i have a 56 chev with a 71 chev 350 with stock block. it has camel 64cc heads and in the near future i want to get it bored and install some higher comp pistons.i  would like to have about 10-1 comp. i keep reading about replacement pistons 20  thousands dowm in the hole.i i dont want to lower comp. what pistons should i use. it is a 4 speed with headers a high rise and 373 axle thanks, it has a summitt cam with 480 lift and i think 280 dur. this is probably too much cam for my engine bit i want to use it.can i use cast speed pro pistons and still get decent comp thanks phil

aion pistons.i will be useing for street and a few strip use.

believe you me, you dont want to get 10:1 compression using a dome piston on a common SBC, there is much better ways of getting this compression. with iron heads, 10:1 compression, and dome pistons, detonation will more than likely be a main-stay in your engine. Find a good static compression calculator on the internet and go from there, also keep in mind that compression ratios calculated on a spreadsheet can be much different from your orginal thoughts once you actually use a buret and cc the engine. Tighten up the piston to head (or quench) clearance and with 350 cubes and a 64 cc chamber you should be where you need to be for pump fuel

awhy you dont tighten up the quench clearance and bring your compression ratio to 9.0-9.5:1 for a little insurance purposes, even though the advertised duration on the cam is somewhat high, the gain from 9.5:1 to 10:1 is probably minimal and you put yourself closer to detonation, and it would even be nicer to run regular instead of premium at the price of gas these days

there is also another side to compression, dynamic compression is the type that is more important to someone looking to push compression limits on pump-gas, intake valve closing position has major play in this, and a way to compare dynamic compression with what you can easily measure is a cranking compression test. Westech in Socal says that 180-200 lbs cranking compression is about as far as you want to push on pump gas but some great tuners, usually with the aid of electronic engine management can push this number to the 220 range. Keith Black says that 8:1 measured dynamic compression ratio is all that pump-gas will handle (calculate measured dynamic compression here, this spreadsheet also calculates estimated cranking compression, i use this figure but not as a main-stay as with other engines ive "tested" it on, the figure was 10-15 psi high)

well i agree it is hard to find off the shelf pistons with the compression height you want but just figure out the distance the piston is in the bore yourself, if your block hasnt been decked your in trouble here, if it has, more than likely its decked to the blueprint spec of 9.025, if you are unsure where it has been decked check with your machinist who has done it. The crank throw (stroke divided by 2) + rod length + piston compression distance= piston placement at TDC. So with your setup look for a piston compression height (assuming stock length stroke & stock rods) as close to 1.585 as possible, this will get you zero distance "in the hole" at TDC, and your piston to head clearance can be maintained using your head gasket only, which can be as tight as .030, but probably should be in the realm of .035-.045

hope this helps!

Speaking of pistons.... I have started gathering parts for the econo / fuel mileage 400 for my 82/85 Blazer 2wd (it's an 82, but it has an 85 front clip). I figure I'll need about a 30cc D dish with the 64cc vortechs. I found one on KB's website that Bogie linked recently, but it's for 5.7 rods. I have the 5.565 original rods.

If no one makes a 30cc D dish for a short rod, then I suppose I have two options: purchase custom pistons or acquire 5.7 rods.  

It seems the budget wont be as small as I hoped...but it never is, is it?

i see your problem, i checked speed pro, je, srp, arias, CP, howards ect only to find nothing,  more than likely the cheaper way to go is the getting some 350 rods, stock rods will work fine, shouldnt have to put too much money in machine work in to get a set ready, custom pistons will probably put you back $600-$700

the only thing i can think of when switching rods is the rod to cam clearance, there is a way that the 5.565 rods are made to help them clear the cam in the 400 blocks, a 350 may require grinding but maybe if your cam is small enough there wont be any problem here, if there is problems here a small base circle cam or capscrew rods are in order, both causing problems, one in durability and function, and one in the pocketbook, this is just one of those mock up assembly kinda things...

no budgets arent easily followed, but you already knew that...

ok... so....

This leads to another question. With the 5.7's, will I have to re-balance the assembly? I recall hearing that a balance is acceptable within 20 grams of the original balance ( I don't know the weight difference between the 5.565 and the 5.7). This motor will probably never see over 5000 rpm's, and spend the majority of it's time around 2000 rpm's.  If paying for a re-balance is going to be necessary after paying for new rods, then it seems the custom pistons aren't such a bad choice.

and back to keeping "budget" in mind, if I were to use the traditional dish pistons for the stock rods, and lower the comp. ratio down to about 8.5 : 1, will I be able to run 87 octane here in close to sea level Fl? How badly will that hurt the efficiency of the motor with the vortech's efficient chamber design ( i.e., will the motor be a turd that is detonation prone)? 

Should I throw the budget out the window?

