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First it will have a brand new gasket and freshly torqued down bolts. The Z24 HG failures sure isn't from the compression ratio (8.2 : 1) and most HG failures on other engines are not compression ratio related but extreme compression ratios and engine mods, big cams and more carburetors.... and over heating. The Z24 over time and 100k tends to loose it's clamping force on the gasket and why re-torquing the head bolts once a year is recommended to prevent this.

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On 3/27/2021 at 2:41 PM, datzenmike said:

A guy named Patric Smith in Vegas has a Z24 with Z20/22E intake and KA sensors ECU injectors etc.

 

Temperature sensors....

Z20E and Z22E are 22630-P8100

 

S13 KA24E is 22630-N4200

S13/14 KA24DE is 22630-51E00

 

On 3/28/2021 at 3:58 AM, KELMO said:

Patrick Smith is usually at the Williams show and usually brings a 720....or 2.

I have met Patrick Smith in Williams and have also oogled his 720 Z24 with Z20/22E intake and KA sensors ECU injectors etc.

 

I had forgotten about this truck.

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  • 1 year later...

Leave it to Mike at Ratsun to have answers to my question. I swapped heads on my z24 and noticed a drop in compression . I thought the previous head had high compression -180psi tested- because of some 10 over pistons and a surface done on the head . Maybe I had the smaller chamber head ! Damn the luck I put a cam in a head with lower compression this time around . I still have the head sitting in a box for sale , I guess I will bust it open and find out for sure . I had no idea there were differences in the Z24 heads 

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As near as I can tell there are no differences between all Z24 heads. They were only used on the 720 truck and identified by the squarish with rounded corner intake ports while the Z20 and Z22 are round with EFI notches in the tops. All Z20S and Z20E, and all Z22S and Z22E (S=carburetor and E= EFI) had the same combustion chamber size. I've measured two of each and all were 57cc.

 

Only the W04 head used on the '83.5-'86 720 Mileage option trucks with the Z20S engine had smaller combustion chambers. I haven't measured one of those but by assuming a comparable compression of 8.5 and reverse engineering it comes out close to 45cc. If this head were put on a larger displacement Z24 the compression ratio would be almost 9.5 to one.

 

 

 

If compression dropped after a head change, then possibly it needed a good valve job.

 

 

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  • 5 months later...
On 3/25/2021 at 3:01 PM, datzenmike said:

Not convinced that the W04 exhaust ports are smaller. Measure them.

 

My bad. I assumed the W04 being a Z20 would have the smaller round intakes.

 

Thank you so much for the pictures.

Mike, I just stumbled on this. It's in an old thread but relevant to anyone working on a NAPS-Z engine/cyl head today.

 

I am converting from Z24i 10W (TBI) head to W04 head from Z20S carbed and MPG option from an '84 720. You were right with your intuitive comment about assuming that the Z20 would have the smaller, round intake ports. The W04 head that I pulled at the JY has the round ports with e.f.i. notches in the head (but round, non-injector ports on its carbureted intake manifold). I am shooting for 9.5:1 c.r. end result and counting on the NAPS-Z chamber design for efficient and complete burn to minimize need for spark advance and risk of ping.

 

This particular project I am working on is an '86.5 D21 4x4 that I bought not long ago in poor running condition with many issues. The oil was clean and clear; the coolant had a floating tan milky, mucky organic layer. I pulled the head and there had been oil under pressure being pushed into coolant (at 30 psi oil pressure vs 13 psi coolant pressure) at the head gasket interface where the copper oval insert locates in the HG (seals oil galley route from block to head for valvetrain). There are a lot of other issues with the engine but nothing huge (cracked exhaust manifold, etc.). Retrieving the organic layer from the aqueous throughout the entire cooling system was a pita.

 

Onward. Note this is not related to several Z/L hybrid projects I have done or have in the works. Discussion of the L series head do not apply and will confuse discussion. Here I'm referring to stock Z24i short block and use of a NAPS-Z head. My goal is high efficiency, low emissions, with useful lower rpm power. The function is not a high performance engine for off-roading or racing but one for driveability/utility as well as decent emission control; plus just see what I can do with some ideas.

