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Ok so, I'm finally getitng around to building my d16z6 for my del sol. old engine is out, and disassembled. I've got eagle rods, cp carillio 10.5:1 pistons (75.5mm bore) and all the machine work done to the engine, bored to 75.5, decked, head deck with full valve job, crank polished, and everything cleaned. But heres my question. I previously asked what compression I should run, and I was told 9.5-10 would be what I was looking for, and was pointed in the direction of a compression calculator. Well, I hadnt done the machine work yet, so what I could add into the calculator was near zero, so I decided to buy rods and pistons. When looking at my options I saw off the shelf choice for 9.0, or 10.5, and naivly thought that anyhting else I could do to change compression would be minor compared to this. Cut to today, and I've done a ton more reading, and have found that 10.5:1 on 91 pump (all i have readily available, and this will be a daily) will not be a good combo. So, I went back to the compression calculator, and plugged in everything I have, except for the decking on the head and block because I'm not sure how much the shop took off. So my questions are these
When in the calculator, if I assume there is no decking done (which there is I just dont know how much), and with the .027" headgasket I got, I get 10.72:1 which is concerning to say the least. When I change the headgasekt to .056" I get right on the money at 10.00:1. Can Just that small amount of headgasket thickness make a difference?
I'll call the machine shop to see if they have the details about how much they took off the head and block, but it was a good few month ago now, and im concerned that they dont have that info anymore. Assuming they dont, how can I measure how much is gone, or what would be a safe assumption?
Basically, I want to end at 10:1 compression, and already have the pistons, and likely cant return them. It seems to me that I can just run a thicker head gasket to compensate, and it looks like cometic makes pretty much as thick as I could need, so for example lets say I find out that the machine shop took off .015" total, supposedly I could run a .070" heagasket and end up at 10.02:2 which is close enough. Is there a downside to this? I also see some people having over bored headgaskets, why would someone want to do that?
Oh, i also meant to ask, and i know this is the wrong forum for this but someone should have an easy answer, ill get into tuning more after the car is running, but I seriously do not understand how a d series could have an ignition table. How does a car with a distributor change timing? I thought the way it worked is you connect a rotor to the camshaft, the rotor hits each plug wire, which ignites each spark plug. If this is the case, is this not a fully mechanical system? How can you change when the rotor makes contact with the cap electronically???
...but I seriously do not understand how a d series could have an ignition table. How does a car with a distributor change timing? I thought the way it worked is you connect a rotor to the camshaft, the rotor hits each plug wire, which ignites each spark plug. If this is the case, is this not a fully mechanical system? How can you change when the rotor makes contact with the cap electronically???
because this is the rotor shape:
the orange strip at the lower left is the electrode that feeds terminals in the cap. it's got about a 10-15° sweep across the face so it can fire at any point while that is rotating past the cap terminal. where/when along that edge that happens is what the ignition table is controlling.
9.6:1 is stock compression, no? also this is only the static compression. the dynamic compression is what's going to matter in the end, and you won't really measure that so much as tune to work with it.
So you're aware
-there have been street-able D16 builds with static compression around 12-13:1, though 11.5:1 is more common
-many K-series and J-series engines come off the lot with 11:1 compression including the ones that are in the minivan
-the right cam and adjustable cam gear are going to allow you/your tuner to dial in the right dynamic compression to balance performance and reliability.
It's good to know what your static compression is, but don't spend all your energy fussing with getting some exact number.
because this is the rotor shape:
the orange strip at the lower left is the electrode that feeds terminals in the cap. it's got about a 10-15° sweep across the face so it can fire at any point while that is rotating past the cap terminal. where/when along that edge that happens is what the ignition table is controlling.
Ahhh ok so rather than this limiting you from changing timing at all, it just limits you to a mechanical range where the cap and rotor are in contact, got it that makes sense
9.6:1 is stock compression, no? also this is only the static compression. the dynamic compression is what's going to matter in the end, and you won't really measure that so much as tune to work with it.
So you're aware
-there have been street-able D16 builds with static compression around 12-13:1, though 11.5:1 is more common
-many K-series and J-series engines come off the lot with 11:1 compression including the ones that are in the minivan
-the right cam and adjustable cam gear are going to allow you/your tuner to dial in the right dynamic compression to balance performance and reliability.
It's good to know what your static compression is, but don't spend all your energy fussing with getting some exact number.
