Realistic Octane Requirements

[MadBill]

Use the correct old gm air cleaner base so you can use a high rise dual plane manifold. None of the aftermarket bases are right or as good as this gm muscle car air cleaner base.

You mean a drop base air cleaner? I remember watching a video of some different filters and bases tested and the drop base showed a power loss over a standard base air cleaner. Whichever you use, fit the tallest air filter possible. I see a lot of C3 owners going with a 4" filter and a 2" drop base, it seems like.

An apples to apples comparison would be a 4" filter with a 2" drop base vs. a 2" filter with a zero drop.

[grandsport51]

See Old HRM Comparo.

RL-11458-93492

[grandsport51]

I apologize it didnt post as a link

https://www.hotrod.com/articles/air-cleaner-assembly/

[F-BIRD'88]

My real testing on various cars says different.
I
This is the best air cleaner, and it also FITS the car.
You really just need the base.
Remove tge choke horn (holley) or use a hp style carb body.

[Bill Chase]

I am starting a new SBC 400 build and have some logistics questions.

The goal is to have a reliable and fun street motor that also teaches me a lot about building an engine. Its semi budget but more about learning how to build an engine, something I've never done before.

I just had the donor 400 CI block cleaned and checked for cracks etc and it looks like it will clean up nice at 0.020" over. The Machine shop is checking the line bore (machining if needed), decking and boring cylinders with plate. They are wanting me to mic the pistons to machine the bores to size. I am having some trouble identifying the correct combination such that I don't have to use race gas nor octane boosters.

The rotating kit I'm leaning towards is internally balanced, 4.145" Pistons, 5.7 Rods, Cast Crank from eagle (Kit B13470020 )

This kit, set at a deck height of 9.025", and assuming a head gasket at 0.043" Thick, with 64 cc Vortec heads equates to a CR of ~10.8 which is about what I was targeting.

A deck height of 9.025" and 0.043" Head gasket is a squish of 0.068" which from some of my reading seems to high? If I reduce this further with a smaller head gasket my CR goes to ~11 really quickly. Will this be too much for a street engine with 91-93 octane pump gas? Does anyone have any experience with something similar?

My second question comes in debating hydraulic roller vs flat tappet and cam specs. I am looking at Comp Cams K12-408-8 which is a milder roller cam. Since this will go with a Vortec head I am planning on having to cut the valve seats to allow for over a 0.420" lift.

With the faster closing exhaust will this act to artificially increase the compression ratio further, driving up the octane needs?

These may be myself thinking to much into these things, so please let me know some of your opinions. I've learned a lot reading at speed talk so all is appreciated.

Not an expert but I will tell you how I do it. I use performance trends engine software. Plug in all the parts I am going to use. Yes the program gives you projected HP and Torque, but it also calculates dynamic compression, and projects a advance curve to keep it from spark knocking. So I take the time to CC heads and get an actual static compression ratio, plug the numbers into the program with the octane fuel I want to use, generate the advance curve, put my distributor in the distributor machine and play with the springs until it matches what the program wants. It has never failed me yet. On my last EFI project, simply took the program advance curve and adjusted the timing maps to fit, worked like a charm.
This method may not be perfect, but it beats an educated guess. It also tells you what is possible long before you buy parts and melt pistons.

What software exactly is it you're using, I'd like to get a copy of it?