P90 vs. P79 Cylinder Head for NA 3.1L

[NewZed]

My comment was really directed at anyone that discusses detonation, not your comment specifically.

 

I agree completely, all RPM matter because that's what driveablity and overall performance is about. I think a lot of this discussion gets diverted by a focus on peak HP numbers. I've seen some good articles in the past on average power under the curve versus peak numbers, and how that is a more meaningful measure of engine performance, but the forum discussions on high CR always seem to drift back to peak HP. Flat torque curves, part-throttle driveablity, etc, get pushed aside. I think that one of your responses in the past was about increased power across the rpm range, improved driveability, etc. I was hoping to direct things back to that perspective.

 

All I'm hoping for is more detail than "10:1 Cr, 32 total advance" gave X peak HP, or similar from anyone who has actual experience running high CR. More details on driveability, the pros and cons of high CR, did they run a "normal" timing curve or ignition map, and how they are making it work.

[30 ounce]

I'm running 34 deg. advance with the setup described above. The only hint of pinging I've ever heard was a very hot day last summer when I had 91 octane in it. A local station has 93 octane and that solved it. I was wondering if the .06mm squish area we made welding the chambers helps reduce detonation? (I was told that it would) Does reshaping the chambers help? (was told that too) What is the limiting factor here? Poor combustion chamber design? Thermodynamics? Hot spots in the chamber?

 

I was worried about running 11.5:1 but Bowers Racing (did my head work) Isky (my cam manufacturer) both recommended it. It seams to have worked just fine.

[NewZed]

I'm running 34 deg. advance with the setup described above. The only hint of pinging I've ever heard was a very hot day last summer when I had 91 octane in it. A local station has 93 octane and that solved it. I was wondering if the .06mm squish area we made welding the chambers helps reduce detonation? (I was told that it would) Does reshaping the chambers help? (was told that too) What is the limiting factor here? Poor combustion chamber design? Thermodynamics? Hot spots in the chamber?

 

I was worried about running 11.5:1 but Bowers Racing (did my head work) Isky (my cam manufacturer) both recommended it. It seams to have worked just fine.

 

 

When?

[30 ounce]

When?

When what?

[Leon]

I'm running 34 deg. advance with the setup described above. The only hint of pinging I've ever heard was a very hot day last summer when I had 91 octane in it. A local station has 93 octane and that solved it. I was wondering if the .06mm squish area we made welding the chambers helps reduce detonation? (I was told that it would) Does reshaping the chambers help? (was told that too) What is the limiting factor here? Poor combustion chamber design? Thermodynamics? Hot spots in the chamber?

 

I was worried about running 11.5:1 but Bowers Racing (did my head work) Isky (my cam manufacturer) both recommended it. It seams to have worked just fine.

 

Combustion chamber design is a big part of it, along with spark plug location. You can't do much about the latter, so the former is altered. A smaller, more efficient chamber allows for a more controlled, repeatable and faster burn. Modern pent-roof chambers with central spark plugs are more efficient in this sense, thus you see the higher compression ratios that cars run today.

[Lazeum]

It's funny to see how each thread about 2 heads end up being a N42 vs P90 discussion & detonation   

 

Just to bring more details about detonation. Hopefully I'm right (  ) & it will help enlighten the concept for others

 

 

 

 

Detonation is due to 2 explosions in one combustion chamber. One is created by the spark plug, the other by the high pressure built in the chamber because of the first one.

 

So the game is too have the explosion from the sparkplug to occur fast enough to burn everything before the pressure becomes too high to ignite the unburnt remaining gases. So 2 parameters comes into play: the distance the flame has to travel & how good the mix is between air & gas.

 

 

 

 

I've drawn some sketches, between how the flow air/fuel is mixed + distance, I was trying to show why quenched chambers are more suitable.

 

Edited December 11, 2010 by Lazeum

[ozconnection]

It's funny to see how each thread about 2 heads end up being a N42 vs P90 discussion & detonation   

 

Just to bring more details about detonation. Hopefully I'm right (  ) & it will help enlighten the concept for others

 

 

 

 

Detonation is due to 2 explosions in one combustion chamber. One is created by the spark plug, the other by the high pressure built in the chamber because of the first one.

 

So the game is too have the explosion from the sparkplug to occur fast enough to burn everything before the pressure becomes too high to ignite the unburnt remaining gases. So 2 parameters comes into play: the distance the flame has to travel & how good the mix is between air & gas.