Ah, I realize I did not give enough context in my original question. The reason I'm aiming for lower compression is because this car will eventually go turbo. I went with a higher comp ratio because i wanted less turbo lag, better mpg, and I didnt want the engine to be a dog na. So while yes if I was remaining NA, I might go for something even in the 11-12 CR, because I'm going turbo I'm more concerned with the compressions ratio. I dont want to have to decide between pulling so much timing that the car doesnt make as much power as it should, and running some fule additive like octane booster, water/meth injection, etc. Also I was told stock static CR for a d16z6 is 9.0:1
But really my questions are less about what CR I should be at, and more about how I can change the CR, because right now it looks like ill be wanting a bigger head gasket, and I really just want to make sure that that really does effect CR as much as the calculator suggests, and I want to know if there are any downsides to running a pretty thick headgasket like a .056" or a .070".
I also want to know what a good estimate for the decking and resurfacing would be or if and how I can measure it.
The point about dynamic compression is a good one, and I should do some more research in ways to control it, but really what I'm trying to avoid is running a compression ratio that when turbo, ends up with me pulling crazy amounts of timing or have to mess with the cam timing a bunch just to avoid knock or having to run something other than 91, the only thing I want to have to inject into my engine is what I can buy at the chevron down the road
Changing the thickness of your head gasket alters the dimension between the center line of the camshaft and the center line of the crankshaft... causing all kinds of engine event issues that you do not want.
The only proper way to alter your compression is to change the pistons... and if an off-the-shelf piston doesn't fit the bill, consider a custom set from JE, CP, Wiseco, etc.
Changing the thickness of your head gasket alters the dimension between the center line of the camshaft and the center line of the crankshaft... causing all kinds of engine event issues that you do not want.
The only proper way to alter your compression is to change the pistons... and if an off-the-shelf piston doesn't fit the bill, consider a custom set from JE, CP, Wiseco, etc.
So while I've read in other threads that running a thicker head gasket can have these effects, 1. I still dont fully understand why spacing out the head and block effects these things, 2. if its such an issue why are there so many people who run thicker head gaskets with no issue? is it only an issue in theory and not in practice? and 3. I have never, ever read anywhere on the internet a person saying "you shouldnt deck your block and resurface your head because it changes the center line of the camshaft and the center line of the crankshaft" which is bothersome to me, "running a .020" thicker headgasket?" "youre going to mess up all sorts of specific theoretical engine dynamics." "decking and resuracing for a total of .020"?" "oh of course you would want to do that you wouldnt want the head not to seal?" I havnt even seen someone say, "you should get a headgasket that as much thicker as material you removed to cancel out those effects" which that combined with the peple who do it with no issue makes me think its not the issue everyone cracks it up to be
I get that the correct way to get my compression exactly where I want it would be to have everything be stock compression and run different pistons, but I already have the pistons (too late to return them), and I definitly dont want to shell out for custom, so I need a solution for my situation, not a theoretical best solution. If I buy, for example, a .066" headgasket to use, assuming a range of decking and resurfacing of 0.003"-0.020", the compression calculator puts me at 9.84-10.23. Is that range of assumption safe for the decking and resurfacing? Could it realistically be more than 0.020"? and is the only downside this theoretical change in timing, quench, ect?
and I still have a good few questions that have gone completely unawknoledged. After decking and resurfacing how can I measure how much is gone? and I also see some people having over bored headgaskets, why would someone want to do that?
So while I've read in other threads that running a thicker head gasket can have these effects, 1. I still dont fully understand why spacing out the head and block effects these things, 2. if its such an issue why are there so many people who run thicker head gaskets with no issue? Who says that they don't have issues ? People that do dumb **** usually don't report this back in the forum. is it only an issue in theory and not in practice? ISSUE doesn't have to mean engine failure... it can also mean the lack of performance, overheating, and premature wear. and 3. I have never, ever read anywhere on the internet a person saying "you shouldnt deck your block and resurface your head because it changes the center line of the camshaft and the center line of the crankshaft" I said the DISTANCE between the two , not the centerlines themselves which is bothersome to me, "running a .020" thicker headgasket?" "youre going to mess up all sorts of specific theoretical engine dynamics." "decking and resuracing for a total of .020"?" "oh of course you would want to do that you wouldnt want the head not to seal?" I havnt even seen someone say, "you should get a headgasket that as much thicker as material you removed to cancel out those effects" which that combined with the peple who do it with no issue makes me think its not the issue everyone cracks it up to be This is EXACTLY what you should do... and if you haven't read that anywhere, you are reading from all the wrong places.
