triple 40 webers...best head to run with?

[Guest DATTO]

hey guys

have the oppurtunity to try some triple 40 webers, what would be the best head to run with this setup, i was thinking E88 with the big stamp instead of the little stamp E88 heads, or i was told a N42 head. what do you all think,,,im gonna run a mild cam as well, 280 duration...and thats about it...just want to get moderate power...thanks for your help in advance.

[Lockjaw]

P79 milled 80 thousandths, or P90 milled the same.

 

A friend ran 8.40's with a P79, a cam, header, and webers. In the 8th mile. He had a bigger cam (290 duration) and milled 110 thousandths but that is to much for the street.

 

No N series, no matter what people say, the P series is the best.

 

I should have mine on and running soon, I will report back.

[RedNeckZ]

I am now running a E-31 head on my L-28 block with dish piston. It has been ported and polished with big valves. I am also running the 45mm DCOE's triple setup. Had it jets set up for Colorado and now live in NC and it is now running a little lean. Have to order some bigger jets for it. Almost any head from E to P series will work. I prefer the E-88 heads a lot. Have 4 of them in the garage. How much are you looking at spending to get it up and running. The choice is pretty open after that. Good Luck and let us know how it goes.

[Dan Baldwin]

First off, what's your displacement? At 2.8 or more, you'll want bigger carbs than 40mm. And for a mild cam and moderate power, you're likely better off with the stock FI or SU carbs, or 2" Jaguar SUs. Triple carbs are the LAST thing on my list of engine mods ('bout to install 44mm 3X2 OER Racing carbs in place of 2" SUs).

 

Now, lemme defend the N42. It is the only stock head that has smallish combustion chambers (only the E31 has smaller), big valves, and square exhaust ports (no liner). No one has ever demonstrated to me that there are any performance disadvantages to the chamber design other than vague references to increased likelihood of detonation. I've run over 10:1 on street gas with the stock cam and was able to run 36 degrees and (inadvertently) even more full advance at rpm with no problems. Now I'm at 10.8:1 compression, with some chamber reshaping, porting, and a 302/.550" cam (all done at Sunbelt), running 93 pump still. The N42 has MUCH smaller combustion chambers than the P-series heads, not nearly as much (if any) milling required to get a decent compression ratio. More milling means you either have to take up a lot more slack in the chain and advance the cam timing, or use cam tower shims and live with slightly screwed-up cam/rocker/valve geometry. In any case, you'll likely want to have professional headwork done before going triple webers.

[Guest Luigi]

I have been watching this (and other L6) threads for a while because I'm thinking of building a 2.8 .040" over, N42, w/mild cam and webers. Before you balk at the webers, realize I'm not married to 'em, I got 'em free (2 sets 40mm w/cannon intakes), and although I work at a shop that specialises in older british cars, the 2" Jag su is a fairly elusive beast.

That being said are the 40's so small for a 2.8 that I should bail on 'em? I know just enough to be concerned about signal strength with a 45mm. Ditto w/40mm and giant chokes.

Lastly, Dan are you pleased w/Sunbelts work? I'm down to them or Gerolomy. Any input is appreciated. Who ground your cam? custom? how did you arrive at the specs.?

[Dan Baldwin]

The "How to Modify your Nissan OHC Engine" book has the following formula:

throttle bore = square root(liters/cyl * max rpm)*.82

main venturi = square root(liters/cyl * max rpm)*.65

 

This would dictate 47mm throttles for a 7000 rpm 2.8 liter.

Now that I think about it, that may be a bit much. Bob Hanvey made good power to 7300rpm

with his 3.1 liter, breathing through (I think) 40mm carbs. I should know better than to offer advice where I have no experience, but most of the experts I've talked to seem to agree that the 40s are better for smaller displacements, and 44+ for over 2.8, for hot street/mild race engines. But if you've got 40s, throw 'em on there and see what happens!

 

I sent my tired stock N42 cylinder head down to Sunbelt in January. Got it just before my second time trials event of the year (had to drive the 240SX for the 1st event , but set

a class record with it, on street tires, and with little to no brakes:), May 19th. Event was at Summit Point, on a Monday/Tuesday. Spent Saturday and Sunday installing the head and all ancillaries, put a battery in it 1st thing Monday AM, started her up and drove 9 hours down to West Virginia! Won my class (of 3 cars), despite a brake problem.

