620 Rally Build

[oxfordarctic]

Alright, I'm looking to go with a full custom rally build on my '73 620 because why the hell not. Also mostly because I'm using a "free" engine out of my buddy's '97 BMW 328i.

 

Here's the main rundown:

 

- Custom engine mounts and placement (might need to adjust the firewall; not entirely sure yet until we mock up the engine)

- Custom trans tunnel to fit the 5 speed ZF

- Custom fully independent suspension with loads of travel

- Sloppy turbo build based around a Garrett ball bearing; not entirely sure how big of a turbo yet

- Basically make a stupid rally build probably making upwards of 500whp on the "incredibly-ridiculous-and-probably-shouldn't-be-a-thing" tune map

 

I know this will be a crazy money sink and whatnot, but that's not why I'm posting here. All I need to know is really a few things and to update on the progress of the build; albeit very slow progress.

 

Thing #1:

What steering rack would benefit me most in this setup? Guessing is welcome here, I'm just trying to gauge possible options.

 

Thing #2:

Rear end ratios. This poor 620 came with the 4.87 diff and I'd rather not keep it. I'm thinking maybe something along the lines of 4.23? Suggestions on what vehicles to rip a diff out of to frankenstein into this ungodly conglomeration of stupidity.

 

Thing #3:

Axles/wheel hubs. Also would like suggestions on what vehicles to tear apart and force onto this idiotic death trap.

 

Thanks for taking the time to give input. If you're here just to see how this ends up killing me, welcome aboard.  :frantics:

[banzai510(hainz)]

If the 620 is running already then just leave it.

 

Why waist money doing this when you can buy a better rally vehicle almost already done.

Just because motor is FREE is not a good idea. Seen this idea never get to the finnish stage

 

 

Buy a Ford Ranger 4x4 cheaP

[oxfordarctic]

The 620 is just a shell. And as I stated in the post, I know this will be an expensive project but I'm doing it just because I can. So telling me to not "waist money" doesn't help.

[Stoffregen Motorsports]

I'd love to build a 620 rally or desert truck. Sounds awesome.

 

You may consider a Toyota 4x4 rear axle right out of the gate. Gear ratios are more plentiful and very cheap. Lockers, limited slips, axle shafts, disc brake kits, etc are all relatively inexpensive on a Toyota axle too. Depending on the width you desire, I would probably start by looking at a '87-'95 rear axle. It should be about the right width and it's a lot stronger than the earlier housings. A Tacoma housing can also be used, but they are a bit wider still. Be careful choosing a Tacoma housing as the most prevalent out there has a 8.4" diff, which is harder to find parts for. You want the regular 'ol 8" diff.

[oxfordarctic]

I'd love to build a 620 rally or desert truck. Sounds awesome.

 

You may consider a Toyota 4x4 rear axle right out of the gate. Gear ratios are more plentiful and very cheap. Lockers, limited slips, axle shafts, disc brake kits, etc are all relatively inexpensive on a Toyota axle too. Depending on the width you desire, I would probably start by looking at a '87-'95 rear axle. It should be about the right width and it's a lot stronger than the earlier housings. A Tacoma housing can also be used, but they are a bit wider still. Be careful choosing a Tacoma housing as the most prevalent out there has a 8.4" diff, which is harder to find parts for. You want the regular 'ol 8" diff.

 

Appreciate the input! I'll start my search with the 4x4 axles. Depending on the width, I could probably just swap the whole rear axle, hubs and all, right?

[Stoffregen Motorsports]

Yes, the whole thing.

 

A donor Toyota axle will set you back anywhere from $50 to $1000 on Craigslist, depending on what parts it's got, but if you want to find a stock one, try looking here - http://www.car-part.com/

 

I use that website all the time. It's a database of all the wrecking yards across the country.

[]2eDeYe]

Look for one from a 96ish 4runner, they will typically have an electronic locker stock. 

[Stoffregen Motorsports]

That would be the TRD package. Prerunners and Tacomas came with that axle too.

 

I have DIY wiring schematics for the electric locker if anyone is interested.

[UnderControl]

Based on very limited research 500hp is pushing your luck on an unopened 2.8. That said GT35s seem to be the preferred turbo although I'd venture to say a GT3076R would be a good fit. The 30 is rated to 525 and would spool almost instantly on a 2.8. Step up to a GTX30 and power rating goes up a couple hundred hp without sacrificing spool.

[oxfordarctic]

Based on very limited research 500hp is pushing your luck on an unopened 2.8. That said GT35s seem to be the preferred turbo although I'd venture to say a GT3076R would be a good fit. The 30 is rated to 525 and would spool almost instantly on a 2.8. Step up to a GTX30 and power rating goes up a couple hundred hp without sacrificing spool.

 

Yeah, the 30 series would definitely be a minimum for this build. I've got a GTX3071R single conversion on my Toyota Chaser which is rated for 650hp max, so probably something along those lines for the turbo would be what I go with. The 2.8 is getting cams and ITB's - despite them being kind of a pain to tune with a turbo setup, and of course the basic upgrades for this build such as mhg, arp head studs, injectors, fuel lines, etc.

[Lockleaf]

Why go for the additional expense and effort of itbs at that point? I've always understood them to shine NA but not change much once under decent boost.

[oxfordarctic]

Why go for the additional expense and effort of itbs at that point? I've always understood them to shine NA but not change much once under decent boost.

 

Yeah, the 2.8 flows well with an M50 intake manifold, but the ITB's provide even better airflow which is important when trying to run higher amounts of boost. The internals and block can handle quite a lot of psi and power, but the oem style intakes can't always keep up with the airflow needed. The older BMW straight 6's are great engines, but they don't have a lot of output NA, so boost is really the only way to break even the 300whp mark.