I have a 400 bored .030 over four eyebrow flat tops, 74 cc afr 180 comp heads .039 head gasket and it clatters at about 2300 rpm with 93 octane fuel.  I pulled all the plugs and tied throttle wide open and cranked each cylinder over 3 times or so and the gauge reads about 198 to 200 on all cylinders.  Want to know if I did this right and if so how do I calculate my compression to see if I have to much for pump gas.  

Calculating compression the old fashion hand crank method rather than an on-line stop where you punch in some numbers and get an answer is as follows.

Total cylinder volume divided by the volume above the piston.

Total cylinder volume is the sum of 1) swept volume and 2) the volume above the piston.

-1) swept volume is the sum of the following equations:

+ bore and stroke (bore/2) squared, times pi (3.1416), times (stroke), times 16.4 conversion to cubic centimeters

+ Clearance volume from piston crown to cylinder deck nominal .025 with SBC is a similar equation (bore/2) squared, times pi, times (clearance heigth), times 16.4, equals cubic centimeters

+ Gasket volume is calculated the same as clearance volume equation above.

+ or - the piston crown shape's volume, flat tops add or subtract nothing, dishes add to the volume equation, domes subtract from the equation.

+ combustion chamber volume

All these added (or subtracted) together result in total cylinder volume.

2) The next equation is the summation of volumes above the piston when it's at TDC. This is all the stuff that makes up total combustion space volume and is the sum of all the above questions for crown to deck clearance volume, gasket volume, piston crown shape volume, and combustion chamber volume.

Taking this to work you've got a 4.150 inch bore/2 is 2.075 then squared is  4.3056, times pi 3.1416 is 13.527 sq. inches, times the stroke of 3.75 equals 50.725 cubic inches of swept volume per cylinder, times 16.4 is 831.883 ccs.

The piston crown to cylinder deck at .025 inch times 13.527 sq inches is .338 cubic inches, times 16.4 is 5.546 ccs

The gasket probably a bit bigger than the bore but ignoring that small amount the volume is 13.527 sq inches times .039 inches which nets 8.652 ccs.

The piston is a flat top so has no effect on the equation except for the valve eyebrows which are probably around 4 ccs.

The combustion chamber is 74 ccs, valve heads may reduce this some.

Wracking and stacking the numbers you should have a cylinder volume of 924.081 ccs divided by 92.198 ccs in the combustion space, which equals a static compression ratio of 10.023 to 1. I haven't taken into account how much volume the valve heads take up in the combustion chamber, these would tend to raise the CR a small amount.

For any cast iron head this is about a full ratio too high from premium unleaded, for aluminum heads iffy maybe a half ratio to high. But cam timing comes into effect as does your rather small ports for a large engine. As the cam gets into longer duration with increased overlap and late intake closing events, more compression is requred at idle and low RPMs to recover the lost "trap" mixture from  these events. However, your selection of small intake ports will increase mixture velocity at lower RPMs and the resulting ram effect will tend to "super" charge the cylinder in the low and medium RPM ranges when compared to a 200 or 220 cc port head.

Things you can do without ripping the motor apart are to richen the mixture, slow the speed with which the advance comes in and or reduce total advance, reduce intake temperature with an outside cold air source, reduce engine operating temperature.

Reducing engine operating temperature can be as simple as putting a 140 or 160 degree thermostat into it, but admittedly that's getting a bit chilly for good lubrication and drying moisture out of the oil. Another thing you can try is an oil cooler, the help this is that it lowers temperatures inside the crankcase and especially on the bottom of the piston crown. such a cooler should include a thermostatic valve that switches oil off from the cooler when the engine is cold and it should have an independent fan.

You can stiffen up the rear gears, the lower ratio combined with a faster turning motor increase the mechanical advantage the engine has to move the vehicle's weight, this will allow the throttle to be closed a bit which also reduces mixture density which reduces burn speed which reduces detonation tendencies.

