http://item.mobileweb.ebay.com/viewi...id=94101765923

http://item.mobileweb.ebay.com/viewi...401&cmd=VIDESC

Im looking for 10:1 or a little higher CR because im running the cc306 cam. What do you guys think of these pistons? And can someone tell me what the .125 dome shape means? I only see this on one of the ads and what is the 3.5 cc and -3.5 cc?

 

Is it the size of the dome or the size of the reliefe valces or something different?

 

I forgot to mention my heads are 67cc

 

Using the .125 domed piston with 64cc heads, stock stroke, .030 bore, zero decked and a .030" gasket you'll be near 10.5:1 - but if you're running them in the hole and a more common (thicker) head gasket your compression will be lower. Also just be sure you've got a head with an older wedge style chamber - if you're using a fast burn / vortec or other heart shaped chamber those pistons might hit.

The 3.5cc is used in calculating the static compression ratio - a flat piston with NO valve reliefs is "0" where it doesn't add or subtract to the total volume. The piston 'dome' will take up 3.5cc of chamber space when calculating, the "flat top" pistons you had add 5cc to the chamber as they have reliefs cut into the piston face. A quick and dirty example would be if you ran zero deck height, no gasket and the 64cc heads - with the domed pistons you'll net 60.5cc total chamber volume, and with the "flat tops" you'll net 69cc chamber volume.

Google up a "compression ratio calculator" and while you're at it - search for "dynamic compression ratio calculator" (I feel it's a MUCH better way to pick a compression ratio for your goals) - you'll need your cam specs, piston specs, block deck height, stroke, bore, head gasket compressed thickness and bore, etc. Some will even go so far as to ask piston to wall clearance and distance to top ring to get the tiny volume that's between there added into the compression ratio.

 

Im using summit vortecs. 67cc

 

You'll need a vortec specific dome designed piston, or run a thin head gasket.

5cc Flat tops, non-decked block (~.020 in the hole), .039 gasket, and the 67cc chamber gets a 9.5:1 compression ratio.

Run the steel shim head gasket (.015" to .019" depending on whose gasket) and then zero-deck the block to get the piston up will net 10.4:1 - but you'll probably smack the piston on the quench pad at speed.

The best way to get the 10.5:1 would be to angle mill the heads down to ~62cc and run the flat top piston about .015" in the hole with the .015 shim gasket. Flat pistons have better flame propagation than domed pistons and generally will be lighter and rev better.

 

Damn. I was about to order those pistons. Theres no way I can run those? You know for sure itll hit the head?

 

Is 9:5:1 still ok with the cc306 cam? Can I still make some decent powet with that compression?

 

http://item.mobileweb.ebay.com/viewi...212&cmd=VIDESC

I guess these are a better option for me then? I still dont get why these say +5cc and some other say -5cc

 

The dome pistons won't work period. Fuhgeddaboutit. Their dome shape doesn't match the shape of the chamber.

A thin head gasket will only make it worse, by moving the head closer to the piston, thereby increasing the amount of interference where the square-ish dome hits the heart-shaped chamber. Bad "advice".

Those particular flat-tops have the extra "rebuilder" .020" of deck clearance; meaning they will be around .045 - .050" "down in the hole" at TDC. They are "designed for" a compression height of 1.56", but I doubt they will MEASURE 1.56". (they haven't for anybody else) Instead you will find that they are ACTUALLY 1.54". Not a particularly good choice if compression is to be maximized.

The Keith Black hypers are the full 1.56" CH; therefore only require .025" - .030" to zero-deck to them. http://www.summitracing.com/parts/ue...make/chevrolet Not that much more money, AHELLUVALOT less fiddling around.

+5cc means the valve reliefs can be treated as adding 5cc to the chamber volume for "calculator" purposes. -5cc means the net of the domes and he valve reliefs has the equal but opposite effect.

Buy the KBs and have the block decked to the end result.

 

Ok so I was using the calculator on summits page with the keith blacks. I would need to deck the block to make the deck clearance .020. And use a 0.015 head gasket to get 10:1. Seem right?

 

It depends... What are you wanting to build - a street terror or a drag strip 'street' car? Pump gas (and what octane) or will you run race fuel? Where do you want your power range to be? Automatic (what stall?) or manual trans? Are you wanting something that will feel like a much bigger engine on the street or something that you can wind out to 8K rpm on the track and turn in some good times? Do you care if it gets crappy gas mileage and surges at low RPM?

Plus WHICH exact 'cc306' cam are you thinking of running - the 7-306-8, the 8-306-8 or ???

 

That seems about right - thought you wanted "a little higher' so I was shooting for 10.5:1?

Honestly I'd go for closer to zero deck height and run a more commonly available and better sealing composite or MLS gasket if you're going to be on the street a lot. The steel shim gasket is OK for an iron block/iron head combo but it's not the best at sealing if the surfaces that are marginal, will see heat extremes or aren't prepped properly. It's kind of an OLD trick to get a little more compression out of a flat top engine if you can't run small chamber heads in a spec racing class.

EDIT: use a couple of the DCR calculators and post up the DCR results...
http://www.wallaceracing.com/dynamic-cr.php
and
http://www.projectpontiac.com/ppsite...tio-calculator

 

Manual trans. Its going to be a nice street car. Almost a dailey driver. Trying to shoot for 400hp. Ive talked to people with the cc306 cam and they said power band is up to 7k so I will be spinning up to 7. Of course with arp bolts. Octane gas doesnt matter to me 91 or 93. Running the 7-306-8 cc306 cam with 1.6 rockers.

 

So your saying deck block to 0 and use a regualar stock thickness head gasket?

