Spitfire questions

I assume you mean prirace.com? (a google of RPIRace turned up some SoCal BMW tuner).

Yes, they do. Pricey tho... very easy to build a $20K+ Spitfire there...

quantumechanics.com is another nice place to day-dream... (upgraded diffs and T-9 conversion kits)

Spitbits.com (mainly parts, but also nice Bell stainless exhaust systems)

canleyclassics.com for all sorts of Euro eye-candy parts.

Ian F wrote: I assume you mean prirace.com? (a google of RPIRace turned up some SoCal BMW tuner). Yes, they do. Pricey tho... very easy to build a $20K+ Spitfire there... quantumechanics.com is another nice place to day-dream... (upgraded diffs and T-9 conversion kits) Spitbits.com (mainly parts, but also nice Bell stainless exhaust systems) canleyclassics.com for all sorts of Euro eye-candy parts.

Haha oops helps if I get the letters in order.

In reply to Curmudgeon: Yah, I built those manifold adaptors for Jeff's engine. Here's a link to a dimensioned drawing (including FI bungs) for anyone that wants to DIY:

http://www.flickr.com/photos/13867611@N04/2081915359/in/photostream

It used industrial minespray hose from carb to adaptor; it's springwire reinforced, takes the heat, pressure, fuel, oil.

Carter

I used to race a 1296cc MkIII many years ago. Spits were one of the best handling production sports cars if you did a few simple mods. We used to de-arch the rear leaf spring simply by flipping over one of the leafs which then gave a bit of negative camber or you could back then buy a competition leaf spring already de-arched. Some people then added a camber compensator, but many felt it wasn't needed once the rear leaf spring was de-arched. I took mine off and ran without it with no ill effects, but definately run a camber compensator if you are using a stock set up. We then added comp front springs, a fatter front sway bar and Konis all around. My old Spit was pretty fast in the day. It quite often won its class in regional races back in the 1970's. You can get decent power with the right engine mods. A 1500 with twin webers/cam/headers/CR is nice.

Google for the Spitfire forum. I know you'll get lots of info there..

Is it a zombie thread if it's less than a year? Er, I mean two years?

Why is it so difficult to get a concise description of the evolution of the Spitfire rear suspension?

I have the impression that they were basic swing axle cars with a leaf spring above the axle from the beginning, then in '67 (?) got the Rotoflex rear suspension, which if a bit bodgy, actually provided something roughly approximating upper and lower arms (even if the upper arm was still the leaf spring)... Somewhere in there was the "swing spring" arrangement which didn't stop it being a swing-axle car, but mitigated the tendency to jack and tuck... (I'm not super clear on how, but I haven't paid a ton of attention to it...

I'm deeply puzzled that PRI's IRS kit not only sticks with swing axles, but is even sold to revert Rotoflex cars to this evolution of the swing axle... It may decouple the L and R sides, but I can't see where that upper arm is actually doing anything to help the roll center; just there to aid the fore/aft location of the axle... Not many pictures on their site, maybe I have it all wrong.

There's got to be a better way. They're too cool to suffer that suspension...

ransom wrote: Why is it so difficult to get a concise description of the evolution of the Spitfire rear suspension?

Every Spitfire ever made was a swing axle.

Early Spitfires had a fixed spring perched on top of the differential. Prone to jacking or wheel tuck, hence the recommendations for camber compensator or limiting straps.

Later they increased the wheel axle length to get better leverage and decrease the jacking or wheel tuck

Right behind this they installed the swing spring on top. It's a leaf spring that pivots, acting like a camber compensator.

That's the entire history of the Spitfire rear suspension.

In reply to foxtrapper:

What about the Rotoflex cars which added a lower control arm and a Rotoflex (guibo?) coupling at the outboard end of the axle, allowing the wheel to not just orbit the inner U-joint?

Rotoflex was on the GT6 only and is sort of a bastardized IRS. About the only positive is the axles aren't stressed members of the suspension. Geometry is still a bit fubar.

I saw one guy use the PRI rear coilover kit on a Rotoflex chassis. He posted a picture of the bare chassis. Why he thinks this is better I'll never understand. The camber-curve looks totally berked up...

PRI's IRS kit is really meant to work with their HD rifled axles, but it's still putting more stress on the diff flanges...

Upgrading a Spit rear suspension is a screwy way of moving around your weakest link.

As much as I love Spitfires (and my own GT6) I have no delusions about trying to turn it into a Miata-killer... It's more fun to simply accept them for what they are.

Yep, as Ian says, GT6 only.

GT6 went swing axle, rotoflex, swing axle.

Triumph dumped the rotoflex and went back to the swing axle design, but with the swing spring. It just works.

