Custom Cylinder head building.. What's Involved?

[DemonZ]

Cool Paul, I can breath a bit easier. I PM'd you.

[BRAAP]

Cool Paul, I can breath a bit easier. I PM'd you.

 

 

Just replied to your PM...

[BRAAP]

Phils head is about ready to ship. Just waiting on the Lash pads to arrive from Nissan, hopefully early this coming week, then a quick cold valve adjust, package, then off to Phil via UPS.

 

This update is the valves, springs, spring seats and stem seals. When installing the valves, you should always use some form of lube on the valve stems even if it is just plain motor oil, we prefer to use high pressure assembly lube on the valve stem before installing. When installing valve stem seals, you want to make sure and use those little plastic condoms that are supplied in the stem seal package, (top picture, middle valve stem). This protects the seal itself from getting cut while going over the keeper grooves. Those little plastic stem covers are always too long so I always just cut it half. When installing these Ford V-6 Viton stem seals, you can use a 3/8” drive, 12mm deep well Craftsman socket to “gently” push the stem seal onto the guide and it will seat with a positive click. Be very careful and don’t’ get the seal cocked on the guide, but “gently” push it on using the palm of your hand. The socket, or whatever tool you are using, should “only” be touching the outer metal rim of the stem seal, NOT on the upper seal portion of the seal that surrounds the valve stem itself. When using the Felpro Viton seals like these, extra care needs to be taken as it is very easy to ruin the seals when installing them. The inner rubber lining of the seal itself can easily get caught and tear and then it will wad that rubber lining up on top of the guide itself causing the top of the seal to bulge out. We’ve had many a so called “mechanic” bring cylinder heads to us that they had just done a quickie valve job “themselves” for a customer, only to find that head they just assembled and installed now smokes terribly and they can’t figure out why. That is when they finally bring it to the machine shop to figure out what they did wrong. Most of the time we find that the stem seal was incorrectly installed, either they forgot to use the little plastic condom and the keeper groove tore the seal, or they wadded up the seal as described above, or they didn’t seat the seal all the way down on the guide itself and it popped off the guide. While on my soap box ranting about mechanics, the other bad habit these same mechanics have is with that scotch brite pad on the end of an angle head die grinder! I can’t remember how many heads I’ve resurfaced because a mechanic got over zealous with his “surfacing disc”. The common excuse given was, he wanted to save a head surfacing fee for the customer who came into their shop with a blown head gasket and thought it was just a bad gasket, (usually there is another reason WHY the gasket blew, but you can’t tell these guys that). They then go on to create another blown gasket as soon as they fire up the engine cause the head surface now has waves big enough on the deck, to surf on caused by their little air powered gasket remover. I’ve had to shave as much as .030” on one occasion to save a young mans attempt at cleaning the old gasket off of the customers cylinder head! He was fresh out of auto tech school and tried his darndest to remove ALL the old gasket material, and boy did he do a good job of removing that old gasket… as well as a lot of aluminum…. I still chuckle over that one… I really don’t have an issue with those buffing discs, we use them all the time. It is “how”, “when”, and “where” they are used that is key.

 

Ok, enough ranting about mechanics. Here are tonight’s pics till the lash pads show up…

 

 

 

[Zmanco]

The MN-47 is a round port head. The round exhaust ports' date=' (with the liners still intact), are excellent for mild race and hot street engines. Also of note, All the round port heads, (N-47, MN-47, and P-79), have a smaller intake port. At approx 1/2 “ into the port, the port takes on a “D†shape, this helps bias the port centerline which in turn helps to aim the incoming air flow toward the center of the cylinder. This is great, but for maximum effort high RPM breathing, that smaller port is a hindrance to overall flow. These “D†shaped intake ports compliment the round exhaust ports nicely for mild to hot street, and mild race applications. Especially for a street engine that is asked to have some civility at part throttle conditions like having to drive through town back and forth to work and in stop and go traffic on your way to your favorite bonsai back road. These "D" shaped intake ports and round exhaust ports found on the N-47, P-79, and MN-47, in my opinion, offers the best performance with the least compromise in around town drivability and low end and mid range torque.

The square exhaust ports of the N-42, E-88, and P-90, allow for considerable exhaust port alteration allowing the engine to breathe freer at the higher RPMS, though low rpm performance will suffer as a result. The Intake ports of these same heads are also larger than the intake ports in the N-47, MN-47 and P-79, so less carving.

