brutus

The problem with having anything adjustable is people will then adjust it. Adjustable waste gates on 930s were great for repair shops as owners would...."im going to pump it up to 40psi and see what it does. " or something like that.
This engine has NEVER been tuned right with numerous shops adjusting it over the years. So pump up the fuel pressure and do some more hard hiway "dyno" pulls and sooner or later there may not be anything left to tune.
Not wanting to spend the money to sharktune it is not an excuse to keep on doing it wrong.

mark kibort

Its not my call. hard to argue with the lump, running for 15 years, badly .
anyway, i agree, and ill see how far he will go with allowing me to help him do it right. i do think many discount the ecu of the 928. keep in mind, mark and I raced and are still racing for many years, using the stock ecu, with no mods but fuel pressure andy dyno runs. the obvious thing ot me, with the experience with my car and this one is that the 30lb ijectors is way too much! 24 would be the sweet spot and problably would be fine from the start with out a tune, at stock fuel pressures. again, his net hp is a little less than i got out of the holbert machine, with stock injectors and ECU. (same as other GTs with the same mods as well, netting the same shapped and level of HP curves)
going from my 320rwhp with stock injectors, to 375rwhp with 24lb injectors is no stretch. for him, its a no brainder and the 30lbers seem large, unless it is shark tuned.

mark kibort

agreed. that will have most of the answers

mark kibort

There are no car gods, only devils. my goal with all my cars and these are extremely beaten on race machines is make sure fuel is safe, thats i. I trust in porsche to make a good ecu, which they have. (not great , but good) . If run 4.7 liter systems form 170hp to 290rwhp with no mods other than fuel pressure. Ive done this a few times, and got the holbert car to 335rwhp from 289rwhp safely as well. Ive use NOS on all the motors , and never had a problem, and did it in a way that kept fuel ratios proper (sub 12.5:1).
did i optimize? no but i have not been a crazy person yanking on the fuel regs aimlessly

mark kibort

got to spend some time on the 6 liter this morning. belt tension check, and fuel pressure check and adjust. tension good, and pressure was raised to 40psi from the 19psi that it was set at. also, did a check for you guys that think that the guage is wrong due to vacuum. i pulled the vacuum on the guage and it is only 3psi difference. doesnt even spike that much on blips , equal to no vacuum as a peak on blips.
hooking up the AFR and going for a drive. i imagie hard start hot problem will go away.

tension gurus, what do you think the hot vs cold tension is on the timing belt. did a test hot last, and stone cold on a 50 degree morning today. any guessers?? and why?? show your work!
.

mark kibort

alll the running issues are gone. 40psi seems like a good spot to start, since im at 44psi with 400cc's more engine and 50 more HP. plugs look good, time to do a compression test tomorrow.

way more power, like a different car all together!

mark kibort

anyone know how the speedo and odometer works?? the speedo is functional, but the odometer is not working at all. places to start?? thanks.
Mark

brutus

broken odometer gear is very common.

IcemanG17

Odo is most likely a broken gear......kinda a PITA to get too...but common...

polo classic

there is some logic to your think, but honestly the best way to start is to set the fuel pressure to what it was when the tune was made. That your more powerfull engine with more cc uses a higher pressure has got nothing to do with the map calibration. Also remember that manufacturers numbers show fuel pressure with no vacum, e.g. pull the vacum line of the fpr when adjusting.

When I'm asked to map cars with adjustable fuel pressure regulators, I refuse to map them until a OEM non-adjustable unit is fitted. I have tried mapping one car with a adjustable fpr, and just turning the "****" a few degrees, the AFR jumped all over the place. This was a 200 hp 1,3L turbocharged 4 cylinder engine with #24 injectors, stock was #19, not that it matters, as calibration was for the bigger injectors.

If I got all the posts right, the car had been to several places, and they had turned down fuel pressure to avoid high AFR in the lower rpm band. Thats the thing with fpr's. You really can't tune with them. When you adjust it, you adjust it in all rpm's, not just where you need it.

Adjusting fuel pressure from 44 psi to 51 psi can change the AFR as much as a whole point across the range.

Basicly "tuning" with an fpr is a hit-and-miss affair, best left alone...

My guess is that the calibration started at or around stock fuel pressure. I'm not that familiar with 928's (but with Bosch LH-Jetronic) most of these systems work with 3-3.8 bar fpr with no vacum. Thats where I would start, then hook up a wide band lambda and a sharktune.

