As I progres during the build I'll learn quite a bit in terms of do's and don'ts and I hope that the info here will help budding builders.
| Chassis | Engine | Transmission | Steering | Electrical | Induction | Guages |
| Fuel system | Pedals | Suspension | Wheels & tyres | Bodywork | Racing only | Driveshafts |
To make the build easier, it's far more convenient to have the chassis on a movable dolly. The design shown here is constructed to factory specifications:
Cutting list - all 2"x2"/50x50mm 16g Box steel unless specified:
Bracketed colour key relates to diagram. You get all the elements you need from two 6m lengths (standard supplied length for 50x50 box section steel).
You'll also need four ML384-1 swivel & brake castors from Machine Mart or similar. They're polypropylene wheels with a plate size of 79.4 x 104.7 and can withstand a 102kg load (per wheel). Order code is 051320095 and they're 4.69 each.
Whilst it's conceivable to put almost any engine in an Ultima, the facotry specification uses a Chevy, so that's what I'll deal with here. There are several UK suppliers and builders out there, but I'd presonally recommend (as do the factory) American Speed in the US to supply a 'turnkey' unit for the Ultima. American Speed have supplied many engines for Ultimas, GTR's and CanAms and know their stuff. More importantly, they know what'll fit - including all the ancilliaries. I know that some people are concerned that importing an engine should something go wrong? Well, being factory recommended and supported, most issues can be resolved by Ultima with parts being shipped in 24 hours. Anything major (under warranty) of course will mean a trip back to the US. But, given the price differential between a UK supplied engine and a US one, you could afford many trips before there was a parity between the two. For example, a fairly stock .350 from American speed will set you back around 4,000 GBP, whereas I've heard of the same engine in the UK coming in at 7,000.
With this in mind, the most common question I get asked is 'How do I go about importing one and how much does it cost?'. This is in fact, far simpler than it may seem. In fact, American Speed do almost all of the work for you, organising crating, shipping etc. You just need to tell them which airport you'd like it sent to. As far as cost goes, you'll have to pay import duty/VAT on top of the shipping on the declared value of the goods. If you are VAT registered, you will be able to claim this back. If not, you will have to apply for a Psuedo TURN. The shipping agents handle all of this and will simply send you a form which you fill in and send directly to HM Customs & Excise. The Psuedo TURN number comes back very quickly (same day in some cases) and with this, the handling agent can process the delivery. You can now either pick it up from the airport (not recommended unless you've got a tail-lift van) or have it delivered.
In short, adding the cost of crating, shipping, import duty and VAT will add about 1,000 GBP to the cost of the engine. Still a saving of 2k over the UK equivalent!
There a two variants of a G50; "long" & "short". The "long" box as the name suggests is longer and will stick out the back on a Sport or Spyder. The "short" box has a transverse mounting at the rear and as the name suggests is slightly shorter.
Porsche changed the design of the release fork in 1988. Pre. mid 1988 the release fork had needle roller bearings inside it ran on a 15mm dia bar. The release bearing guide tube was 34mm dia. After mid 1988, The release fork (now PN 950 116 712 3R) was revised to run on an 18mm dia bar with the bearings in the box at each end of that bar. It is possible to have the box modified by 930 Motorsport, Warrington who have the facility to machine out the 15mm hole to 18mm to accept the new bearings (cost about £100). Also the release bearing guide tube is now 32mm dia. If you do buy a clutch separately, it is a simple matter of modifying the box. TIP: When fitting the box to the engine, tie the release fork to the release bearing using an elastic band. This will hold it in place and allow you to get the pivot bar into the box and will be lost when you start the engine
Always buy a box complete with:
These bits can be expensive to replace.
1987 911 G50s have an 8 digit code stamped in the bottom, for example 'G50/0073H'_'12/00050'
Transmission types:
Visit Powerhaus II for alternative gear ratios for those that want 200mph!
