Yelo

What I would like to discuss here is the difference between two motors of similar displacement but with different valve-train systems. The engines I would like to compare are the GM LR4 4.8L and the Ford Modular 4.6 SOHC.

First I'd like to compare the actual engines:

LR4 4.8:
Engine configuration: Single In-The Block-Cam Pushrod V8
Compression Ratio: 9.5:1
Bore: 3.779"
Stroke: 3.27"
Block: Cast Iron
Heads: Cast Aluminum
Pistons: Hypereutectic Aluminum
Rods: Forged Powdered Metal
Crankshaft: Cast Iron
Stock Cam Specs: 191*/190* .466"/.477" 114lsa
Stock Head Flow Intake Port CFM Numbers (1.89" valve):
.200": 137
.300": 187
.400": 223
.500": 237
.600": 243
Power Ratings:
HP: 275hp @ 5200rpm
Tq: 285ft/lbs @ 4000rpm

Typical Aftermarket Head CFM Flow numbers (2.02"/1.57" valves):
Intake-----Exhaust
.200": 133 .200: 108
.300": 194 .300: 147
.400": 242 .400: 183
.500": 274 .500: 205
.600": 296 .600: 220

Typical Aftermarket Camshaft Specs: 220*/220* .535"/.535" 112lsa

Modular 4.6 SOHC:
Engine configuration: Single Overhead Cam Per Head V8
Compression Ratio: 9.4:1 (9.3:1 - 9.74:1 depending on year)
Bore: 3.552"
Stroke: 3.543"
Block: Cast Aluminum
Heads: Cast Aluminum
Pistons: Hypereutectic Aluminum
Rods: Forged Powdered Metal
Crankshaft: Cast Iron
Stock Cam Specs: 192*/184* .535"/.505" 114.5lsa (186*/194* .505"/.534" possible too)
Stock Head Flow Intake Port CFM Numbers (1.752" valve):
.200": 102
.300": 138
.400": 153
.500": 156
.600": 160
Power Ratings:
HP: 260hp @ 5250rpm
TQ: 302ft/lbs @ 4000RPM

Typical Aftermarket Head CFM Flow numbers (1.78"/1.452" valves):
Intake-----Exhaust
.200": 116 .200: 98
.300": 162 .300: 135
.400": 192 .400: 162
.500": 213 .500: 182
.600": 218 .600: 193

Typical Aftermarket Camshaft Specs: 218*/228* .550/.550 113lsa

Both engines are fully capable for 400fwhp with a heads/cam/exhaust/tune...but use radically different parts to do so....

Now that we've got a good numbers comparison here's where the <TECH ONLY> portion of this thread comes in:

Can someone explain to me exactly HOW these engines, which have radically different architectures are making similar power in stock form....and why does the 4.6 seem to be able to do this with not only less displacement, but also significantly lower-flowing heads and a less radical cam. Does it have something to do with the overhead cams ??, or is it the square bore/stroke, or is it cam profiles ??.....help me out here to understand this

I'd like a in-depth technical discussion here....I REALLY have no idea how the 4.6 is capable of doing what it's doing, and why it responds to heads/cams combinations that if put on an LSx would make it untunable/undriveable....I know this is the GM Performance and Technical section, but as I've been a member here for almost 4 years YOU are the guys I turn to for answers......

Mangled03gmc

iTrader: (95)

I can only guess that the 4.6 makes what it makes because of teh overhead cams , the bore and stroke is so close. Only reason I can say is that even the v-6 motors are making crazy hp for what they are, the ones that are are all overhead cam motors.. Sry but thats about is exact as I can get for ya.

PSM

iTrader: (3)

This is my stab at an explination. The 4.6 seems to be a bit more tq based then the 4.8... prob partially due to its being more of a square cylinder and not so bore happy like the 4.8


i found this cam info for the 4.6... seems different from what you have

"From 1991-'98, the SOHC has .482-inch valve lift, with duration of 204/208 degrees intake/exhaust. With the PI heads in 1999, Ford went to .535-inch valve lift intake and .505-inch exhaust, with reduced durations of 192-degrees intake and 184-degrees exhaust. This approach improved low-end torque according to Sean Hyland."


Now lets look at the cams.... they seam to have similar durations... with the 4.6 having a bit smaller exhaust. If you notice the 4.6 has a much greater lift than the 4.8 on both lobes... perhaps that helps it breathe a bit better with its choked heads. I have no idea what the exhasut port flows look like. That could contribute to the power profile. The comp ratio is a bit more on the 4.6 (9.73 vs 9.5).

One thought on the heads is that maybe... just maybe the heads flow a bit too well for the 4.8 in stock form and since they attempted to give the 4.8 some low end for truck use they had to rob power from its potential. Having "choked" heads doesn't necesarily mean low power.. they could aid in port velocity and help rather than hurt.

Other ideas are rotating mass of each motor, piston friction, pumping losses...

Take all of this with a grain of salt... for it is all jsut a guess

Yelo

I corrected the exhuast port lift number....sorry for the type and thanks for catching it.

