170 MPH Phase IV Falcon XA GTHO???


Ok Aussies, you've heard me rabbit on about top speed calculations and all that crap. I've just been reading the latest Australian Muscle Car (AMC)magazine, and would like to take issue with the claim that a stock 1972 Phase IV Falcon XA GTHO would do 170 mph.

I've run some calculations, and I'm ready to eat shoelaces again over this one....if I'm wrong!

The XA was a very smooth bodied car, and the earlier XY 351 GT HO Cleveland was a 350 hp (SAE net) *6000 rpm engine when blue-printed, according to Mick Webb. I have no doubt that if you could rev it to 7 grand the 780 cfm Holley would flow 488 hp net, and that a 290 degree cam could hit the 450 hp barrier. I don't doubt that with an engine like this you'd get 274 km/h (170+mph).

But a stock blueprinted 351 GT HO Cleveland, even with gas flowed heads and low detonation combustion chambers?

From my calculations, at 170mph (274 KM/H) the tyre drag would be about about 13 kW. Then you'd loose around 29% of the flywheel kW figure. Then you'd have to factor in a frontal area equal to a XD/XE/XF/XG/XH Falcon (that's the silohette exposed to the wind), which is about 2.25 m2, or around 24.2 sq. ft.

The drag factor (cd) would be less than the XB/XC Falcon, which was supposed to be 10% more than the XD. The XC was about 0.55, the XD around 0.5, the XE around 0.48, and the XF a little less. So lets say 0.44 and give the big XA the benfit of the doubt.

Do the sums, and

(274*274*274*0.44*2.25) all divided by 76716. That gives 266 kW needed at the road wheels.
Then do an estimate on a 215 mm wide tire on a 1570 kg car at 274 km/h. Take that Honda CRX's 6kW at 240 km/h, a baseline for tyre losses, and mutiply it by 1570/900...this gives 10.5 kW rolling resistance. Then multiply the 10.5 KW by the % increase in section width. That's about 11.5kW. Then work out the increase in speed from the 240 km/h CRX, and mutiply by the factor. That gives 13.2 km/h

266kW+13kW=279 kW needed on an engine dyno...374 rear wheel horsepower.

Then the drive train loss is around 1.29for a Toploader , and a need for over 482 hp net at the flywheel. That's 360 Kw at 7000 rpm with a 39.2 km/h per 1000 rpm top.

Sum-up is that 170 mph needs over 480 horses just to get the amount claimed by AMC to be possible.

Somewhow, I don't think so!

It takes 650 hp to get a NASCAR to 200 mph, and even down Bathursts Mount Panorama circuit, that pushing it for any small block Falcon.
Well I'm e-mailing Australian Muscle Car (AMC)magazine anyway.


I know this was legit, even if the rev counter was 550 rpm optimistic at 145 mph indicated. Those were the GTHO days. Who will build their six to go like this?

A Barra 240 T in an XR to XF would do it easy!!!!!
I have always thought that to be one of the greatest photos the world has seen.
Who started off this 170 mph in an XY.
It was always 140mph on the hume!
A major magazine writers were late back to Ford and had to do an incredably amount of driving to get an early production Phase three back to broadmeadows.
I have never heard anyone say it was 170mph!!!!!!!!
The original photo was touched up to read around the hundred mile an hour for the magazine.
The original photo untouched was published much later.
Now can we get back to reality.
Also while Im at it!
Bloody speed is all about how much power you can obtain.
If you want to push an XF through to 200 mph. Then build an engine to do so.
All this prattling about drag figures and gearing and god knows what else is fine in an engineering class but this is NOT AN ENGINEERING class.
Thanks but NO thanks.
Good boy! :stick: Backlash Lives!

I didn't mean to go so far....honest! :oops:

:rolflmao: :rolflmao::rolflmao::rolflmao:

P.S. Won't stop me though. I'm an obsessive compulsive type, and an obnoxious sucker too. Next time I come to Aussie, I'll ring ya and you can give me a good kicking!
Please warn us when you are coming to Aus. so we can hide, or bolt everything down, or whatever! 8)
Maybe too late, Richard. His brother's already here (in Bondi; where else?).

The man has positioned himself with the perfect "legitimate" excuse: "I was just visiting my brother and saw the need for a comprehensive discourse on drag coefficients and nodal static pressures to inform the locals about Ford Australia's two steps forward, one step back product evolution and... How was I to know that the rostrum I took over is the St Mary's pulpit?"

you gotta remember car companies exagerate everything they can espiecally car horsepower to lure you into buying there car i know a guy that works for Corsa special vehicles and at test drive days where all the big companies send in there drones all the cars are tricked up so they handle better have more power and so forth so these magazine gurus go and say all the good thing these car companies want
Thats funny, i guy i know who works a CSV said the same thing too...
Its doubtfull that the XA 351 had much more power than the XY, which would have had around 380bhp @ 6000rpm or so. they would need lots more than 290degree cam to get over 450.
The only way the XA would have done that sort of speed would have been down "conrod straight" at bathurst. otherwise its doubtfull.
170mph is a lot of speed by any imagination.
Yeah, that's wot I thought too. It makes me upset with all the crap about 170 mph Phase IV GTHO's. I read the AMC article, and scurried away getting as much info as I could to suss out what was fact or fiction. I'm a Ford fanatic, but I also think any mechanical or aeronautical engineer would see that the claims of 170 mph on the flat from a stock GTHO Phase IV are not credible. I'm not a registered engineer, but I deal with facts and bull**** every day from people who think they know it all.

Rather than confuse the hell out of Americans, I'm dumping this info in here, so get yer cricket bat ready, Backlash!

