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truck needs to go fast faster


TasoZ24

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Hey guys, now with the electrical done (much help to ratsun), im bored.

With engine running properly, im back to winding the roads nice n smooth like. One thing I would like more out of this truck is acceleration.

The engine has been rebuilt less than 10k miles ago (so says craig) and Thorley headers seem to be the only upgrade to engine. Runs like a dream starts like a new age button ignition.

New carb would be next on my list. Here a lot about Webers, but can use some other options.

Any advice on engine to 60 faster, and nice pull when I drop gears would be greatly appreciated.

Sweet spots on tach would be helpful, but no tach at the moment. Shall be saved however, thanks guys nice to be part of Ratsun, love these little trucks.

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32/36 or 38/38 if daring. The Z24 is under carbed anyway. Under $300 and a good bang for the buck.

 

Another is to swap the differential for a 4.11 or 4.375. The engine tag under the pass side hood hinge on inner fender will have your current ratio. Bottom right on tag probably HF39. This is even cheaper and an even better bang for the buck. Both would be even better.

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Thanks for tips sorry about double post, out here in the sticks= horrible service. The differential is a nice idea, any recommendations for ones that fit?

About the weber, the 32/36 will produce a noticeable difference without mpg drain? Not dogging it just nice on highway.

The exhaust system can wait until I get more intake, stock carb is next to go more than likely. Replaced most components since ive had it, looks and drives great now.

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Thanks for tips sorry about double post, out here in the sticks= horrible service. The differential is a nice idea, any recommendations for ones that fit?

 

On the tag DMike was talking about is your size. 3.9, 3.8-whatever it is. 

 

Look at the tags of trucks older than yours. 

 

The 1979 620 has a 4.11 gear set. 78 and older trucks will be 4.375, down to 1969? The 4.3 will be a huge jump in acceleration for you. 4.11 might be better middle ground. 

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The setup in my truck is bone stock motor with a Weber 38/38, 4:38 aluminum housing rear end and stock exhaust with a thrush turbo. Does a consistent 17.5 in a 1/4 mile. Could be better with a new clutch, new tires and aluminum wheels.

 

They made 2 different housings for the 4:38 though. A steel housing and an aluminum housing. The steel ones cam in the '78 and older 620 and the aluminum ones cam in the 521s. Not sure if all 521s but I got mine out of a '71. My dad also got his out a '72 I think.

 

Me and my dad have the exact same setup except he got his Thorley header and a thrush welded (2 1/4 all the way back). He said the header improved his gas mileage and after we did a little test hit he came out on top and was still pulling so he can probably hit the 16s with his setup. But like I said the only difference between out trucks is that he's got a header.

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To add to what Mike said, free flowing exhaust. 2.25" piping and a turbo muffler.

 

If replacing the system because of damage or wear you could go 2.25" but the stock is still good at 2". Most definitely a lower restriction 'muffler' but not a fart cannon. Turbo muffler is good.

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Let us talk about the RPM change here now, if you going down the hiway at 70mph with your 389 gears in the rear, your engine is likely turning about 3000rpms in 5th gear, when you change over to 437 gears, at the same speed of 70mph, your engine will be turning about 4000rpms, sure it speeds up quicker, but the engine rpms will be 25 percent higher.

I have what you are looking for(Alloy 437 gears), but you have to know the draw backs also, most folks are trying to lower there rpms on the hiway, not raise them.

 

4.375 sounds sweet. Will call yards looking around. Got a job in Eugene this weekend so I might have better luck there.

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Stock 720 tires are P195/75R14 and are 25.52" diameter.

 

 

IN 4TH GEAR.... At 70 MPH that's 3,587 RPM with a 3.889 diff.

 

Same as above but a 4.375 diff..... 4,035 or roughly 400 RPM higher  at 70 another way to look at it is you will be revving about 12% higher than before at any speed.

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Gotcha so mpg will be a factor there. Well im just wanting to pass trucks and old people with a bit more confidence and not kill my mpg too bad. Once my 02 frontier is up here, this truck will be all play. For the moment its my daily.

With the Webers, the 32/36 seems like the way to go for every day driving, and mpg stays about the same from what im understanding. Does it improve the performance by a noticeable difference? How bad is the 38/38 on the mpg? Most my driving is done around town, but ill have modern vehicle up in May.

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The 32/36 is a progressive secondary carb, meaning the first barrel opens to about 3/4 before the secondary begins to open. Better on gas this way and also a smaller carb. It won't give better mileage but can sometimes equal it.

 

The 38/38 is a synchronized carb. When you step on it, both open. It's basically a large two barrel carb. There is a tendency to give it too much gas all the time. It's a larger carb and made for V6 and small V8s and will normally give shitty mileage unless you keep your foot out of it.

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Yeah the double barrel sounds a bit touchy, 32/36 sounds like it will be fun when it has to be.

Also just replace master and slave cylinder, im guessing the clutch itself isnt too pretty. Any suggestions for a nice clutch/flywheel kit?

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If you plan on building it up a little later why not get the 38 right? The Weber 38 has an idle circuit jet for each barrel. I learned that the engine runs off the idle circuit jet 80% of the time. When under acceleration is when it runs off the main jets and air corrector jets. So technically however big your jets are will depend on your gas mileage. I shift early and go light on the pedal so that saves gas quite a bit. My freeway cruising rpms are at 4,500 max but don't know the speed cause spedo is disconnected.

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Been thinking the same thing. Might just get bigger because once in my frontier im going to want to go big anyways. I figured ill be easy with it and ill have a tach by then so I can manage better. Never had carburetor before, but have been doing my home work trying to get a better idea on everything. Was an alignment tech for six years so I can turn a wrench but still gaining vital knowledge on engine work. Third nissan truck and this guy is by far my favorite, so much easier to play with.

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Welp ,made it to San Diego with no problems. But either carb or clutch is acting up. Think carb is sticking. Well im going with the 32/36 weber and 4.11. Seems like good combo and will keep moderate change in mpg. New clutch is in the near future, any suggestions?

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