 

Im just trying to get close to lt1 compression 10:4 cuz I know this cam performs awesome in lt1s and it needs high comp for this cam. Sound about ok or does this sound conpletely retarded? I mean I can get the keith blacks .30 over and keep stock deck and use stock headgaskets and get 9:5 but would that still make decent power and work with that cam?

 

9.5:1 static would be a dog with that cam.

Honestly you really should shoot for around 11.25:1 and run that cam 3-4* retarded to get the DCR up around 8.5:1 for a good street engine and keep the RPM's where they'll do the most good. At 10.5:1 and 4* retarded you're right around 8:1 which might even run fine without knock on mid-grade gas

Daily driver, stick, and that cam doesn't sound like a super combo if you have to drive a lot of traffic as it lopes a bit and traffic can become a pain - an automatic with a loose stall would be a little more forgiving in traffic. If you don't do parking lots and traffic then it'll be tolerable. Honestly if you choose a cam to better match the compression and make better power in the low-mid RPM range it'll produce much better torque and "feel" a lot faster as the torque will pull hard off the line and be more fun to drive stoplight to stoplight where you can't wind the thing out to 7k without some room

 

Im goin to shoot for 10.5 thats if I deck to zero and run a 0.20 head gasket

 

And hopefully my clearance will be ok

 

.020 is WAY too close for my comfort on an engine you're expecting to spin to 7k on stock (or stock-ish) rods and hyper pistons with average clearances...

I'd feel more comfortable recommending you stick around .035" quench (piston to head deck clearance) if you're keeping the bore clearances tight and bearing to crank clearances on the tight end... Otherwise .038-.045 is what I'd shoot for with those components. Remember the pistons are going to rock in the bore, the rod/piston will stretch a bit at high RPM's, the crank / bearing clearance will get reduced under the load of trying to change directions, etc. All that makes the running clearance a lot less than the static clearances.

It's not about just one piece... it's a "package" where everything specs out and works together....

 

So id be ok decking it to zero? And running a .035 or so head gasket?

 

I tuned a similar cam but slightly less overlap on a .060" over 350 with aluminum heads. About 9.6 to one i think, i didnt get the exact piston specs or gasket thickness but car ran ok with it. Would have loved another point of compression but it certainly wasnt to doggy. Bottom end with a cam that big on any 350 will be alittle soft, as torque curve wont begin until 3600 and up. Now the heads are alittle restriction so it may make ok power by 3200 but still want to peak in the 4000-4500 range for torque and likely carry higher depending on the intake. We ran stock converter for awhile and you can tell the powerband was all top end. 3600 stall woke it up but still alittle soft off the line. Would have preferred a 4000 stall for track use. Still a bottom 12 sec car and would have went 11's if it wasnt for bad valvesprings

If you have iron heads that will help some as more heat will be kept in chamber. Aluminums should try for atleast 10:1 with the 306 cam. Its a stout cam for a 350.

 

Ok well im jot fetting the kieth blacks I read up on them and everybody breaks ringlands on them and there crap. So im not putting them in my motor. Ill try and find another brand but im sticking with .30 over to help boost compression

 

No, not at all.

Deck the block to ZERO; and use a .039" gasket.

The reason "everybody" breaks ring lands with the KBs (or any other pistons), is because "everybody" set the gap too tight. When the gap is set right, they work fine; as good as any other piston in that regard. Don't diss the product because "everybody" is not as smart as you, and can't (or won't) build their motor properly.

You can't bore a 350 block .30" over. That's more than a quarter inch. About as far as you can go is .060"; but there's no sense in taking a block all the way to its end-of-life size at the first service. Go with .030" instead.

The 07-306-8 and 08-306-8 are identical cams as far as the lobes. Only difference would be, the 07 might not have a fuel pump lobe, and will have the long dowel pin to drive the LTx water pump. That said, there's not much sense in buying the 07, since you'll just have to modify it back into the 08 to use it.
None of which has any particularly material effect on compression.

 

Thats what I meant. .030 sorry. Found the pistons I want to use http://www.summitracing.com/parts/pbp-p2256f-030. I still need to figure out what compressed head gasket thickness is for the compression calculator and factory deck clearance and play with this http://www.csgnetwork.com/compcalc.html to see what I would have to deck to. To get close to 10.5

 

Don't fear the internet hype on the KB's breaking ring lands off - that can happen to any cast piston where the ring end gaps aren't set right (too tight) or the piston to wall clearance is too tight for the application. Too many guys run tight specs and then throw boost or nitrous at it and butt the rings and crack or even rip off the ring lands. I've built and run a LOT of circle track engines with KB pistons in them over the years and have not once had a piston failure and that was turning engines to 7200 and some as high as 8400 RPM for ~50 laps a weekend all year. Plus I know a lot of guys running them on drag engines too without a problem - I've only built one drag engine and it was a 355 that I had put together from old circle track parts and then threw a 250 shot of nitrous at it and had fun on the drag strip - ended up running it for 3 years at the strip then sold the engine and the guy is still running it.

Just read the information sheet that comes with the pistons (or on their website) about setting piston to wall clearance for them and the ring end gap recommendations.

 

DON'T WORRY ABOUT IT. Wrong place to spend your mental energy; completely unproductive. It varies WIDELY, often by over .010" from one cyl to another ON THE SAME MOTOR, and hardly ever is within .005" on all 8. Virtually always AT LEAST the "spec" of .025" and usually ALOT more. Just assume that it's wrong (because it is) and prepare to deal with it. Have your competent racing machinist set it to ZERO by decking the block the exact right amount to match the measured height of the rotating assembly. Then just use a common ordinary regular 7733-PTwhatever they're up to this month.