Ex-Racer Spitfire Mk1 Rebuild

[yorkshire_spam]

Newman TRIS/300/435 Race Cam ? Cool! 

59 minutes ago, Escadrille Ecosse said:

40-80 80-40 for the Newman

14 minutes ago, Nick Jones said:

slightly confused about which Newman one you have as the numbers don't match what they publish now

300 deg and 40-80/80-40 - seems to match @Nick Jones ? 

 

[Nick Jones]

23 minutes ago, yorkshire_spam said:

300 deg and 40-80/80-40 - seems to match

Lift doesn't though....... 0.315" quoted.

[yorkshire_spam]

16 minutes ago, Nick Jones said:

Lift doesn't though....... 0.315" quoted.

Humble apologies, it's late and I'm tired and still working... Sorry!

[Escadrille Ecosse]

Hmmm. That's very interesting you are quite right Gentlemen.

I got the info from my notes which date from 2007 and are I must admit not very good on this specific thing, I don't even have the invoices for the cam or rockers and I usually keep everything. All I have written down is "40-80 80-40 300 dur, 0.325" lift, install 110 ATDC no.1 inlet". Not even a note stating who made it but I always had it in my head that it was from Newman. I am very sure that the lift is more than the Kent because I remember clearly the other work that had to be done on the head - and especially the financial pain of the rocker gear - to get it all to fit together.

I did some Googling on t'internet and found this page on Spitfire cams by Paul Geither.

http://auskellian.com/paul/links_files/spitfire_cam_specs.htm

Newman PH4 is a 40-80 80-40 cam at 110 ATDC but as you say Nick it is only 0.290" lift.

Kent and Piper both do 300 degree cams with a big lift but these are asymmetric and the lifts don't match.

The only other symmetric 300 cam on Paul's list is the Isky Z-307 but that has even more lift.

So I am stumped.

All I can confirm is that it is a much more driveable cam than the Kent TH6 it replaced.

One other thing from the Paul Geither list is that the lift of the Kent TH6 he has is different from the TH6 I had back in 2003/4 when I built the engine. So maybe that's the difference with the mystery cam in my car and the current Newman cam although seems a bit of a long shot.

Would be interesting to measure the cam profile - anyone done this?

[PeteStupps]

On 5/29/2020 at 9:12 PM, Escadrille Ecosse said:

Would be interesting to measure the cam profile - anyone done this?

I haven't but I bookmarked an illuminating thread on the subject! 

 

 

[Escadrille Ecosse]

Pete. Thank you, that is superb.

Although my head hurts now and I am going to have to read it over a few more times to get it all.

Alan, thank you too for all your efforts. Informative and hugely funny too.

I see an attempt to measure the 'knobbly stick' as John calls it in my future. 

[Nick Jones]

Yep, that is a fine bit of work by Alan. He was wanting to combine that with his work on rocker geometry by measuring the actual lift at the valves vs. crank degrees, which is likely to provide quite a different picture and compare a few cams. Sadly his time ran out first.

Must put his tech threads together so they don’t get lost.

 

[Escadrille Ecosse]

Sad to hear that Nick. Thank you though.

[Escadrille Ecosse]

More sticky stuff over the weekend.

I didn't have a mould for the inner reinforcing panel for the Spitfire bootlid as it was deemed 'excess weight' when building the car and without a handle or the inner frame somewhat redundant anyway. But I do need one for the new lid which is a bit or an issue. However I had an old Honeybourne boolid stashed away in the garage which came with an inner panel although very ropey and not good enough to take a decent mould off.

So I have spent the weekend sorting well enough to take a transfer mould from which I can make a part I can use to make the final mould. Needed cutting back and a lot of filling to get it about right, particularly the lip where it fits to the lid which wasn't at all to the right profile.

Then a coat of primer to seal the surface for the release coat.

And the gelcoat and layup. I stuck a block of PU foam on the back to give me something to hold it with when I come to make the new part.

[Escadrille Ecosse]

Back to suspension. Rear end first!!

At the back it's about managing swing axles to keep camber and track changes to the minimum so as to keep as much of the rear tyre on the road which all comes down to short travel (stiff spring) and low roll stiffness (swing-spring). I started off with the 1500 swing spring which worked reasonably well but wasn't stiff enough. It is also heavy and as with all leaf springs there is a lot of internal friction which makes the ride less than supple.

