Top speed on highway for 720

[datzenmike]

Good to know. This anti scuff additive isn't needed on roller cams as much but 'flat tappet cams' it's essential. Tell the truth I don't know if a synthetic oil will work for this or not. If not, you are risking long term wearing out of your valve train. One thing... don't trust the oil makers word.

[Charlie69]

I run the Rotella 15/40 in all my trucks my newly rebuilt L20B and Z20S will run the Rotella 30 wait for the first 500 miles and then the 15/40 after that. Using WIX filters.

 

My 86 2wd King Cab has ST wheels and 205 75 14 tires.

[matrophy]

5 hours ago, Charlie69 said:

I run the Rotella 15/40 in all my trucks my newly rebuilt L20B and Z20S will run the Rotella 30 wait for the first 500 miles and then the 15/40 after that. Using WIX filters.

 

My 86 2wd King Cab has ST wheels and 205 75 14 tires.

Are wix filters the hot setup?

[datzenmike]

I think they are same as NAPA Gold and very well made but what ever you do don't use fram filters. Always change the filter with the oil.

[matrophy]

I actually change my filter halfway through the oil change interval. I think I used Bosch this last time.

[ckm319]

My 1984 4x4 would only do 65 when I got it. After a lot of refreshing and a Weber it will do 80 but it doesn't feel right so I only do it from time to time. My brother bought an 82 new and he claimed he was pulled over for 96! I don't think mine would do it or would I want to. Vehicles now are made to go faster and handle better.

[bottomwatcher]

My 82 4X4 with 31s, z24 and a 280zx trans would cruise at 80 at 3k rpms. It took a while to get there and this was flat ass Florida. I remember driving cross country once with all my windsurfing gear on the roof racks and hitting Montana. This was back in the day when they didn't have a speed limit. I think I could make about 60 everybody just blew past me. You know you are underpowered when a headwind impedes progress.

[matrophy]

2 hours ago, ckm319 said:

My 1984 4x4 would only do 65 when I got it. After a lot of refreshing and a Weber it will do 80 but it doesn't feel right so I only do it from time to time. My brother bought an 82 new and he claimed he was pulled over for 96! I don't think mine would do it or would I want to. Vehicles now are made to go faster and handle better.

I agree that it doesn't feel right when I get the truck going downhill with a tailwind and approach 70+. Seems like the handling becomes kind of iffy. I have no need to go above 65 and I guess I was just wondering whether something might be wrong with it after hearing others claiming to reach higher speeds. If it would stop raining here, I want to do a compression check and check the valve lash as suggested earlier just to verify that everything is the way it is supposed to be. This truck only has 68000+ miles and I want to keep it running as long as I can. 

[Charlie69]

My 86 King Cab is 2 wheel drive and I have rebuilt my front and rear suspension with all Moog parts and am running the KYB Gas-A-just shocks all the way around, factory ride height. Fresh alignment and it loves to cruise at 85.  Getting a complete rebuilt Z20 rebuilt 5 speed ready to install soon.  If I do not like the Z20 I am rebuilding a VQ35 for it with a 4 speed automatic.  I like to cruise from point A to point B quickly.  I am not getting any younger!  LOL

[matrophy]

2 hours ago, Charlie69 said:

My 86 King Cab is 2 wheel drive and I have rebuilt my front and rear suspension with all Moog parts and am running the KYB Gas-A-just shocks all the way around, factory ride height. Fresh alignment and it loves to cruise at 85.  Getting a complete rebuilt Z20 rebuilt 5 speed ready to install soon.  If I do not like the Z20 I am rebuilding a VQ35 for it with a 4 speed automatic.  I like to cruise from point A to point B quickly.  I am not getting any younger!  LOL

I skimped out when I rebuilt my front end and bought some  'factory closeout' parts on RockAuto. The Mevotech and AC Delco parts I bought are fine but now 6 months later the rubber is all cracked and split on the cheapos. My theory is that these probably sat in a warehouse for 20 years and the rubber deteriorated while they were sitting. I have to replace the cheapo ones and go with Moog, Mevotech or AC Delco. Shocks and rear suspension are on the list.

[ckm319]

What I tend to forget was that the speed limit was 55mph when these were built at least in the south. I could cruise at 70 in mine but I usually take the slower roads when I drive it. I do wish they made these new again!

i

[bottomwatcher]

Yep the motto was 55 arrive alive! We could save a lot of gas going back to this but people would riot in the street. I don't go over 65 in mine. Big tires, corners like a 3 legged elephant. It probably has less than 1000 miles on a front end rebuild so all good there. I just drive the back country roads with it anyways. I drive like in my 68 beetle thinking these things are only slightly safer than motorcycles.

[Charlie69]

I keep my trucks in the best mechanical condition I can.   I drive my trucks like I stole them so they need to be maintained.  Next saturday my 86 King Cab will go in and have the tires reballanced and rotated.  If all goes well I will be putting the Z20 5 speed in it the following week end.  I have to emission test in June for my new 2 year registration.

[datzenmike]

I find that when you drive it like you stole it you are more aware of how well it is working..... or not. 

[Charlie69]

I believe your are correct Mike.  I know when something is not right with my trucks sooner than someone that just puts around.

 

Shawn the person with the custom green vert 521 used to just put around with his truck,  But after getting Webers and parts for the Webers from me he has realized after tear down his Z24 for a rebuild that the putting around did a major carbon deposit in his head and valves.  He now drives it so it does not carbon up as bad.  He does not drive it like he stole it.  LOL

 

You need to wind a motor up under power to blow the shit out of the head from time to time.  I have fun in my trucks and I also work my trucks hard also.

