Forged 4.0L Supercharged Engine Ideas

[CobraMarty]

I have an idea that I want to share for inputs. I am very interested in installing the Boostec/Sprintex supercharger on the XJ. I like this system and can learn alot about it on the stock 4.0L 162,000 mile engine. I am concerned about the mileage, so a new engine is what I am thinking about.

Instead of building a 4.6+ stroker I was thinking of building a 4.0L forged engine. My thought is that a 4L will be a little cheaper and more fuel efficient than the 4.6 and the extra money can be used on other parts.

My engine build would be: 4.0L
forged crank 12w,
H beam forged rods,
forged 9:1 pistons,
505 Perf head, http://www.shop.505performance.com/product.sc?productId=307&categoryId=41
505 Perf roller cam, http://www.shop.505performance.com/product.sc?productId=186&categoryId=31
505 Perf main bearing cap girdle http://www.shop.505performance.com/product.sc?productId=283&categoryId=23
505 Perf SS valves http://www.shop.505performance.com/product.sc?productId=197&categoryId=23
505 Perf roller rockers http://www.shop.505performance.com/product.sc?productId=245&categoryId=37
and all the little bits to get it together.

My idea is that this 242CI engine can put out about 240HP and the supercharger at 6-7 pounds boost will pump it up to 350HP/350TQ. I think that this is a realistic goal and is probably at the near limit of all the XJ componets- D30,C8.8,transfer case,AW-4,cooling,etc. The 4.0L will keep good economy and the supercharger will kick it up.

Any ideas or thoughts on a forged 4.0L SC vs. forged 4.6-4.7 stroker SC engine? I think that the stroker will cost $1000-$1500 more to build and that savings can pay for the roller cam and rockers.

 

[O-Gauge Steamer]

The biggest difference in the price of the stoker is the crankshaft. 4.2 Crank kits, for whatever reason, appear to cost up to $200 more than the 4.0 kits. Beyond that, the rods may be a slightly different price but I will bet by not much.

Cams are the same price regardless and, you do not want one with a lot of overlap or long duration. This is something folks tend to overlook when purpose building a Forced Induction engine. The more overlap you have, the more boost you throw out the exhaust whilst both valves are open. And, with positive pressure, the need to hold the valve open longer is eliminated as well.

At this time, no one that I am aware of, makes a FI Cam for the Jeep engine. I am getting the cams for the Rovers I am doing out of England.

Thing is, an FI engine is a different animal than a NA (normally aspirated) engine. Several "rules" of performance engine building go right out of the window.

Here is today's word for that function.

Defenestration: The act of throwing someone or, some thing, out of a window.

As for gains, with a 9.1CCR and 7.5lbs of boost, you should anticipate a 30% to 40% gain over a NA engine with the same configuration. So... You would be looking at 312hp to 336hp. Doubt you will get 350hp out of it. The engine dyno run will be interesting. Be sure to post it.

 

[sidewaysstarion]

The biggest difference in the price of the stoker is the crankshaft. 4.2 Crank kits, for whatever reason, appear to cost up to $200 more than the 4.0 kits. Beyond that, the rods may be a slightly different price but I will bet by not much.

Cams are the same price regardless and, you do not want one with a lot of overlap or long duration. This is something folks tend to overlook when purpose building a Forced Induction engine. The more overlap you have, the more boost you throw out the exhaust whilst both valves are open. And, with positive pressure, the need to hold the valve open longer is eliminated as well.

At this time, no one that I am aware of, makes a FI Cam for the Jeep engine. I am getting the cams for the Rovers I am doing out of England.

Thing is, an FI engine is a different animal than a NA (normally aspirated) engine. Several "rules" of performance engine building go right out of the window.

Here is today's word for that function.

Defenestration: The act of throwing someone or, some thing, out of a window.

As for gains, with a 9.1CCR and 7.5lbs of boost, you should anticipate a 30% to 40% gain over a NA engine with the same configuration. So... You would be looking at 312hp to 336hp. Doubt you will get 350hp out of it. The engine dyno run will be interesting. Be sure to post it.

The general mathematical formula for building a turbo motor is for every Bar of boost you feed into the motor it's going to double the horsepower. so if he ran 7.5 psi of boost which is half a bar and the engine made 240hp N/A that would net him and extra 120hp, thus making his final power numbers 360hp. You factor in the parasitic loss of the supercharger and you get ~340-350hp.

 

[CobraMarty]

That is what I hope for.
Using this particular cam it is 210/216 @ .050, .451"/.477", 114* centerline, 1200-5200rpm. Mild duration and wide CL for EFI engine. This engine doesn't need to scream and rev to 6000. By using the roller cam and roller rockers and ported head, good exhaust I think that it should easily do 1.0HP/CID which is very mild by today standards. Most SBC can make 1.2HP/CID with good out of the box parts. So that is about 240HP N/A. Add the supercharger at 7 pounds boost using 7/16 (I use 16 instead of 1 bar 14.7) = .4375 as % increase in HP,
That is 240HP x 1.4375 (7pounds boost) = 345HP.
So if I can get 1.02HP/CID I can get to my 350HP goal.
Building the best N/A engine makes the best boosted engine.

