Hey, new guy here.  I am a Spitfire guy although it has been many years since I have driven one.  For 20 years I have had a nice Toyota 4AGE Blacktop sitting in my garage and now I am going to put it to use.  I recently bought two 1979 Spitfires and between them hope to get one running sporting the 4AGE and 5-speed trans.  I know the rear diff and axles won't be up to the task so I have been working on a solution to provide a 4 wishbone transplant with a heavier diff.  I want something that has enough strength to accept a turbo V-6 if, at a later date, I decide to go that way.

So far here are units that I have considered; Miata, Subaru, BMW, Audi, 240Z, Mustang with an 8.8 diff, and custom home built.  Most of these are assembled in a factory sub-frame which can drop out as a unit, which is attractive.

The first hurdle I need to resolve is how to fit one of these units into the rear of the Spit' when the track on a larger car can be up to 10" wider.  And a second hurdle is that most of these use McPherson struts by design and adapting short coil overs can be challenging.

Width or track can pretty easily be done by cutting and rewelding the shortened axles if they are tubular.  The downside of that is as the axles get shorter it of necessity moves the A-arms inboard and toward one another.  It seems to me that this would provide less stability as the whole subframe would need to be narrower then.  Another factor is that smaller-width suspension assemblies come from smaller cars which use more fragile differentials and axles defeating two of the purposes of the swap in the first place.

So I am in a quandary as to what to do.  What is the best option for grafting an existing rear sub-frame assembly to a Spitfire rear end?  It looks like a Frankenstein would have to be created.

Randy

Check out my article on the 7.5 Toyota differential here:

http://forum.britishv8.org/read.php?3,22861

Jim, your article on the 7.5 Toyota makes me wonder if a Cadillac CTS diff might be an option, as well.  It appears to be about the same size and is available in a number of ratios, as well as in a locker version.  They are quite common in junk yards--and while not the strongest casting (it's aluminum and had to be upgraded for the CTS-V), it seems that for something light like a Spitfire, it might be an interesting option.

One option you didn't mention is the C4 Corvette rear suspension. I use that suspension at full width in my car but it can be narrowed fairly easily by shortening the half shafts and lower arms (camber rods). If you look at the video at about 3:10 in you can see how he narrowed it to work in a Bug Eye Sprite. https://www.youtube.com/watch?v=Z4WcDXftxKk&t=1111s . The differentials come in two versions: Dana 44 (manual trans cars) and Dana 36 (automatic trans cars). The Dana 44 is very strong but also very expensive. The Dana 36 is much more affordable and has plenty of strength for your application

Have any of you had experience with modifying the C4 suspension to coil over and tossing out the leaf spring?  My worry is that the leaf would really restrict narrowing and be difficult to work with to get a proper spring rate.  Otherwise, it appears to be a good choice for the Spitfire.

Randy

You can't use the leaf because it is a one piece fiberglass unit that can't be shortened or have the rate reduced by taking out leafs. I have coilovers on mine and it is a simple matter. The bracket that attaches to the upright was changed when I discovered  the shock was topping out on droop, I used the one on the right to correct it.

Have you looked into the Nissan R200?  They use them in plenty of high hp setups across their lineup.

Infiniti R200 is the same as Nissan with better ratios.

Basically what Rob Ficalora uses behind his 302 powered MGB

'1996 Nissan Skyline viscous limited slip differential (same R200S case as Nissan 240SX). 3.54:1 gears. Uprated halfshafts from "The Driveshaft Shop" in Salisbury, North Carolina.'

Personally I like the Jag IRS but it might be a bit much for a Spit.

Jim

What do you suppose the Nissan R200 or Infinity setup could withstand in terms of HP/torque?  I know the drag set uses the 8.8 inch Ford gears with brutal launches and high horsepower and they stay together.  Not aluminum cased, however.  I was wondering about an 8.8 Lincoln set-up myself.  Light-looking and abundant 8.8 diameter gearings here in the USA to choose from.

Regarding the Lincoln axle.  I saw one for sale recently and it had no springs or shock adsorbers. Just airbags with an air pressure ride control.  Could this possibly work for a track car?

I recently bought a 4-link rear axle/suspension from a 2005 Passat wagon.  It was the model with a 1.8T inline-four and 4motion AWD.  It is very beefy but maybe too heavy.  Aluminum differential but steel everywhere else.  Does anyone have experience with that beast?