The PRI set up is a swing axle. He can dance as he wishes, but the motion of the suspension is around the u-joint, and is unchanged. I've seen it. The geek in me sees nothing but a really expensive spring change, nothing more.

Yeah as far as I can tell PRI IRS is a piece of crap. I have not heard a single good thing about it. I am going to just have to live with the swing axle because vintage racecar.

I don't know that I would call it that, but I just don't see where it makes any change in the geometry of the rear suspension. It's still a swing axle, and the wheels move through the exact same arc of motion.

All he's replacing is the leaf spring, which has no effect on the geometry.

The Spitfire/GT6 are both derivations of the Herald chassis and running gear. A GT6 is basically a Spitfire with a 6 cylinder motor. So just about any of the Spitfire/GT6 pieces can be swapped, usually as a bolt-in. The Rotoflex was a clever way (Chapman-esque clever) to get a 4 link IRS instead of swing axle. It's basically just an SLA design, but upside down. No one complains about that design. Those throwing stones at using the transverse spring as the upper link should redirect their ire at the implementation of the cast iron lower link, equalled only perhaps by the T-Bird IRS lower link as the heaviest and most inelegant piece ever designed. Another thing, when modeling the camber curve, remember that we are dealing with a quarter elliptic spring section, not a solid link. This means that effective length decreases with deflection, since the spring curves rather than pivots, drawing the top of the vertical link inwards more than a link would, increasing camber. I doubt that many (any?) of the suspension modelling software packages get that part right. In addition, since a leaf spring is very stiff in transverse plane, there is no need for upper fore/aft location, ie upper trailing arms. Given that, the PRI system is basically just a replacement for the transverse spring, requiring the addition of coilovers to perform spring duty. On a Spitfire (or non-roto GT6), the spring is not really a suspension member, it has no effect on camber. So the PRI setup does absolutely nothing on those, even though it will bolt up. On a roto GT6, there is an opportunity for improvement, since the inner pivot could be relocated to alter the camber curve. I'm not aware that this opportunity was taken on the PRI design. And anyway, the same effect can be had by relocating the lower pivot.

That said, I tend to agree, enjoy them for what they are.

Carter

Guy in my club put a fancy rear suspension on his car. I don't know which one, but it was fancy and expensive and changed all the "bad" stuff about the spitfire's rear suspension, dumping the swing axle setup. With no other changes, he was 6 seconds faster around Hallet with the new setup.

erohslc wrote: In addition, since a leaf spring is *very* stiff in transverse plane, there is no need for upper fore/aft location, ie upper trailing arms.

That's a good point I'd never thought much about before - the PRI kit adds two more bushings/flex points to the upper "control arm" in a manner of speaking.

I will say there are a number of PRI products I like.

The MC carb kits look good and from what I've heard are about as close to bolt-on-and-go as you can get for that sort of thing. Not cheap, but you're paying for his developement time.

I'd say few would argue his exhaust systems look freakin' cool, regardless of any performance gains.

I'd probably run the PRI (or similar) axles on a Spit for racing.

The brake kits and 4x100 hubs seem decent.

It's mainly the IRS kit that leaves me confused. Just not sure what he was trying to achieve there. Yes, you can tune the ride height eaiser with the coil-overs, but it seems removing most of the tranverse leafs and going with a lighter c/o spring would have been just as effective.

This is the supension section of the sideways forum and some of those guys really know their stuff when it comes to spits. They shot down that PRI setup years ago.

http://sideways-technologies.co.uk/forums/index.php/forum/8-suspension-handling-tyres-and-brakes/

Ian F wrote: ... The MC carb kits look good and from what I've heard are about as close to bolt-on-and-go as you can get for that sort of thing. Not cheap, but you're paying for his developement time. ... It's mainly the IRS kit that leaves me confused. Just not sure what he was trying to achieve there. Yes, you can tune the ride height eaiser with the coil-overs, but it seems removing most of the tranverse leafs and going with a lighter c/o spring would have been just as effective.

Bolting on those PRI quad MC carbs is easy.
Getting the jetting and whatnot set to run well so you can go .... not so easy.
Some folks have reported 'minimal' after sales support.

Not a bad notion on removing all but the main spring leaf.
Another coilover strategy replaces the spring with a long narrow A arm (narrow because there is limited space, only about 6" wide above the diff).
But there is actually room for a short upper trailing link on each side, especially if you are talking about a racecar with limited suspension travel.
The 'Kastner Link' was a mod where the front of a long upper trailing link passed through an opening into the cockpit to the pivot point.
The rulesmakers poo-poo'd that one though.

I've always wondered if you could make a bolt-in DeDion rear, with a fabricated tubular spaceframe instead of a solid tube.
Might have to design the spaceframe as pieces that bolt together, in order to snake everything around the frame, diff, etc.

