heads

[1 fast z]

"So if .5 will loose "nearly ALL quench" how do low compression motors not detonate themselves to death? I'm not knocking you down, I just want to understand your philosophies on the subject."

 

 

 

IT's called REVERSE DOME. You map out exactly what the combustion chamber looks like, and you dish ONLY in that area, this way you can still acheive MAXIMUM quench. Ask and TOP engine builder, and they will verrify my statement.

[BRAAP]

The Squish is VERY important to making the engine detonation resistant as 1fastZ stated. This squish isn’t a cure all for running absurd compression ratios but it does allow an engine to run a higher comp ratio before the onset of detonation with a given grade of fuel. Now how much more comp ratio can this high squish head run before detonation starts? Good question. Sorry I don’t have that answer.

Ideally if you want to drop the comp ratio without loosing this squish you would want a custom piston with a CNC dish machined in the top of the piston but this dish to be machined “only” under the open portion of the MN47 chamber and this dish to only be large enough in volume to bring the comp ratio down to what the engine builder deems “safe” for that particular application. In doing this you will keep that very important squish.

As per Gollums links, (great article on Detonation by the way), a small sphere for a combustion chamber would be ideal, so by having this piston dish shaped with that theory in mind, you would drop the comp ratio to a level that is a little less sensitive to the differing grades of fuel that is available.

As 1fastZ stated, if you use too thick of a head gasket you will negate all the benefits of the Maxima N-47 chamber design, at that point, you may as well used the Z N47 head as the thicker gasket has now made the combustion chamber itself the full size of the piston top. Ideally you want the piston to come up within only a couple thousandths of an inch while the engine is running. 1fastZ’s recommendation of .030” piston to head clearance is a good safe clearance which allows for slight piston rock, thermal expansion etc.

[Gollum]

Quench is mostly in chamber design, I still don't understand how .5:1 difference will make a huge difference. Is that smallist distance really gonna make THAT much a difference in where the air/fuel goes? I do realise that quench is one of the biggest factor for detonation, but I always thought with a flat top piston setup quench relies 100% in head chamber design. I still don't uderstand why lowering the compression would yield such a sever result as to loose almost all quench.

 

Like i said, i'm not trying to debunk you or anything. I just want to learn something from you, so please don't get too defensive.

[1 fast z]

Actually, I run about 22 though of piston to head clearence on my motors, but I just didnt wanna say that, so then every jo blow, goes out and does that to their motor, without taking the correct percautions, ya know. Yes, if you have a high quench head, and you have say .060" piston to deck clearence, and then you take that same motor, and make it .025" you will see NOTICABLE HP increase, as well, you will be less prone to detonation.

 

 

I am not just making up stuff I have "read" somewhere, I have actually tested these therorys. Again, This is just what I have learned, you dont have to use one bit of my advice, im just trying to shed some light.

[BRAAP]

Gollum,

Lets see.. You understand that the quench is an important aspect of detonation resistance, but don’t understand why lowering the comp ratio by .5 by only using a thicker head gasket wouldn’t help make the engine less prone to detonation?

I’ll try and explain this in a different way. (It sure would be much easier if I could draw this out. I’m much better at conveying ideas visually. Oh well, here goes any how…)

 

Quench is only achieved within a given piston to head clearance. By adding a thicker gasket you are increasing this piston to head clearance therefore the quench then no longer exists.

 

If you can lower the comp ratio on an engine with a nice high squish/quench head, then yes, the engine will be less sensitive to fuel grade and less prone to detonation, however, it is “HOW” you lower the compression ratio that makes the difference.

I’ll cover 2 examples;

1) If you lower the comp ratio by .5 just by using a taller head gasket, now the piston is further away from the head deck surface and now you have lost your quench/squish as the chamber is now an open chamber and extends over the entire cylinder, not confined to the smaller open region that surrounds the valve in the head, i.e. the combustion chamber. This would be similar to the open N-42 and Z N-47 heads.