 

 

 

 

I've drawn some sketches, between how the flow air/fuel is mixed + distance, I was trying to show why quenched chambers are more suitable.

 

 

Those pics are with flat top pistons I assume.

 

What about those heads with dished pistons? I read what Paul wrote but your drawings don't include that scenario...or do they?

 

Please clarify your information.

[BluDestiny]

Dished pistons do nothing for the chamber design, swirl effect or quench. They literally just lower the comp ratio by about 1 point. Lower CR means less likely detonation

[Lazeum]

Those pics are with flat top pistons I assume.

 

What about those heads with dished pistons? I read what Paul wrote but your drawings don't include that scenario...or do they?

 

Please clarify your information.

With dished pistons you could create some quench with the solution on the right on my picture. I've made this drawing with MS PPT, the intent was to show a concept 

 

So even with dished pistons, a correct designed open chamber can get some quench, that's the basic idea.

Edited December 11, 2010 by Lazeum

[didier]

The main problem in the L engine head design is the internal casting, with a horizontal web leading to a poor vertical coolant flow toward the block,

I get N42, N47 and P90 on the bench, and i have made water flow tests, it's a real s....t

I think hot spots in the 5 or 6 th are a legend, hot spots everywhere in these castings

 

"reverse flow "

[johnc]

E85.

[didier]

E85.

 

ah ah !

heating values : Kilojoules/ kg : gasoline : 43,,,,,E 85 : 29 !!

[Dan Baldwin]

Tee hee, it's been a while...

 

Must throw in my .02 regarding the N42 head's detonation-proneness (or, in my experience, the apparent lack thereof).

 

It got long, so here's the short version of what I've run, all on pump gas (91-93 octane), with an N42 head:

 

3.1 liter, stock N42 head (shaved ~.10 from previous rebuild), stock N42 cam, unshaved KA24E pistons, 2mm gasket, 240Z carbs.

10.25:1 CR, 10* initial/35* total advance, no apparent pinging

 

290*/.490" Schneider cam, 2" Jag carbs, 10.25CR, timing bumped back up to 18* initial/43* total, 180rwhp

 

310*/.550" Sunbelt cam, Sunbelt porting and minor bowl work, 3x2 45mm carbs, ~10.8:1 CR, 217rwhp at 43* total advance, 235rwhp at 34* - 38* total advance

 

Rebuild w/ eyebrowed 89.5mm KA pistons, 11.3:1 CR, 255rwhp at 35*

 

Recent rebuild of middle 1/3, shaved head, 11.6:1 CR, not dyno'd, still running 35* on pump gas.

 

 

 

My original 3.1 build was done way way back in ~1995. Totally stock N42 head with ~.010 taken off, stock N42 cam, N42 block bored 3mm over, KA24E pistons (not shaved), 240Z rods, 2mm head gasket, ~10.25:1 CR, stock 240Z carbs. I had previously been running ~15-18* static advance with the L24, and found that I had to back this to 10* to avoid pinging. Unbeknownst to me at the time, this was about where I wanted to be anyway, at ~35* with mechanical advance at elevated rpm.

 

So, stock N42 head, stock cam, over 10:1 CR, no prob on 91 octane at 35* total advance.

Ran it that way a few years, then put in a Schneider 290/.490 cam and 2" SU carbs, and was able to bump the advance back up to ~18*. Pulled 180rwhp at the dyno.

 

Eventually Sunbelt ported and did modest bowl work on my N42 and installed a 310*/.550" cam that allowed use of lightweight valve springs, and Igot a used set of 45mm 3x2 OER Racing carbs. I used a 1.5mm gasket (2mm minus one of the .5mm sheaves), CR now pushing 11:1.

I took this setup to the dyno to check a/f mixture. Pulled 217rwhp, nice... Then I decided to play with the timing using the dyno's adjustable timing light and found that I was running 43* initial + mechanical advance! Backing it off gave a big power bump although no pinging had been noted previously. Continued backing it off and found that it made the same 235rwhp between 34* and 38* initial+mech advance. So I run it at 35* to be on the safer side.

 

Then I wasted the bottom end at VIR by running it low on oil (it had been living on borrowed time, as long as I'd been tracking it I'd lose pressure on extended right-handers). Oops... Abacus in Norfok VA did the rebuild, now with 89.5mm KA pistons, eyebrowed to allow a thinner head gasket, 1.16mm (2mm minus one .5mm and one .33mm layer). CR bumped to ~11.3:1. Pulled 255rwhp with 35* advance. Yee-haw...

