Stock exhaust manifolds vs headers
I believe RRR & Volaredon had their cylinder heads cut 0.100 to raise the comp ratio. RRR said his comp ratio is now over 10:1.
Mine is 0.020 over (I wanted to bore the least amount as possible to eliminate the wear and taper that oversized parts were available for)
No sense to go "straight to 60 over" unless your block actually needs 60-over to correct for wear
I had my block decked 0.030 and the head 0.070.
I guessed on the block since the motor was in pieces missing rods and pistons when I got it.
A guess based on how far I had heard on the forums that a stock 225 "usually is" in the hole at tdc.
So are my pistons (stock style sealed power) shorter than the originals or was my block "tolerance stacked" and "taller than spec" from the factory? Or both?
I then found out that most "rebuilder grade" pistons are actually a shorter deck height than stock to "compensate" for any chance of a CR increase because of the bigger diameter however minimal that increase might be "thanks EPA". Most stock unrebuilt 225s are claim d to be about 0.180 in the hole at TDC.
Mine is that, after the 0.030 shave. So had I not shaved the block I would have been at 0.210 in the hole. I was hoping for 0.120-0.150 max but I wasn't pulling it back apart again and sending it back to the machine shop, once I had the short block home and assembled.
I then had the machine shop CC the head ( because they had it at that point, not me) and tell me what it came out to, and decided on a 0.070 shave on the head to get the chamber CC volume where I wanted it to tailor the compression ratio.
I cc'd the head when I got it back and the head ended up where I had hoped it would actually.
I also added SI brand oversized valves at 1.70/1.44, and ported the head the best I could, as far as I dared without chancing breaking thru into the water jackets as then the head would be scrap metal with lots of time and grinding dust "for nothing'.
There's a series of articles on a 67 dart with exceptionally low miles that was donated to a community college in PA and these articles tell of the headaches they went thru to get it going. It had sat for years and the original engine was seized, they detailed the build and reasons for what was done. That engine ended up with pistons at .210 in the hole. They discovered it after getting it running and were disappointed in Dyno numbers compared to "what was advertised bach in the day". I think at one point they pulled the head and shaved it to increase compression for more power.
One difference between my engine and RRRs is mine is in a d150 and his is in a light assed 64ish valiant. Our end goals were the same/ as in improving performance, but yet different in other ways because of our respective applications.
Some mods are universal no matter your goal while others differ because of them.
