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Quote: "If you have a MODIFIED engine (i.e. more displacement) the properly tuned D-Jet system will run lean. "
Not at all ranges. At low rpm the intake manifold will have less vacuum than stock, so the computer thinks you have your foot in it further than you do. Remember musclecars and the more radical they are the lower the vacuum, until you end up running a vacuum canister? What you'll find is that at low rpm, light throttle, you'll be rich with a big cam.
I've got the opposite problem to that: feeding 162 cu of stroked b23 with a d-jet. It will have either a T or an A cam, so huge low rpm vacuum. The injectors will hardly want to spray, thinking the thing is under decceleration! ;)
I'm writing a new web page about alternatives to richen it.
See below l
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Here's what I've got so far:
My project is to build a naturally aspirated b23 to 2626-2655 cc's. I've done a b20 to 2392cc's with an offset ground crank giving 89mm stroke and a 92.5mm bore. It's the same thing Topi at TRS did, and Dave Barton did with his 245 turbo. The b20 based motor works well in a lighter car like my PV544... but the overall character (& weight!) of my 73 142GL seems to want something more, and I want to try something new.
I've researched the swap to the OHC motor and want to do it the absolutely simplest way- bolt the b20 oil pan and transmission to it, set it in vertically and build motor mount plates to set it where I want it. The transmission wouldn't change, and I don't want the injection to change either. I have a 164E
throttle body that is a separate casting, and larger than a 140 piece, (larger than the b23ft piece, too) but still takes the same D-jet throttle position sensor. The coolant sensors will find new homes on the OHC head, and I'll use a k-jet auxiliary air valve for trouble-free cold starts. I'll have to have a plenum fabricated to go between the throttle body and the b23 manifold flanges .
The idea is to set it up for torque. So a short cam, lots of compression, bigger valves, and some light porting. Should make at least 150hp. Could be 170hp with a big cam, but that's not my thing.
I know that I should consider an aftermarket setup, especially the SDS one, as I'm only about 2.5 hrs from their shop, here in Canada... but I want to try the d-jet. Money's an issue, as well. So that leaves me with D-jet, carbs, k-jet or LH-jet. My experience is k-jet is junk. Lh-jet would require a lot of rewiring and additional sensors. Carbs might be a thought. Two SU 2inch carbs as sitting here might be fine, but they aren't fuel injection...
They can be set up to work very well in all aspects, but they are basically a backward step.
Thus, my D-jet tweaking page.
The injectors are rated by a flow test at 43.5 psi at 43.5 psi the flow rate should be approx 475-490 cc/min which translates into 375 cc/min @28 psi.
As you are probably aware, those are unusually large flow rates. However, because of the way d-jet works [batch fire of two injectors at a time] you are only effectively getting half that flow rating.That it's halved explains quite a bit, as on first glance the system has about double the injector capacity required by the 80% of maximum rule-of-thumb used by manufacturers.
I also wonder if changing the distributor firing cam calibration by filing some off, would work to boost fuel flow by making it so that the injectors would have the capability of firing a maximum of about 65%/65% of the time,
rather than 49%/49% ?
Some have tried wiring in a variable resistor with the in head temp sensor or air temp sensor in order to trick the d-jet brain into increasing pulse width - that was the principle behind the IPD dial-a-mixture in the 70's and 80's.
I have access to test a modified box from Ipd through a friend but it is not for sale. I forget which sensor circuit they tapped into, but they replaced an internal fixed resistor with a pot, which was why you could dial _out_ fuel as
well as richen it. You could accomplish much of the same effect by dropping fuel pessure and adding in a pot. If you are going to play with these circuits, make sure your pot or resistor selction has enough resistence, as it takes
a great deal to make a noticeable change
More on that later...
One idea that was kicked around for a while for using d-jet on motors with major amount more power potential was to use a system from a 164 and have the extra two injector harnesses [ie wire pairs]attached to an injector in the cold start injector position. That, or keep the cold start and weld one or two injector bungs into the plenum in the appropriate places.
My first question on hearing that is why you'd need the 164 set up. It's all electrical. Couldn't the driver circuit of the 4 cyl box support the
amperage draw of another injector on one circuit? Then you'd have 5/6ths of a 164 system, or more precisely, 5/4ths of a 140 system. If you were to use a 164 box you'd have the 164 system possibly with one injector short...
I'd be inclined try the 4cyl-box based set up first, especially as the vast majority of 164E are the late low compression spec & were 130 hp, and a good 2600cc four should make 160 or so...I'd think that a late 164 box
set up firing 5 injectors would only support 5/6ths of 130 hp=108hp.
Your starting point also affects your chances of success. Volvo used
different boxes on different engine combos, so a b20E had more fuel going in than a B20f with the compression dropped.
