1985 Monte Carlo SS assessment

[kevm14]

Another thing is making the rest of the gauges work. Which isn't that important right off the bat. Some of the sensors may be the same (coolant, oil pressure) so maybe it won't be too big of an issue.

Let's see...

Speedo, either a JTR type VSS/cable conversion thingy, or this: http://www.dakotadigital.com/index.cfm/ ... prd886.htm

It also sucks that the speedo houses the odo.

Fuel...0-90 ohm most likely, and obviously driven from the sender directly.

Volts: pick that up anywhere.

Temp: Will need to research to see if the LT1 sensor (driver's side head) has the same resistance curve as what the gauge is expecting. It just may. If not, you get the one you need and thread it in.

Oil: same deal as temp. Make sure LT1 sender has same resistance range. Switch to the sensor that you need. Probably not a big deal.

Tach: LT1 is PCM-driven, and I think the tach signal can be modified. Need to verify that, so I wouldn't worry about this, either. Worst case, you get this: http://www.dakotadigital.com/index.cfm/ ... prd127.htm

[kevm14]

More tach research:

The signal from the PCM to the tac is 4 pulses per revolution DIGITAL signal

Ok so a converter is probably needed. The Dakota Digital one was fairly reasonable ($85).

But the BEST part of that converter is this compatibility warning:

Product not compatible with '86-91 VW Vanagon's and other similar models

[kevm14]

That would have increased grip though, to Kevin's point, and I still didn't hear about Monte's blowing the rear even with posi.

That is why many swapped cars actually do fine with their original diff if you don't abuse it. You aren't actually putting more torque into it than you were before, assuming the previous drivetrain had the ability to spin the tires.

But when you put slicks on, and launch off the trans brake on a prepped track, on boost, well, that's an entirely different thing.

Think of the peak torque even a weak engine like my L05 can end up putting into the rear axle. 300 lb-ft * torque multiplication from the converter * 4L60 1st gear (3.06) = 2,020 lb-ft out of the trans, through the driveshaft and into the pinion, and multiply THAT by another 3.42 (diff ratio) and you get up to 6,900 lb-ft @ the axles, at launch. The torque multiplication through the converter diminishes rapidly after launch, meaning 920 lb-ft into the pinion and 3,140 lb-ft @ the axles post launch. Still quite a bit.

The point is, wheelspin occurs before these peak numbers and therefore, the only thing more torque will do is accelerate the axles (inertia being the only transient extra load, and dynamic friction being less than static so that may somewhat cancel out).

[Adam]

So staying with the 7.5" and upgrading the carrier to a POSI unit (which replaces the weaker spider gears) should be safe enough until I want 1.5 second 60' times.

[kevm14]

That's my assessment.

[Adam]

/thread?

[Adam]

Also, that Dakota Digital speedometer thing is amazing.

[kevm14]

Yeah, its cool that they make that. The RPM of the speedo cable isn't nearly as fast as you'd think, also.

I want to say the old mechanical GM speedometers were calibrated to 1,000 rotations per mile, and the drive gear on the trans output shaft drives the (much greater toothed) driven gear on the speedo gear.