 

Anyway, with the newly ported and reworked cylinder head, and new cam (grind developed by Sunbelt) with lighter springs, my straightaway speeds at Mosport and Watkins Glen went from ~122mph to ~130mph! Lap times went from 1:43s and 2:22s respectively a couple of years ago to 1:40s and (gulp) low 2:17s! (note: I am not a race car driver, and my car is not a race car. I'm pretty happy if I can post times similar to the top ITS cars/pilots)

 

One downside: though I told them my piston heights above deck (+.022" for the raised "ring", +.003 for the flat area), I wound up with an intake valve/piston clearance issue. Clearance is only .045", with the cam retarded ~6 deg. I calculated that would go to .030" clearance if I went to the #2 hole in the cam sprocket, so I left it. So now I've got very poor low-midrange grunt. The engine doesn't wake up until maybe 3500-4000. This is a factor coming out of some corners, and is very annoying. But that's sort of the risk I took having them work only on the head. As it is I'm really looking forward to getting the pistons cut for valve clearance, so I can advance the cam timing and hopefully get some more midrange torque.

 

There's probably nobody better than Sunbelt for building a high-performance Nissan L6.

[Bob_H]

Well, "Bobby" with his 40mm SK carbs and 3.1L put down 180 hp through 7k with a much smaller cam than Dan.

Actually, in all fairness, I paid someone to jet the carbs on the engine dyno. It took a lot of work b/c they were sooooo far off to begin with That and Chuck really knew the triple carb setup.

That formula Dan provided is biased more towards race carburetion. By comparison, the same shop that built my motor, ran a 2.8L in a GT-2 car,(300zx, they got a weight break not running the VG30). That motor make ~330 hp to my ~220,(I give mine as a reference only b/c it was the same engine dyno). They ran 50mm carbs with the venturis removed. Yes, it wouldn't idle below ~2000 rpm, but the venturi's were restricting the motor at high rpm. It was funny to look at, for it reminded me of the TWM throttle bodies. Nothing then a throttle. That was their approach, everyone elses is a bit different.

That being said, for the cam sizes Dan is running, I believe 40mm would be to small. I think my carb setup would be good through about 210-215 hp at the wheels. After that, I would be choking the motor. My current cam is only good for about another 5 hp and 20 lb-ft of torque. I still need to build a heat shield,(BTW Dan, consider a heat shield MANDATORY). The important distinction I made when building my motor was the daily driver status. I wanted a car that my Mom could hop in and drive to the store if she needed. So mine pulls cleanly,(and strong) from idle in fourth. I think if I did nothing other than switch to 45's, I would lose a little bit of the low speed driveability and might gain 10hp on the top end. The key is tuning.

So if you already have 40's, go for it. I would suggest limiting your cam size to something smaller than Dan's, maybe bigger than mine,(which is the Motorsport Auto 2003 grind, .460 lift, 270/280 split duration Schneider cam). Search out and find someone who really knows sidedrafts and can tune them. If you can marry them with a chassis dyno session, expect to pay 2-400 and have a great running car.

Dan said:

There's probably nobody better than Sunbelt for building a high-performance Nissan L6.

 

I agree 100%. Their new cam profile seals the case. Expect to pay a bit more, and have to wait a bit longer, but it is worth it.

 

And Lockjaw said:

No N series, no matter what people say, the P series is the best.

 

Sorry, I have to disagree with this. I helped perpetuate this myth on the Datsun Workshop when I first built my 3.1. For a stroker motor, it is not bad, for a 2.8, it sucks. Shaving .80 thou is A LOT and requires a bunch of work to set the cam back up correctly. Sure, Bryan Little did it and told everyone on the Datsun Garage how to do it. However, think about this for 1/8 mi times: Norm is in the low 8's, like 8.1 with an N-42 and SU's. Sure, his experience is vast for drag racing, but I'll be so is Lockjaw's friend.

The N-42 is a plug and play head and is hard to beat. Now for a Turbo, you can't beat the P-90 series.

-Bob Hanvey

[Guest Anonymous]

I tend to agree that the shaved "P" series head isn't necessarily the ultimate head. Any "N" series or even "E" series will work fine and as it was already stated, usually don't require any shaving other than that required to get them straight. The real key is to have unrestricted square ports and big valves. Chamber design does have some influence, but unless you're running super high compression ratios i.e. 13-14:1 you're not going to notice any real difference.