CR on the 99+ 4.6 is 9.4:1.....I added that info above too

I have wondered if the 4.6 heads rely on port velocity instead of overall port flow....but at high rpm's I wonder of the smaller intake valve is capable of flowing enough to fill the cylinder. I'll try to get exhaust flow numbers

PSM

iTrader: (3)

I believe that adding more duration to a cam is a way of compinsating for bad head flow. That could be why the cams on a 4.6 are much more driveable.

also.. i hate to be a pain in the ***..... but i found this (notice the comp change in 2000 along with the TB change... man they are small)


1999 4.6 SOHC 260HP Mustang Engine
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Throttle body: 66.8mm (2.630 inches)
Intake manifold: composite, cast No. XR3E-DC
Cylinder heads: cast No. RFXL3-CZOD
Combustion chambers: 42.40cc
Valves: 1.752/1.417 inches
Rockers: roller type, w/1.80:1 ratio
Camshaft lift: .505/.534-inch lift Duration (I/E) @ .050" 186/194
Compression ratio: 9.30:1
Pistons: hypereutectic w/.188-inch dish



2000 4.6 SOHC 260HP Mustang Engine

Throttle body: 65mm (2.560 inches)
Intake manifold: composite, cast No. XR3E-DC
Cylinder heads: cast No. RFXL3-CZOD
Combustion chambers: 42.45cc
Valves: 1.752/1.417 inches
Rockers: roller type, w/1.81:1 ratio
Camshaft lift: .505/.534-inch lift Duration (I/E) @ .050" 186/194
Compression ratio: 9.74:1
Pistons: hypereutectic w/.188-inch dish

Yelo

Erm......well, then I'm not sure on CR so I'll throw all choices into the description, but I'm going to stick with what I've got for cam specs, I'm going straight out of Sean Hylands book (How to Build Max Performance 4.6-Liter Ford Engines) for that info so I'm pretty sure it's right ('99/'00 had both Romeo and Windsor motors, each had different internal components from the other....the Romeo motor was discontinued in '01 and internals were redesigned for the Windsor so this may be where the different cam specs come from)

BTW.....where did that info come from, I'd love to have another resource to get info on these

PSM

iTrader: (3)

http://www.modulardepot.com/modspecs.php#top

Ya sorry for being nit picky but here is where I found the info... I read a bit on the different 4.6 block/heads in hot rod, but not enough to remember all the facts. I hope you get more opinions in here.. it could be a very good discussion since both motors are very different.

BTW how do you like the stang... I love how those motors sound.... much bigger than they are. My fav stang was the last gen cobra... 4.6 s'charged with IRS. I think ford went to cheap with the new cobra... iron block and axle in the back.... making it even more nose heavy. If they went alum block and IRS they would have taken weight off the front and put it in the back making the distribution much better

treyZ28

strange how it makes more torque at the same rpm (and a lot more) yet makes less power at the same rpm (4.6 vs 4.8)

first off the numbrs dont make any sense. In order to make 285hp at 5200 rpm, you have to have 287.9ftlbs. GM claims their peak torque is 285ft lbs at 4000rpm. BS right off the bat- something isn't right. GM is obvously undervalueing the torque to make it appear that the torque is lower.

A big bore, short stroke engine with big open runners and big valves is going to make its peak torque higher than a big stroke, short bore, small valved, small runner engine. So I'd venture to guess their torques are ACTUALLY damn close- which they should be. Torque is basically entirely displacement dependent when engines are similar (comparing stock, production, same era OEM engines- no a 77 smog motor to a NASCAR engine)
Also strange because bigger bores should make more torque.

at 4k rpm the 4.6 and 4.8 have 302ft lbs and 285 ft lbs respectively. [/color]
at ~5225rpm, they have about 260ftlbs and 290ftlbs respectively.

That should tell you something about the torque curves

at least between 4k and mid 5k- the 4.8 is basically a flat line. the 4.6 drops 30 ft lbs. I'm guessing this is because the 4.6 makes its torque way lower than the 4.8- which it should, given its specs.

Id like to see each on a dyno. I'd venture to say the 4.8 would out torque the 4.6 after 3k all the way to 6k and have more torque under the curve. The 4.6 might actually be a better tow engine.

Black02Z71

I really don't think you can compare a car engine to a truck engine. Those 4.6L ratings are for a mustang, which has a dual exhaust system with h pipe.

The 4.6L only makes 231hp at 4750rpm and 293 ftlbs at 3500rpm, in a truck.

If you were to put the 4.8L and the car 4.6L on an engine dyno with similar exhaust setups, then I can see comparing it.

The mod motors are great for peak low end torque, and are useless at higher rpm. If you go drive an f-150 with a 4.6 or 5.4 you'll know what I mean, they feel like a super strong motor, till you give it some throttle, then it almost feels like your going slower. Even the new 3v 5.4L is the same way, it feels really torquey at low rpms, but as soon as it downshifts it feels gutless.

treyZ28

ahh that explains part of it. we're comparing mustang to truck engine.

I agree about the 5.4 3V. I almost bought one after hearing all the hype but decided I liked my 4.8 w/ tune better Well, I certainly love the Lq9 + tune more, thats for sure, not to mention the $6-10k in my pocket. Their back seat of the ext cab sucks too.