PorschePhD

Colbat,
I have no issue with a reply. However please be advised I give a lot of info and at some point I have to protect myself. It is not as easy as I said as opening the ports and calling it a day. At that point you create more flow at idle as well and in the midrange. Not a good thing. Fluid dynamics is not very easy to deal with and when you talk about casting a new unit the cost and time to design it would be prohibitive and the cost to actually cast a mold and make them would be even more ridiculous. At the end of the day financially it makes little to no sense. Monies would never be recouped. The way we do it works well and is fairly economical. It has proven to be a very viable option for a low cost.

The heads are slightly different. They are not as large as you mention though. There are also two versions of the cast head. Neither is identical for the record. As far as your wrench thinking you have enough fuel, well it depends on what he considers is safe. I am conservative because of the box of pistons with holes from others who have built motors claiming they were safe. In time they are not. AFRs need to be conservative and when it comes to 400RWHP you will find that the factory system can not move enough fuel to keep a safe range. A car that drives 2000 a year will live 6-7 years this way...maybe. One that drives 12K a year, you have about 7 months. It is a matter of mileage and how much things will hold on before coming apart. I have three motors right now that are all suffering from the same issue. Hole in the piston.

m42racer

Cobalt,

I too are a little confuses here. Are the Banjo's and Bolts opened up? If not, what difference does anything internal do to the flow. If the pressure is constant once the WUR has gone thro' its thing, the volume of fuel delivered, must be a factor of the smallest restriction. Banjo, banjo bolt, fuel Line or injector, the smallest hole will determine the volume. Same pressure but larger orifices, more fuel in mass. Keep the same sizes, the only way to increase the fuel volume would be pressure.

Whatever can be done to increase the volume, whether its internal or external will help. The problem then with the CIS, is that any change in fuel volume with constant pressure is all across the RPM and MAP curves. You need more fuel in the Torque band because of the changes made to the engine, but not necessarily below or above the Torque band. This is why a system that adjusts the pressure will help regulate the fuel mass, based upon inputs or RPM and MAP.

Simple and effective way to control the CIS system, but still not an EFI system. Many here would just like a way to add the fuel when and where they require it, instaed of been disadvantaged with getting it everywhere.

I think the internals of the fuel head are very simple. Its not rocket science. Once opened, the changes required to flow more fuel should be easy to understand. Whatever the answer is, its a mechanical device that has 2 non adjustable running functions. Constant pressure and fix orifices.

He has the right to protect his mod. In this game, copy cats are everywhere. I still think that any mod to the Head is 1/2 what is required. It takes care of the size issue, but not the variable pressure.

FM9

I am not clear. Is the fuel head mod only done to USA cars or do ROW 930s benefit from this mod too?

PorschePhD

Yes, We do this mod to the ROW and US heads.

cobalt

Stephen,

I understand and in no way want you to divulge proprietary info on what you do to the fuel heads to make them flow better. Believe you me we are all appreciative of the info you do volunteer and the improvements you offer from your research. I was just trying to figure out if there was another approach that may do more. As you said it may not be practical from a $ perspective but would be interested in knowing if a redesigned head would gain us any benefit. I was under the impression that the plunger and the WUR controlled pressures and the job of the fuel head was to just direct the flow, which is the restriction. Apparently there is a bit more to it than that.

Maybe you can explain to me why the 3.6T head is not better than the 3.3l head. I was told by several people it is and that it can handle more HP than the 3.3l unit. Porsche obviously felt there was a need to make changes and redesigned the head for this particular model. Although the standard fuel pressure remains consistent with the the 3.3l it is running 50MB more under full boost. At .15 bar over stock I don't see why I should be so close to endangering my engine. Shouldn't this allow additional hp gain out of the 3.6L engine that is not obtainable in with the 3.3l head in stock configuration? Am I asking too much if I inquire to what the pressure and flow gains are to the modified 3.3l head? ALso would the same gains over stock be observed in the 3.6L head?

Thanks,

PorschePhD

Anthony,

I do not know why people are telling you that the fuel head is different. It is not. After 87 all the fuel heads until the end of the 3.6T in 94 were 930 220 923 00. Any model after 930.68 all carried the same head. There were various other changes, but the head remained the same. As a general rule of thumb with the mod you have on that head the system will lean out. What number have you dynoed at? What AFR? If you had the chart this would also allow us to really take a look at where the system is at a whole.

FM9

How much does it cost to do the fuel head mod and how long does it take?

cobalt

I was told the part number was 930 110 923 00 and that some changes were made including an additional sensor and other minor changes. I was also told that pressure under boost was adjusted from 250 MB for the 91-92 964's to 300 MB for the 94.

Does the added pressure afford the 94 additional HP gains over the earlier models or is it just a simple adjustment?

My charts read fine and there was no evidence of running lean. I do not have the specific info with me so I don't want to waste your time with wrong info I may or may have not remembered correctly. It was tested several times on a Dynopack by a well known mechanic who frequents the list from time to time. The car runs about 350+ rwhp at 14.8 psi with the HF turbo and B&B headers. I am still running the cats and was thinking about replacing them with 100cell race cat or removing them completely. I am concerned I will be inviting a lean condition as others with these same changes see an additional 20+ hp without the cats. I would rather spend the money on the fuel head mod than on the race cat right now. However my mechanic insists it is not necessary at this level.