 

Properly jetted and choked, 40mm triples can work quite well on a mildly tuned 2.8L. In my experience, they are a bit more streetable since they offer increased air velocity at lower rpms when compared to bigger 45mm carbs. They will hamper top-end performance on a highly tuned engine, however but the tradeoff in low end performance may be worth it to some people.

 

As a case-in-point, my friend has a built 2.8L running over 10:1 compression and an L7 cam. He has 40mm DCOE carbs installed with 36mm chokes, which are the largest size you can readily get for the 40mm carbs. His engine is very responsive and pulls strong to 6500rpm but begins to flattern out after that. I've driven this car and can honestly say that it is quite streetable and certainly has more power than a SU setup. If he gets any crazier with his cam and/or compression however, he's going to need to step up to the 45mm carbs to get the performance he expects since most cam changes to these engines keep shifting the powerband up and up and up...

 

My car, a Rebello 3.0L runs 45mm carbs with 38mm chokes. It is not as street friendly as the previously mentioned 40mm carbs and 2.8L but certainly has much more power. Part of this is obviously due to the fact that this engine is fully built by Rebello, but the second part of the equation relates to the fact that the engine pulls much harder at mid-high rpms than my friends car and doesn't fall flat until just before redline which is set at 7500rpm, although I usually shift ~6800-7000rpm.

 

What am I trying to say? I guess that if you have 40mm carbs, you can certainly use them so long as you understand that if your real intention is building a real highly strung engine they're going to fall a bit short. For a street driven 2.8L, I'd say that 40mm carbs are just about right but beyond that you need bigger carbs.

[Lockjaw]

Well I know there are alot of you E and N series head fans out there, and you can believe what you want to believe but I have seen two identical cars one with an E31 head that was milled and unknown amount, and a P79 milled 45 thousandths go at it, and while it was close, the P79 head car could pull away even shifting at 5500rpms, far short of the 7k that most Hipo datsun cams pull to.

 

I am also aware that people all have different opinions, and that is fine, but what is so hard about setting up the valve geometry. For a hipo cam you have to have springs, so get retainers that are not stock, and increase the lash pad the same thickness as you shim the cam towers.

 

As for my friends car, according to a vericom, it was making 240 hp with SU's, and I can guarantee you they were not setup like Norms are. This was a simple mill the head 110 thousandths and throw a big cam in it and go. When he converted to webers, they were 40 mm webers with 33 mm chokes. He started out at 28, but I convinced him to try my 33's since I had dialed them in and knew how to jet them.

 

His car was every bit a match for a turbo car, the one he had previously raced and lost to, with a stock turbo, big exhaust, cartech fpr, Conquest intercooler, and 14 or so psi. That turbo car ended up running very low 13's at the drag strip at mph that would make Norm green with envy.

 

As for square ports, get the P90 head. It has the same conbustion chamber as the P79. Nissan put a lot of development work into the P series heads, they flow well, have a nice closed combustion chamber, and a high swirl design, like almost every high performance head on the market today for any car that is OHV.

 

So if you consider someone with an unported head, stock bottom end, 290 duration cam, with 33 mm chokes in webers a race car, then I guess his car wasn't that fast. He sure put it on some people though.

 

Anyway, I have my head set-up, and will hopefully have the bottom end yanked out and honed out soon, so I will report back. Believe me, if I thought any other head other than a P series would run better on my car, I would have it. If you haven't tried one, you should.

[Dan Baldwin]

I still say an N42 is the best stock head for an N/A application. I personally wouldn't feel comfortable shaving 110 thou off, though it is done. I just don't see the need when the N42 is readily available. Haven't seen enough evidence one way or another to prove which is best in equivalent setups. That would take a dedicated EFFORT. All I've ever seen or read is that the P79/P90 MUST be better because Nissan put so much effort into them. Maybe true, maybe not, but a P79 car with Webers that MAY be as quick as Norm doesn't quite prove anything.

[Synlubes]

Hey Ya`ll

Just wanted to add my 2cents worth!

I run a stock L28 block, unworked N42, with 3000 to 6500 cam and 45mm triples(webers).

The formulas talked about, are for all out racing(and I do agree)!

I set my carbs to those same formulas(using 36mm chokes and jetting to match)and founded that the car DID run very well above 4000 rpms, but was not getting out of corners well. I droped down to 32mm chokes, reset jetting and found the car much better around the entire race track! I did loose a little power at high rpm, but what I gained was having better power coming out of turns! There is usually more going in and out of turns than long strights on most road tracks!