 

In short, the N-42 offers more “all out†potential, but at the cost of low rpm and part throttle drivability. This same radical head on a street engine that is to be driven around town would be a poor choice. This N-42 works best at WOT and above 4000 RPM, where as the round port heads do their best, (depending on how they are set up and built), from as low as 1500 RPM up to 6500 and will have decent manners around town.[/quote'] I hope this isn't a thread hijack since it has been quiet for a few months now.

 

I currently have an N42 head that was freshened a few thousand miles ago with a valve job and new seals. My plan before reading Paul's comments was to put a reground cam 284/.480 into it. But I also have a spare N47 head with about 80k miles, history mostly unknown. I'm wondering if I might be better off switching to this head? The rest of my engine is an L28 w/flat tops, triple webers, square port header. My driving is mostly weekend street, and as many track days as I can get to. I do need to be able to drive it "politely" on the street when required, but it's not a daily driver.

 

So is it worth switching to the N47 with unknown history vs. keeping my known-good and recently refreshed N42? I've spent most of my Z funds on rebuilding the bottom end so I don't have a lot left over to refresh the N47.

 

And would there be any significant issues running with square port headers on a round port head? I've heard it said that it doesn't make a differnece and that it's only the reverse (round port headers on a square port head) that's a problem.

[BRAAP]

I hope this isn't a thread hijack since it has been quiet for a few months now.

 

I currently have an N42 head that was freshened a few thousand miles ago with a valve job and new seals. My plan before reading Paul's comments was to put a reground cam 284/.480 into it. But I also have a spare N47 head with about 80k miles' date=' history mostly unknown. I'm wondering if I might be better off switching to this head? The rest of my engine is an L28 w/flat tops, triple webers, square port header. My driving is mostly weekend street, and as many track days as I can get to. I do need to be able to drive it "politely" on the street when required, but it's not a daily driver.

 

So is it worth switching to the N47 with unknown history vs. keeping my known-good and recently refreshed N42? I've spent most of my Z funds on rebuilding the bottom end so I don't have a lot left over to refresh the N47.

 

And would there be any significant issues running with square port headers on a round port head? I've heard it said that it doesn't make a differnece and that it's only the reverse (round port headers on a square port head) that's a problem.[/quote']

 

 

Daniel,

As for your project, there is no need to switch over to the N-47 from the N-42. Any gains that you might realize from that swap would be to minute to worry about. Though you do have a much bigger issue at hand, detonation! An L-28 with Flat top pistons and the open chamber N-42 head, (or Z N-47 for that matter). This combination is well known for not being pump gas friendly even at a measly 9.5:1 comp ratio, they WILL detonate even with premium pump gas and a mild cam. I’ve witnessed this first hand on more than a few engines that others built and have also read about from LOTS of other people as well. Yes, the ignition timing can be backed down to help subdue the audible knock, but by doing that you are giving up LOTS of power by retarding your ignition timing. I would much rather loose a whole point of compression using amore ideal head, (P-79 or P-90), and be able to run ideal ignition timing. I.e. sacrifice maybe 3 % HP due to loss of compression ratio to regain 10-20% HP with ideal ignition timing. Don’t rip over dollar to pick up a dime. 10 degrees of ignition timing can be worth more power than even 2 points of compression.

If it were me, I would ditch the N-42 and N-47 for either a P-79 or P-90 head as either of these two heads complement the flat top pistons MUCH better and will allow you to run ideal ignition timing on pump gas allowing your engine to run a max effort.

 

I could go On and ON in this post, (as most of you already know), so instead of repeating myself here, I’ll refer you to a couple of threads that cover 6 cyl L-series heads in great detail, covering all the nuances of each of the L-series 6 cylinder heads and has been referred to as the most informative write up on L-series heads thus far…

http://forums.hybridz.org/showthread.php?t=104420

 

 

And this thread covers detonation with the L-series and squish chambers. (just ignore the little tiff about someone’s ¼ mile times discrepancy)…

 

http://forums.hybridz.org/showthread.php?t=105653

 

 

 

As for mismatching headers and heads… Yes, the square port headers will work JUST FINE on round port heads. Many of us have run that combination with NO issues and made great power.

 

 

Hope this helps…

 

Paul

[Zmanco]

I had heard I might have detonation issues, but so far (1500 miles) I haven't been able to hear any although I realize that's not the best method. But I have been listening closely, driving with the windows up on the really hot days trying to hear it. Perhaps it's because I live in Colorado and do most of my driving above 5000 feet? Or maybe because I've limited my total advance to about 34 degrees?

 

Paul, I really value your advice and I'm not trying to argue with you. I'm just trying to compare what you're saying with what I'm experiencing with this engine. Perhaps I'm missing something else?

