Is this a Nailhead?

Looks like 2 Nailheads in a marine application

 

That's an AG-330 start cart for the SR-71

Yes. Nailhead

 

Twin 425s.

 

I've posted a thread about that starter kit, if I remember well it said two 401's.

Edit:

I stil had this screenshot from the article.
Same photo as the one in the first post:

Click screenshot to read the full article



Also:

In the mid-1970's, the engines of the start carts was changed to Chevrolet LS-7 454's.
The Chevrolet big block engines developed 465 horsepower each.
Even so, for many years they were still referred to as the Buick's.

 

From a post on the AACA Forums:

Starting at about 2:20 you can hear the Nailheads beginning to wind-up.
By about 2:30 they're really singing!




The Buicks would reach 4,800 to 4,900 rpm, the redline on the start cart, just to get the J58 to 3,200 rpm.
Overspeeding of the Buicks caused by a probe hang-up contributed to the occasional thrown connecting rod and oily parts dropping out from under the cart.

Idle speed for the J58 is 3,950 rpm, which could drive the Buicks to over 6,000 rpm.
The potential for engine failure, as well as the Buick exhaust stream, required the crew to stand only at the ends, not aside, the start cart.

On engine launch there was one AG-330 Buick for each SR engine.
For the first time observer of an SR-71 launch, the engine starts in themselves were almost indescribable.

For one thing there was no mufflers on the Buick engines.
As the Buick RPM was advanced, flames almost three feet long erupted from the side of the start cart.

It truly sounded like the beginning of the Indianapolis 500.

Combine that sound with the steady increase of SR-71 RPM to engine TEB ignition at 3,200 RPM
and then idle aircraft engine speed as the Blackbird comes to life.

 

I can assure you, they were 425s. I blew up more than a few. There was a start cart that had 1 425 and 1 401 (we never did find out why) and it would barely get the J-58 up to speed.

 

I forgot about the start cart. Looked like a friends flat bottom vintage race boat.
I have a good idea what it sounded like as I have some experience with Nailhead flames and open exhaust but higher Rpm than 6000. Awsome sound it is! Loud too!
My little sister liked it so much she became a Navy flight surgeon so she could fly too. She is even Carrier flight certified.

 

I believe that the transmissions were Dynaflows. It is my understanding that the Nailheads were selected for just that reason. The SR-71 people didn't like the gears shifting as was the case with other automatics. Someone on this forum said that when they went to Chevys because parts availability for the Buicks was becoming a problem; the Hydramatics were locked in high gear.

 

You are correct Sir! Twin Dynaflows feeding a common gearbox. I don't remember what the Chevy's used, but a TH 400 is likely.

 

You were an SR-71 ground crew member? A marvelous heritage, my friend.

 

Thanks. I was an assistant crew chief at Beale AFB for my first 5+ years in the Air Force.