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Unread 01-06-2014, 02:59 PM
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Default Re: Vorshlag Miata LS1 Alpha Project

continued from above

You can see Ryan welding the front mounting position of the crossmember tubing at the tow hook mounting plate, which is a beefy piece of plate steel bolted to the front of the chassis with plenty of bolts on both sides. With these two main crossmember pieces in place several things were then test fit. First, 3 different LSx oil pan designs were fitted to see which provided the best clearance to the lateral tubing member that was still needed as well as clearance to the NB Miata steering rack.

Each oil pan design had some advantages and disadvantages, with the total depth of the pan's sump driving how low we could get the drivetrain in the chassis, and the front section of the pan limiting where the steering rack would end up. In the end we chose the oil pan from the 1998-2002 Camaro, which is commonly available from the aftermarket. The Holley swap pan and the GM Muscle Car swap pan both had issues that could not be overcome. Luckily we didn't have to settle on a fabricated oil pan (these always seem to leak), the GTO double-hump pan (we have used that one and do not like it) or another cut-up OEM pan. There are good baffle/trap door kits made for the Camaro pan (Improved Racing's unit is preferred) and we have a lot of miles on track with this oil pan and baffle in BMW E36 LS1 swaps.

This is our prototype front NA/NB engine swap crossmember - additional gusset plates and tubing will be added before final welding

The final LSx oil pan we picked ('98-02 Camaro) is shown above, after the lateral tubing member was tack welded in place. Two vertical tubing members were also added, welded mid-way from front-to-rear and landing on some plate steel that bolts to the stock crossmember front mounting holes (which doubles as the upper control arm inboard mounting point). This makes for a completely bolt-in tubular crossmember, with extra mounting bolts/locations, once we get it into production (we will replace the OEM tow hook tie-down plates with a new, Laser Cut plate version). It also has a LOT more room for the engine and exhaust headers, so we can develop real exhaust headers - which can make upwards of a 50 horsepower difference on an LS1 V8 over the block-hugger super shorty headers some kits are stuck with. And this crossmember could work with a LOT of other engines as well.

We weren't going for the "lightest crossmember on the market" here, as I cannot count how many lightweight tubular crossmembers I have seen bend or fail. No, we wanted the STRONGEST possible fabrication we could come up with. The .120" wall thickness on the 1-3/4" DOM tubing we used might be overkill, and we could step that down to .095" wall on a later prototype piece (we will surely make some tweaks to this design before it is ready for mass production), but when it is completed we will weigh this first tubular unit vs the stock OEM stamped sheet steel fabrication and see where everything shakes out. A crossmember is not somewhere you want to skimp on.

Throttle Body Clearance, Air Cleaner Routing, Possible Hood Ducting?

Of course before the oil pan and engine heights were finalized we tested with an intake manifold and throttle body on the mock-up LS1 engine, then tested with the stock hood in place. We had plenty of room up top, but realized that due to the short length of the Miata engine bay the intake inlet tube would have to go "over the top" of the radiator support (yes, this means we have to lose the factory hood latch). We've done this type of air inlet re-routing before, like on our TT3 Mustang shown below.

This was one of the many custom tweaks we had to do on that car to make room for a deeply ducted hood, which vented the back of the radiator and made the front splitter much more effective. This had an accidental side effect of offering a lot more cooling capacity (and front downforce) to that car, so we might do something similar on this LS1 Miata, and of course use a bigger radiator at the same time.

Ducting the Mustang's hood made the front splitter we built MUCH more effective, both for cooling and front downforce

There are plenty of Corvette style air filter housings we can choose from, which was the air filter we ended up with on our TT3 Mustang. So after the intake manifold was fitted the Miata's engine height was locked down, and the driveline down angles were set at the transmission. Next up it was time to burn in the RX8 suspension mounting points to the new crossmember...

Final Welding of Suspension, Brakes Added

Our fabricators Ryan and Olof made some steel mounting plate sections on the bench that were then fitted to the tubing and tack welded in place on the crossmember. Then the suspension was mounted up, the wheels were added, and everything was set to ride height... to re-check camber, caster, toe, and then camber and caster change with suspension travel. Obviously you don't want caster change with suspension travel, so that was dialed out.

It doesn't look like much but dozens of hours were burned getting these mounting points welded in, measured, moved, and tweaked. Mazda-sourced eccentric bolts are used at the same suspension mounting locations as the RX8, to be able to adjust camber and caster. And while some of you suspension savvy readers might point out that the upper arm's mounts aren't perfect (we wish they were about an inch higher), they are as perfect as we could make without cutting the frame out of the NB chassis or going to custom control arms. There's a lot to be said for re-using OEM forged aluminum arms, which can make for easier service and maintenance down the road. We checked the dynamic camber change and it turned out to be pretty reasonable, too. Remember: Vorshlag specializes in suspension development, so this was an area we really made sure to get right. And we could see something in track testing that might make for future changes before this kit goes into production, too.

Seeing the old front suspension and brakes on the shop floor next to the new stuff is quite a difference. We're upgrading from a 254 x 20mm vented front Miata front rotor to a 323 x 24mm RX8 Sport front rotor. Going with RX8 hubs gives us a lot of Big Brake upgrade kits to choose from down the road, if needed. This customer wants a car he can track, autocross and street drive across country - and it will have 450+ hp and sport 285mm tires, so it will have some extraordinary braking requirements for an NB Miata.

These RX8 calipers and rotors are all Centric premium units that we sourced new, so it should make for a good starting point for track and street testing. We will also add front brake ducting, at a minimum, before it sees any track testing. That makes a huge difference on most road course cars we deal with, and it doesn't cost a lot nor does it have any downsides for street driving.

What's Next?

With the front crossmember, brakes and suspension nailed down and in prototype form it is time to move to the rear suspension. The front bits had so many variables that all cross over each other, but without steering involved we're hoping the rear will go more smoothly and quickly. As you can imagine the customer is getting anxious to drive his car, and wants to run events this year, so we've got to get crackin!

None of the OEM rear control arms, brakes, and hubs will be re-used. Again, we felt that the small-ish rear hub's inner spine size would limit the power capability of any halfshaft that could be built for these cars. I've seen fellow racers shred axle after axle in LS1 equipped Miatas, and I don't want to get stuck with those limitations on our swap. So this means it all has to come out and we get to start over. Yay.

The diff housing we are using is of course the 31 spline Ford 8.8" aluminum IRS casing that was used on the 1999-2004 Mustang Cobra. This was also the same housing used in Lincoln MarK VIIIs, and steel versions were used in the Thunderbird and Explorer chassis. The new S550 Mustang chassis looks to have the aluminum version as well (we should have one of these Mustang's soon for chassis/suspension development in late 2014 and a full season of racing in 2015). All this means is these diff housings are both common and affordable, not to mention strong as an ox. Aftermarket choices abound for gearing and internal differential options, too. We also have the rear uprights chosen, which are a commonly used unit for Cobra kit cars.

The real motor needs to be installed, of course, along with the accessories/brackets and clutch system

For now we will use the OEM rear subframe to mount things to, at least during mock-up. Once these uprights and the diff housing are mounted and set at the right heights and locations, we will fabricate upper and lower control arms, check the suspension geometries, then move to the halfshafts. This will entail a lot of fiddly work, measuring and calculations, of course, but compared to the front bits (which had to have an engine, transmission, suspension and crossmember all mate up) it should be a little less work.

Until next time, thanks for reading.
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