I'm hopping up a 292 Y Block and have some questions. Stock Iron Heads. Ported. 2.02 Intake and 1.60 Exhaust. I'm looking at static compression ratio, and dynamic compression ratio's and these are the numbers that I've calculated. Let me know what you think: Engine Bore Size: 3.830 Piston Stroke Length: 3.610 Head Gasket Bore Diameter: 3.937 Gasket Compressed Thickness: .047 Combustion Chamber CC's: 65 Piston Dome: 0 (I'd like to run the domed pistons, but I can't!) Piston Deck Clearance: 0 Intake valve closes at ABDC: 70 degrees Al***ude: 4500ft Static Compression Ratio : 10.167 Dynamic Compression Ratio: 7.826 Obviously there are still a lot of things that I can do to tweak those numbers however I need to. But my concern is that I'd like to get the dynamic compression ratio up a little bit from that number. I know that detonation is a big concern. But, from what I've read, detonation won't really come into play unless your DCR is closer to 8.5:1 on iron heads. My target would be close to an 8.25:1 DCR. So, that being said, what are your thoughts on where I'm at?</pre>
Probably the only way to get the DCR up would be with a different camshaft. Intake opening earlier and less overlap with the exhaust. Top end power would fall off a little but the torque would come in at lower revs.
You should be able to use a .035" thick headgasket if one is available? Maybe buy a custom one? This would be about as close as I would run her. You do realize that the DCR will increase if you go smaller on intake valve closing timing. I can't use my D2K program to check how much less timing you will need tho to help you out, sorry. That said, I bet an Isky Z-25 solid lifter cam would be just what you would like.. Call Ron I. and flat ask him. pdq67
I have a domed piston that I can run which would add up to 10cc of volume to the piston. Which would add any amount of compression that I'd like. But, my concern is detonation. If I stay under about 8.5:1 on dynamic compression I'd be alright? Maybe? No? I'm a crazy newb?
If you've mocked the engine, and it has a TRUE .000" deck, then I'd be looking at quench issues. I can't remember what a Y block head looks like from the chamber side; does the deck cover part of the bore (like SBC) or is it an 'open' chamber where the chamber pretty well covers all the top of the bore. If it's the latter, there's not much you can do for quench, but if it's the former, you might either look for a thinner gasket, or have the block decked so that you have the pistons .010-012" above deck. Conventional wisdom a**** most guys is that on an N/A engine, .030" of quench is running the risk of mechanical interference at speed, .035" works real well, and you start losing effectiveness much over .045". You might PM Jack Vines (Packard V8); he's probably forgotten more about old engines than I'll ever learn. -Bill
one way to minimize detonation is to optimize quench distance. With Ferrous rods, get that piston quench pad closer to the head--.035" to .040". Thinner head gasket or get those pistons up out of the deck. It won't help your DCR, other than the couple cc's of combustion chamber reduction, but it will definitely give you some detonation resistance. Dang!!! type too slow, thecarfarmer beat me to it!!
I was wondering about quench as well with the Y. The chamber is about half the size of the bore- so it is covered. I can have my deck machined with the piston .005-.010" out of the whole for the sake of having a better quench area. That would move the gasket volume down and increase the DCR.
A better quench area helps reduce detonation! Wow! I didn't know that. What would be the "ideal" quench distance with my set up? .035-.040" of an inch? I've got Eagle Featherlight aftermarket rods. And custom aluminum pistons. I posted earlier that the pistons can be domed up to 10cc's, or flat top. (I think that I've heard that flat topped pistons are almost always the better solution. But I don't know....)
Some guys make a lot of power with domed pistons, but for most guys... unless you are 'in the know', really super smart, lucky, or do a lot of R & D, you'll be better off with trying to get the compression with little to no dome, and shaving the chamber. And re: quench, a number of guys consider that decking the block .010 to get the quench to a useable value will be more of a help with detonation than the extra CR will be a hindrance. Also, I plugged the #s in your first post into a handy spreadsheet I picked up; unless the fact that it's 12:35 AM is getting to me (possible), it spat out that your combo only has 9.6:1 mechanical CR. I'll check and make sure I got this right in the morning (the other morning, ya' know, after I sleep). BTW, what's the rod length, cam duration at .050, and lobe spread? -Bill
Cometic gaskets will make you any gasket thickness you desire,At .000 deck i would leave it and take .010 off the gasket.Bumping up static will bump running cr.Giving you .037 squish is perfect.Advancing the timing events 3-4 degreeseWill close the intake event earlier raising running cr also. Your close enough to make what you got work,Remember static cr is just that a number,running cr is what your after. Good stuff.
