ya prolly only be a few thousands of an inch. well two things im doing one its a head off another 4afe that has like 50K miles on it so i want it to be checked to make sure its flat and its gonna be used as a race engine so every little bit of performance i can get i want so if shaving the head can help me gain a horsepower or two might as well do it while im at it right. well ill do some checking then and see how close i can come without breaking the valves ha
thought id share a good how to guide to doing what i am going to do. for checking valve clearence
What Tools Do I Need To Be Able To Do This?
This is one of the rare instances that only simple tools are required. Some considerations are necessary that if you plan ahead of time your process will be easier. Read the list of tools, the engine parts needed and their descriptions below:
Short block with at least one piston/rod assembly installed.
It is required that on engines such as the big block Chevy that has different handed pistons that you do at least two cylinders so as to verify each design.
The cylinder heads, with milling and valve job complete.
All modifications need to be completed on the cylinder heads you plan on testing. You may use the head with light pressure testing springs, but chamber volume, surfacing, valve job, and lash settings, etc., must me complete or you will need to re-test.
Cylinder head bolts or studs
Whether you are using bolts or studs as your cylinder head fasteners, you will need to have some available. You may use used fasteners for this test.
Head Gasket (preferably a used one for this test)
A compressed gasket (used) will be more accurate than a new head gasket.
Camshaft and specs for the cam you are using as well as what rocker arm ratio you intend to use.
You must know what your cam lift values are going to be with this combo. If you plan on possibly using multiple cams through the season, it would be best to test each one. If you plan on running a high ratio rocker arm, you need to test with that rocker arm on the cylinder head.
For cutting the modeling clay
You need to place modeling clay on the tops of the pistons. DO NOT use PlayDoh, it springs back after compression and will not be accurate. Modeling clay is available at most art stores and will be perfect for this exercise.
You need to torque the cylinder head to specified torque values.
Crank Turning Socket or other turning device
You will need to spin the engine and a crank turning socket is the easiest way to do this.
Dial Caliper or other "accurate" measuring device
After you have rotated the engine and removed the cylinder head ... you will cut the clay in various locations and then you will use the caliper to measure its thickness.
There is something in the service manual about testing whether a head is flat by testing it with a ruler. You can shave it if it is off by so much and otherwise you should get a new head. I don't have the service manual at hand at the moment, so I can't quote the the numbers. Of course, the manual doesn't say whether the reason for discarding the head is clearance issues.
From feedback from ones that have done it before - most have taken just thousands of an inch off and switched to a thinner headgasket. Usually the result is bumping CR half a point increase. If you couple that with some low cc dished pistons (if I remember correctly - 7AFE pistons dished to 12cc's, 4AFE dished to 8cc's) to almost a full point in CR. Some have tried to get it to 11:1 CR, but that usually ends up running into some problems with proper flame propagation (quenching issues) and poor driveability (more likely due to timing issues).
Quick rule of thumb for most shaved cylinder head projects - for every 1 bump in CR (ie. 9:1 to 10:1) will net you about 5%-10% more power. Mostly dependant on head flow, overall design, and timing control. Adjustable cam gear would be great to have, but with the scissor-cam design of the FE-head engine - might be tough to get the most from it. Better than nothing though.
Couple the increase in CR with better cams, P&P, engine management for fuel and timing, standard bolt ons like I/H/E, make sure that fuel and fire are up to the job - all without compromising drivability - I'd say you should have no problem making an extra 20-25HP to the wheels. That is on the order of 30% increase in crank horsepower - which on the fuel efficient 4AFE, is HUGE.
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