70s Grand Prix car

Hello.

I have been on this forum for a some time but not made a significant post; this is my first.

Recently, I have become quite interested in grand prix cars from the early 70s. I was fortunate enough to see a Mclaren M23 recently in the paddock at Goodwood. I found it quite captivating. I do not have enough money to buy a genuine article. As such, it might be good to do some sort of “recreation” in the style of such a car, be it Ferrari 312, Lotus 72 etc..

I have not really got a very clear specification yet, but I have written out a list of some areas that should be focused on:
 

1. Ground clearance should be reasonable – in my experience, a car that’s too low is not practical to set up on anything other than a billiard table.
2. Sprung mass should have low drag. Low, chiselled noses are favourable. Side radiators and a floor hinging pedal box will facilitate this.
3. Drag from non body elements (brakes, halfshafts wishbones etc..) should be minimised to clear up flow off the trailing edge of the front wing.
4. CoG should be low – much of this will likely be influenced by crank centreline. Driver’s position also has a significant effect, but (at least when working within a given wheelbase) the engine configuration also is a big factor: Usually, a V8 takes up a good deal less length than a V12.

I recognise that this is an ambitious project and I will have to keep an eye on the costs, but I think it would be very satisfying to complete such a car. What are your thoughts ladies and gentlemen?

You've got very clear, very basic goals as your foundation. That's always a good way to start.

What else are you thinking about for it?

In reply to Mr_Asa :

I have been playing with some rough numbers on paper and I have some targets:

I am convinced that the wheelbase should be reasonably long (98 to 101”) to minimise pitch through a reasonable primary ride characteristic without having unduly low spring rates. In addition, packaging a physically large engine becomes a bit more straightforward.

Front and rear track depends largely on tyre/wheel package.

Longstone have a chart with the Dunlop classic range up to R7. The widest available 650M15 CR65 is 11.6” section with a tread of 8” on a wheel dia of 15”. These are probably a touch too narrow, particularly given the round sidewall construction, but they’ll do for a start. Between 57 and 59” seems like a good start for the rear.

For the front 54 to 56” seems sensible? “M” profile is also available on 13” wheel: 550M13 CR65 is 10” section 7” tread.

Some of the 70s GP cars have comparatively narrow rear tracks when taken from the centreline of the tyre. However, due to the extreme width of the tyre, the outer rear track is considerably wider overall.

Total mass should be as low as practicable. A “finger in the air” is around 1,200 lbs without driver or petrol.

It does not do to save 50 lbs on the mass but not have suitably stiff structure. Conversely, it is not of great benefit to increase torsional rigidity too much, especially when considering the tyre carcass stiffness, and the spring rates to be able to use the tyre. As such a torsional stiffness requirement of 10,000 lbs.ft/deg for the first degree seems realistic without massive mass penalty.

Essentially, trying to figure out whether this is viable or not; it's easy to start and not be able to complete a project.

In reply to ferrariwill :

The real difficult part will be the transaxle. Since those were always exposed in 70's era cars  you will need to source one that at least gives a nod to the originals.  
Don't focus on exactly replicating aero details,  Since you're making a tribute car rather than a tool room copy you have allowance to go bigger in the engine compartment without fear of critizm .  ( well except for the one jerk know it all). Most who. See such a creation will be happy if you get the colors close and the number right. 

In reply to frenchyd :

Hello,  In the past for mid engined cars I have used Volkswagen/Audi transaxles, specifically those from Passat B5/B5.5.  This time I may try to use a Porsche 911 transaxle but inverted so that the input shaft is below the diff axis.  I have not really got far enough into it to see what the package would be, but it would look "okay" - maybe not period hewland, but perhaps acceptable?

Sounds like fun.  I look forward to seeing what you have planned

I'd recommend reading up on anything you can find out about the Scarbo SVF1.

Here's a article Roadkill magazine did on it: http://www.roadkill.com/kicking-sand-at-a-historic-ferrari-in-the-ls-powered-svf1/

I would think it will provide some insight, if not plenty of motivation to produce a finished product. 

