Mustangs vs. Falcons in Appendix K

[JonWolfe]

In the recent thread about why we race historic cars there were a few queries about Mustangs and Falcons in Appendix K. For those that are interested here are the key differences.
The chassis/floor is not the same but very similar, the Falcon is slightly narrower and the rear rails differ in shape slightly too. It’s possible to repair Falcon chassis rails with Mustang ones but it’s not a direct replacement. There are other detail differences such as steering column length and rear axle width too.
As someone suggested the Falcon Homologation was for the Monte Carlo rally in 1964 and allows for fibre glass or alloy front and rear wings, doors, bonnet, boot and bumpers which makes for quite a weight saving. The papers for both cars allow 15” diameter wheels (most Falcons and early Mustang production cars had 14” wheels with drums) but only 5.5 inches wide for the Falcon. The Mustang must run with all steel panels but can use 7 inch wide wheels. Both cars can use Kelsey Hayes style disc brakes at the front.
The engine spec is the same other than the Falcon can use tubular exhaust manifolds but they must run upwards from the heads then back down by the bulkhead – they are not as good as the type that run downwards but are a significant improvement over Falcon style iron exhaust manifolds which are pretty dreadful. Mustangs must run iron exhaust manifolds but they are better than the Falcon’s iron ones. Roller rockers are not allowed, the ball type rockers must be retained.
Interestingly the front turrets are about 2 inches closer together on the Falcon so downward facing exhaust manifolds are near impossible anyway.
The Falcon must use a Borg Warner T-10 gearbox whereas the Mustang can use a top loader, they can both use either an 8” or 9” rear axle.
The upshot is that the Falcon is lighter and potentially/ultimately marginally more powerful but with narrower wheels.
That's all I can think of for now!

[morninggents]

The papers I have show the Falcon at 980 kg (FIA No. 1250) and the Mustang at 1200 kg (FIA No. 1329). A significant difference.

[John Turner]

Significant indeed; much of it down to the homologation of the lightweight panels that Jon mentions, presumably. Should it not slide around a lot more with those skinnier tyres, too?

[Al Weyman]

OK intersting so why can a Mustang not use the Ford Tri Y headers that were fitted to the 289 Hi Po engine, I know this for a fact and they were genuine Ford factory offering as I had such a vehicle years ago with the High performance engine, tri Y headers, front discs and four on the floor, proper car and all original I loved it. Also what about rear axles was the 9 inch homolgared for both cars?

BTW just to clear something else up, roller rockers don't give much in themselves however...... to run a roller camshaft with roller followers they are mandatory and thats what will really make the difference, roller follows apart from releasing lots of horses through less frictional losses also allow far steeper ramps to be used on the camshaft, but roller rockers on their own are not worth nothing of significance over a standard rocker.

[esper]

Originally Posted by Al Weyman

BTW just to clear something else up, roller rockers don't give much in themselves however...... to run a roller camshaft with roller followers they are mandatory and thats what will really make the difference, roller follows apart from releasing lots of horses through less frictional losses also allow far steeper ramps to be used on the camshaft, but roller rockers on their own are not worth nothing of significance over a standard rocker.

Arent roller rockers nicer for the valve tips as well ?. no horsepower gain but less risk on breaking?

[Al Weyman]

Maybe marginally but all the publications I have ever read is that there is no significant advantage, there is a roller tipped ball type rocker as well not a full roller maybe they would be allowed, I have a set at home actually that came off an 'Apps K' engine allegedlly.

[Moosehead]

Its the rockers not the cam or followers when were talking rollers. The standard tin rockers are only good for 6500rpm on a good day and then not for long. The rest of the engine will rev more and so the errr enthusiastic driver often suffers from chronic misfire as the rocker splits! Of course there is another option but perhaps I'd better not mention that

Legend, myth or whatever has it that the Falcon was homologated without an engine in the car hence the low weight

[zefarelly]

a block with no guts ?

I've heard even the mega budget cars can't get under 1000kg.

[JonWolfe]

The actual Monte Carlo Falcons ran at about 1450kg (with tools and spares aboard)and around 250 BHP. Getting down below 1200kg is a pretty good target but as said, much lower than that needs some 'creative' thinking especially as an FiA roll cage is adding up to 40kg to an already heavy car. On the rear axle, the Falcon left the factory with a 8" unit but the ratios listed in the Homologation papers are all 9" ratios, otherwise the 1250 papers are silent on whether a 9" axle is specifically allowed. The papers also state in an addendum that an iron gear box case is acceptable; the inference then is that an alloy one is allowed too otherwise why mention it?

[Jeremy Hall]

Originally Posted by Al Weyman

OK intersting so why can a Mustang not use the Ford Tri Y headers that were fitted to the 289 Hi Po engine, I know this for a fact and they were genuine Ford factory offering as I had such a vehicle years ago with the High performance engine, tri Y headers, front discs and four on the floor, proper car and all original I loved it. Also what about rear axles was the 9 inch homolgared for both cars?

.

Homo Logos Al -the same number-homologation required the applicant manufacturer to certify that they had made 1000 identical cars,some lied as we know.
Items which were offered as extras, goodies etc are not/were no the same as items which were homologated.