 

A good look at the ZAPS-Z technology is: https://www.jstor.org/stable/44631647. I am going to incorporate vortex generators of the original design (see jstor and pics).

North American engines may not have used these. Don't know. Note that these were not used with multiport e.f.i. Z20E or Z22E because they would interfere with the injector  placements. Instead, I converting a Z24i TBI intake to round ports {thank you Stoffregen Motorsports for the epoxy idea, see pics.} and I am using the vortex vaned-gaskets (see pics) but with TBI and intake rather than a carb. It's curious that the W04 head has a fuel pump block-off plate but is carb'd, it must use an electric fuel pump instead of mechanical. Compare the pics of carb'd intake manifold Z20 (MPG option) to the Z24i TBI intake. MPI precludes using the vortex generators, but the upstream TBI shouldn't. I want the c.r. increase that the smaller chamber W04 head will give and will run premium gas, colder plugs, and tune the mixture by wide-band. 

 

I plan to use the OEM Z24i optical signaled distributor repurposed as my crank angle sensor to trigger two separate wasted-spark systems, one for each plug of the dual plug combustion chambers. I'm going to set them up as simultaneous fire with each of the two wasted sparks per cyl fire to the same wasted-fired cyl. This means that I'll use twice the number of coils (four) than the usual two that a 4 cyl wasted-spark single plug per cyl engine needs. Each spark plug of the two per cyl has a simultaneous but independent circuited generation of spark. I'll use dual-platinum plugs in conjunction with the wasted spark ignition. There won't be the retard-effect coil/plug separation as the OEM system uses or any sort of overlap spark timing, but instead two separate fixed but simultaneous systems (like typical aircraft recip engine redundancy). Optimal flame travel and complete burn with minimal spark advance is my objective in this approach. 

 

I'm going to reassemble the Z24i with the W04 head, the modified Z24i intake as round port with vortex generators, using the stock TBI and stock dual plug ecu setup first. I'll run it after checking cranking cyl pressure, establish the baseline running condition, check mixture with wide band, make sure no coolant leaks or issues and then test drive it and proceed from that point.

 

I have a Speeduino unit to do this conversion with: https://speeduino.com/home/  It can use optical trigger, can work with TBI dual injector, and can do wasted-spark. I especially like the revolutionary open source aspect of Speeduino. I have some camshaft position sensor designs for mounting signal generator to front of camshaft chain sprocket and pick-up mounting location from the open side of head.

 

In the pics you can see that I've indexed the plugs in the W04 head as I want them to be. Due to the order of the int and exh valves in the Z-engine cylinder head the vortex generators have opposite spins as needed to direct vortex through intake valve toward the most open, deepest part of the chamber in each case. Obviously they hinder flow some but this engine is not intended for high rpm.

 

Once I get this squared away as above I may mount the two TBI injectors on the intake manifold about where the manifold vacuum signal/fitting are now located, just before the 'Y's'. I'll source vacuum for fittings from somewhere else on the manifold (see pics of W89). There must be good negative steady pressure at those two points which is why they would put vacuum signals symmetrically in those locations. I would first leave the stock TBI throttle valve in place but experiment with relocating the two injectors downstream at runner junctions.

 

That also would let me then remove the stock throttle body to adapt the VW-sourced mechanically progressive (see pics) throttle body with its small throttle plate (low speed) and large secondary plate (high speed) throttle body (see pics). Note the restrictor lump/wedge attached to only the leading edge of 1/2 of one side of the primary plate to enhance progressive flow and transition. As the primary plate opens it progressively moves this obstruction out of the airflow. I assume this dual function feature of the primary plate/bore optimizes transition over to the big secondary plate/throttle bore opening event. See sequence of pics of that.

 

I might consider incorporating a low pressure twin-scroll turbo later if na results are good. I have one from a Mini that I would attempt to adapt. The turbine spindle axis will need to be at an angle to the vehicle axis...so??... It makes no difference. Also, not important right now. One thing at a time and proceed. 

TBC.