Leaf springs aren't used much on cars these days (Corvettes excepted) but they are used on light commercial vehicles as there are a lot of packaging benefits. However to address the weight and harshness most of these use mono-leaf springs with a single leaf made of tapered steel rather than a number of separate leaves bound together. One of these for the Spitfire would be good but they are complex to make so not really a practical proposition. However composite leaf springs made from e-glass fibre and epoxy are also quite common and are also relatively easy to make - I had heard about the Corvette for this one. From a DIY perspective fabrication is fairly straightforward however getting the right stiffness is a lot more tricky (spring equations involve a lot of 3rd and 4th powers) and when spring eyes are needed as on the Spitfire it gets a bit more complicated.

Searching the internet identified one company in the US that would make bespoke composite springs and at the time the reviews were quite complimentary and the price very reasonable. The company is called Flex-A-Form and I believe they are still operating although ownership has apparently changed and the reviews have become less positive. I duly provided details of the required spring dimensions, eye-to-eye length, spring width, arch height and rate along with my credit card details and about two months later the spring arrived in the post.

Wow.

Most immediately obvious is the weight - or lack of it. It weighs just 2.3kg less than a quarter of the standard 1500 spring at 10.6kg and more for a heavier duty one. The next is just how supple the ride is on the car even with an uprated spring.

The main problem which I had anticipated was that it would need an alternative method of allowing it to pivot and also locate the spring against twisting as it also forms the upper location for the rear suspension. My plan was to fit curved sections of aluminium bar above and below the spring, almost like a bearing and mount this lot inside a cut down swing spring spring-box with a hard polybush pad and everything located by the pin into the hole in the top of the diff. Location fore and aft was provided by the spring box which I lined with bronze and hard nylon sheet shim.

In practice it worked exceptionally well, very smooth and with very little roll stiffness providing excellent handling at the rear. Unfortunately the shims preventing fore and aft movement wore very rapidly the result being like an extreme form of axle tramp on acceleration. This would get so bad that it was actually audible and visible outside the car. Replacing the shims would sort the issue but not for long and was very difficult to predict. Made worse by the design of the box which is not very rigid fore and aft.

Sadly therefore I had to eventually replace the composite spring with one for a GT6 Mk3 decabered by about 1" and fitted with a 1/2" spacer block to get the right ride height.

The composite spring is still in the garage though and I plan to re-fit it at some point with a revised mounting arrangement as it is truly a marvelous piece of equipment. I would thoroughly recommend such a spring for anyone using rotoflex suspension without hesitation.

There were two other rear suspension issues that I wanted to address with the car. First of these is particular to hillclimbs and sprints and is about getting the best standing start possible off the line. Timing for these events is done by breaking a light beam set across the start and finish of the track with a timing strut fitted to the front of the car. Some tracks have additional timing beams at various points that enable individual sector times to be analysed. One of the most interesting of these is a beam set 64 feet from the start line. Breaking this beam 2 seconds after the start beam indicates and acceleration of exactly 1g off the line.

As a small RWD car with sticky tyres made more so by pre-start tyre warming spin-up the Spitfire should be able to achieve 1g or perhaps slightly better. Single seaters and 4WD cars with slicks can achieve significantly better with the best technique. Not easy given that the start line of a track is generally quite polished after many starts. Unfortunately with its swing axle the Spitfire is at a serious disadvantage because rear end squat causes the camber to increase and the tyre contact patch decrease dramatically. The initial grip is so good it almost bottoms out the suspension, and then the inner edge of the tyre gets overloaded and it starts to slip excessively. So a way of limiting squat without affecting the handling was something I was after. The ideal would be a near rigid axle that returns to normal as soon as the car gets under way.

Mechanical traction control devices are permitted under the rules providing they cannot be controlled from the cockpit while moving – the rules here mainly thinking about things like anti-tramp bars. One of the ideas I came up with was to fit a pair of air springs between the leaf spring and the body. Pumped up before the start to stiffen up the back the pressure would then be released on launch. Simple in principle but gets more complicated to engineer the more you think about it. Same with pneumatic pistons. Another thought was a reverse version of the ‘cable over the diff’ trick using something like a brake cable under the car that could be tightened to stop the suspension dropping on launch then release automatically once the car got away. Again difficult to engineer practically.