Then adjust warm-idle to be have AFR 14,7, or a bit leaner. Next step is going up to say around 3000 rpm, and see if AFR is safe, adjust, drive again and so on until you have reached the revlimit (providing it shows no sign of knock). Then you can look at the ignition curves. You also need to make sure the fuel pump works the way it should. Check that the pressure is the same across the board (adjusted for engine vacum)

Also, don't worry about injector size beeing too big. The only cars I've come across that the #30 are to big, are on 1,3L 8v 4-cyl crossflow engines. It is all about calibration. I have made calibrations for 1.8L 16v 4-cyl that use #60 injectors with nice AFR all over

Just some food for though
Here are two ignition curves, one a 2v head, the other a 4v head, same manufacturer, same ECU. The fuel curve follows the same pattern, as far as differences is concerned



You can run these two calibration on the 4v head, but there is no guessing which calibration works better

Get your friends calibration sorted, take the car for a spin, and enjoy the results

Rob Edwards

Polo- Welcome, you must be new here. Pull up a chair, there will be a rebuttal to your 'claims', forthcoming.

polo classic

Thank you,

Chair pulled up....LOL

Yes I'm fairly new to Porsche's. I dreamt of a 928 S when I was 18 years old, some 20 years ago. Not quite there yet. Porsches are way too expensive where I live ( the cheapest Boxster is around $130,000).

Up til now I have only played with VW's. The car I have mapped thats made the most power so far is 1986 Golf 16v with a KKK K24 and 264 hp at the wheels on the dynapack, 306 @ flywheel on Mustang....

So far I have made calibrations for around 50 cars only, so still on a learning curve here.

mark kibort

Polo, keep in mind, it doesnt matter , as you say, for idle AFRs, because the system is closed loop and the AFRs will always be in the 14.7 range, because thats how the system works. all the hoopla about wrecking an engine is only valid and relative when you start going near WOT. WOT is open loop, using the MAF input and RPM signals. we are not tuning hondas with MAP systems . so, the stock pressures with stock maps are around 50psi. the vacuum does little or nothing an is not really that important, due to the fact that we are using the fuel reg for one thing and one thing alone, WOT AFRs and power. (however, i pull the vacuum to see what i have anyway and its only 3psi lower at best) best power is found in the 12.5 :1 AFR range and if we could play with timing, that would optimize it further there too. dont lke to get it too close at the dyno, because on the track, things change and they can change greatly. so, i usually tune with fuel, using stock maps and get the AFRs to be under 12.5. if i dip in the 11.5s, so be it. i wasting gas, but the car is safe. much richer and you run the risk of fouling plugs and cylinder wash down..

so, WOT, can be optimized to a point. mine respond pretty well and is safe from 4000rpm to 6600rpm at 12:1 and ends up in the 11.5 range. I dont want to lean it out any more due to the fact that lower pressures dont atomize the fuel as well. PLUS, if i really cared that much about squeezing the extra 10 hp with fuel alone, i would figure out a way to shark tune it.

Now the 6 liter is smaller by 500ccs, and when you go WOT, its using less air than the 6.4 liter, and during open loop operation, you are getting the fuel injector duration functioning from inputs of the MAF and RPM signals. (along with the WOT fuel maps ). so by turning up or down the fuel regs, we can change the AFRs in WOT mode pretty well. not perfect, but we can get it to a safe range this way. So, all things being equal but the 400ccs less, means less fuel pressure WOT means it will have a better fuel ratio because the fuel duration might be the same , worst case, but the pressure being less will optiize the fuel / air ratio , by flowing less fuel, and this will be better for the amount air that is moving into the cylinders.

so yes, we changed the fuel pressure from 55psi to 45ps and it did change the fuel ratios , during WOT a hole point. 10.5 to 11.5 and 12:1 for the most part. i would go lower, as it was very close to optimal.
certainly if I COULD, i would shark tune it and use the maps for the 30lbs injectors, but rememeber, we did some tests with a stock brain and found that my tune was pretty good and safe. dont know if there is much power to be found with tunin only fuel, timing possible, and both together, maybe another 20hp if we got it to the edge. Id rather take the 10 hp and be a little safer

jcorenman

Polo, Thanks for your thoughtful post, it is a very good overview of how to go about tuning an engine. And I agree completely on fuel pressure: When you have the whole fuel map to work with, one more variable is just trouble. Stock fuel pressure is 3.8 bar (55 psi, vacuum disconnected) which works fine.

The problem here is that the 928 overlapped development of electronic motor control, the early models were the mechanical CIS systems and the later models were the first of the "modern" digital systems. The 87-on cars used Bosch LH 2.3 fuel injection computer, and the EZK ignition computer (with knock detection and individual cylinder retard). But this is all before OBD-II and standardized diagnostic and tuning systems. So the only tool available for tuning the maps is the "Sharktuner" developed by John Speake (JDS Porsche) and Niklas Kämpe. The cost is less than one Porsche-Buck ($1K) but that's still a lot more than an adjustable fuel-pressure regulator.

The 6.0L engine that Mark is trying to help was built before any of this was available, and the only tools available for tuning were changing injectors, fiddling with fuel pressure, and some "black boxes" which tried to fool the ECU's. It worked OK, to a point, but significant changes require significant changes to fuel (and spark), which requires re-mapping t do it properly. In the "old days" we could fiddle with the distributor weights and change jets, but without access to the maps we can't even do that. The physics haven't changed however, and for most of us horsepower is still is produced by lots of air mixed with the right amount of fuel and ignited at the right moment.

dcrasta

Welcome man, that was very well said. Seems people are going to do what they want to do (And its their choice). Cheers!