Fellow Dopers, I’m toying with the idea of fitting a replacement engine and gearbox combination into my 1966 Shelby GT350.
Now I know, I know… purists be calm… I’m keeping all the original engine and parts for “numbers matching” reasons but let’s be frank… an almost 40 year old 289 Hi-Po Windsor with a 750 Double Pumper Holley Carb is a pretty tired and agricultural setup. I mean, it goes like a jet, but holy shit it runs rich and chews the fuel. I’d rather pull the Windsor and Top Loader out, stick it in the shed under some shrinkwrap, and put in something more modern and more refined so I can use the vehicle as a daily driver if I want.
So my question is this - down here in Australia the major manufacturers like BP and Shell provide a 98 Octane Unleaded Fuel. I’ve been doing lots of research lately and it seems I can buy some amazing brand new “short” and “long” block Windsor combinations featuring alloy heads, and all manner of different compression ratios etc. Ergo, I’d like to know the following… on 98 Octane Unleaded Fuel, what is the safest maximum compression ratio that YOU would run on a brand new “custom built” Windsor “performance” engine - say, and engine in the 350 to 400 fly wheel horsepower range?
I’m currently steering towards a 302 block with the 347 stroker crank, fitted with all the go fast quality bits - in particular I’m very impressed with the Edelbrock Performer RPM camshaft, alloy heads, and Pro-Flo EFI system (which has a CPU already burnt specifically for the cam timing and c.i. capacity). But the engine compression is variable based on what heads and conrods you buy - that is, the heads come in 58, 60, and 62 cc chambers and the conrods are variable in length too - all of which determines final compression ratio.
So, fellow Dopers! Let’s have some fun! Come with me on an esoteric virtual engine rebuild and see what we can come up with!
All input is gladly welcome. I already have a rough idea of budget, but it’s fun to consider the “all bets are off” options too. 
My, how times have changed! I can’t believe I’ve had to bump this after 24 hours because no-one has posted - in a car thread no less!
What on earth has happened to the SDMB? It used to be that car threads were the most popular of all in General Questions.
Oh well, here’s hoping I get better luck 2nd time around!
Is 98 Octane a straight up comparison to U.S. octane ratings?
Octane like that used to buy 11:1 compression ratios without sneezing. You are going for 350 horses in a 302 motor. So, the compression ratio has to be higher than 11:1, but your question is “what is the safest” ?
I’d imagine it’d be quite high relative to the 11:1.
I’m not committing just yet.
Gearhead around here jump on other gearheads, so I’ll find your thread and gt some better answers.
“Safest Maximum” ?? Maybe think in terms of ‘most practical’.
Go with the longest rods you can use with the pistons and crank you get to use.
With aluminum heads, and 98 octane, I’ll bet you can run 11.5:1 without having to cut back on timing. If it knocks a bit, a simple alcohol injection kit will fix that.
Of course if you rebuild the old engine and tune it right, it should not be such a gas hog - running rich is not a function of the big carb. Jetting, maybe some vacuums leaks, broken power valve…
Can you post some pics?
For 62cc head chamber volume, 11:1 looks good at that octane level.
60cc about 10.5:1 and 58cc about 10:1.
I think I’m being fairly agressive…errr…really agressive You don’t see much above 11:1, so I can’t justify exceeding that as the upper limit, and all specs would have to be spot on…cam, etc. … Great alum heads and what not…
The availability of 98 octane keeps making me nudge my cap of 10.5:1 - 10.8:1 up a bit to - gulp - 11:1
The factory have been upping the CR with smaller CC heads when using aluminum heads - like in the neighborhood of 11:1 and we only get 91 to 93, 94 in a few select areas where Sunoco may be found. An even fewer select Sunoco’s sell GT-100, which is street legal 100 octane unleaded - with that I can take my 8:1 CR engine and blow 22 #'s of boost with no knock - and that is with iron heads - aluminum heads are more forgiving of knock.
Are you planing to do any work to the heads - it is a good time to do some bowl work, smooth around the valve stems, and port match the intake and exhaust - 3 angle valve job and back cut the valves - all helps and is all solid permanent benefit - not like N2O.
Is the 98 octane R+M/2?