need a heads recommendation Compression related.
That is a most excellent question and I never thought about it... but all my three cams have been installed with ICAs of 62 to about 68 degrees. I don't know if that means anything. The 292 had the latest ICA ( up to 76* when retarded),and I couldn't love that cam. The 270 had the earliest and That I did love. I even loved that one straight up, now with an ICA of 65......
Have you not tried anything lower?
We all know (generally speaking) that larger will support more ratio.
No one was talking about Dcr or cylinder pressure. The engine shops were saying 9.5 was tops for 91 gas. I wasn't buying it. I had to work out by calculator and protractor, and write my own formulas for figuring Dcr. Then to top it off, aluminum heads had just come out about that year 1999, so nobody could tell me how that was gonna affect the Dcr. So I winged it, .....
I’m surprised to read this because from one metal to another dynamic compression ratios aren’t effected by metal material. Just cam timing.
IMO, generally speaking, on a broad term as not to zero in on any specifics in the industry or persons within. Because your then potentially laying blame and asking for names.....
I’ll just start with the actual smart people in the biz who have already figured out what kind of cylinder pressures require what kind of fuel. The DCR vs octane = no detionation. Or “pining or knock.” And how the cam timing effects the DCR.
As the smart guys figure this out and pass along the information, it becomes like a grade school game of telephone. Start with 1 message and then it becomes another one at the end. This is the misinformation line that we all are victims too.
These are the wives tails, etc....
The best way to relay this information (or any) is to use the KISS method of Generalization and make a broad statement of compression ratio with octane to use with it. This is where we end up with the general rules of safe ratio with fuel on intended purposes and cam sizes that are good to use within the parameters of operations on the intended purposes of the vehicle and its performance arena.
Going outside these recommended guide lines can invite disaster on a number of levels. The first and obvious one is getting a tank of bad fuel.
When it comes to cams and DCR, it becomes a bit dicey to zero in on a exact pressure. IMO, this is due to having to many thing to flexible in calculations.
1st, actual math of the engine and it’s static compression ratio. (SCR)
2nd, cam timing events in the early days were never published and secret.
Actual data to the public and many speed shops were a big fa ZERO! Just advice from the manufacturers of parts were given and not even from the engineers that designed and tested them.
So, as the general rules and suggestions were passed down, the now familiar standards being what we know them as are still in place for iron heads.
1pt. More for the aluminum.
8-1, regular cars and/or small cams and add on parts.
9-1 most high performance street cars (DD) and light racing
10-1 street strip/heavier racing- 50/50 race fuel
11-1 fuel race fuel for best results.
These general rules can be bent within reason or semi disasters result and should be traveled at your own peril. This is why using the KISS method on ratio/cam is kept that why with the rule bender of to big of a cam use not to exceed the proverbial 1 or 1-1/2 step bigger than suggested. Or you need to increase the ratio for effectiveness to operate the cam as intended. The reverse for a small cam and to much ratio, less cam.
Because fuel is more of a limitation than anything else.
I probably couldda run closer to 200 on 91; others here on FABO have said that they are over 200 on pump gas, with aluminum heads. But I'm quite happy at 177 and 87E10.
Probably. Except you would need more cam.
I have been able to run 93 on a 10-1 with the 292 cam. IMO, it wasn’t a problem.
Your issue with the cam IMO is misuse of a huge Hyd. in the street. I think you didn’t go fa enough in the envelope on that one and the current builds you have seem implausible due to octane level used and listed DCR pressures in psi.
That purple 292/.509 has a listing in the MP speed tips section that IMO, shows your min. For decent usage. That cam is much better served at another point in scr ratio w/higher gears and stall.