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I look forward to your build. I have very similar goals with my Z24 build, but opted to pursue MPFI to increase efficiency. Basically, I am building a KA24T the hard way. I like the concept of Speedunio, but I do not believe it handles MPFI. 

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On 4/6/2023 at 6:26 PM, frankendat said:

I look forward to your build. I have very similar goals with my Z24 build, but opted to pursue MPFI to increase efficiency. Basically, I am building a KA24T the hard way. I like the concept of Speedunio, but I do not believe it handles MPFI. 

Hi, yes Speeduino can do mpfi. If I had a 200SX mpfi set-up I'd be working with that in combo with the Z20 W04 head on the stock Z24 short-block. But I don't have one of those intakes presently. I'll set it up with TBI for now since I have that whole W21 system already.

 

It is likely that the W04 head on the Z24 short-block might make for a higher c.r. than I want according to number crunching. I've decided to take an empirical approach by assembling with an inexpensive Fel Pro HG but using a 0.020" (.5 mm) copper HG shim initially. If I want to bump the c.r. up, I will remove the shim. That's easy. You can just block the timing chain, remove the cam sprocket, lift up the head/int manif/ exh manifold as a unit and service the HG. Much faster than r&r manifolds from the head just to remove the HG shim. You can use an engine hoist to lift the unit/assembly up enough and ease it back down the same way. I have done it without the hoist on both 4 and 6 cyl inline OHC engines but it is hard on the L/S spine that way.

 

I'm assuming that whatever configuration I can make work with TBI, when I do convert to mpfi with the more uniform and precise fuel distribution it will also tolerate an increase in c.r.  I'd rather start with the lower c.r. and easy means to lower it than to go too high and have to face those issues.

 

 

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3 hours ago, RetroRocket said:

Hi, yes Speeduino can do mpfi. If I had a 200SX mpfi set-up I'd be working with that in combo with the Z20 W04 head on the stock Z24 short-block. But I don't have one of those intakes presently. I'll set it up with TBI for now since I have that whole W21 system already.

 

It is likely that the W04 head on the Z24 short-block might make for a higher c.r. than I want according to number crunching. I've decided to take an empirical approach by assembling with an inexpensive Fel Pro HG but using a 0.020" (.5 mm) copper HG shim initially. If I want to bump the c.r. up, I will remove the shim. That's easy. You can just block the timing chain, remove the cam sprocket, lift up the head/int manif/ exh manifold as a unit and service the HG. Much faster than r&r manifolds from the head just to remove the HG shim. You can use an engine hoist to lift the unit/assembly up enough and ease it back down the same way. I have done it without the hoist on both 4 and 6 cyl inline OHC engines but it is hard on the L/S spine that way.

 

I'm assuming that whatever configuration I can make work with TBI, when I do convert to mpfi with the more uniform and precise fuel distribution it will also tolerate an increase in c.r.  I'd rather start with the lower c.r. and easy means to lower it than to go too high and have to face those issues.

 

 

I have parts from 200SX MPFI setup, if you are looking to take that path. You are correct the Speedunio will do MPFI, I was confusing sequential ignition and individual cylinder fuel metering. The gentlemen at SpeedyEFI are great to work with on injection.

 

It is my belief that the farther any system is pushed from factory parameters the more unreliable. It is my belief that higher revving engines lack the longevity of lower revving engines and longevity is a key component of reliability. I understand there exists an abundance of anecdotal evidence regarding these beliefs pro/con.

 

 A stock Z24 pushes 103hp @ 4800rpm and pulls 137 ft. lbs.@ 2800rpm.The increase in HP and Torque, which will result from increased cylinder bore (+1mm) and increased cylinder compression between 9.5 and 10, will supply all the engine power/torque performance I require and without my new found interest in electronics, would have been the end of it.

 A stock KA24E pushes 140hp @ 5,600rpm and pulls 152 ft. lbs.@ 4,400rpm. The KA24E is MPFI, 9.1 compression. My take away from this information is twofold.

Reliability. The stronger bottom end of the Z24 will handle compression in to 10 without problem.

