Jump to content

big and nasty headwork

Recommended Posts

alrighty, after a race on suday at a local track, the honda kids were all porud of their 12 second all motor cars that were gutted, lexan windowed out.


blah blah


now, i already have the bottom end to support what i want to do, but not the head.


if you were to build a head {e31, early e88} yes, thats right, you can keep the p series stuff. going big and nasty on the port, cam, springs, retainers, so on and so forth.


what would you do?

Link to post
Share on other sites
  • Replies 105
  • Created
  • Last Reply

Top Posters In This Topic

um' date=' gee, thanks?


that pretty much, more or less made no sense. i already knew that. more or less going for cam specs, spring rates, lashpad's, oversized valves. {remember, ths is not going to be a turbo car}


if some crazy japanese guy can run 9's in the 400m with an L28. i don't see why i can't run 11's[/quote']


Got a bit of a chip on ya shoulder son? I won't go into the self-mocking statements you made though. :)


The head requirements for a turbo car are more or less identical to those of a N/A car from what I understand.


The spring rates you want depend on the revs you want to be pulling, and the cam profile (and boost pressure for FI peoples). The cam specs you want depend on when you want your power mainly, and AFAIK the largest valves you can safely use are 47mm inlet and 38mm exhaust valves.


Its all a juggling act and a matter of optimising the torque curver characteristics you want.



Link to post
Share on other sites

I think the car Silent mentioned was a s13 stripped and gutted with a L28 motor built only for drag in japan.


You also have to remember that when you raise performance that you are eventually going to loose some reliablity/longevity of the motor. With these motors, there are a limited amount of thing that you can do to it before it will eventually crap out on you, but thats the same with any car. Its just that with these its just a bit more limited.

Link to post
Share on other sites

All I'm going to add to this thread regarding L28's in the 9's is "Old News".

For a "Link" I will refer you to the Carboy "L-Motor Issue" containing the "L-Motor Shootout" at Fuji Raceway from 1989.

11's and 12's were all over.

There were L's in S130's doing 9's and 10's...


It's old news in Japan. Real old news.

Link to post
Share on other sites

So a rude guy posted a short question(with plenty of non-coherent sentences, but showed no tech know-how or quantitative baseline) in a forum....


Someone replied....but not what RG wanted to hear, so RG was rude to him.

Someone else replied....but still not what RG wanted to hear, so RG was still rude . Another one replied....again not what RG wanted to hear, so RG was rude again. Someone flamed RG....this is definitely not what RG wanted to hear, so RG flamed back. Now he's rude to everybody. Then, someone banned RG....RG says to everybody : "wtf is YOUR problem?"




I doubt you are ever going to build a 11 sec N/A L28. In fact that kind of attitude will not get you very far neither. Personally, I know a local guy who runs a N/A Z into high 12's; on top of that, there are several guys here that also run in 12's with N/A and carbs but since you are going for 11's you won't be interested.

Link to post
Share on other sites

rude? if you want to think that ok. words are taken out of context, and placed into a, "rude way of comming across".





i left it an open question for random theroy's on it. one person has an idea, another person has another. i have a pretty good idea on what i plan on running as far as valve train, and such things. i don't plan on having this car being anywhere near streetable, nor anywhere near pump gas friendly. {it barely is now}

shaving about 600 lbs off the car, adding another good chunk of hp, and some tuning here and there will get me close to the goal.


everyone has goals, we always don't reach them.


anything over 300 rwhp would be a quick lil car. even if it require a DFI setup.

Link to post
Share on other sites
Guest RubberBerner

Well if you port the heads more than the valves will flow, all you're doing is killing velocity-which is much more important on an N/A motor than a forced induction motor. Also seeing as how this is going to be an NA setup-im sure you want to rev higher than the usual L series. Valve springs and titanium retainers will save your precious pistons, and valves. I'd get my head flowbenched after i get the valves i've selected, i'd go with a 45mm intake and a 41mm exhaust valve. Also with a large bore, a nice 3 or 5 angle valve grind will pick velocity back up nicely. What cam are you going to go with? thats where you need to start out...then you can use the lift from that cam on the flow bench to see how far open the valve goes.

Link to post
Share on other sites
  • Administrators


I’m sure there will be those that disagree with my opinions and statements below and can even show documented proof to back up their claims, and I encourage that. I in no way claim to be THE Datsun performance guru, I’m just passing on the info I’ve gleaned from my own personal experiences over the several years that I have been building and playing with Datsun L-series engines in hopes that others will take this info and build upon it and in return share their success and failures from which all of us, myself included, can learn even more on how to get better results with fewer mistakes along the way.