My next setup well be L28 turbo block, 40 over flat tops, P90 head(w/ alittle bigger cam), same carbs w/ a little ajusting. The P`s(p90) are the best, due to Nissan`s development, they have beter flow than the other heads!

Just some other opinions!!!

[yo2001]

Nissan did record 10HP increase with p79 head with flat top pistons. I think that's conviencing enough. I had chance to compare the older E88 head which is indentical to N42 head and P79 and P79 does look better because the intake runner are less curved with less pocket area and also P79 is close chamber with more quinch area. BTW, the round exhaust ports does flow 10% less on the flow bench but the exhaust flow is not really critical for a street car shifting between 6500rpm to 7000rpm. Intake flow is what makes the difference. Norm used to run ported intake head with stock exhaust ports.

 

This argument can go on forever. I think the time slips should prove the myth. I run 9.7@70mph in 1/8mi, 15.4@90mph in 1/4 with stock 8.3:1 '78 EFI motor with 274 cam from MSA. I'll be running 10.3:1 with a shaved E88 and same cam on 78 bottom end. I'll let you guys know the result.

 

I almost forgot, how about 40mm side drafts with no venturis? I've heard that from older Toyota guy. That's 40mm wich is about same as 45/44mm with venturis.

[DAW]

What if you could take a P79 head and lower the roof to decrease the combustion chamber volume? Let's say, lower it by the distance equal to the difference in length between a P79 valve and an N42, E88, E31, N47, etc, valve...now would that be a great L6 head or what? The quench configuration of a P79/P90 and the high compression volume of the E31... There is such a head and it's abundant in JYs, it just needs upgraded intake valves, springs, and L28 cam. DAW

 

P.S. N47 from Maxima, not 280Z.

[Bob_H]

Ok, time for a corner-carvers type reply. I don't like heresay or claims that are hard to prove/back up. I will first start by saying this is not a personal attack,(if you take it that way, eat more wheaties), it is challenging your ideas and asking for more concrete proof.

And for those unfamiliar with corner-carvers.com, here is a post that should give you and idea:

Corner Carvers suspension tech forum post about KB

Be forewarned, it is not for the faint of heart. If you like to sing songs while lightly strumming the guitar, stay away from that link. BTW, it follows a previous post from one of Kenny Brown's employees,(they make Mustang stuff). The first half is somewhat pointed, the second deals with the products. Good site for track knowledge though.

Ok, on with the show.

and you can believe what you want to believe but I have seen two identical cars one with an E31 head that was milled and unknown amount, and a P79 milled 45 thousandths go at it, and while it was close, the P79 head car could pull away even shifting at 5500rpms, far short of the 7k that most Hipo datsun cams pull to.

And my response is SO? First, there are no two identical cars. Tuning, compression, tires, brakes, rear end ratios, tranny ratios, relative condtion of all of the above, etc.. All those play into something like that, and ESPECIALLY the skill of the driver. If a moron took Norm's 240 to the track, I bet the best we would see is very high 13's, low 14's. He smokes the 1/4 because he can launch that car and turn sub 2 second 60 foot times. In addition, he changed the gear ratios of his transmission for drag racing. Also, saying they were shifting at 5500 and somehow implying that if they went all the way to 7k they would be faster is absurd. In some cars, yes, in others no. It may have produced no power up there and was actually faster shifting at 5500. We have no dyno sheet or acceleration runs to look at. In my stroker, I get the best acceleration short shifting second and third gears, by almost 500 rpm,(discussin 1/4 times).

Second, the E-31 is a terrible head for serious performance, likely your worst choice. It used to be the one to use, because of the small combustion chamber. But without proper unshrouding of the valves,(not to mention bigger valves to at least match the later heads size), and some good port work, it is no good in a performance application,(talking serious performance). John Coffey has built what I consider to be the ultimate NA L6. He is putting out a fair amount over 300 hp, (he asked not to give out the final numbers) with a very wide power band,(3-4000 rpm), and (drum roll please), an N42! If he and Sunbelt Motors,(arguably the best in the business for L6 motors right now), thought the P series heads were better, I am quite sure they would have chosen such. However, with unlimted choice, they chose the N42. Why? Because it is a great head and very easy to modify. While I am a big fan of the P-series, and use it on my car, I don't reccommend it to anyone not building a stroker motor, and a full stroker at that.

 

but what is so hard about setting up the valve geometry. For a hipo cam you have to have springs, so get retainers that are not stock, and increase the lash pad the same thickness as you shim the cam towers.