 

Then at the '05 Zconvention track day at Watkins Glen, the #6 intake was leaking in air and I burned that piston (chamber OK). Oops again...

 

Then last year I detonated the middle two pistons/chambers by running with a partially stuck throttle on the middle carb (1,2,5,6 pistons and chambers showed zero evidence of detonation, those pistons were left in for the middle-1/3 rebuild). Oops yet again... Chambers #2 + #3 had to have welding done (THANKS, Brad!), which led to the deck having to be shaved, chambers now 42.0cc, current CR is 11.6:1, still running full advance on pump gas, no problemo.

 

So, long/short, you can run full advance on a decently high-compression setup with the N42 head. But lean it out and there's not much margin (which may also be the case with the "better-chamber" P-heads for all I know).

 

Again, this is just my 0.02...

[didier]

thank you for your experience, good to know !!

[Gollum]

E85.

 

Amen!

 

I also wonder how much detonation issues people have stemmed from fuel or cooling issues, even if they're inherent to the design of the parts people were running. We all should know about the cooling issues of the L head, which can be numbed with more pressure, or extensive drilling and rerouting as seen in the sticky. But then we have fuel issues too. Many people are running carbs which aren't exactly known for wonderful atomization. Plus you're also having to balance them, otherwise you could have lean chambers which are more detonation prone while the others might be chocking rich.

 

I'd love to see studies of the quality we've come to expect from people like Ron and Paul (like regarding the trigger wheel testing) in regards to fuel and timing control in high compression L engines and when ping is detected and under what circumstances.

 

There's enough conflicting stories by trusted people that it makes me think there's more going on than we realize.

[kce]

Sorry for the extended absence... I had to do some "real life" stuff ("real life" sucks).

 

There is much excellent information so far!

 

@Dan Baldwin: Thank you very much for sharing the details of your buildup. That was exactly the kind of information I was looking for. I'm just trying to get an idea of what it takes to make a N/A aspirated L6 perform decently without spending $10K (although, since you haven't attached estimated prices... maybe you did spend $10K? ).

 

@Gollum, didier, johnc: The other half of preventing detention is dealing with cooling and fuel issues as you so rightly pointed out. Using good quality gasoline seems like a good place to start but I imagine fuel charge homogeneity, fuel atomization, and appropriate fuel:air ratio are all very important in maximizing the performance potential of a given cylinder head/combustion chamber/piston combination (that's probably a topic for the Induction sub-forum). However, a quick question... why does the cooling system suck so badly on the L6 series cylinder heads? Is it just a design limitation? Is just 70s tech?

 

 

 

http://www.davidandjemma.com/mazda/FAQ/quench.htm

 

While I am definitely not a mechanical engineer, I have been reading up a bit on combustion chamber design and quench. Now, I cannot say one way or another, whether that guy in the linked article has any clue what he is talking about, but most of it seems to ring true... although there seems to be a lot of weaseling. For example, why does adding quench (say a flat top piston combined with an N42 cylinder head) aid in creating fuel charge homogeneity via "better mixing"?

 

Other than to prevent detention, why would you prefer a lower static compression ratio setup like the N42 over the potential higher static compression ratio you could generate with a P90 or P79? Where I come from what you are looking for is as a high of a static compression ratio as you can get away with, a small volume combustion chamber (that is, the low surface area to volume ratio) and a cam with the duration to match. Maybe I have no idea what I'm talking about? (I should probably go re-read all my Vizard books).

[Leon]

I didn't have a chance to read over that full article yet, but it seems like the guy knows what he's talking about.

 

Regarding L-series cooling, here's the sticky: http://forums.hybridz.org/index.php/topic/59029-head-cooling-on-cylinder-5-solutions/

 

For being a non-engineer, I think you have a good grasp on things. If you're interested, pick up a copy of Heywood's book, otherwise known as the "IC engine bible."

[Dan Baldwin]

@Dan Baldwin: Thank you very much for sharing the details of your buildup. That was exactly the kind of information I was looking for. I'm just trying to get an idea of what it takes to make a N/A aspirated L6 perform decently without spending $10K (although, since you haven't attached estimated prices... maybe you did spend $10K? ).

My original 3.1 build cost I believe on the order of $2500 for all parts and machine work. That was with stock head/cam/SU carbs, and made a killer street engine. The big hp builders were cam and head porting done by Sunbelt which I got a great deal on, and a used set of triple 45mm carbs. Total spent on those was also ~$2500.

Random avoidable misadventures have cost me more over the years than the basic setup.

