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Old 03-13-2017, 03:18 PM   #1 (permalink)
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Default Lowering cylinder pressure with higher compression?

I have been looking through a lot of posts trying to figure out my build and get everything as efficient as possible. I want to build my D16Z6 to 10:0-10.5:1 SCR with 0.5mm overbore to have a fun daily driver with decent low-mid torque. I also plan to add a turbo, still deciding which one. I'm shooting for 250whp but want something big enough for 300whp (while still staying within its efficiency range) just in case I want more power later. I also plan to add water injection to lower IAT and prevent det during boost, tuning with Neptune. Probably going to have to run 89-91 octane depending on how well I can reduce cylinder pressure. Seems to me to be the best way to get a fun street car that still gets decent gas mileage and limits the chance of detonation when you get on it, but I want to go further in and pay closer attention to the finer details in order to have a more efficient setup.

The question is what is the best way to get the compression I want while preventing knock/det and make power efficiently? From what I've found online, the best way (other than adding fuel) is to increase quench/squish and/or install a cam with good overlap in order to bleed off excess cylinder pressure.

But how exactly do you increase quench in a D16Z6 (I know the Y8 head has better quench but I want to keep my Z6 head) and is there a cam would work for what I'm trying to achieve? I've tried and just can't wrap my head around cam profiles.

Hell, if I can get good quench and the right cam, paired with a good tune, I could probably get away with 87 octane (which would be awesome).

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Old 03-13-2017, 10:20 PM   #2 (permalink)
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Quench is a very tough subject because its very specific to application, and complex in how it actually affects the combustion process.generally all motor you want nice tight quench clearance preferably around or less than .040 thou. however as you go up in boost you want to have larger quench clearances due to problems with compressing a much denser charge into a very small space possibly causing detonation in small pockets on the quench pads.

I would highly suggest googling about quench under boost and see what you come up with big boosted v8 engines and apply that to what your doing.

Here is a thread on here talking about quench https://www.d-series.org/forums/engin...lk-quench.html
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Old 03-13-2017, 11:44 PM   #3 (permalink)
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overthinking the issues......

you'll have to ditch the 87 octane and go E85...

Myself I start at 11.5:1 compression and a small turbo.....

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Old 03-14-2017, 05:54 AM   #4 (permalink)
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Originally Posted by cervan View Post
I would highly suggest googling about quench under boost and see what you come up with big boosted v8 engines and apply that to what your doing.

Here is a thread on here talking about quench https://www.d-series.org/forums/engin...lk-quench.html
I have tried googling and haven't come up with much on the subject when you start adding boost to the equation. I have already read that article and it helped a little, but as you said it is all very application specific. I'm just not sure how to achieve a tight quench with a Z6 without throwing compression through the roof. Is it even possible?

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overthinking the issues......

you'll have to ditch the 87 octane and go E85...

Myself I start at 11.5:1 compression and a small turbo.....

400 whp and mpg, info can be found here....
I have seen a few articles here about quench, most of them involve you, cervan, and acid-beaver in the discussion. Also saw a few articles about P29 pistons in a D16Z6. I would rather avoid E85 as this will be a daily driver. I know with proper tuning, good quench and the right cam you can use 87 octane at 10.5:1 compression. If I remember right there was a guy running nearly 13:1 on 87, though he was N/A. If I have to run 91 I don't mind, but I want to stay around 10:1-10.5:1 with a somewhat larger turbo at lower boost so I'm not in boost unless I want to be. Then when I am in boost I'll have the meth injection running only water to cool the intake charge (artificial octane), if I end up needing 50/50 I can. I'll do what I have to do to make it work, I'm just trying to brainstorm to see what is possible and try something a little different.

