Cranking compression A/fuel

Working on A/fuel car and having issues with the compression effect on tune-up. We got backed into a corner due to lack of crank available. Have two ordered but like everything else. Wait,wait and then wait. Bought one off another racer.The problem is .050 shorter than what we broke.Putting piston down .025. Long story short. working thru few piston rod combos.. Guys assembling thinking one combo gave correct compression. We ran cranking compression. was around 260. Dropped gasket about as much as he is comfortable with. His thinking is we have same compression as before due to cranking being about same. My thinking is we are still lower due to how car respoinded to tune. We put our baseline which has run 5.25, .28, .30 and .032 and different tracks similar conditions. Ran no wear near it and left like turd. Had same thing with compression bite us in but in Gainsville and could not get up on tire. Hence my thinking same problem. Knowing that intake closing effect cc as does cranking speed. Both are as close as possible to previous checks to eliminate variables.

My question and looking for opinion and/or experience here. Could we have a decent drop in compression yet see almost same CC numbers?

 

been told by a few 300 plus is needed for hard running setup. I figure cam timing and maybe even more compression only ways we get there. Also open to suggestions on getting 30 to 40 lbs more. Cam timing and compression my only thoughts.

 

Since zero replies I am guessing either nobody else is checking or just checking and not concerned about how high.

 

Are you still running the same camshaft? And if so, have you double checked the cam timing? Also, have you noticed any detonation problems?

 

same cam. Owner who assembled the engine says the same place. Probably is. We have never had the 300 psi cc. We are trying to get there. The performance drop I am about positive is due to the installation of some different parts that are not giving us same compression. While cc is close to old combo.I figure compression can still be down some and not totally show in cc test since compression is only part of equation . I would like to yank engine,put on stand and cc the combo so we know what compression is. Only thing is nobody ever did that with old combo. Just went off advertised compression.
Old parts ran strong or decent with best of 5.25 which is still about .1 off what we need. If new stuff gave same compression it should have run in the area of high 5.2- to low 5.3-'s not the crap it ran.
Doing more invetigatging this weekend. Maybe not issue and we have something else stupid going on that we need to find.

 

good luck...i hope you get it figured out, can definitely be frustrating!

 

Well after a day of claying piston to head. We fianlly changed cam setting 4 degree gave us another 15 psi cc. Now wish I had gone 6. but take what I can get. Plus added another .-2 compression with gaskets. Bad side is no one knows exactly what compression was at before all the swapping of parts. Again not my car not my money so can only push so much to go thru every piece. Getting closer