to hear if anyone has javascript turned off thus making program inoperative. I hear about 10% of users do, but don't know if that statistic is valid.

[buwalda]

Maybe I'm missing something, but I fail to see the 'benefit' of a DCR figure. For instance, is it not going to vary at different rpm? As volumetric efficiency changes thru the rpm range, different amounts of fuel/air will be drawn into to the chamber for compression. So, at which rpm do you choose as a reference? Also, using the 'advertised duration' will give varying figures. If you use a Comp Cams hyd, they usually quote their hyd cam figures at 0.006"; Crane often use 0.004" . Could get a different DCR for essentially the same lobe profile because of a difference in the quoted 'advertised duration' figures. Two identical cams used in identical engines except one has ported heads, will have different DCR's because you would expect the ported heads to flow more air; but the calculator would show the same DCR for each engine.
The very fact that it is called 'dynamic' means that it is changing. And that is exactly what it is doing, constantly: changing. I feel there are too many variables involved to get DCR from a formula or equation.