Piston question

dartfreak75 said
I'm now creeping up into the mid to high 10s can I still run pump gas in the high 10s or low 11 range?

Compression ratio is not the enemy.
Cylinder pressure in a no-quench chamber is the trouble maker.
You can control the pressure with size and type of cam.

It is generally accepted that safe pump-gas pressure ceiling for cast iron heads is 160psi for open chambers and 165 for a tight-Q design.
If your engine comes in at 10.5, and you are at or near 800ft elevation, then for 160psi, your Ica (intake closing angle, will need to come in at around

Static compression ratio of 10.5:1.
Ica of 70*, 800ft
Effective stroke is 2.64 inches.
Your dynamic compression ratio is 8.01:1 .
Your dynamic cranking pressure is 159.55 PSI.
V/P (Volume to Pressure Index) is 131
Depending on
your tuning skills this will run on 91 gas at WOT with full timing.But notice the Ica is 70*; that's a pretty big cam, and the VP of just 131, is pointing it out. My math puts that 70*Ica on a cam of
284/292/110 (there are others)
Which would typically net to [email protected]. which IMO, is a lotta fun for a while, but not really a long-term thing.
Especially with a VP of just 131. That will make the bottom "soft", requiring a hi-stall TC and performance gears, and that takes away the cruise factor.
Read about VP here V/P Index Calculation

No, for a streeter, you want a VP well into the 140s, so you can run a more conservative stall and gears, so you can drive 65mph for more than just 30 minutes atta time.
So if I target 140 using the Wallace calculator, I get

Static compression ratio of 10:1.
Ica of 63*,800ft
Effective stroke is 2.81 inches.
Your dynamic compression ratio is 8.06:1 .
Your dynamic cranking pressure is 160.88 PSI.
V/P (Volume to Pressure Index) is 140
So notice
I had to drop the Scr to 10flat and selected a 63* Ica, which is ~2 cam sizes smaller. So my math gets
270/276/110.(there are others).
Ok from the earlier 284 to this 270 is 14* or 2 cam sizes, so I estimate 35hp or so lost at the top, traded for 140-131=9 points of VP or 9/131=6.9% more bottom end, In my opinion, a good trade, cuz it lets you run the same 6.9% less gear so say 3.55s instead of 3.73s. And you can run about 2 sizes less stall, or about 400 rpm; say 2600 instead of 3000.

But that 35hp is gone forever......... unless you set your engine up for a tight-Q and run the 5psi more pressure.
Lets try something

Static compression ratio of 10.2:1.
Ica of 63*, 800ft, tight-Q
Effective stroke is 2.81 inches.
Your dynamic compression ratio is 8.22:1 .
Your dynamic cranking pressure is 165.15 PSI.
V/P (Volume to Pressure Index) is 144
Check it out!
First notice that the only change I made was to increase the Scr from 10.0 to 10.2, which brought about 5 psi.
The 5 extra psi is good for I'm guessing one cam size in power, but notice the VP came along for the ride, posting another 4 points. 144 is a very good number for cast-iron heads.

Here it is for 89 gas
Static compression ratio of 9.8:1.
Ica of 63*,tight-Q, 800 ft
Effective stroke is 2.81 inches.
Your dynamic compression ratio is 7.91:1 .
Your dynamic cranking pressure is 156.89 PSI.
V/P (Volume to Pressure Index) is 137

Please note;
1) this is an exercise in explaining options; not a build recommendation.
2) 140Vp makes a real nice streeter.
3) a 270/276 cam is a great powerhouse for a streeter. I ran that in my alloy-headed 367, and would still be running it today,20 years later, had it not dropped lobes for lack of ZDDP.
4) For a streeter;Scr over 10/1 with iron heads,is treading on thin ice and requires best pump gas.
5) A more relaxed build would be to run 89 gas giving you some head-room for less than optimum tuning skills, and for the occasional tank of bad gas.
6) tight-Q, by itself, is not the Holy-Grail of a performance engine. But for a streeter, it can take an undriveable on 91 gas engine, right into the fun-zone, by helping to NOT-CREATE detonation in the first place, so you don't have to tune around it. Read @Wyrmriders posts#31&38 again and pay attention.
7) to get tight-Q in your 65cc iron-chambers, you may need a step-D cup WITH a raised Q-pad, to reduce your Scr enough to run a 270* type cam. Thank goodness they make those now, and you don't have to pay a machinist to build them for you.
8) because so far only the heads are written in stone, you are in a prime position to set yourself up with a long-term, no changes required, powerhouse street engine; if you take some time to co-ordinate all the components and cut specs. Take your time and do it just once.