4.0 SOHC Performance Motor Build | Page 15 | Ford Explorer Forums - Serious Explorations

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4.0 SOHC Performance Motor Build

I've been helping the mustang crowd come up with a decent set of rods to use in place of the stock forged I-beam rods and I've found a couple different options out there. I want to use this thread for documentation purposes for all the options found and eventually, there will be info about all things needed to build this motor along with the estimated cost. Finally, after the research is done I'm going to put a motor together.

The Objective

A 4.0 SOHC that will consistently hold 500HP and 600HP at the drag strip. (for a decent cost) - in other words, if this can't be done for a certain price, then a different motor is a better option.

Stock 4.0 SOHC INFO

Deck Height 8.858
Bore 3.953
Stroke 3.31
Rod Length 5.748
Piston Pin Height 1.44

Cylinder Bore
Diameter 3.9530
Out-of-round limit 0.0010
Taper 0.0010

Piston / Rings
Standard DIA 3.9520 3.9528
.5 MM OS 3.9716 3.9724
1 MM OS 3.9900 3.9910
Piston to bore limit 0.0012 0.0020
Compression Ring end gap (top) 0.0080 0.0180
Compression Ring end gap (Bottom) 0.0180 0.0280
Oil Ring Snug Fit

Crankshaft and connecting rods
Crankshaft endplay 0.0020 0.0126
Connection rod journal DIA 2.1250 2.1260
Out-of-round and Taper limit 0.0003
Bearing oil clearance (desired) 0.0003 0.0024
Bearing oil clearance (allowable) 0.0005 0.0020
Connection rod endplay 0.0036 0.0106
Main bearing journal DIA 2.2430 2.2440
Out-of-round and Taper limit 0.0003
Main bearing oil clearance (desired) 0.0008 0.0015
Main bearing oil clearance (allowable) 0.0005 0.0020

Valves and related
valve seat angle 45 Degrees
valve seat width 0.0600 0.0940
valve seat runout limit 0.0020
Stem diameter standard 0.2740 0.2750
stem to guide clearance 0.0010 0.0020
valve face angle 45 Degrees
valve face runout limit 0.0010

68CC cambered

lobe lift (intake and exhaust) 0.2590
Allowable Lobe lift loss 0.0050
endplay 0.0003 0.0070
Journal DIA (ALL) 1.1000 1.1040
Bearing Inside DIA (ALL) 1.1020 1.1040
Journal-to-bearing (oil) clearance Standard 0.0020 0.0040
Journal-to-bearing (oil) clearance Service Limit 0.0060


Rod Option 1

The first rod option is a Forged H-beam Manley rod that states it holds 700-800HP on a 4.6 V8. We v6 dudes have to overkill here because 500 HP on a v8 is different for 500HP on a v6.

4.6 L Stroker w/ 22 mm pin and a 2.000" crank journal
Part No. 14044-8
Center-to Center 5.850"
Big End Bore 2.125"
Big End Width .940"
Pin End Width .940"
Pin Bore .8671"
Gram Weight 612

Here is the rod.

With this rod option, the rod journal (big end with the lip) will have to be narrowed by .064" per side. It should only be the little lip you see sticking out. The chamfer will then have to be re-cut and this should be it.

This rod is longer than the stock 4.0 SOHC (Stock is 5.748" and this one is 5.840") this means the custom piston being made needs to have a shorter pin height.

Custom pistons with floating pins will then need to be made to whatever compression you want. These rods go for around $579.50 for a set of 8. This means if you buy 3 set's for a v6, the fourth set is free. Furthermore this means the rod cost per rod will be $72.44 (Not counting the machining cost) If we estimate the machining cost, say 150.00 per set of 8, we come up with $91.19 / rod.

The H-beam rod option already available for the 4.0 SOHC is $125.00 per rod so you can see we've already beat that.

So, to recap this option.

Estimate $91.19 / Rod
Estimate HP the rod can handle is 700-800HP

This should be good for 500HP on the 4.0 SOHC

Rod Option 2

SBC rods.

UPDATE (9-5-2009) - I've decided to go this route for rods. The first option is still available; however, the cost was the deciding factor.

The second rod option is a SBC eagle H-Beam rod that is 5.7" long from center to center. The stock 4.0 sohc rod is 5.748" so this rod is .048" shorter. This means the custom piston being made needs to have a longer pin height depending on the compression desired. The rod journal bore on this rod is 2.1" where as the stock 4.0 SOHC has a 2.125" rod journal. This means the bore has to be opened up. The cost per a set of 8 is lower for this rod ($359.00) so this puts us at $44.87 / rod. The machining cost will offset this and I'll update the thread when I get the info.

The good about this option is the ARP rod bolts are 7/16" where as the first option has 3/8" rod bolts.


Compression Ratio for boost

UPDATE (9-5-2009) - I've decided to go with a 9.5:1 compression ratio (custom forged piston) and then get the piston tops coated.

Here is a formula for helping pick a compression ratio for a boosted engine. Anything between 16:1 to 18:1 is what to shoot for on a street set-up. Anything above 20:1 is race car country.

((boost psi / 14.7) + 1) x motor compression = effective compression.

Here is the 4.0 SOHC with 9.7:1 compression running 14 LBS of boost...

Effective Compression

Here is the 4.0 SOHC with 9.5:1 compression running 14 LBS of boost...

Effective Compression

Here is the 4.0 SOHC with 9.5:1 compression running 16 LBS of boost...

Effective Compression

Here is the 4.0 SOHC with 9.5:1 compression running 50 LBS of boost...