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Old 03-15-2017, 10:15 AM   #5 (permalink)
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87 octane with 10:1 isnt particularly hard to accomplish, but adding boost makes tuning much more important that you get it correct the first time or else you might end up with broken ring lands on your first pull. i would highly suggest a set of forged 2618 pistons if you want to go this route, because even a little bit of detonation at full throttle will eat up the ring lands on stock pistons. if you want to try it on the stock stuff, by all means go for it. But from my personal conclusions the stock pistons are too fragile.
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Old 03-15-2017, 10:54 AM   #6 (permalink)
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Originally Posted by cervan View Post
87 octane with 10:1 isnt particularly hard to accomplish, but adding boost makes tuning much more important that you get it correct the first time or else you might end up with broken ring lands on your first pull. i would highly suggest a set of forged 2618 pistons if you want to go this route, because even a little bit of detonation at full throttle will eat up the ring lands on stock pistons. if you want to try it on the stock stuff, by all means go for it. But from my personal conclusions the stock pistons are too fragile.
I am definitely planning to run forged pistons and eagle rods with this setup. I'm just curious on how to reduce the chances of detonation, mechanically in a D16Z6. From everything I have been reading it's most about head design/flow along with quench and valve overlap to reduce cylinder pressure. I just cant seem to find much information about how these vary in a turbo application. Also it seems that increased compression is a byproduct of tightening quench. So is there a way of improving quench without increasing static compression beyond 10:5.1?

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Old 03-15-2017, 01:41 PM   #7 (permalink)
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Run a flat top or dished piston to lower compression
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Old 03-15-2017, 02:53 PM   #8 (permalink)
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Run a flat top or dished piston to lower compression
I'm not trying to lower compression. I'm trying to increase it, while tightening quench, but without bringing compression too high. Not sure if it can be done, that's why I'm asking. According to zealautowerks, if all I did was swap pistons it doesn't work. Flat tops would increase the compression to over 11.5 compression, dished pistons (less dish than stock) will give me the compression I'm looking for, but doesn't seem to do anything to give better quench.

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Old 03-15-2017, 06:29 PM   #9 (permalink)
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I am definitely planning to run forged pistons and eagle rods with this setup. I'm just curious on how to reduce the chances of detonation, mechanically in a D16Z6. From everything I have been reading it's most about head design/flow along with quench and valve overlap to reduce cylinder pressure. I just cant seem to find much information about how these vary in a turbo application. Also it seems that increased compression is a byproduct of tightening quench. So is there a way of improving quench without increasing static compression beyond 10:5.1?
the entire point of quench is to compress the charge into a single space, ignite it , and then let the flame propagate evenly throughout the rest of the chamber. this was a major deal back in the 80's when this pent roof style combustion chamber was developed because the combustion chamber didnt have a lot of swirl. Swirl or circular motion inside of the combustion chamber allows the fuel to be burned more evenly as is the same with tumble, or gas rotation perpendicular to the crankshaft. without alot of turbulence or swirl/tumble the flame front travels more slowly and could lead to multiple flame fronts, and less overall thermal efficiency since less energy is transmitted to the piston at higher leverage angles (meaning it releases its energy later in the stroke).

However if you squeezed all of the gasses into a smaller space, rather than inducing swirl/tumble you could achieve the same thing. And in comes quench. quench displaces the intake charge into the combustion chamber in the head. Allowing the dense mixture to be ignited and then propagated down into the rest of the chamber as the piston travels downwards. Having too much clearance between the quench pads means you could possibly have detonation problems as the flame front comes down and then suddenly expands quickly to fill the small pockets of dense charge that ignite very quickly (detonation).

Where does that leave quench on a boosted motor? well its a much denser charge, so that means that even the charge between the head and the quench pads on the pistons are much denser possibly allowing for it to be ignited even at .040 thou clearance or less (and this propensity to ignite goes higher as the boost goes higher, not sure if its linear however).

Or instead of going for less clearance, go for more and eliminate the quench pads all together. above .100 should be enough to get you out of the quench danger zone. if you wanted to keep 10:1 CR and still have quench pads, you would need a custom piston with a valley in the center to the edge of the quench pads mirroring the combustion chamber in the head.