Now for the not so real disclaimer…

The opinions viewed in this post are purely the views of me, myself and I, and I reserve the right to view my opinions anyway I see fit whether I’m faster than you or not!

Void where prohibited - batteries not included - licensing and taxes extra - the surgeon general has determined that lack of horsepower causes cancer in laboratory rats - optional equipment shown



Ok, now on to the post….


Dave Andrews summed up the valve spring rates and cam specs pretty well.

John C., beautiful setup you have there. I would like to see more specs on your power plant and some performance numbers, like vehicle weight, ¼ mile ET and trap speed, dyno figures, etc. if you have them. It’s nice to see and appreciate someone else’s work at the level yours is built to.

Rubberberner also added some technically valuable input as well.



Here is my input. I apologize for the novel. When it comes to tech items such as this, I tend to ramble on and on and on.


When it comes to making power N/A, displacement and RPMs are the rule. As much of both as you can financially afford is the key. The “bottom end” is where you build reliability and durability, the top end is where the power comes from. As for displacement, up to around 3.0-3.1 liters is doable on a realistic budget, but the cost curve starts a real sharp shift upwards from here, (this is where the V-8 conversions start to look real good. $$$ per HP, the V-8 swap is pretty hard to beat). As for RPM,s the weak link in the Datsun engine tends to be the crank, this is assuming that you have already installed good quality aftermarket rod bolts and the pistons are forged, not OE cast. Now if a good billet crank can be had, the rods are next in line. A good friend did some testing some years ago, (Carey M, if I misquoted you here, please jump in to clarify), and found that with as light a flywheel as possible and with a quality damper, i.e. fluid damper, the L-28 crank is good for 8500-9000 RPM, after that he was experiencing crank breakages at the rear of the crank. A billet crank should allow for more RPM.


Now, on to Datsun L-series cylinder heads…

The biggest air flow restriction in the Datsun L-series head is the valve curtain area, i.e. the region between the valve head and the valve seat when the valve is OFF the seat. In all my L series engine builds, unshrouding the valves is always the first place I start. Even on mild street heads, I perform moderate valve unshrouding. Next, if the head is a square port head and will be used in a race only application I’ll widen the bowl to slow down the flow of air in this region. This allows the exhausting gasses to transition from the vertical plane out of the chamber to the horizontal plane on its way to the header with less chance of loosing the laminar air flow across the port floor. In dong this, the laminar air flow across the port floor will remain, (keeps the boundary layer intact), if this laminar flow separates from the port floor you will now have turbulence and this will restrict air flow considerably. (you may or not be able to catch this on a flow bench as a flow bench doesn’t measure the dynamic air flow in and out of the ports. I’ll expand on that at the end of this post). If the head has the round exhaust ports with the liners, all I do is blend the back of the valve seat into the liner. All of the heads I do, whether for street or full race, also receive a nice 5 angle valve seat, (sometimes only 4 angles can be performed do to space constraints), that I perform in house here at Rusch Motor Sports using Sunnen seat cutters, (I’ll be offering radius seats soon), and the valves are treated to a 30 degree back cut and the exhaust valves sometimes even get a nice little 45 degree chamfer on the chamber side of the head. All this extra valve and seat work mostly benefits air flow at low valve lifts, i.e. as the valves leave and return back to the seat itself.


Here is my personal take on the L-series heads.

E-31 and the early E-88 heads with the E-31 chambers are decent heads. They have the same potential as the other N-series heads when rules permit extensive carving. My opinion is the best place for the E-31 and the early E-88 is for a restoration project, or for a performance application where class rules dictate no material can be added to the chambers, no carving can be performed on the head and the update/backdate rules apply to the engine as an assembly, then these heads are a great choice. Now if you are not bound by those kinds of rules, you do have other choices available and being as the E-31 is becoming so rare now, these other heads are an easier option from a financial and availability stand point.

The N-42 head is a great maximum effort race head if class rules allow extensive carving and welding to the head. In this case, weld the chambers, open the exhaust ports as described above, perform some serious valve unshrouding and “waa laa”, you now have a wonderful maximum effort race head that would SUCK on a street engine. (Side note; If you intend on having your valves unshrouded and have not done this type of work before, you are best served leaving this to a qualified experienced engine builder, preferably one that has been successful in extracting noticeable to impressive documented performance gains. If you are not sure what you are doing, do not attempt to unshroud the valves yourself. In experience can hinder the flow worse than what the heads were stock.) Of course there is more to building/machining/porting a maximum effort cylinder heading than just welding a chamber and/or unshrouding valves. There are items such as setting spring heights, clearancing the retainers, stem seals, and guides for the mega lift cam, deciding on just how far to go with oversize valves even to the extreme of offsetting the valve guides to allow even BIGGER valves if the cylinder bore permits, etc.