It is not always that simple. What if you are dealing with a regrind and a reduced base circle? How about going from a stock cam to a Crane cam? And how about not all lash pads are the same size even on one given motor? How does the avereage joe deal with that? Yes, it can be worked through, but like tuning webers, it requires knowledge. I am not about to reccommend to people that they start messing with their valvetrain geometry. Sometimes it works out perfectly with no shimming/etc required. But sometimes it is a nightmare. It is like craps, you roll and you might win or lose. I did it and know what is involved. Unless you really know what you are doing, I cannot suggest you do it.

As for my friends car, according to a vericom, it was making 240 hp with SU's, and I can guarantee you they were not setup like Norms are.

First, NEVER use a Vericom to discuss hp in a rebuttal or to prove your case. Only chassis dyno's #. Engine dynos are even suspect. You can talk ACTUAL times for that car on a track or power to the wheels. Otherwise, the data is only as good as the user input.

I can take my G-tech, (yes, not as good as the Vericom), and it shows I have 300+ hp in my 3.1L. I have run it at the track and on the chassis dyno and an engine dyno. I know it produces nowhere near that much. There are far too many variables for what you stated. If you plug in Norm's times into generally accepted power equations it shows a bit more hp than he actually has. Again, a function of how hard he is able to launch that car, coupled with the gear ratios. When I plugged in my times into the same equations, the power was nearly the same as the chassis dyno. But I now have a 3.9 gleason,(had a 3.54 open), much wider stickier tires and a better ratio set in my tranny. Haven't been back to the track, but power to the wheels is the same, and I know it will go faster. My point? They are guesstimates, nothing more and not a good way to prove a point.

This was a simple mill the head 110 thousandths and throw a big cam in it and go. When he converted to webers, they were 40 mm webers with 33 mm chokes. He started out at 28, but I convinced him to try my 33's since I had dialed them in and knew how to jet them.

What head, what motor, what tranny, what rear end, what tires, how was it tuned???? All those and more are a significant factor in how well they work together and how well they run and importantly, how it compares to another car. And, they make a difference in how the car is jetted/setup. As I said above, for power, unless you are talking actual 1/4 mi times or chassid dyno numbers, you are talking guesswork.

His car was every bit a match for a turbo car, the one he had previously raced and lost to, with a stock turbo, big exhaust, cartech fpr, Conquest intercooler, and 14 or so psi. That turbo car ended up running very low 13's at the drag strip at mph that would make Norm green with envy.

And my friend beat this 13 second car, and I beat him, so I must run 11's! Be careful, that is starting to sound borderline rice. Comparisons to other cars, unless on the track itself are totally pointless. See my link on street racing after this paragraph to show how something as small as .5 sec difference can make in a equally match race. And you said the turbo car ended up running low 13's. Do we take that to mean it was not running low 13's when they raced? And I would expect the MPH to be higher for a turbo than Norms. And what was the setup of the turbo car? 240/280/280zx? tranny rear end? how well was its state of tune the day it raced. Was it cooler or hotter when it ran the low 13's at the track vs the day your friends car raced it? See where I am going? The comparison does nothing for us the reader except produce smoke and mirrors. Your friends car in question may indeed be a well setup mid 13 second car. Or it may be a mid to high 14 second car that sounds fast. The actual difference btw those two types are hard to quantify.

Here is the street racing link:

Street Racing is a crock

 

Nissan put a lot of development work into the P series heads

And they didn't put that development into the N and E series? The E series was an evolution of the 4 cylinder heads. The N series was an improvement on that,(look at the N47 with its D shaped ports and such). The P-series was designed for the ZX. The application was different as was the requirements. That alone does not imply it is better.

they flow well,

They flow well? Well tells the reader absolutely nothing. They flow well in comparison to what? A blow dryer? The N series flows well too. And the heads with liners flow well. I just told the reader nothing. The reality is the ACTUAL flow btw a P-90 head and an N-42 head for the exhaust is almost identical. No difference. The P-79 and the N-47 with their liners have great,(not just good) exhaust flow with very minor work. The radius coming out of the combustion chamber is larger, making it eaiser for air to make that 180 degree turn out to the header,(we are talking performance here). Just b/c the square ports are bigger doesn't mean they are better. They have more potential in a race application, but until you are talking serious turbo or race levels of power in a NA motor, that extra flow is not requried. (I know you would not use an exhaust liner'd head in a turbo). I have seen flow charts for both types of heads. Until you get some serious port work, you cannot tell the difference btw an N-42 exhaust and the P-90 exhaust flow. And for that matter the N-47 and P-79. Those four head are within a few % of each other.

have a nice closed combustion chamber, and a high swirl design,

Closed combustion chamber? And how many people on this board do you think know what that means? Can you adequately explain the difference between an open an a closed combustion chamber? I can, but I don't think it really applies to our heads. You have a smaller area,(talking flat), that is the combustion chamber, but the volume is bigger, so the effect is not as significant.

