Blue73Red

My compression ration calculates out to 11.3 to one. Can I run 93 octane pump gas? If not, can I use a thicker head gasket to knock down the CR? How much will thicker head gaskets reduce the CR?

Thanks

The Money Pit

I run 10:1 with aluminum heads and if I run too much advance on hot days I can hear slight pinging. If you're not running aluminum heads in Florida,I'd drop that compression down to under 9:1.
Gaskets aren't going to help you here.

GrandSportC3

I'm running around 10.25:1 compression on my engine with iron heads.. and I have no pinging at all.. Well - I only use Chevron Gas...

The Money Pit

When I was designing my 406 I used a simulater software program to play with cams,CR etc,and it generated hp outputs and recommendations for problem areas.I was surprised at how wide a range of CR I could run with the 406 and not have an issue with octane.The range is nowhere near the same with a 350. I have no idea why,but with the cam I chose I could run to 12:1 without pinging. Interestingly the higher CR produced slightly slower ET estimates than the 10:1 I ended up with. Guess the cam was working against the added CR.
Now I was running the simulation with 110 degree LC on the cam,and I'm sure if you run 114 ,you may be able to get by with 11:1 in a 350.What was the LT-1 running back in 70.Of course the gas we have now is sooo much better. :lol: :lol:

Matt Gruber

does the car run well on 94? that is very important missing info.
or are you building a motor from scratch?
or are you just guessing what's in there?

Robert N

11:1. When mine is rebuilt, it will be built to spec. I have a local station that can supply 100 octane and the car is a weekend toy. I can sacrifice power and drow the advance for use on lower octane or use additives known to work.

The Dude

11.3:1 won't necessarily cause a problem with pump gas just because it's a "high" compression ratio. Other things come into play, such as your cam specs, your heads, the shape of your piston tops, your combustion chambers and the quench distance. Having said that, though, I would seriously consider using aluminum heads on your buildup if only because the rule of thumb is that they will allow a CR of one full point higher than comparable iron heads. BTW, my 406 has a 10.5:1 CR and it's perfectly happy with 91 octane pump gas.

OatBoy

thats true, a lot of duration on the cam will bleed off a lot of pressure at lower rpms and reduce the risk of pinging, still that seems a little high to me.

Blue73Red

i am building it from scratch.
The parts kit that i ordered says that the CR will be 10.7 with 64cc heads. I am running 462 64cc double hump heads and the Summit 1107 cam.
I did not take into concideration that the pistons are not flattop. So the correct CR is in fact 10.7.
According to Desktop Dyno 2000, if I take 10.7:1 CR and use a thick head gasket (.051) with a piston opening of 4.2, the CR will drop to about 10.0:1 :crazy:

Matt Gruber

.025" deck?
with that 234x244x114 cam
it sounds about right to me. with a .039 gasket.
it needs decent CR with that large cam.
However, there are endless opinions on this topic. So, you may end up :confused:

Twin_Turbo

stock deck (roughly .025) + piston slightly down the hole at TDC (not at 9.000) + 0.039 gasket = >.060 quench height!!!!!!!!!!!!!

Matt Gruber

some articles suggest everyone needs ideal quench. not true!
i ran .025 deck and .038 with no problems.
Keep in mind the famous Hemi has no quench area at all!
would like to see .015 head gasket tried in this in the future.(as i now have in mine)

Twin_Turbo

the hemi doesn't have quench since it's not a quench type head but has hemispherical chambers. Possibly this is the only drawback of the hemi head, the absence of a quench area makes that they miss out on the extra turbulence for better mixture distribution and increased flame travel. There's no such thing possible as ideal quench, ideal is no quench at all, piston hitting the head. There however is a range for good quench. Quench is essential to making power and preventing detonation. Sure you can run stock deck and the head gasket you want but what dcr? Don't care about CR because any long enoigh duration cam will lower the cylinder pressure in the operating rpm range so you can be detonation free.


[Modified by Twin_Turbo, 4:56 PM 8/17/2003]

jimtreber

My 406 was built with a 10 to 1 package. But when assembled and cc'ed (with fluid), it came out over 11 to 1, around what you have on your engine. Unfortunately, I was using Rhoads lifters which, at lower rpm, drops duration and overlap but increases your cylinder pressure which is where the octane problems are. So Comp Cams ground a special cam for me with more overlap. I also found that adding 1 gallon of 105 racing gas to 15 gallons of 93 unleaded gave me all the octane I needed. The small amount of lead in the 105 helped make a big jump.