Re Phase III:-

* Old Ford race greaser Mick Webb was on record in 1989 for saying the best blueprinted QC Phase III engine he dyno tested read 260 kw net, or 350 hp.

* Yank 4V HO engines, (built from the same seasoned block, in the same Cleveland Ohio factory before Ford Australia rebuilt it in Geelong) without the 780 cfm carb or the slighty milder Phase III cam, had a gross rating of 380 hp @ 5800 RPM from the 1983 US Car Craft magazine. The US Boss 351 factory figure of 330 hp gross @ 5400 rpm was true, but the extra 400 rpm gave another 50 gross ponies!

* Ford buckled over the US insurance claims. Ford just took the figure from earlier in the power band, like the 340 US Chryslers with the hotter than E55 cam (275 HP gross @4800 rpm was true, but 330 hp @5400 rpm was truer still!). Ford Aussie was even more conservative. 300 hp wasn't even the net installed figure!

*Even the first DeTomaso Panteras ran 326 bhp net @5400 rpm with the silly old Autolite 4-bbl and milder than GTHO hydraulic cam. So for the last Hoey Phase iii, I think 350 hp net @5800 rpm is right, and 390 hp gross at 5800 rpm is also correct.

* Lastly, the 6150 rpm rev limiter, if it was taken off, wouldn't have raised the top speed much any way. I'd say the Shaker would have been receiving a light supercharge of compressed air into its 780 Holley carb, and that even with a conservative 350 hp net @ 5800 rpm, at any thing over 6200 rpm the milder cam than the Phase II would have ensured there was no more than 320 hp past 6200 rpm. So 145 mph on a flat was your lot, with or without rev limiter.

Re Phase IV:-

Bill Santicione did lots of head work on the closed chamber heads, and there was yet another cam change. I'd say he'd be lucky to have got better than 375 hp net at 5800 rpm for this engine. Fact is, a 2V 302C headed 351C with 11:1 compression, short side blending and much better exhast balance, along with a hydraulic cam and 3310 750 cfm carb can do that 375 hp, and it would have been a better matched engine. 4V heads are a screw up exhast port wise, but the headrers for the Phase IV would have been as good as any available today.

Doing the sums, 375 hp at 5800 rpm would yield only 228 km/h with a set of 3.00:1 gears. Then the 242 km/h at 6150 rpm would give a need for 340 hp net, which it would have had at those rpm. A 150 mph road car, no more.

I think that those guys who claim 170 mph on the flat in there stock Phase IV Falcs are bull****ters of the higest order. A race car with open exhast, and a different cam, no worries. But 170 mph at 7000 rpm is just plain crap. A 5-speed Ferrari Daytona 365 GT/4 had a heck of a job getting 174 mph with its smooth aerodynamic shape with minimal frontal area. And it had 352 hp.

In the Australian Muscle Car article, three guys I respect the most seamed to state the Falcon in question was a true 170 mph machine. Much as I respect David Bowden, Bill Santicione and Howard Marsden, I know from the facts that a stock GTHO Phase IV couldn't do 170 mph on a flat. At Bathurst, no problem.

I hate bull****ters. And I don't care if they build awesome Fords like the above dudes.
Just to support your theory.
There was a lot made of the trip that Alan Moffat made to America with two XA two door GTs. This was reported by the local papers and I believe it was fuel for the anti high performance media of the time.
These were supposed to be the ultimate of the evolution of the 351 ci engine.
These cars were listed as achieving 160 mph on an oval curcit. This is a figure that I believe to be the ultimate that could have been achieved with the barn door type of styling and with out any wind tunnel work to speak of.
I cannot remember the exact year but it would have been early seventies.
Using the Doug McMillan HondATA formula published in NZ Performance Car in 1997, the power consumption for speed figures are based on this 9 or ten input formula.
A cd ( co-efficient of drag )
B Frontal area ( 10.76 x m² = sq ft)
C Vmax³ (maximum speed^3)
D Drive train loss (excluding tire drag, I used 1.27 in this case)
E Air density Correction

For aero drag , that's

(cd*FA *mph*mph*mph * 1.27)
Divided by 147733

Then add tire loss

F Average tire width in mm of one tire.
G Dressed weight of car with driver in Pounds
H Vmax ( this time, not cubed)
J Tire load factor ( always 8)
K Friction divisor for Asphaltic Cement
The rolling resistance HP loss is

divided by 60185866

Add the two together, that's peak HP for any given V Max

For Alan Moffats Race 1973 XB Falcon Hardtop tested at Michigan a performance testing site, 160 mph requires 409.02 hp Net to overcome aero drag and + 20.00 flywheel hp net to overcome rolling resistance. That's 429.02 hp net to do 160 mph.


For 170 mph, the same car would need 490.60 + 21.26 hp net, or 511.26 hp. Elsewhere, I calculated that it takes 505.6 hp for a XA GT 351 to do 170 mph, and just 264.2 hp to do 140 mph.

At 153 mph, the top speed the XA Phase IV did, 371.5 hp net at the flywheel at the 6150 rpm rev limiter on ER60 15 tyres. It's not just drag factor and frontal area from aerodynamics, it's rolling resistance, drive train, and air density. This is how we know the Phase IV had at least 20 hp more than the Phase III, because 144 mph ( the highest speed Mel Nicholls saw) required 311.4 hp net in an XY GTHO Phase III , which, with 350 hp net could have done 149.9 mph with a set of 3.00:1 gears.

Figures from Hondatas LSR road load calculator, which uses the same formula Doug Mc Millan published in his 1997 Land Speed Record article when he took the 155mph 97 cubic in New Zealand Land Speech Record in my Provence.

See https://www.hondata.com/cars/crx/techart.html