i have 350 out of a 70 model camaro.  it is suppose to have either 350 or 360 hp stock.  the guy i bought it from said his dad had something done to it to slow it down a bit.  he said that his dad either changed pistons or retarded the timing.  i took the heads off and found that the motor had flat top pistons.  the heads are the 64cc high performance heads.  the motor is supposed to run at 11:1 compression, but i dont know if the motor came stock with flat or dome pistons.  does anyone know if these high compression motors came with flat or dome pistons.

It came stock with flat tops. Problem today if you're running on the street is finding fuel with enough octane at the pump to manage 11 to 1 with cast iron heads, aluminum for that matter, will be difficult. The old trick was to back off timing lead to reduce octane requirement but this makes a poor running gas hog out of the engine. The real solution is to get the compression down around 9 to 9.5 with a "D" dish piston. Another trick is to use thick or doubled head gaskets, but this makes the quench clearance too wide reducing turbulance and increasing sensitivity to detonation, the very thing you're trying to eliminate.

The other problem is that these old heads will suffer from valve regression resulting from running on today's unleaded fuel. The solution here is to have hardened valve seats installed or replace the heads with modern versions that have induction hardened seats. GM and the aftermarket offer many choices.

Bogie

if i changed my compression down to 9 or 9.5, wouldnt my hp go down to about 280 or 300.  i want to keep the hp if possible.  the motor ran fine on pump gas about 10 yrs. ago.  what is the difference in dish style pistons.  

Without having all the info on what you have you should be between 9.75 and 10.25 depending on your headgasket choice and the distance your piston is down the bore at TDC.

Dropping some compression will cost you some power but if you can't run pump gas in it what good is it to have the compression that high. 

Dish style pistons will help you decrease your compression but you will still be left with soft valve seats and old heads.

There are ways around the higher compression.  The static compression ratio is just part of the story.  Look at the link below for a little more info.

http://www.kennedysdynotune.com/Dynamic%20Compression%20Tech.htm

OldBogie is right though...you sould go with some newer heads.  If this is a purely street car with no radical cam or large single plane intake you could go with one of the many aftermarket 165cc heads out there with around a 72cc chamber volume you should be good to go.  Again that depends on your head gasket thickness and bore, the valve releif cc's in your pistons, and how far your piston is down the bore at TDC. 

9:1 to 9.5:1 is kind of a generic ideal compression range.  It is proven to work though.  Your ability to run on pump gas depends partly on your cam and your ignition timing though.  Have fun!

I don't know what kind of fuel was being used by the owner of this car 10 years ago. Some areas of the country may have still had leaded or low lead premium which would have worked. Yes reducing compression will cost some power but mostly bottom end torque with a long duration cam. High compression with high performance cams (read that long duration, lots of E to I overlap with a short LSA, and late closing intake) was mostly used to recover low end torque that's lost with these long winded cams. The optimum real dynamic compression is about 8.5 - 9.5 to 1, so the mechanically measured compression is raised to recover the low to moderate RPM power losses of high performance cams to compensate for the compression lost to mixture escaping on overlap or being reverse pumped back into the intake till mixture velocities become forceful enough with increasing RPM to overcome these losses. High compression adds little or nothing but problems at high RPMs as the cylinder begins to overfill and over compress, then like a super/turbocharged engine, the timing has to be retarded to prevent detonation so severe it blows the engine apart. There are old tricks like using water or water/alcohol injection at high RPM to cool the mixture. This adds power by keeping the endburn temps under the detonation/preignition limit plus the water turns to steam absorbing temps and expanding about 20 times its liquid volume. The alcohol not only burns but  has a much higher innate octane rating than petroleum fuels. But remember that when water or alcohol is introduced ahead of the intake valve that it also reduces the space that the fuel and air mixture could occupy, so there is also a power loss going on. Proper high speed and power loading timing is difficult to achive without computer control of the timing advance amount and rate. In the good old days of centrifugal and vacuum advance systems, as long duration cams required more base ignition advance, the technique was to weld the slots of the advance mechanism to remove some mechanical advance so more could be run initially and still limit the total amount to something the engine could live with.  Todays computer systems can be programmed to not only manage the base setting but also retard the timing at high RPMs to prevent preignition and detonation. These systems can be run closer to the edge by also employing a detonation sensor where no retard is applied unless the sensor "hears" detonation and then pulls the advance back. These are much harder tricks to do when you're limited to mechanical and vacuum systems.