The Z car N-47 head is a great street head. This head becomes almost ideal for the mild to hot street engine and even the mild to moderate race engine especially if the chambers can be welded up, (pretty much turns this head into the Maxima N-47 head which is a slightly more efficient chamber than the E-31). This “peanut” or “kidney” shaped chamber when used with flat top pistons or matching* dished pistons gives the ideal quench area which makes for a more efficient combustion process. To make use of this “kidney” shaped chamber on an L-28 running pump gas you will need matching* pistons. What I mean by “matching* pistons”, is a set of custom pistons from JE or other comparable source that has CnC the dish directly under the open portion of the “kidney” shaped chamber, not the entire surface area of the piston as is the OE 1975-1980 L-28 and all L-28-ET pistons. Any how, with this ideal squish, the engines optimum ignition advance will be less than the open chamber heads optimum ignition advance due to the more efficient chamber design. This happens because the flame front doesn’t have as far to travel to consume the entire air fuel mixture within cylinder, it now is in smaller area so the flame front doesn’t have to travel all the way to the other side of the cylinder during the ignition sequence. To better understand this concept, just visualize the open combustion chamber as being a flat wide circular disc, the diameter of the cylinder itself containing the air fuel mixture with the spark plug on one side, vs a small kidney shaped ball containing the same volume of air and fuel. Ideally a sphere shaped chamber with the spark plug in the dead center would be perfect, since that isn’t realistic, tuners just try and get as close to this ideal as possible. Some engines came for the factory much closer to this ideal, ala HEMI heads, etc. As for those round exhaust liners in the N-47 and P-79 heads, they actually flow VERY well. The liners offer a nice gentle radius as the air flow transitions from a vertical flow out of the chamber to the horizontal plane where it meets the header which keeps the air flow moving undisturbed even at high velocities where as the square ports with their really sharp short side radius doesn’t allow the air to make that transition with as much ease. What happens is the boundary layer of air along the port floor can and will separate causing the air to slam into the roof of the port and tumble along the floor of the port when the velocity gets high enough. This is not a good thing in the quest for power as this turbulence is very disruptive to air flow. This why we make that region of the port, the bowl, larger in an effort slow down the air flow to keep that laminar air flow across the port floor. Of course this only happens at very high velocities. Also, all L-series heads starting in 1977 have a slightly smaller intake port volume. What the engineers did was cast one side of the intake port wall with a “flat” in it, “D” shaped if you will. This reduction in cross sectional area starts approx ¾ of an inch into the port. This port shape is supposed to help bias the air flow as it enters the chamber more towards the middle of the combustion chamber itself, steering away from the chamber walls is passes the valve head. In theory this helps to reduce some of the air from slamming into the chamber walls of the combustion chamber. I don’t have enough hard evidence to back up this theory, but I do feel that this port bias does not detract from the performance potential of the cylinder head one bit.

Now we get to the P-79 and P-90 heads. The combustion chambers of these heads are IDEAL, almost perfect once the valves are unshrouded. The only down side I see to the P-series heads, (and this down side is for the extremely radical ragged edge engines, not so much for the milder even hot race engines), is since the chambers are taller, (valves are now shorter as a result), the floors of both the intake and exhaust ports now have an even sharper short side radius and as stated previously, this is a detriment to flow as velocity increases. The transition from the horizontal plane to the vertical plane on the intake and vice versa for the exhaust, is not as smooth as the N-series and E-series heads. Now don’t take this as I am bad mouthing the P-series heads cause I’m not. I really like these heads for hot street and mild to moderate race applications. They are an inexpensive way to get the ideal squish using an OE flat top piston with a compression ratio compatible with pump gas. I have built several and will continue to build the P-90 and P-79 heads for street and mild race Z’s. What I’m saying in regards to the P-series from the stand point of building THE mega extreme N/A performance power house that is at the ragged edge of making useable power over a very narrow yet very high RPM range such as a best of the best N/A drag racing engine, these items should not be overlooked.

Maxima N-47 head. What a darling mild race head this is. For mild to moderate race engines on a budget, using flat top pistons in an L-28, or even opting for pistons with a slight dome for greater than 13:1 compression, this is my go-to head. Just have your machine shop cut out the old intake seats and install the larger seats for the 1.73” or larger valves, have a competent Datsun engine builder/tuner unshroud the valves, blend the exhaust seat into the liner, and “waa laa”, a moderately high compression ratio race engine that will perform rather well up to 8000 RPM with the right cam, induction, and exhaust system. With a set of custom pistons machined so that the dish is directly under the open portion of that gorgeous peanut chamber, this head, in my opinion, makes for the perfect street head or mild race engine that runs pump gas. At the moderate level of race and above, I tend to prefer the N-42 with welded chambers and opened up exhaust ports.