And high swirl? Squish maybe, but certainly not swirl. And I quoth:

A 'squish area' is a part of the combustion shamber that is made to very nearly come into contact with the piston when the piston is at top dead centre. There's usually less than 0.020" (0.5mm) clearance in these areas in such cases. What they do is cause the combusting gasses to rapidly travel towards the centre of the combustion chamber (or where-ever intended) and increase turbulence, thus increasing the combustion rate.

For those who want to know the difference btw a closed and open combustion chamber, here is a picture of a closed one, the second is the same type head, but open:

Closed combustion chamber, Toyota 5 valve

Open combustion chamber Toyota 5 valve

Notice the flat area of the cylinder head on the closed chamber is more in the shape of a star, where the open chamber is more circular. It is not just the flat area, but the whole chamber in relation to the valves. But I digress.

 

Next:

 

So if you consider someone with an unported head, stock bottom end, 290 duration cam, with 33 mm chokes in webers a race car, then I guess his car wasn't that fast. He sure put it on some people though.

We weren't discussing what makes a race car or not. But you were fine until the last sentance. I sure have put it on a bunch of people as well. And? It is irrelevant to proving your point and only weakens the defense. Along the lines of "I beat this Supra rolling down I-85"

I close with this. Lockjaw, I realize I broke down most of your post, but this is not about you, nor is it an attack on you. My P-90 page and Bryan Little's pages are a big reason why many of those myths are out there. I have finally corrected my pages. Bryan has made his setup work. He could have gotten very close if not better results with an N-42. Its personal, and he wanted to be different. Everyone runs the N-42. Your backgrond is a turbo motor. And for a turbo, there absolutely is no better head. But for a high power NA 2.8, the P series are mismatched and require too much work for them to make decent power. The N-42 yields the same result for a much lower entry price/knoweldge level. I just got sick of smoke and mirrors as defense to ideas/performance. It was not you, this has been building up for a while. I expect the same from everyone. If you are going to give an opinion, say it is that. When you start talking about performance being better than something else, it is no longer opinion. You are now "educating" someone else on the net. And we all know the high quality we often find on the net. I am posting this to set a higher standard for proof. Talk about your setup, times and dyno numbers. Saying you walked on a Z28 means nothing. A granny could have been driving an automatic and had a 2 second reaction time.

The defense rests your honor:

-Bob

[Bob_H]

yo2001 wrote:

Nissan did record 10HP increase with p79 head with flat top pistons. I think that's conviencing enough.

I don't think its is. They swapped to flat tops, and the compression ratio went from 8.3 to 8.6:1. Put the flat top pistons with an N-42 and you have better performance than the same motor with a P series head. It is a compression game.

I had chance to compare the older E88 head which is indentical to N42 head

No, it is not identical. It has a different design on the combustion chamber, different size valves,(you said old E-88) among other things. They are not the same head, that is why they went to the N designation. And not all N-42 heads have fuel injection notches either.

and P79 does look better because the intake runner are less curved with less pocket area

Looks better? Come on. You again told us the reader nothing. It does have slightly less curve in the intake, but that is more a function of the sideways D shape of the port. It allows the air on the bottom eaiser movement into the chamber. But the N-47 has the same design.... And less pocket area is NOT a good thing. That is why "pocket porting" is endorsed for your first time porting. The idea is to enlarge that bowl area making that transtion into the chamber eaiser for the airflow. I do assume that by pocket area, you are refering to the bowl behind the valve in the intake runner. If not, please correct me.

And:

BTW, the round exhaust ports does flow 10% less on the flow bench but the exhaust flow is not really critical for a street car shifting between 6500rpm to 7000rpm.