Should I change my game plan (using the vortech heads), and just go with flat tops on the stock rods, and a larger chambered  head like the SR Torquer?

 In the long run, I just want to have the most fuel efficient, yet simple carbureted, 400 that will see occasional towing. I would love for it to get 18 to 20 mpg when not towing. Over time, that savings would pay for an intially higher cost engine.

yes more than likely the assembly will have to be balanced, but not unless the custom pistons are very near or slightly under the stock weight of the piston the engine will have to balanced anyway, you could get around this and get a torquer head with a 76cc chamber, well then your giving up chamber efficiency and giving up flow, which may or may not be important to a tow rig, but a vortec head will probably make more low end torque, even way down low where you'd like it for your ride.

if the quench clearance is good and the chamber design is good and timing is set at a sane level then running more than 8.5:1 on 87 sounds to me like no problem. The tradition pistons are horrible if you mean the stock cast ones, as they have a full circle dish thats horrible for quench, and that is what bogie has drilled into our heads about making a engine more detonation prone

more difficult than people think to build a budget motor isnt it?, haha

Yes I was referring to the old traditional full dish piston... but I've decided to throw out that option. It defeats the purpose I'm attempting to achieve.

BRC has a compression calculator or their web page  http://www.brcpistons.com/calculations2001.html    and it seems that flat tops with -5cc valve reliefs under 76cc heads would still be too high of a compression ratio (about 9.8) for a regular unleaded burning, steel headed, tow vehicle.  So, I'm back to figuring the best combo for the vortecs.  A 23cc D dish comes out to 9.38:1 with .020 deck, .036 head gasket, .030 overbore, and 3.75 stroke. The 30cc D dish comes out to 8.829:1.  I can play with head gasket thicknesses once I know where the deck height is... but, what is the ideal compression ratio to shoot for with the vortec heads in this regular unleaded burning, carbureted truck?

*edit* After re-reading this, it seems the obvious choice is to use the bigger 30cc dish, as I can tighten up the quench with thinner head gaskets or deck surfacing, to attain the "perfect" compression ratio, which only makes it more efficient.

I've decided not to worry so much about the budget, in favor of building this motor to be the most efficient I can. A few hundred dollars more for the better motor would pay for itself eventually.  

... and yes Gibs, building a budget motor is a little tougher when you are trying to build a purpose specific one. It'd be easy to copy some magazine article to just put a motor together inexpensively, but I'm trying to customize it... tailor it toward high torque, low octane, best fuel mileage. Much of what I'm posting here is almost a blog, or my findings as I'm doing research, while getting advice/ bouncing ideas off of you guys too. Who'da thunk that nobody makes a D-dish piston for a stock 400 rod length?

who would of thought that is right, but it is probably because all these "performance gurus" tell people that there is no performance capability with the stock length rod and if you are re-building one never to use them, when in truth there is nothing wrong with very low R/S ratios for low RPM wide operating band engines, even though there are disscussions were ratio's under 1.5:1 or 1.6:1 (take your pick i guess) cause very excessive cylinder wear, but there has been no evidence that a short rod long stroke motor can live a life as a towing rig for a lot of miles so id just go with it, if it were me, good luck, i think you've got a good head on your shoulders and can make good decisions about this

I have cast pistons .100 dome like the LT1 had. motor is 350 bored .030 over camel hump heads 64 cc . comes out to about 11 compression. 284 duration 480 lift. I run ultra 94 sunoco gas with no problems.  

but like i said cranking compression is a better way to "see" your octane limit, for the hell of it, what is your cranking compression? and what are your extended cam specs?

What kind of pistons are those it sounds like about what I am looking for with my combination. thanks phil  

mine are speed pro but just about any piston mfg should have them. keith black piston mfg makes them.  

I have a detonation problem on a 1968 Camaro RS 4 speed with a 327 stock block, 350 iron crank, OE 64cc iron heads, OE 327 iron intake manifold, KB 10:1 domed pistons, and an Elgin cam with 214/224 degrees@ 0,50 lift and 282 advertised duration. The engine was rebuit, blueprinted and balanced. I run a Quadrajet 4bbl carb and open element air filter. I have retained the ramshorn type exhaust manifolds but added a 2 1/4 inch freeflow dual exhaust system with a crossover pipe. Timing was first set @12 degrees BTDC but has already been retarded by, I think, 2 degrees yet detonation persists.
I live at 4800 feet above sea level in Johannesburg ZA and fill up with 93 octane lead replacement fuel. I add Wynn's octane booster as specified but for some reason it helps only sometimes to reduce detonation under hard acceleration. The engine seems to run out of usable revs @ about 5200 rpm.
My question is whether the improved flow when installing headers will reduce the detonation problem. If so will the addition of a more efficient intake manifold also help? Will any of this increase usable rpm?  

Thank you.