Thread: Question about formula 4 dynamic comp.

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I'm trying to use the calculator on another website that is often recommended and the problem I have is where you plug in your valve timing degrees ABDC. My comp. cams timing card has all this info at .006 and the calculator on the other website asks for it at .050. Is there some conversion I need? The intake closing is not the same at .006 as .050, is it? I wouldn't think so. I called Comp. Cams cam help number and they couldn't help. The cam in question is the XE 262H for the small block chev.

call comp tech they should have that for you and no .006 is not the same as .050

Originally Posted by DennyW

Heres how you figure it. Right from Comp cam tech. You have to multiply the .006 x the rocker ratio.

http://www.compcams.com/technical/Ca...106-07/5-7.pdf

Heres the Crane does it also.

http://www.cranecams.com/?show=newsLetters&no=408

Multiplying the tappet lift by the rocker ratio gives you valve lift. He needs to convert .006 lift to .050 lift so he can use it in the compression calculator. I'm not sure how you would convert it.

guys,,,wouldn't it be the advertised number he needs to use then?

i do. . i would just call comp they made the cam .they should know the events at .050 and seat to seat

Originally Posted by elcaminokyle

I'm trying to use the calculator on another website that is often recommended and the problem I have is where you plug in your valve timing degrees ABDC. My comp. cams timing card has all this info at .006 and the calculator on the other website asks for it at .050. Is there some conversion I need? The intake closing is not the same at .006 as .050, is it? I wouldn't think so. I called Comp. Cams cam help number and they couldn't help. The cam in question is the XE 262H for the small block chev.

If you go to KB-silvolite.com, they have a compression calculator. That's the one I use. They will ask you intake closing point... OR... you can add 15 to the .050 ABDC. I would put in the .006 spec that you have, that should be very close to intake closing.

Originally Posted by FAYLUR

guys,,,wouldn't it be the advertised number he needs to use then?

Exactly... the valve closes at .006 lift which is advertised.

you are right

The KB calculator says to add 15 degrees to the 0.050" tappet lift to get you close to the actual 0.006" tappet lift point. They're figuring that there is about 30 degrees of cam rotation between the 0.006" tappet lift figure and the 0.050" tappet lift figure, 15 degrees on the opening ramp and 15 degrees on the closing ramp. To use it with a 0.006" tappet lift figure, simply use the 0.006" figure you have and do not add 15 degrees. In researching this point of engine building, most posters on other sites agree that the KB site is conservative, so that instead of using the ideal 8.00 to 1 that other calculators produce, use results that equal 8.25 to 8.50 with the KB calculator.
http://kb-silvolite.com/calc.php?action=comp2

Of course, when optimizing the DCR on a motor, you have to be certain that other areas of the build are in synch. Squish optimized at 0.035" to 0.040", chambers polished and sharp edges chamfered to eliminate hot spots, spark plug electrodes de-burred with a fine wet/dry paper, no gasket overhang into the cylinder (try to match the gasket to the widest point of the cylinder at the top of the bore where the bore is chamfered to assist getting the rings into the bore on assembly so that you have neither gasket overhang or a crevice where mixture can hide and be left unburned) and perhaps routing the PCV into the headers instead of polluting the fresh intake charge.

I think PCV stands for positive crankcase ventilation. I don't think you'd have unburned fuel in your crankcase anyway. Oily sure, but unburned fuel in the crankcase and everywhere else that gets oiled seems unwanted.

You're right I do need to read more posts on this site which I find informative and enjoyable. Wish I had found the forum a long time ago. It's good stuff!
Now, I have seen alot of drag race cars running a tube coming from the breather on the valve cover down to the header collector. I don't know if it's a PCV valve, it may not be, but I know I have seen it many times. I think I even read about the purpose or benefit in one of the car mags. Something about the exhaust gas pulses helping to draw out crankcase fumes or pressure or something like that.

Hang around Kyle....some of our techs are so hard headed on this site they don't stop digging until it's answered properly....which is fine by me...I would like to see what the earth's core looks like.... ...seriously, you want the right answers? It will be found and discussed here on this forum.

Here are some kits from Jegs....
http://www.jegs.com/webapp/wcs/store...10002_10449_-1

And some pro and con discussions on another forum....
http://forums.corvetteforum.com/show....php?t=1450082

It all depends on whether or not you have to pass emissions in your area and how environmentally responsible you feel. The simplest way is to install a filtered breather on each valve cover. Some guys have experimented with using belt-driven or electrically-driven smog pumps to evacuate the crankcase with varying degrees of success. I've read more bad than I have good. Seems the problem is that most pumps will pull too much vacuum, pulling oil away from the main seals and wrist pins. About 15-16 inches seems to be the limit before you create another can of worms. Also, the OEM type belt-driven pumps tend to sieze up and throw the belt.

In the end, anything you can do to prevent foul crankcase vapors from polluting the fresh intake charge will be to your benefit, particularly when approaching the upper end of dynamic compression ratios.

i have tried the vac u pan on the street they just do not work that good have had cranK CASE venting issues with it. with a ex it just will not work at hi RPMs when getting off it will blow the stick out and push oil out of the dipstick tube the back pressure or lack of draw shut the valves in the vac u pan and the crank case fines a way to vent also i have had low speed smoking where the engine was pushing more oil up on the walls and make it smoke this type of vent system was tried on a 462.468. 548 .572. never had any luck with it it could be made to work but i just use open breathers in let it do its thing and had never had any more issues with venting the case