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JelmerPatrol

Low down torque==>long intake and small valves?

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I have been searching a lot but everyone want maximum horse power from their L series because a Z is a sportscar.

I have a Patrol which is powered by a L28 with a single carb. It is ok powerwise but I need more torque.

 

The Patrol L28 is a F54 with dished pistons and N42 head.

 

No I made a plan to have some more torque and EFI and these parts I already have:

 

  • Flat top pistons (OE) Nissan)
  • Megasquirt
  • 3-2-1 header
  • LD28 intake manifold

I plan on using a higher compression so I was thinking a E31 head would be suitable because they have smaller valves which should be better for low down torque.

The long runner diesel intake should too (after a EFI flange with injector bungs and a flange for a throttle body is welded on)

 

Am I thinking right?

 

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Interesting!

 

- There is always the stroker option, but that is maybe a bit pricey?

 

- I am curious if there is any camshaft options that could help, I don't see how same duration but higher lift could ruin your low end torque.

 

- Are you sure you have dished pistons? F54 did come with flat right?

 

Curious to hear what the other more knowledgeable people thinks.

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How often are you driving at wide open throttle? I think cam choice would be most critical. High compression helps too. The best torque mutiplier your vehicle has is the transmission and gears in the diffs. Most 4x4 guys kill thier torque with big tires without changing the gearing to compensate. If you input torque on the drive shaft is 200lbft and the ratio is 3:1 the the output is 600 lbft. If 4:1 then its 800 etc.

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I changed to shorter gears and with most driving it is ok but sometimes you just need some more "oomppf" to get thru a mud hole or up a steep hill. And this is where the little L28 has not enough torque. It can't pull it in second gear low range. So if I had about 20% more it would do it already.

 

I'm sure the engine is a F54/N42 with dished pistons, this is how all Patrols came. They are made up to '88 like that.

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Forgot about the larger diameter! I did say smal valves because a E31 and E88 have smaller valves.

 

I also have a JDM spec L28 from a Laurel or Cedric and this engine has a twin butterfly throttlebody. I think this is a good intak to use than.

 

29087232623_857f2a2024_b.jpg

29711839125_0cfb626145_b.jpg

 

Now I have to find a camshaft grind with more lift but not more duration.

I emailed Delta camshaft but they don't respond so maybe I should try Isky?

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Personally, I would not go with a Comp Cams. Their baseline cams are all 110 degrees Lobe Separation Centers for just about every engine type they grind. 110 degrees is not ideal for most engines. Shorter Lobe Separation Angles build more bottom end Torque. I would recommend a Custom grind from someone like Isky, Colt Cams ( PNW grinder )  or Sunbelt. Talk to them and tell them what you are doing. I wouldn't be surprised if they recommend a 108 to 106 degrees Lobe separation Angle.  Go with as much lift as you can get, up to about .465". The extra lift will not hurt Torque at all. Lower end RPM range is important. If you can maintain 2,000 rpm ( that's not very high ) you may find more Torque by going to a 260 degree cam with a tighter Lobe Separation angle. . It's all about efficiency and matching components. I'd see what Isky says.

 

I believe that the changes you are making to the engine will net you a LOT more torque gain than 20% you require. Biggest changes are higher compression and EFI. F54 with Flat Tops and an N42 head are going to give you around 10.3 to 1 CR. Lack of quench with the N42 head is not so much of a problem with what you are doing, as the well known detonation issue happens at Peak torque and higher RPM's. Typically 3,500 to 5.000 RPM's. 

 

The Patrol engine with it's low compression ratio, single carburator and mild camshaft can be improved a lot. Don't forget, these vehicles are designed to be used in countries that may have VERY low quality fuel and minimal parts supply and service capability. . Thus they leave a lot of power on the table.

 

I wouldn't bother with the Diesel manifold. IMHO the Diesel manifold could be detrimental to engine efficiency with your plans. Use a regular L28 EFI manifold ( no Turbo ) . EFI multipoint injector systems are not as sensitive to runner Volume as Carburated engines because the manifold is dry. The gasoline L28 runners are more than long enough and small enough to generate extremely good Torque. Especially, with more compression and some timing tweaks. Use a stock 55mm TB. Larger TB don't help Low rpm engines.

