Don Terrill’s Speed-Talk

can any one say how small the chambers of a 781 had can be made by flat-milling before you start getting into mis alignment issues with intake manifolds.my thoughts at this point would be to bump compression along with cam changes. if I raised compression closer to 9.5:1 from 8.9:1 would that give me the increase i'm looking for on it's own?and would the cam "work" better as is? could end up a upper-end overhaul to find more torque i'm looking for.
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Read my posts.

Here is a approx on the compression ratio and what to do.

If it is a .030 over (461) or .060" over (468) 454 BBC with those +14cc Dome pistons and the pistons at tdc are .025" below the deck at TDC and the heads are typical 118cc
And the head gasket is typical felpro 4.37x .040"
The compression ratio is 8.87 TO 8.98 :1 now

If you were to flat mill the heads to 114cc and check that
and use the thinner GM Chevelle 454-450HP LS6 head gasket .022" thick
the new cr will be 9.47 to 9.58 :1cr.
Milling those head down to be 114cc chamber volume is no the absolute limit but is reasonable.

Those heads can range from 118 cc to 123cc chamber volume so you have to measure the chamber before and after milling to know the real Volume.

The good old OEM GM NOS LS-6 454-450hp chevelle head gasket can still be found.
You won't find it at the GM dealer parts counter any more. (unless they have NOS)
There is a similar thin plain steel shim Detroit and Mr.Gasket steel shim head gasket too.

Install clean and dry on clean dry surfaces. No sealer is required. Re-torque head bolts after
a warm up-cool down cycle. Not that hard.
Read my posts on moving the current camshaft for this. It will have a profound effect
too.
if you do mill more than .030" off the heads then mill the intake surface of the head
too to correct alignment. The auto machinist will know how and how much for a BBC.
You will not know exactly how much to mill off the heads until you CC the chambers
to see the current chamber volume. They vary a bit. This is a guide.
Measure your stuff. Measure again after machining to get it right.
You can get a very good result if you do the details.

You can get what you want with the Dual QUAD with the right carbs and setup or go with the
Single 4bbl dual plane hi rise.
There is a vary cool dual plane Dual quad 2x4 intake in both low rise (C-66-O) and Hi rise design "performer RPM air gap"
Do not use the 750 VS holley carbs on your OFFY dual quad.
600's will work,,, AFB's are way better. The "Street Demon" carbs are cool and will work great.
2 x 625's are fine.

Cool free PC compression ratio calc tool for you
Here http://www.maverickracing.co.uk/compratiosoft.htm

If you want to get over 10:1cr you will have to swap the heads for the smaller chamber Closed chamber oval port heads (pre 1971) or swap the pistons for the larger dome pistons

You can google search to find the casting numbers you want EG: 1969 427 390hp "390" castings
The chamber volumes of these early pre 1971 closed chamber oval port heads vary a bit 98,100 104, 110 depending on what motor they are off of.
They flow about 10cfm less than the open chamber BBC heads but make great power and torque
and get real good with porting and larger 2.19x 1.72 valves.
The stock 1.72 ex valve is fine and the larger 2.19 in valve is a nice boost
with hand porting.
Again install with the .022" steel shim head gasket for effect.
if the piston is below the deck by .025" ish at TDC you want the thin head gaskets.
Not that hard.

You can get the result you are after by reworking what you got there.

looks like I will advance the cam 4* this winter and go from there.Hoping it brings the torque in earlier,will use my degree wheel but should end up at 106*icl.Might wait to cut the heads for awhile(unless it snows like hell this winter)I work in public works! I found a shop here in Conn. that has a CNC program for 049/781 so I'm sure he's the one who would know what I'm looking for also. would be nice to get the comp up to 9.5/9.7 area and no higher. the offy intake is a fully-divided single plane low-rise. why I am I hearing bad things about the holleys? just curious? I have spent quite abit of time getting them set-up,using pro-form main bodies with down leg boosters,vacuum tube in primary venture (just like the first 3310's) to secondary pods for correct signal.a balance line between pods(like ford427's) and replaceable air bleeds.also installed replaceable IFR jets to get air/fuel set with an O2 sensor. the BIG thing was I had everything already. those new demon "3-bbls" got my attention but in all honesty the Performer/q-jet (like fully-divided plenum) will be back on at some point, trying to straighten out low end torque to attually use the 3:08's again around town.THANK YOU for your help

Heads,

You might hunt up an old pair of -206 BBC Large oval heads whose closed, bathtub, chambers CC down around 96.7 to 98 cc's. Then install the thin MrG.,.020" thick shim head gaskets too! I have the shims in my 496 now.

As for cam's, I have two in my bedroom closet that I bought new through the years just for this type of farmer, work-truck engine building. Never did use them so they are just sitting there.....

The 1st is an ERSON part number Hi Flow AH!
Specs are, 284/218(maybe 220 now?), 111/111, .542'' lift.

And

The 2nd is an old Clevite part number 1065!
Spec's are 309/221/327/235, 106/115, .500"/.506" lift.

These are way old school cams that will flat do what you want to do, imho!!

And if you look around, the prices for them are right!!

pdq67

I would look at a small solid cam too, with a 4 speed bottomend is king on the street , with a 308 gear , , but idle vacuum is a little less critical , so I would tighten up the LSA , 108 would be tempting

INCREASE LOW END TORQUE:

Ditch the 2 x 4 intake manifold, go with a good quality dual plane manifold, designed for the carburetor you will use - no carb adapters.
RV style hydraulic lifter cam with little overlap.
Quadrajet, Carter/Edelbrock, Holley carburetors can all be made to perform well in a torque-producing engine. Carburetor builder/tuner must have total knowledge of how carburetors work PLUS a thorough knowledge of the carburetor being worked on . . . . . . . .

started to re-think my ideas. will go back to a dual-plane ;more then likely the RPM Q-JET with one of my q-jets.really don't feel like lifting the heads off! lol but re-thinking of going for a small roller instead. found this Howards grind;219*/227* 110*/106*@.050 .555/.555. 1600-5000 rpm range. I would think it would work out better with my static comp. and create the low-end torque. any thought?

I would go with the ERSON cam I mentioned earlier instead of a hy-roller, only because of the cost difference is all.

284/218, (or maybe now 220?), 111/111, 542" lift.

pdq67

I would start with Closed chamber oval port heads.I think it would do a lot.
One important thing is. right vacuum advance. It is very important for driving the feeling

The closed chamber BBC heads are dogs! The open chamber heads ALWAYS make more HP and torque. Use a piston with a small dome (LS6 style if on a budget) and mill the head to get the desired compression. You'll be glad you did!