I get that the correct way to get my compression exactly where I want it would be to have everything be stock compression and run different pistons, but I already have the pistons (too late to return them), and I definitly dont want to shell out for custom, So, what you are saying is that since you made the wrong choice for pistons, you intend to build your engine wrong instead of spending more $$$ to make things right ??? so I need a solution for my situation, not a theoretical best solution. If I buy, for example, a .066" headgasket to use, assuming a range of decking and resurfacing of 0.003"-0.020", the compression calculator puts me at 9.84-10.23. Is that range of assumption safe for the decking and resurfacing? Could it realistically be more than 0.020"? and is the only downside this theoretical change in timing, quench, ect? It appears that you HAVE read a lot about many of the issues that I didn't take the time to flesh out here like timing, quench, tensioner failure, etc... it sounds like you really KNOW what to do here, you just don't like the answers and you are hoping that someone will jump in and support you in your bad decision. Just remember that you will be solo when it comes time to PAY for the bad decision.
and I still have a good few questions that have gone completely unawknoledged. After decking and resurfacing how can I measure how much is gone? and I also see some people having over bored headgaskets, why would someone want to do that?
First, unless you ABSOLUTELY have to... do NOT deck the block. There is no reason, unless the surface of the block is damaged or warped, to cut it. You NEVER do it just because...
Measuring the block height is difficult because the dimension is from the centerline of the crank main journal to the top of the deck surface. Most home/hobbyist builders do not have the proper tools to measure this. The gasket surface of the cylinder head will have some "milling" indicators along the outer perimeter... these appear to be a round button shape recessed into a "U" shape cut-out in the head surface. They are typically a rough reference of .037" to .040" depending on the head type when the head casting is new and uncut. Measuring these will give you an approximation of how much material is missing from the cylinder head surface. Now, since you know the correct thing to do is measure how much is missing and add this value to the head gasket thickness to "put it back", then do it. If your ultimate difference is a thousandth or two or three plus or minus... don't sweat it.
Factory head gaskets have a bore opening that is .020" larger than the bore. This is because there is some flexibility in the installation process where the head gasket can move off center slightly on the dowels... and if the gasket cylinder bores were to be the exact same dimension as the cylinder bores in the block, a few thousandths of the head gasket edge will overhang into the bores. This material gets red hot during combustion and can cause pre-ignition or detonation.
I’m running a JDM D15B with a Y7 head, headers, Y8 intake manifold and Y8 TB (yes there’s a way even with the Y7 Head) and my compression ratio is 10.11:1. Also have a cold air intake. This setup however is pretty damn good for what it is. Got a short shifter also. Coilovers, NRG Steering wheel. But you are fine with 11:1 compression.
Also to comment on the guy above me. He is right I used a DIY gasket on both the intake manifold and the exhaust manifold and I could smell the small parts of overhang burn off clear as day.
Dont go with a super thick gasket. Not worth it. Unless it’s one of those JDM gaskets that use the thick plastic type rubber crap…. Reusable gaskets and they last forever.
First, unless you ABSOLUTELY have to... do NOT deck the block. There is no reason, unless the surface of the block is damaged or warped, to cut it. You NEVER do it just because...
Measuring the block height is difficult because the dimension is from the centerline of the crank main journal to the top of the deck surface. Most home/hobbyist builders do not have the proper tools to measure this. The gasket surface of the cylinder head will have some "milling" indicators along the outer perimeter... these appear to be a round button shape recessed into a "U" shape cut-out in the head surface. They are typically a rough reference of .037" to .040" depending on the head type when the head casting is new and uncut. Measuring these will give you an approximation of how much material is missing from the cylinder head surface. Now, since you know the correct thing to do is measure how much is missing and add this value to the head gasket thickness to "put it back", then do it. If your ultimate difference is a thousandth or two or three plus or minus... don't sweat it. Ok, ill look into this, ill also see if the shop has a good way to measure and take it back to them if they do
Factory head gaskets have a bore opening that is .020" larger than the bore. This is because there is some flexibility in the installation process where the head gasket can move off center slightly on the dowels... and if the gasket cylinder bores were to be the exact same dimension as the cylinder bores in the block, a few thousandths of the head gasket edge will overhang into the bores. This material gets red hot during combustion and can cause pre-ignition or detonation. ok thank you, this was the answer I was looking for I couldn't find, and sure enough when I looked at the cometic head gaskets they list a .020" overbore that I didnt see
Thanks for the in depth reply, and yes, I am saying that because I did not buy custom pistons, I'm trying to understand the downsides of fixing it in an unideal way. (and yes I read more from the time of the first post and my most recent, hence the refference to timing and quench, which I still dont fully understand) I understand roughly the theoretical issues (quench, timing), and I've heard some generic practical problems that this comes with (detonation, overhearing, premature wear) but I still dont understand in reality what problems it will come with. I dont have cash to eat the cost of my 750$ pistons and go get new ones, so I have to decide between the downsides of running a thicker head gasket, and the downsides of running 10.46:1 on 91. (the comp I get on the calculator with the pistons I have, assuming stock headgakset (.037") and no decking or resurfacing) And from what I can tell the minor inefficiencies, with running a headgasket that brings up my head .017"(The difference in headgasket I would need to run to bring the comp ratio downt o 10.05:1), is less than having to pull crazy amounts of timing to run safely when I do go boosted. or whatever else I'll have to do to correct for the 91 pisswater I have convienent access to. So while I understand that the correct thing to do would be to do it right (this is my first engine build so next time I wont make the mistakes I did this time) really this time I just need to understand the downsides, and decide which I'd rather deal with
I’m running a JDM D15B with a Y7 head, headers, Y8 intake manifold and Y8 TB (yes there’s a way even with the Y7 Head) and my compression ratio is 10.11:1. Also have a cold air intake. This setup however is pretty damn good for what it is. Got a short shifter also. Coilovers, NRG Steering wheel. But you are fine with 11:1 compression.