Randy

Does anyone have a web page(s) or more pics of the Nissan installation that Kenny Ard posted?

Randy

How much power to do plan to send to this IRS?

R200 is a little over 8" and will handle a lot of power. I had a picture of a Datsun Z drag car popping a wheelie years ago. The half shavts and cv's are the weak links.F150 axles with Dodge Intrepid hubs fix that. I have a R230, 3.67 ratio out of a TurboZ in my garage that is a little over 9" that I would trade for a R200.

I will be using a 4AGE Blacktop initially and claims for that engine range from 160-170 HP stock.  Later I may replace it with a modern V-6 and that could run up to 400 HP.  In a car as light as a Spitfire, and without drag race starts, I think an 8" ring gear could probably cope.  I am quite sure an 8.8 Ford diff would handle it.  What I don't want to do is graft in something so heavy that it defeats the advantage of using a light car.

what pictures would you like?

I know these differentials handle up too 400 hp and maybe more

I got my installation kit from GoodParts.com he's got good info on these diffs also

The last few days I have been thinking more of selling my Toyota Blacktop and instead am looking into the Chevrolet 3.6 V6.  It is a 60-degree V and would squeeze into a Spitfire I think.  You can source one from a Chevy Impala pretty cheap and a FWD unit works fine to bolt up to a RWD trans.  302 HP normally aspirated.  It weighs only 70 LBS more than a Toyota Blacktop.  I think I found one locally for cheap today

What do you suppose a Blacktop in like new condition is worth now?  Mine includes the air inlet system with box and filter and the wiring loom and computer control box which I sourced from a guy in Australia.  Also the 4 independent throttle bodies and linkage and the swoopy tubular exhaust header stock from Toyota.  Looks very racy and totally angry. :-)

Randy

Randy,

I assume you are speaking of the so-called High Feature GM V6.  If so, make sure you check the timing chain history on it--or get one with very low miles.  I have another project (an early 2003 Cadillac CTS) that I plan to replace the engine with a late model HF V6.  I picked up an engine with supposedly only 20,000 miles for $900.  Also be aware that these engines, unless you're lucky, don't usually come with the ECU, which can be a bit of a can of worms.  I did find a new ECU on eBay for a couple hundred, but I was pretty lucky in that find.  Also, most of these engines have harnesses for automatic transmissions--I assume you will want a manual.  If so, you may want to consider getting an engine from a Camaro, which often came with manual trans--and you could be lucky in getting the trans with the engine.  The engine harnesses for these cars are not cheap--often as high as $500, so you can be money ahead to get one as a complete set (engine, ECU, harness, and trans).

Hey Randy, I don't know how much research you've done yet, but this is the same package as what i doing now with a TR6.

I can tell you that with enough effort you can get anything to fit BUT I would be concerned about hood clearance and ground clearance, these engines are taller than most. To get it to fit under the hood means the oil pan is below the frame rails. Their are cut down oil pans but all i could find was one that only shortened it a 1/2 inch.
 
Another area to measure is width between frame rails, the oil filter either has to be a remote or use the rear-wheel-drive set-up which moves the filter up by the valve cover. I preferred that style but can't fit it.

As far as wiring harnesses and ECM there are options, There are LFX sites on Facebook with lots of info and v8Miata and Kiesler Automation sells kits for swaps. I highly recommend Kiesler.

Any info or measurements you need let me know.

Ken

Many thanks Ken.  I am headed out to a wrecking yard today to snoop around.  Tomorrow a 50% off sale starts and they have both a Cadillac CTS and a correct-year Impala for parts there.

Randy

The FWD engines are cheaper, but you'll end up buying the parts to swap it over. Best bet is buying a wrecked Camaro or CTS someplace and getting all the parts you'll need; I sure wish I had. Whichever way you go you'll need the rwd oil pan to mate too the transmission.  Something else to consider the Cadillac trans is the preferred if you can find one.

Kenny, I assume you mean the Cadillac *manual* transmission is the preferred option?  Either way, if he wants a manual, better to get an engine with the manual, or he'll need to either modify the engine harness or replace it.  I have an LGX engine, by the way.  Good call on that oil pan--I had forgotten that I'll need to source one for my project.