Now for that flow bench info I promised earlier on…

Since a flow bench cannot duplicate the dynamics that are happening within the intake and exhaust tracts while the engine is actually running, i.e. sound pressure waves, pressure surges, exhaust heat, fuel enriched intake charge, valve overlap extraction, etc, flow bench numbers are nothing that should be used for comparing one head to another or bragging how good one thinks their head is! The best way to use flow bench numbers is using the SAME flow bench to compare ONE cylinder head for improvement after modifications have been performed, making note of any changes in air flow whether improvements were made or lost, nothing more. Flow benches do not represent what is actually going on within the intake tract OR the exhaust tract as mention previously, i.e. Dynamic air movement, pulses, waves, heat, etc!!!!. In real life, the valves are opening and closing causing the air to stop and move, stop and move, over and over and being as air has weight and is compressible, this constant surging will cause the pressures to rise and fall FAR above and below ambient. Depending on RPM, runner length, runner cross section, port shape, number of bends in the port and radius of those bends, valve shrouding, air density, cam timing in relation to the piston movement, (this has a HUGE effect on how the air gets moving within the intake and exhaust tracts, hence lopey idles, hard hitting powerbands, etc), there could be higher than ambient pressures at a particular RPM, i.e. a natural supercharging effect, that is why intake and exhaust runner lengths are TUNED! We have all seen where almost all Nascar engine builders have achieved over 110% volumetric efficiency on a naturally aspirated 2 valve engine by tuning the intake AND exhaust tracts to a specific RPM with specific runner cross section and runner lengths. This tuning is taking full advantage of the Helmholtz principle. Your basic garden variety flow benches do NOT and can NOT duplicate this, I’m not even sure if there is a flow bench made that can do this. The only real measure of how good a port can make HP, is to mount that head on an engine and run that engine on a Dyno, (and this is what we are REALLY after right, HP! Not just some arbitrary static flow number through a head port)! An example would be if one head that on one flow bench indicates it will outflow all the others tested, when all are attached to equivalent short blocks, the high flowing head could easily make LESS power on the dyno, but then again change the configuration a little with a different cam, intake tract, piston some shape, etc, the results would get even more confusing.

Ok, I think I’m finished now.


Inhale…… WHEW……..


Thank you all for allowing me to take up so much band width.


Paul (BRRAP) Ruschman

Rusch Motor Sports

Link to post
Share on other sites

holy hell batman, that was what i was pretty much looking for. someone who knows something about nissan heads. what it would take to get it to the zone im looking for.


as it sits, im running a 3.1 stroker, with a fully balanced bottom. put down a measly 192 rwhp in the summers heat. {measly coompared to my older 400+ awhp dsm's}


i have three heads at my disposal. early e88, late e88, and a N42. of these three heads, which would yield me the best all out nasty race prepped. 45mm+ triple carbed race engine. and what would the range of price be?. if say, i sent "braap} the head to do. because no one here in town has a clue about them anymore. i'll supply the valves, springs, seats, and cam, either a 560 lft, 300 dur. or a 620lft 304 dur. as you can tell, im not going to daily driver here.


i have been told by a couple people the early e88 would be best, and others the n42. im still researching things here and there. there is no class limit on what i want to do. the engine will probably be pulled this winter, and gone through, rings, bearings, stuff of that sort. im not looking to spin the motor to anything above 9 grand {diesel crank doesn't like this}

Link to post
Share on other sites



Don't ever apologise for the amount of useful information/opinions/effort you just gave us.

Keep it up,


PS, if you get a spare second (hehe) would you give us some information about a FI setup? I would assume everything is identical. Flow is flow, but some ancillary considerations come into account. Like a N42 head closed down might require dished pistons, which in turn might increase the necessary pin-height required. The context I am talking is no-expense spared turbo race engine. Everything custom (if necessary), including crank, rods, pistons, crank girdle, etc etc.





Link to post
Share on other sites



True, "rude" is subjective. I said you were because you gave me attitude after I said something that you already know. Well how am I supposed to know what you already know then? This is small stuff, it's not that important, just when I read your response, for a moment it felt like getting a rain of piss for trying to help.


A local guy(owns a bodyshop) here built his 240Z with all fiberglass exterior(hood, fenders, hatch, doors) except the roof. He was using triple Mikunis and runs 12.9. Car has centerforce clutch, and of course cam and engine works. The details of which I don't know. He only said he spent a lot of money on the engine & drivetrain. However the car still has regular glass on it and is still streetable. If you build a dedicated drag car with a stroker then there might be a chance.

Link to post
Share on other sites

  • Create New...