Holly Pro-jection system
notes from the z-car list

Webmaster note: The following article is an amalgam of notes from a Datsun Z bulletin board but very informative for Morgan Plus 8 owners looking in this direction. Most of the problems encoutered were due to the fact that the Holly Pro-Injection is designed for a V8 and not the Dastun's 6 cylinder engine. I have a happy report from the one Plus 8er I met who has done this switch. You will note that there is a happy advantage for some Plus 8ers in that the system fits on the Holley 390 CFM.or Weber 500 intake.


The first impression is that they paid more attention to the packaging than they did the unit. The packaging is top-drawer with separate compartments for each component and the injector assembly in its own  naccel.  They should have put the effort into the product.  The fit and finish is typical of what we've come to expect from American companies and illustrates why the Japanese own the manufacturing segment of our economy.  Very little of the die casting flash was trimmed.  One  hunk of flash blocked the throttle from fully opening.   Apparent design changes were accomplished by drilling random holes through casting bosses obviously meant for something else.  Several VERY thin metal membranes were removed that were left from the intersection of 2 machined passages.  These would have eventually cracked off and entered the engine.  A couple of hours with a die grinder and some fine burrs cleaned things up but I should *NOT* have to do this.

The control box is all analog and is the ultimate in simplicity.  It's  inputs are throttle position from a pot, water jacket temperature and a tach signal.  There are adjustments on the box for idle, midrange, WOT, "choke" and acceleration enrichment.  The "choke" pot really does nothing regarding enriching the mixture and instead sets a temperature setpoint  for dropping the fast idle.  Which brings up an interesting "feature". The throttle body contains a standard high idle solonoid that jacks up the idle speed when the engine is cold.  What it does NOT do is jack up the idle when the air conditioner turns on.  The manual makes special note that the control unit does not support that mode of operation which is stupid.  2 diodes and the solonoid can be triggered by either the control box or the A/C.  This mod is already in place.

The  injectors look a lot like standard TBI injectors except that  they're just enough smaller that standard ones won't fit.  A GM-style TBI fuel pump comes with the kit that must be installed near the tank.  A return  line is necessary (no problem on the Z) for the bleed-type pressure regulator. A large fuel filter that looks strangely like the one on 75 and above Z  injection systems is  included.

The electrical connectors are those first rate units that use the little green silicone rubber gaskets on each pin (who makes these things, anyway?) All wires are contained in split corrugated tube.  Cable ties are included but fuel line is not.  Strange. Spend an evening going through the system, measuring every-
thing (electrical and mechanical) and cleaning up the mechanical fibers.  This is essential to anyone buying such a kit.

Pro-jection update

The Pro-jection system is in!

The short review:  It works.  Pretty well right out of the box too. The time constants for acceleration and cranking enrichment, idle mix and a few other things, being designed for a V-8, are a bit off.  The throttle bores are over 2" in diameter each which means that when the plates open, LOTS of air moves.  With a small engine, a whole lot of acceleration is required to avoid bogging.  With the holley carb, I had to add the high capacity accelerator pump, use the fastest cam and open the spray nozzles way up so I'm not surprised at the  Pro-jection system performance.  The range of adjustments is just too  narrow.  I had to lower the fuel pressure several PSI to permit the mixture pots to have any effect.  This made the acceleration enrichment  too small.  The control box is dirt-simple, consisting of a number of analog op-amp function generators and some timing circuitry.

The accelerator and starting enrichment (too much) are the only two performance complaints I have.  The car mortally flys compared to the carburator on the same manifold.  Despite the engine only being a tired  260, I could fairly easily pull away from Jialin's 280 when we were testing tonite.  One of the most gratifying improvements is the instantaneous throttle response.

This system has cured a second problem.  With the carb, the engine would detonate rather heavily under WOT conditions.  I now know that it was probably leaning out on the secondaries despite the high capacity fuel pump.  Damn, I hate carburators.  With this unit, the engine pulls strongly right up to 7000 rpm.  Making a VERY rough estimate of mileage by watching how many miles I traveled before the gas gauge came off the  full peg, the mileage should be >20 mpg.  I'll update the net as I gain more experience.  I REALLY look forward to the improved hot  weather performance.

You must remove metal from the intake manifold to make it match the throttle bores.  Holly tries to  make this thing be a one-part-fits-all.  Unfortunately, one part could fit poorly unless you check and adjust. The mounting holes aligned  up properly but the throttle bores were greatly offset from where the 390 CFM 4 barrel was.  I also had to add helicoils to the intake manifold because the countersunk allenhead bolts supplied were too short to pass through and accept nuts.  Minor problem but a killer if you don't have helicoil tools.

