just wanted to know i wanted to overhaul an engine with new rings gaskets bearings ect. and i also wanted to ad new pistons only but keep my crank and rods what kind of piston can i use to get good compression im looking at either an flat top with 2 valve relf. or would a piston with an .100 dome be to much i kind of want to use the .100 piston im either going to use stock heads polished or vortech heads with comp cam extr series probaly wit an 454 lift cam or an step above the motor is going to be daily daily driver.im probaly going to use an iron high rise intake and headers.also whats the highest compression numbers i can run on pump gas without having detonation thanks  

Setting the Vortecs aside for a moment, it's necessary to know what the "stock" head is you intend to use by casting number. There are a lot of different kinds of "stock" heads out there and they vary quite widely as to port shape and volume, combustion chamber shape and volume, spark plug location, angle and seal type, and valve size. Different displacement engines have different combustion chamber and port volumes and sizes. A 305 head has much less chamber volume than a 350 head of the same year and crossing the heads would upset compression with way too much if a 305 is put on a 350 or way too little if a 350 head were to be placed on a 305. However, some hot rodders have used 305 heads on 350's to increase compression, but it has to be planned on the front end as this will push the volume of the piston dish requirement. The 305 head will also run out of port volume and valve size unless these things are addressed as part of the head rebuild.

Smog heads have large volume open chambers, these start in the early 1970s and are found till the mid eighties. Heads previous to the SMOG era and heads after 1986 get better in terms of combustion chamber shape. Starting in the mid 1970's heads were subjected to a exhaust seat hardening process to allow them to run with unleaded fuels and not suffer seat regression and wear. These heads must be checked very carefully as they are even more subject to cracking that Chevy's already high crack rate.

Combustion chamber shape has much to do with how much compression the engine can tolerate on a given octane fuel. Open chambers are prone to detonation and preignition as their shape and surface ratios don't do an adequate job of controlling the flame front. They depend upon a ratio of inert exhaust gases being recirculated, low compression ratios, mild cam timing, and reduced advance in terms of amount and rate to control detonation/preignition. With anykind of performance work the engineering of these heads is in trouble.

Similar problems develop with domed pistons for different reasons. The dome interferes with the burn rate, slowing it down, while pressures and temperatures increase because of the mechanics of the design. This increases the probability that the mixture will explode rather than burn, resulting in detonation.

For a street engine the best approach is moderately high compression achieved with a flat top or a "D" shaped dish piston, consistent with overall compression from combustion chamber volume. This works well since these pistons don't impede flame travel like a domed piston, and reduce end burn temperatures, thus the likelihood of detonation. This is because a wedge chamber is divided into two parts the open or pocket area where the valves and sparkplug reside; and the squish and quench area opposite the pocket. The way this works is that the area where the flat part of the combustion chamber wants to be real close to the piston crown as the piston closes toward TDC, like about .050 to .070 inch. This is good for managing detonation but bad for emissions. As the piston closes on TDC compression, the mixture is squished out from between the flats toward the spark plug. This really stirs things up and is good for power, efficiency and emissions. As the flame front proceeds and pressure and temperatures increase, the flame front runs into the close flat surfaces. The sudden increase in surface area compared to the volume pulls this end burn heat out to the cooling system. This reduces the flame front temperature and prevents it from exploding which is the detonation you hear. This is good from a power standpoint, but really runs up the unburnt HCs and contributes to CO output as it terminates the reaction before the CO goes to CO2.

The Vortec head changes the intake port height and size which improves flow, but also requires a matching intake. The big difference is in the shape of the combustion chamber, which is a return to the classic Ricardo chamber invented by Sir Harry Ricardo back in the 1930s. It does a superior job of getting fresh mixture in and controlling the flame front. It gets around the emission problems by using timed fuel injection and a 3 way converter. For a hot rod engine where having to pass a SMOG inspection is not a limitation, these heads will deliver a good 40 horses over SMOG heads and 10 or so more than pre SMOG performance heads. The ideas found on the Vortec are also available in cast iron and aluminum from GMPP and the aftermarket.