Efficiency. Only as it relates to MPG. To achieve greater power more fuel is required. A KA24E 3 valve head makes more horsepower at higher RPM because (in part) it uses more fuel. The 2 valve Z24 head, creates less horsepower at lower RPM because it uses less fuel. Adding air can substitute for fuel, but too  lean creates a BOMB .

Low rpm/low boost, increases efficiency.(again mindful of bomb) Some late model Audi's incorporated an air compressor and accumulator to supply boost at low rpm, I have yet to find one of these units at a salvage yard, but it is good to know the idea has been proven. I like "tractor motors" i.e. big piston high compression engines that generate torque at low rpm. Lower rpm with fuel air efficiency maximized, on paper, conservatively, will yield mpg in the high 20's to low 30’s.

There are so many factors that contribute to mpg, my numbers will not be real until all is done.

 

I took some time CCing my head and trying to determine the exact amount of fuel/air (standard or forced)that creates the most efficient cycle. Such information must be available, but I soon found myself lost in information that exceeded my understanding. I doubt that I am near the limit of energy in gasoline, but there is a limit and limits to the efficiency of mechanical devices. Whenever, possible I ceramic coat engine and drivetrain components to lower heat and friction, but again limits.

Air resistance is an area that I have no plans to address and old Nissan trucks are rolling bricks.

As mentioned there are so many variables to mpg it is impossible to accurately forecast.  I am trying to enjoy the journey.

 How does this relate to your build?

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Hi, I would not be choosing a Z24i to be my engine of choice, I'm just working with what is in my D21, the short-block. I'll live with the limitations of a NAPS-Z engine for this.

In the past I've just gotten NAPS-Z bottom end stuff to build L-head/Z22 based 4cyl versions and left the cyl head of the Z engines behind in the JY rather than pay for the head.

There were some interesting engineering innovations explored by Nissan during the development of the NAPS-Z engine in the 1980's. I'm starting from stock baseline Z24i, incorporate the good features, expand on and retrofit newer ignition/fuel mgmt technology. I'll purge compromises that I can mitigate, and see what I can end up with.

I'm sure I can learn something during the course of the process. 

 

I am not all that keen on having a 96 mm stroke inline 4 cyl in the first place. I am not going to be doing any heavy hauling, towing, etc., with this little short wheelbase pick up. I already have Ford pick ups for that. This will be a little run-around 4x4 that can negotiate hills and some snow with good low-end torque and get decent mpg doing it.

 

Note: I try to keep my projects distinctly separate but with the L-series/Z-series overlap of dimensions it can be challenging. I am also conjuring up a hybrid L-peanut head/Z24 block + 0.080 overbore/ 91 mm Toyota 4YEC pistons. That is a completely different engine project in development and details of that are in other threads; not this Z24 NAPS-Z head project thread. My L-head engine projects, in 4 and 6 cyl versions, are numerous over the years. Some are described in other threads, some are waiting in the wings. What I do is hobby or 'art' for my enjoyment. I see potential sometimes where others consider only what has already been done as their options. It's the process of taking a different perspective and then developing an idea from that perspective. I think we waste far too much in the US in general. Case in point: all of the discarded NAPS-Z cyl heads laying around.

 

Who knows something about an inline nissan 6cyl NAPS-Z engine? It was not a North American-use engine afaik bit I have seen pics or drawings.

One of my sons is active duty in Japan. EOD. Due to covid-19 restrictions I've had to cancel several planned trips over there. I'd be getting together a JDM shopping list for him but he stays too busy (did you know that some of the deepest powder in the world falls on Japan?  he certainly does).

Cheers.

TBC.

 

Quote: "if you love what you're doing when you're wasting time; you're not wasting time."

 

 

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7 hours ago, RetroRocket said:

Hi, I would not be choosing a Z24i to be my engine of choice, I'm just working with what is in my D21, the short-block. I'll live with the limitations of a NAPS-Z engine for this.

In the past I've just gotten NAPS-Z bottom end stuff to build L-head/Z22 based 4cyl versions and left the cyl head of the Z engines behind in the JY rather than pay for the head.