 

 

Edited May 18, 2020 by Charlie69

[Stinky]

I was running late for work this am...i had 3 minutes to spare.

 

I was effortlessly running 80 on I-70.

[matrophy]

On 5/14/2020 at 2:17 PM, datzenmike said:

The stock tire for a 2wd is 195/75R14, these are 25.5" tall or diameter. If yours came with taller ones you are reading low. Just for example a 30" tire would be reading 60 but you would be going 70.

 

Your friend with the smaller tires? His speedometer will read higher but will be going slower.

 

I suggest pacing with a friend who has a newer car and see what you are actually doing for speed. But on the face of it you should be capable of over 70 I would think.

 

 

In no particular order...

 

Look down the secondary barrel with a flashlight. (engine off) Have someone step down fully on the gas pedal and push up on the secondary diaphragm. Is the secondary butterfly free to fully open in the vertical position? While there check the primary too.

 

Next time the engine is fully warmed up take the top off the air filter and look. Is the choke flap fully open and vertical?

 

Take one intake side plug wire off and put an old plug in the end and place on a grounded surface. Have someone turn the engine over with the starter or start it. Do you see a spark jumping the gap? If yes replace the wire and do one of the exhaust side plugs. You should see sparks on both sides.

 

 

Take the valve cover off and set the valve lash to 0.012" on a hot engine.

 

Check that the ignition timing is 5⁰ advance.

 

Could the catalytic converter be part plugged or is it or any of the exhaust pipe crushed?

 

 

 

Here is something non related but should be addressed by every Z24 owner. The Z24 tends to blow the head gasket every 100K. To reduce the chance of this happening the correct thing to do is re-torque the head bolts every tune up or say once a year. The procedure is to do this on a COLD engine. Loosen ONE bolt and torque to 60 ft lbs, then move onto the next bolt. Make sure that only ONE bolt at a time is loose and you can do them in any order you like. The sooner the better you do this.

 

 

 

 

 

 

Question about re torquing head bolts: The truck has 69000 miles so I doubt the re torquing was done by PO although they did seem to maintain it pretty well.

 

Anyway, should I just check the torque or definitely re torque each bolt?

If re torquing, do I completely remove each bolt and make sure it's clean or just loosen and re torque?

Do I re torque in stages or just for to 60 ft/lbs in one go if I remove the bolt? 

 

I saw a YouTube video that suggested that the bolt be removed and cleaned and I'm wondering if the bolts are grimy then what about the hole that the bolt goes in to?

[datzenmike]

On 5/14/2020 at 2:17 PM, datzenmike said:

The procedure is to do this on a COLD engine. Loosen ONE bolt and torque to 60 ft lbs, then move onto the next bolt. Make sure that only ONE bolt at a time is loose and you can do them in any order you like. The sooner the better you do this.

 

Right there. Loosen one bolt, torque to 60 ft lbs. Provided that only ONE bolt is loose at a time you can do in any order you like. This avoids all being loose and coolant leaking into the cylinders and then you DO have to torque in sequence and stages.

[matrophy]

4 hours ago, datzenmike said:

 

Right there. Loosen one bolt, torque to 60 ft lbs. Provided that only ONE bolt is loose at a time you can do in any order you like. This avoids all being loose and coolant leaking into the cylinders and then you DO have to torque in sequence and stages.

Got it. Thanks. Completely removing each bolt sounded like overkill. I ran a compression test as I work through the list of tasks you provided so I can verify that my truck doesn’t have anything wrong with it to affect top end speed. I am wondering how to interpret the results:

 

Cylinders in order 1 to 4 (psi)

cold 140, 140, 150, 175

wet 175 1-3 and 200 for number 4. 
plugs looked OK but #4 was ‘dirtier’ but not oily

 

[datzenmike]

By 'wet' you mean a warm engine? If I say "The two adjacent low cylinders when cold could be the gasket beginning to blow between them but way too early yet to be sure. I wouldn't worry about it." you probably will so just check every tune up and see if it gets worse. Re-torquing the head bolts may help.

[matrophy]

2 hours ago, datzenmike said:

By 'wet' you mean a warm engine? If I say "The two adjacent low cylinders when cold could be the gasket beginning to blow between them but way too early yet to be sure. I wouldn't worry about it." you probably will so just check every tune up and see if it gets worse. Re-torquing the head bolts may help.

'Wet' was squirting oil in the cylinders. Engine was at operating temperature throughout.

[Madkaw]

I took mine out on the highway for the first time in a while . Just installed new rear leafs , so all the suspension has been rebuilt or replaced . Tires are old ,  but have lots of tread . I got her up to 75 pretty easily . I really appreciate the 3.88 gears now . I was turning 3k at 75 , which I though was reasonable . She road pretty good even with no interior and the windows rattling a bit because no weatherstripping. When I get a full interior and some new highway tires I will be in good shape . Even though the suspension is stiff, it wasn’t much worse than my VW Alltrack. It will be interesting to see MPG on the highway . 

[olskool720]

slow and low is the tempo, no need to go fast anyways

[matrophy]

Don't know about the low part but slow is definitely the default🙂

[7twentyguy]

My lowered 85 ST does 80 all day long, if I put my foot all the way down I can hit triple digits, I’ve got titan 18s with 40 series tires, I had  a buddy pace me . At 100mph, my speedometer is just over the 100 mark. I did make a ram air intake from a keriyakyn air cleaner off of a Harley , my thought is “the faster you go the more air you shove down the carb.