Modding my 4jb1t for 250hp

[paulthepilot5]

Roderunner wrote:Interesting project you have happening, I hope that you keep posting updates!
On the possible crank snapping problem, apparently they usually snap off at the front just behind the harmonic balancer, partly because this is where the torsional vibrations are more concentrated. Add in some excess fanbelt tension helped along by the screw in belt tensioner adjuster and the front of the crank gets pre-loaded a tad too heavily in many cases. Excess injection advance which can induce "nailing" (that tapping noise) also magnifies the torsional vibration seen by the crank, so some minor cold engine nailing might be ok, but if you can avoid it....
The other vulnerable spot on a 4 cylinder inline engine is the big end of no. 3 cylinder, as it also gets a much larger dose of these destructive vibrations,at 3000 revs, which leads me to the flywheel....I know that the standard flywheel weighs a lot, but shaving it down contributes to the torsional vibration problem, so unless your building a 1/4 miler I would think twice before losing some weight off it. The 3000 rev. vibration band is a bummer because it's often co-incides with the open road cruise speed, so you could be cruisin along at part throttle and 5 pounds of boost (light load) and have the no. 3 bearing shit itself. (Don't ask me how I know this lol) all for a few pounds worth of flywheel weight!
On the pump plunger, I believe that the Australian 4jg2 engine has a 12 mm pump plunger from the factory, but I can't remember if it was the electronic pump or the pre- electronic pump, it's something that you can chase up if you feel inclined.
In my case the crank snapping may have been caused by a loose harmonic balancer. But as you said, not an uncommon thing in these.
They do cruise a lot better at lower rpm, I changed my diff ratio so sit at around 2400 @100kph. And it makes 1st a bit more usable at the drags.

Seems to be a general no no, advancing the timing in the Isuzu’s. Does make more power, but at a price. I was running more advance than factory, but I was also running water/meth which slows down combustion and peak cylinder pressure. I have actually dropped the compression ratio a little on the rebuilt engine, make things a bit nicer for the high boost.

[dieselguy86]

How did you lower compression? Thicker head gasket or did you machine the pistons? Was thinking of possibly machining some valve relief and the bowl some to lower mine to somewhere around 17:1.

[paulthepilot5]

dieselguy86 wrote:How did you lower compression? Thicker head gasket or did you machine the pistons? Was thinking of possibly machining some valve relief and the bowl some to lower mine to somewhere around 17:1.

Shimmed the head, running around 17:1. not much margin to machine the square pistons. Be careful changing the bowl, can have a drastic effect on combustion, as well as the height of the injector nozzle in relation to the bowl.

[dieselguy86]

I have round bowl pistons to put in. Was just going to de-lip them and re profile the cone in the bowl to a more modern design. Going to need more area in the bowl to handle the extra fuel/ heat. Not going to change the bowels depth or diameter, just refine the problem areas, and then ceramic coat it.

Btw, i sent you a pm regarding injectors.

[dieselguy86]

So did some more exploring/ research today. While looking at the list of nozzles, i noticed that the common rail nozzles had the same size holes, amount of holes, and degree of spray. Difference was they had what is called a dlc, diamond-like coating. This is because here in the U.S. we switched to ultra- low sulfur diesel which has a sulfur content of <5ppm. Pretty much took out all of the lubricity in the fuel. So they use this coating to survive the lack of libricity, but the mechanical nozzles don't have this.

So i just happened to have a common rail injector out of my 6.6L duramax. I took the nozzle out and wouldn't you know it, it fits the 4jb1 injector. The only difference was, the stock 4jb1 nozzles pin has an extended portion that protrudes up and contacts the spring, where the common rail nozzle did not. It was flush with the end of the nozzle body.

Anyways tomorrow im going to make a call to the leading fuel injection place not far from me, too see what they have to say. It would be really nice to have the dlc for maximum durability. I'll see if i can upload some pics later so everyone can see what I'm talking about.

[paulthepilot5]

dieselguy86 wrote:So did some more exploring/ research today. While looking at the list of nozzles, i noticed that the common rail nozzles had the same size holes, amount of holes, and degree of spray. Difference was they had what is called a dlc, diamond-like coating. This is because here in the U.S. we switched to ultra- low sulfur diesel which has a sulfur content of <5ppm. Pretty much took out all of the lubricity in the fuel. So they use this coating to survive the lack of libricity, but the mechanical nozzles don't have this.

So i just happened to have a common rail injector out of my 6.6L duramax. I took the nozzle out and wouldn't you know it, it fits the 4jb1 injector. The only difference was, the stock 4jb1 nozzles pin has an extended portion that protrudes up and contacts the spring, where the common rail nozzle did not. It was flush with the end of the nozzle body.

Anyways tomorrow im going to make a call to the leading fuel injection place not far from me, too see what they have to say. It would be really nice to have the dlc for maximum durability. I'll see if i can upload some pics later so everyone can see what I'm talking about.

So are these a 4 hole nozzles your looking at?

[dieselguy86]

No i believe the 6.6 duramax is a 7 hole nozzle. Probably not going to use that nozzle, i just wanted to check if it would fit. The coating would help the life of the injector tremendously.