I've recently had some discussion of quench and head gasket thickness regarding the flathead six Mopar, and GWhite has been doing the legwork for custom thickness gaskets. You might PM him, he has been talking with a company called "Gaskets to Go" about sandwich gaskets. You have to make the call as to whether you'd rather do the machining for use with off the shelf parts, or have custom parts made.
I believe the ideal quench space is around 28-34, I may be a little off with that? As far as detonation I don't see a problem with 8.5 or 8.7 dynamic as a problem. If it is a problem you could install a cam with a higher duration that would give you some cylinder bleed with more valve over-lap.Just a thought?zrxlover
this concept is perhaps the single most "unknown" concept a**** non professional engine builders, (and some "professionals" I know) and it is quite possibly, the MOST important consideration for optimizing ANY engine's performance. The idea is, the closer the piston to the head, the more heat is transferred away from the top of the piston into the head, which is then transferred to the water, which is then..... The cooler the piston top, the less likely a spontaneous combustion event. Then follows that you can run more timing and/or less fuel, both of which equal MORE POWER!!!!! They also can reduce the amount of carbon and other "junk" buildup in the chamber or on the piston, which under extreme pressure and heat can become glowing hot and..... The down side is, if you "push it" with the tuneup, you're headed back toward heated piston tops and detonation again.
The quench isn't so much about transferring heat. Heat in the cylinder is what power is made of. The quench causes the fuel mixture to swirl and tumble around which mitigates detonation and promotes a more complete burn. I could think of a more eloquent way to say it but I don't have the time at the moment. Long story short, getting the quench right is one of the most important parts of an engine build. It allows you to use more compression with less chance of detonation, you'll need less total timing to make peak power, and you may even see an increase in fuel economy. Zero deck it and run a gasket that compresses to around .040. Pretty simple. http://ncperformanceinc.com/
It will have a influence on it but at high rpm with little effect.Squish when determaind correctly will leave the piston tops so clean it will appear almost not run.Chamber shape has alot to do with it also.Its mostly a cauculated judgement call,aluminum rods heavy pistons and small wristpin dia teamed up with sonic rpms are reasons to run a bit wider. Unless you teardown a combination you built its only a caculated guess to get from real close to perfection. As a safe starting point in general i shoot for .028 to .035. G***er 38 your right on with your reply btw.
Exactly - since these are "heat" engines - maximum power would derive from keeping 100% of the heat within the combustion g***es, rather than allowing the heat to escape either to the pistons, heads, cylinder walls, oil or coolant... .
I agree with ya'll let the heat out the exhaust and the heat in the cylinder to a certain temperature. I have found that 175 deg. F.to 185 deg. F. makes the best power, that is what I have found.Better quench makes a better uniform burn over the entire piston top producing a more efficient running motor.
Sorry it's taken me a while to log back in. The rod lenght is 6.125" and the duration at .050" is 236.
I also need to find out from the piston manufacturer what the sidewall clearance needs to be for my pistons. They're custom aluminum pistons. From what I'm gathering the "optimum" quench area is really an educated guess. But, everyone seems to say the .035-.040" of an inch realm is as close as I should run to still maintain a safe distance. And NO to the domed piston.
What's also interesting is that every calculator gives me slightly different numbers. Theoretically measuring the same things. For instance United Engine's Calculator Static compression of 10.167:1 Dynamic compression of 7.760:1 Wallace Racing gives me these numbers: Static compression ratio of 10.167:1. Effective stroke is 2.66 inches. Your dynamic compression ratio is 6.85:1 . Your dynamic cranking pressure is 129.74 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, al***ude, and boost of 0 PSI is 6.85 :1. V/P (Volume to Pressure Index) is 95 (Wallace Racing does take my al***ude into account- 4500ft) Further, if I look at what United Engine refers to as "effective" ratio I get this number (they add 15 more degrees of rotation to account for actual valve closing event- 15 more degrees from .050" to .000" lift): Effective compression ration: 6.668.
you are absolutely right!!! I focused my reply on only a small part of the issue, and completely ignored the larger issue. Thanks for straightening me up!!!
