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Old 09-14-2009, 06:03 AM
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Jason Jason is offline
Join Date: Jun 2009
Location: St.Louis, MO
Posts: 1,246
Default More power from your D24T! (updated 1/3/11!)

First, and most important, your engine needs to be in good mechanical shape before trying to up the performance. Besides the obvious things like timing belt replacement, oil changes, etc, your pump timing should be checked and injectors should be at least pop tested and or rebuilt before you really try and turn up the power. (Probably not needed if you have a lower mileage engine, but how many of these cars have low mileage any more?) Worn or leaking injectors can really hinder performance and possibly damage the engine. In addition, more fuel and boost with incorrect injection timing can also damage parts, most likely the head gasket.

Now for the fun part, more power!

Most everything I have read has said the factory air box is not a restriction. Looking at the size of the filter, I think that is reasonable to believe. However, the inlet to the fenderwell is necked down with a plastic insert. This can be one of the first things to go. It pops out and you are left with just the outer tube into the fenderwell. While your at it, make sure flap connected to the T-stat still moves and the box can suck cool air from the fenderwell. You can change to a open element cone filter, but the stock turbo isn't all that loud so don't expect the big whistle like the bigger diesel trucks have.

If your running the stock turbo and don't plan to push lots of boost, the factory size exhaust will probably be ok, but the mufflers need to go. Most are just a pile of rust inside anyway. If you don't want loud, install a straight through style muffler back in the system. Straight piped is the way most go, as these engines have a great sound! If you want deeper, step up to 2.5" after the down pipe. Go 3" and your neighbors will think a dump truck is comming up the street! If you go with a different turbo, or plan to push more than 15lbs of boost through the stocker, stepping the down pipe up to 2.5" is a good idea.

Before we really turn up the power (pump "adjustments") you should at least have a boost gauge. A EGT gauge is also nice, though I have been told the stock pump/injectors cant push enough fuel to damage the engine because of too high of egts. Either way, a EGT gauge is a good idea. Above 1200 pre turbo is not going to be good for the engine. It may be able to handle higher, but I wouldn't want to try and find out on my engine!

Pump adjustments:

AFC adjustment:

Very CAREFULLY, pull up on the rubber diaphragm and it will slide up. Look at how the shaft that the diaphragm is connected to is tapered towards the bottom. I refer to it as being cylindrical, but slightly off center. It has a "deep side" and a "shallow side". You want to position it so that the pin rides on the deep side of the shaft. While your in there, remove the plastic washer than the diaphram bottoms out on. Its white plastic and sitting on top of the star wheel (which looks like a gear). Shave around .100 off it. If you look at the wear mark on shaft where the pin has been riding, you will see that it doesn't travel all the way down to the deepest point. Shaving the washer down will alow it to get to the deepest point. Next, crank the star wheel down at least a turn or turn and a half. This will reduce the tension on the diaphram and reduce the amount of boost it takes to push it down. This helps increase low boost fueling, but will increase smoke. You can adjust this with the screw and jamb nut on top of the housing. Bottoming it out will give the most fuel with no boost to start with, and more fuel from there as boost increases.

You can also grind the pin with a deeper ramp for more fueling under boost. This is an article from a Cummins forum, but its the same pin:

Full power screw adjustment:

Before moving this screw, read below!!!!

What is a runaway?
A runaway can occur while turning up the fuel on the VE injection pump, the reason they run away is that the control collar can't move far enough towards the "defuel" end of the plunger (making the spill port area smaller), and the backpressure in the spill port becomes high enough that engine speed goes out of control. This is why they will idle OK but then hang at high RPM. At low RPM there's not enough backpressure to start the runaway.

How do you prevent a runaway?
With this procedure you can help prevent a runaway better then the old method of slow increments.
With every 1/2 turn of the fuel screw, snap the throttle. IF the throttle hangs in the upper RPM's before coming back down your on the edge of runaway, or if it will not comeback down to its prior RPM, back your fuel screw back out at least 1/2 turn.

How do you stop a runaway?
Remove the intake on the engine, and have a board handy to cover the inlet into the turbo. What your doing is choking the engine should the runaway occur. This will shut the engine down.

Now for the max fuel screw, as even with out extra boost these motors can still use extra fuel. Loosen the 13mm jamb nut and turn the screw in as stated above, around a 1/2 turn at a time, checking to see if the engine wants to "hang" when you rev it. If your just looking for some extra power, turning it in untill the screw bottoms out on the crimped on collar will give a pretty decent increase in power. For more power and fuel, you will need to remove the screw and get the collar off. Be carefull when removing the collar not to damage the threads, as your jamb nut will end up tightening down where the collar was as you turn the screw further in. As you turn the screw in, you will need to readjust the idle back down. When your done, have a friend put the accel pedal to the floor (with the engine off) and check to see that you are still getting full throttle. You may also need to adjust the linkage on the pump lever closer to the pivot point in order to still get full throttle after adjusting the idle. In addition, you may need to bend down the stop tab on the accel cable pulley to alow everything to move enough to allow the arm on the pump to move far enough to idle down.

More boost:
You can just cap off the blow off valve at the front of the manifold and gain a few psi. The dump valve opens around 10 to 12 psi. If yours is like mine, it opened and the boost went down to 8 psi. Easiest thing to do is just find some kind of large rubber cap and slip it over the outlet tube, and clamp it there. If you still have everything connected to the stock turbo inlet, you can reinstall the stock hose back over the cap and clamp the hose over it. You should have a boost gauge before doing this, as this was the point at which I found out my wastegate was bad and with the dump valve closed, the turbo was pushing 25lbs of boost! From here, you can install a manual boost controller (ebay has them cheap) and turn the boost up more. Depending on how good of shape your head gasket is in, you may or may not be able to hold much more boost than stock, so do this at your own risk. Assuming things are in good shape, 15lbs of boost is probably max for a non intercooled engine with stock bolts and head gasket. I have been told engines with a good gasket and properly torqued heads that haven't been over heated will hold 20 to 25lbs of boost with an intercooler. If you don't know the history of your engine you could be taking a risk pushing it to the limit. If you really want to push some boost and keep the head on, step up and install a set of ARP studs. They have been shown to hold 40psi with a stock 3 notch head gasket.

Speaking of that dump valve, I found on my engine that after it was capped off it leaked boost between it and the manifold, and after I fixed that, between the two pieces its made of where it is crimped or glued together. I would remove the whole damn thing and get a 1-1/2" rubber plumbing cap from Home Depot to cap off the manifold. When I did this the turbo spooled up MUCh faster, it was a night and day differnnce. I highly recomend removing it!

Adding an intercooler in next if you want to run more boost, though you will need to upgrade to either head studs or a steel headgasket, or both if you want to hold it in for any lenght of time. Even at stock boost with the stock turbo, an intercooler is a great upgrade and will add some power. The intercooler will help keep EGTs down, and you will make more power at the same boost level compaired to running no IC. There are many ways to go about it, but mounting up a ebay front mount intercooler is probably the easiest. If you can find a NA D24 manifold, that will make plumbing the system much easier. Otherwise, you will need to modify the stock turbo manifold. There are no real specific recomendations here, as there are so many ways this can be done. Check the forum for pictures of how it has been done, and go from there.

Another intercooling option is water/meth injection. If you are into the turbo diesel performance scene, you have probably noticed this is becoming more and more popular. Less plumbing, no bulky intercooler to try and fit up front, and the good systems are adjustable. There are also home made setups that are low cost and work well. Check out the sticky in the performance section for the write up on building your own water/meth injection setup.

Bigger/different turbo options:
Unlike the 4 cylinder 1.6, we were lucky enough to have a T-3 style turbo, with a T3 exhaust flange manifold. This really opens up the options for a different turbo. The stock turbo can push 25lbs of boost, but not that efficiently. If you plan to run more than 20lbs of boost, than upgrading the turbo will really wake up the power. The stock turbo has a .36 A/R exhaust housing which helps it spool very quickly. At first glance, it looks like it would be restrictive, but after doing some research and talking to some D24 experts, I found out its actually a well designed housing. Here are some possible combos..

Stock hot side and center section, with larger trim T3 cold side.
Stock is .42 A/R. Some people have done this with good results if your just going for a few more pounds of boost and all around better power. A larger trim cold side should push more air and help clean up some of that smoke from the extra fuel your throwing at it. Turbo technology has come a long way since the early 80's. More than likely, a newer cold side housing and impeller will be more efficient than the stocker.

T3/T4 hybrid turbo.
I built one using the stock center section, so the oil inlet and drain would bolt back up without modification. If you want to really wake up some power, the T4 compressor housing is the way to go. Side by side, the T4 compressor housing dwarfs the T3. A great middle of the road exhaust side would be a .48 A/R. It will spool well but the drive pressure will be lower than the stocker. I have run the .63 A/R hot side, and it doesn't really spool well untill 3500rpm or so. Especially with the auto trans, this makes for smokey around town driving when your rpms are in the 2 to 3k rpm range.
When swaping exhaust housings, you will more than likely need to swap the impeller shaft as well, the stock turbine is a odd size stage IIish thing. The turbine blades have a wierd depth that must have been something they were doing in the 80s but not anymore! Most all T3s found on cars in the junk yard will be a stage 1 impeller, while the chinese turbos found on Ebay are stage III. I used chinese T3/T4 parts to build my turbo with no problems. Since they are a copy of the standard T3, the impeller shaft fit the stock center section with no problem. It is possible to use the internal waste gate that they come with, however the shaft has to be bent slightly and the canister repositioned away from the oil cooler. I found it neccesary to drill a new hole in the canister mounting plate to be able to place it where it needed to go. Also, the T4 compressor housing is so big the oil feed line will no longer reach (it has to go around the housing). I used the stock ends and a piece of braided stainless oil hose to make a new longer one. At this level, a 2.5" or larger down pipe should be used. The stage III exhaust housing has a 2.5" outlet so steping it down to the stock down pipe size will not be helpfull!

T4 compressor

my T3/T4 hybrid

Stock down pipe next to 2-3/4" down pipe

There are many possible turbo options... If you have a combination you would like to share, please pm me what turbo parts you used and I will include it.


SOLD but not forgotten! 1984 760 Sedan, built D24Tic/ T-5 swapped
9.90@71mph in the 1/8th, 2.2 sec 60' (burning tires off through 1st gear)
My engine build: http://www.d24t.com/showthread.php?t...t=engine+build
T-5 swap: http://d24t.com/showthread.php?399-W...to-quot-w-pics!

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