1976 406 TH400 3000stall switch pitch, 4.11, nitrous

Matt Gruber

tips for high CR
1. block heat riser
2. cold air intake
3. use power valve to richen
4. use short tip plug on pesky pinging piston.
5. use forged pistons with nodular iron top ring
also
unshroud the valves to gasket will add 1 or 2 cc's
consider modern high swirl heads, aluminum can take more C :cheers:

CHRIS718

I HAVE BUILT SEVERAL 406 ENGINES UTILIZING A TRW FORGED PISTON 2349 F/ 30 AND A2352 F/ 30WITH THE FACTORY ALUMINUM VETTE HEAD AT .040 OVER AND STEEL SHIM GASKETS NETTING 11.0 AND 11.9 SWEPT VOLUME COMPRESSION RATIOS AND BETWEEN 32 AND 34 DEGREES OF TIMING SUCESSFULLY WITH 92 OCTANE AND NO DETENATION.THIS WAS DONE 3 OUT OF 5 TIMES WITH AN OFF THE SHELF CROWER CAM SELECTED BY REED OLIVER OF CROWER CAMSHAFTS.MOST NETTED AT LEAST 16 MPG ON THE HIGHWAY OR BETTER AND RAN HIGH TO MID ELEVENS IN THE QUARTER.THE KEY WAS NOT OVERFILLING THE CYLINDERS AT CRUISE RPM AND USING THE EXTRA ENERGY AVAILABLE FROM A HIGHER COMPRESSION RATIO TO MAKE MORE POWER WITH LESS FUEL AND THROTTLE ANGLE.DAVID VIZARD,IF ANYONE HAS HEARD OF HIM ,A WELL RESPECTED CYLINDER HEAD SPECIALIST MADE ME AWARE OF THIS TECHNIQUE ABOUT 10 YEARS AGO.THE 400 CAN BE MADE TO PRODUCE HIGH HORSEPOWER AT THE 3500 TO 6500 RPM RANGE AND STILL MAINTAIN AN ABUNDANCE OF TORQUE AT A CRUISE SPEED FOR EFFICIENCY AT 2200 TO 2600 RPMS.THIS ALSO WAS ACCOMPLISHED WITH 1 AND 5/8 AND 1 AND 3/4 INCH HEADERS AND A DUAL PLANE MANIFOLD WITH CARBUERATORS RANGING FROM 650 TO 800 CFMS.OF COURSE WE DIDNT RUN IIS WITH A 650 BUT WE DID WITH A MODIFIED 750 AFB IN ONE COMBINATION.11.56 AT 116 MPH.VERY RESPECTABLE FOR A CAR THAT GETS 15 MPG AND DONT PING .IN MY OPINION A 9.5 CC DISH AND A 2ND DESIGN CORVETTE ALUMINUM HEAD WITH 2.00 AND 1.55 VALVES IS ALWAYS THE WAY TO GET AWAY WITH IT .IN ESSENCE YOU ARE CREATING A SPHERICAL COMBUSTION CHAMBER WHICH PRODUCES EXCELLENT QUENCH SWIRL AND THE MOST AMOUNT OF CRANKSHAFT SPINNING FORCE EXTRACTABLE FROM THE AMOUNT OF INGESTED FUEL.THIS TRANSLATES TO LESS REQUIRED IGNITION TIMING AND IT REVERSIONAL INFLUENCE ON AIR INGESTION INTO THE MOTOR.W3E ARE GOING TO HAVE AN ENGINE COMBINATION SECTION AT http://WWW.CKPERFORMANCE.COM SOON THAT SOME WAY FIND USEFULL.ALL ARE INVITED. :rant: :cuss :cheers:

HDIronman

I have L2304F forged pop up pistons in my 355ci. CR with 64cc chambers would be 11:1, however I have 67cc chambers and I am using an .051 head gasket which adds 11.3cc to the chamber. This gives me approximately
10.23:1 static CR. I have a long duration COMP CAM 280H grind cam and my dynamic CR is around 8.6:1. I have no ping at all using 93 octane fuel.
:cool: