Rear diff can only transfer as much preload as it has (plus potentially some load gains from the ramps) but its much more limited than tire on the ground. Something needs to give the diff to bind against. This is why I have such an aggressive rear diff, I want to get on throttle really early even while my rear tire is in the air. If I have 100ft-lbs of preload, then I can transfer that much torque which is enough accel to get the weight transfer and plant the wheel.

If you dont have preload, then its just going to spin till it touches ground. And a fast wheel that all the sudden sets down is not good.

For front diff, its easy to spin up the inside front. A torsen diff works ok but its still very little torque to bias when you need it, and once it spins the center starts doing funny things. A good clutch front will have minimal preload cause you have the tire on the ground (if you dont, you have other problems) and be a 1way to be as free as possible when turning. That last point is where you really feel the difference against the torsen. But also with enough power, not lighting up the inside front is a big gain. Both AutoX and Track cars are gaining from 1way clutch front.

 

1-way clutch type in front for sure.

re: the preload on the rear diff - i'm not sure i follow. are you saying the rear diff can only lock up to the point of how much preload it has? otherwise, if the ramp is pushed far enough to the point where the wheels are 100% locked, then doesn't what I was thinking hold? All torque goes to the wheel that is putting power down? i.e., if the diff is locked, both wheels must turn at 50mph. If it takes 30lbft of torque to turn the wheel in the air at 50mph, and both wheels are locked, then the wheel on the ground should get the 270lbft, on a 300lbft torque car? maybe (probably) not completely understanding where in that interaction preload would come into play

 

If you have 30ff-lbs of preload on the rear diff, then thats all you can transfer between the two when one is in the air (plus I think the gain on the ramp angles, but not 100% sure on that). So if you have no preload, you'll just spin the tires, if you have 30ft-lbs you have something a little over 30 the rear can do before it all goes to spinning the inside. On my car its 90-100 ft-lbs of preload.

 

Sounds like : think engine torque on a dyno sheet. once the differential sees more foot-pounds of torque than the preload (plus possible ramp) you're going to spin the wheel that's in the air.
IF so, theoretically, if a 300ftlb Car had a 300 foot pound preload, it would never spin a tire.
if I am understanding this correctly.

 

so the diff can only lock the amount of preload it has? the "gain on the ramp angles" is a pretty big asterisk though isn't it? That's where all the locking action is to push the clutches together to actually lock the diff

 

Ramps are definitely part of (if not the dominant factor) the equation for how much power you can apply with one wheel in the air. You need enough preload to support enough torque to drive the ramps to full lockup.

 

This is what I assumed. With zero preload the ramps just aren't going to do anything and the standard evo rear difff with the cone washers wears down pretty quick and the preload fades quickly. But I definitely felt the front diff going bad more than the rear diff by way of corner exit understeer.

 

ok i think this makes sense to me. enough preload to push the ramps to lock the clutches. once the clutches are locked, and the tires lare locked, the wheel in the air should get the preloaded amount and the wheel on the ground should get the rest? it shouldn't matter too much i guess at that point, since it should touch the ground not long after the power is applied

 

if they are locked, aren't they are powered equally?

 

that's not how i understood it. they go the same speed, ie 50mph but if a wheel is in the air maybe it only takes a marginal amount to go 50mph since there's no ground resistance.. if it only takes ie 50lbft to go 50mph on the lifted wheel, wouldn't the rest have to go to the other?

 

Here's a though exercise, Imagine you have a hypothetical strain gauge on the axle to measure torque. How much strain (directly relating to torque applied) do you have in various scenarios.

If you have a wheel in the air it can put down zero torque. The act of it spinning up will use up torque (torque = inertia * radial accel) but power transfer to the ground isn't completed. So technically, all torque that goes to the rear with a locked diff and one in the air must all go to the one that can apply torque. But its sort of irrelevant, its going to do what its going to do.

 

so all of the torque in terms of work will go to the outside tire, technically, because torque = force * distance? i guess i'm wondering in terms of power shuffling how the mechanical will behave

 

I've been doing my homework on fuel systems to convert to an E85 set up that will accommodate a larger turbo (500-600 whp range).

I'm thinking of running a Walbro 525 single pump (any reason to stick with 450?), but running the power wires for the pump through a bulkhead fitting rather than using the stock plugs/clips inside the tank, which I worry about melting with steady WOT usage on track. I'd keep the stock connector in place for other functions, like the fuel level. Outside the tank I'd splice in a rewire kit into the power wire for the pump, triggered by a Hobbs switch to supplement the factory voltage under higher boost conditions. I think this is the simplified dual voltage mrfred approach, if I understand it correctly. I'd also splice into the factory harness a similar gauge ground wire to the chassis. In order to run an inline filter on the pump side, I'd run STM's -6AN feed line kit from the pump to the stock rail and splice in an E85 friendly 10 micron filter. I'd keep the stock rail, stock FPR and stock return lines. Because I'm always worried about fire, I'd cover the feed and return lines under the hood in Aeroquip fire sleeves.

I also will install a fuel pressure gauge and 5v pressure sensor on the feed side of the stock rail.

Does that sound like a good plan? Will the Walbro 525 not overrun the stock FPR when running stock wiring for power at lower boost? Do I need to do the 9/64" drilling for the siphon?

Thanks for any advice.

 

The walbro 450 will run out at around 580-600whp with 1650 injectors depending on the setup. The 525 will flow enough that the injectors become the limit around 615ish. That sounds like you have the right idea for wiring, you can have the hobbs switch set to come on at 5-10psi of boost. Except the ground, just make that a dedicated 10ga ground wire; don't worry about the factory ground wire or anything.

Both the 450 and 525 over run the regulator, even with the siphon drilled to 9/64 (drill siphon required with either pump). It's easy to tune around because higher pressure at ultra low (idle and cruise) pulse widths actually makes bigger injectors act like smaller injectors and makes them more consistent. The two cars I have running ID2000's actually idle and cruise better with 55psi base pressure. So it's not really a concern.

I would replace the OEM rail with an AEM or other drop in replacement for the factory rail, it has more volume and will help maximize power availability for a given pump/injector combo.

Also, the 450 and 525 go int the stock housing without modifying or deleting the factory filter assembly, so there's no need to run an inline fuel filter.

Good idea on fire/heat sleeve for the return line. I would also replace those hose sections with new, STM can you the correct Gates hose to replace it with it.

Hopefully that answers everything for you.

 

Watching the new Speed Academy video of them putting a G30-660 to upgrade from their G25-660 the lag on it seems pretty miserable I know its a hub dyno but showing 300ft-lbs at like 5200 rpms which was 900rpm slower. So even the G25 waw 4300 and the smaller turbine only making low 400s. Wonder what that translates to dynojet? Either way is that just what subies see?

Are we just spoiled with short runners to get low 3ks to 300, 500hp, and 8k reving? Seems like a hard sell to ever build a suby with that weak potential

(Slight trolling, still not very impressed tho)