Getting worried-----

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Thanks guys, got the degree wheel, the piston stop, the crankshaft turning socket and a Cal Custom air cleaner to match my Cal Custom valve covers I plan on using. (I now have 4 sets of valve covers and two new air cleaners to go with my four master cylinders:)I will CC the heads this weekend and post the results so you guys can help me with the rest of the CR calcualations. I am really having fun with this stuff. Nothing like taking care of the details that make the car one of one! :blob:
Cheers---DR
 
Well I thought I was on my way to determine my SCR but with domed pistons above deck, there should be a -number in the equation which Egge tech support cannot help with. It looks like the TMM method of CC combustion chamber/fill cylinder @ TDC/fill cylinder @ BDC, total volume over combustion chamber CC will give SCR per Mike's calculations. I guess that is the way I will have to do it as well unless anyone knows of another way. It seems simple enough on the surface but I am learning way more than I wanted to know about determining SCR and detonation tolerances. I have been advised to keep my SCR at or below 9.5:1 to be safe.
Frustrated and getting a headache----DR:pale:
 
DesertRat said:
If I understand what I am reading, this setup is a little milder than the one I have planned. But you don't state your SCR.
Click to expand...

Yeah, that's because I don't know. It was a basically stock rebuild other than the hydraulic cam. At the time the factory solid cam wasn't available. I've never heard of anyone else using the TRW pistons (this was back around 1992 that I built it) but I assume they were intended to maintain the factory CR (I know people say the Egge ones don't). I have about 90K on the build -- it has been dead solid reliable. I even put in a track day at Willow Springs in 2010. I used lead substitute until it was well broken in, then just 92 octane. The engine is out of the car now -- I refreshed the heads and had them mildly ported while I was at it, and replaced all the soft plugs as one had started weeping. I also degree-ed the cam just for fun (and because I replaced the timing set), and to find out how I had installed way back when. It was installed straight up (plus 4º advance built into the grind).
 
DR
If you are not concerned with getting the full potential from your combo, then a 9.5 Scr is a nice safe number.

Keep in mind that Scr is just a way of accomplishing the actual Dcr target. If you put that 256 cam in a 9.5 engine the Dcr will fall into the basement(I love saying that), and performance absolutely will not be optimum.It won't be that much slower though. The Wallace calculator puts the Dcr at 8.0 with 9.5 Scr.and that 256 cam with a 56* ICA. Since 8.5 would likely be the ceiling with iron heads, you are only 6% low.
Myself, I would be targeting that 8.5Dcr, which requires a 10.1Scr with an ICA of 56*.I am pretty confident that I could make it work with your chosen parts.
For example retarding that cam to straight up, puts the ICA at 60*, and would drop the Dcr to 8.3.Shazzam.
But again, since the chamber volume has not yet been determined, I think you are jumping the gun, in the worry department. As for me I'm kindof excited.
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Reading this over I noticed that bumping the Scr from 9.5 to 10.1 is .6 of a point. And that extra .6 point gets the Dcr up from 8.0 to 8.5, a .5 of a point.
But retarding the cam just 4*, drops the Dcr from 8.5 to 8.3, that's .2 of a point.
Seeing that in print, I would not hesitate to target 8.5Dcr. Not one second.
For the 90% of the time that you will not be running WOT, that extra .6Scr will be paying great dividends in; a)part throttle performance, b)fuel mileage, c)throttle tip-in, and most importantly,d)off-the-line,part-throttle pull.
Some of these attributes can be obtained with the 8.0 Dcr. It will just take more throttle to get. Of course fuel-mileage will be less with the lower Dcr, and cannot be recovered. And throttle tip-in will be a tad lazier. However, most of these would likely go unnoticed, cuz you would have nothing to compare them to.
Personally,I would target 10.1Scr with an .028 gasket. Then if I just couldn't keep it out of detonation, the .039 could solve it.The difference is only about 1.9cc; but it represents nearly 3% of the chamber volume.
 
I have been running the numbers I know, will know more this weekend. Called Lunati and they offered to custom grind me a #60403 (old part #) with a 112 lobe separation to calm it down a little and work with my motor. I think my 60401 will work though once I get all the #'s in. Egge recommended CC'ing the dome with a clay mold which I am prepared to do. Still won't know deck position but should give me an idea. I am learning that there is no rock solid rule and everyone has the answer but it will be different from everyone else. In any case, by the time I get through this I will be competent to do the work and chime in. I may also own two camshafts to go along with my 4 master cylinders, 4 sets of valve covers and three air cleaners. Depending on the head volume and dome, it is looking like a 10.4 static and 9.13 dynamic with the thin head gasket and my 401 cam.
DR in learning mode------
 
Checking the dome volume is done by pushing the piston down some amount deeper than the top of the dome. Then measuring the amount of liquid required to fill the cylinder to the top.That amount is then subtracted from the calculated amount that would have been required to fill the cylinder, if the piston would have had a flat top.This takes care of any eyebrows right away too.
It is common to select 1/2 inch down, or 1 inch down, as may be required to cover the dome.The measure must be exact, and must not move during the process.
On a 3.66 bore, each inch is 172.406cc, so an error of just .006, would introduce a 1cc error in volume, so be careful.
 
AJ/FormS said:
Checking the dome volume is done by pushing the piston down some amount deeper than the top of the dome. Then measuring the amount of liquid required to fill the cylinder to the top.That amount is then subtracted from the calculated amount that would have been required to fill the cylinder, if the piston would have had a flat top.This takes care of any eyebrows right away too.
It is common to select 1/2 inch down, or 1 inch down, as may be required to cover the dome.The measure must be exact, and must not move during the process.
On a 3.66 bore, each inch is 172.406cc, so an error of just .006, would introduce a 1cc error in volume, so be careful.
Click to expand...
Got It! I can make that measurement happen with a couple redundant checks for safety. doesn't account for +_ decking but should get me in the game. I can assume a .010 for overall below deck after calculating the dome volume. I am starting to get this deal!:cheers:
 
Thanks to all who helped me with all the issues involved here. I CC'd the combustion chambers in the heads today and got good numbers. 6 chambers are 62.5 CC's and 2 chambers are 62.75 CC's. Photos and write-up are on my build post. Looking like I am going to want a little more agressive cam but the down test in the block will tell the final story. Thanks guys!
DR:burnout:
 
Check the height from the center of the pin hole to the flat area on the piston top too., to see if it is 1.749".
 
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