Looking forward to the build.

In reply to MTechnically :

I like the SVF1 very much.  Very fine work all round and excellent finish.  If I go ahead with this build, I suspect it will take a long time.  I have budgeted about 18 months for design, 6 months for tooling and maybe 2-3 years for manufacture.  But first I will check to see if it's feasible, hopefully all on this forum can point me in the right direction.

In reply to ferrariwill :

for a car this light, I think the Audi 01X transaxle would be a decent choice.  they are *cheap*.  

I agree, the Audi trans ought to be a good fit.

Have you done much fabrication work before?

In reply to MTechnically :

That rear shot directly behind the exhaust is just sex

In reply to Mr_Asa :

Indeed. Can't go wrong with an eight into one collector. Thing is GNarly

If it helps the general rules the cars were built to are here https://historicdb.fia.com/regulations/period-appendix-j

This guy has some good looking fiberglass bodies

https://losangeles.craigslist.org/sfv/pts/d/racing-car-bodies/7057335987.html

What will the car be used for?  Track days, modified for street use?d

In reply to Brotus7 :

Yes, this will be the 5th car that I have done.  The fourth is in progress now and should be "done" sometime in the summer/Autumn.  I usually start the next before the present in complete.  If you are interested, I will take some photos?

In reply to stuart in mn :

Testing and track, I think the IVA rules are a difficult to circumnavigate elegantly.  Mudguards, lights, number plates are not that easy to make look good on an open wheel car in my view.

In reply to Rons :

thankyou

I have had a little more thought about the mounting of the engine. I believe it is an advantage (and is within keeping of the era) to use a stressed block arrangement. I.e. the front face of the block attaches directly to the rear face of the tub and the rear suspension is attached (via bracketry) to the rear face of the block.

Since the general construction method of the car will be stressed skin, utilising the engine as a stressed member can save a great deal of mass.

Engine performance should ultimately be in the 450-500 HP range, but I am not sure that this will be possible initially.  My principle concern is that of displacement; I do not think that this power level will be possible with my ability from 3 litres I.e period correct GP car.  Quick calcs suggest to get 160+ HP/litre requires M.E.P in excess of 200 lbs/sq” at in excess of 10,000 RPM. 

Ignoring the obvious difficulty in achieving the required volumetric efficiency (VE) and the associated gas exchange, the inertial loading will be very difficult to manage.  

I am much more comfortable in cheating by increasing the displacement significantly, reducing the max RPM and reducing the VE

ferrariwill said:

In reply to Brotus7 :

Yes, this will be the 5th car that I have done.  The fourth is in progress now and should be "done" sometime in the summer/Autumn.  I usually start the next before the present in complete.  If you are interested, I will take some photos?

We love seeing builds, please post up some pictures.  It seems that you know what you're in for, and have a better than average track record fimor actually finishing.

Welcome to the GRM neighborhood!

For your engine a Cosworth DFV may be a bit pricey, but one of the early 3.0 litres was the Repco which I believe was a Buick Rover aluminum V8 block with overhead cams, and that makes the pushrod V8 almost kinda the same thing.

In reply to Brotus7 :

This was the first car, the picture is not brilliant it does not taper as much in real life because I was on step ladder leaning a bt; photography is not my skill!

In reply to ferrariwill :

This is the fourth car, late 60s style GP. stressed block, stressed transaxle case, stressed fuel tanks and coolant system. Aim is to be 230 lbs lighter than the first, but torsional stiffness is about 3 times better.  Bulkheads are steel, skins will be aluminium alloy. 

ferrariwill said:

In reply to Brotus7 :

This was the first car, the picture is not brilliant it does not taper as much in real life because I was on step ladder leaning a bt; photography is not my skill!

