2003 Mach 1 engine in a 1999 Cobra?

srochefort · 02-27-2009

Please read the whole story before offering input. I did the Eaton swap from a 2003 Cobra to my 1999. Everything went fine, had to switch out a "lot" more than was originally anticipated. During the 2nd day of a track event, I broke a piston ring. (My tuner, Pro Dyno, told me not to be running it at WOT, sorry Dan I should have listened) Anyway, the plan was to buy a long block and drop it in. However the $6000+ price tag is not an option right now. So, I found a complete setup from a 99 Cobra from MPS Auto Salvage. I figured I could just put it back to stock for now and have the other engine built later. I chose the buy it now option on ebay and immediately paid for the engine. 2 days later, they sent me an email saying that someone had purchased the engine from the store front, 2 hours prior to me buying it online. Now they are offering a 2003 Mach 1 engine in it's place. And now for my questions.
1. Will the Mach 1 fit into my 99 Cobra? Keep in mind that I have already swapped it for the 03 model and I do not want to do any more custom work. I still have all the stock 99 parts.
2. Is it beneficial? I know the 99 Cobra engine is rated at 320 HP while the Mach 1 is 305. Also, it is from an automatic which has the 6 bolt crank. My car is manual.

Gary Paul · 02-27-2009

Comparing the 4.6L DOHC V8 in the 1999 + 2001 SVT Cobras with the 4.6L DOHC V8 in the 2003 + 2004 Mach 1 Mustangs, both have aluminum blocks, aluminum heads, aluminum intake manifolds and utilize the same engine mounting points.

The Cobra motor has 9.85:1 compression with 320hp and 317 lb/ft of torque. The Mach 1 motor has 10.1:1 compression with 305hp and 320 lb/ft of torque. They use different heads and different intake manifolds with the Mach 1 designed for more mid-range power and the Cobra for top end horsepower. However, the Cobras all came with 3.27:1 rear gears while the Mach 1s came with 3.55:1 gears. A stock Mach 1 should be a bit faster than a stock '01 Cobra, but if you swap 3.73:1 or 4.10:1 gears into the Cobra and get it into its higher power band quicker the Cobra will easily take the Mach 1.

One problem is that the 4.6L in the 5-speed manual Mach 1 has a forged crank and 6500 rpm redline, while the 4.6L in the auto Mach 1 has a cast crank and 5500 rpm redline from the factory. I would not want the cast crank for my car and don't recommend it for yours. Sorry.

srochefort · 02-28-2009

Thanks for the input. I decided to not get the Mach 1 engine due to the 6 bolt cast crank and the lower redline. Good news though, I found a 2001 Cobra motor with 50,000 miles on it for about the same price. Unless I am mistaken, this should fit right into my 99 Cobra with no changes at all. Thanks again, and wish me luck.

Brutal Metal · 03-01-2009

Yes Mach 1 automatic Cranks are inferior, go with the 2001 Cobra motor, it's a direct replacement!