EFI QUESTION FOR JAKE....

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mike373
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EFI QUESTION FOR JAKE....

Post by mike373 »

Hey Jake....

What is the displacement limit on your EFI that uses the original Djet plumbing??? 2056??? 2270??

Thanks in advance,
Mike
MASSIVE TYPE IV
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Post by MASSIVE TYPE IV »

I have used the electronics on a 2270cc Daily Driver a couple of times already... Just don't expect big RPM out of the plenum/runners on an engine as large as a 2270.

I am building a "new" engine for my 912E (2270 DD) and will utilize the stock plenum/runners. I have the same set up on the 912E now with a 2056 "E" spec engine and it works really well.. That 2056 is getting tired though... And I'm too used to the power!
mike373
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Post by mike373 »

So.... This setup would most likely would work fine for a midrange/hot 2056 ??? What kinda rpm range are we talking for a 2270?? Like in the 5k range? Also...is there a TPS sensor for this setup?

Thanks,
Mike
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raygreenwood
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Post by raygreenwood »

I have found that the stock plumbing...is good for about 2.1...maybe 2.2 liters max. After that, the plenum needs to be upsized...and the runners either lengthened (in a pinch)...but more probably increased in diameter. Going to a "slightly" larger TB as you increase will help as well.

If you are pulling through radically more air than stock....then you may run out at 2.0. Ray
MASSIVE TYPE IV
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Post by MASSIVE TYPE IV »

My 2056 spins up just fine to 6250 RPM or so, but no power increase can be felt after 5500...

When switching from carbs to FI I could definately note the midrange power increase.
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Tom Notch
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Post by Tom Notch »

Mine runs pretty damn good with the stock runners and plennun at 2.6 liters.............

But I don't twist past 6k-6.1K, I didn't spec it to turn higher.
Tom

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Dean
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Post by Dean »

I have a recently megasquirted 2056 using D-jet hardware. I have noticed that at WOT, the manifold vacuum measured in the plenum increases as RPM's increase. I believe this is due to restrictions wth the throttle body. I imagine that is costing me some hp on the top end. Here is a log, I'm not 100% sure but I think this is a third gear pull, notice how the Map signal starts increasing.

Image
MASSIVE TYPE IV
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Post by MASSIVE TYPE IV »

Yep, either thr TB or the plenum size may be too small for the combo that you have.
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raygreenwood
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Post by raygreenwood »

Yup....I had part of this conversation a while back in reference to why D-jet tends to lean out as the rpm increases....when at WOT or near WOT. The problem in D-jet is two fold: (1) The vacuum....which dropped to near atmospheric when the throttle was opened....begins to pick-up again as the increaseing rpm....outruns the plenum volume. I know this happens..even on a 1.7, because adding a TB of say...2-3mm larger, only pushes the problem further upstream (rpm wise). Adding an even larger TB...is not practical (on a street car) due to the loss of low end variablilitty in throttle response. (2) Along with this re-emergence of vacuum in higher rpms...you have a lack of proper balance of armature spring pressure in MPS in D-jet. In other words....as the throttle cracks open....the D-jet MPS unloads too quickly. This gives a large burble of richness...that then leans out a bit as the spring returns. The re-emergence of vacuum only makes this worse in the higher rpm. It can be tuned out with a few mods.

The problem with the plumbing in D-jet....is a combination of a plenum that is just slightly too small (on the 2.0 plenum)...and a TB that is just maybe 1-2mm too small (on the 2.0). The 1.7 plenum though sized a little closer to correct....suffers from runner volumes that are a hair small.

For a 1.7....a good combo for better breathing is: .... 2.0 914 runners, 1.7 plenum and a 2.0 bus L-jet TB.

The 914 2.0 plenum...needs about 150 cc's...and about 2mm larger TB.

Better yet for all of them....a very tiny progressive.....like with a primary of 45mm and a secondary of 10mm. Perhaps try a solenoid bypass valve with a vacuum switch activation.....or a TB mounted single pole switch...to bleed extra air into the plenum when at wot. Ray
Santas Brother
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Post by Santas Brother »

What size is the stock throttle body ?

Funny you should mention a progressive throttle,
I was just thinking about converting a vacuum secondary carb
to use as a throttle body,with electronic injection,keeping the
secondaries vacuum operated.

Small primaries would give good drivability,larger secondaries
would open only as required.