[Dan Baldwin]

FWIW, I ran a stock N42 head on my 3.1 at 10.35:1 on pump gas with full (35 total) advance for years. Currently running 11:1 with a pretty big cam (310/.550"). No probs on pump gas.

 

However, the ZCCNE club car with N47 stock cam on flat tops had to run with timing retarded by ~8deg.

 

Go figure...

[TheNeedForZ]

FWIW' date=' I ran a stock N42 head on my 3.1 at 10.35:1 on pump gas with full (35 total) advance for years. Currently running 11:1 with a pretty big cam (310/.550"). No probs on pump gas.

 

However, the ZCCNE club car with N47 stock cam on flat tops had to run with timing retarded by ~8deg.

 

Go figure...[/quote']

 

I bet your big cam creates a lower dynamic compression ratio at lower rpm. The shorter stock cam creates a higher dynamic compression ratio, hence the detonation.

[zeiss150]

I have an N42 with flat tops and a 2mm head gasket giving me 9.2:1 CR. I have had no audible detonation. I've put it in 5th gear going 20mph and floored it and no audible detonation. I'm not saying paul isn't right I'm just laying out my experiance. I have a mild cam 460/ 270 and my timing is 35 degrees. I'm running 91 oct. but I'm trying to go turbo anyway

[BRAAP]

Daniel,

There is a chance that you are not experiencing detonation. The fact that you live a mile up, helps reduce your chances of detonation due to less air pressure, (i.e less natural boost).

 

I’m going out on limb here. I’m going to touch on a few controversial topics here that should be covered with much more depth than this, but being as I don’t have the time to explain the physics behind all of this, and that I don’t want to hijack this thread any more than I already have, (yeah, sorry excuse right?). Either just take what I’m posting at face value or if you do have interest in these topics, I urge you to research them on your own. There is lots of good info out there. For example, I highly recommend anything written on these topics by David Vizard and Jeff Hartman. Their writings are backed up with years of practical experience.

 

Dan Baldwin’s personal experience is similar to Daniels, which I would gather is due to Dan B.s more aggressive cam. In practice any how, a more aggressive cam tends to be less sensitive to detonation. It seems that a more aggressive cam tends to allow an engine to run more static compression before the onset of detonation than milder cams for some reason that I do not fully understand, but am trying to figure out. I do not subscribe to the dynamic compression theory as I will describe further down. My guess is that the L-series has elevated combustion temps beyond what would be considered normal, for one reason or another, and that is why they are so octane sensitive to begin with. Some say that that more aggressive cam profiles offer less dynamic compression. Yes, this is true, but ONLY at lower RPM’s. Conventional wisdom dictates that if a bigger cam allows the engine to make more torque at the torque peak as compared to a milder cammed equivalent, that torque increases is because of more cylinder pressure at that RPM, i.e. it is making more dynamic compression at that RPM, therefore more natural boost. If dynamic compression is the reason for the engines propensity for detonation, then a larger cam “should” be more susceptible to detonation especially at torque peak, based on the “pressure” theory. Hmmmm…. Then why isn’t Dan Baldwins engine detonating more than and OE cammed equivalent?... My theory is further down this post;… It is just that, Pauls theory, so don’t take it to the bank, just yet….

 

I probably should be a little more specific in my comment about flat tops with open chamber heads detonating. It is VERY common that this combination is prone to detonation, though there are a few cases of this combination running with no issues. The example that Dan Baldwin brought up, an OE cammed flat top L-28 with an N-47 head having to back off the timing by 8 degrees is the norm that we see. In practice, (but not according to the dynamic compression theory any how), A bigger cam tends to help, especially at the lower RPMs where cylinder pressures are less, i.e. less dynamic compression. The only explanation I can conjure is theoretical at this time, and that theory is the natural EGR that takes place with a more aggressive cam profile does help to cool the combustion temps so that pump gas wont ignite prior to the “desired” ignition event…. Also, during the valve overlap event, a larger cam profile allows more “cool” intake charge to flow through the chamber which would help to remove excess combustion temps.

 

Again, this is just a theory at this time and I’m sure that this theory has been busted and there is more logical explanation out there.

 

 

FWIW, the typical street engine is only 75-85% volumetric efficient. I.e. it only produces 75-85% the amount of torque that its actual displacement would allow if the cylinders were to fill 100%. NASCAR engine builders have been able to extract over 110% VE, (Volumetric Efficiency), without the aid of super chargers, Turbos, or Nitrous through strategic valve timing, intake design, and exhaust tuning, etc. They are achieving essentially un-natural super charging taking advantage of the Helmholtz principle. (This would be a post that I honestly don’t have time to write up this month… )

 

 

Ok, I’ll stop there.