I think your compression ratio is a bit high but should be OK, your cylinder pressures at cranking seem a bit high, I would have expected something more on the order of 170 to 180 pounds. This begs the question as to whether the block was decked or the heads milled, which would reduce upper end volume and increase compression ratio. The same question could go to rod length, did you make sure that between 5.56 (stock 400), 5.7 or 6 inch that you have the right piston. The pin hole gets run up and down the piston depending on rod length. A stock 400 pin position with a longer rod would push the piston too high in the cylinder which would reduce combustion volume resulting in a higher compression ratio. I'm just throwing things for you to go back and think about.

Bogie

The block has been decked and I was told that the piston should be .010 from top of bore.  6 inch rod and I have the pistons for that rod.  I notice that it doesn't clatter until it warms all the way up to operating temp which is about 190-200.  I have 373 gears but havent't got them installed yet.  I have a msd 8361 dist. and I have been playing with the springs and I have it at max advance comes in at about 3000.  The initial is at 16 and total is 34.  If I bring intial to 14 throttle response is slow and it still clatters. Head gasket  is fel-pro 1014, cam is comp cams 12-422-8.  Lately I have been trying with the spark plugs and the ones I am running now are NGK 5155.  I think the are to hot because several of them are snow white after normal driving conditions.  I have just been kind of trial and error with the plugs because I haven't been able to find exact info on how they should burn with these heads and combo.  I started out with AC 41-629.  I went to the different brand because I caouldn't find anyone at local part store that could give a colder or hotter ac plug and know what they were giving me because ac changed the part #.  My next plug to try is a Autolite AP 3923 wjich is colder than the plug I started with. It clatters with all different plugs I have tried so I was thinking I would try a colder plug to stop it from rulling lean until I figure out what is what.  The ac plug, 3 and 8 were snow white and and the others had light sutty look.  I don't know where to go on the plugs, just tryin.   Its a shame that you know guys who claim to be big time racers and engine builders, but you offer to pay them what ever the charge  to HELP you tune your vehicle and you still can't get them to do anything.

You can easily pull coolant temp back to 160-180, I presume you live somewhere in east Texas from your handle, having spent a fair chunk of my life outside Houston in South Shore Harbor (i.e. League City) I'm pretty familiar with the warm to hot and humid weather so you could ease back on operating temp without ill effect. I wouldn't necessarily recommend that cool if you lived up north.

Plug reading, timing and fuel mixture rather go together. Problem is that getting these things straight isn't a simple three way choice, mathematically this is a (n+1) cubed combination so the quantity of choices gets too big too fast. The white plugs could result from too hot a heat range, too lean a mixture, too much advance which can be either or both too fast an input or simply too much which I guess can be thought of as too much for the RPM. The sooty plug can be too cold while the mixture is still too lean and the timing too much. Plug color tells you something, you've just got to figure out what

 
I'd do three things in this order:

I sure do appreciate all the info.  WIll pick up the thermostats in da morning, and work on getting the cash to get the gears installed.  I stay in far east texas about 20 minutes west of Shreveport. I will limit the driving until I get them installed, because I have never done it before.  I know a guy that knows a guy that has a chasis dyno and does it for 60 bucks so I wil get that done also.  I was looking for some info on the proform main body about the adjustable air bleeds and etc.

Thanks a bunch, don't know what I would do without you guys, since you can't pay people to do what they say they can do

Well guys im back.  It's East Texas406. Had to make a new screen name, haven't been able to login since the changeover of the board.  emailed tech dept. but havent heard back yet.  Well since the last time I have went to a 180 thermostat and installed the gears myself.  Did a little online research and reading and I installed my eaton posi unit and a set of 373 gears.  It has eliminated all of the clattering and it pulls pretty good.  Have a new fuel pump and regulator to install next.  On the gears I drove it some miles and it has a lite roar and low rpm, cruising at about 35 mph.  As long as it is under load at 45 to 70 mph, I have no noise. I pulled the cover off and it is and you can see where it is running  in the center, maybe a little high and the lash is set at .009. I installed new bearings when I installed everything.  Any help would be appreciated.  