2) If you manufacture a piston with a dish large enough to drop the compression ratio by .5 and this dish is directly under the open portion of the chamber itself, then you still retain this quench area and when the piston comes up to TDC, there is essentially NO space between the piston and the head deck surface, so the combustion chamber is now confined to only the small region that is in the head around the valves and in that little dish pocket in the piston as well.

In short, if you use a taller gasket, the quench NO longer exists.

 

Not to muddy the waters any more than they already are, by using the OE L-28 dished pistons with a P-79 and P-90 heads, you loose that quench because the OE L-28 dish covers a very large portion of the top of the piston itself. An ideal dished piston for those heads would be one with the dish under ONLY the open portion of the chamber itself.

 

Any how, hope this made sense…

[Mack]

o.k. Jmortensen I see some of your points. I do always state that I get ping because of the crappy stock EFI. If i were running carbs that I coudl tune, I could get rid of it. This guy (original poster) is runnig carbs, so he could tune it out if he has the time and know how. I agree with a few of your points, but disagrree with others.

 

A big nasty cam would HURT me, not help me. At least with stock EFI. A big nasty cam would let even more air into my engine, without the EFI being able to account for it from its crappy RPM/fuel tables. so, my engine would run even leaner. I was just stating that I could unleash a whole new tide of HP with a cam AFTER I got the proper fuel management. will probably need bigger injectors too. 180CC's would not cut it with a cam.

 

Nice video, reminds me of MSA last year. I ran a 68.1 on thier course, with really crappy front tires, roasting my rears through multiple gears. next closest 280ZX was 75 seconds, i think. oh, and the only suspension upgrades I have is KYB GR-2's and gas adjusts, that are 10 yrs old, so its all motor and driver, baby!! LOL!

 

No offense, but I still have a hard time beleiving a 250RWHP 8.3:1 motor. hell, lots of people on here struggle just to get 250RWHP, let alone on pump gas.

 

 

Bastaads car and his freinds.... we do NOT know the condition of either of the engines.. his freind could have had scorred cylinder walls, needed a valve job, any multitude of factors. only way to REALLY test would be to run different heads on the same block, with same carbueration, within the same day.

 

 

the quench thing..... Gollum, by running a thicker head gasket, you are putting clearance inbetween the flat spot on the head (the part that is NOT part of the combustion chamber) and the piston. anything more than about .035" and it starts to get bad. Its a place for gasses and liquid gas to become trapped and detonate all on their own. thats why if you used a thicker headgasket to drop the compression raito, you would negate the quench effect and end up worse off than where you started. EDIT: just saw BRAAPS post. that about sums it up. Another way you could lower compression raito, but keep quench woudl be to unshroud the valves, and/or take some metal out of the combustion chamber.

 

The P47 thing, HA ha!! ACTUALLY if you look at it, it truely is a bastard child of heads. It shares spark plug bosses, valve lengths, and intake port design with N series, but it has all the coolant holes, combustion chamber design, and production run dates of the P series heads. 6 of one, half a dozen of the other. I just got sick of typing Maxima N47, and if you look at it, it does look like a P series at a glance, without breaking out the micrometers and getting all technical on its ***, lol.

 

 

and yeah, what do I know? Ive just put 20K on this motor and drive it day in and day out, lol!!! I knwo ping is bad and I will invest in megasquirt before spring. but by then, hopefully 1 fast Z and I needent worry ourselves with the mere mortal heads currently available for L series motors.....

[1 fast z]

Ok, Ill let out a bit more information.

 

 

 

 

To get the MAXIMUM quench say on a turbo motor using a P90 head this is what you do. Make the Piston to Head clearence about .025". Then, put in one piston at a time, as an assembley on the crank, rod, etc. Then put "prussion blue" on the head, around the CC. Then put the head on with NO head gasket, then bolt it down. Then take and "bump" the piston and let it hit the deck of the head. This will then give an EXACT map of where you want to make your dish. You DONT wanna go outside of your "map" though, although, you can stay inside it, as much as needed.