Effective Compression
(Okay, this is a little much)

A motor with 8:1 compression running 18 lbs boost VS a 9.5:1 compression motor running 12 lbs boost will have almost the same effective compression and about the same peak power. The big difference will be where you see the power, and how much of a demand will be placed on the supercharger/turbo. Obviously, the 9.5:1 motor is going to have far greater torque and low end power as the boost is only starting to come in. It is also going to be much easier to find a blower/turbo to survive at only 12 lbs of boost -vs- one that would have to put out 18 lbs of boost. It is now very easy to see why a higher compression motor with lower boost is becoming so popular.

Assembly Instructions

Download SOHC_Engine.pdf from FileFactory.com

There's still a BUNCH of work that needs to be done here so this should be considered "A work in progress" until I remove this line from the thread.

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The changes (I remember cuss I don't get to work on it often)

Wider tires so I can give if more gas out of the hole.
PVC evac system with the help of the turbo to pull it out (didn't do much if you ask me)
Exhaust cut-out right off the turbo
Meth injection
9 to 12lbs of boost

The rest is just supporting mods. I'm probably forgetting something.

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I didn't run this past weekend but my buddy did!

I promised this along time ago. Not a great pic but better than nothing. This is my X sitting in the back yard and getting hungry.


Yes, they actually look pretty good on a sport. The fronts had to modified to fit, bored out. (not the hubcentric part but the lip where the center cap fits)

So I still have to have center caps custom made to fit the fronts. The rears fit perfect. I'm running 255-50-18's on the front and 295-45-18's on the rear.

no grey cladding anymore, which really makes a difference in my opinion. I used bed liner and krylon fusion satin (over a year ago); seems to be holding up quite well.

I'll try and get some clearer pics soon.

Looks great Jake!!! It wouldn't hurt to take a few more;)

Any chance of hitting the track this year or is it over for you? I didn't get to do what I wanted this year because I had a big purchase recently(;)) and that left no money to play with. Also got the lady a new car so that didn't help either, but it's a sweet and quick ride. Hopefully 2012 will be the year that I can take the #1 NA spot if my Explorer feels up to it....

Edit: Didn't see your previous post. Have you lowered it at all or is that in the works???

No, I still want a lower time with what I have, so the track is still on my to do list. But like you, other priorities take front seat to this.

It's lowered by 1" now but needs a little more. (another one on my to do list)

I want to start driving this everyday so I'm working on the comfort part of the truck. I've actually done a lot of interior work and want to add custom seats soon. Maybe a sub. I'm going to put a cat converter back on it and have the cut-out before that. (so I'll have the best of both worlds) fun fun fun

I'd like to throw some information in this thread... Now this research and these parts are based on a 4.0 OHV motor with 49CC heads so when calculating compression take that into consideration... but here it is...

Probe pistons from for a 331/347:

Bore 4.000"
Compression height 1.175
20.1cc dish

Eagle 6.000" rod for sbc with journal bore turned out 0.025" to mate to the 2.125 rod journal on the 4.0 crank

with a stock 4.0 crank

These parts are advertised to handle 700hp in a v8, meaning it'll be able to handle whatever i throw at it basically (350-400 rwhp)

This combination of parts gives me a .013" deck clearance which should give me plenty of quench in the cylinder.

with my 49cc heads i'd be sitting at 9.51:1 compression, which is exactly in the range that I am wanting to be at.

Bottom line.. i think this has great potential! The only thing i really gotta figure out first before going forward is what the machining will cost to get the rods reworked a little, don't think it'll be too far outta the park though. I'll have a spare 94 4.0 motor here in a couple weeks that i can tear down (90-94 blocks are thicker and allow for the 4.000" bore without compromising a ton of strength)

Interesting, they can reach to a 4.0 bore. What exactly is the bore spacing of the 4.0 blocks?

If the rod lengths are that close to a common 302 or Chevy, I'd be working out a stroker piston and rod, and have the crank turned a bit.

i'm not sure on the bore spacing, but the most knowledgable guy i know on these older 4.0s stated that the 90-94 blocks can safely hold a 4" bore and i believe him.

as far as stroking the motor.. i'm not really interested in it because it'll raise the machining cost quite a bit and i rather keep it a fairly easy, good revving motor which ill have with the current picked combo of parts

Jake is going to get a new 4.0 engine built one day, and find a trans strong enough to take the power. He and lots of people could use any new information that we can dig up.

It looks like a strong stroker crank may be the one needed special part for the engine.

yeah a stroker crank would be cool, but i only know of morana's stroker kits/crank available.

The parts i listed would work for either ohv or sohc, but you'd probably want to run a smaller dish on the pistons to bump the compression to where it should be since the champers on the sohc heads are about 11cc larger.

I have a couple emails out to some machine shops getting quotes on what the machining will run for the rods and the bore.

I'm trying like heck to get in the 12's with a the stock block. I would really like to make this goal before I continue.

I'm trying like heck to get in the 12's with a the stock block. I would really like to make this goal before I continue.

yes man that would be awesome! I just really don't want to blow a rod or break a piston and hurt one of my very expensive heads... Just piece of mind that i know i can run a more aggressive tune and more boost and not worry about the motor pooping out due to over stress

I got a quote from a shop... It's about $125 for the work to the block and about $125 for the rods to get worked. Def not bad

Not bad at all

I'm trying like heck to get in the 12's with a the stock block. I would really like to make this goal before I continue.

I know you can do it, I did! Your combination is real close to mine. I went 12.70's on 8# boost.

It would suck if I'm at 12 lbs of boost and can't do it. I'm just not sure cuss I haven't been in a while. The good thing is the trans seems to be holding right now. I do have the 1-2 flare when at light throttle which seems to be getting worse. I hope that's not a sign.

Constructed a new down pipe with a side exit exhaust. 4" stainless into a 4" cat converter, no muffler, going from round tubing to oval for clearance out the passengers side right before the rear tire. Learned to weld with this project and will post pics after a do the final slash cut.

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