ross flat top piston compression on my 1970 455

stock hei with limited vaccum and silver springs.

 

When you assembled it, how far were the pistons below the deck?

Or if you have the piston specs, tell me the compression distance or "CD".

JW

 

pistons are flush with deck.

 

Follow the advice given and confirm your timing following the Larry thread. It doesn't matter what the initial is, make sure the total mechanical advance is 34*. If it is already at 34* pull it back to 30* and see what happens.

If you still have problems after the actual timing has been ascertained and you end up with only a small amount of ping there is a possibility that retarding the cam 4* could help you out. Hopefully the cam was degreed in so you know where it is actually at. With the cylinder pressure you have a little low end torque loss won't matter. I'd also make sure I have a good MSD ignition and cold plugs in there to keep ping at bay.

Making some assumptions I would say your low side best case compression is right at 11.8:1 with a flattop piston at "0" deck so I don't think the above will be enough. This is assuming .030" overbore, 68 CC head chamber, standard .040" head gaskets. If the heads were milled more than a small amount or the valve relief was smaller the compression will only go up. However installing a .080" thick head gasket would net 10.7:1 and a .100" thick unit would net 10.25:1 with the above numbers. Your actual numbers will probably be different. This is a good example of getting all the important measurements before the engine is put together so you know what you actually have compression wise. The good thing is if you decide that head gaskets are the way to go when you pull the heads off you can actually measure what you have and then calculate actual compression ratio and then order your gasket. You can sneak by with 10.7 on pump gas but I'd be double checking everything before ordering to make sure. The one drawback to such thick gaskets is that the tight quench you had with the flattops would be gone.

Now, if it was my car and I didn't have to drive a bunch of street miles I'd be adding some high octane race gas to the pump gas and get rid of the ping that way. Confirm 34* max total timing and start mixing in the race gas until it goes away. Unless you have way higher than expected compression(12:1 or higher) you should not need too many gallons added to get rid of the ping. You definitely don't want to be getting on it with the ping so I'd go generous early on with the race gas, maybe 50/50 to start and with successive tries you can cut back on the race gas if it is too much.


Maximum best timing and some amount of race gas will give best power and lowest ET's so I'd be doing that at the track at least once before I'd start dropping the timing or compression ratio. By the way, nice Chevelle.

 

From the pictures, and what I know about Ross Flat tops, he has a 7cc valve relief, with aprox 65cc heads.

Figure 12.5-1 or better.

You have two real choices here.

Run 112 octane race fuel.

Take the engine apart and install dished pistons, to allow optimized operation on pump fuel.

Target 10-1 with that camshaft as "safe".

JW

 

Convert over to E85:grin:

 

Yes, that would be the 3rd option.

:TU:

 

What about ...Sell those Iron heads and apply funds to a set of TA Alum Stage 1 SE heads? Run thicker head gaskets :TU:

 

Did you use a dial indicator to verify this?

 

I'm hazarding a guess but I don't think they have many E-85 stations in P.R. but that would be a great way to make good with the compression. I may be wrong though.

The engine should be a torque monster.

 

I got specs together for calculator and I have an estimated compression of 12.72. ou:

 

kinda what I figured all along...WAY too much CR for iron heads.

 

What would be the benefits of aluminum heads?

 

Thermal conductivity will allow almost a full point more compression tolerance with pumpgas and the probability that the chambers maybe larger than your irons if they have been decked, along with of course more powa

 

Faster heat dissapation, about .5-.75 point, #60lbs off the top of the engine, porting flow capabilites between 320-360 / 200-250.

Your monster needs a correct ground cam and full flowing heads....and God help whatever you put behind it to attempt to apply the power to the ground...it is just money...uh

 

To even think about getting away with +210 psi cranking with iron heads, the following concerns need to be addressed;
Coolant temp low, no 195* thermostats here.
Air inlet temp low, no radiator or exhaust pre-heated hot air.
NO sharp edges left around the combustion chambers after milling the heads.
As cool of a heat range plug as you can get away with. Not an appropriate place for precious metal here.

These are working against you;
Altitude where you drive? I didn't catch where you were.
Vehicle weight and gearing. Lighter is much better.
Anything that reduces load to the engine near the bottom of the powerband helps you. Higher converter, deeper gears...

Slowing up the ignition curve to fully advance at a higher rpm MAY help.
Cams with a wider LSA tend to reduce cylinder pressure throughout the torque curve.
Wider exhaust valve seats help that valve run measurably cooler.
Reduce backpressure in the exhaust system.

Regardless of dynamic compression, incandescence and combustion chamber temperature needs to be thought about while the parts are being selected.
If you were already hearing pinging in neutral you should think about inspecting your rod bearings and measuring the roundness of the rod's bearing bore.

This is an expensive gamble to try any of this.
Definitely better off with alloy heads and more cam.

Good luck ray:

 

If it was my motor I would run a thinker head gasket and alcohol /water injection
Jamie

 

Order a E85 carb from quick fuel and be done with it. What kind of fuel system is in the car?