 

Regarding Ignition Timing. The Megasquirt is really going to help in engine drive-ability because you can control the ignition timing much more accurately and use an asymmetrical curve.  Ignition timing is the big secret to building Torque and Power. Smart Turbo car tuners know the secret is not running as much boost as possible, but rather, running as much ignition timing as possible... without encountering detonation. Modern EFI cars all run on the ragged edge of detonation. That's how you get efficiency, power and mileage. Early EFI systems without knock sensors and Wide band O2 sensors did not allow the accuracy to maximize Ignition timing... so manufactures always had to be a bit conservative.

 

Using the Megasquirt I would defiantly run knock sensors. Set static timing to 15 degrees BTDC at idle, then quickly ramp up to 32 BTDC  by 2,500 rpm and 34 by 3,000 RPM, then you may want to taper it off to 30 - 32 degrees  between 3,500, and 5,000 rpm.( This is the detonation prone RPM range with the N42/N47 head design ).  You will need at least 98 RON with a 10 to 1 + CR combo.. if you don't want to run Premium fuel then consider your engine build and maybe stay with dished pistons and juggle CR to get around 9.0 to 1. ( Or just program in a bit less timing with the Megasquirt ).  But with good fuel and the Megasquirt, the N42/Flat Top combo can be made to run quite happily and reliably IMHO. 

 

Don't forget your AFR's. You can cool the engine and reduce chance of detonation by running a bit on the Rich side. On a 4x4 or Mud puller build to RBT ( Rich Best Torque ) instead of LBP ( Lean best Power ).  Definitely run a WB O2 sensor.

Edited by Chickenman

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Actually, machining the piston crown can be a good way to reduce CR with out losing any quench if done correctly. Just machine a dish in the center of the piston. Do not machine off the whole Crown top. By machining a dish in the center and retaining the Flat Top standard height around the circumference, you still maintain a squish area.

 

Factory Nissan Flat Tops are approximately .023" above the block deck. Dished piston's are approx .020" below deck height. The .020 Negative deck height is what really drops CR and adversely affects quench.  If the factory dished pistons had a deck height of zero, that would increase CR ratio a bit while still maintaining some quench.

 

Welding the combustion chamber on an N42/N47 head is ultimately the best way. But it is not cheap.  IMHO, machining the pistons can be a good way to drop CR and maintain some quench, while being more affordable. And it's a better method than just using a thicker head gasket. 

 

Try to copy the factory design and have your machine shop calculate the dish necessary. The factory pistons as shown below have a fairly large diameter dish. You can reduce the diameter of the dish to get a CR of around 9.5 to 1 and maintain some resemblance of squish. That should be OK on 95 RON.

 

Factory Nissan dished piston. Note large diameter dish. Reducing diamter of dish, will help maintain quench.

 

IMG_6586.JPG

Edited by Chickenman

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Why not just get a maxima n47 head? High quench design. Small ports, etc... Would put his CR around 10.8:1

 

Have to run good gas but with proper tuning and run it a tad bit rich,should be a great head choice for the build.. came on the 80-83 maxima gas engines.bolts right up

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one thing you can do also to increase compression without changing very much about your engine if you think it's solid is to change the head gasket to a fancy, super thin one. you might be able to get yourself a few points there, without touching the shape of the head or the piston. 

 

alternatively, you could keep the short block as is (in the truck even) remove the head and have it machined/shaved.   but you'd need to verify valve clearance on the pistons and make certain of the type of gaskets you'd need, in case the shaving changed the shape of the head to block contact. 

 

alternatively-alternatively (   :P  ), you could have the block shaved a little bit, and keep your dished pistons and your head... again, if the valve clear them, and if your head is flat enough to bolt right on to a new, shinny flat block surface.  

 

 

be careful in setting your cam timing after any of these though as the difference in deck height screws it up some. 

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