However there is a way of building a degree of anti-squat into the suspension geometry itself. This is by ensuring that the radius arm rises forward from the axle to the body of the vehicle.

Unfortunately on the Spitfire the radius arms run pretty much horizontal or slightly down from the axle which encourages squat. Lowering the back of the car just makes the situation worse.

So what I did was move the pivot to the bottom of the vertical link which shows the effect on the angle of the radius arm.

This picture shows the two positions side by side as well as the adjustable rod ends at the top.

The other issue I wanted to try and deal with was the effect of rear suspension travel on the rear wheel alignment, toe in/out. The short length of the trailing arms and their location on the body that their effective length changes quite significantly as the suspension moves up and down. Which in turn effects the toe-in and handling of the car. This is most critical on braking where any reduction in toe-in increases rear end instability

Ideally the body location should be at the same distance from the centreline on the car as the inner suspension pivot which for the swing axle cars is the UJ although this is not really feasible due to the chassis being in the way!

Next best thing would be to use the GT6 rotoflex location point (located to match the inboard pivot of the lower wishbone on the rotoflex cars). However I was concerned that without the wide base of the lower wishbone and chunky rotoflex upright there was insufficient support to prevent rotation of the relatively lightweight swing axle uprights which would only stress the swing axle and it’s bearings even more.

However it then occurred to me that changing the location of the radius arm on the upright would also help the alignment problem. With the standard radius arm alignment braking initially causes the rear end to rise, the effective length of the radius arm to increase and the wheels to toe-out – bad thing.

Modifying the uprights to anti-squat also ensures that on braking the angle of the radius only increases and the more it does so the more toe-in is generated. A poor mans Weissach axle.

https://en.wikipedia.org/wiki/Weissach_axle

Two birds with one stone.

The effect of all this is not actually enormous but it is noticeable, the car being notably more stable and secure on braking, especially in situations where the car goes light over a brow at the same time. Of which there are a remarkable number on hillclimbs!

Next time front suspension

[TimBancroft]

Fascinating article, thank you.

Car build message threads are very interesting.

[yorkshire_spam]

Awesome stuff, a fascinating read

[Nick Jones]

Very interesting stuff indeed. I’m left wondering why Triumph didn’t do it your way........

waiting for Steve to comment on the composite spring. IIRC he used one briefly, but a bit too successfully, and it got banned.....

[Escadrille Ecosse]

I suspect it may have had something to do with starting off with the 948 Herald!!

I am really interested in hearing what Steve has to say on the composite spring. I like the idea that it was considered to be too much of an unfair advantage.

[GT6Steve]

15 hours ago, Escadrille Ecosse said:

I suspect it may have had something to do with starting off with the 948 Herald!!

I am really interested in hearing what Steve has to say on the composite spring. I like the idea that it was considered to be too much of an unfair advantage.

You've pretty much said it all.  Does your spring have the central locating stud?  I used all six studs to clamp it with a U shaped ally saddle on top to save a few more grams and didn't note any side shift.

The GT6 is a different animal than the Spitty of course but I exploit the radius rod locations to promote rear steer with body roll with a bit of toe-out when in the turns.  I've also done extensive testing to ensure minimal camber change throughout the range of my relatively soft suspension.  Several mentors over the years have extolled the virtues of soft well adjusted suspension and my handling results prove the point to me.

 

BTW, mine was the first Triumph from Flex-a-form 

[Nick Jones]

24 minutes ago, GT6Steve said:

You've pretty much said it all.  Does your spring have the central locating stud?  I used all six studs to clamp it with a U shaped ally saddle on top to save a few more grams and didn't note any side shift.

Yeah..... but I think the point is that you were very happy with a fixed centre because roto, whereas he wanted it to work as a swing spring because swing axles. Positive location whilst allowing it to pivot is a challenge.......

Did I remember the ban part right - did you get a full season out of it?  Trouble with being quick..... those who can't keep up look for ways to slow you down!

[Nick Jones]

Found this blast from the past

and this

 

[GT6Steve]

Ah...  good point Nick.  I glossed over that bit though I did briefly ponder why it would slip.  I got a few races out of it before it was noticed.  I think I sold it on to someone for a street car.  Long time ago now.

