ok, first my cam stats:
Cam Style: Mechanical flat tappet
Basic Operating RPM Range: 2,800-7,200 RPM
Intake Duration at 050 inch Lift: 252
Exhaust Duration at 050 inch Lift: 260
Duration at 050 inch Lift: 252 int./260 exh.
Advertised Intake Duration: 290
Advertised Exhaust Duration: 298
Advertised Duration: 290 int./298 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.540 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.558 in.
Valve Lift with Factory Rocker Arm Ratio: 0.540 int./0.558 exh. lift
Lobe Separation (degrees): 110
Intake Valve Lash: 0.016 in.
Exhaust Valve Lash: 0.016 in.

engine: 406
bore: 4.155, stroke 3.75, cyl head volume 64cc, rod length 5.7, block not zero decked (piston .025 in the hole).

using

* RD = 1/2ST * (sine ICA)
* RR = 1/2ST * (cosine ICA)
* PR1 = sq root of ((RL*RL) - (RD*RD))
* PR2 = PR1 - RR
* DST = ST - ((PR2 + 1/2ST) - RL)

from Dynamic CR yields a dynamic stroke of 2.255 (i think).

Questions is: in this equation, where they want ICA, is that Advertised Intake Duration: 290, or is it another number.


If it is the 290, that yields me a dynamic compression of 7.08:1 with a static of 11:1 with the 4cc flat tops, do I need to run more compression ? Can I run more than 11:1 on pump gas with iron heads ? Whats the deal here.


Thanks for the help

 

I think I answered my own question by looking at the comp cam card
Valve Timing At 0.015
Open Close
Intake 39 71
Exhaust 83 35

i replaced the 290 with 71, and got 8.5:1 with an 11:1 static CR, I think this is right this time, and it looks like my combo has good dynamic CR and will be fine on the iron heads on pump gas even at 11:1!

 

yep, you got it right. That's a pretty huge cam, so that explains why you can get away with high SCR, due to your ok DCR.

use a thin head gasket for better quench if you can. Polish those combustion chambers too.

 

I've been looking and I cant find a .015" head gasket, even though thats what I need for proper quench .... I really dont want to bring the block BACK to the machine shop to have it zero decked. Any idea where to find a .015 head gasket ?

 

you can't be looking too hard.

On summit I searched, you can get a head gasket from .015 to .051", not quite in .001" increments, but close.
Gm steel shim gaskets (factory stuff) is .015". Felpro composite aftermarket stuff is probably .039-.041". Everything inbetween is a nice mix of composite, steel shim, copper etc. search on summit, get a p/n and brand, then drop by your local parts store.

 

i noticed the .015 in a 4.100 bore w/ no steam holes, but with the 400 i need a 4.155 bore and steem holes. Should i just get the 4.100 bore one and hog it out and drill the holes ?

 

Im quoting this from another site.

Something you should think about if you are attempting to run pump gas.

 

it's pretty tough to "drill" .015" thick stuff, and opening up the bore size on that would be tough.
Most gaskets have a 4.166" bore, hmm, you should be able to find one like that. Call up a gm parts guy and ask for a head gasket for a 400SBC, tell him you want a steel shim style, that should get you the right one.


and yea, low temp t-stat, CAI, polish chambers and piston tops if possible. Avoid lugging it with large load, high timing, high temp, low RPM. (I don't think you'll be doing that with that car anyway, but that's the killer).

 

Here is my two cents. Personally I think that DCR is to high for iron heads. It would be OK if you were running aluminum heads. Next I would get the blocked decked. You need to make sure it is square with the crank. Also it will help with your quench and selecting a proper head gasket. I have a good DCR calculator but I don't know what thickness of head gasket you used.

One more thing 400's usually run a little hotter than say a 350 SBC.

 

so should closer to 7.9:1 be better for DCR ? thats arounds where im getting with 15cc dish pistons, and a .021" gasket (pistons .025 in the hole). Let me know if that sounds like a better setup.

 

My research has been regarding aluminum heads. I have seen 8.00DCR with iron heads but you have a 400 which may be different. Just to a lot of internet searching. Excellant posts out there.

 

You're headed for a disaster in the real world.

You're trying to build a motor based soley on DCR theory (using only the intake closing point) without taking in all the other factors that effect actual peak cylinder pressure in the *running motor*.

Build a true 10:1 400 motor with a 0 deck clearance. (.040" quench clearance) Open up you heads to 68cc. (Do a little deshrouding.)
using a -15cc piston and felpro 400 gasket.

Use this camshaft comp cams #12-502-5 installed 4 deg advanced on a 102intake c/L. You'll have more torque and power, without exessive cr.

You can look up the cam and calculate the DCR yourself. Your static compression ratio will be 10.07:1.

 

i dont actually think that i'm in too bad of a position right now. Im looking at the following.

1) the cam i listed stays
2) heads staying at 64cc
3) 15 cc dish pistons
4) either run a .021 head gasket, or deck it to .005 and run a .041 gasket (likely)

either way it will give the following
STATIC COMPRESSION RATIO 10.331
DYNAMIC EFFECTIVE COMPRESSION RATIO 07.888 w/ 5.7 rods
QUENCH .046