Starting with electronic fuel injection and roller cams a whole new game for these relationships came into play. With EFI and rollers, designers can cut back on duration, increase the lift and lift rate, widen the LSA, and reduce both overlap and late closing of the intake and still gain power. The reason for this is that EFI fuels the engine much more precisely than a carburetor and there is much less unburnt mixture lost during overlap and reversed pumped past the otherwise late closing intake valve. This markedly increases trapped or dynamic pressures without resorting to the old trick of real high compression to compensate for lost bottom end torque.

However, even with a carburetor, using a modern cam profile and modern heads with the heart shaped combustion chamber it's possible to maintain high power outputs with more moderate compression ratios.

If we're talking a pure race engine the old rules still largely apply so you will find drag engines with ratios up around 13-14-15 to one, but these are very tough to drive on the street as they demand extremely high operating RPM and constant attention to gear selection and of course you just can't get fuel of sufficient octane at the corner 7-11 store.

The Vortec head as an example of modern fast burn chamber design. It has the heart or kidney shaped chamber which greatly enhances swirl, and protects the intake flow from passing out the exhaust with the beak that projects between the valves.  The swirl not only helpd to mix the fuel and air together for better combustion but very importantly the swirl cools and cleans the spark plug and helps cool the exhaust valve. This results is a more consistant and stable spark and by cooling the valve head makes for a better seal with the seat reducing mixture leakage past the exhaust valve and reducing hot spots that could cause preignition. Reducing preignition and detonation by this means allows greater static compression than has been tolerable in years past with unleaded fuels so since 1987 with EFI and especially since 96 with Vortec chambers we've seen compression ratios return to the low nines in cast iron heads and into the tens with aluminum. These chambers also burn faster which reduces the need for lots of spark advance which produces a softer burn that is at once more detonation resistant by placing pressure and temperature maximums at and after TDC instead of before which reduces effort lost by the crank to shove the piston thru high pressure and temperatures prior to TDC, thus more power is made available to move the vehicle. These modern features combined with better port shaping is worth at least 40 more horsepower than the best of the old high performance heads with no other changes.

This magazine did a head comparison article this month that's well worth reading.

The "D" dish piston found at Keith Black-Silvolite and other places is used to dial in the mechanical compression ratio. Having a lot of distance between the piston and the heads quench step makes an engine more detonation sensitive and fuel hungry than necessary. Holding this dimension to .040 to .060 including the gasket thickness is ideal. The "D" dish compared to the factory style circular dish does a much better job or promoting "squish" and "quench" which results in better power and efficiency.

The step opposite the sparkplug performs two functions. The first called squish, squeezes the mixture out a high velocity toward the spark plug as the piston closes on TDC. This increases fuel and air mixing which burns faster and more completely making power by using the fuel efficiently. The second factor called "quench" slows the end burn by sucking heat out because of the large surface area to volume ratio thus preventing spontaneous combustion which is a major cause of detonation.  A "D" dish or flat top piston is perfect for controlling this feature. Pop-ups have the effects of causing the overall chamber to act as a quench, reducing thermal efficiency which then requires more fuel to make power. They also interfere with the speed of the flame front by slowing it down. This requires more advance that puts you into complex games of trying to find optimium advance rates that aren't so advanced that the engine losses power as the early ignition attempts to drive the crankshaft backwards and of course the resultant ultra high peressure and temperature doesn't melt the pistons or blow holes in them. The factory's cheap solution for years has been to use a circular dish in the piston. This allows them to use the same piston on the left and right sides of the block, essentially doubling piston production of the part number which minimizes their cost per piston. This round dish results in inadaquate amounts of squish and quench, this suboptimizes power and efficiency which you pay for with additional fuel by driving with more throttle opening to maintain a given performance level. Goverment CAFE and SMOG requirements over the last 20 years have driven the manufacturers to stedily improve their engineering and manufacturing to meet these mandates. The result is that modern V8s produce more power and get considerable better fuel economy doing it.

Bogie