Well guys I was trying to do a top speed run last nite on the 210 near Angeles' Crest, and the following happened...

I started normally in 3rd on the ramp, gunned it till redline, shift, 4th, redline, shift, 5th. I am now @ 110 mph at around 4200~4300 in 5th at full throttle. Then suddenly the car just wouldn't go any faster - it started slowing down little by little, like there was a fuel cut or something.

That section of the freeway is GENTLY upslope, so that might have been a problem, but I've recently tried a top speed run on the 5 and it took me to the brink of 125 (I drive a vert with limited mods).

What is wrong?

 

Sounds about right for a stock 'vert

 

What's 4th gear max out at?

If I remember correctly 5th is overdrive on the NAs and is funcational on the TIIs.

 

Get some mods so you can wind out 5th gear . BTW there is no governor (but there is a rev limiter at 7600/8600) on FC's.... or any other RX-7 for that matter.

 

my completely stock 91 vert hits 120 in 4th gear by the 8K redline and tops out at 127mph in 5th gear with the top and the lights up (lots of drag).

Kris

 

Are your 5th and 6th ports opening? what year is your vert and what mods have you done?

 

5th is an overdrive in both cars; 0.762:1 for a Turbo, 0.697:1 for an NA (S4). Why wouldn't 5th be "functional" on an NA?

 

NZconvertible,

Isn't HP & torque the other determining factor on gear ratios & top speed? And for us gear ratio novices what exactly denotes overdrive vs a normal gear?

I'm thinking of the VIPER where they max in a gear lower than top gear here

 

my bone stock 87 with dirty fuel injectors topped out at 120.

 

i was doin 140 and was still puling veay slowly

 

my vert hits a wall at 110 too (top down). it is still accelerating but slowly, this is about 5600 rpm in third (automatic).
I'm not sure if my 5 an 6 ports are working I don't feel any boost at 3800, so I'd guess they aren't. The mechanism is pretty hard to move on them.

 

5th is .711 on the NA US spec 'verts

 

I had something similar going on last week. I was in the middle of nowhere in Wyoming on I-25 on my way to Montana, and I was only able to hit 125/130 on a flat highway with the windows up and headlights down. I've hit 135 before, but that was going downhill. I'm thinking the 5 & 6th ports are messed or something.

 

redline 4th gear was 120mph i think it was 210kmh
and with 3 people in the car and yes that was stupid to go that fast with passengers in it .

 

Top speed is mainly governed by power and aerodynamics. The NA has less peak power, but it also has a slightly taller final drive. So the engine is lower in the rev range at the same speed. It means a ratio less than 1:1, so the engine is turning slower than the gearbox output. On most road car gearboxes, 4th is 1:1 and 5th is an overdrive of around 0.7:1. That’s because the Viper’s 6th gear is 0.5:1! It’s simply too tall for the engine to make enough power to go as fast as it can in 5th. This is common in 6-speed gearboxes with these “moonshot” 6th gear ratios.