[Escadrille Ecosse]

Hello gents, just catching up. Thank you for the replies all good stuff.

As you say I was trying to use the composite spring as a swing spring. I fitted sections of curved aluminium top and bottom to provide the 'bearing' and used the pin bolt on the bottom of the spring to locate in the hole int the top of the diff to keep it in place and stop it moving side to site but allow it to swing on the 'bearing' and polyurethane pad in the spring box.

The issue I had was an oscillating rotational motion horizontally. Difficult to explain in writing so here's a sketch which I hope shows the problem better

As for the other details that's all very good although with the swing axles the only way to minimise camber change is to limit rear travel. Not really ideal but lowering the back end on a stiff-ish spring and allowing as much roll as possible is best you can do on the swing axle cars.

I wasn't really aiming for the rear end steering effect with my modifications but they do work that way. In a corner toe-in increases on the inside wheel and becomes toe-out on the outside.

Not sure when you got your spring Steve but it was interesting when first I spoke to Flex-a-Form back at the end of 2004 they were dead keen on making one for me and indicated it would be no bother as they had the basic details from an earlier job - quite probably yours!

I like your use of a fewer number of thicker steel leaves as an alternative. The fewer leaves the less internal friction and hysteresis in the spring which allows for a much more supple ride better for keeping the wheels in contact with the black stuff. I had also tried going down this route before the composite spring but had to give up because I couldn't find anyone in the UK prepared to make one for me - although mine would have been a little more complicated as it needs the kick in the centre of the top leaves to allow for the swing. Would like to give it another go though.

One other thing with that link Nick - having read it to the end I found I had made a contribution about the spring back then although I had completely forgotten doing so.

Old age I fear.

 

[Nick Jones]

1 hour ago, Escadrille Ecosse said:

One other thing with that link Nick - having read it to the end I found I had made a contribution about the spring back then although I had completely forgotten doing so.

So had I....... 

Was interesting that Steve reckoned back then that no (US) racer was using a swing spring.  But presumably you considered this essential.  Certainly makes things harder.

There is such a lot of good stuff lurking in history on this forum!  Much of which I've forgotten about or only recall in very general terms. Somewhere (in that thread I linked to I thought) Steve does confirm that his came from Flexaform and was the first they made for a Triumph.

[Escadrille Ecosse]

Nick - I have toyed with the idea of trying a fixed spring from time but decided against it. Think it would work fine on a racetrack and probably OK on the road too for a light, lowered car but on hillclimbs especially there is just too much camber change on the tight rising hairpins and you'd just lift a wheel and lose traction.

This next installment is about the front suspension development.

Mods to the front suspension were all about trying to improve turn in and behaviour under braking whilst the front end has to manage most of the roll control front and back.

The Triumph front end is basically a very good base design, as shown by the number of specialist cars of the 60s and 70s that used some or all of the components.

However it does have one major design issue in that the caster angle is achieved by the crude expedient of tilting the whole unit rearwards which promotes dive under braking. This is then made worse by the inclined spring/damper unit which gives the effect of a falling rate spring!

Adding additional shims to increase negative camber adds to the problem by increasing the inclination of the spring.

Not much you can do about the basic wishbone geometry without a complete redesign and there is only so far you can go with stiffer springs on a car that is driven to events and has to cope with sprint and hillclimb surfaces that can be a lot less smooth than racetracks.

There are some tricks you can play with the anti-roll bar geometry to resist dive (as done with TR 7s) and I did have a look at that as the principle is fairly simple. However execution is more complicated and is a bit of a bodge for double wishbone type suspension so I dropped the idea.

In the end I decided to try an do something to reduce the falling rate of the front springs. A few sums showed that changing the angle of inclination of the springs by even a relatively small amount had quite a big effect on the rate change.

Bit of geometry shows that with the standard suspension setup setup a 2” lift at the wheel results in a reduction of about 11% in the spring rate, or approx 12% with a ½” shim stack under the lower wishbone mounts (to get 2 degrees negative camber).

The bottom location is pretty much fixed – camber adjusting shims aside because I was not going to get into modifying the wishbones given the forces involved.

So that means moving the top mount outwards on the suspension turrets. To allow easier and more accurate camber adjustment and to limit the shimming at the bottom I was fitting a pair of the adjustable top wishbones from Canleys. The space inside the these determined how far out I could move the top mount, which was 1” with 2.25” ID springs.

