Cascade Crew

[chevymad]

Sometimes much different profiles. In highschool I had one set of tires that were square, so the tread was flat almost from the sidewall over. 245's were 12" wide. Another set of 245s were much taller and only 10"

[Alphius]

You could probably do something like a 255 width in the front and 295 in the rear pretty easily and keep the tires tucked into the wells.

I'm not sure how the wheelwells differ between a thirdgen and fourthgen, but I had a '94 Z28 with 315s on 17x11 in the back and 275s on 17x9.5 in the front. No mods and they fit fine with no rubbing.

[QwkTrip]

I don't want to sound like I'm constantly moaning about things, but.....

I finally got a PC laptop and got the Holey HP EFI software loaded. Been looking at it and it is a stretch to say that it is a plug-and-play self-tuning system. All it does is create fuel maps for you. Everything else is up to you. I guess I will have to be a part-time tuner after all. Dammit.

Spent almost all day just trying to hunt down injector latency time for my injectors. Still haven't found it. Got a list of a hundred things to hunt down after that.

Bosch EV14
624 cc (60 lb/hr) @ 58 psi
FoMoCo B556V

[Alphius]

No tuning solution will be able to do that sort of thing automatically. Pretty much every "Self-Tuning" EFI will only do fuel tuning based on wideband AFR feedback.

You'll have to start with some values from a similar injector as close as you can get, then refine from there.
http://www.msextra.com/doc/pdf/html/Megasquirt3_Setting_Up-1.4.pdf/Megasquirt3_Setting_Up-1.4-37.html
http://www.miataturbo.net/ecus-tuning-54/how-find-your-injector-dead-time-56061/

Feel free to ask any questions here, a lot of us have done pretty extensive tuning using a variety of engine management platforms.

[QwkTrip]

Thanks. I definitely will be taking you up on that offer.

[QwkTrip]

I got a 315/35-17 tire from a co-worker for fit up. It is a full 1.5 inches wider than my 275/40 tires.

Looks like a steam roller under the car. But I must have been around too many truck tires because it looks so short! Definitely won't look right without lowering the car further. But it seems I can fit it if I get out a hammer. The front of the wheel well will need some aggressive persuasion though.

What is the basic rule of thumb for clearance needed to avoid rubbing?

[aaron_sK]

315mm is 1.6 inches wider than 275mm so the math adds up.

My very unscientific method for clearance has been to pull the springs and use a jack to cycle the a-arm/axle up to the bumpstop. Then pound 'til it doesn't touch.

It's trickier on a thirdgen though, because the panhard bar causes so much lateral movement.

[QwkTrip]

I'm guessing a panhard relocation will help reduce lateral travel. Who sells a good kit that is focused on handling and not just exhaust clearance? Seems like everybody is trying to sell it for dual exhaust clearance. I want somebody that pays attention to it actually working!

[Dewey316]

[Alphius]

The UE one'll do ya good.

[QwkTrip]

I figured out how to do reverse lockout with the HP EFI.

The key is getting a speed signal that the Holley HP can understand. It is looking for a Hall Effect speed sensor and the T56 doesn't have it. Holley HP software calculates ground speed (MPH) from the measured frequency (Hz) of the speed sensor. It needs the following to do the calculation:

* Speed sensor "Pulses Per Rotation" (PPR)
* gear ratio
* tire size

I already wired my car to provide a square wave by tapping into the cruise control signal of the Dakota Digital SGI-5c that I am using to operate my speedometer. Problem is that the output is 2000 Pulse Per Mile (PPM), while the Holley HP needs a Pulse Per Rotation (PPR) of the speed sensor. The trick is to input the correct PPR so the MPH calculation is calibrated to the PPM speed signal being fed to the ECU. Basically, I needed to create a virtual speed sensor.

Given:

Speed signal at 2000 Pulse Per Mile
3.73 gear ratio
26" tire diameter

Solution:

a) Distance traveled per tire rotation
(26 inch)*(pi) = 81.68 inch

b) Tire rotations per mile
(63360 inch/mile) / (81.68 inch/rotation) = 775.70

c) Virtual Speed Sensor, rotations per mile
775.70 * (3.73 gear ratio) = 2893.35

d) Virtual speed sensor, Pulses Per Rotation
(2000 pulse/mile) / (2893.35 rotations/mile) = 0.691

Only problem is the Holley HP software accepts only whole numbers. Set PPR = 1 and then fake the gear ratio to compensate.

(0.691 * 3.73) = (1 * Y)
Y = 2.58 fake gear ratio

Now I have a custom Input that measures MPH, and I can go set up a custom Output to operate the reverse lockout solenoid.

[Twilightoptics]

Isn't a mag sensor and tone ring hall effect? It's still creating a/c voltage.

[QwkTrip]

I think a Hall Effect sensor gives a DC square wave that switches between zero volts and some other value, whereas magnetic pick up gives an AC wave. Both have a frequency proportional to speed.

An ECM can use a DC square wave in raw form because it is basically a bunch of on-off events. An AC wave needs conditioning for the ECM to deal with it.

I might not have full grasp of this because I didn't care how things work. I just knew I had to provide a square wave so I got one.

[Twilightoptics]

Gotcha. The old school way was to wire the lock out to the brake switch. No brakes, no reverse.

[chevymad]

[QwkTrip]

I do brake and shift at the same time. Speed based is fool proof.

[Twilightoptics]

Maybe get better at shifting lol. I never had a problem. 4 to 5 is the most likely issue and up shifting with brake ? :0)

[aaron_sK]

The only possible fear is doing a 6-5 downshift with your right foot on the brake and slipping into reverse.

In practice this will never ever happen unless you are some kind of weirdo driver. The only time you ever do a 6-5 downshift in a T56 is to merge into a faster lane or when approaching an uphill stretch of highway at a low-ish speed, and you will never right foot brake in those situations. If you are downshifting for braking compression (i.e. running up against slower traffic) you will go 6-4 every time otherwise you won't get enough revs.

That said, Jon's solution is technically correct (the best kind of correct!), and if you are going to spend 20 years putting a smallblock into a Chevy you may as well do it correctly.

[QwkTrip]

Good news! I found a shop in town that will weld up my torque arm and a few other odds and ends I need done. And they will come get my car with an enclosed trailer so that I don't have to wait until May when the salt is off the roads.

[QwkTrip]