Data? on the N-42 or P-79 head? vs. the P-90 or the N-42? Or an E series? And where did you get this data? the Net/someone else? Just raising the bar for "posting" info on the net. If you are going to educate, back it up. And second, where you shift has no bearing on the previous statement. For all non-race cars,(just that, not raced at or on a track), you are only going to shift at a max of 7000 anyways. The only reason you go over that is you put some serious mods into the head, camshaft, and rotating assembly to witstand higher than 7k. There are few if any street setups that require or produce good power with the "stock" L6 cylinder head over 7k. I say "stock" to mean unmodified or pocket type porting, i.e. minor and cams of less than .500 lift and 300 duration. A .490 lift and 290 duration cam would push the limits of my defintion.

SEATS!

-bob

[Lockjaw]

Bob since you are in VA, go by and see Rob at the Z doc. If Rob is still there, he should be able to tell what's up with the P79 head.

 

All of the stuff "we" did with the P79 was back 10 or more years ago, and to be honest, I am not sure there were dynojets widely available at the time. We did not care about what a machine said at the time, we cared about what the car did. The guys car ran 8.40's in the 1/8th mile. While I am certain there are some NA guys out there who can run that fast or faster, that is still getting down.

 

As for setting up the valve geometry, I don't really care if the average Joe can't handle setting up his head. I can handle mine, and if someone has questions, email me and I will walk them thru it.

 

As for the cars, they had the same flat top engines, same trannys, same diff's, same diameter rims, hell they even had the same header. The E31 was unshrouded to BTW.

 

All I am really saying is I have seen with my own eye's what the P79 can do. Have you? Yeah I may not have hard data, but I have seen it with my own eyes, and that is all I need to know.

 

So anyway, you can believe me or not. Those who have taken the effort to try the P series head know what the deal is. If you choose not to try and believe, more power to ya.

[Bob_H]

It never was about believing you or not. Yes, I have seen a P-79 and a P-90 on a NA car outperform a similar N series. I have seen it the other way as well,(N beat P). I have driven them and built others. It is already established I have one and am a big fan of the P series heads. The whole point of that diatribe was to raise the bar on posting. I realize you and others may not take it that way, and I can't help there. Things like the cars are the same, vs the description you just gave make a difference. The little tidbit of it ran 8.40's vs some other cars 1/4 mi time is huge. That starts to give concrete proof and strengthen your case.

The only real opinion we have put in any of our posts is what head is best for NA motors. And it is just that, an opinion that we all expressed as such. As soon as you start talking about specific performance, it is no longer an opinion but fact, and should be backed up as such. And it should be noted that when I send my head into sunbelt for the new cam setup, it will be a P-90A, not an N-42.

No N series, no matter what people say, the P series is the best.

That was from your first post. To qualify it with "no matter what people say" is stating quite clearly that you are the only correct source,(or more correctly, your view is the only correct one). It highly depends on what the end user wants. John C showed the N-42 can be an incredible head for serious performance, so it is my opinion that either can be the best. It is important to note that John was/is running very high compression, like 13.6:1. To take a P series and run it to that compression requires incredible work on the head and money for pistons. Again, I would personally run the P-90 for a similar application. (By similar, I mean almost everything but lower compression for street gas).

The reason I believe the N-42 is better is the minimum amount of mods required to make good power. Minimal if any shaving,(which means no monkeying with the valvetrain), minimal if any porting, and just bolt it on. That is why I endorse it vice the P series head. For 75%+ of the people here, they are getting a professional to setup up their head, or are doing it themselves and don't have the experience. Often, the "professional setup" is by a local builder who has little if any experience with L6 motors.

An unported, unshaved N-42 can provide 200+ hp on a L28 with an aggressive cam and good carburetion setup. To get the same performance from a P series requires some significant shaving on the head and re-setup of the valvetrain.

Bottom line for everyone:

Provide proof, back up your claims, and no absolutes. And oh yea, the N-42 is the best! (sorry, had to )

-Bob

Remember, its all in good fun.

[yo2001]

So changing the compression from 8.3:1 to 8.6:1 give you 10HP? that's only 0.3 different. I doubt that. So if I go from 8.3:1 to 10.3:1 I get 60HP+? That's alot.

 

I was comparing 73 E88 head which is open chamber head unlike the E31 head. E88 does have smaller valves but same head chamber shape as N42/N47.

 

Also, I got a flow bench sheets of the P79 and N42 here. I can scan them and send them to you if you want.

 

Well, When I said less pocket area, I meant intake runner behind the intake valves like you said. But what I meant when I said less was the P79 has better transition because the valves are set higher and there are less transition there. Sorry I don't explain thing good.