Also to comment on the guy above me. He is right I used a DIY gasket on both the intake manifold and the exhaust manifold and I could smell the small parts of overhang burn off clear as day.
Dont go with a super thick gasket. Not worth it. Unless it’s one of those JDM gaskets that use the thick plastic type rubber crap…. Reusable gaskets and they last forever.
I'm not good with 11:1 to go be boosted on 91, and it seems like youre talking about intake and exhaust manifold gaskets, this thread is about headgaskets...
Ok update, took it back to the machine shop, the head was resurfaced .006"-.009", he was saying how much got taken off depends on what it was from the factory, and that the spec had a small range, hence the amount taken off is a small range, and he said the blocked was decked about .007". so now that I have my number, about .013"-.016", I can add that to my headgasket, which would mean I would run the .051" headgasket, and have compression of 10.48:1. or, I could run the .066" head gasket for a comp of 10.12", or I could run the .070" headgasket for a comp of 10.02, the .066" would be .015" off and the .070" would be .019" off. So now that I Have some more concrete numbers, how bad is it to be that much off? From what i understand as far as timing goes, 1mm is about 1 degree of timing, and .019" isnt even half a mm. And for quench? how bad of a difference is this? tuning for 10.48:1 vs 10.02 seems significant to me, how significant is it compared to my head being .019" higher?
Reading some more, it also seems like running a thicker gasket would be good because it will increase my p2v(piston to valve) and p2h (piston 2 head) clearances, which I want because in the future I'd like this to rev to 9k, and from what I understand you need those higher clearances to do that. am I misunderstanding something about these things?
Run the .051" thick gasket to get you back to proper spec. If the pistons are flat-top style... or even a low height "flat dome" style to make a compression ratio of 10.50:1... everything will be fine. For half a point of compression reduction, the extra gasket thickness causes FAR more trouble than what it is worth. As for the better P2V or P2H clearance with the thicker head gasket... the former will only be a problem if you have a really high lift/long duration camshaft profile and the latter doesn't even apply unless you have stretchy connecting rods. LOL
When you boost this engine... the difference between a 10.50:1 engine and a 10:1 engine is only going to be 1-2 psi LESS boost to be equally safe on your crappy pump gas. Next question: Why do you want to run 9K RPM ?
Run the .051" thick gasket to get you back to proper spec. If the pistons are flat-top style... or even a low height "flat dome" style to make a compression ratio of 10.50:1... everything will be fine. For half a point of compression reduction, the extra gasket thickness causes FAR more trouble than what it is worth. As for the better P2V or P2H clearance with the thicker head gasket... the former will only be a problem if you have a really high lift/long duration camshaft profile and the latter doesn't even apply unless you have stretchy connecting rods. LOL
Ok, This makes sense, and I dont think I'll ever want to run too aggressive of a cam, and no my rods are eagle steel forged so I wont worry about that.
Originally Posted by JRCivic1
When you boost this engine... the difference between a 10.50:1 engine and a 10:1 engine is only going to be 1-2 psi LESS boost to be equally safe on your crappy pump gas. Next question: Why do you want to run 9K RPM ?
This is significantly less important to me, but I like the idea of a high reving engine just for the fun factor while driving around the street, I havnt done a ton of looking into this yet because it wont matter til im boosted and do headwork, as my head will stay completely stock for a while. But I mentioned it just because the extra clearance might matter for it
High revving engines don't last for long... no matter how much $$$ you spend. For longevity, I wouldn't rev the engine any more than about 500 RPM beyond peak power.
Questions about calculating compression
Re: Questions about calculating compression
