11.5 compression, Iron Head, 91 octane

[Topsp33d]

Okay give it to me straight, how feasible is this if I run a cam with an IVC of 74*? I can come up with 8.5 dynamic compression. What if I back timing way off for street and run race gas at the track?

The heads have dual quench pads and 11* valves so they are efficient fast burn style.

[mt-engines]

Well.. disregard the dynamic compression.. whats important is vehicle weight, gearing, tire size, converter speed. Altitude climate etc.

[Topsp33d]

3000 pounds give or take
3.5 rear gear
28” rear tire
TKO600 (2.87, 1.89, 1.28, 1.0, .64)
2500 feet above sea level
Tucson AZ where the humidity is always low and I plan to drive anywhere from 60s to 90s farenheit

[KnightEngines]

Ouch, manual trans, I probably would want comp closer to 11;1.

[mt-engines]

Ouch, manual trans, I probably would want comp closer to 11;1.

Especially with that hot under hood air temps Arizona brings.

[1980RS]

Put in a cam with a 114° LCA it'll run great. My last one did with 11:1

[Firedome8]

Have cam king grind the cam and dont put as much advance in it possibly a retarded position this will work better than retarded ignition timming. Possibly water injection ? Take it to a chassis dyno for initial tuning.

[Topsp33d]

Ouch, manual trans, I probably would want comp closer to 11;1.

Well if I find 3cc in the chamber to grind out I can actually hit 11:1. Chambers poured 52cc and are dual quench so I kinda want to open the chambers up to a ls7 shape. Might find those 3cc or more

Put in a cam with a 114° LCA it'll run great. My last one did with 11:1

What’s the big lsa do, reduce overlap for cleaner air? Or is it an earlier opening to relieve heat?

[F-BIRD'88]

If all it took was a later closing intake valve a Pro Stock racing engine would run on 87 octane gas.
It doesn't. Your engine is going to want 100 R+M/2 octane gas.
For street use on a pump gas retard the timing as required to avoid detonation.
4-6-8 deg as needed.
Water/methanol injection does wonders too.

[HQM383]

Is the bottom end together yet?

Grinding on the heads is hard to put material back if you want that 52cc’s in the future without having to surface the head. Haven’t mentioned what engine but can the pistons have 3cc’s taken out somewhere?

Of course if it’s a crap chamber then reshaping may be the best course of action.

Went full circle there didn't I. Anyway the piston might be an option.

Is the an IVC of 74* at .050"?

[Tuner]

Ouch, manual trans, I probably would want comp closer to 11;1.

Well if I find 3cc in the chamber to grind out I can actually hit 11:1. Chambers poured 52cc and are dual quench so I kinda want to open the chambers up to a ls7 shape. Might find those 3cc or more

Put in a cam with a 114° LCA it'll run great. My last one did with 11:1

What’s the big lsa do, reduce overlap for cleaner air? Or is it an earlier opening to relieve heat?

Depending on other elements of cylinder head design which discourage knock, such as port shapes which induces swirl and tumble, chamber shape, etc, for best anti-knock behavior it could be better to have more quench deck area than reduce compression ratio, and definitely better to have tight quench. Quote Smokey Yunick, ".035" to .040", minimum preferred."

[HQM383]

If all it took was a later closing intake valve a Pro Stock racing engine would run on 87 octane gas.
It doesn't. Your engine is going to want 100 R+M/2 octane gas.
For street use on a pump gas retard the timing as required to avoid detonation.
4-6-8 deg as needed.
Water/methanol injection does wonders too.

Does this use the formula:

Static compression ratio + cylinder head material = fuel octane rating?

[Tom68]

Stroked Windsor with a single plane and a decent size cam, should get by, don't put a dual plane or a long runner efi manifold on it.

Why not soften the chambers and then it'll be ready for a shot of nitrous as well.

[rebelrouser]

First I am not a wiz bang engine builder who claims to have it all figured out.

I have built a lot of street engines and while I agree dynamic compression is not the only factor in choosing a octane fuel for an engine it is a factor, as dynamic compression goes up octane requirement go up as well, at least in my experience. I have also built several truck pulling engines that ran in classes requiring pump gas only for fuel, and most had close to 12 to 1 static compression, but low dynamic compression and they worked, a couple did very well and won a lot of hooks.
I may get flamed for being simplistic but most street engines that I would have a concern for spark knock I do this simple thing, input GOOD info into my performance trends engine program, it will predict if spark knock may be an issue and generate an advance curve to take into account what octane fuel you are using. Then set up the distributor or set the timing maps in the computer to match that curve, and knock on wood it works very well. Most issues with knock are not at WOT, but midrange and low speed lugging.
I had a student that built a 300 ford six cylinder for a show truck, and it knocked terrible, did the engine program, fired up the distributor machine set the curve and it ran perfect afterwards.
Don't have a distributor machine, then have a buddy raise the rpm at 100 rpm increments and use a timing light to plot the curve on graph paper, used to make my students do that so they understood advance and how to use a timing light.

[F-BIRD'88]

If all it took was a later closing intake valve a Pro Stock racing engine would run on 87 octane gas.
It doesn't. Your engine is going to want 100 R+M/2 octane gas.
For street use on a pump gas retard the timing as required to avoid detonation.
4-6-8 deg as needed.
Water/methanol injection does wonders too.

Does this use the formula:

Static compression ratio + cylinder head material = fuel octane rating?

No formula.. 45 years experience.