boondocker

What is the actual head volume for 7A heads?...I'm getting a lot of different opinions off the web. I'm finding my new build is very sensitive to octane and according to my calc's my compression is 10.92 (too much for the cam I'm running).
Bore = 4.087
Stroke = 3.385
gasket compressed = .040
head volume = 69
deck = .020

...and flat tops

MDchanic

I think that it varies enough, especially if you had any work done, such as valves or seats, that you've really got to measure it to be sure.

- Eric

boondocker

The heads were redone, 3 angle, new seals, 5thou cleanup etc...
I mistyped on the calculator, head gasket diameter...estimated compression is now 9.88. I live in a small town outside of the city and the expensive gas here tends to sit, which I suspect effects it's quality. The exhaust pops when the air filter is on, when off it runs fine. If I get my higher octane gas from the more travelled gas stations, the engine runs great with the air filter on or off (I've confirmed this on many fill ups).

cutlassefi

What cam are you running?

boondocker

comp XE262

Tony72Cutlass'S'

The tech section on 64-90 heads says that they are 64cc. But i do agree with eric, Unless you have a bone stock engine, i'm sure it has changed a little.

bigD

it's my understanding that the big block heads tend to be a larger cc than rated, i don't know if this holds true for the small blocks as well.

have you tried any fuel additives with the lower octane gas? maybe a can of seafoam or marvel mystery oil with each fill up will cure what ails ya? small price to pay...

Tony72Cutlass'S'

For what it's worth, I dumped that rislone ZDDP stuff into my crankcase to "apparently" make my oil better suited for flat tappet camshafts.

But Seriously, my lifters stopped ticking, engine sounds better.

maybe It's just me, or maybe my car just badly needed an oil change. But for 7 bucks a can i'll take the hit.

J-(Chicago)

Stop into your local paint store (not big chains like home depoo)
Sherwin Williams is a good place to go, but an auto paint supply house would be best and cheapest.

You can pick up a 5 gallon bucket of toluene for around 20-30 bucks. It's 114 octane by itself.

Mixing at a 10:1 ratio gets you 2 extra points of octane.

89 octane X 10 gallons= 890
114oct X 1gal= 114

890 + 114 = 1004

1004 points ÷ 11 gallons = 91.272... octane

boondocker

This is a solvent, right? Is this commonly used as an octane booster? This would be a lot cheaper than the extra .10-.15 per litre I pay over 87 Octane.

AZ455

Why not just buy an oil that contains ZDDP already and use it every oil change? How much does the Rislone ZDDP add to ~5 qts?

Shell Rotella T 15w-40 oil is 1200 ppm ZDDP. You may get more out of the additive, don't know.

Edit: According to page two of http://www.barsproducts.com/tech/4401_tech.pdf you will get a bit more ZDDP from the additive than the Shell oil.

J-(Chicago)

Correct. Toluene is one of the ingredients in gasoline that gives it's octane points.

You're basically just putting an extra shot of rum in your cola for a better "effect".

Just be aware, that it takes away cylinder wall lubrication as a trade off, so don't go crazy with it. A lot of race cars used to run just toluene, but they got rebuilds every other race.

J-(Chicago)

Or you could check the status of the IOGEN corporation in your Canadian backyard, and eventually go to an e-85 conversion. They're putting a huge effort into E-85 up by your neck of the woods.

boondocker

yeah i know, i'm surrounded by cornfields.

joe_padavano

What, you're afraid that something on the web might not be correct?

All the published numbers trace back to the factory and/or NHRA blueprint numbers. The as-cast volume of ANY head will just about always be larger than the blueprint number to allow for resurfacing.

Tony72Cutlass'S'

Cool! I'm not sure if we get shell rotella oil up in these parts. When i go to the hardware/auto store, the rislone stuff is all i could find.. Figured it would be better than nothing.

What does the shell oil cost per gallon?

yankees

NHRA.com has all of those specs for the #409147 7A heads


Intake Volume CCs = 153

Exhaust Volume CCs = 138

Vega

Cold starts are worse though, not a big problem where im at but in canada i could see it getting annoying

joe_padavano

And yet, neither of those numbers is the combustion chamber volume, which is what the OP asked about.

yankees

64 CCs according to 442.com and the factory can be anywhere from + or - 2ccs. At least that is what we find on our BBC closed chamber heads 106-109cc

It's a simple measurement at any machine shop or at home. Buret, Vasoline and a flat piece of clear plastic. Don't forget you valves and spark plug.

cutlassefi

68cc is more the norm. And that XE262 is too small for almost 10.0:1

Vega

what might a good comparable cam be for that compression? And does SBO and BBO make a difference on cam choice? (for example, slightly larger cams for BBO slightly smaller for SBO) Im thinking something in the mid-270s

Warhead

The blueprint spec is for NHRA stock class specs, and has nothing to do with what was installed on vehicles. This is the minimum cc's allowable by NHRA inspection in tear down, when they verify a car is within "the rules".

All #5, #6, #7, and 7a heads will be around 68cc's from the factory.
Throw in valves, and seats being cut, thicker gaskets and it will take more than a .005 cut to get it back to what the factory made it.

Jim

coppercutlass

now im not sure on this one but cant you run a thicker gasket if that's the desired cam you want i know they make gaskets thicker than .040 but price might be a tad bit more

cutlassefi

[QUOTE=Vega;333196]what might a good comparable cam be for that compression? I'd do something around a 220/228 at .050 depending on gear etc. And does SBO and BBO make a difference on cam choice? (for example, slightly larger cams for BBO slightly smaller for SBO) Yes, but also 350 vs 403 or 400 vs 455. Im thinking something in the mid-270s. That's only part of it. The at .050, intake centerline and lobe sep also matter as well.

Vega

True. I was just going for a general size as its easier to match size with compression and then you can go in and work the specifics to your valvetrain and all

I would think 10.9 would be too much compression for street gas. Idk maybe gasoline in Canada is different than in the US. I was planning to run 10.5 and ive even 2nd guessed myself on that thinking it might be too high for pump gas

cutlassefi

Marginal with aluminum heads, no way with iron.