Article: The Dennis Leech Boss 429 Mustang

[Steve Holmes]

Man, that is just awesome. Thanks heaps for posting that Pauly.

[Kiwiboss]

Hi Pauly, can you e-mail that article direct to me at mailto:?subject=&body= im sure this Boss 429 is owned by Wuan Gonzales in Texas, a very unique race Boss Mustang, don't think is has any USA Trans Am History?

Dale M

[zombie289]

Lemme know if it came thru Dale

[Kiwiboss]

Lemme know if it came thru Dale

Yes, got it Pauly, great article and as you know, stuff that i like!!!

Dale M

[Steve Holmes]

Received this really great message from Les Moyle regarding the Dennis Leech Moss 429 Mustang:

My name is Les Moyle and I live in Exeter, Devon, England.

In the early 1970's I worked for Dennis Leech, as a mechanic, and had the
pleasure of working on the Boss 429 Mustang. I was involved in the
installation of the 429 motor and fabricated various mountings and the
stainless steel headers. These went into a 4 into 1 collector on each side
and exited under the doors in a 4" diameter steel pipe. The noise was
tremendous when fired up in the workshop. We always worked on the car at
night as we had to make money on customers cars during the day time. When
preparing to go to a weekend race we would usually fire the engine up just
before we loaded it into the transporter. This was usually about midnight.
Our main police station was about half a mile away and within about 5
minutes of firing up the engine at least two police cars would arrive. Not
to tell us to stop but to marvel at this thing throwing flames into the
night sky and enjoy the spectacle.

At one race at Silverstone the 429 threw a rod right through the side of the
block. I remember a photographer, from Autosport magazine, managed to
capture this and the caption was "The Biggest Banger in The World". Funny
the things you remember from your early years. I was 22 years old then and
now I am 64 this year.

I also remember the 4 valve per cylinder heads going on along with the
Dennis Leech made slide throttles and fuel injection. We put it together and
loaded the engine into the trunk of an S Type Jaguar and Dennis took it to
Weslake to put it on the Dyno. Seem to recall 600Bhp at the flywheel. First
time out it was enough power to sheer off the first motion shaft of the
gearbox. This was a very thick shaft, about 1 1/4 inch's as I remember.

Sadly I do not have any photos so it is nice to see the ones on the web.

[zombie289]

Wow thats awsome Steve, it's stuff like this that makes this site one of the best....Whats known about these 4 valve Boss 429 Heads, or am I reading this wrong??

[Steve Holmes]

Some more info here from Les, regarding questions I asked about whether he was involved with any of Dennis' other race cars:

I was involved with another car of Dennis's but this was a Chevron Formula 5000. I remember we raced against the likes of Alan Jones, before he moved into Formula 1. In fact I remember some races that dennis entered had both Formula 5000 and Formula 1 in them.

The Chevron was not the fastest and struggled against the Lola's that mostly filled the grids.

I think dennis was much happier in saloon cars and returned to that, eventually, with a Rover. I had left his employ by this time.

Dennis raced a Ford Falcon, very successfully, before the Mustang, but this was before I worked for him.

I have been looking through my stuff as somewhere I have a few Polaroid photo's of the Mustang. I have to keep looking now. One of these was taken after a particularly hard shunt, that took the front left hand corner off the car. It happened at Silverstone, at Stow Corner. The rear drive sheared on one side just as Dennis floored the throttle and turned the car sharp left into the bank at a very quick pace. A new corner from another car was sourced from the USA and grafted on. Once done you wouldn't know it had ever happened.

[Steve Holmes]

And reply to my questions about that very special Boss 429 motor and 4 valve heads:

The 4 valve heads were aluminium and one pushrod operated a duplex rocker which opened two valves. There were no head gaskets as such, just a lot of O rings for each oil way and waterway. The seal on each cylinder was made with a gas filled steel ring that sat in a groove machined into the block. Probably telling you something you already know.

After the pushrod through the side of the block incident, at Silverstone, a new block was ordered from the USA. It turned up but one bank was machined about half an inch short and had no recesses for the O rings and cylinder seals. I remember Dennis having a heated discussion, on the telephone, with someone in the States, trying to get them to understand the problem. Today it would be easy with digital photo's and the internet. Nothing like that in the early 70's. I think they thought he was pulling a fast one and trying to get another free block. It got sorted but I think we missed some race meetings.

After one engine rebuild, we did them in house, one of the heads cracked around one of the studs holding the head to the block. We did not discover this until late into the night before going to a race meeting the next day. It was discovered after a run up of the motor and when turned off we could here a noise like water running. In the dead of night the garage was eerily quite so any noise was easily heard. Removed the rocker cover to see water coming from around one of the studs. The engine was allowed to cool for a while and the water was drained. A large amount of Araldite Epoxy was mixed and applied to the offending bolt and the car loaded into the transporter. Off we went to the race meeting and avoided putting any water into the car until just before practice. I think it all held together for the race meet and fixed properly on our return. Memory a bit scat on whether a new head was sourced or it was welded.

Yes, the rear wheels were very wide and were probably off a single seater formula. I think Formula 1. To accommodate such wide wheels the rear axle was shortened by about 6 inches on both sides. Specially machined half shafts were required for this modification. Right next door to Dennis's garage was a machine engineering company and they had the equipment and knowledge to carry out this work. It was very convenient. This company (Phoenix Engineering) also machined all the components for the slide throttles designed by Dennis. Sadly this company is no longer in existence.