Id like to say that this is what ive learned over the years, i may be wrong and if someone has something to add in please do.
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Old 03-16-2017, 07:14 AM   #10 (permalink)
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Or instead of going for less clearance, go for more and eliminate the quench pads all together. above .100 should be enough to get you out of the quench danger zone. if you wanted to keep 10:1 CR and still have quench pads, you would need a custom piston with a valley in the center to the edge of the quench pads mirroring the combustion chamber in the head.

Id like to say that this is what ive learned over the years, i may be wrong and if someone has something to add in please do.
Awesome! Thanks for the great info. I figured it would be something like that, but you never know unless you ask. Looks like I'm stuck with dished pistons to get the correct compression (maybe some rollerwaves) or talking to a piston manufacturer to get some custom made flat tops.

So what about cams to reduce cylinder pressure with overlap? Is it even worth it? I've read that it's great to run a cam with more overlap to bleed cylinder pressure with higher compression motors in turn lowering octane requirements, but then again these were NA articles. Then I found this...

"With forced induction, a long overlap between the intake and exhaust duration is going to allow an excessive amount of the charge air (pressurized inlet air) to slip right out the exhaust.
This will lower your charge pressure from excessive flow, lowering your boost, as well as increase your BSFC (brake specific fuel consumption) meaning less fuel economy, and larger injectors to do the same work."

Is that something a VTEC cam can fix by having more overlap before VTEC and less later in the rpm range, where detonation is less of an issue? Is it even worth it to mess with it, or keep a smaller cam and let higher octane and cooler IAT do the work? Keep in mind I want efficiency, not necessarily budget friendly (which I know defeats the point of building a D).

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Old 03-16-2017, 05:41 PM   #11 (permalink)
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Awesome! Thanks for the great info. I figured it would be something like that, but you never know unless you ask. Looks like I'm stuck with dished pistons to get the correct compression (maybe some rolkerwaves) or talking to a piston manufacturer to get some custom made flat tops.

So what about cams to reduce cylinder pressure with overlap? Is it even worth it? I've read that it's great to run high lift/duration cams to bleed cylinder pressure with higher compression motors to lower octane requirements, but then again this in NA. Then I found this...

"With forced induction, a long overlap between the intake and exhaust duration is going to allow an excessive amount of the charge air (pressurized inlet air) to slip right out the exhaust.
This will lower your charge pressure from excessive flow, lowering your boost, as well as increase your BSFC (brake specific fuel consumption) meaning less fuel economy, and larger injectors to do the same work."

Is that something VTEC can fix by having more overlap before VTEC and less later in the rpm range? Is it even worth it to mess with it, or keep a smaller cam? Keep in mind I want efficiency, not necessarily budget friendly (which I know defeats the point of building a D).
overlap and boost go against eachother, i just spec'd out a turbo cam for my turbo 6.0 ls motor and it had an lsa of 117/112 thats -6 degrees of overlap.

the reason for that is because obviously you dont want to be forcing unburned fuel out of the exhaust when it could have been filling the cylinder. And also these effects will be compounded when you go higher in the rpm range. Scavaging effects turbo engines just like NA engines however the effects are somewhat covered up. if your running a good turbo with a decent drive ratio you should always have more pressure on the intake side than the exhaust. this means you can push the exhaust gasses out very quickly and start filing the cylinder much sooner than if you had alot of overlap. So if you had -6 LSA and your exhaust valve shut sooner, you could start filling the cylinder much sooner. Also the higher in rpm's you go the faster that the exhaust can be evacuated and the cylinder filling can happen sooner.

what your talking about doing is having a cam made with alot of overlap on the low cam and zero to negative overlap on the high cam, very strange combination. I dont think that would be a good combo drivability wise, as to bleed off enough compression you would be lowering your vacuum, making your brakes harder to use and generally less power on the low end while driving around. however, it might have a nice sounding idle. and quite possibly one of the softest vtec hits ever seen.
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Old 03-16-2017, 06:54 PM   #12 (permalink)
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what your talking about doing is having a cam made with alot of overlap on the low cam and zero to negative overlap on the high cam, very strange combination. I dont think that would be a good combo drivability wise, as to bleed off enough compression you would be lowering your vacuum, making your brakes harder to use and generally less power on the low end while driving around. however, it might have a nice sounding idle. and quite possibly one of the softest vtec hits ever seen.
Yeah... Like I said in my first post, I haven't been able to wrap my head around cams. They just straight up confuse me. I see all those numbers and my head starts spinning lol. Thanks for clearing that up. So definitely just a mild turbo cam for me then and I guess I'll have to talk to Larry over at Endyn to see what we can do about getting what I want as far as pistons go.