Very nice!  I like your engine choice.   At 31 inches it's a bit long and massively too heavy,  although some of that weight can be removed and power dramatically increased  over stock at a modest cost. 
retaining stock components the connecting rods can be lightened without the use of a machine shop. A vertical mill or even a drill press will remove nearly a pound per rod of mass that only exists to provide a luxury level of smoothness. A simple hand made jig will allow a remarkable degree of repeatability. 

 Once the rods are lightened. The crankshaft which weighs 78 pounds can be lightened accordingly.  The simplest and cheapest way is to cut down the radius of the counterweights in a lathe. While that won't be the absolute lightest way to reduce the weight of the crank it can be quickly done with nearly any lathe in an hour or two. 
those two items will cut nearly 100 pounds from the engine.  ( since they dramatically reduce the inertia as well the engine will rev much faster ) 

There are other ways to reduce weights but each gets multiples more expensive. 
The power of that engine can be seriously increased again at a nominal cost.  The carburetors hurt to the tune of 20 horsepower over fuel injection. But offer simplicity.  Equally simple are two inch SU's and they can actually make more power than the stock fuel injection.  If you notice, the stock manifold dips  down to pick up heat from the water manifold. That costs over 20 horsepower. Straighten that out and the carbs will no longer clear the bonnet of an XKE but will make more power.  Add the SU's and there is another 15-20 horsepower.  
If you really want to look more like an era engine, Weber's will work , but wow the expense!!!!  Not just the carbs and manifolds but all the Jets, air correction meters, etc etc  Racing with them back in the late 1980's I carried more than $2000 worth of tuning parts with me and every track session required changes based on changing air density.  That was knowledge gained after 4 dyno sessions chasing one or two horsepower at a time.  
SU's adjust themselves to a much greater degree and really don't cost  so much power as air density changes.  With SU's changes are done with a screw driver or the little wrench in seconds.  
You  can modify a fuel injection manifold with a simple piece aluminum angle. and use 3 common 1&1/2 inch SU's per side  not only pick up a few horses but look more like  a racing engine of  the era.

Finally in such a light car that engine will really respond  to either a set of Kent or Piper's regrind camshafts.  As much lift and duration they can offer
that will get you solidly to 400+ Very real horsepower. ( you start at 242 ) 
     Don't go to the expense of welding up the lobes or going to billets.  Those  will require the bigger lifters which require machine work to the cam follower blocks.  While there is more power, the additional cost per horsepower gained is hard to justify. 

Yes you can get that engine to solidly over 750 horsepower but at a really serious cost. 

In reply to frenchyd :

Very fair points regarding the Jaguar V12... Some alternatives for this new car:

It seems that a large(ish) displacement V8 would give acceptable mass and very good packaging.  A flat plane might give reduced pumping losses when used at wide open throttle near the top of the torque curve.  

Cross plane V8s have overall even firing and vibration, but the firing order along each bank is uneven, possibly leading to secondary vibration.  This can be dealt with using balance shaft(s) but this consumes large amounts of power at high RPM.  From what I understand, power consumed though parasitic loading increases at the square of the speed.

Straight 6s have perfect primary and secondary vibration characteristics – ideal for a car where the engine is stressed and vibration is a problem.  However, I am not sure a straight 6 is a good idea from a gas exchange point of view. Reducing the speed at which the required power is produced would necessitate an unrealistic increase in individual cylinder displacement.  This would giving poor gas exchange at high RPM, yet at a "large" 700cc/cylinder, the engine would still have to be producing 120 HP/litre.  I am not sure that more than 6,500 RPM would be easily achievable without some issues occurring with longitudinal whip, leading to very high reliance on volumetric efficiency to “get the job done”

Another option is a 12 cylinder.  High windage and frictional losses are traded with low inertial losses.  Perfect primary and secondary characteristics are traded off with length and mass.  Cost to manufacture is higher.  Pumping losses are low.  Vacuum losses are low.  Gas exchange at high RPM is excellent as cylinder displacement can be small.  CoG is a bit higher than a 90 degree V8 if a 60 degree angle is used.

Any thoughts?