There were some interesting engineering innovations explored by Nissan during the development of the NAPS-Z engine in the 1980's. I'm starting from stock baseline Z24i, incorporate the good features, expand on and retrofit newer ignition/fuel mgmt technology. I'll purge compromises that I can mitigate, and see what I can end up with.

I'm sure I can learn something during the course of the process. 

 

I am not all that keen on having a 96 mm stroke inline 4 cyl in the first place. I am not going to be doing any heavy hauling, towing, etc., with this little short wheelbase pick up. I already have Ford pick ups for that. This will be a little run-around 4x4 that can negotiate hills and some snow with good low-end torque and get decent mpg doing it.

 

Note: I try to keep my projects distinctly separate but with the L-series/Z-series overlap of dimensions it can be challenging. I am also conjuring up a hybrid L-peanut head/Z24 block + 0.080 overbore/ 91 mm Toyota 4YEC pistons. That is a completely different engine project in development and details of that are in other threads; not this Z24 NAPS-Z head project thread. My L-head engine projects, in 4 and 6 cyl versions, are numerous over the years. Some are described in other threads, some are waiting in the wings. What I do is hobby or 'art' for my enjoyment. I see potential sometimes where others consider only what has already been done as their options. It's the process of taking a different perspective and then developing an idea from that perspective. I think we waste far too much in the US in general. Case in point: all of the discarded NAPS-Z cyl heads laying around.

 

Who knows something about an inline nissan 6cyl NAPS-Z engine? It was not a North American-use engine afaik bit I have seen pics or drawings.

One of my sons is active duty in Japan. EOD. Due to covid-19 restrictions I've had to cancel several planned trips over there. I'd be getting together a JDM shopping list for him but he stays too busy (did you know that some of the deepest powder in the world falls on Japan?  he certainly does).

Cheers.

TBC.

 

Quote: "if you love what you're doing when you're wasting time; you're not wasting time."

 

 

Your son's in Explosive Ordinance Disposal? The Japanese won me over, when I worked with a group of exchange students, they overflowed with integrity.

But back to building, it almost sounds like your bad mouthing the old Z24. The Z24 is designed very well for what it was intended to do and that long stroke aides in creating great torque. The Z24 traded some performance for lower emissions and I just want to trade it back and benefit from the precision of engineering achieved in later decades. But, it will always be a tractor motor. If your bummed about performance, a KA24E rebuild would be very similar in terms of time and money. KA24ET engines have been modified to 1000hp (according to ka-t.org) It sounds like you're singing "If you can't be with the one you love, love the one your with.." when the "one you love" is available.

Quote: When I think about all the good times that I've wasted having good times.-The Animals

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On 4/6/2023 at 3:27 PM, RetroRocket said:

I plan to use the OEM Z24i optical signaled distributor repurposed as my crank angle sensor to trigger two separate wasted-spark systems, one for each plug of the dual plug combustion chambers. I'm going to set them up as simultaneous fire with each of the two wasted sparks per cyl fire to the same wasted-fired cyl. This means that I'll use twice the number of coils (four) than the usual two that a 4 cyl wasted-spark single plug per cyl engine needs. Each spark plug of the two per cyl has a simultaneous but independent circuited generation of spark. I'll use dual-platinum plugs in conjunction with the wasted spark ignition. There won't be the retard-effect coil/plug separation as the OEM system uses or any sort of overlap spark timing, but instead two separate fixed but simultaneous systems (like typical aircraft recip engine redundancy). Optimal flame travel and complete burn with minimal spark advance is my objective in this approach. 

The above bit grabbed my attention. There was a paper published on Z24 ignition advance. I will locate it and attach.

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8 hours ago, frankendat said:

Wow- lots to digest if you understand all that - lol. Currently I’m playing with valve timing on my motor . Currently running my Mikuni cam 6 degrees advanced . I am running 33 degrees of ignition advance . The Z head has no quench area to speak of , so timing advance will be limited for sure .

