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truck needs to go fast faster


TasoZ24

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Cool. New tires going on soon.not sure what direction to go with it yet tho. Either something normal at stock hieght or raised a bit and fatter tread for not sinking in mud on farm.

My torsion bars are maxed out and I have 29" maxiss bighorns on it. Does great on the road and gets decent gas mileage. 950 for a whole set from swabbys
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Ok bad synchro ring. First time to bust open transmission case, much more simple than I thought, yet still clueless. Been reading up on my fs5w71b and should hopefully have parts tomorrow. Everything else looks good but going to replace bearings while im in there.

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With tranny pulled im goin to swap differentials to a higher ratio. Going for more get up but still having good range in first and second. Thinking the 4.11 would be a nice transition and the 4.375 would have me at high rpms way to quick in low gears, any thoughts on this?

Running with a 3.89 right now, pretty sluggish

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That's only a 5% step up in RPMs. Assuming you can easily turn 5,500 RPMs and still have significant pulling power then in 4th gear you would be going 107MPH. A 4.11 differential will be just 6MPH slower. Here's another... At 5,500 in 1st with what you have now you would be going 32.2MPH... a 4.11 will drop that to only 30.5MPH. At 50 MPH with 3.889 you would be revving 2562RPMs and with a 4.11 it would only be 2,707RPMs. I don't think 150RPMs at 50 MPH is going to give you the edge you want.

 

A 4.375 would be a 12% change and just under 2,900RPMs at 50 MPH or about 400 RPMs.

 

28.7MPH in first at 5,500RPMs. Or second comes about 4MPH lower

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Peak HP is at 4,800RPM, while Peak Torque is at 2,800RPM for the Z24 engine. So for a good balance of both, I've always shifted between 3,100-3,400. However, your diff-ratio, transmission, etc.. will probably make a difference in those numbers. 

~Peter

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I assumed you had a Z22. The Z24 (actually any Z series) are not big revvers and while they can rev they have run out of steam above 4.5K. They do, however, make tons of low speed torque. The Z24 was a truck engine, for pulling a heavy load in a heavy truck and it was good at it. 

 

Changing the rear end will not change the engine torque or hp points. It will allow the engine to be revved higher at the same speed it is now. Revved higher it will be closer to peak torque and pulling harder than it is now. (at the same speed) This increase in torque is  exchanged for mileage and top speed.

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I got my information regarding the Z24, but my current truck runs a Z22S. Both engines have similar power curves; regardless of what any ass-in-the-seat dynos will tell you, they both make HP at higher RPMs and Torque at lower RPMs. 

 

~Peter

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What is safe rev limit for my z24?

safe rev limit is 6200 for a stock engine. Its in the glovebox owners manual.

 

I shift normally at 25ish, but could use some numbers to go by.

That explains why it is sluggish. I would normally shift at 3000, and when you want to accelerate more quickly shift at 4000-4500.
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I got my information regarding the Z24, but my current truck runs a Z22S. Both engines have similar power curves; regardless of what any ass-in-the-seat dynos will tell you, they both make HP at high RPMs and Torque at lower RPMs. 

 

~Peter

Are you calling 4500 rpms high?
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How nice. Thanks for all the info fellas. Yall take all my questions out of decision making. Its all muddy under my car port now, but will take off punkin later. My seal are toasted on it anyhow. What would be the easiest rear 4.375 to find? 4x4s?

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The early model I believe is the 1980 L20B Engine. The Z22 I believe red lines at at 5500 RPM same as the Z24.

 

The engine redline is the maximum safe continuous RPM of an engine that won't cause damage to any of it's parts. Usually this is relative to piston speed vs. the strength of the rod bolts. A very conservative formula is stroke in inches X rpm divided by 6. Your answer should not exceed 4,000 ft per minute piston speed. The acceleration/deceleration forces on the rings, pistons and rods and bolts gets very severe above 4,000. The Z22 has a stroke of 3.6248" so 6,600RPMs will give 3,987 ft/min piston speed. Obviously stronger rod bolts and forged rods, stiffer valve springs, pistons and rings etc. will allow you to go higher, but for a stock engine Z22 it's about 6,600.  A Z24 would be 3,971 f/min @ 6,300. This is +- but close, probably conservative. Going faster than 4,000 ft./min will not automatically blow up your engine. 

 

The power peak is the point at which maximum horse power is made. For a Z22 it's around 100 @ 4K ... ish. but could still be pulling hard and making 97 hp at 800 RPMs higher. Peak hp is misleading same as the torque peak. It has to be determined on a dyno, there is no formula for this.

 

I got my information regarding the Z24, but my current truck runs a Z22S. Both engines have similar power curves; regardless of what any ass-in-the-seat dynos will tell you, they both make HP at highER RPMs and Torque at lower RPMs. 

 

~Peter

 

This is better.

 

Funny thing about HP. There is no way to directly measure it. Torque is measured by a dyno and HP computed from this. HP and torque are intimately related. A flat section of a torque curve means the HP is doubling with every doubling of the PRMs. You want as high and flat a torque curve as possible.

 

The Z series engines are very efficient at low (below 4K) RPMs The intakes are 'small' and have high velocity which helps cylinder filling and breathing isn't a problem at low speed. This produces a high torque engine.

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How nice. Thanks for all the info fellas. Yall take all my questions out of decision making. Its all muddy under my car port now, but will take off punkin later. My seal are toasted on it anyhow. What would be the easiest rear 4.375 to find? 4x4s?

 

All 620s other than the early L16/18 automatics and the '79 manual had 4.375s in them.

All 521s with L16s had them

Early 720 4x4s had them but swapped to a larger diameter driveshaft and pinion yoke around '82??? and the earlier smaller yoke won't fit them.

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Neighbor has tools and knowledge, got kit today, so tomorrow...

Once im moving again ill be able to rightfully search for a rear differential or pick one up from another ratsun member. New tires and alignment are in order... then MAYBE I can start on inside. Body will be last.

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  • 6 months later...

Sorry to say that Truck Norris is no longer with us due to flipping.  His guts are being donated my 75 620. Build is in progress, trying to figure out this pic posting so i can start a proper build thread on it. Thanks for all the help on this guy, no one else is allowed to drive my 620 so it should be around much longer.

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