 

 

Sorry for going so far off topic with this thread.

[JMortensen]

Dan was running pump 93 octane. That's a big difference from a guy in CA running oxygenated 91. That's my theory on why he didn't have detonation.

[Dan Baldwin]

I should clarify that I was running the stock N42 head (shaved ~.010") with *stock cam* on the original 3.1 build for a number of years. ~10.35:1, running full advance, on 93 pump.

 

Now I'm running 11:1 with the big cam. I had wanted to go ~11.5, but it just wasn't happening due to piston/valve clearance issues. I'd have to go with custom pistons vs. KA's with machined valve reliefs (which I probably shoulda done with the last rebuild).

 

The reason cammed engines can run more compression ratio is that they're have very low V.E. at lower lugging engine rpms, so chamber pressures are lower. They only start to get good V.E. at higher rpms, and at higher rpms detonation doesn't have as much time to take place. So you can run higher compression ratios before detonation is a problem, DESPITE any additional pressure from slight supercharging effect you can get with reflected wave action at higher rpms with more valve overlap.

[Zmanco]

Daniel' date='

As for your project, there is no need to switch over to the N-47 from the N-42. Any gains that you might realize from that swap would be to minute to worry about. Though you do have a much bigger issue at hand, detonation! An L-28 with Flat top pistons and the open chamber N-42 head, (or Z N-47 for that matter). This combination is well known for not being pump gas friendly even at a measly 9.5:1 comp ratio, they WILL detonate even with premium pump gas and a mild cam. I’ve witnessed this first hand on more than a few engines that others built and have also read about from LOTS of other people as well. Yes, the ignition timing can be backed down to help subdue the audible knock, but by doing that you are giving up LOTS of power by retarding your ignition timing. I would much rather loose a whole point of compression using amore ideal head, (P-79 or P-90), and be able to run ideal ignition timing. I.e. sacrifice maybe 3 % HP due to loss of compression ratio to regain 10-20% HP with ideal ignition timing. Don’t rip over dollar to pick up a dime. 10 degrees of ignition timing can be worth more power than even 2 points of compression.

If it were me, I would ditch the N-42 and N-47 for either a P-79 or P-90 head as either of these two heads complement the flat top pistons MUCH better and will allow you to run ideal ignition timing on pump gas allowing your engine to run a max effort. [/quote']Well, Paul, you did call it correctly. Now that I have more miles on the engine and it's been much warmer, I have picked up some pretty audible detonation. It only occurs at low revs, and only at part throttle. By 3500 rpm it goes away (I think - hard to tell due to all the noise from the webers and header), and it also goes away any time I go to WOT.

 

I tried retarding the timing to 0 at idle, but it didn't make any audible difference. I also tried adding octane booster, even the good stuff (108) but it makes no difference that I can hear.

 

The frustrating part is that the engine runs GREAT! But I'm guessing that this much audible detonation is not something the engine can live with over the long haul.

 

I had a spare cam reground to .480"/284 along with regrinding the rockers. I had planned to put this into my N42 head, but given the pinging I'm now rethinking.

 

So on to my question: I have located a P79 head for a reasonable price. If I just put the cam into it and use a Felpro gasket, LEngine says I should be around 8.8 CR (I'm bored .030 over). I've read about the mod to shave the P79 .080", raise the towers with shims, raise the springs, etc. to get the CR back up around 10:1. Is it worth the extra effort and cost? I'm thinking it is since most of my driving is on the street where I can't be making all the racket that 6k+ revs (and webers and dynomax muffler) make. In other words, I need the engine to be strong over a reasonable wide range of rpms.

 

Quick recap:

 

N42 block bored .030 over

flat top pistons

weber DCOE 40 carbs

6:1 header

'80 distributor with no vacuum advance

currently N42 head, thinking about P79

 

Thanks again for everyone's inputs. It's amazing how much experience there is on this board!

[JMortensen]

Well' date=' Paul, you did call it correctly. Now that I have more miles on the engine and it's been much warmer, I have picked up some pretty audible detonation. It only occurs at low revs, and only at part throttle. By 3500 rpm it goes away (I think - hard to tell due to all the noise from the webers and header), and it also goes away any time I go to WOT.

 

I tried retarding the timing to 0 at idle, but it didn't make any audible difference. I also tried adding octane booster, even the good stuff (108) but it makes no difference that I can hear. [/quote']

Search and read up on octane booster. That little bottle probably raised your 92 to 92.2 octane. You need a lot of that stuff to make a difference. I was buying it by the gallon (tolulene and xylene that is) and mixing it myself. My L28/E31 combo with a .490/280 cam pinged until I got up around 95 octane.