I started with a cylinder pressure of 150ish and with 6 degrees of advance in valve timing netted 170ish pressures . Fortunately I have full engine management control so I can change a lot of parameters . You can only get so much out of a turd though - lol. 
I only have a butt dyno to go by , not sure if I would pay to do a true dyno tuning . 

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18 minutes ago, Madkaw said:


I only have a butt dyno to go by , not sure if I would pay to do a true dyno tuning . 

When you're done the dyno is a nice place to see if the numbers match your butt....

Near me I have a dyno I can go to, they do the driving but I had to do any changes or tuning and it was fairly cheap.... I think I paid around 200 and I was there for a little while....

Because I picked a non busy week day they were pretty accommodating....

Friday's and weekends are real busy for them....

Another way is to see if they have a dyno day.... sometimes clubs will do that... or the shop will just have an event... you get 3 pulls usually for cheap with a bbq.....

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27 minutes ago, Crashtd420 said:

When you're done the dyno is a nice place to see if the numbers match your butt....

Near me I have a dyno I can go to, they do the driving but I had to do any changes or tuning and it was fairly cheap.... I think I paid around 200 and I was there for a little while....

Because I picked a non busy week day they were pretty accommodating....

Friday's and weekends are real busy for them....

Another way is to see if they have a dyno day.... sometimes clubs will do that... or the shop will just have an event... you get 3 pulls usually for cheap with a bbq.....

I have a 240z that spends my dyno budget . It is cool to watch the curves move with the change of valve timing . With the Kameari sprocket it’s about 15 minutes or less to change valve timing - so it’s doable if the dyno guy is okay with cracking open the valve cover . 
I’ve found the calculator based on quarter mile and weight is pretty accurate on my Z - but the 720 doing a quarter mile would require a calendar -lol.

Mayne when I mount a turbo I would venture to do a dyno . 

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One good method for checking on "performance gain" on a 720 without breaking any laws on the street.

1. Find a flat road or if you don't have any use the same section of road.

2. Pick like third gear and stay in it. That eliminates any variation with shifting.

3. Start holding say like 25 mph. Stomp on it and start timing. Stop timing at 55. There is plenty of time there to see if you repeat this process after engine mods whether there is a performance gain.

     You don't get hp numbers but more accurate than the butt dyno and only costs time and gas.

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1 hour ago, bottomwatcher said:

One good method for checking on "performance gain" on a 720 without breaking any laws on the street.

1. Find a flat road or if you don't have any use the same section of road.

2. Pick like third gear and stay in it. That eliminates any variation with shifting.

3. Start holding say like 25 mph. Stomp on it and start timing. Stop timing at 55. There is plenty of time there to see if you repeat this process after engine mods whether there is a performance gain.

     You don't get hp numbers but more accurate than the butt dyno and only costs time and gas.

Yes- that was my plan . I’d rather do 4th one to one ratio- but a passing gear would be 3rd for sure and that’s where you want it most for passing . 
Did I just think passing and 720 in the same sentence ? LOL

 

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2 hours ago, Madkaw said:

Yes- that was my plan . I’d rather do 4th one to one ratio- but a passing gear would be 3rd for sure and that’s where you want it most for passing . 
Did I just think passing and 720 in the same sentence ? LOL

 

There are tricks for passing. One step is to turn off AC. That gains noticable hp. 

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Vortex generators? They will help at idle and low speed but at high speed they just inhibit flow. The engine wasted power pulling harder to suck ait past them. They are in effect a restriction to flow. The KA24E and KA24DE have swirl generators spring loaded against a vacuum actuator. High intake vacuum closes the vanes when flow speed is low and it's harder to atomize the injector spray. As speed and load increase the vacuum drops and the vanes open for maximum flow.

 

 

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15 hours ago, datzenmike said:

Vortex generators? They will help at idle and low speed but at high speed they just inhibit flow. The engine wasted power pulling harder to suck ait past them. They are in effect a restriction to flow. The KA24E and KA24DE have swirl generators spring loaded against a vacuum actuator. High intake vacuum closes the vanes when flow speed is low and it's harder to atomize the injector spray. As speed and load increase the vacuum drops and the vanes open for maximum flow.

