The discrepancy could be due to stock tach lag, because my speedometer is on. GM doesn't make the most accurate tachs, that why Im looking into a shift light. I found a calculator for this question http://www.f-body.org/gears/. It shows 85mph @ 1900 rpm..I'm getting 1800 prm @ 85 mph and it says 103 mph at 2300 RPM. Like I said, haven't gotten up that fast again to double check my readings. Makes me miss living in the middle of nowhere. Even with this data, its still shy of your "83-84 mph at 2000rpm in 6th " numbers. Like you said, the math doesn't lie. Guess either your tach or speedo is off too.

Even with all that, try running low 13's (stock), getting 18-26 mpg, and running RPMs like those in an old big block (or even a small block). Thats why I got rid of the 70.

 

That's exactly what I'm doing in my '80. Of course, the engine isn't stock, but even the carbureted 350 has plenty of torque to move me along in 6th. 18-20 on my in-town commute, 25mpg highway. That was the whole reason for the T56 swap (which I did in the spring of '95).

Note that the calculator doesn't tell the whole story. a 275/40/17 will be 25.66" tall, just on calculation. However, with the weight of the car on it, the "rolling diameter" of the tire is smaller. Tirerack.com has rev/mile info on most tires, and I find them to be accurate (since it is loaded tire data from the manufacturer). For the Goodyear Eagle F1 GS (the tires on my, and likely your, car) 275/40/17, that's 811 revs/mile. Plug that in, and see what you get.

 

Your calculations are based on things being perfect. That the problem with basing everything on math, there are variences in the real world and if you don't consider them your math is off. When you get to taking measuerments to a hundreth of an inch, there are many variences. Tread wear, that'll give some varience. Especially at that level of measurement. Inflation pressure will affect diameter also. You say your speedo was checked by radar, but radar isn't extremely accurate. It has to be tuned, it can reflect off other surfaces, etc. Thats why most decent police departments give you about 5 mph leeway on speed.

Don't believe me. Go hop in an M6 4th gen and see what RPM they run at those speeds. I'm NOT turning any higher than 1900 RPM at 85 MPH, actually its just barely above 1800 RPM.

I still don't see what this has to do with getting a 327 running w/an LS1 car.

 

im sick of seeing this post i want it gone!.

its not hard to make a car beat a ls1 just put your @$$ in to it.

 

Iagree and I started it