 

 

 

Another trick is to use a solid copper head gasket, with stainless orings in the block, and make the gasket an EXACT continuation of the bore, this will also yeild the HIGHEST quench.

[Gollum]

I just totally figured out why you loose the quench, I understand now.

 

I WILL admit I don't have alot of experience in headwork, BUT was I wrong in my origonal statements? I simply wanted to stress the fact that putting a MN47 on a flat top motor isn't all that "simple" and there are things to consider, such as the fuel system. On any ZX car under smog regulations this is a BIG issue. Expecially in CA since a megasquirt system is basically illegal.

 

If anything I'm glad for this thred. It could clear up alot of things for people considering the swap in the future. And now I can personally say SEARCH next time someone comes looking for MN47 information.

 

Hope there's no hard feelings left here.

[Mack]

naw, there is no hard feelings, its just the internet, after all!! HA ha!

 

I still think you guys are looking at this whole detonation/ping issue the wrong way tho.

 

USUALLY, people run big cams to "bleed off" dynamic compression at lower RPM's when you are running too much compression for street gas, correct? well, I dont have ping at low RPM's. I have ping at high RPM, when and only when the AFM maxes out. My ping is NOT a compression issue, it is a fuel delivery issue. You can make ANY compression ratio detonate if you lean it out enough.

 

It could aslo be the fact that my whole set-up (might) breathe better at higher RPM, with the semi ported head, port matched intake manifold, removed injector screw bumps (some of those were BIG), and the 60MM TB, and i also have a high flow air filter. If the engine flows more at high rpm, there is no way for the AFM or ECU to know about it, since even in a stock engine the AFM and ECU just "guess" at how much air is going into the engine beyond 3500RPM. so, since teh ECU thinks its a stock engine, its gonna feed it stock fuel requirements, which is not enough, even with a mild cam (which I kind of have, 256* vs. 248*) The more airflow beyond 3500RPM, the more the problem compounds itself.

 

well, to say that my PING is not a compression issue is not TOTALLY fair. It does ping at an A/F that a stock compression car would not ping at. But, with proper tuning and a better A/F, it would not ping. and I bet I wouldnt have to go below 13:1 on the A/F to get it to stop, which is completely acceptible under WOT for a street engine.

 

catch my drift?

[BlackBeaut]

Thanks for the pic Mack, that's spot on.

 

Anyone got any idea what the typical cc is for valve relief pockets on the top of a piston? I've just been messing around with lengine.exe for an engine based on a 3l stroker (88mm) bore, flat top piston +0.030" deck height, HKS 1mm gasket, that comes to 12.14:1 CR, based on a 39cc chamber. If there's a 5cc dish on the pistons the CR drops to 11.03:1. Would valve relief pockets be around 5cc or less?

 

For sake of discussion this is for a NA engine, 300deg cam, ITB setup with programmable ECU controlling fuel and spark.

 

For the sake of my bank account, it's not going to happen for a while

 

Cheers,

Rob

[JMortensen]

No hard feelings here either, I just didn't want to keep saying the same thing again and again and again while 1 fast z and Mack said their same thing again and again and again. We seem to be past that point now.

 

Mack, about the mixture being your only problem. I think once you do your aftermarket FI you'll find that you still need high octane gas or a cam. I haven't used a MN47, so I'm basing this on my E31 experience and extrapolating from all of the other info I've read over the years with regards to the L series and compression. Maybe you WILL get away with it, I don't know what kind of gas you have in AZ. If you were in CA I'd say you don't have a snowball's chance in hell. I think you guys are the ones who bear the burden of proof though. If it works for you in AZ fine, make it work in CA crap gas then I'll be all for telling people CATEGORICALLY that the MN47 on a flat top block is the best way to go.