 

 

I'll drive the engine with; and then without, the vortex generators and see what drivability changes there are. I expect restriction to high flow but if it otherwise runs best at lower flows and gets better mpg then maybe I'll consider a low-pressure turbo to help force air through the restriction. I'd never even seen them before except in that jstor paper. But then I stumbled upon a NOS set for cheap by Beck Arnley. They will not work with mpfi due to how they locate/interfere. I'll see what effect they have. Easy to remove/eliminate. The swirl generators on the KA24 seem to function a bit differently. They vary the velocity of intake air and thereby increase the pressure and speed of airflow while max flow is not being called for because rpm is low. Flow restriction isn't much of a factor if the engine is in a low flow operating speed. At lower rpm there is less overall flow so the restriction matters less or not at all. Increasing airstream velocity at lower speeds enhances fuel atomization, distribution, and therefore low engine speed tunability and emission control. Above a predetermined rpm the plates move out of the airstream to allow more flow capacity before the plates become a choke. This function isn't unlike the Offenhauser dual-port carb'd intake manifold design that used bisected runners cast in to isolate low flow/higher velocity air characteristics from the high flow considerations. The primary barrel was apportioned to about 40% of runner's area/volume and the larger secondary to the other 60%. This enhanced low speed throttle responsiveness, better fuel atomization and helped mpg around town. The secondary barrel opening also became less of a lean sag event and a smoother transition to wot. I've used these street-friendly manifolds quiet a bit in conjunction with wide-band idle jet, main jet, and air corrector jets on L-engines and toyota R-engines. They aren't a road race application because the partitioning along the full lengths of manifold runners is a fixed restriction that becomes a choke to maximum flow potential at high rpm, just like the NAPS-Z designed inserts will. Making such a compromise for the sake of drivability for a street-utility engine may be worth the trade-off. Winter or all-weather tires go with this set up. Racing slicks go with twin DCOE's, big cams, and high rpm.

 

On 4/10/2023 at 7:58 PM, frankendat said:

Thanks for the article. There has been a lot of discussion about the crossflow NAPS-Z head characteristics and flame-front progression re the initial spark timing needing to be minimal and still having an effective 17* optimal power placement advance due to enhanced flame travel (i think i have this right?). datzunmike has discussed this aspect before as I recall. The MPG option 720 Z20S had a spark-knock retard feature for the ignition circuit as it was 9.3:1 c.r. whereas the Z20 engines in the other vehicles were 8.5:1. The feature was probably more of a protection if too-low an octane fuel is used to guard against pinging and engine damage, rather than any finesse of tuning. The Speeduino accepts knock sensor input iirc, so I'll incorporate it. 

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All sounds good on paper... like a lot of tuner stuff. The Z series had dual plugs so a lot of this won't apply to single plug engines. Dual plugs have (obviously) two ignition points so the mixture is consumed faster so less ignition advance is needed to reach peak cylinder pressures at that sweet spot at around 17 degrees after TDC where the rod and piston can efficiently capture and make use of the downward pressure. Earlier and the crankshaft/rod/piston are too vertical and too late and the piston is accelerating away too fast. The point of the NAPS system is less burning time getting there so less time for oxides of nitrogen to form. (BTW the CA engine is also a NAPS with dual plugs) 

 

At higher speeds but light cruise throttle, the turbo will recapture some of the lost exhaust energy and help push the air into the combustion chamber at higher speeds. This saves the engine some pumping losses and increases efficiency but isn't needed at lower and mid range where restriction isn't a problem. At heavy throttle it will just add hp. I guess a small turbo that starts boosting ASAP would be best and set for a few pounds like you mentioned but these run out of beans at high RPMs so not that great at high boost.

 

The dual plane Offy intake does have higher primary air speeds but this is mitigated by the air suddenly entering the huge intake port where it slams on the brakes and slows down. I would think the divider in the intake is taking up space that could be used for more flow. Again it seems sensible on paper.

