Stock Convertible Top Speed (on flat)
 

I have a 1990 n/a convertible. Last night I had the opportunity to push it's upper speed range. The car pulled strongly in 1 and 2 (automatic), but begin to bog down in 3 around 110 MPH. REVS increased slowly if at all (this is around 5500 rpm if I remember). Of course shifting to 4 did not help the situation.

I have previously gone 120 on a downhill, but this was flat ground.

The headlights were up, the top was down, so aerodynamics could have been better, but I still expected to get 130 before hitting the wall.

I am pretty sure my 6 ports are not working (finally moved to a place with a garage, hope to fix that next week).

The car is stock. Not even an intake upgrade.

I just want o find out if this is normal, or if I might have some engine problems.

This may not be too much help because mine is a 5 speed and I had the top up, but...

a couple of weeks ago I hit @123 mph before I had to shut it down because I was coming up on traffic. That is with an '88 with slightly low compression and the headlights up.

Dan

The headlights up, will probably subtract about 4-5 mph. They are about the least aerodynamic automobile body parts that ever came out of Japan.

121 is the factory rated top speed on the 88 US 5 speed version.

I would think that the US spec 5 speed '89 might get to 125, but wouldn't think that the 90-91 (the heaviest, lowest power to weight ratio of any RX-7 and stuck again with the 3.9 rear end) would hit anything past 120 without modification.

How about a GXl stock? Just wondering

Is that from experience, drag coefficient computations or pure speculation?

121 is the factory rated top speed on the 88 US 5 speed version.
 

"121 is the factory rated top speed on the 88 US 5 speed version. "'

Really? i hit that last week at Tobay beach w/ my 88 vert, racing my friend's 328i .. it felt like the car had more to go though. i was at 4th gear at i hit 6rpm barely..
clean stock engine=cleaned it w/ toothbrush the day before=) w/ exhausts and y pipe... hmm.. we'll see.

Entirely just a guess. I saw a chart rating the amount of horsepower needed to take 5 similar modeled cars to 100mph according to thier drag coefficient and a small difference made a noticable change. If the headlight creates as much of a drag as they apear to; I would think 4-5 mph could be realistic. But this is all just my opinion and I'm not that knoledgable.

Anyone know the factory rated top speed on a '89 GXL? (coupe vs. convertible)

Okay so I will get this out before all the BS flags go up, I got my '88 Vert up to 138. Here they come, okay I had an exhaust, bonez race pipe, magnecor wires, bonez intake, cold air box, decent clutch(don't remember which one). The car also had Tokico HP's, Tokico Springs, Racing Beat Sway Bars and Endlinks. The engine had great compression though and was in a great state of tune. Of course the top was up and lights down and the suspension being new I am sure helped keep the power to the ground. The vert has since met a tree thanks to me, I loved that car but she was crushed. Anyway just thought I would put my .02 in.

Adding horsepower will almost always increase top speed (unless it it gear limited). But top speed is like an acid trip; once you get to a certain point, it takes alot more the next time.

Is that supposed to be the end-all figure? Just wondering because mine went above that with only gutted cats and nothing done to my 6 ports, turbo rearend (should be the same) and low compression. 4th gear still had some left.

Dan

I'm happy to discover that there isn't a real big problem with the car. I guess that 160 mph speedo is more fat advertising.

You guys are mis-understanding the concept of top speed.

When the factory quotes something it is one of three things.

1. It is the top speed of the car (again in stock form) for a 3 (or 5 depending on the company) mile run on flat or banked with under 1000ft altitude (typically also a test track). Usually best of 3 or 5 runs. If you are cruising across the plains in cool dry air and have 10 or 20 miles to get up to 120, I am sure you might actually pass that factory number.

2. It’s what the factory claims is the run for insurance purposes hoping not to have the insurance companies raise the premiums so more people can afford the car. (Mazda did this one the series 5 and 6 turbo RX-7s, they actually reported lower than any mag or article reported.)

3. It’s what the factory electronically limits the car to.

Also, just because your speedo says that you are going 130 or 140 MPH doesn't mean your car really is. Japanese and American Speedos are noted to be bad at above 85 MPH (I saw one series 4 RX-7 and a RA6X series Celica that their speedos were off more than 10 MPH at 100, reporting 110 but the car actually trapping only 101 and 100 respectively).

My own speedo on my T2 converted ‘vert is off almost 3 MPH at 80 MPH, so I don't doubt that although I saw 130 on the speedo on my drive between San Diego and the Bay area yesterday, it was really only 125 or less.

No, the verts came with a lower rear gear (3.9), for better mileage in 88 and 91 (and some claim 89 and 90 as well, but I don't have proof one way or the other).

Anyway a higher gear (4.1 as found in the T2 rear ends) should let you go a little faster.

actually, the lower the gear ratio (3.9), the higher the top speed and better mileage...and the higher the ratio(4.3), the better acceleration and worse mileage because the engine is spinning at a higher RPM at cruise than the lower ratio rear end
Grace and Peace
Matt

The problem is too keep the RPMs up in a pulling range longer, so the lower rear end gearing actually hurts in this case.

If there was sufficent power to drive the car to redline in 5th, yes your statement would be correct.

Cool. Thanks for the info. That is kind of funny because the car seems to be slower than what it was. Of course, nobody said my memory was perfect either. :)

Dan

90 Vert 42k original pampered miles....im the 2nd owner! :P gonna fix her up to be a beast!

Fred

http://www.rx-7.net/uploads2/1007949052.jpg
That is the fastest I've had my vert, and it has RB full dual exhaust, K&N intake, underdrive pulley, and maybe 100 lbs. dropped from it. 5 speed though, and I was in 4th gear at about 7300 rpm. I did this around 2:30-3:00 in the morning, and just happened to have a digital camera with me, so thought what the hell....

Thats not bad, you are at 129 based on RPM unless you changed the rear end or tire size.

Man, i've only gotten mine up to 110... Is there something wrong with my vert? It's really clean i've made sure of that... :) it's a 91 that's as fast as she'll go even in 4th.. how are yall gettin them so fast ?

It is a vert it got the 3.909 final drive ratio, plus I'm running on a 50 series tire, not 60.

Is it an auto or stick? What mods have you done (altough i took my vert to 125+ when it was stock)? Keep in mind your vert is a lot heavier than mine too(300 lbs.). When do you shift into 4th gear? I wait untill I'm almost at the fuel cut in 3rd (around 105 - 110 mph).

What size 50 series?

if you are using the standard 225/50 15 your actual speed was only 124 MPH