I am putting together a '66 327 bored .040. I have a chance to pick up 11-1 pistons. I am building it for the street, almost a daily driver. I have double hump heads, I have not decided on a cam yet, but I have 2x4 tunnel for it. Should I run these pistons, or get a lower compression ones? I am running a 200R4 transmission, a 9" rear end with about 488 gears I'm going to run pump type gas. It's going into this car. The 350 in it was for mock up only. I need your input! Thanks, Pat
Nothing is more aggravating than fighting detonation in a street car. Most of the time you end up with backing off the timing and end up with less power than with lower ratio. A 327 with steel gaskets and 461 heads and flat top pistons was rated at 10.5. Most mistakes to much carb, cam and compression in a daily driver
I run a stock 327/300 & use Non ethenol Gas and the Car runs like a raped ape & that has a 3.73 rear & a powerglide trans! Just my 3.5 cents Live Learn & Die a Fool
Larger cc heads will bring down the compression.Do you know what yours are? One of the common mistakes made building a car is using a part just because you have it,or can get it cheap.You then spend money trying to work around,or live with your first choice.I would rather lay out the money for a wiser choice,and not have to fight the car to get it to driveability. I think 10:1 is going to make you happier in the long run.
If they are a solid dome they can always be trimmed to fine tune a slightly lower compression ratio. Whether that is viable or not depends on your cost to get them, and if you know anyone who has a mill or lathe. Any idea of the brand or part #?? Been a lot of BS passed around over the years as far as "11:1 compression pistons".....the factory HiPo piston and it's TRW replacement(L-2166NF) that every shadetree mechanic has called a "11:1 piston" isn't actually 11:1 unless the engine is blueprinted to race spec....block decked, factory style head gasket, minimum volume chamber heads at around 61-62cc. In a common undecked block, Fel-Pro composition head gasket, 64+cc "Hump" head assembly that actually measure out with a burette at 65-66cc.... they barely reach 10.2:1
I don't have experience with the small block pistons, but on the big blocks, the 396 was rated 10.25:1 with stock pistons and closed chamber heads, and I never had any trouble with pinging...but later put those heads on a 454 that was actually 10:1, and it was a pinging nightmare. So you'd best do some good calculating, and also look at dynamic compression ratio with your cam specs.
I say put some 12.5 to 1's in it jack the timing Big roller cam stick VP fuel in it and go run the shit out of it. Oh and don't forget a four speed and 4.88's.
Put a timing plate on base of distributor, set timing for "having fun" and another setting for "commuting". I used to just mark the base and block for normal use and a advance mark for Friday/Saturday nights!
LOL I have always done that by feel. There are a lot of little tricks for running too much squish. Water injection or Methanol injection help. Longer rods. Knocking back the timing, you can even buy some electronic pieces that let you adjust your timing from the driver's seat. My suggestion is to keep your quench tight and drop the compression a little bit 9.5-10.5:1 on a short stroke small block with iron heads is about as far as you want to go on todays panther piss gasoline for one that you want to cruise around in.
Just smoothing our the corners of the pop up can knock off some and look to Cometic gaskets for different thickness of head gaskets. All the old SBC’s had shim style and Felpros are .042”. Cometics go up to over .100” If it were me, I do this on every engine I assemble, buy a 100cc/ml burette acrylic ones are inexpensive ($28 on Home Science Tools) on the net and get a 1/4” thick piece of plastic(Ace hardware/McMaster-Carr),make a cover for your combustion chamber with a hole and measure the cc’s. Put some vasoline on a piston top wrapped with masking tape and fill with plaster of Paris. Now cc your pop up and put all the numbers in the compression formula on KB Pistons found on line. If you have all the cam and rod specs it will tell “real” compression too and just not static. You can do this all for less than $40 and have the tools to use again. It’s better to know than guess.
There is Nothing on my commute! I live it the mountains in east Tn. I have to drive about 23 miles to town, also the first gas stop/ Which is the way I'll drive it to town, I get the usual octane as most places. If I drive the other two directions it's 45-60 miles to bigger cities, which I don't think they'll like my open headers there. The first way, they shut the streets down at 4 on Fridays, and let the Hot Rods run around on main street.