 

Anyhow, a time slip or a dyno sheet is what I want to see. I've seen what P79 can do but I've not see anybody running N head with same result. Except may be Norm but he's kind of out of question.

[Lockjaw]

Bob I said in my first post the car ran 8.40's. It did. If you want some details, I will give you some details. It was a rebuilt flat top ZX engine we picked up for 50 bucks that had a rod knock. The guy took it to a "bubba" machine shop, had it honed, resized the rods, polished the crank, and he put it back together. The head was milled 110 thousandths, and not shimmed. He ran SU's at first with a crower 290 duration .490 lift cam that I can get you part number on if you would like.

 

He had a MSA header 6 into 1, 2.5 inch exhaust with a sonic turbo muffler, and 3.90 gears with the ZX 5 speed with the .745 over drive.

 

That is it. He later went to my webers, a 3 inch exhaust, and 4.08 gears, which is what he ran 8.40's with.

 

Thats it!!!!!!!!!!!!!!! There was no special tuning, he didn't lighten the car, nothing. No port matching, nothing special about it at all.

 

I mentioned the vericom because that was all we had at the time, and I don't believe the numbers on the vericom any more than I believe the 0 to 60 calculator I plugged my ZX into and it said I run 3.79 seconds to 60. It is merely a device to give you and IDEA of where you are. Hard numbers are better, I don't disagree. But either I can say the vericom says it made 240 hp, or I can say something like, I think it makes X amount of horsepower since we never put the car on a dyno.

 

What I will say about the car is this. I have never been in a normally aspirated car that pulled as hard as that one did. I ran that cam in my car with a E88 head, and it wouldn't fall out of a tree. Maybe he had a really good combination, and when he put the engine together everything just clicked, I don't really know.All I do know is this, the thing got down, and it was very powerful for what it was.

 

So conviced are myself and another witness that we are both building flat top bottom ends, I am going to run the P79, my friend the P90. We will both have 3 in to 2 into 1 headers, likely the same exhaust, our cams will be within a few degree's of each other and ground by the same grinder. Yeah not quit apples to apples, but my friend has access to any head he wants, and he is running a P series.

 

I am not sure where you came up with this "higher level" deal you are talking about, all I know is a guy put a post out there asking for opinions, and I gave mine. Like it or not it stands. If you think the N42 is better, fine thats your opinion. I happen to not share it, and if you would like me to change my mind, you will have to do more than argue with me on a board.

 

I would also like to clear up a couple other items too. First, I don't really care if someone lacks the knowledge to properly set-up a head. Thats not my problem, thats their problem. Second, I don't really care about wether or not someone has good or bad driving skill at the dragstrip either. If you suck at the drag strip, practice and get better. All you do is muddy the waters when you start throwing stuff out there like that. Finally, I don't really care about Sunbelts reputation either. If you want to spend your money there, go ahead. Personally, I would rather be able to say my car is fast and I built the motor instead of saying, Hey I paid Sunbelt 10 grand to build me a 300 hp NA engine.

 

Personal attack? Nope, just one guys opinion. If you want to continue to argue, send me an email, the board is not here to argue on.

[johnc]

Ya skip a topic for a couple days and look what happens!

 

Given enough time, money, and talent any L6 head can be made to make good power. The only valid comparisons that we (as non engine builders) can make are between stock, unmodified heads.

 

I had a discussion about this exact topic with Jim Thompson before he started on my 3L and a couple years earlier with Don Potter. Both agreed that the early E88 (for 2.4L) and the N42 (for 2.8L) were the best heads to use assuming you couldn't do any modifications. This is coming from engine builders who have build (combined) hundreds of ITS L6 engines over the years. One caveat - I think the P79 is not ITS legal on the 280Z and no one runs a 280ZX in IT that I know of, so Jim and Don probably never really looked seriously at that head.

 

The E31 got a good reputation because its closed chamber increased compression and horsepower enough to overcome its smaller valve and reduced port flow. Since then, the above two guys figured out how to reach the ITS 9.5 to 1 compression limit other ways, they prefer the E88 and the N42 because you get the best of both worlds.

 

Going back to DATTOZG's original question about using (I assume) an unmodified head on his 2.8L I would go with what Jim and Don go with when they build racing motors for paying customers.

 

As a side note, when it comes time for me to refresh the N42 on my 3L Jim wants to build up a P90 head. He thinks there might be ways to get a little more out of that head (for reasons he wouldn't tell me) then what I'm getting out the N42. FYI... my N42 is heavily modified.