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Discussion Starter · #1 ·
Hey guys, i'm new to this forum, but i've been doing a lot of reading and research on mod motors. I have 1991 notchback currently putting out 306 hp and 311 torque with a worked 5.0L pushrod motor. I'm considering doing a swap to a 03/04 5.4L mod motor from a Navigator. I'd like 400hp and 500tq I have a few questions that I'm hoping you guys can help me out with...

  • I see that these motors are rated at 300HP and 355 ft/lbs, are these numbers accurate?
  • I've been considering just running it carb to avoid the wiring headaches of fuel injection. What intake manifold/carb could I use for this?
  • What should I do as far as cams/heads to reach the power goal stated above? and will the stock bottom end handle the power?
  • I know AJE makes the K-member and the tranny crossmember, but which 6 speed manual will bolt directly onto this motor?
  • Opinions on custom headers? Will a huge amount of power be lost by keeping the stock manifolds?
Sorry for the n00b questions but i'm really new to the mod motor thing. I'm just trying to be a part of all this new technology that seems like it puts the pushrods i love to shame :cry2:

Thanks in advance for any help!!

Chris

here's my car: soon to be lowered/shocks and struts/10th anniversary cobra wheels
 

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Check out this thread of my build.
The thread is VERY LONG but many pics.
It IS possible to do it in a fox chassis.
400 RWHP is relatively easy to make with a 5.4 NA.

http://www.mach1registry.org/forums/showthread.php?t=57118

I am currently finishing up the car,
and building a 5.4 32V motor for my buddy's 98 Cobra.
 

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Discussion Starter · #3 ·
thanks for the link birdman, i read through pretty much your entire build thread... as far as the swap goes i'm not sure there are enough similarities between a 1991 and a 2004 for it to be of much use to me logistically... although all the info on the motor and your sources for parts will surely be extremely helpful, thanks!

do you have any advice for me before setting out to do the swap? how do you feel on the carbed vs. EFI dilemma? how about the heads and cams? thanks in advance!

Chris
 

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Actually, a lot of things WILL work.
And go EFI.
Best of both worlds for a DD or weekend warrior.
Use the Aussie intake.
I have plenty.
I also have a couple of OE (modular) crossmembers here.
 

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Discussion Starter · #5 ·
thank you very much for the advice birdman, i didn't mean to imply that your thread wasn't helpful, because it definitely was, i'm sorry if it came off that way, i promise it was not my intention


would you suggest just running the stock navi bottom end, heads, and cams, with the aussie intake? are you selling the ones you have or saving them for when they become more rare?
 

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I am doing the same build with my 92' notch, and am save up for birdman's kit. I think it would look killer opening the hood of an older fox and seeing that engine combo, by the way birdman what is your kit going for now-a-days. Pm me the price when you get a chance.
 

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For a street car birdmans intake is the best bet, unless you want a high rpm race engine dont get any of the short runner intakes ie sullivan or mmr.
 

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thank you very much for the advice birdman, i didn't mean to imply that your thread wasn't helpful, because it definitely was, i'm sorry if it came off that way, i promise it was not my intention

would you suggest just running the stock navi bottom end, heads, and cams, with the aussie intake? are you selling the ones you have or saving them for when they become more rare?
No worries.

You can use Navi heads, but there is a minor intake port mismatch.
I do have a set with 600 miles on them available in the parts for sale section.
Also 99-01 or 03-04 Cobra/Mach 1 heads can be used.
On a Fox, I think you may need to use manual brakes.
A nice, relatively smooth and torquey setup might be FR500 cams.
They are not perfectly setup for a 5.4, but will run well.
Modmax rods w/ARP bolts are around 500 at Lethal.
I think Mahle makes forged flat top pistons with a 1.2mm
offset pin, and those will get you a shade over 10:1 CR.
There are a few guys on here who have done a 4.6 32V swap
into a Fox chassis car.
the wiring would be identical to what they used.
I also have a 98 Cobra motor, pretty much complete in the next week or so.
 

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Discussion Starter · #10 ·
thanks again birdman! if i wanted to save some cash, would the stock Navi bottom end and rotating assembly hold up to 400 horsepower and 450(?) tq n/a in street trim? i wouldn't be revving the thing past 5500 rpm or whatever the cams make peak power at... i know pushrod 351w blocks are good for that power level and much more, but as you know by now, the mod motor thing is new to me, but could i make those levels safely without tearing into the shortblock? thanks!

Chris
 

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You should be ok at that power level. The navi has 9.5:1 compression, it has a forged crank but not rods and pistons. The block is good for upwards of 600-1000 RWHP, there are cars out there with that much on the stock block.
 

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Agreed, stock bottom end will be ok at those RPM levels.
 

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Discussion Starter · #13 ·
Thanks for the info guys, I've been doing some more reading. So far as I can tell I'll need the motor, T56, intake manifold, AJE K-member and tranny crossmember, as well as the complete computer and wiring harness from the Navi. Is there anything I'm missing? I have a few more questions though, please excuse me if they sound stupid or ridiculous to informed ears like all of yours.

I'm clueless when it comes to the mod motor fuel system stuff, can I run my stock fox tank and 255 lph in-tank walbro to the navi motor? Will the T56 bellhousing bolt up to the navi motor? Will I need a custom driveshaft, or a different rearend? Thanks in advance for any help.

Chris
 

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The navi harness is the wrong harnes and computer to use. I would use a cobra computer and harness. The tank should be fine and the pump should be fine but the fuel rail may not match up where your fox fuel rail did making it difficult to connect the fuel system. Call D&D performance (http://www.ddperformance.com/) for the T-56 swap. They can hook you up with all you need to put it in and make it work with your swap. Your rear axle should be good if its an 8.8 and not a 7.5.
 
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