Another problem is that this unit is about 1/2" taller than the old 4-barrel. That means that my Moroso air cleaner won't fit.  I'm going to have to do some serious jerry-rigging to solve this problem.  I suspect that my answer is going to be to remove the intake manifold and mill it on a slight angle so that the whole assembly sits lower in the engine bay.

I think I mentioned it in the last  update but another SERIOUS problem has to do with Holly's quality control.  The throttle body was designed for a stepping motor idle speed control though they do not support one now.  That means there is a LARGE passageway cast just below the throttle plates.  After the bores are bored, there is only a tiny sliver of metal between the bores and this passage.  Unfortunately these  slivers are necessary to seal the throttle plates at idle.  My solution  involved die grinding the slivers down until what remained had at least 0.5 mm thickness and then backing them up with epoxee.  A number of 1/16" holes drilled about gave the epoxee something to bite into.  A bit of pocket-
knife machining brought the epoxee back into round where the throttle  plates would seal.

Other minor problems included a large hunk of casting flash keeping the throttle from opening fully.  I had to trim that down and remove some extraneous tabs on the throttle lever in order that it would clear the manifold.  None of these problems are fatal but they do require time and skill to remedy.

The biggest bitch is Holly's typically totally shitty documentation. It's written for the complete moron.  It's a Heathkit-style stick-this-wire in-that-socket  step by step that gives no explaination for what you're doing or why.  The "theory of operation" takes all of 2 paragraphs.  No schematic is supplied.  Crude pictorials with NO wire labels are all that's available. I've often wondered why high performance magazines tend to read the same way they did 20 years ago with practically no technical content.  The manufactures give the customer no information so the customer remains ignorant.  Pedantic things like labeling the acceleration enrichment adjustment pot "accelerator pump" and the cold start enrichment "choke" are really pissers.  However, the bottom line is that the hardware works well.

2 full  12 hour days.  That's a lot of work for what is supposed to be a bolt-on replacement.

Subject:  Pro-jection daily update

Today was a 90+ degree scorcher.  It would have had the carburator drooling all over itself.  Not a problem from the injection system.  What a pleasure to not have that worry!

I've learned a couple of things about details.  One has to do with throttle geometry.  I was having a real problem with transitioning off idle.  A major factor was the fact that the butterflys are so large in the Pro- Injection system that they suffer a lot of vacuum resistance.  This manifests itself as added force needed to open the throttle that goes away once the throttle cracks a bit and dumps manifold vacuum. 

Moving the cable from the old carb to the injector resulted in the idle position being a bit past perpendicular.  In other words, the throttle had to move a bit before the lever axis and the cable formed a 90 degree angle.  The lever at a 90 degree angle gives the most mechanical advantage. Herein lies the problem.  With this geometry, the maximum mechanical  advantage was realized just about the time the vacuum force was being broken. The lessened vacuum force combined with the favorable leverage made the throttle leap across that point.

Tonight I cut the braket and rewelded it so that the 90 degree angle  occures at idle.  The best mechanical advantage is available  when it's needed the most - right off idle.  By the time the vacuum dump happens, the mechanical advantage is headed way down.  The change could not have amounted to more than a quarter of an inch.  What a difference it made!  Not only does the throttle now open smooth, the apparent bog is gone. I believe what was happening was that the throttle snapped open enough to dump vacuum but not enough to develop an acceleration enrichment  signal.  They obviously take a derivative of the throttle position voltage to do the acceleration enrichment and the small but fast movement probably
did not exceed the threshold.

Even though is is a major improvement, I'm not satisfied.  I ordered a gear blank from Boston Gear today.  I'm going to machine a quadratic cam on it and use it to actuate the throttle according to a square law response.   This will produce a roughly linear air flow vs accelerator  movement response.  This idea is not new - BMW did it with cams and  levers on my 635CSI.  But I'm doing it simpler.  A quadratic cam that the throttle cable pulls against is much simpler than the BMW rube  goldberg arrangement.

Subject: Re: Holley Injection system

The Holly system makes no attempt at smog compliance (though it will meet the idle sniff test), it is capable of better  performance  than the stock system.  The controller box contains adjustment pots for  idle, midrange, WOT, acceleration enrichment and cold enrichment. Thus, you can (and must) tune the engine while you drive.

The Pro-jection throttle response is instantaneous and it makes significantly more power than stock if for no other  reason than the throttle bores look like sewer pipes and the mixture  can be tuned rich enough for power.

I talked to an engineer at Holley.  They are currently working on a computer for the projection that will be digital.  It can be programed with a pc AND/OR with a few trim pots.  The system will use a few more sensors including MAP for forced induction systems."