Gear |
Transaxle | 1 | 2 | 3 | 4 | 5 | Notes |
| G50/00 | 3.5 | 2.059 | 1.409 | 1.074 | 0.861 (after 1988 0.868) | Final drive ratio 9:31 | G50/01 | 3.5 | 2.059 | 1.409 | 1.125 | 0.889 (after 1988 0.892) | G50/02 | 3.154 | 1.895 | 1.333 | 1.036 | 0.861 (after 1988 0.868) | G50/03 | 3.5 | 2.059 | 1.407 | 1.086 | 0.868 | G50/04 | 3.154 | 1.895 | 1.333 | 1.029 | 0.868 | G50/05 | 3.5 | 2.059 | 1.407 | 1.086 | 0.868 | Final drive ratio: 3.333:1 | G50/10 | 3.154 | 1.895 | 1.407 | 1.086 | 0.868 | G50/50 | 3.154 | 1.789 | 1.269 | 0.967 | 0.756 | Beefier internals, differential cover, and case | G50/52 | 3.154 | 1.789 | 1.269 | 0.967 | 0.756 | Not as strong as G50/50 |
Transmission and Clutch Overview: G50
In 1987, the G50 gearbox was installed into the Carrera 3.2 911. This transmission used Borg-Warner syncromesh instead of the Porsche-design balk-ring system to improve the shift quality and lessen the effort required to change gears, especially from a stop. These gearboxes were rated at 221 ft/lbs of torque. The G50’s have been utilized with several variations of gearing and speeds. The 993 series was the first 911 offered with a 6-speed version of the G50 design. These later units also introduced significantly improved clutch cooling.
Other versions of the basic design, called the G50/52 series, were used in the 3.3 C2 Turbo and 3.6 C2 Turbo cars. These transmissions also have stronger differentials and cases and a type of Limited Slip differential that locks 20% under power and near 100 % on the overrun to minimize trailing-throttle oversteer. All of the G50 cars use the 240mm clutch size introduced on the earlier Turbo cars and they are now hydraulically actuated.
Ring & Pinions and Limited Slip Differentials
In order to fit a compact transmission with the requisite features in the 911, Porsche uses very steep hypoid angles on the ring & pinion gears. This make these parts, the most highly stressed part of Porsche transmissions. This requires a GL-5 rated lubricant to protect these components against premature failure. Ring and pinions are problematic areas of these transmissions and require careful setup for any G50 used for competition or high-horsepower applications.
Porsche also offered several other ring and pinions for racing including 7:37 and 7:33 ratios. These are not always available due to limited manufacturing qualities. The G50-series used a final drive ratio of 9:31 and the Turbo versions, G50/52 used larger, stronger ring and pinion gears.
If you do decide to change the ring and pinion in your gearbox, make sure that you get the appropriate one for either the mechanical or electronic speedometer.
Porsche has offered the ZF clutch-pack type limited slip differential in almost all 911’s and 930’s since 1966. These units are quite strong and can be set for locking factors of 40% to 80%. The clutches need replacement under racing conditions to maintain proper lockup but these are quite trouble free. An 80% locking factor is difficult to drive on the street, especially in wet conditions, but for open track racing these are quite popular. Street or Autocross usage requires the LSD to be set at 40%; simple to do with the proper parts.
There are now other LSD options for G50 transmissions called Torque-Sensing differentials. These are gear-type units as opposed to the ZF clutch-type ones, and do not require any parts to maintain optimum performance. This unique, patented design allows full differentiation between the wheels as well as providing power to both sides and they produce less understeer than the Factory LSDs. Guard Transmission makes an excellent one as well as the unit from Quaife.
For Autocross and normal street driving, the Torque-Sensing units are more benign in their operation but they do not improve the handing like the Factory clutch-pack units do. The ZF or Guard Transmission LSD's really stabilize the car under braking and help reduce trailing throttle oversteer.
Transmission Modifications for Improved Performance
One of the first things an builder wishing to improve the acceleration of their car should consider is changing gear ratios. The wide gear ratios used by Porsche are a result of designing for street drivability, fuel economy and emissions, not best performance!!
A close-spaced set of gears in any car adds an "effective" 50 HP to the acceleration potential. Reducing the RPM drop each time you upshift keeps the engine in the most productive parts of the torque curve. One must experience this to fully appreciate this effect.
There are several options for shorter gear ratios depending upon usage, tire size and ring & pinion ratio. There are even computer programs that will help you select the proper gear ratios.
G50 Transmission Modifications
These transmissions as used in the Carrera, C2/C4, C2 Turbo and 993-series cars are more expensive to buy gears for, compared to the 915 and 901 units. The availability of gearsets is very good with these units. Porsche’s racing program and the availability of high-quality aftermarket gears make these transmissions very attractive for street & racing applications.
When used with very high torque engines and large rear tires, the ring and pinion assemblies are prone to premature failure. Differential side cover deflection and undersized ring and pinion gears for the power levels are responsible for transmission failures not generally seen in Porsches used for endurance racing to such a degree. Auxiliary cooling and pressurized lubrication systems are necessary in these applications with this transmission. The G50/50-series is probably the strongest of this generation of gearbox although these are 5-speed units.