 

Other than to prevent detention, why would you prefer a lower static compression ratio setup like the N42 over the potential higher static compression ratio you could generate with a P90 or P79?

I want to run as high a C.R. as possible while not having any issues with detonation running pump gas and being able to run at least ~35 degrees ignition advance. In *my* experience with the N42, I was able to run 10.25:1 with the stock (~.010 shaved) N42 and currently at 11.6:1 with further head shavage, porting, and minor bowl work and a pretty big cam.

When the headwork was done ~9 years ago, the word from the guys who did it (probably about as knowledgable on extracting power from the L-series as anyone in the U.S. at the time) was that the N42 I had was as good (maybe better) a basis for a decent-hp N/A L-engine as the P-heads.

 

The P79/P90 heads have been touted as allowing much higher compression ratios, and I have heard of people with N42/N47 heads running into detonation issues at lowish C.R.'s, but in my experience, I don't think the N42 is giving up much if anything in terms of C.R. vs the P-heads.

 

Where I come from what you are looking for is as a high of a static compression ratio as you can get away with, a small volume combustion chamber (that is, the low surface area to volume ratio) and a cam with the duration to match. Maybe I have no idea what I'm talking about? (I should probably go re-read all my Vizard books).

Agree with running as high a compression ratio as you can get away with, adding that you still want to be able to run at least ~35* ignition advance. To me, though, you maximize c.r. *after* cam selection. You cam to get power in the desired rpm range, and *then* run as high a C.R. as you can with that cam. I.e., you don't run a big cam so you can run higher c.r., you run a big cam for the desired torque/power vs. rpm characteristics, then maximize c.r. for that setup.

Edited December 24, 2010 by Dan Baldwin

[JMortensen]

My own experience with an E31 which has better quench than the N head but not as good as the P head and had all the rough edges in the combustion chamber smoothed out and chambers cc'd, etc was that while running about 11:1 compression with a .490/280 cam, I needed 95 or 96 octane to prevent pinging, which I had to mix race gas and pump gas to get. I did have to drive it once on 91 pump gas and had to run 0 degrees advance at idle, and was worried about burning up the exhaust valve the whole time I was on the road.

 

My previous build was a dished piston with that E31 and the same cam. It probably had about 8.5:1 compression, ran on 87, and despite all the warnings you see for cams saying "only for high compression motors" it worked just fine. Definitely had more bottom end with the flat top pistons, but I could drive it daily with triples, the cam, a heavier pp, and 2.5" exhaust with no problems at all, and it made a LOT more power from the mid range on than the smaller cam I had used before.

 

I think a more important thing to look at is how much power you're going to get out of that extra point or two of compression. I think if you try to find some specs for that you might find that you're not getting a whole lot for the extra effort, so if it's not a full on race motor, then why bother to run the compression right on the edge where you need to worry about detonating it to death? And if it is, you might as well use the N head, because it will probably require a bunch of chamber reshaping to get the compression up to 13 or 14 to one anyway, and the smaller chamber is probably the better one to start with.

[kce]

I hope everyone had a nice holiday. Please see my inline comments.

 

 

I didn't have a chance to read over that full article yet, but it seems like the guy knows what he's talking about.

 

Regarding L-series cooling, here's the sticky: http://forums.hybridz.org/index.php/topic/59029-head-cooling-on-cylinder-5-solutions/

 

For being a non-engineer, I think you have a good grasp on things. If you're interested, pick up a copy of Heywood's book, otherwise known as the "IC engine bible."

 

I'm still working through the L-Series cooling thread... lots of information there. I'm just surprised that an aluminum cylinder head has so many issues with cooling, and hot-spots.

 

The Heywood book looks excellent although I have a feeling some of the math is over me head. Maybe I'll grab it along with Frank Honsowetz's How to Modify Your Nissan/Datsun OHC Engine.

 

 

 

My original 3.1 build cost I believe on the order of $2500 for all parts and machine work. That was with stock head/cam/SU carbs, and made a killer street engine. The big hp builders were cam and head porting done by Sunbelt which I got a great deal on, and a used set of triple 45mm carbs. Total spent on those was also ~$2500.

Random avoidable misadventures have cost me more over the years than the basic setup.

 

I want to run as high a C.R. as possible while not having any issues with detonation running pump gas and being able to run at least ~35 degrees ignition advance. In *my* experience with the N42, I was able to run 10.25:1 with the stock (~.010 shaved) N42 and currently at 11.6:1 with further head shavage, porting, and minor bowl work and a pretty big cam.