 

[CobraMarty]

Sure I could do it with a stroker 4.6/4.7 285CID @ 1.0HP/CID = 285 HP x 1.25 (4pounds boost/16) = 355HP. But that's makes it too easy to hit the goal of 350HP. Who wants it easy? 4.0 should be more economical than 4.6/4.7 and would have a little less TQ, the boost will build up the TQ, and hit 350HP/350TQ goal.

Finding a 4.0L forged crank might be a bit of a problem.

 

[Talyn]

Why go through all that expensive and effort and leave it a 242?

Also, if you want longevity the roller cam is not the way to go. $20 for one valve? Try looking at valves for the Dodge/Jeep V8 Magnum engine.

As far as camshafts any number of companies can grind you a custom cam to fit your needs. No need to buy an off the shelf cam.

 

[O-Gauge Steamer]

Sideways,
Yes, I know what the formula claims. I also know what I have seen on a dyno. The best I think Marty will see FI over NA is 40% More likely to be 30%.

One of the biggest issues is going ot be the cam and there just is not one yet available for FI. I am working with a Crower on both Rover and Jeep cams but it will take a substantial order to get the price down to being worthwhile. A custom cut cam is spendy. If they make a couple of dozen, the unit price drops. Also, the cam will need to be displacement specific to be most effective. So, you see the problem I am running into on the Jeep side. 4.0L, 4.5L, 4.6L, 4.7L, 4.9L. The middle three displacements are close enough to not matter greatly But the two ends justify different cams. So that is three grinds. Basically two grinds as how many 4.9s are out there. Those folks can just get a custom. Or run larger valves.

 

[Talyn]

If they are that spendy talk to another company. Isky did a custom for me that was $90. There are also several smaller companies that would do customs.

 

[CobraMarty]

What's the problem with the roller cam and longevity? Distributor gear?

 

[Talyn]

Its a cast core. You will be lucky to get 100,000 miles out of it.

 

[CobraMarty]

THat's not bad, At the rate I drive it that will last 20 years or more. I guess the advantage of having other cars.
350/350 sounds so nice. Maybe have to move it up to 4.6L.

 

[Talyn]

Maybe have to move it up to 4.6L.

Thats what I would do. Will 9:1 be low enough?

 

[CobraMarty]

I still want it to run decent off boost. If it was an all out 15 pounds boost nondriver, then 8:1 and crank up the boost. I wish the alumn head wasn't so pricy, I would look into that and run 9.5:1. I still only want to run max 7 pounds boost.
Maybe destroke it to 3.0L and turn up the boost to 15 and still end up with 350HP. So many different ways to the same end. I like torque myself and would rather build it to maximize it.

 

[bpas328xi]

In all honesty, it would be extremely cool if someone could build a 24v crossflow head for the 4.0. (yeah... probably easier to swap for another I6)

A forged 4.0 with a fair amount of boost running through it would be interesting though (25-30psi).

 

[streetxj]

A hydraulic roller cam conversion doesn't sound like a bad idea even for a stock 4.0. Less friction than the flat tappet. But 1225 beans is bothersome. :nono:

 

[bpas328xi]

A hydraulic roller cam conversion doesn't sound like a bad idea even for a stock 4.0. Less friction than the flat tappet.

Yeah. I remember someone saying that they don't last long. (he then said that they last 100,000 miles... :dunno::huh: That's a long time if you ask me. rofl.)

But 1225 beans is bothersome. :nono:

I'm sorry but I don't quite follow... 1225 beans?

 

[CobraMarty]

$1225 is a lot but it 'Includes timing chain, 3/8 chrommolly push rods, roller lifters, linkbars, cam button and bolt, Beehive valve springs ,retainers and keeper.'

 

[Milford Cubicle II]

Yea that's kinda what I was thinking. 1200 sounds like a lot but you're also getting a lot for it.

About the "cast core" thing, I have no idea - I haven't heard that before. And how much of a durability compromise it is I also have no idea. I haven't known or heard from many, if any, people running them :dunno:

That being said, going with a roller cam would indeed be an improvement in almost every way.

 

[streetxj]

Yeah. I remember someone saying that they don't last long. (he then said that they last 100,000 miles... :dunno::huh: That's a long time if you ask me. rofl.)



I'm sorry but I don't quite follow... 1225 beans?

It's a way of saying bucks or dollars.

 

[blubullett]

If you have the money I would be all over the roller cam. There is a reason EVERY engine made since the 90's except the 4.0 uses a roller cam.