The Rennsport website has a picture of a G50 6-speed transmission that was extensively modified for the Daytona 24 hour race. This gearbox was used in a 993 3.8 RSR that finished 12th overall and 4th in GT-3. The pressurized lubrication system in the photo provides cooled oil to all gear sets and the differential. This unit also was equipped with a special side cover and custom-made 4th and 5th gears. Needless to say, this was not an inexpensive enterprise due to the number of hours required to accomplish it.
Lubrication Issues
Oils are always a subject of opinion and controversy. Everyone’s opinion is based upon personal experience. G50-series trannys really work well with a full-synthetic gearlube like Mobil 1 or Redline. The Borg-Warner type syncros work better with a real slippery oil. Generally speaking, transmission additives are not recommended besides the LSD improvers sold by GM dealers for the times that you need to eliminate LSD-clutch chatter.
Other gearlubes might be just fine too, but caveat emptor.
I have just touched on this subject. Consulting a gear chart for your transmission will show you what your gear splits are and what you can change. Not all of those gearsets are always available so factor this accordingly. Setting up a transmission for racing or even aggressive street use may be best left for professionals due to the component costs, special tools necessary, and the consequences of a small mistake. Ring and pinions require a special fixture to set the depth and backlash properly.
Since changing gearsets can make a stock engine much more fun to drive, this should be near the top of your performance modification list. Installing a set of close-ratio gears is the equivalent of adding 50 HP to the performance of the car.
Further information can be found at the Rennsport site.
Additional thanks to Mark at Adequatespeed for the info.
The steering system is pretty straightforward in the Ultima, thanks to a solid factory design. Provided you've got the rack mounted the correct way up then you should have few worries
However, like all things with the build - 'if a job's worth doing' etc. - it pays to check that it's working at its optimum, rather than just slapping it onto the chassis. It's a lot easier to do it early on in the build than trying to rectify handling problems later on!
Anyway, with this in mind. The factory recommends further 'fine tuning' by doing the following:
I found it invaluable to fully familiarise myself with the loom before attempting to fit it to the chassis. Take time to 'tag' up the many connections with a description of what each one is for.
Take time to plan exactly what you're going to need for your electrical requirements. Fog lights, cigarette lighter (power for mobile phone/radar detector etc.) and where you're going to place them. You may have to make up sub-looms to extend the wiring if you're going for a non-standard dial layout. The Stack instrumentation that I used required a fair amount of loom reworking to get the various sender readings back from the engine bay. Remember, there's nothing to stop you from using the original wiring in the loom that was made for this purpose, rather than having to use the Stack wiring loom. Make sure any connections are properly made and secure. Protection from the elements and corrosion is advised too. I crimped, soldered then re-crimped and used shrink sleeving on mine! There's nothing worse than chasing down a problem that's caused by a dodgy connector.
Finally, if you're going to use an electrical cut-off switch (advisable from a security point of view as well as safety), then plan the location of the switch and the associated feed cables before you get too far into the build. Don't bother with the crappy cheapo jobs that cost a fiver and just cut the battery feed, the engine can still run from the supply from the alternator. A pukka FIA job is worth the extra cash, as it cuts the coil feed too which will kill the engine.
Ah fuel. Well firstly - what to use? Well, the shortest answer is to use the highest octance fuel you can get your hands on! In the UK this means Shell Optimax. Not only will you be getting a bigger bang (and bill!), but it will reduce the possibility of pinking (pre-detonation of the mix in the cylinders) in warmer weather. This is especially important as some installations can run quite hot.
Next up the tanks themselves. These have a combined capacity of about 80 litres which is good for err.... some miles ;) Range is dependent on the engine, but this certainly isn't an Eco-car!!! Make sure you protect the exposed faces of the tanks against abrasion from road debris. I used a thick stone-chip paint to deflect the worst of it. Take care to seal the edges properly where they come close to the sidepods as a stone stuck between the tank ally and the GRP could puncture the tank.
Finally, fuel pumps. This has been cause of much debate in the Ultima fratenity, but the best advise I can give is to STICK TO THE FACTORY RECOMMENDATIONS! The factory supply Carter pumps which pump something like 66 gallons of fuel per hour. That's a LOT of fuel! I have a fuel pressure sender on my Supercharger and even with full throttle, there's plenty of fuel pressure to keep the carb bowls full. One thing to be careful of is the flow rate of any filters you may put in the system. Make sure they're high flow otherwise they'll constrict the supply. I use a twin pump setup with one pump per fuel tank feeding into a central 'T' junction, this then flows through a high flow filter and on to the carb. Both feeds have one-way flapper valves to ensure that if one pump fails, the other can't then pump directly into the other tank potentially causing an overflow.