Ok one more thing, just cause I can't seem to find it and its on topic... How do you calculate quench (or I guess it would be squish) when you have dished pistons? I know you have subtract (add if it's in the hole) the piston to deck height from the head gasket thickness, but what about the depth of the piston? How do you calculate that without having the piston in hand? Can you do it with the domr/dish cc?
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Old 03-16-2017, 07:55 PM   #13 (permalink)
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Yeah... Like I said in my first post, I haven't been able to wrap my head around cams. They just straight up confuse me. I see all those numbers and my head starts spinning lol. Thanks for clearing that up. So definitely just a mild turbo cam for me then and I guess I'll have to talk to Larry over at Endyn to see what we can do about getting what I want as far as pistons go.

Ok one more thing, just cause I can't seem to find it and its on topic... How do you calculate quench (or I guess it would be squish) when you have dished pistons? I know you have subtract (add if it's in the hole) the piston to deck height from the head gasket thickness, but what about the depth of the piston? How do you calculate that without having the piston in hand? Can you do it with the domr/dish cc?
quench is measured at TDC, if you know the compression height and have a technical drawing of the piston (such as a flat top, or symetrical dish) then you would measure from the top of the piston at tdc to the head.

typically you would measure the rod length, piston pin dia, and piston compression height to get piston height in block. then if you know your head gasket thickness you can get your piston to head clearance and ultimately your quench (since quench on a y8 is zero deck with the head, z6 is .040 out of the bore). measuring quench with a dish piston means measuring twice, the ring diameter and then the dish diameter and subtracting the height difference from the ring diameter quench amount.
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Old 03-16-2017, 08:36 PM   #14 (permalink)
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(since quench on a y8 is zero deck with the head, z6 is .040 out of the bore). measuring quench with a dish piston means measuring twice, the ring diameter and then the dish diameter and subtracting the height difference from the ring diameter quench amount.
Thanks, I figured it would have to be done that way. I was just trying to figure it out using zealautowerks, so I could play with compression numbers with different pistons then figure out the quench from there. I just wasn't sure if there was a way of calculate it based on the dish/dome cc for a given piston, without a technical drawing. I guess every piston is manufactured differently to achieve the same compression so I guess that's the only way.

And holy crap, I didn't realize the quench on a Z6 head was .040 out of the bore. That's a lot to mill/deck. I guess there really isn't a good way of getting any real quench (<.030) with that head. Maybe I will end up having to swap a Y8 head (my brother wants to swap anyway) on if I want to go for quench.
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Old 03-16-2017, 09:20 PM   #15 (permalink)
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Thanks, I figured it would have to be done that way. I was just trying to figure it out using zealautowerks, so I could play with compression numbers with different pistons then figure out the quench from there. I just wasn't sure if there was a way of calculate it based on the dish/dome cc for a given piston, without a technical drawing. I guess every piston is manufactured differently to achieve the same compression so I guess that's the only way.

And holy crap, I didn't realize the quench on a Z6 head was .040 out of the bore. That's a lot to mill/deck. I guess there really isn't a good way of getting any real quench (<.030) with that head. Maybe I will end up having to swap a Y8 head (my brother wants to swap anyway) on if I want to go for quench.
its alot to mill, but it has been done before. i dont know if i would suggest it for a high comp turbo motor though. if you want to know your compression ratio with a dish piston you will need to know the cc's of the dish and then you can put that into zeal autoworks. You can also figure out how much quench your piston ring will have on a dished piston by looking at the piston to deck height.
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Pick a fuel source and tune around it. Locally I have enough E85 sources if I ever chose that route.