This gives a spring rate reduction of only 6% at the same 2” bump. Moving the top mount further out gives diminishing returns – as you would expect really. And also increases the leverage on the suspension turret.

Pretty simple mod. Some 3mm channel welded under the turret and 1.5mm above.

With the 2.25” springs there are a lot more rate and length options so I settled on 500lb x 8” long and while I was at it went for the upper spring retainers on the damper rather than the Triumph three bolt plate. All saved a chunk of weight too.

Photo shows the difference between the two springs on the original standard length AVO dampers. These were right on the limit with the Triumph diameter 12” springs and far too long for the new springs and I replaced them with shorter AVOs (12” open, 8.5” closed).

All bushes were replaced with hard red polybush at the same time.

This week I've been working on the boot lid reinforcement panel. I took a part from the transfer mould

and then used that to make the final resin infusion mould. Finished lid mould in the background. Looks a bit piebald as I used two mixes of coloured gelcoat and got the grey tints slightly different!

After I've trimmed the edges next job is to start on the door skins. Need more materials though which I'll pick up later in the week.

[Nick Jones]

Some clever details on this car..... that shifting the spring pick-up point outwards is not one I've seen before, but simple and presumably effective.

 

[BiTurbo228]

I can already tell this thread is going to make me re-engineer bits of my car! Excellent work, especially on the suspension

I'd forgotten about those composite leaf springs. I've got an issue that I've been trying to work out about front and rear roll stiffness on mine (roto rear so different principles). My issue is that the roto rear spring sits way too high and I don't want to use a lowering block as it throws off my geometry. The roto rear spring is a bit soft anyway, and a Spitfire one will be softer. My current thinking was to add in some supplementary coilovers like Alfa GTV6/75 people do to supplement their front torsion bars. Some 80lb springs would mean that the balance should be pretty neutral F/R and it might even be stiff enough in roll that I can delete the front ARB. However, a stiffer composite leaf could sort out both problems!

Another option would be your brilliant idea of making adjustable spring mounts on the upright. Have you run them for a while, and if so what's the longevity? A properly ride-height adjustable rear would be useful!

Love the idea of extending the front spring mounts as well. Would mean getting different springs for me (again), but I've definitely marked that one down as something that needs to be done on mine. Will mean going over my spring rate calculations again as it'll change the wheel rate, but I hadn't considered the change in spring rate as it compresses. Very smart!

So many good ideas  

Oh, and the conversations about cams has got me thinking about mine. It's a TriumphTune Sprint 90, which interestingly has an asymmetric profile. Makes me think I should have gone for something different...

[Escadrille Ecosse]

Hi B/T. Thanks for the nice comments

Light coilovers would be an interesting one to try.

I have seen pics of these on US race Spitfires. The PRI conversion also used them although I was not at all convinced by the engineering of the PRI stuff.

They kind of defeat the purpose of the swing spring though so I never pursued it.

I'm not the only one to have had the idea of the adjustable uprights and I have seen a few since making mine. Jon Wolfe being the most obvious. He used to make the bits for you to weld up yourself. I don't know if he still does.

I have found the rod ends to be pretty reliable on the Spitfire although it doesn't do a huge mileage. Been on the car 10 years and still fine. Fitting the rubber boots and filling with grease helps keep the muck out which is key I think.

One thing to be aware of is that you don't shorten things too much or you will find the leaf spring hitting the brake cylinder/brake pipe. Part of this depends on how tightly the second leaf of the spring has been wrapped round the eye of the first leaf. There seems to be quite a variation between the original springs and the various remanufactured ones. I did have one remanufactured one that couldn't be used - with the car on the wheels there must have been over an inch between the wrap and the underside of the bottom leaf.

If you can get a composite mono-leaf spring then that I think really is the way to go as you can choose the rate and the height.

[BiTurbo228]

Yeah I think light coilovers would be interesting. For me they'd allow fine adjustment of the ride height without the adjustable spring mounts (I think that might cause issues with my geometry again, but will check).

They would defeat the purpose of the swing spring definitely, adding to both bump and roll stiffness.

How much did yours cost, if you don't mind saying? Just looking to budget. Oh, and what stiffness?