Ford Repair Questions? Ask a Mechanic for Answers ASAP
I'd say you have high blow-by, with your uneven compression readings.
The readings are low to excessively low for a camshaft like that.
Does it still go ok?
Maybe you should look at a better crankcase breather system.
I'd say a 302 with heads/cam like you have should hp peak at 6500 rpm easy.
So is it now time for an engine refresh?
What happens at 4000 rpm, misfiring? Valve bounce?
Yes, I know the feeling.
I've had a 308 that was gutless to 4500 rpm, I've had another 308 that went a scalded cat to 7200 rpm.
One was near stock, but high mileage AND high blowby.
Compression pressure also stops the pistons wanting to "fly out the top", if that makes sense.
I would sit back and decide on a plan of refresh.
No, not generally.
Pennzoil makes a 20w50 marketed as "street machine" oil.
Do you have the cam specs handy?
What others parts went into the last build? Rockers, pushrods, lifters, cam drive, head studs, bearings etc?
You may find the springs are getting soft/lazy.
I see the cam is a fairly wild hydraulic flat tappet for a street car.
How many miles on the bottom end?
I would be performing a leakdown test to determine where the losses are occurring.
My bet is past the rings.
How often, did you need to adjust the lifter preload? Did the lifters ever become noisy and need readjusting?
I have one of my cars in the same predicament as you. I have to bite the bullet for a short motor, because of low compression on one cylinder and high blow by. No amount of tuning will solve my problem or your problem.
Can we do a leakdown test on your engine?
The oil level with an aftermarket dipstick will have a SIGNIFICANT impact on engine performance if incorrect either way.
How much did you use at last oil change?
If the stock sump is still used, drain the oil, and add the correct volume (say 5 quarts), run the engine, wait 10 minutes, then see where it is on the dipstick.
If the crankshaft was swimming in oil, there is your crankcase oil breather issue or part there of, AND your rpm/horsepower loss.
And then we'll see where we go next.
Have you had any further success towards an answer to your problem?
Possible reasons for compression loss past the rings include if the ring gaps are larger than max spec, the gaps are lined up, one or more rings are stuck in the piston from flattened top ring land, worn ring lands from ring flutter.
Generally any combination of excessive clearance or no ring tension on the bore gives compression loss.
Now, it sounds like you'll do what I did.
A very quick pass on a honing machine, careful cleanup of pistons, etc.
If a ring doesn't rotate easily, it is also binding in the ring groove.
Hopefully the short motor rebuild will make it a rocket again.
I would still the heads inspected while they are off.
Will be a good time to get the compression up, to into the mid 10s if decent fuel is available.
The cam you have is fairly wild for a 302, so 10.4-10.7 or higher if you dare.
And a decent ignition, preferably not MSD.
I like ICE. (Ignition)
Pertronix is good.
You need to do the calculation from all the "volumes".
Swept volume: bore and stroke
Head gasket volume, Cylinder head volume, piston dish or dome volume.
I'll work it for you if you can supply your piston and head volume.
While the engine is apart, there are many ways to increase compression, generally mill cylinder heads.
Ok, with a crushed head gasket of .030, your current compression ratio is 9.96 (near enough 10:1).
With a flat top piston, you would end up at 10.66:1 which might be a little high for your fuel.
If you mill the heads down to 56cc, you'll end up at 10.23 (say 10.25:1).
I need to know what crushed thickness head gasket you are using, I have assumed .030 in the above maths.
Comp recommends "needs 9.5:1" meaning at least 9.5.
Their wording should be minimum.
Your .047 works out to 9.51:1.
I would run as high as your current pump fuel will allow safely.
Early 10s should be ok.
Recheck piston to valve clearance as a mockup assembly, lightweight checking springs etc.
I would put the engine at say 15 BTDC, drop the distributor in until it picks up the cam gear, then rock the engine forward, and partly back until the oil pump drive realigns, at that point the distributor should just drop in.
Get the engine back to your timing point, check your static position, fit timing light, fire it up, adjust timing at idle etc.
Now you know how to do it, it's a case of having the engine in the right place when you pick up the cam gear.
Noting where the rotor button and the distributor reluctor wheel are in relation to the balancer is the trick.