Alternative (better cooling) Fan for 914?

Dave_Darling · Post by **Dave_Darling** » Tue Jul 23, 2002 10:23 am

I think a rising-rate fuel pressure regulator might do you some good. It should provide additional fuel pressure when you're at WOT and the manifold pressure is higher (lower vacuum, whatever) which should provide a larger quantity of fuel for a given injector opening.

Per Ray's suggestions, you might want to adjust it so that it goes up no higher than 36 PSI. I'd think ~28 at idle (highest vacuum) and 36 at WOT might let you adjust things to avoid that lean condition at WOT, and still give you a half-decent mixture elsewhere.

The multiply-adjustable ones are expensive, but in your case might really prove worthwhile!

Are you running in PCA Zone 7? BP class, perhaps?

--DD

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1974 VW-Porsche 914 2.0 (Type IV powered!)

Pelican Parts' 914 Tech Geek http://www.pelicanparts.com

ray greenwood · Post by **ray greenwood** » Tue Jul 23, 2002 3:54 pm

Dave has a good suggestion with the rising rate reg. I still am not clear as to wether you were adjusting the MPS while running...or on the bench. Bench is just a baseline. Its totally differnt than adjustment while running. When the engine is running, you can simultaneously be in the enrichment phase of the MPS...WHILE in the enrichment phase from the moving throttle valve switch. This can over enrich you if your initial settings of th MPS are overly rich to start with. Over-enrichment is the most common source of lost power in D-jet. Like serious losses. On the bench, you have no idea when this will occour, so you cannot set up for it. Baselining on the bench is just to get you running smooth enough that correct enrichment adjustments can be done while driving.
The only thing to watch for on a rising rate regulator is the fact that you will now have four sources of simultaneous enrichment...none of which is connected to each other by any source of feedback. This is part of the difficulty I am describig above. You will have minute part throttle enrichment due to changes to the aneroid vacume chamber...while doing relatively little change to the copper plate. The copper plate is an additive factor...for sharp acceleration and mid loads...to the chambers within. It unloads the chambers quicker...and like a brake booster, this differntial pressure not only drives the rod farther into the armature...it accelerates the rate it drives the rod at. There is more than one factor to the rods movement. How far and how fast. Add to that...the throttle valve switch....and you have enrichment that may not be matched to the movement of the load stack in the MPS.
The four tiers of simultaneous enrichment are:
(1) main chamber stack in the MPS--affects injector cycle rate
(2) copper diaphram-enhances speed of change in injector cycle rate...and rate itself to some degree.
(3) Throttle valve switch-adds untimed injections..mimics an accelerator pump in a carb
(4) The rising rate regulator. It adds fuel based on vacume flucuations...not signals from the MPS...so it would be best to match its vacume movement to the MPS. If its adjustable...slave its vacume line to the vacume chamber of the MPS. Ray

914Racer · Post by **914Racer** » Tue Jul 23, 2002 11:41 pm

Yup, we're in the BP class. Gotta keep that Djet and 2 liter.

So the engine comes out, the heads get all new seats and we go to the dyno to see exactly what's going on. Hopefully we'll be able to figure things out and get our head temps straight. Then maybe we'll better our record of completing 2 of 8 events in the past 16 months.

Thanks again,
Greg

Dave_Darling · Post by **Dave_Darling** » Wed Jul 24, 2002 1:14 pm

I hear (second-hand, original source is supposed to be Bontempi) that boring the throttle body oversize can help as well by changing the vacuum signature at WOT and high RPM. (And that's what we're concerned with, isn't it?) Charlie Davis on the Rennlist (and PCA's 914 SIG) has gone about 2-2.5mm over and said the overall results were good, "if you bumped up the fuel pressure a bit".
http://members.rennlist.com/chuxter

--DD

------------------
1974 VW-Porsche 914 2.0 (Type IV powered!)

Pelican Parts' 914 Tech Geek http://www.pelicanparts.com

ray greenwood · Post by **ray greenwood** » Wed Jul 24, 2002 2:53 pm

Dave, going to the 2.0 throttle body on a 1.7 did help somewhat ...this problem. It may do the same in this case. What it did for mine was to increase the overall speed at which vacume dropped. It increased the sensitivity...which allowed me to adjust a little farther into the scale. What I am worried about...in this case....is that either there is still partial vacume at some point at WOT (nearly impossible) casuing the MPS to not max out enough at that point...or he has reached the end of the stroke available...for one adjustment or another...for enrichment at high rpm. It may be as simple as adding 1-2 psi fuel pressure. That would be my first move. If that did not do it...change it back....and use the main mixture screw. If that does not do it...chnage that back. Bearing in mind that both of those adjustments will enrichen across the whole scale ...which will maybe not be desirable. If none of those work...and the copper plate is maxing on the outer stop...it may not be getting enough stroke. Since the #'s through the mid range, part throttle area seem to be good...I would suspect that the inner stop screw (not the center main load screw) but the one surrounding it...with the 7mm internal allen key fitting...is screwed in about 1/3-1/2 turn too far. This will not let the copper plate vacume in far enough before it conatacts the intermediate (key hole slot plate). This shortens the total stroke and limits theexpansion of the inner chamber and hence the movement of the rod. If you screw this out....the outer stop will have to be screwed out the corresponding amount,,,and the main mixture screw, screwed in the same corresponding amount to keep all else the same......This means same depth mind you...not thread turns. Use a micrometer with a depth foot. Not all of the threads are the same pitch....meaning that a 1/2 turn of the surround screw for the inner stop...may not be thesame actual distance as the center main load screw or the outer plug screw, which is the main stop. Ray

kevin powers · Post by **kevin powers** » Wed Jul 24, 2002 6:58 pm

i did'nt read all of the replies so if someone has suggested this i'm sorry. are you sure the thermostat operates correctly and that the wire cable running to it is adjusted correctly?

kevin