 

BTW a larger cam won't just bleed off compression at low rpms. It does do that, but it affects cylinder pressures across the rev range, and this is why it affects the torque curve all the way across the rpm range. This is because it lowers the "dynamic compression ratio" and a larger cam LOWERS the DCR. If you want to learn more about that you can read Grumpy's 4000 links on this post http://forums.hybridz.org/showthread.php?t=99918

 

With regards to my old engine's power output, I don't know what to tell you. I only did the one gtech test. The car was pretty quick but didn't have much bottom end because the compression was so low. The new engine is much snappier off the line. Both pulled hard at the top end. I was able to chase down Mustangs and Vettes on big tracks with it. Believe what you want to believe, I know what it did.

 

That issue does really wonder what compression is actually worth. I mean Briann510 is making 278whp at something like 9.5:1 compression, and he uses a smaller cam than I have IIRC. Granted he has a 12% larger engine, but if you knock his numbers down by 12% then he makes 245, I think the calculator I found online said I made 248. So I guess the issue is exactly how much is that 1 point of compression and the larger cam worth.

 

I think that in an L series the BIGGEST hindrance is the SU's or FI. Second thing is the puny cam, and I would couple that with some headwork. I've said this before, but when I put the triples on I got an immediate 40 hp at least. My wife went from getting a little sideways on freeway onramps in the Z to literally being scared to drive it. As BRAAP said before though, the engine should be built for a purpose, not just a collection of parts, and when those parts all work well together, the difference is AMAZING.

 

I don't understand your seeming reluctance to get a bigger cam. If you don't have to smog, you should be WANTING aftermarket FI like 1 fast z has or triples, and a big cam. Your engine would make a TON more power.

[Mack]

Actually, I moved back to MN now, and there is 93 octane as far as the eye can see, so its not bad at all!! But, when I was in AZ, if you hunted you could find 92, but most places were 91. It ran fine on 91, even in 110+ heat. As long as I didnt mash it and take it to redline.

 

On the E31 note, It really is a crap shoot. The E31 has a different comustion chamber design than an MN47 (you win 1 fast Z). While the E31 is high quench, its not as much of a quench design as an MN47 (ugh, it hurts everytime I type it, J/K), its just basically a small chamber. Or at least this is what I remember My E31 head looking like before I sold it. I still have on, but its on a car right now. bone stock early early 71.

 

I have a fairly decent understanding of DCR and what not, and I do realize that by lowering the DCR, you get to a point where a high C/R motor will not ping as much because the intake and exhaust are open at the same time and it allows some compression to "bleed off" at lower RPM's. Thats why Im saying the MN47 is an awesome head. Im running 11.4:1 on pump gas and I don't need to lower my DCR to not ping at low RPM's.

 

I'm guessing a LOT of Briann510's power lies in the headwork. I mean, it IS a rebello motor afterall, and he has made NO secret of how much he spent on it, HA ha! now, THAT would be an interesting motor to do side by side comparisons on in regards to HP vs. compression!! trouble would be getting the same amount of head work on 2 different heads.

 

I COMPLETELY agree with you on the fact that the L series intake manifolds are the kiss of death. Luckily Spork is starting to make aftermarket EFI manifolds that are actually affordable!! as in ~$500!!! not bad! One of those would do WONDERS on a megasquirted engine!!! You know, every now and then I get bad ideas of throwing my 40pph mikunis on this engine, but I cant bring myself to have a carb'd 280ZX, lol!

 

I dont have a reluctance to get a big cam, I just have a reluctance to get a big cam RIGHT NOW, with the stock EFI. If I did that, it would exacerbate the problem. I need programmable EFI FIRST, then I go for the big cam!!

 

I hope when someone searches this thread, they can get something useful out of it other than you and I just responding to eachothers posts!! HA ha!!! Of course, there has been some good info come to light in this post, so all is not lost!

 

BTW, when I put this head on my flat top block, I put on a 60MM TB and did the port match thing as well as removing the intake bumps all at once. The difference was night and day over a P79. the extra almost 3 points of compression made it a lot snappier. Like I said, I dynoed it ONCE, with a faulty IC unit and it made 141 RWHP @ 4100RPM's. Most L28E's (runnig similar mods, but stock heads) are lucky to break 100rwhp at that point in the powerband. I would LOVE to get MS, a cam, tune it and go back!!!!

[JMortensen]

Actually, I moved back to MN now, and there is 93 octane as far as the eye can see, so its not bad at all!! But, when I was in AZ, if you hunted you could find 92, but most places were 91. It ran fine on 91, even in 110+ heat. As long as I didnt mash it and take it to redline.

Which in my opinion is definitely NOT running fine.

I have a fairly decent understanding of DCR and what not, and I do realize that by lowering the DCR, you get to a point where a high C/R motor will not ping as much because the intake and exhaust are open at the same time and it allows some compression to "bleed off" at lower RPM's. Thats why Im saying the MN47 is an awesome head. Im running 11.4:1 on pump gas and I don't[/b'] need to lower my DCR to not ping at low RPM's.

Again, the compression doesn't just bleed off at LOW rpms. It does it at ALL rpms. And again, you'd make a lot more power with the bigger cam, even though it is "bleeding compression". Pointing out that you don't need a bigger cam seems to be a point of pride for you. But you ARE pinging, and you WOULD make more power with a bigger cam. And a lower DCR WOULD help with the high rpm pinging as well.

I'm guessing a LOT of Briann510's power lies in the headwork. I mean, it IS a rebello motor afterall, and he has made NO secret of how much he spent on it, HA ha! now, THAT would be an interesting motor to do side by side comparisons on in regards to HP vs. compression!! trouble would be getting the same amount of head work on 2 different heads.

You're guessing and I'm guessing. Kinda pointless. But since we're engaging in conjecture, I'd also like to know how much that headwork is going to matter when he still has that tiny cam in there? I think he's running the .460/260 cam that MSA sells. I know a couple racers who bought that cam and then kicked themselves for it later. It's too small.

I COMPLETELY agree with you on the fact that the L series intake manifolds are the kiss of death. Luckily Spork is starting to make aftermarket EFI manifolds that are actually affordable!! as in ~$500!!! not bad! One of those would do WONDERS on a megasquirted engine!!! You know, every now and then I get bad ideas of throwing my 40pph mikunis on this engine, but I cant bring myself to have a carb'd 280ZX, lol!

Use Spork's manifold and sell those 40s. They're too small.

BTW, when I put this head on my flat top block, I put on a 60MM TB and did the port match thing as well as removing the intake bumps all at once. The difference was night and day over a P79. the extra almost 3 points of compression made it a lot snappier. Like I said, I dynoed it ONCE, with a faulty IC unit and it made 141 RWHP @ 4100RPM's. Most L28E's (runnig similar mods, but stock heads) are lucky to break 100rwhp at that point in the powerband. I would LOVE to get MS, a cam, tune it and go back!!!!

I still think the ultimate proof would be dyno sheets of your car with the CURRENT setup on premium unleaded at the timing you currently have set, then another with a couple gallons of race gas and the timing cranked up.

[Gollum]

I personally wanna see a smog test sheet on mack's car more than a dyno sheet...

 

There's lost of talk around here in CA about copression issues with smog. I've talked with countless performance mechanics, smog refs, engineers, and all of them don't understand why the new S2000 can pass CA smog laws on such a high compression. Many turbo cars out there hit just as high of compression on boost, but only under WOT. During the smog tests the turbo eliminates alot of emissions my creating a more complete burn and the motor is lower compression to begin with, so it's easy to pass smog for them. But somehow honda performed a miracle.

[Mack]

BlackBeaut>>>> for valve releifs on a piston, i would figure no more than 2cc's. 5cc's is a little excessive, i would think. Sounds like the motor you have in mind would be a screamer! ITBs are DEFINATELY the way to go. Ive had a ride in 1 fast Z's car, and it is bloody fast.