I remember the 429 being shoehorned into the Mustang as it was not a true 429. The suspension turrets had to be extensively modified to get the much larger engine in. It originally had a 351 and this was shoehorned into an AC Cobra owned by a guy called Channing. He had a garage in a place called Dorchester, about 50 miles from Exeter. He used to hill climb the Cobra for his recreation. It had a 302 in it and I remember we put the 302 heads onto the 351 block. Not an easy job as water and oil ways did not line up. Into the machine shop next door and weld up some of the waterways and machine heads as required. Worked a treat.

[zombie289]

Wow, again awsome info Steve, The concept of a 4 valve Boss 9 is mind boggling, that thing musta been a monster!

[Steve Holmes]

Yeah, it was a pretty ambitious project Pauly, don't you just love people who think outside the box! The car appears to still be for sale, I really hope it goes to someone who restores it to its Boss 429 guise.

[Steve Holmes]

In the mid-1980s, Eric Walker purchased the Leech Mustang, complete with 429 motor and a spare 429 in bits (but missing the Leech built fuel-injection system) and added it to his growing collection of ‘60s and ‘70s American sedans to have competed in the BSCC, including the Terry Sanger Falcon Sprint, and Martin Birrane ’70 Mustang. All three vehicles were in original condition, as last raced, and showing the stresses brought about by years of being pounded upon. With nowhere to race them, Erics plan was to hold on to the cars until their values rose once again, then sell one of the Mustangs to pay for the restoration of the other. Unfortunately a divorce in 1987 forced him to sell the cars. The Falcon went to Sweden, while the two Mustangs eventually ended up back in the US.

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Interesting to see the Kar-Kraft built 1970 Mustang prototype that was raced by Martin Birrane in the UK and Europe in the early 1970s, as pictured above when owned by Eric Walker in the 1980s, was up for sale at Mecum Auctions recently:

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[Jac Mac]

[ATTACH]21414[/ATTACH][ATTACH]21386[/ATTACH][color="#0000CD"]4valve per cylinder Boss 429? never seen a pic of that animal, sure your not getting that mixed with whats known as the 'Boss9' recently reproduced by John Kaase & crew?
After a bit of research I would suggest that it might have been a 'Calliope' motor that was fitted, these shared the 429 bore stroke etc, were 3 valve per cyl with a forked rocker for each pair of intakes, Two camshafts in block, one above other with top cam servicing exhaust rockers.
HP ex HM was in the order of 630, same engine spent time in the G7A sports cars , calliope pic on left, boss9 on right.[/color]

[Steve Holmes]

Jac, I'm pretty sure they either had them made or made them themselves, specifically for this engine.

[Terry S]

[ATTACH]21414[/ATTACH][ATTACH]21386[/ATTACH][color="#0000CD"]4valve per cylinder Boss 429? never seen a pic of that animal, sure your not getting that mixed with whats known as the 'Boss9' recently reproduced by John Kaase & crew?
After a bit of research I would suggest that it might have been a 'Calliope' motor that was fitted, these shared the 429 bore stroke etc, were 3 valve per cyl with a forked rocker for each pair of intakes, Two camshafts in block, one above other with top cam servicing exhaust rockers.
HP ex HM was in the order of 630, same engine spent time in the G7A sports cars , calliope pic on left, boss9 on right.[/color]

I always thought the Gurney-Weslake heads were still 2 valve but had a very much better breathing design and were lighter.
Also thought only for 302 and 351 Fords. Have I been wrong?

[Jac Mac]

[color="#0000FF"]Terry, first you have to differentiate between Gurney-Weslake & Weslake alone.
G/W built three versions of the 2 valve heads to suit the 289/302/351 blocks with 4.38" bore spacing, also built a 3 valve head with outboard inlet ports/center of vee exhausts for single seaters based on same motors.
Weslake alone have built many cylinder heads for many different makes thru the years, many of these being 4valve per cyl & pushrod operated. Thats where the head for the engine in question may have originated from[/color]

[Terry S]

[color="#0000FF"]Terry, first you have to differentiate between Gurney-Weslake & Weslake alone.
G/W built three versions of the 2 valve heads to suit the 289/302/351 blocks with 4.38" bore spacing, also built a 3 valve head with outboard inlet ports/center of vee exhausts for single seaters based on same motors.
Weslake alone have built many cylinder heads for many different makes thru the years, many of these being 4valve per cyl & pushrod operated. Thats where the head for the engine in question may have originated from[/color]

Thanks Jac. What you are saying is in line with my understanding.
What confused me was Steve in post #2 saying they were "Gurney-Weslake heads with 4 valves per cylinder".

[psychospence]

Where did you get the engine pic from? Just curious, it happens to be my hand in the photo!!

[Jac Mac]

Where did you get the engine pic from? Just curious, it happens to be my hand in the photo!!

[color="#0000CD"]Pic was among a few emailed to me by one of the previous UK owners, now if you can remember where & when it might have been taken & any story behind how/why the carb is removed & the somewhat unkempt engine bay appearance ( possibly carb fire/extinguisher residue?) I will pass that on to him. I dont think the pic was taken during his ownership.[/color]

[Limezed]

The Kar-Kraft Mustang appears to still be for sale
http://www.rkmotorscharlotte.com/sales/inventory/active#!/1970-Ford-Mustang-Boss-302/134505/247555
Would be nice for Dale's series, now where did I leave that spare US$280k

[alfettafan]

Finally, after literally years of searching i managed to find the copy of Auto Enthusiast magazine from May 1973 which featured the Dennis Leech Mustang. Attached below are the 3 pages scanned from the mag:-

Hope it is ok to post here, cheers, Alistair