2nd Gen 5.12 rear top speed?

[mbuskuhl]

Anyone have an idea on top speed for a 2nd Gen with the 5.12 rear, ITS motor, 5th gearing turning 7600+ RPM? I know there are many variables but is it 120, 130 mph? More/Less?

[benspeed]

I had a nice 9/10ths prepped 87 ITS RX7 with a 5:12. I would put top speed at 140 MPH. This was at Pocono on the huge straight. I was drafting an E36 that still had a working speedo and he put us at over 140. This was with the GTU 5th gear.

[seckerich]

If you are running a 5.12 and GTU fifth (.76) you will run 122 @7000, 131 @ 7500, and 140 @ 8000. You will run out of motor before you run out of gear. This is with a 225/45/15 hoosier. Just for reference at 8000 you are :

1 30 mph
2 53 mph
3 77 mph
4 106 mph
5 140 mph

Have fun.

[mbuskuhl]

Thanks for the info! As you might have guessed I wanted to know just how fast I was going recently.

I ran Texas World Speedway 2.9 CW at a NASA race this past weekend. Half way down the straight near the start/finish line I was maxed out... my HP peaks at around 7200 (per the Dyno) and really starts to show effects over 7800. I ran it to 7800 and just coasted the rest of the way - 225/50/15 Toyo RA-1's and not sure on the 5th gear, although I just had it rebuilt but don't know where the donor tranny came from, perhaps I should look into this on the next rebuild go around..... guess I was going about 135mph. :happy204:

[C. Ludwig]

My gear calcualtor says 7800 with a .756 OD and 5.12 final gear gives you 143 with that tire size. I'm saying something isn't adding up there. One hell of a long straight or a serious tail wind if it's accurate. The other speeds quoted are with the 45 series Hoosiers. The 50 series Toyo is quite a bit taller and as a result faster at the same revs.

Also, if the engine is built properly and you're not having temp issue you should be fine to rev to 8500 at minimum. Keep your foot in it.

[Mike Guenther]

Did they make the GTU in 1986?

[Andy Bettencourt]

Did they make the GTU in 1986? [/b]

Why? They are all on the same spec line so you can use the tranny from any year.

[mbuskuhl]

One hell of a long straight or a serious tail wind if it's accurate.
[/b]

Very long straight... for the data junkies I've posted what I know. Information overload... I don't care, no secrets here and little to no IT in the SOWDIV, heck no other PT racers even at this NASA event. Any input can only help. So, how fast or is this a new direction for the thread?

Car - '86 VIN, 89'+ body

Track Conditions- Mid 80's, sunny, no wind (at least everyones EZ up was not moving)

Motor - S4 built by RX7.com by previous owner but only break in hours on a dyno. S5 flywheel?, Bonez intake, custom ceramic header w/ 3" pipe, FPR, etc... No cooling issues w/ Ron Davis radiator, 160 thermostat, Flatout Motorsports splitter, oil cooler, and some "creative" cooling duct work. Water ran at 190-200, Oil 190. I run fuel at 30 PSI since the FPR install. Shift light set at 7500 RPM

Dyno from 3/31/07 on a Dynojet 224X at 78 degrees outside - 30 PSI fuel, 13.63 air/fuel ratio, peak 167 HP at approx 7150 RPM - ran to 7800 RPM and had 159 HP which also was same HP at 6300 RPM. I do not know if I have a rev limiter but it sure feels like it. Anything over 7800 and it doesn't want to really keep going, maybe up to 8000 but definately not 8500. Can post dyno sheet upon request.

Rear - 5.12 with Mazda comp LSD

Tranny - unknown 5th gear as donor tranny is unknow. Bought it randomly and had rebuilt to use as primary tranny.

Tires - Toyo RA1 225/50/15 shaved

Track Picture - Clockwise racing that day - nice long turn before the main straight
http://img117.imageshack.us/img117/585/29milesi2.gif

Video: MOST IMPORTANT!
http://www.youtube.com/watch?v=AdsMY4eSAzM


Opinions and commentary welcome :eclipsee_steering: