Northstar rebuild: Will style (Page 108/119)
Will DEC 06, 03:03 PM

quote
Originally posted by copperhens:

Hey, Will!
I am curious what fuel pump you will run in your car?




quote
Originally posted by Will:

@$$uming it turns on the next time I apply juice, I have a '96 Corvette pump. It's nice and quiet, unlike the Walbro I tried in my Formula.



Revisiting this: The car has a '96 Vette pump. The EV6 injectors from the STS-V & XLR-V LC3 engine are rated at 55-60 psig fuel pressure, referenced to atmosphere. Since the '96 'Vette ran ~45 psi of fuel pressure referenced to manifold pressure, the pump isn't "rated" for the pressure required by the injectors. I'll run it there anyway and if it can't keep up, I'll upgrade to a Deatchwerks or similar aftermarket pump.
Will DEC 07, 09:10 PM

quote
Originally posted by Will:

Also, I snagged a 3.91 F40 from a '03-'04 Saab late last year... it's been kicking around the back of my van in a tote for months and months. I finally verified the ratios and dropped it into "storage" next to my '09 Saab F40 with High Feature V6 bellhousing. My aim is to snag an '07 G6 F40 and merge it with the 3.91 F40 to build The Mule's eventual transmission. The '09 Saab trans will get married up to a LLT of LFX to be ready for... something. It has MU9 gearing, so I'd love to get an MT2 0.62 sixth for it.

I was surprised to find that it looks like this box has a Torsen or similar diff.






Circling back for a sec...
This thread mentions a factory Saab helical LSD... so apparently I lucked out in that this transmission has one. Sweeeeeet!

https://www.uksaabs.co.uk/U...php?p=929894#p929894
Trinten DEC 07, 11:18 PM
That is an awesome find!!

I know there are folks out there that produce other types of LSDs for Fiero-swappable transmissions, for my money and half-educated opinion, helical is top shelf man. Congrats on lucking out with that!
Will DEC 08, 02:31 PM

quote
Originally posted by Trinten:

That is an awesome find!!

I know there are folks out there that produce other types of LSDs for Fiero-swappable transmissions, for my money and half-educated opinion, helical is top shelf man. Congrats on lucking out with that!



Thanks!

There was a Torsen for the 282 and a Quaife for the Isuzu way back in the day. There's a Quaife and OBX's bad copy of the Quaife out for the F23 right now. There's also a Quaife and a WaveTrac out for the F40 (and I *THINK* those also fit the F35).
Other than the ones I just listed, the current crop of "limited slip" devices for Fiero transmissions is junk. They are just dumb friction devices with fixed preload. The best they can possibly be is a one-wheel-burnout preventer. Preload tops out about 90 ftlbs. Because there's no mechanism to increase bias torque when the diff is transmitting torque, bias torque is also 90 ftlbs, which is very low.

Each diff is a tool with its own uses and strong points. A helical is great because it's nearly transparent and never wears out, as long as there's oil in the diff. A helical diff applies (lesser axle torque) * (torque bias ratio) to the wheel with greater grip. A basic helical diff is great for a FWD car because it has zero preload torque, so it does not affect steering at low speeds or low driveline torque. However, if one tire leaves the pavement, the other loses drive. Since the tire off the ground can take zero torque, 0 * (torque bias ratio) = 0 torque to the other tire. Bias torque (the torque difference between axles) can be several hundred ftlbs or more, depending how much torque the unit is transmitting.

A Quaife has a small spring-loaded clutch pack in the middle of a helical diff. This gives it a small amount of preload torque, so it does affect steering in FWD cars. With one wheel off the ground, a Quaife can deliver (clutch preload torque) * (torque bias ratio) torque to the wheel still on the ground. Otherwise it's the same as a helical diff.

A Salisbury/clutch pack style diff operates a bit differently. It has a spring loading clutch disks in the diff, so it has a static preload. The spec for BMW 188mm diffs is 65 ftlbs static for the production versions. Driveline torque pushes the spider gear shafts on ramps which drive the end plates to squeeze the clutch packs, making bias torque a function of throughput torque. Bias torque can be several hundred ftlbs or more in these units as well. These units are extremely tunable, as number of disks, spring stiffness and ramp angle can all be changed (with varying degrees of difficulty) to change the characteristics of the unit. The ramp angles can even be different for forward torque and reverse torque, leading to different behavior from the LSD at corner entry than at corner exit. Helical diffs can not do that.

ZF made vast numbers of their clutch pack diffs for German car makers, as well as Ferrari. These are tunable within limits. They have 2 disks per side stock, but can go up to 4 with minor machining on the case. Springs can be swapped. Changing the ramp angles requires a jig grinder.
OS Giken and a few others make very nice aftermarket versions for which one can just order expanders with the desired ramp angles... for $$$.

There are also more modern units that use electronically actuated clutch packs... Those are a lot more difficult to swap in.

[This message has been edited by Will (edited 12-08-2021).]

zkhennings DEC 09, 04:57 PM
Any LSDs exist that work similar to a torque converter?
pmbrunelle DEC 10, 12:43 AM

quote
Originally posted by Will:
However, if one tire leaves the pavement, the other loses drive. Since the tire off the ground can take zero torque, 0 * (torque bias ratio) = 0 torque to the other tire. Bias torque (the torque difference between axles) can be several hundred ftlbs or more, depending how much torque the unit is transmitting.



That limitation is overcome if the driver presses the brake pedal to give some drag to the tire that's in the air.

Isn't that a part of driver's training for Humvee drivers in the USA?
Will DEC 14, 01:29 PM

quote
Originally posted by pmbrunelle:

That limitation is overcome if the driver presses the brake pedal to give some drag to the tire that's in the air.

Isn't that a part of driver's training for Humvee drivers in the USA?



Yeah, HumVees have helical diffs and pre-loading them with the brakes is one of the tricks to getting those trucks to keep moving with one wheel in the air. The Army wanted something a soldier could "just drive" and not have to worry about putting the vehicle into the right configuration for the terrain he was driving on.... because what would be the first thing he forgets to do in combat?

Tapping the brakes for traction is generally not something that one wants to do in a fast car, however.
Will DEC 14, 01:30 PM

quote
Originally posted by zkhennings:

Any LSDs exist that work similar to a torque converter?



Not sure what you mean by that? You mean with a viscous coupling? Yes, they exist, but were never built for Fiero transmissions. My 1988 BMW 325iX has a viscous in the center and rear diffs, as do AWD DSMs. Z32 300ZXs have optional viscous LSD rear diffs.
Will DEC 20, 01:21 PM
Put the coil pack together last weekend







Didn't get any pics of the bore in the adapter, but had the first iteration of the single plate throttle adapter cut
It still had serious clearance problems. The water manifold is *NOT* in place in this photo.





Got this measurement over to Eric, who confirmed that the 8 wire throttle actually has a larger dimension than the 6 wire unit, so I won't be able to switch to improve clearance.



And this measurement was a big PITA to get.

After evaluating the fit of this first iteration of the adapter, I'm pretty sure I can make it work this way, but not this revision. The bore in the manifold is 3.120" while the edge on the throttle is 3.030". The bore in the adapter is 3.030 to match the throttle. The bore in the adapter ended up tangent to the BOTTOM of the bore in the manifold, so I can move the adapter bore up until it is tangent at the TOP of the manifold bore. There wasn't really any room to move the throttle around on the adapter; I did a decent job getting that right the first time.

I ALSO noted that if I angle the 3.030" bore in the adapter such that the long axis of the resulting ellipse is 3.120" on the adapter surface, that angle is 14 degrees. Angling the bore to offset the throttle gives me another 0.90 in a 3/8" plate. I think between moving the bore up to tangency at the top of the manifold plate and angling it 14 degrees further up, I should have "plenty" of clearance to make everything work.

However, the bolt holes are overlapping awkwardly, so I need to put some more thought into how to deal with that.

I do need to test fit with the motor on top. That's the original orientation, so it's actually "right-side-up" that way. However, I need to counterbore the adapter plate and get (cut/make) shorter M6 screws in order to do that.
zkhennings JAN 19, 09:52 AM
Any updates?