 

 

Again' date=' the compression doesn't just bleed off at LOW rpms. It does it at ALL rpms. And again, you'd make a lot more power with the bigger cam, even though it is "bleeding compression". Pointing out that you don't need a bigger cam seems to be a point of pride for you. But you ARE pinging, and you WOULD make more power with a bigger cam. And a lower DCR WOULD help with the high rpm pinging as well.[/quote']

 

I will say this again. a bigger cam with my current set up would HURT. no matter what I do, i will not get rid of the pinging on stock EFI, unless I get an adjustable FPR. I've dialed the timing back to almost 0* and it wont go away. the only reason I am pinging is because of a lack of FUEL. Ken Hawkins ran into this problem as well, I think. I will get a bigger cam after I switch over to MS and get my fuel delivery problems sovled! HA ha

 

the cam thing is a point of pride for the MN47. the fact that i can run a small cam on such high compression and not have it ping (lower RPM's, when enough fuel is going into the engine) gives validity to the theory of "QUENCH".

 

 

 

Use Spork's manifold and sell those 40s. They're too small.

 

HA ha!!! no way man!! those 40's are going on my 71 240Z with the original L24 and E31. its gonna be a nice old school, era correct build. I also have an old, big gold electromotive ignition box and mallory coil to go on it.

 

Although, those 40's would probably flow a little more than the stock crappy 30MM EFI intake runners.

 

GOLLUM>>> i would also be interested to see an emissions chart on my car. It does not concern me tho, because my car is registered in North Dakota, HA ha!! What does a high CR produce more of? is it HC's? or is it NOx? I always thought that a higher CR had a more complete burn than lower CR engine. but, I can never remember emissions laws, theories and what not. How much of a C/R does the S2000 have? I know the 350Z's run about 10.25:1, and the pass just fine.

[Gollum]

S2000s run 11:1 and I thought before the .2 liter increase they were 11.5:1 but I just looked it up and it seems to be 11:1 as well.

 

The hotter a burn the more NOx is created. It also becomes EXTREMELLY hard to ensure an 'even' burn, wich is much more important. Another thing to consider is the first gen 2 liter S2k was the highest HP per liter than ANY production car in the USA has seen. Yet somehow thier emission levels are realativelly low. Quite odd.

[RacnJsn95]

I can get 100 octane from the pump (at certain stations) here... MWAHAHAHA!!!!!

[Gollum]

Yea... well.... ... .... ...

 

...do you see that view in my sig? I see that and better every day...

 

 

...that's about all I got man. I'm outta ideas...

[Pyro]

I think you guys aren't considering an important topic on "quenching heads".

 

The high quench head is not less prone to detonate. For example, if you use 38 degrees of timing on a 10:1 cr L28 it will detonate no matter which head that you use (quench or non quench)

 

What quenching does for you is increase the flame travel speed. Allowing a high quench head to use less total ignition timing to make max power. It is not the head that is less detonation prone, it is the lower timing that makes it less pingy.

 

So, a 10:1 cr L28 with a N42 may require 38 total degree of timing were as a MN47 on the same engine may only require 32 degrees. And 6 degree does wonders to reduce ping.

 

So, it is possible to turn down the total ignition timing without losing power. In fact, it must be turned down for max power.

 

I personally wouldn't run 11:1cr L28 on pump gas without a big daddy cam (240+ degrees at 0.050'") even with a MN47.

[hoov100]

I personally wanna see a smog test sheet on mack's car more than a dyno sheet...

 

There's lost of talk around here in CA about copression issues with smog. I've talked with countless performance mechanics' date=' smog refs, engineers, and all of them don't understand why the new S2000 can pass CA smog laws on such a high compression. Many turbo cars out there hit just as high of compression on boost, but only under WOT. During the smog tests the turbo eliminates alot of emissions my creating a more complete burn and the motor is lower compression to begin with, so it's easy to pass smog for them. But somehow honda performed a miracle.[/quote']im getting my car smogged next weekend and im running an l28/n47 setup on regular (runs like crap) and ill send you the data sheet.