[opelitis5]

What should the compression reading be for a 245 degree both sides @ 050 cam and 8.0 to 8.5 pistons w/76cc smogger heads?.?. We know it is a mismatch and, no need to go on and on about it, but, what should the compression guage readings be for the above??..
Now if we change out the heads to 64cc units - what should the reading be..
If we wernt to 58cc heads where would the guage read???
The 76 cc heads are stockers and engine runs outts wind at 4G.
I am sure this isn't the only mis-match that exists in our midst. eh..
Thanks!!
T.

 

[SSedan64]

http://www.kb-silvolite.com/calc.php

 

[454C10]

first, a cam that big needs valve springs. this could cause the engine to fall down on power at low rpms.

also, your engine needs about 40 degree of totally timing with those heads.

8:1 cr with a cam that size will barely make enough cylinder pressure to start. maybe 80 psi.

adding 64 cc head with raise the cr to about 9.25 which is still too low. maybe make 120 psi on the compression gage

58cc will help but the ports are small which will choke off power.

you also need to make sure the vale spring can lift high enough for that cam. If the valve train can't make that lift, then it will eat up the cam lobes and thrash the engine bearings. A 245 degree cam at 0.050" typically has more lift than a stock valve train can handle.

you will be better off changing to 64cc heads and dropping a few cam sizes. 218 to 224 degrees at 0.050" with 64 cc head (9.25:1 cr).

or pull the 245 degree cam and put in a edelbrock performer cam (204/214 at 0.050"). This cam will make power to 5000 rpms. 1000 more than you are getting right now.

use oil additive with your cam. www.zddplus.com.

 

[techinspector1]

If you know the cam is a mis-match, why don't you yank it out of there and install a cam that matches up with the static compression ratio?

 

[opelitis5]

Just for the heck of it, I did a compression test on a couple of cylinders yesterday with 2 different screw-in type guages and came up with 110 lbs and 130 lbs.. First one was a mite low so I borrowed my friend's and his came out to 130 lbs.. Will try mine again on a known compression engine.
Now the Cam Dynamics 12417B cam is an ancient 283 or 327 "stocker cam" with 244 at 050 on both sides and lifts of 388 or .393..
Crane gave me the info since they bought out Cam Dynamics.. Don't have it in front of me, but since I made the mistake of overcamming I thought it might be interesting to see what I could do with the friggin' mismatch..
Put a vaccum guage on the old Holley 600cfm and brought the vaccum up to over 10 lbs at idle from a fairly low 8lbs.. Had to turn down the idle speed with the new found vaccum i.e. carb was set too rich. Brakes feel better now and we are not going around with that crying eyes look..
Engine has a Single Plane Weiand EX-cellerator intake on it - the one without the plate and is pretty good, but my totally stock 76 cc heads with Z28 springs die out at 4000. I hear ya 454C10, re. what I should do, and am just a screwin' around with a totally mis-matched combo and learning a bit w/o putting out bux as I have a few parts a hangin' around, so to speak.. Kinda happy TechInspector chimed in as he has a neat posting on "bringin up the vaccum" which I have on my favorites list.. Will be changing to another cam and a set of fake camels meaning "over the counter" date models next year and since it is not that cold up here as of yet, I have decided to play a bit and not spend $$ on the mismatch - maybe a set of intake gaskets - along that line.. I have a real old SP2P intake somewhere that might come into play in lieu of the Weiand.. Now for sure it ain't gonna rev over 4 to 4500 rpms.
Sorry about being long-winded but this subject of vaccum and obvious mis-match is real interesting and I don't have the want or the $$$ to buy me way out of it..
Thanks for the info guys and I do appreciate it..

 

[opelitis5]

Sorry about the description of the "stocker cam" it is an old NHRA stocker cam that HAD to use the lift as it came outta GM, but the duration was upped a whole lot and still legal to run.. Maybe a pre-cursor to the Muther line of Comp Cams' units sold today.. Got a wicked idle to it, but along with the neat idle there are other things to consider like not much vaccum for power brakes at a rpm idle level of 675 to 725 rpms - mebbee 7 lbs vaccum.
Just found some lbs yesterday re-setting the carb and she feels a heck of a lot safer applying the binders now...
T.

 

[opelitis5]

Just dug through 30 years + of papers I have and the Cam Dynamics Cam in the 355 76cc headed engine is CD 431 D8 1245 242 degrees duration at 050 alongwith the lifts of .394.. RPM levels start at 3500 and end at 7000 rpms.
Cam was supposed to be installed 4 degrees adv but she went in straight up..
Called Crane for specs and now the cam is a CHSX024 741 transitional number.
The 12417RB cam mentionned above is my old SBC roller unit..
I don't have the valve opening events in front of me but I am sure the intake is a "late closer"..
T.