hellraZor

Ok I know that gearing has everything to do with top speed and power and torque only mater when getting to top speed.... Now my question is if you do a v8 swap with a 350ci engine and a TH 350 trans. Would the lower redline limit of the V8 combined with the gearing on the th350 have a higher top speed than my 77 280z with an automatic trans and everything stock....????????

jmanz6

The top speed is figured by the redline of the engine (V8 redline is about 5500) times the gear ratio of the trans (TH350 3rd gear ratio = 1:1) times the gear ratio of the rear differential with consideration of the tire diameter. All things being equal (no overdrive on the stock ZX auto trans), the ZZX would have a higher top speed because it can rev higher. Redline on an L6 is between 7-8k. Not hard to figure out. NOW, the V8 would be faster getting to the V8 top speed...

emo236

the s30 chassis issue as far as hitting high speeds isn't necessarily just the lack of power and gearing, it's more related to the aerodynamics of the design. If you want to hit high speeds, you'll need things like a G-nose conversion, spoiler, front air dam, etc. Even then, you'll still experience some "float" at high speeds. Have you ever gone 100mph or over in your s30? It's scary, the front end begins to float quite a bit!

veyenyl

With no aero mods, I think that top speed would be about the same or very close based on the aerodynamic inefficiencies of the S30. I don't think the L28 redlines at 8k either. They seem to fall flat after 6k. I had a 240Z with a 327 and TH350 and I hated freeway driving with no overdrive. Off the line it ran like a bat out of hell though

hellraZor

what do you guys mean by S30

veyenyl

S30 is the chassis code for '70-'78 Zs.

jt1111

I had my 260 to 125mph once and had plenty left, but I put a 5 speed with a 0.63 overdrive ratio in it and would recommend that to anyone doing a v-8 swap. I turn under 2500 rpm at freeway speeds. I put a 350 in an RX7 once with a turbo 350 and hated it because of the high rpms needed to actually highway drive it.
JT

theramz

Other factors in top speed are that your speedometer is a cable wire that drives a little slipping clutch in it. It can be off 10MPH at high speed. The Z tach is also inaccurate. A gear ratio is similar to a fulcrum/lever. The higher ratio (first gear) means the fulcrum is closer to the work, easy lift. With a .6 overdrive, the fulcrum is almost at the handle. To reach redline in any car you have to have lots of torque and aerodynamics. 125 MPH is believable for a good runnig Z. But when you figure you are traveling the length of a football field including the end zones in two seconds, it's realistic to believe there is a margin for error.

jt1111

I understand the fulcrum idea. I wasn't trying to brag about, or embelish the my car, I was stating what I did. My speedo actually read 135 but I figured 125 was a modest guess. I was answering the question above. My z has a healthy 350 in it with a WC t-5 tranny. I did the math on paper, and with the 0.63 gear ratio, tire size, and rear end ratio in the perect world, with no drag or other fatcors, the car would do 212 mph at 6000 rpm. I will never get there, and know the car could never actually reach that speed. At "approx" 125 mph, however, I did have plenty of rpms left but did not push further for 3 reasons. 1 - the car, with a stock body, did start to feel like it was floating at that speed. 2 - I was way past a speeding ticket and did not feel like the trouble, and 3 - I started to pick up a vibration from either the stock 14 " tires, or the modified V-8 driveshaft. I wanted to let HellraZor know a V-8 swap with a TH350 will probably not allow for the top speeds he is looking for, and might not match the top speed his z has being stock. Especially if his Z came with a 4 speed which does not have the inherent slip of an automatic.

theramz

The post was directed to the math. I assumed a L26 which actually has a top speed of 120 mpg. A healthy 350 V8 should go 145 if set up right. I am only trying to compare all this talk about top speeds for L motors or V8s when the advertised speed for exotic sports cars such as Viper or Ferrari is no where near the math assumptions here either. The only true way to check actual speed is through a set of lights not a 30 year old speedo.

jt1111

I agree theramz,
I will be trying at a set of lights when I correct the vibration I have. That was a touch spooky. But, speedo off a bit or not, I hope if hellraZor does this swap, and is interested in top speed, or a good highway criusing car, he thinks seriously about not using the turbo 350 tranny and elects to go with some form of overdrive tranny.
JT

theramz

Yeah, that will be sweet! I found that my 240Z, lowered with Tokico springs and shocks, all new bushings, handles much better now at 100+. It' on a slight rake so I think that helps keep the nose down too. I think an airdam will also help you. They say the G nose adds 10 mph to the top but I don't like the looks.

bjhines

Here ya go. VIDEO.

I hit top speed in my 1973 240Z all the time. My speedo says 155MPH at the end of the straight... but with low profile race rubber the actual speed is only 130MPH. It is redline in top gear though. She won't go any faster.