It's not going to be a daily driver, but I will get into it at times and take off for awhile, just not everyday, probably once a week. "A 327 with steel gaskets and 461 heads and flat top pistons was rated at 10.5." using which pistons?
This started because I need to buy pistons for my 327. Someone has a set of 11:1 with 3 hrs running time on them when he found he had missed a crack in the water jacket, and is starting all over with a different engine completely. He will sell me these for real cheap. I guess I need to do more checking into it. Lets say it has 11:1 after it's all said & done. In theory, what would it take to lower it to 10.5:1 other then cutting the pistons, after it together. Thanks, Pat
Larger chamber heads.Thicker head gaskets.Cam with over lap. Your cheap pistons are going to cost you money.If your 18 I understand if your 40 your late for this life lesson......
Thick gasket to lower compression can bite you in the ass. An engine with tight quench(close piston to head clearance) at TDC of .035-.045" ideally, up to maybe .055" will usually have better detonation resistance than a 1/2 point lower compression but a wide quench of over .060". Thicker gasket lowers compression but can raise octane sensitivity and create a situation worse than the higher compression ratio engine. Thicker gasket is always a last resort. Find out the piston part number, or get us a picture of the dome and see if it is a solid dome or a hollow dome style, figure out exactly what head you plan to use....and come back to us with that info and we can help you sort everything out.
A 300 hp 327 had flat tops remember this was with steel shim gaskets If those are stock chevy pistons at 11.1 the use of .040 head gaskets will drop the ratio about half a point.
It looks like I'm not going to get the 11:1 pistons. I need to buy new pistons since I had it bored to +.040. He has these with only 3 hours tops running time on them for $100. From what everyone is saying I'd be better off with some flat top, and steel head gaskets. I want to get the compression up to around 10:1. I am not sure on what cam to use yet, I believe I need to get the pistons in first. It's been years since I've built a stop light/street car, that I have to figure it all out again. I'm trying to keep it era right block & heads. Sure I can get better heads, but I'm keeping the 462 heads. I am thinking about having 2.02 valves put in and screw in studs, 3 angle grind, new guides, and check for cracks. The same thing I'd do with any head. Someone ported out one head, so I guess I'll have to sit down, and see if I can match them. Thanks, Pat
"since I had it bored to +.040" It's already been bored without buying pistons first? Has it been final honed? If so your gonna play hell getting your piston clearances rite on.
Cast pistons very seldom are the first thing to fail. You drop a valve the cast piston will break up where a forged will be damaged but most likely stay together. Super charger or spray where detonation comes into play is a different matter.
This is not the big issue it used to be, now that pistons are all run on CNC machines... been quite a while since I've seen a set that varied more than .0003-.0004" across the whole set and weren't right on the target diameter. Go back more than 15 years though, and you probably ought to have them in hand before you finish hone.
Don't even bother with plain cast, buy at least a hypereutectic. They'll handle right up to 450Hp without flinching, and will go farther yet if you are careful on a little bore extra clearance and on top of the tune. Most of the cheap plain cast are the reduced height "rebuilder" grade, .012" to .020" shorter height and that plays hell with getting tight quench clearance and a decent compression ratio.
This is very true but sounds like it was bored not having the pistons in hand plus the fact that they have been installed and used previously...………………………….
Different pistons different weights, does he have a balanced assembly? If so it would be a shame to break it up.
I had to have it bored to see how much it would take to clean the walls ' It came out at +.040 over. It is Not a finished bore. I have to buy pistons to finish it! It was at +.030 when I got it, but had marks in one cylinder, that needed to be remove.
If I'm bored +040 with flat top pistons, with 462 (64cc) double hump heads. What do I need to do, to get up to 10:1-10.5:1 compression? I was looking at: SBC 327 Keith Black Hypereutectic Pistons Dome 11.3:1 4.040 Bore KB157-040, What would it take to back them down to 10:1-10.5:1. I really would like to raise it up to around the 10:1.
I will just sit down and balance them all out to right on, the same, as I did with the pistons I am replacing. Then he will balance out the crank, damper, flex plate, everything for me. I just need to figure out what I need to do, first. I want it to be right, whether I"m right or not, I need to know what's right, not a kinda right. I thank you all! I have to decide on witch to get , those Keith Black Hyper domes, or some Hyper flat top pistons. Thanks, Pat
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