Carter

bearmtnmartin wrote: http://sideways-technologies.co.uk/forums/index.php/forum/8-suspension-handling-tyres-and-brakes/

Thanks for this. A lot of info, a lot of filtering needed...

In reply to ransom:
Umm ... how to be diplomatic here.
Like you say, a lot of filtering needed.

Take some of what you read in that thread with a grain of salt.
Some very good content, mixed with ... other stuff.

Keep an open mind, but ask more questions before you commit to any solution based on what you read.

In reply to erohslc:

Oh, I'm picking up what you're putting down. Been putting down some of it myself.

I'm not one to buy that leaf springs as suspension links, cast iron control arms, leaf spring stiction, or Triumph's best guess at controlling production costs in the '60s are likely to be optimal answers...

I think I prefer this thread.

Don't lose track of what a Spitfire is though. It's a crude, weak and slow little car from yesteryear. You can spend a fortune building one up, and it'll still get blown into the weeds by a stock Miata.

If you simply want to go with a custom or kitted rear end, go for it. But if you're thinking it will transform a Spitfire into a competative winner, you might want to reconsider a few times.

Forget not that you don't see these setups under the racing Spitfires, usually.

This may be an easy answer if I spent 2 seconds to search but,

What is a typical live axle swap for a Spitfire? Miata stuff?

Recommendations? Strong enough for a turbo Duratec 25 or Ecotec and yet lightweight? Most everything I have fooled with was Ford 8.8" which is pig heavy.

In reply to Gasoline:

Browsing through the BritishV8.org profiles, none are typical and all require major surgery to install.

Converting to a LRA transfers the loads away from where the factory designed them to go - the rear of the car is supported by the differential mounts since the transverse spring bolts to the top of the differential. Not to mention the swing axles are above the frame rails.

foxtrapper wrote: Don't lose track of what a Spitfire is though. It's a crude, weak and slow little car from yesteryear. You can spend a fortune building one up, and it'll still get blown into the weeds by a stock Miata. If you simply want to go with a custom or kitted rear end, go for it. But if you're thinking it will transform a Spitfire into a competative winner, you might want to reconsider a few times. Forget not that you don't see these setups under the racing Spitfires, usually.

It's a particular affliction of mine; I like old cars' styling and weight, but want to bring them up to date in every mechanical way.

Unfortunately, my impression is that outside of Production racing (and I could be totally wrong about that one, too, but I have the impression you can pretty much tube chassis a car there), you just don't have a free enough hand to do these things and still have a class to race in.

So it would be somewhere between an engineering exercise and a car for trying for FTD outside any particular class at local autocrosses.

It really looks like the way to approach a Spit with the intent of making everything really work well is to do the chassis over from scratch. You could do like in the link I posted above and build a new chassis rear and cut the old one off, but by that time, you've done so much work and now you're being let down by the front suspension and chassis flex...

So, you're absolutely right; I'm not sure there's any way you can say such a project makes sense outside of the desire to have that light and lovely little car on a chassis that actually works...

A few years ago I talked with the owner of Ratco (makers of TR4/6 aftermarket frames) about making a Spit frame. Nothing ever came of it, however, likely due to much of the problems discussed here.

I think the problem is in the packaging and you really have to look at one of the cars in person to really understand. There's a lot of "if-then" areas with trying to fix the Spit frame as so much is dependent on other parts of the chassis and related choices.

A Spitfire is a deceivingly tightly packaged car. When you open that huge bonnet you think, "Wow! Look at all that room!" but in reality there's barely enough room for what's there and even then they had to make compromises.

ransom wrote: So, you're absolutely right; I'm not sure there's any way you can say such a project makes sense outside of the desire to have that light and lovely little car on a chassis that actually works...

Stock Spitfire chassis isn't bad. Not hard or complex to tweak it and make it better.

Out back, spacer block in between the differential and leaf spring to lower it further. Camber compensator if you've an early fixed spring model.

Up front. Lowered springs. GT6 coils with 2 cut out work very well. Heaver anti-roll bar.

Good shocks all the way around. I'm oldish school and still run Koni reds, but Gaz and a few others are lot easier to adjust.

For steering, replace the rag joint with a TR6 u-joint in the steering column. Mount the rack with urethane or aluminum bushings.

Brakes, use good pads and braided steel lines.

Kick the camber out negative 1-2 degrees up front, toe it out about 1/4-1/2 degree.

The car will now go like stink around turns and you'll grin big time.

For power, advanced ignition timing, dual SU's, headers, and cam replacement (early stock model is hard to beat).

For legs, get an overdrive box. Drop in swap.

It still cannot outrun a Miata, but it's a heck of a quick Spitfire now, and still perfectly doscile and driveable.