Any thoughts ?
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Post by MASSIVE TYPE IV »

Yep- The Super 2 liter is using one.... With a vac secondary! That way until vacuum is high enough and the primary basically runs out of steam the secondary stays closed!
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raygreenwood
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Post by raygreenwood »

Good stuff! :D You guys are getting your heads inside of the plenum and runners.....and getting a "feel" for what the air is doing. I have long said...that in FI...its not just as simple as calculating runner and plenum volume by the engineering books...and running with it. Its testing and emperical data.....and small encremental moves.
I will measure the stock D-jet TB's when I get home. I do not have a stock 2.0 914 (vertical) TB to measure. L-jet TB's are fine too.
I use the 2.0 L-jet bus TB on a 1.7 because it is roughly 2mm larger (if memory serves). It made a nice, and noticable difference in throttle repsonse.

One design I am playing with is a boat tail bullet shaped, tapered "pintle"....to retrofit onto existing TB's...in place of the butterfly plate. This will allow adjustable TB opening size on a stock 1.7 TB (for example).....to a range of between 45mm to 6omm...with one single part.
The variation is made... by how far the cable pulls the pintle out of the TB bore. Its adjusted by means of a cam disc that the cable pulls around .

This would also....get rid of the throttle shaft protruding through the TB. Getting rid of the plate and shaft....gets rid of a BUNCH of restriction and turbulence.

The object with this cam...is to change the ratio of the cable pull. Right now...for instance...if your cable/pedal stroke moves the butterfly in a 1:1 ratio....you might get say....20mm of travel on the pintel, exposing the equivalent ring of open area around the pintle....equivalent to a 45mm TB opening. Since the taper on the pintle gets increasingly smaller toward the inside end.... if you increase the amount or rate the pintle is pulled out....by going to say a 1:2 pull ratio on the cable.....you increase the open area around the pintle.....to that of a larger TB.
At this point....the single one I have made...is made of torlon (660F teflon based plastic). That plastic is too expensive for production of this part (maybe)....but works great.

The "pintle" is supported by a rod that goes through a hole in its middle. The rod is supported upstream inside of the intake boot by a "hoop" that is mounted on the TB. the return spring to keep the pintil closed in the TB...is on the rod....and presses against the hoop. The Throttle shaft is short and stubs into the top of the TB just like normal. It stops at the inside and does not protrude into the bore. It has a flange and a bearing. The TPS...has been moved to the top side. The cam is on the throttle shaft right above the TPS. The cable from the cam to the pintle.....runs in a groove along the top leg of the hoop that supports the rod through the middle of the pintle.
Jake...these are easy to make. If you are interested...I will scan my drawing and send it to you. Ray
DNHunt
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Post by DNHunt »

I assume you are referring to the 3-5 kPa change at WOT

I have a 2270 that is one of Jake's kits (Jake is very familiar with this engine) with a stock 914 2.0 intake. The only change I have made is the throttle body is bored to 50mm. I'm running MS snd I have logs similar to this. I'll search for 3rd gear pulls at WOT to see if I have the same pattern and I'll post later today.

By the way, the engine pulls to 7K as reported in MS, that's well beyond the 7K on the tach. I suspect it will go higher. Of course I realize just because it will spin that high doesn't mean it wouldn't like more air.

Dave
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raygreenwood
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Post by raygreenwood »

3-5 kpa at WOT.....would be enough to trip up D-jet. It can actually be worse..depending on your exhaust and cam...and how the engine is tuned. I have measured as high as 5" of mercury at WOT with stock TB on a 1.7 above 4500 rpm.

But some things to bear in mind, it depends upon where in the manifold you are measuring the vacuum. I have found actually less of this problem downstream in the runners....than I have in the plenum. But since D-jet pulls its signature in the plenum...thats what I worry about.

If you are using a MAP signal...perhaps you cull pull a signture from teh runner base over a certain rpm. Ray
DNHunt
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Post by DNHunt »

I looked my existing logs and found 1 2nd gear pull to 6800. There was a couple kPa drop. Interestingly, to me at least, the greatest drops occur at partial throttle and higher RPMs.

If I follow the reasoning above, it seems like the air entering the plenum is not sufficient to replenish the plenum. Could this be an indication that the larger bore throttle body is at least partially offsetting the need for a larger plenum? It would seem that this is not such a big deal at partial throttle opennings but, might this give a little insight into the volume issue of the stock plenum?

I haven't figured out how to post an image from my hard drive here so I haven't posted any logs.

Dave
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