Boss 429 Mustang V8

can anybody tell me what these motors were?
Which block/heads, real world power etc?
I remember drooling over them as a teenager, and thought they were THE BUSINESS!


I used to own a 1969 Boss 429 Mustang. MY # was KK429 NASCAR 1998.

It is a 429 CID with 4-bolt mains, forged crank, giant oval-shaped intakes, semi (as mine was) or full HEMI heads, and it didn't use head gaskets. The heads were separated from the block by little O-rings.

They were rated at 375 HP but reality was more near 550.

The car was totally awesome and I regret selling it to a man in Portland, Oregon back in 1977. I was getting married and thought I needed the money.

All I have remaining is an intake valve (it's huge), some photos and some super 8 film.

Thanks for your posting and if you ever put one in a MKII (I don't believe it would fit a MKI) be sure to let everyone know.

Thanks a bunch,

"Scuse my ignorance..but is the block related to the one used in the 7 litre GT40's..which, I believe, had water circulation dramas, and therefore tended to overheat?
No, the Boss 429 is a completly different animal. The block is basicly a 4 bolt main 429 (part of the Ford 385 engine series of 429 & 460) with semi-hemi heads. The LeMans winning 7 liters were 427's (ie Cobra)and belong to the Ford FE engine series of 352, 390, and 428 motors.

I forgot to mention that the Boss 429 was developed to compete with the 426 Chrysler HEMI in NASCAR. NASCAR wisely banned the HEMI’s from competition. You can now find Boss 429’s competing in the IHRA drag racing Pro Stock series except displacement is now in the 800 cubic inch neighborhood producing around 1400 horsepower with carburetors.You might want to check out the following web sites for Ford motor discussions. for the 427 series for the 429 series



Point of interest...

When Ford dropped the GT40 program, they
sold (2) leftover MK IV chassis to one of
Shelby's mechanics for next to nothing.

The mechanic (Charlie Agipou) and his brother
cut the roof off, dropped in a Boss 429, and went Can-Am racing. Unfortunately they were
underfunded and not very successful.

Rumor is they still own the car in Southern

One of the Agipou cars J9, which wasn't raced is still owned by them and is being restored. The other J10 was destroyed but it's "remains" were and are still being built into a MK-IV clone.
The LeMans MK-IV 427's if anything ran cool.
J5 the Foyt/Gurney car ran much of the race with it's radiator intake partially blocked off with cardboard. 35 years later my Mk-IV, with electric radiator fans and overspeeded water pump is fine on the street even on very hot days.
Mark IV J6,
Is your car the Gurney/Grant winner
in '67 ? It sounds like you are enjoying
the car and driving it. Being a retired
police officer I would have pulled you
over just to get a look at that beauty. I
bet that's happened before too.

MY car is J6 the Donohue/McLaren car that finished fourth overall at LeMans in 1967. J5
is the Foyt/Gurney car that won and it is in the Ford Museam. For years these numbers were confused. There is a pix of my car in the forum under MK-IV. It's the yellow #2 car.
I have been stopped but only in a friendly way.