Compression & octane questions

[BB73Challenger]

OK, so 1st off I have been doing a lot of "on paper building" for my new motor (thanks again Al)
As of right now it has 915 iron heads, and I have been toying with the thought of going with aluminum heads.
I've been thinking more on aluminum as the iron heads would require a race fuel or octane additive OR a change of cam and watch my timing.
The combo I'm debating would put me in these numbers:
4.375" bore
4.150" stroke
4.380" head gasket
.040" thick
78 CC comb. chamber heads
4 CC's for the valve reliefs in the slugs
And finally the piston being .010" in the hole

From what I see that should still be a healthy 11.84 (rounded up) to 1.
Now I can get 93, and don't intend on these numbers getting me by on just 93 pump gas.
My thoughts were to use Kemco octane boost, adding a good 5 points to get me more in the ballpark of 98.

I know the general rule is iron is good on typical pump gas to about 10:1, and you can usually add a point for aluminum.
Will 98 still not cut it?
Is there no formula for this, and more of a trial and error?
Is there maybe something else flawed I'm not thinking of?

Again thankyou guys for your input!

[Moparal]

Jeff, you have a .020 head gasket not a 40.  Stroker and I was going over your numbers last night and saw that if you went to a 40 hg and 84 cc heads like eddy type you would be around 11.5  he used a program, and gave a more specific number, 88 cc was like 10.78    we figure you have 12.25 in the engine right now.  He will see this and reply im sure

[Moparal]

Jeff, here is your cam

lanati  60342  solid  3 bolt

566 intake   586 ex
.377 in .391  ex  lobe lift
adv dur  280 288

duration at 50  251 in  259  ex

valve lash  .014   .014
centerline   106 in  114 ex

timing at 50 thou tappet lift       btdc  20  abdc52    bbdc  64   atdc   16


hope this info helps

[Moparal]

6.760

[BB73Challenger]

well 88 cc eddys at 10.80 to 1 will give him 9.14 static and about 188 cranking with those cam specs! (assuming around 1200 altitude)

So what's that mean 

The 040 HG and 84 CC's sound like I'm getting to more where I want to be.

[moper]

In short, with iron or aluminum, that setup is too high for pump fuel. I run tight quench.. With the RB bore I'd be setting up for a .035" quench regardless of head material, but both closed chamber. Most pistons I am aware of have larger vakve reliefs... Closer to 6-7ccs but I will assume you already found the pistons...lol. What I would suggest is a larger chamber (use aluminums) and leave them at 84ccs. The deck height would be -.005, or .005" above the deck. Using the .040 gasket that gives you around 11.4:1 and a dynamic around 8.8:1. This will ru well with pump premium unleaded (around me thats with 10% ethanol). I would not go past 8.8:1 with any head or any quench help. It's just too much pressure for the fuels I get from  the pump. With good quench (meaning tighter than .040) but iron heads, I think you will have issues above 8.3:1 on pump premium.

[Road_Runner]

Man, I have read this entire thread a couple of times and I can follow the general line of thought, but I'm sooo unclear about how to compute all that is being discussed.  I've been looking at 440Source's compression ratio charts for their 383 stroker kits and at least from them I don't see a way to get to what I thought the optimum cr of 11:1.  I'm at 1000 ft sea level here, so if I understand correctly I'm going to have to be even more careful with going to high on my static CR so is 11.5:1 too high?  Another combo yields around 10.25 which I was thinking was too low, so with 93 octane pump fuel am I thinking right on this?  Starting with 'only' a 383 I know I'm going to have to be aggressive with the combination to get the HP & TQ numbers I'd like to see.

Thanks, Jim

[BB73Challenger]

OK, I think I've got the idea of where I need to be.

Thanks SO MUCH you guys, all of your help & number crunching is greatly appreciated. 

[Road_Runner]

440source website is a "general" way to look at the setups they "sell"! you can get a piston made for your desired compression you want! ALSO get a custom cam made and not a "shelf" cam as I noted above as the timing events are important and be as honest as you can to the cam mfg about your setup! good luck!

Thanks for the info, I guess when the time comes I'm going to have to depend on the stroker kit seller & others to figure out the right combo since I think its going to be a while before I can do the math on all the variables that go into cam, compression, bob-weight, rod-length, etc. etc.!!!

Later, Jim

[HP2]

Here is a decent online calculator that will help with a few of the parameters around your ratio and also includes tabs for boost and altitude. You will still have to do the math to find out your static ratio, but this is a good dynamic calculator that will help you see what your engine will actually see when running.

http://www.rbracing-rsr.com/comprAdvHD.htm

[Road_Runner]

Here is a decent online calculator that will help with a few of the parameters around your ratio and also includes tabs for boost and altitude. You will still have to do the math to find out your static ratio, but this is a good dynamic calculator that will help you see what your engine will actually see when running.

http://www.rbracing-rsr.com/comprAdvHD.htm

Bookmarked, thanks!

[HP2]

Others can chime in on this one, but I think 180-190 psi is close to the max you want to have to run on pump gas octane of 91-93. This can vary some based on chamber design and quench characteristics, but 180-10 is probably the safe zone.

So building an engine to maximixe the cylinder pressure to the available octane of the fuel is how you make lotsa power.