Bogie

well the casting # for the heads are #333882 i dont know if that will help u or not but i think il go with the flat tops with the 2 valve relf.im not sure if that will help me as far as power .but as long as i can produce more power than the motor originally produced il be alright.by the way do u think il produce more power than the motor originally produced.the motor came out of an van around a 78 to 82 model the pistons in the motor has a slight dish to it with 4 valve relf but the heads #333882 came out of an box chevy caprice 4 door.your response is well appreciated alot by the way u got to be the best i ever came across theres nothing u dont know man il tell ya thanks again OLDBOGIE!!!!!!!!!!!!!!!!

882s are emissions-era 76cc chamber heads.  They were used almost always on 350ci engines from the factory, so I'll assume we're talking about a 350 engine here.

Almost all 350 engines that came with original 882 heads also sued dished pistons from the factory (about -12cc of dish).  This yielded a true  compression ratio of about 8.2:1 although GM regularly rated these engines at 8.5:1.  DISMALLY low compression for performance.

A simple change to flattop pistons and a .030 overbore on the block (common if you're rebuilding) will get compression up to not quite 9:1 if you use a fairly thin GMPP .028" compressed thickness head gasket.  Better but still not great.

Putting in a typical .100" dome piston, everything else the same as above, and you'll be in the 9.3:1 range.  Much better for performance.  I'm not a fan of domed pistons in a small block, but in this case, their use may be warranted.

Vortec heads are a totally different bag of worms.  Just from a compression standpoint they are 64cc chambers which means you won't need anything more than a flattop piston to get compression into the mid-upper 9s.  Pay attention to what Oldbogie says about the differences between Vortecs and older intakes as far as intake manifolds and valvetrain.  They are NOT a bolt-on, even through they will..... um...... bolt on.

hey thanks for that info let me ask u something will that 9.3:1 allow me to use pump gas or would i have to buy special additives or do i need to stick with the flat tops?by the way i was going to keep the motor as is i really didnt want to bore it unless i have to which i dont hink i have to its in good shape.and also would the dome pistons make contact with the stock heads? your response is well appreciated.and thats to everyone that responded thanks!!!!!!!!!!!!  

The 333882 head was used on SMOGer 350 and 400 engines through the mid 1970s and early 80s. They are an open chamber head advertised as 76ccs in the real world they're probably larger. They came in a small valve 1.95/1.5 and large valve 2.02/1.6 versions. Like most smog heads they're prone to cracking, so you need to get them magnafluxed before doing anything with them. Their ports are pretty small, especially for a 400 engine but even for a 350 at about 160 cc for the intake and 60 for the exhaust. Heads after 1976 most likely have induction hardened seats which are needed with unleaded fuel. Rebuilding a set of old heads may likely require new valves for larger head and possibly stem diameters, replacement guides, new stem seals, cleaning, fresh cut seats perhaps replacement of one or more, rockers, studs, and possible milling. All these parts and operations become very expensive very quickly, which is why I suggest looking closely at new SR Torquers for your application.

The cost of rebuilding these heads would be at least close to half (or more) the price of a set of World SR Torquers, which would be a quantum improvement in port volume and chamber layout. Vortecs always look cost attractive, but they require a unique intake manifold which is a bit pricey. The SRs can be had the way you want them to match the manifold you've got. E-bay is a good source of new, rebuilt, and used heads; I highly recommend looking there. Any GM Chevy heads newer than 86 require a different intake than what you have. At a minimum the two (on each side) center bolts have an angle changed from 90 to 72 degrees; others have fewer fasteners in relocated positions making matching an older intake nearly impossible unless you’re a pretty good machinist.

If you're really stuck with the 882s, I go with a flat top piston perhaps a minimum dome piston. This will not only increase compression but inspire some mixture agitation which will improve power and reduce detonation tendencies. Actually I'd go with flatops or a "D" dish" no matter what head I used. The "D" dish could be required to adjust the compression ratio depending upon the volume of the combustion chamber in the selected head. You can use the gasket to adjust final volumes a little bit. A typical steel shim runs about .022 thick, the composite gaskets run around twice that thickness. So gasket selection can have the same effect as milling .020 from the head.

There's no point in milling these heads beyond what's necessary to keep a flat deck. There's not much meat in these things, cuts over .020 really weakens them. You could use a steel shim head gasket but these require flat head and block decks.

Bogie