IPD fiddled with d-jet quite extensively in the 80s and came up with some very powerful race motors, or relatively so. They ran to rules (SCCA?) that seem to have limited displacement to 2.0 liters, and/or specified a maximum overbore. I used to have a dyno sheet supplement (or was it the last page of the race parts flyer? I was 12 or so at the time!) that compared the common 2x45dcoe intake set up to their modded D-jet, showing peak hp and torque. They were at 190 odd hp either way with a small horsepower advantage to the highly modified d-jet set up, but a small torque advantage to the dcoe's, likely due to being able
to do better tuning with the carbs to follow the needs of the engine through the entire rpm range. I've wondered about the fuel curve: the torque curve and thus fuel consumption curve of a 2.0 190hp engine is going to be quite different to a stock b20f. I'd imagine the curve they came up with was right over about a 1000rpm span and "kind of OK" for 500rpm above and below that, for a total of, say, 5500-7500 rpm...
As I understand it, their access to the guts of the box was never sophisticated enough to _recurve_ the output except with a race only
three knob box that they never marketed to the public. I supppose this was what the race motor used.
Apparently, their race motor also used a different throttle body
(from a BMW 3.0cs or maybe 164E) and moved the injectors back into a new position on the plenum, something that has dubius merit- no better fuel/air
mixing because it's longer and colder path, and a good chance of hurting VE, as fuel that has evaporated takes up more room in the intake stream.
I think that the easiest thing to do is raise the fuel pressure -if you have 20% more displacement than stock and you raise the pressure to 43.5 psi you would have 22% more flow. Mind you 43 psi would likely be causing some leakage at the injectors...
I have an old IPD flyer that says when using their 2130cc kit that you should not crank the fuel pressure beyond 32 or 34 psi at the most, as the injectors will leak. I don't know if maybe they weren't just trying to sell the dial-a-mixture boxes by saying that, though no particular reason to be suspicious.
It does seem they tried a pressure boost and found it lacking. However, I do know that David Hueppchen in WI runs a p1800 in vintage racing, that puts out about 150 and all he's done as far as I know is crank the pressure up. I'm not sure what the ITB cars run d-jet or DCOE's, but they make 150hp as well.
BTW, if someone is smart enough to check my math, but doesn't know the flow principle, from 29psi to 43.5 psi (+50% psi) is only a 22% increase in fuel, as you compare square root of the pressure, not full value.
For my project the stubs of the LH manifold will get used. I've got a plan to seal and hold in the injectors. They fit the pockets quite well as far as depth, but I'll have to use several O rings on the nose of the injector as the
injectors are loose in the pockets. My project should make approx 150-165 hp, so at that level,
I have options-
_#1/ one I haven't mentioned is adjusting the manifold vacuum sensor. I'd read on two web pages of being able to adjust that. One page was for 914 Porsches, where switching from 1.7 to 2.0 liters is common. Another was for Volvo b20's, then I found : http://www. Apparently there is an adjuster, which is sealed behind a cap, the cap is sealed behind epoxy. Once you get to it,
it can be used to set mixture in two stages.
-#2- set up a pot in the coolant temp sensor, air temp sensor or both.
Ipd did seem to get results this way. You can also put a step or steps in the fuel curve by doing rpm activated circuit changes.
_#3- another injector making five in total
_#4- fuel pressure raised to 40-ish giving around 20% more fuel
_#5- find bigger injectors- bosch #0 280 150 041 is bigger. It was used on 6.9 Mercedes for one year (worldwide production 470!), and on Cadillacs as a Bendix product built to the Bosch license. Expensive if they can be found at all. I'm doubtful about electrical compatibility with anything else. I can get MSD and Holley injectors, as well as Bosch, but all are set up for 12v (as far as I know) and D-jet uses 3V to the injectors. So running three volts to 12v injectors, the injectors might not open, the box might fry, all kinds of problems would almost surely crop up.
Don't do that.
_#6- modify distributor trigger to run overlapping batch fires. I'm told the box won't recognize this and will not respond, but I don't know of anyone who has tried this.
_#7- I should start with a 70 1800E box or a 71 142E or 1800e one, as they are calibrated about 10-12% richer.
Problem is that having such good vacuum at low rpm, as well as making power down there, the box will give me too lean a mixture. It will richen at high rpm, but that is less a concern. I do know that with a good ignition and tight quench it will run on a leaner mix than is ideal and still have good driving characteristics, just be down on power. My hope is that with all the above options I will come up with some combination that works transparently, ie as good as the O.E. function. It may well work better, as I will have vacuum advance (not retard), no emissions worries, and an engine spec with inherently smooth idle and excellent throttle reponse.
But that's not all of the plan. My plan then is to run an ultra basic nitrous system, using the small solenoid, a brass jet and just nylon line. Used on ATV, watercraft and snowmobiles to great effect. NOS sells a precut fitting to calibrate flow. You can buy from 11.5 hp to mid 60's hp fittings.
Usually these are set up one to a cylinder, but I'm thinking just one total just after the 164 throttle body would do. I then need fuel to support that extra oxident. Thoughts that way are that I have a 164 cold start injector that is higher flow than the b20 one. I'm thinking of triggering
that to get an approximate fuel boost, then use a fixed resistor in the coolant temp sensor to get the mixture right. I'd set up that circuit so that the triggering of the nitrous solenoid would break a non resistored (or through a pot) circuit through the coolant temp sensor and force the circuit to
go over to a parallel resistored (or double resistored) circuit.
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