 

I had a spare cam reground to .480"/284 along with regrinding the rockers. I had planned to put this into my N42 head, but given the pinging I'm now rethinking.

The cam will definitely help. It's worth a shot since you already have it. That may be enough to solve the problem. If not, there's always a bigger cam.

 

So on to my question: I have located a P79 head for a reasonable price. If I just put the cam into it and use a Felpro gasket, LEngine says I should be around 8.8 CR (I'm bored .030 over). I've read about the mod to shave the P79 .080", raise the towers with shims, raise the springs, etc. to get the CR back up around 10:1. Is it worth the extra effort and cost? I'm thinking it is since most of my driving is on the street where I can't be making all the racket that 6k+ revs (and webers and dynomax muffler) make. In other words, I need the engine to be strong over a reasonable wide range of rpms.

The lower compression ratio will cost you power particularly down low. Shaving and shimming will get you back to where you are now with respect to compression and hopefully the quench will help with the detonation. I haven't actually seen anyone quantify exactly how much quench is needed to prevent detonation. I think this is one of Dan Baldwin's problems with the quench issue, and at least in that respect he's right. You could "prove" it for us, but IMO this would be a last resort as you already have a fresh head.

 

First thing I'd try is the cam. Second thing I'd try is a different bigger cam. If you can make that combo work then you'll save all the machining costs. You already have the rockers ground. You could try the cam and if it doesn't work swap in a different cam. I know they say you're not supposed to, but I pulled the cam towers and swapped a cam and had no problems at all. Just pulled the spark plugs and drained the coolant beforehand, and retorqued the head bolts after. Did it on my L twice (on the same headgasket). Also did it on my 22RE, that one was a little sketchy because you have to pull ALL of the head bolts.

[Dan Baldwin]

It only occurs at low revs, and only at part throttle. By 3500 rpm it goes away (I think - hard to tell due to all the noise from the webers and header), and it also goes away any time I go to WOT.

 

Are you running vac advance? It sounds like it might be adding too much advance at part-throttle. You might try running it with the vac advance disconnected.

 

Increased load when going to WOT should normally make it detonate more.

 

GM's and Harley's used to detonate under light-throttle cruise conditions and it was considered "normal"! Trying to maximize economy and minimize HC emissions, they ran as close to (just over?) the limit as possible with vacuum ignition advance and lean A/F mixtures.

[Zmanco]

Are you running vac advance? It sounds like it might be adding too much advance at part-throttle. You might try running it with the vac advance disconnected.

 

Increased load when going to WOT should normally make it detonate more.

No, there is no vacuum advance connected. I installed the webers shortly after I rebuilt the engine with this combination of flat top pistons and N42 head. When I had the DGV carbs on, I never heard any detonation. Immediately after I installed the webers I began to hear what sounded like faint detonation when the throttle is partly opened, say between 20 and 50%, and only at low revs. Even when I retarded the timing to the point that the carbs were spitting and backfiring (front firing?) there was no change in the sound. That's part of what has me confused.

 

But last Saturday it was very warm, close to 100 ambient, and I heard the detonation louder, and over a wider range of throttle. That's what convinced me it was really detonation and not some other strange sound. BTW, it doesn't have that somewhat random sound that I'm used to hearing. It's a more regular sound that rises with engine speed. Very strange. Does any of this make sense?

[JMortensen]

Did you just put the Webers on then? Are they tuned? You might be way too lean at cruise. There are some good threads on tuning Webers here that might help you out. I guess I ASSumed that you had them running correctly.

[Zmanco]

Jon, the webers are pretty close to done. I have an O2 sensor and can tell that I'm not lean when the detonation occurs. The only time I ever go lean is during the transition from idle circuit to main, and after the last change to the idle jets it's barely noticable. I'm probably going to go up one size further on the idle jets, but was waiting until I put the new cam in before making any more changes. As you know, it's not cheap experimenting with weber jets

 

Do you think this is part of it? I had read that being lean can make detonation worse, but it was so loud last Saturday that I figured going a bit richer wasn't likely to solve it. Perhaps that's a bad assumption?

[JMortensen]

Tough to say from this end, sorry. If the AFRs are OK then I'll revert to my previous suggestion of trying the bigger cam.

[Drax240z]

Any chance your webers are just out of balance? They make a fluttering sound that I could see mistaken for detonation if they are off balance by any apreciable margin. It is much easier to hear at light throttle than at any other driving situation.