I have found that using a constant but metered flow PCV works better than a fluctuating spring controlled one. Whenever pcv kicks in and out on D-jet...it will be dumping unmetered gasses/air into an environment that is already being acted upon by the MPC...best to keep it constant. A 13mm plastic marble used in flower shops to put in vases, with a 3-4mm hole drilled in it...stuffed in line, works great.
This weekend was a good experiment. I put my twin cam distributor in. It basically injects #1 and #4 at the same time. It is set so injection of #1 starts at just before half lift...so there is significant inward air draw. #4 is just before it cracks open...less waiting. The original injection cam duration was about 190 degrees. I cut this back to about 150...leaving a gap. #3 and #2 are on a seperate cam...moved around about 90 degrees...(I havn't miked everything out just yet). The subtraction of about 40 degrees from each cam duration length alowed moving one cam around to get the injection closer to the valve opening point. #2 and #3 now open at the same locations in valve lift as #1 and #4. Problem...and solution. The duration of injection available during the valve open cycle on #1 and #2 are now excellent (I made up the difference by bumping fuel mix up a hair at the pressure sensor...and with about 2 PSI more fuel. But #3 and #4 are about 15% low in available injection time.To make this up, I split off the the fuel rail to those two injectors to a 2nd pump, with a seperate regulator ( I was already running separate pumps per rail, so this was simple)and move the fuel pressure up just a bit. Eventually, it will be simpler to put larger injectors on these cylinders, that run the same pressure. What I gained is equal flow...with nearly sequential injection from ganged/paired injectors. I did this by the way, using four seperate burrettes, two harnesses four injectors...all slaved to the 1 set of trigger points. In other words, the car is already running, I just have a seperate whole injection system running off of the same triggers to get injection points and fuel rates set up. Maybe in a week I will go ahead and swap the whole system, set the fuel mixture and see how it runs.
Also this weekend, I made a new sensor loop that works fantastically. It uses the existing CHT, hooked to an intake air temp sensor mounted into the cooling air discharge area below the left head, and looped to the upper intake air temp. sensor in the inatake manifold. I had to make a slight fuel mix adjustment, but what this does...is let the CHT saturate with heat (which it does...so it doesn't react as quickly to temp spikes and quickly goes to the end of its range...especially in traffic, at moderate outdide temps with high barometric pressure...fall and spring...giving idle and flat spots and some times hot starting problems...sound familiar?) The air temp sensors, give the over-all range of the CHT a .300 +.300 Kohm resistance boost. They change temp. much quicker...because intake and cooling air do also and also because they are not in actual constant contact with the aluminum of the head. This is the main problem with the CHT. Changes in head temp of 10-30 degreees are significant...but not to the CHT, because once the head hits about 300 F...the temp is almost maxed...and cant really cool off. The CHT sets the base line head temp...the air sensors move the temp. baseline around quicker. Much better throttle response. Eventually I will move to an adjustable thermistor. The point of this post, is that there are quite a few changes you can make to D-jet...with a little creativity. Over 100 hp with a 1.7 liter is not difficult...but takes a lot of tuning to get it right. Ray
FI HP Mods?
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Dave_Darling
- Posts: 2534
- Joined: Thu Apr 27, 2000 12:01 am
FI HP Mods?
In the current Grassroots Motorsports issue http://www.grassrootsmotorsports.com they talk about how they got 113 HP out of a 2.0 liter D-jet motor.
How'd they do that? The old-fashioned way: Increasing the compression, putting a slightly-more-aggressive camshaft in it, adding a tuned header exhaust, lots and lots of head-work, and a whooooooole bunch of dyno time tuning and tweaking the D-jet to get everything to work correctly. I talked to Tim Suddard, and he said it took something like 30 hours of dyno time. Not to mention careful assembly and balancing everything.
--DD
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1974 VW-Porsche 914; 2.0 liter Type IV motor
How'd they do that? The old-fashioned way: Increasing the compression, putting a slightly-more-aggressive camshaft in it, adding a tuned header exhaust, lots and lots of head-work, and a whooooooole bunch of dyno time tuning and tweaking the D-jet to get everything to work correctly. I talked to Tim Suddard, and he said it took something like 30 hours of dyno time. Not to mention careful assembly and balancing everything.
--DD
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1974 VW-Porsche 914; 2.0 liter Type IV motor