PorschePhD

Each car will sometimes follow its own foot print. So in this case you may be fine. I did not realize you were running the cat. That is actually restricting a ton with the HF. Sort of like sticking a potato in the tail pipe. They are constantly breaking down and causing huge back pressure. Once removed you may find that you tip the scale.

The heads are the same as mentioned from engine number 930.68 on. The original 930 ran several WURs so I will use one of the latest. It ran 3.65 warm and under boost dropped to 2.9 bar.

The C2T 3.3 ran 4.5 bar warm and reduced pressure by 1.1 bar under boost. The 3.6 ran an additional 50 millibars less than the C2T on enrichment. The effect is the same as if one had adjusted the pressure in the WUR manually by moving the pin. The heads themselves though were identical to the 930.68, M30.69 and the M64.50. Farther more a reduction on 4.5 bar warm would leave a control pressure at 3.4bar. Still more pressure than that of the earlier car. Remember higher control pressure less enrichment at the same value across the chart. The 3.6 is actuactually enriches the same as the earlier cars. BTW all specs are typically within +-.20bar.

Keep in mind these pressure also have additional values added or subtracted to them by altitude enrichment etc.

Not sure if I have helped or confused the issue that much more.

cobalt

I understand that the Cat is highly restrictive. The car is quite powerful as is and far superior to stock, however I feel that the back pressure has a lot to do with performance regarding turbo response. So I am most likely safe unless I take it to the next level, which places everything in perspective and is most likely why I am being told I am safe at this level.

I am running the cats because here in NJ they have rolling roadside inspections and will physically look for cats and place the car on rollers to test emissions. Not that I plan on passing the test but the lack of cat is a very costly fine in both $$ and points against your license. Not worth the issues to remove the cat and get caught. The 100 cell cat is acceptable for street use but the cost is extreme and still more restrictive than no cat.

Like you said if I were to remove the cat or go with the 100 cell cat I might be jeapordizing safety. I would love to see what this car can do with the 100 cell cat but if I need the fuel head modification 1st I would rather be practical than chance destroying my engine. In either case for the few thousand miles a year I get to drive it I find the expense to switch cats too prohibitive especially if I detonate a piston.

Based on what you are saying it sounds like I should stay were I am unless I do the fuel head modification first and then change out the cat later on.

How much would the fuel head affect the AFR and I am assuming I would need to adjust the settings based on a dyno immediately after having the head adjusted or cat replaced.

SEW QUIK

Stephen,

What kind of a drop in gas mileage can we expect with the fuel head mod? I know that this will be highly dependent on other mods, CIS vs. EFI, etc. My car is the ex-Michael Benet 1978 white 930 turbo (CIS, k27, headers, etc.) and I am planning on sending you the fuel head soon when I upgrade my intercooler. I know that mileage is (and should be) a secondary issue when driving a modified 930, but I was curious if you had any feedback from prior customers regarding this issue.

thanks

DonE

The fuel mod does not affect fuel economy until you put your foot into it. Remember, the mod allows more fuel to the cylinders under high load - not under cruise or idle. The mod is should keep you AFR at 12.5:1 if you have tuned the WUR correctly. This is why you do the mod.

Before the EDI conversion, I did this mod almost 2 years ago. Done correctly, it works very well and will be hard to beat for reliability. My car had a little over 400 rwhp and was at home on the track as well as the street.

m42racer

"Remember, the mod allows more fuel to the cylinders under high load - not under cruise or idle."

So, this explains the mod. The only mod that could be done to the fuel head that has any sort of reference to MAP would be the slots in the center plunger. More MAP and the plunger travel is further in the housing. Opening up the slots at the lower end would pass more fuel at that given position. Not sure how the transistion would feel at that point.

DonE

I've not spoken to Imagine about their mod (pretty sure its the same shop/method), but this is what was done to mine. I sent mine off to a shop that measured each of the 6 fuel ports to find out which one flowed the LEAST amount. In the original machining process, each port flows slightly different amounts. From the factory, Porsche made sure the port flowed 100cc per min. By finding the lowest port's volume without the Porsche fitting, you then machine the fitting to match the remaining 5 (reduce their port flow). For example, the lowest port volume my fuel head had was 114 cc per min (max was 119 cc). The fittings were then all machined to flow 114cc per min on all ports. Therefore, my head flowed 14% more fuel than stock.

This then allowed me to fine tune the WUR to adjust a more precise amount of fuel for warm conditions and adjust when the enrichment kicks in (I set it to start at 4 lbs of boost) and give me the equivlent of 12.0:1 AFR. Although my AFR curve was still a bit like a "v", I know of one other person who was able to tune his WUR to produce a dead flat AFR under accel and boost.

In addition to the fuel head mod, I trimmed the air metering plate stop to allow more pin travel. Not sure if this helped all that much since the fuel head was producing 14% more fuel.

The down side to tuning the WUR so precisely was that I had to tune it for temp changes - winter vs summer.

m42racer

Don,

Do you mean the Banjo fittings or the small washers with the holes in them. Seems to me any change in volume any way is a good thing. What ever they do has to be an improvement over stock for sure. Then meter the fuel by controlling the pressure.