The rear end sounds good, a little low on the tooth is perhaps a bit better as the loads are placed where the tooth is thicker. But you reach a point of diminishing returns against the effort to "fix" things; I'd leave it alone.

The gear ratio change demonstrates the relationship between how the engine was set up and what gearing it needs. Basically with the original gears the engine was lugging all the time. It sounds like it's happier.

I'm a big fan of a girdle on the rear end. You can get one at a decent price, 170 bucks give or take, from Summit. These things really stiffen up the center section, you'll hear a significant noise reduction as a result, and they reinforce the spool's bearing caps adding a lot of stiffness to these otherwise rather marginal cast parts. Get a tube of Permatex red silicon sealant for the perimiter bolt face as using a gasket doesn't allow the necessary metal to metal contact needed to transfer loads from the cover back into the case. Some old fashion gooey Non-hardening Permatex sealant on the threads of the bearing cap reinforcement bolts will insure that they don't leak oil, you can also use that stuff on the fill and drain plugs. Finish this up with a couple jars of Lucas Shock-Proof synthetic diff oil and you're good to go.

Good job, enjoy
Bogie  

Hey guys, I haven't been able to get my truck dynoed to check air fuel mixture, and to check my timing curve.  But I have been trying to read my plugs and what I am getting is white plugs after I drive it through all gears to about 5200 rpm and shut it off and let it cool and check plugs.  It starts to fall off on power at about 5200 rpm and I have tried colder plugs and jets all the way up to 76/80.  Initial timing is 16 and total is 34 with MSD distributor pn 8361 and 6AL box, with 373 gears comp hyd roller ext. energy 270 with 495/502 with 1.6 rockers.  AFR 180 comp heads and air gap and double pumper carb, with proform main body  

I think I solved the problem.  I ordered a new proform baseplate due to slack in old one where accelerator cable hooks up so I installed new baseplate and with no tuning it performs like a totally new vehicle.  Extremely great throttle respons and pulls good up to 6000 and I mean it is like I have another 100 horses and on the top end this things accelerates like a rocket, even with the small ext. energy 270 cam with 495/502 lift with 1.6 rockers and a dual plane air gap.  I am very impressed with the performance of the afr 180 comp. heads.  I tuned it today and idle at vacum  is about 16psi at about 800 rpm and initial timing is at 16 and total at 34.  I have the 750 with proform main body, metering blocks. and baseplate.  One question, I install 6inch scat rods and I was told that there is no effect on the street and wanted to know if that is true.  From a dead stand still and just stomp the gas she smokes my bf goodrich tires like the road is wet.  This thing has extreme torque and I am satisfied with it.  Thinking about building a big block 427 to see what all the fuss is about on the big blocks  

Really glad to hear it's running right and smoking tires.

Long rods are an interesting subject. There's two major benefits but neither are earth shaking, more a tuning kind of thing.

First, is really two tings in one. The longer rod makes a better angle between the piston and crank which provides better force transfer from the piston to the crank on the power stroke and reduces rod angularity on the up stroke which takes some side load off the thrust side of the piston and probably helps the rings stay snuggled against the wall.

Second, the piston dwells slightly longer at TDC and BDC. At higher RPM at TDC this helps the breathing with a long overlap cam. At BDC it provies a bit more exhaust blow down time before the engine has to start using power to finish forcing the exhaust out. At both ends the slower pass thru the dwell time eases the dynamic loading on the crank which helps to eliminate shock induced unbalanceable forces.
The down side is something you encountered, at lower engine speeds or with insufficent gearing there is a greater tendency toward detionation because the piston is setting longer thru the TDC compression cycle where the mixture is heating and gaining pressure while realtivly trapped waiting for the piston to start down on the power stroke. It ain't much just millseconds but that's all it takes to make the engine pingy.

Bogie