Here is some track vid of a banked oval (NASCAR style). I am only going 110MPH through the bank. but it is CRUSHING G-force on me and the car. I have some video fomr earlier this day that shows smoke comming from the wheelwells of several cars because they are crushed to the bumpstops and the tires are burning the fenders off. Several Corvettes melted the fender lips.




I am building a V-8 race 240Z that is geared to have a top speed of 180MPH. It will be on track later this year. I should get some good video of that car going 180.

ASA240z

cool video, to bad you posted in a OLD thread.

NismoPick

Technically so did you as his post was 10 days ago.... buahahahaaha.

ASA240z

hmm i see... but that means you posted in an old thread ALSO
"monkey see, monkey do," perhaps?

ThermalWake

**** ive hit 147 in my S30.. it was very light. (floaty) and it was slightly down hill, but its possible in a L28

NismoPick

It didn't take me 10 days to reply to your post.

Is your S30 stock?

ThermalWake

hell no its not turbo, but i have a custom made duel cone cool air intake. ram air. stage 2 cam, header, magnaflow exaust with 3'' exaust 3.90 gears. i have it stripped . the car weighs 2400 with me in it. and y rated tires, sway bars, custom short shifter. i have t ripped apart right now. im almost done porting everything. so im hoping to get 5-10 hp gain from the porting. and im think of for when i start going to the track, making a ram air up in the front with no filter, so it forces a little more air in there.

bjhines

like zis?





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given the fact that I get my top speed runs on a race track with less than 1/2 mile straights.. I can't beat 130MPH. I also have the stock 1972 drivetrain with limited gearing. I don't doubt that a 5 speed with the right gearing and a long enough run will reach 150.

theramz

If you installed the 3.9 rear without changing the speedometer drive gear in the trans, your speed is way off. You can check this by pulling it out and look at the color. 3.9 should have a black (color code)plastic drive gear. I don't think the S30 body with an L6 is capable of even 140mph unless you drive it down the face of MT. Everest.

theramz

I came accross an article in "How to modify Datsun engines and chasis" There was a Racer Brown 240Z that set a new record at Bonneville in 1972. It had a 3.9 diff with a 5 speed. It went through the traps at 155 mph, 7800 rpm in 5th gear! Not bad for a na engine.

bjhines

I often see people stating that their car can hit "whatever" high speed.

There is a big friggin difference in what your speedo says and what speed you are actually traveling.

My speedo needle gets cranked WAYY around to 150-155MPH on the long straights, especially courses with high corner exit speeds onto the straight. I use the speedo to judge how fast I am going in relation to other parts of the track, or the last lap. That is not actual speed. Data aquisition shows my top speeds in the 130MPH range.

The fact is... The original 175HR14 tires that came on the 240Z were very tall wagon wheels. They are MUCH taller than the 225/50/15 race tires that I use. They are still taller than a 205/60/14 that many people use on the street.

My speedo reads ~5MPH over at 35MPH. Doing the math will reveal that my speedo reads 10MPH over at 70MPH. My speedo reads 20MPH over at 140MPH. If I am seeing 150MPH on my speedo then I am actually doing ~129MPH actual.

We also run into another issue that makes it hard to believe ANYONE who says their Z will get to 150MPH. The fact is that even race modified L-28s are falling off their torque peak by the time they are doing 130MPH in 5th gear. Even a high output race prepped engine is going to need to be tuned to get as much airflow as possible at redline RPMs in order to have the torque to break the wind at 150MPH.

That means that you WILL NOT get your S-30 Z car to 150MPH unless you have specifically built the driveline to do NOTHING but reach top speed in a land speed run. It would be a dog on the street. It would be a dog to drive on a road course race track too.

Don't let your ignorance of your tire sizing and gear ratios make a fool out of you. I have driven cars that CAN reach 150MPH and they are in a different league than the S-30 Datsuns.

I am building a V-8 Hybrid 240Z for track use. I have chosen to use the WCT5 with .62 overdrive, 3.54 differential gearing, 275/50/15 tire size. I am using a 327 SBC with a highly modified valve train that should put down a significant amount of torque at 6500RPMs. I expect I will have ~150-160MPH top speed with this combo.

327 block


Feb. 25 1964





461 Corvette heads
Jan 8th 1964





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theramz

Finally! Someone with some real knowlege on how to go fast and what fast really is! To bad your 3000 miles away, I would love to see your car. You've got to post pics of it when it's ready!

D_Zed

My 1983 (the year with the long *** 1st and 5th gears) hit 154 before my rear end was about slide out from behind me and I would of probably died, iunno if the S130 front end floats, never had that issue. All I know is when I shift into 5th after getting close to redline in 4th it starts to feel like my rear end is exremely loose and the cars going to flip from the rear forward lol