Then again I was spraying 85 shot of NAWZ on 87 octane...which was fine until I ran out of injetor and went lean.
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Old 03-17-2017, 01:56 AM   #17 (permalink)
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i thought about this a little more, you might be able to get away with a more standard off the shelf turbo cam.

What you will need is a boost controller or a wastegate that can control boost from your maximum boost (lets say 8psi) down to zero at all rpm ranges. this would allow you to run high compression, yet in the low rpm's not build any boost where you are most likely to get detonation. this would require a separate map made for boost vs rpm.

Google around for electronic wastegate actuator and see if something sparks your interest.
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Old 03-17-2017, 08:30 AM   #18 (permalink)
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Originally Posted by transzex View Post
overthinking the issues......

you'll have to ditch the 87 octane and go E85...

Myself I start at 11.5:1 compression and a small turbo.....

400 whp and mpg, info can be found here....
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Originally Posted by transzex View Post
Pick a fuel source and tune around it. Locally I have enough E85 sources if I ever chose that route.

Then again I was spraying 85 shot of NAWZ on 87 octane...which was fine until I ran out of injetor and went lean.
Hey Bone. I really appreciate your input and I know you are very knowledgeable on these engines, but as this is a daily driver E85 just isn't an option. The closest E85 station to me is about 35 miles out of my way. That's and hour (there and back) of driving just to fill my tank. It IS possible (maybe not practical) to run 10.5:1 on 87 octane (easier on 91) and in a boosted application meth injection is there to save the day when I really step on it.

I'm trying to push the envelope a little and see if I can get it to run reliably on 87, which I understand probably makes me seem pretty dumb. Granted I will probably end up running 91 out of pure fear and for the sake of reliability. Yeah, it's going to take more work, time, money and attention to detail, but it's a hobby so I might as well have fun with it.


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Originally Posted by cervan View Post
i thought about this a little more, you might be able to get away with a more standard off the shelf turbo cam.

What you will need is a boost controller or a wastegate that can control boost from your maximum boost (lets say 8psi) down to zero at all rpm ranges. this would allow you to run high compression, yet in the low rpm's not build any boost where you are most likely to get detonation. this would require a separate map made for boost vs rpm.

Google around for electronic wastegate actuator and see if something sparks your interest.
Great suggestion. I'll have to look into that. Also this is another reason I am thinking of running a larger turbo (t3 or small-ish t3/t4) to build boost later in the rpm range so I don't have to worry about being in boost while I'm just running errands around town or cruising on the highway.

Last edited by Animag771; 03-17-2017 at 04:18 PM.
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Old 03-17-2017, 05:11 PM   #19 (permalink)
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400 whp and mpg, info can be found here....

Are you talking about Rrussell's thread? I just spent A LONG TIME reading that whole thead, including most of the links. Yep that's pretty much what I'm going for, but with higher compression instead of vitaras to give me better low end, out of boost and I'd honestly be happy with just maintaining my 36mpg (I could probably get more by leaning it out with tuning).

I'm thinking it may be best for me to get the -6.26cc rollerwave pistons, witha a y8 head, shave the block .007 and run a y8 (.027in?) head gasket. That would give me a piston to deck height of .000, quench of .027 and 10.4:1 compression at my altitude (760ft).

But I also read this which highly confused me, but I love that torque curve! I understand the idea of using a smaller engine with a turbo in order to match the power output as a larger NA motor in order to increase FE, but how do they manage increased FE in 2 very similar engines with a small turbo that makes most of its power in the low-mid rpm range? How does that not ruin FE? Isn't it constantly under boost at highway speeds?
AutoSpeed - Turbo'd for Fuel Economy

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Old 03-18-2017, 10:19 AM   #20 (permalink)
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Great suggestion. I'll have to look into that. Also this is another reason I am thinking of running a larger turbo (t3 or small-ish t3/t4) to build boost later in the rpm range so I don't have to worry about being in boost while I'm just running errands around town or cruising on the highway.
Sounds like you want a turbo off of a diesel.

The exhaust sides are usually larger than you would want for a given cold side impeller wheel.
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