When the headwork was done ~9 years ago, the word from the guys who did it (probably about as knowledgable on extracting power from the L-series as anyone in the U.S. at the time) was that the N42 I had was as good (maybe better) a basis for a decent-hp N/A L-engine as the P-heads.

 

The P79/P90 heads have been touted as allowing much higher compression ratios, and I have heard of people with N42/N47 heads running into detonation issues at lowish C.R.'s, but in my experience, I don't think the N42 is giving up much if anything in terms of C.R. vs the P-heads.

 

 

Agree with running as high a compression ratio as you can get away with, adding that you still want to be able to run at least ~35* ignition advance. To me, though, you maximize c.r. *after* cam selection. You cam to get power in the desired rpm range, and *then* run as high a C.R. as you can with that cam. I.e., you don't run a big cam so you can run higher c.r., you run a big cam for the desired torque/power vs. rpm characteristics, then maximize c.r. for that setup.

 

Agreed. I guess I am sort of thinking about it the other way around. If any one part did determine an engine's general behavior and characteristics it would probably be the cam. And like you said, pick the characteristics (RPM, desired torque/power, etc.) you want, pick the cam that gets you close to that and then go from there. All very good advice.

 

I got to ask though, with duration of 280+ degrees, aren't you just pushing the intake fuel/air charge right out the exhaust port? Your last configuration for example uses a cam of 310 degrees duration and .550" of lift. I think the biggest cam (in terms of duration) I have run in a SBC has been around 230 degrees duration and .5" of lift (and that was 2.02"/~51mm intake valves, and 1.89"/~48mm exhaust values). How does the engine idle? Can you drive it on the street without constantly having the engine stall out? That thing must sound like a beast.

 

I'm going to assume you went with such a long duration cam for high RPM power... is there any chance you have a dyno chart for any of your engine configurations? I would be really interested in seeing what the torque curve looks like, and where in the RPM you start building power, and what the average horsepower over an RPM range looks like compared to the peak horsepower. Of course, it would be totally understandable if you don't want to share that kind of information or are unable too. Your current info regarding your various engine configurations, and the approximate "back-of-the-napkin" prices have been more helpful than I have words for (other than thanks!).

 

 

 

My own experience with an E31 which has better quench than the N head but not as good as the P head and had all the rough edges in the combustion chamber smoothed out and chambers cc'd, etc was that while running about 11:1 compression with a .490/280 cam, I needed 95 or 96 octane to prevent pinging, which I had to mix race gas and pump gas to get. I did have to drive it once on 91 pump gas and had to run 0 degrees advance at idle, and was worried about burning up the exhaust valve the whole time I was on the road.

 

My previous build was a dished piston with that E31 and the same cam. It probably had about 8.5:1 compression, ran on 87, and despite all the warnings you see for cams saying "only for high compression motors" it worked just fine. Definitely had more bottom end with the flat top pistons, but I could drive it daily with triples, the cam, a heavier pp, and 2.5" exhaust with no problems at all, and it made a LOT more power from the mid range on than the smaller cam I had used before.

 

I think a more important thing to look at is how much power you're going to get out of that extra point or two of compression. I think if you try to find some specs for that you might find that you're not getting a whole lot for the extra effort, so if it's not a full on race motor, then why bother to run the compression right on the edge where you need to worry about detonating it to death? And if it is, you might as well use the N head, because it will probably require a bunch of chamber reshaping to get the compression up to 13 or 14 to one anyway, and the smaller chamber is probably the better one to start with.

 

So you are basically saying that unless, I'm really interested in going with an all out "race-engine" (of course, I don't exactly know what that means for an L-Series but I can guess) configuration, it's not worth focusing on squeezing as much compression as possible out of a given combustion chamber/cylinder head/piston combination especially since the L-Series heads are so prone to detonation. All that approach would get me is a greatly increased risk of engine damage should I screw something up (too lean on the carbs, not enough advance, low octane gas... *cough* E85 *cough*, etc.) with a pretty marginal benefit in terms of performance. So the high static compression ratio and big duration cam is essentially just asking for trouble?

 

On your E31 with dished pistons setup, what exactly do you mean by "heavier pp"? (I'm not not familiar with that term.). And is there any chance you have some rough numbers behind what a "a LOT more power" means? I know at the end of the day, "the-seat-of-the-pants" dyno is really the one that counts but I'm still trying to re-orient myself from SBC-land with it's plentiful and affordable after market (e.g., Hot Rod's 500/500 383).

 

 

Thanks once again for everyone's input.