5.4 ?????

Jrgunn5150 · Dec 8, 2007

Wouldn't a 4.6 piston have a different compression height?

r3dn3ck · Dec 9, 2007

IIRC in stock trim the 5.4 uses 4.6 pistons... they're the same units as the 4.6 slugs. Some aftermarket companies (probe) stock 5.4 and 4.6 pistons that are different in compression height and that ends up with flat tops yeilding like 14:1 compression. Using 4.6 slugs makes for a much easier time getting a forged piston to fit streetable compression ratios without having to go to a big dish. This also makes mega high lift cams easier to deal with as you won't have to notch the pistons.

I use a 4.5cc dish 4.6 slug for 10.5:1.

AaRoN · Dec 9, 2007

Good info in here, lots of reading but good info O0

Jrgunn5150 · Dec 9, 2007

Compression height is the distance from the center of the wristpin to the top of the piston. It has no bearing on compression ratio. If the 4.6 and 5.4 use the same rods (I don't know if they do or not) they can't have the same compression height due to the different strokes, which is why I asked. One way or the other, either rod's or pistons will be more expensive for the 5.4, due to one or the other being unique to a rarely built motor. I'm just curious as to how much?

r3dn3ck · Dec 10, 2007

they don't have the same length rods which makes the compression height a factor in compression ratio. probe offers 2 different sets of pistons, 1 has a stock 4.6 compression height but one is quite a bit taller and removes some of the excess deck clearance that the 5.4 has and turns it into an interference engine where cam selection becomes an issue again (pretty much any off-the-shelf cam will fit the 5.4 without PTV).

I get tired of saying this so please everyone read it thoroughly: RODS AND PISTONS FOR 5.4 DON'T COST MORE. You just have to shop wisely and not accept full pop retail as the price. The pistons are identical. Use 4.6L spec and the deck clearance stays .1+HG.

I got my 4340 H-beam forged rods with ARP 2000 rod bolts for 280 bucks on a GP. You can spend up to 1000 bucks on rods but they're really the same exact cost as the 4.6 rods if you look at MSRP's for both in the same class of rod. Go to ebay, buy the TMD H-beams and be happy with having gotten the best deal to be had. For pistons, I'd recommend spending wisely. If you don't plan on using a power adder then Keith Black HE cast pistons are a great deal. Otherwise, TMD sells Mahle's for 500 and coin with rings.

justinschmidt1 · Dec 10, 2007

So I have a npi engine with a pi intake and adapter plates.

What would I need to make it a 5.4?

Im really interested now.

voidfinger · Dec 10, 2007

Hey red, any one working on a 5.4 3v intake? just wondering... i'm thinking if i'm going to take the time to do some forged internals on the motor i might as well see if the 3v is an option since they flow soooo much better. :xmascheers:

Mesarina · Dec 10, 2007

i have been thinkin about a 5.4 DOHC since a long time... what would i need to do, if i have a 96 Cobra...

Blacksunshine98 · Dec 11, 2007

i just bought a set of 5.4 heads off a harley davidons truck that was supercharged.i am planing a supercharger in the near future will installing them with the bumpsticks that are in the heads now hurt my car at all?

Jrgunn5150 · Dec 11, 2007

Blacksunshine98 said:
i just bought a set of 5.4 heads off a harley davidons truck that was supercharged.i am planing a supercharger in the near future will installing them with the bumpsticks that are in the heads now hurt my car at all?

No, the cams are the same as all PI cams.

Blacksunshine98 · Dec 11, 2007

thanx for the quick responce :santa_afro:

Jrgunn5150 said:
Blacksunshine98 said:

i just bought a set of 5.4 heads off a harley davidons truck that was supercharged.i am planing a supercharger in the near future will installing them with the bumpsticks that are in the heads now hurt my car at all?

Click to expand...

No, the cams are the same as all PI cams.

r3dn3ck · Dec 11, 2007

justinschmidt1 said:
So I have a npi engine with a pi intake and adapter plates.

What would I need to make it a 5.4?

Im really interested now.

You'd NEED a 5.4 shortblock and front cover w/ tensioner and a tune. Better heads and cams and all that jazz is optional. I'd be really concerned about using the NPI heads without proper NPI to PI adapter plates if you're going to use adapter plates for the intake. There's enough ill fitting crap messing up the air flow path as it is without having to deal with that. PI heads are a real boon from what we've seen so far.

Mesarina said:
i have been thinkin about a 5.4 DOHC since a long time... what would i need to do, if i have a 96 Cobra...

Best option is to buy a navigator engine complete. You'll have all the parts and the block will already have the extra hole drilled for the 4v application. Otherwise, you'll need a block and front cover and to decide on an intake solution. To add some K-member clearance go down to a local machine shop with a used stock or tubular k-member and a spare tranny mount and have them whittle you out a set of aluminum spacers .4" thick for each of the attachment points and .2" thick for the tranny mount. This is optional but it'll work to get you a little extra valve cover clearance. You'll have to put the motor in from the bottom as well.

If you call up Al Papito at Boss330 racing (check the corral or google him) he can help you through all the details of converting a cobra to a 5.4. You're staring at 400+rwhp NA if you do a good job on parts selection.

justinschmidt1 · Dec 11, 2007

What do you mean by pi heads are a real boon?

I would be best off getting pi heads,pi cams, the 5.4 shortblock, front cover and tensioner.

How much more power does a pi 5.4 make over a pi 4.6?

Ive been hearing people say it will make like no more horsepower but more torque.

Is it even worth it?

Jrgunn5150 · Dec 11, 2007

It's worth it, and it's hard to make more torque without more horsepower, since horsepower is just a make beleive expression derived from how much torque an engine makes....

voidfinger · Dec 11, 2007

lol yea the 5.4 2v makes more hp ... not a lot more, but the torque is what the 4.6's were lacking to start with... so more torque = more fun and faster. lets put it this way... a 4.6 L pi motor in a 96-98 vert auto running like 14's... and a 5.4 2v PI in same car running 12's... difference? i think so.

justinschmidt1 · Dec 11, 2007

voidfinger said:
lol yea the 5.4 2v makes more hp ... not a lot more, but the torque is what the 4.6's were lacking to start with... so more torque = more fun and faster. lets put it this way... a 4.6 L pi motor in a 96-98 vert auto running like 14's... and a 5.4 2v PI in same car running 12's... difference? i think so.

No way.....

Your telling me if I had a 14.0 second Pi vert 96-98 made it a 5.4 it would run like 12.9?

Thats unbelievable ...literally...I dont beleive it would do that much....maybe from 14.0 to like 13.3

voidfinger · Dec 11, 2007

Can't say for sure but i could see it going high 12's. Plus Red seen it happen so i think it is highly possible.

justinschmidt1 · Dec 11, 2007

jeez..if thats true...swapping pi heads with a 5.4 block might be more worth it than slapping a blower on the crappy npi heads.

If im running high 13s trapping 102 now...according to that I would be solidly into the 12s..which is probably where id be with a blower...

Mesarina · Dec 11, 2007

r3dn3ck said:
Mesarina said:

i have been thinkin about a 5.4 DOHC since a long time... what would i need to do, if i have a 96 Cobra...

Click to expand...

Best option is to buy a navigator engine complete. You'll have all the parts and the block will already have the extra hole drilled for the 4v application. Otherwise, you'll need a block and front cover and to decide on an intake solution. To add some K-member clearance go down to a local machine shop with a used stock or tubular k-member and a spare tranny mount and have them whittle you out a set of aluminum spacers .4" thick for each of the attachment points and .2" thick for the tranny mount. This is optional but it'll work to get you a little extra valve cover clearance. You'll have to put the motor in from the bottom as well.

If you call up Al Papito at Boss330 racing (check the corral or google him) he can help you through all the details of converting a cobra to a 5.4. You're staring at 400+rwhp NA if you do a good job on parts selection.

thanks for the response, i don't remember which heads does the 5.4 out of a navigator has..if they are different, which heads should i use, the ones on the 5.4 or the b-heads of my 4.6? ... getting interested and i haven't finished another proyect yet... lol

voidfinger · Dec 11, 2007

the navi heads are really good but the intake ports are bigger than the average c head. I've seen a thing sold at karkraft that lets you use the navi everything but uses the karkraft top intake lid that makes it work... looks awsome.