It's not that quench is a guess so to speak, but how close before you slam the piston into the head. You want the piston as close to the head as possible. For a starting point .038" is safe with a good steel rod, but you need more with an aluminum rod. On a serious naturally aspirated race engine you will keep making the quench tighter at each refresh until you actually see marks from the piston knocking carbon off the head. G***er38's post was correct also. The air and fuel mixture are better homogenized for a more complete burn. Just make sure you use the correct method for measuring piston deck height correctly. Rock the piston one way and measure, then rock the other way and measure the other side. Then add and divide to get the average. As for the pistons definitely use a flat top if possible. The dome piston interfers with flame travel from the spark plug across the piston. So in theory they would require more timing advance when you want to run the least amount possible so the piston has less pressure to overcome as it reaches TDC.
Heya Dawg, Got the rod length plugged in now. I'm guessing at where your cam is installed at, and the lobe center spread ground in. I'm also guessing you have some valve notches; I budgeted 4 cc for that. All calculators will make ***umptions about things like ring crevice volume, head gasket diameter, etc. So, they'll spit out slightly different #s. If you went in with the intake on 110 (doesn't matter if we're talking straight up ground on 110 centers, or 2 deg advanced but ground on 112 lobe spread), your intake close at .050" would be 49 degrees after BTD That would put your static CR at 9.65, dynamic CR at 7.75, and cranking pressure at 151 PSI. Advancing the intake close to 44 brings the dynamic CR to 8.03, and cranking pressure to 159 PSI Advancing the intake close point to 42 degrees (where it'd be if you installed on a 102 intake centerline; cam ground on a narrowed spread with some advance), kicks the dynamic CR to 8.14 and cranking pressure to 164. Still not real aggressive. Changing to a 'notchless' top, or adding a 10cc dome makes all the above #s jump to piston...........cam ICL.........Mech. CR.......Dynamic CR......Cranking press -4cc(notch)......49................9.65...............7.75.................151 -4cc(notch)......44................9.65...............8.03.................159 -4cc(notch)......42................9.65...............8.14.................164 +0 cc............. 49...............10.11..............8.11.................161 +0 cc............. 44...............10.11..............8.41.................168 +0 cc............. 42...............10.11..............8.52.................172 +10 cc............. 49...............11.52..............9.20.................190 +10 cc............. 44...............11.52..............9.55.................199 +10 cc............. 42...............11.52..............9.68.................203 So, as you see, if you have a true flat top, you might want to have that cam installed advanced, to help build up some low end, especially if it's ground on a wider spread like 110-112 degrees. And, if the domed pistons have notches that offset some of that 10cc of dome, you can kind of extrapolate how that'd work out. If the engine's going in a '30 Ford with a stick, 4.10's, and it's going to sit out in the air and lose some heat, you can push the CR a little more, and run a slightly bigger cam than in a '55 F1 with A/C, a stock convertor, and 3.08 gears. So, all that comes into play, too. 236 @ .050 is pretty healthy for a 332" engine (292... like hell), but it's not unreasonable to run even more in certain apps (like, you want to beat the hell out of the thing and have 4.56's in the back). But it's certainly reasonably healthy. Now, I'm living at sea level, and have never been involved with anything running at al***ude. I'd talk to some drag race guys who've had experience with that, or Bonneville guys, and ask 'em how much to factor in. You might even want those 10cc domes after all. I don't know. But, you'll get a BTTT. -Bill
Listen to this guy. He's a smart one. Nice point about wanting the least timing possible. I'm amazed at how many people think the more the better. The truth is if you need a bunch to make power you've got a pretty inefficient air pump on your hands. Awesome post man, I wouldn't mind picking your brain a little sometime.
I'd like to run the numbers through the KB calc, the one that I've used for decades, but I'll need the intake close at 0.050" tappet lift. I have the 236 @ 0.050" duration, so I can figure the intake close if I know the intake centerline. Do you have that? Also, I think I would go with the 10cc pistons. You are at an al***ude of 4500 feet, so you will have to figure 3% degradation of power for each 1000 ft (less oxygen breathed in each time the cylinder fills). So, figure 13.5% less power than you'd be making at sea level. Less cylinder pressure, less chance for detonation on the same fuel. I would be fine with the 0.047" squish. General recommendations down through the years have pretty much settled on 0.035" to 0.045". Vizard found piston to head interference on a SBC at 0.027". The crank bends a little, the rod stretches a little and the piston grows a little from heat.
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