There are basically three routes to the guages and it's very important to decided up front which tpye you're going for as it affect the loom runs which have to be made before the body goes on:
I'll deal with these one by one.
i) By far the most straightforward is the factory setup. You can go with this system safe in the knowledge that the loom will mate directly with the dials and that the senders will be matched and should bolt straight on. The only downside (if you can call it such), is that the main dials are offset from the drivers point of view, being positioned in the centre of the dash. Everyone who has them seems quite happy with this, but a habit from my racing days menat that I prefer having the info. directly in front of me leaving me to concentrate on the road. Still, they're good quality, look great (Ultima logo'd) and do the job.
ii) You can of course source alternative guages elsewhere if you're on a tight budget. But, the Ultima clocks aren't expensive and unless you're on a mega-tight budget, people will expect to see either the Ultima items or a Stack installation (as per the factory demo) in the car. Remember, 1st impressions count and prospective buyers (should you sell it) will look for these.
iii) This is the route I took for a couple of reasons. Firstly, it means that all the information I need is presented directly in front of me. Second, I can easily 'scroll' through various readings and parameters can be set so that I'm warned early of potential problems (low oil pressure, high water temp., low fuel pressure etc.). The only real pain is that you'll need to mate this system up with the Ultima loom. Well, I say that, you can of course run the Stack loom back into the engine bay (where most of the readings are taken), but you've then doubled up the wiring and made the half of the original loom runs redundant! You'll need to order the correct thread type for the senders (NPT) and you'll almost certainly have to buy a 1/8" NPT tap as well as some sleeve-down bungs for the senders depending on your head design. Of course, this technology ain't cheap, but given the range and control you have over the readings I felt it was a worthy investment. Now that the factory make an excellent GRP pod for the Stack ST series, it makes even more sense.
iv> Purely for the die-hard devotees or electronically gifted. Whilst it stamps the builders 'personality' on the car, future owners may be put off by a bewildering array of readings/technology, that they'll never be able to get support for should things go wrong. I'd avoid this one like the plague.
Not a huge amount to say here that hasn't been said above in the gearbox section. However, I will mention oil. For G50 'boxes, use 3.5l of semi-synthetic 75-90. As far as LSD goes - do you need one? Well, that's an unanswerable question. LSD's on G50s aren't that common. You could fit a Quaiffe ATB to a standard 'box, but you're looking at around a grand (1k GBP) for it. Best bet is to learn better throttle control!
A couple of tips here. Firsty, before fitting the ally panelling to the cockpit floor, us a drill to clean the powder coating from the pedal mounting holes! It's a pain to do it later on. Next, despite what it says in the manual, fit the pedals in the following holes:
This is especially important if you are fitting a cable operated brake bias adjuster. Otherwise you'll have problems with the cable fouling the throttle cable.
Well, more specifically: geometry. Whether using the Intrax setup or the cheaper Avo units, make sure you take time setting up the geometry with the ride height bars before getting too carried away with the build. Again, time spent here could save you a good deal of grief later on. If you can get access to tracking/castor/camber guages then so much the better.
My only advice here is to go with what you can afford. To my mind, wheels can make or break the looks of the car and the Ultima design is not only spot on, but strong too. You pays your money and you take your choice. With 13" rims at the rear, can you really afford to save a few quid and have them collapse at the first sign of a pothole?
Whilst there's no reason that you shouldn't fit the bodywork yourself, for the relatively small cost, I'd get the factory to do the prefit at least. The fit and finish of the shutlines etc. play a vital role in the perceived quality of the final car and the factory's experience of fitting dozens of them is always going to outweigh your own best efforts. Still, it's a rewarding part of the build should you wish to do it. There's still plenty to be done after the prefit stage, but having the basic body properly lined up helps immensely. I used a good quality stone-chip paint to seal the inside of the GRP. This helps cut down the smell as well as protecting it. You'll find it has a positive effect on the gelcoat colour too, making it much richer.
A couple of builders have tried alternative driveshafts from the GKN Motorsport ones supplied by the factory. I know that these have failed whereas I've not heard of any factory supplied shafts giving problems. They're allegedly rated to 1000bhp so all but the maddest installations should be quite safe from harm.
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