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The vortex generators pictured are specific to the round port NAPS-Z head with carb. They aren't intended for max hp or rpm benefit. That wouldn't be a goal for a NAPS-Z head engine anyway. If you take a close look at the pics you can see that they are initiating a twisting of the air column that passes through. Take your index finger, imagine pointing it toward the vanes at the port entrance and rotate in a circular motion in the direction it would be made to rotate if it were a column of air. Pretend your finger is the column of air and note which direction (clockwise, or ccw) the vane will make the air rotate as it routes past the open intake valve and enters the chamber. While still making that rotation direction imitating it with your finger see how that direction carries right through the intake and out the closing exhaust valve at overlap due to the chamber shape. The rotation direction of the air/fuel column is specific to each cylinder's placement of intake and exhaust valve layout. It's not just a random air-twister. But there is a window of operation range where it works best, at lower engine speeds. 

 

Fill a bathroom sink 1/2 full of water and then open fully the drain and note the rate of draining of the water volume. While the water is draining put your index finger into the water and give it a couple of rotations around the basin and observe how the outflow rate increase. The vortex enhances flow through the inlet/outlet (the open drain). 

 

There have been 'vortex-generator' add-on aftermarket gimmicks sold forever. These try to lay claim to a general principle but don't work enough to make any appreciable difference at the intake ports. By the time the air column reaches the intake valve it is unlikely to have any meaningful rotation and if it did, it could be in the wrong direction for some cylinders and actually hinder flow. That's just snake oil, but these specifically-placed and oriented vanes create a localized effect through the chamber. I wonder if addition of a stainless steel exhaust port vortex generator used in concert would enhance or hinder the function of intake charge vortex such that during overlap both the  emptying and filling are sped up by the uniform rotation of what becomes a single moving column, even if briefly. Properly paired/joined exhaust tubing by ignition intervals (i.e., 1 and 4, 2 and 3 as a tri-Y design) after exiting each cylinder would enhance the potential for exhaust extraction. If that isn't done then there's no point in trying to vortex exit flow because it would immediately be disrupted and stalled if encountering exhaust pressure if it were not 180* synchronized by ignition interval..

 

I wonder if the vanes of an intake port vortex generator could be constructed so that they would 'flatten' and yield to the increased pressure and flow at higher rpm and create a lower drag and resistance automatically. Like a 'flex-fan' blade flattening its pitch at speed when its work is no longer needed (due to vehicle speed pushing air through the radiator) and a clutchless rigid fan blade just becomes an impediment to flow and efficiency.

 

As an aside, there are also gimmick devices to pre-vortex airflow into a turbo compressor wheel to initiate air rotation in the same direction of twisting as the compressor spins it. It sounds plausible, but it turns out that if the air is 'blunt' and undisturbed when the compressor wheel blades see it there is a better 'bite' taken on that air than rotating air at mismatched speed, which can cause cavitation. The turbo is most effective if there is a straight steady column of air feeding the compressor.

TBC

 

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7 hours ago, datzenmike said:

All sounds good on paper... like a lot of tuner stuff.

 

 

Actually the water draining from the sink is faster when not spinning. Fastest flow in in the center with a boundary layer along the walls. Spinning it turns multiple times on the way out so has to travel further thus slower. 

 

Buy NISSAN Z24 ENGINE AIR INLET INTAKE MANIFOLD FROM 1987 NISSAN NAVARA D21  4X4 in Inglewood, VIC, Australia, for AU $49.95

 

90 from vertical to horizontal, then another 90 towards the head, then a 45? into a radius. Lots of room for improvement here.

 

Number one cylinder is far left  with intake on left and exhaust to the right so the open most part of the cylinder is to the right. Because of the radius intake bend the air will be crowding the left side of the intake port and traveling fastest there. In the head port there is a downward bend of? what less than 45?? just before the intake valve, and again the flow will crowd the top of the port and be reluctant to turn the sharp radius bend on the bottom. Because of the top flow at the bend the air will want to pass the valve stem slightly more on the left perhaps but definitely enter the cylinder almost in the center and farthest from the cylinder walls. Pretty much directly in line with the exhaust valve. As Visard says: let the flow go where it wants to go, and then improve on it there.

 

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