Need advice for a new shortblock for 03 cobra

[Fordtech7]

I will be using the factory Eaton blower and likely the factory heads although I have gt500 heads laying around. I’m just a newbie but I need a new shortblock. The 5.3 from ford performance had my eye. The 5.0 boss block (4.6 deck) with standard stroked forged crank seemed to be safer option. And of course there are aluminum sleeves built shortblocks with standard bores and optional strike. My car is heavy and it’s a street car. My power goals are a little more than stock 03 cobra specs. Looking for reliability and longevity with that kind of power level for daily use. Looking for insight beyond do a bigger blower. I want to leave that option open for later. Thanks everyone, looking forward to the wisdom here.

 

[tt335ci03cobra]

I recommend Livernois Motorsport. I did a lot of research before having them do my 5.3. They steered me away from some unneeded and expensive ideas which I appreciated (sheetmetal intake, higher compression, hotter cam, etc etc.)

Another excellent engine builder is John Mihovitz. Probably the best there is. He won’t do any build that could have a propensity to fail. He’s legendary. I spoke with him mid way through my build to troubleshoot timing chain failures. Exceptional guy to have had the chance to speak with. Straight shooter.

L&M I’ve heard is also excellent but I haven’t worked with or contacted them.

 

[Fordtech7]

Thanks for your contribution. I will look into those avenues. Interested in hearing more about your build as well...

 

[tt335ci03cobra]

I would defer to their wisdom.

My opinion* or course of action based on what you describe would be assuming 500-550whp so I would build a 650whp capable assembly for added safety.

~9.5/1 compression
•spring for an Ibeam rod to save a little weight.
•only do a big bore/stroker from a company like Livernois. Even the ford strokers and big bores have seen failure (from what I researched in 2014/15) from rod ratio and piston slap. This is when the skirt of the piston leaves the bottom of the block at bottom dead center. It’s bad.
•fuel look into 55# or 60# injectors
•consult with the builders I recommended and compare notes. Honestly, they’ll save you time


Optional just for efficiency and ability to run lower boost.

•port the heads stage 2 port/polish while they off.
•stage 2 blower cam especially if you can find them used. It’ll be expensive to do this though, plan on $3500... but you’ll be able to run lower boost which prolongs the life of the motor.

Boost is a representation of restriction. You could run a 3.0 pulley so as not to stress the components and still make more power than a 2.6 or 2.8 pulley stock head/cam car.

 

[Fordtech7]

Sounds like great advice to me. I think I will follow it. Nice to have some guidance. Thanks for the additional information, it helped me conceptualize my build as well as what avenues to pursue for quality.

 

[zredfire04]

why not just rebuild your current block? you're not going for big power, no reason to reinvent the wheel IMO.

 

[Wings65288]

Livernois was who I was gonna go with but then decided to just build it myself. Had I not done that I would have either gone Livernois OR a hidden gem is ModMax. ModMax knows their stuff, a guy there named Dale was EXTREMELY helpful there and it sounded like they were VERY dialed with our mod motors hence their name lol.

 

[01yellercobra]

I built my 5.3 back when I had a centri. Even daily drove it for a while. So I'm a fan of them. Plus I'm old school and always say no replacement for displacement. That engine made around 500rwhp on a Mustang dyno at 12psi and similar timing. Stock 03 Cobra heads with Ford GT cams and 9.5 compression. I think I still had the stock exhaust manifolds on it as well. The intake was definitely a stock 01 intake.

 

[Fordtech7]

why not just rebuild your current block? you're not going for big power, no reason to reinvent the wheel IMO.

 

[Fordtech7]

I figured there was a lot that could be learned from for building a better motor 15+ years after the fact with all the experience here and the additional resources that are available in today’s world is all, so I thought I’d ask about it... My current block is a no go.

 

[Fordtech7]

I built my 5.3 back when I had a centri. Even daily drove it for a while. So I'm a fan of them. Plus I'm old school and always say no replacement for displacement. That engine made around 500rwhp on a Mustang dyno at 12psi and similar timing. Stock 03 Cobra heads with Ford GT cams and 9.5 compression. I think I still had the stock exhaust manifolds on it as well. The intake was definitely a stock

 

[jrgoffin]

Go with the aluminum block. Here's 50+ pages of build thread with lots of upgrades. Started with the ported Eaton and ultimately went Whipple. Fired it up three years ago and going strong since.

----> Aluminator Gibtec Build

 

[tt335ci03cobra]

A nice teksid is a great starting point.

I went aluminum as well.

If you are unable to reuse your factory block, a teksid is an excellent idea in this application or really any.

 

[Wings65288]

Yeah that's what I used, went to a junkyard and pulled a Teksid out of a '93 Lincoln Mark VIII for $225

 

[blownstang4.6]

What's wrong with your current motor? How much power are you looking to make? What is a litte more than stock 03 cobra specs? 450rwhp? 500rwhp? Your keeping to factory blower so I'm guessing you don't want big power? You don't need anything fancy in that case. I wouldn't even consider wasting money or time on doing any kind of head or cam crap. Put that money towards a better blower if anything. Have your stock motor inspected if there is something wrong with it. Keep the block, crank, rods if in good condition. Toss the junk low compression pistons. Replace with pistons that put you closer to 10.0. What fuel will you be using? Have you considered E85?