despite some calculators fluffy estimates(many don't even ask for gasket spec's).. it's tough to achieve high compression like that on these little motors. Even with a smaller gasket(.039 x 4.060).. and 54cc chambers.. not to mention a true 0 deck.. you'll be lucky to reach 10.5 to 1. You probably wouldn't want to even try to reach that number either because they can be a bear to tune in warmer climates. Otherwise you'll need to be "octane hunting" for premium 93 whenever possible(which is what I used in my SCJ Torino when we lived there many years ago) to give you some margin if the thing ever gets a bit hot. 10 to 1 would be more livable.. but even then.. the tune will still be fairly important even in such a light car.
I'm hoping to stay below 10.5 honestly. As much as I'd love the horsepower, the amount of work some of my friends go through to properly and reliably drive their 11.1 cars is ridiculous. I just got the shipment of pistons and are returning them as this is being typed (UPS store) so hopefully i'll be exchanging for some of the nice shiny pistons youve found. :Handshake So I'll keep you guys updated definitely, and as for the heads, ive contacted both and are asking as many questions as i can. Looks most likely like ill be headed for the $300 ones, but if the springs and valves are new on the other ones, and i can talk him down a little, i may be going with those. It all depends on price and machine work required. I do like the idea of the other ones being ported already though... what do you think?
yeah.. that's certianly true. I run 11.5 - 1 on my AL headed 385 Chevy(with 210-215lbs of cranking compression) but the tuning took days.. that eventually turned into weeks as I slowly dialed in the final "safe tune". Even the little 10.5 - 1 motor(also running 200lbs of cranking compression) I mentioned earlier required more than a few days of backroads tuning and many plug readings to get by with premium fuel through the iron heads. As for the value of port work on those particular heads?.. the exhaust is just past horrible and even someone who isn't a pro at it.. and as long as they aren't chopped all to hell and heavily mismatched.. can easily improve things with mild to moderate porting. So that attribute can be worth it's weight in gold on those tiny little ports. Combining the exhaust work and a cam with more aggressive overlap will help reduce pumping losses and improve scavenging for an easy 20 horses. My only word of caution would be to make sure they didn't try to squeeze more than a 1.94 valve in there as shrouding and PTV clearance with larger cams/0 decks quickly becomes an issue. When the chambers are in stock form.. 1.90's are just about perfect(although a small relief cut nearest the chambers/bore wall will help low lift numbers there too). For the exhaust side.. 1.60's will help low lift flow massively(not to mention overall flow numbers and improve bias).. and therefore improve scavenging as well. They're so bad to begin with.. it's pretty tough to overdo the exhaust with too large a valve/ports anyways. Good luck with it all. PS. if you want?.. I could dig through my parts boxs/shelves to dig up a set of 1.25" springs/retainers that will get you by just fine for a milder .500 lift cam running in the 220's. Seat loads should still be good at well more than 100lbs for any I have since I test them right before I decide to store them. Another old timers trick is to use the old style.. and very cheap.. Chevy z-28 springs in combination with a lighter Vortec retainer package on them. 110lb srpings with lighter retainers.. will run just as good as 125lb springs with heavier ones. I'll be cleaning both shops and getting rid of most of my Chevy stuff this year anyways.. so if it helps you out.. just say the word and I'll start digging around earlier than expected.
I used speed pro cast pistons in my 302 bored out a bit. They are the 10.5-1 pistons, I had my gt40x aluminum heads milled a bit too trying to get more compression. I don't think 10.5-1 is "high" compression honestly. The old starter has no trouble cranking the motor over, and It doesn't ping on regular pump gas (not 91) but a lot of that is probably super conservative timing. A good set of heads goes a long ways, I got mine ready to go and checked out by a head shop for 600$ used with a set of 1.7 roller rockers. It was a good deal and worked out pretty good. Keep a lookout.
91 is not "regular" gas. That's what premium is mostly today. Mine does ping slightly on 91, but with it's loud exhaust, you really have to know what to listen for to notice it. And unless you milled those X heads more than .060, you're nowhere near 10.5 to 1. You're not out of the 9's. Milling them .060 will get them to 57 ccs, that combined with a zero deck piston yields 9.76 to 1.
I call it bull****. You can go on ebay and get some speed pro and get some pistons for less then they can. I used H120cp30 and they are awesome.(9.67:1) I am also using comp cam 35-409-3 cam and 942-16 springs in D0OE heads. Cut the humps out of the heads your self and smooth them up for clear flow pistons and nce the crank. Find some 1970/69 heads and you'll be fine. Save your money and spend it getting good machining and proper balance with your rotating mass. Hopefully you haven't already over bored your block.
Okay. Well I'm getting ready to buy those pistons you suggested earlier. So what kind of ring set should I get with them? Also got those closed chamber heads from the 289 AND the 302 heads for $225. So now I Gatta get valves and springs and rockers and ill be set to go. Seems like the machine work is really good actually. (Machine shop owner was selling them)
I don't remember from before, but did you say the block already been bored or is the machine shop going to hone to fit each piston? As for the piston rings.. Moly would be the best as they are easiest to break-in but if the machine work is already done on the block then you need to ask the machinist what type of ring he did the final hone for............the cross hatch pattern is different for Moly, Cast, Chrome.......................one hone is not the same as the other.
Well they're waiting for me to deliver pistons because they're gonna home it to whichever I bring them.
Ok then, I'd personally go with Plasma Moly faced rings..............same place you got the pistons is where I'd get the rings...........making sure they are an .040 over set.............................or you could ask your machinist which he prefers.
Would you think regular moly would be okay? Plasma-Moly seem relatively expensive and might seem like just too much for what i need. What do you think? ....... Ehhh... screw it. Gonna spend the extra $70 and do it right. So then, im gonna buy these with these. Look/sound about right?
those are the wrong rings for that piston and you'll need to use metrics. File fit is also best since they can be specifically tailored for the final bore size/piston material type. Not trying to prod you into going even further over budget.. but it's really too bad you don't have the extra ching to go for the total seal gapless rings. Despite the steeper price.. I use nothing else even in lower budget stock'ish type rebuilds since they can often outlast the bearings and still have similar leakdown rates compared to a fresh motor. They certainly make more power.. and it's across the entire rpm band too. And when you think about their benefits from a fuel economy standpoint.. not that you prioritize mileage in a performance type motor.. they can very easily help pay for themselves over time.
Sorry, most of the time I am in a "race only" mode. The plasma-Moly are certainly the best and the Moly will last much longer than regular Moly soaked coating......................and as for the pistons, they are perfect. The old myth about not running forged on the street because they will be louder, have more expansion and need more clearance is total bunk.................with better raw material and better machining it just doesn't make since to go with forged unless you can't afford it or just don't want to push the motor hard. Greg has a point about the Gapless rings...............but for the street I'm not sure it's worth twice the price of the Plasma-Moly.................I've used them in every race engine I've ever had and never had any oil/compression issues. I think you've made a good choice....................IMHO
Okay then.. Well sadly, I really can't afford the extra price for the piston rings. The plasma moly are the most I can afford, and even then it's pushing the limit. But I'm curious, are the rings gonna be the right size? It seems the bore in metric is the same as the bore in American standard..so then if the bore of the rings is .040" and the bore of the pistons are 102.616 will they work okay?
has nothing to do with the bore size.. it's the rings THICKNESS that you are concerned with in relation to that particular part linked above. Again.. the rings needed for that piston are 1.5 mm thick.. not 1/16 in thick.. so that part number won't work. Just be sure to talk with the summit tech to get the right matchup and you'll be fine.
