Why's my beetle defying physics?

Give input on tuning as well as any tips and tricks you may have. Also feel free to share base mapping files for various engine types.
bazibbo
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Why's my beetle defying physics?

Post by bazibbo »

H guys...

I am improving things... slowly getting to know my way around my s40 pro run beetle EFI turbo and the cars beginning to pull a bit better although not a well as I'd have hoped though I'm still having trouble with detonation from around 4psi and I've got to run overly retarded to fettle the thing. I've had plenty of help from you lot, and done all sorts of tweeks to sort the detonation problem, ... from adding a chargecooler to ditching the BMW regulated, spur ended fuel rail setup and running a more traditional FPR at the end of the line. I've checked mostly everything, changed how things work.. run MAP only... tps + map... crikey.. everything. Fuel pump, injectors tested... you get the picture.

I'm now back on TPS + MAP compensation and running closed loop, hitting AFRs and retarded enough to stop detonation... but still feel I'm way too retarded and down down power. So, background over, back on topic...

I do remember my mapper was scratching his head as to why my engine appears to defy physics on its boosted fuel compensations.. so... I should be adding fuel thus:
100 Kpa = 0 compensation in fuel
110 Kpa = +10%
120 Kpa = +20% - up to
200 Kpa (1 bar boost) = +100% Which I understand is basic physics :geek:

but he had to add nearly double that...

80kpa +30%
100kps +50%
110kpa +75%
120kpa +80%
130kpa +90%
140kpa +100%
up to 200kpa +190%


Does this give anybody any clue as to why this might be? a DTA settings issue maybe, some alien stealing fuel on boost...

So she's running OK, I'm guessing at around 125 at the wheels, but I'm sure there should be more and York Dragway is beckoning.

any input appreciated
Barrie
Last edited by bazibbo on Tue Feb 12, 2013 12:46 pm, edited 1 time in total.
Rob Stevens
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Re: Why's my beetle defying physics?

Post by Rob Stevens »

You did have the right corrections, I wonder is your fuel pressure rising with boost or is it even connected?
bazibbo
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Re: Why's my beetle defying physics?

Post by bazibbo »

Hi Rob

they set it up on a bmw regulator / filter with a stub end - looked the part but it frightened the vw crowd. You're right though... the fuel pressure could have been effectively falling as pressure rose. It was pressure referanced... but I wasn't there when they set the fueling up :oops:

I could actually have bypassed that by turning on the closed loop and now by running a 'traditional' FPR.

I'm off back there for a second remap soon... wonder if it'll no longer be the case.
stevieturbo
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Re: Why's my beetle defying physics?

Post by stevieturbo »

Something makes no sense.

At a minimum fit a fuel pressure gauge and check that the FPR does what you expect it to do when you apply pressure to the top port.
The actual ratio isnt overly important, but 1:1 increase with manifold pressure makes life easy.

If it had been me tuning that engine, I would simply have stopped when the numbers got that silly, as something is clearly wrong. That itself would leave me cautious about the people doing the tuning unless they spoke with you about the problem and it was agreed to continue

After statics tests have done, leave the gauge in place so it can be monitored when under actual load.

Draw a detailed schematic of your fuel system, to see if there may be any issues there.
bazibbo
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Re: Why's my beetle defying physics?

Post by bazibbo »

hi Stevie.

Same old, same old. I wonder if it's just me and I've built my expectations up too high.

It might be the case that the old fuel setup was the issue, and I've solved it with the new one. That said, there was hardly any improvement over the previous fuel setup after I upgraded it a month or so ago.

Here's the initial pre Christmas 2012 fuel setup, using the BMW regulator. This was the set up when the mapping was done.

Image


oh, and as per usual, thanks for your input guys.


And here's the current one...

Image

I've run with a gauge on this one and am definitely seeing fuel pressure rise and hold on boost... from a static 45 (idle @35-40ish) to a boosted 55psi. I run around 10psi of boost.I stress again that the previous mapping session happened on the old fuel setup.

More traditional in air cooled circles. I changed because I felt it might work... as opposed to the traditional method of testing and problem solving :oops: I'm still obsessed with the motor not performing as it should... I swear there's another 30 or 40 ponies there somewhere.

Here's the engine, which has more bling than before in the form of the chargecooler and less restrictive top curve. (the rest of the car is generic rusty 72 beetle)

Image

The cars running reasonably now. A couple of hours with a capable brother sat beside me and we've ironed out most if not all of the detonation. But I'm still way below the standard '24deg @ 200kpa' I know all engines are different, but everyone else appears to be getting upwards of 160 bhp on similar and less specs. I'm running on a closed loop and have been since the first mapping. I think I've changed too many things to dare turn it off now... thus its off back to be remapped soon.

I'm still hopeful that I've done some schoolboy error with the s40 settings, but we've been through them all loads of times in loads of different setups.
stevieturbo
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Re: Why's my beetle defying physics?

Post by stevieturbo »

At the risk of repeating myself....TURN CLOSED LOOP OFF.

IMO this should only be used after a good base map has been created manually.

Schematic of the fuel setup looks sensible. Only real query....what is the pre-filter ? And does the fuel pump sound nice and smooth at all times ?

As for timing, have you done basic checks and confirmed timing on the screen is what is seen at the engine ? Are you sure about the engines compression ratio ?
What are charge temps like ?

If fuel pressure is maintained with the current setup, then the fuel system should be good. But was whoever was tuning it only changing the MAP compensations, or were they leaving compensations at theoretical standard and tuning the main TPS/RPM map ?

Again, the reason I hate TPS/RPM with compensations. You just never know what the hell you're tuning.
MAP vs RPM is so so much easier. You tune the cells that are right in front of your eyes, and there is no trickery going on in the background to confuse matters.
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ignitionautosport
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Re: Why's my beetle defying physics?

Post by ignitionautosport »

In the DTA manual it says to set the MAP comp to standard and tune using the TPS fuel map, so the boosted portions are spot on (as that is what you tune to) and anything below that is spool-up and it automatically compensates.

I haven't used this myself, I have only done straight MAP vs RPM, but in theory it is better and I do want to try it - I would just feel bad charging a customer for extra time while I work out any issues.

My ideal theory is to tune with intake open to atmosphere, with standard fuel compensations up to atmospheric, tune fuel and ignition, and then add boost and tune the compensation tables - I would expect fuel to need more than the standard correction, as it 100kpa you might be going for 13:1, but hitting boost you might be in the range of 11:1 to 12:1 odd.
I aminly want to tune an engine this way to get my head around the theory and what actually happens in practice, mainly with the ignition correction on boost.

I find it odd that at corrections were made below atmospheric, which makes me suspect something like the main TPS map wasn't touched.
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bazibbo
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Re: Why's my beetle defying physics?

Post by bazibbo »

A few answers...

Pre pump filter is a course 12mm filter to catch rusty chunks from the tank. I think the new fuel setup is working ok, pump's hardly noticeable and pressure appears ok.

I'll revisit the basic ignition checks again next week.

Compression ratio is 7.8 / 1 based on 63cc heads and a 1mm deck height (0.04 I think ) that's about as accurate as I can get on the deck height but it's definately within quarter of a mill, which could put me between 7.6 and 8 to one.

Intake temps ( I think ) are getting up to around 45deg c no higher.

They initially mapped the tps without the turbo and then joined the turbo back in for the boosted environment and I'm using the twin 20 x 14 maps. The closed loop got turned on at the end of that session... my fault!

OK I'm going to get booked back in later this, or early next week.

Homework, at the rolling road is (above and beyond what they'll be doing anyway)
  • - Double check the engine advance matches the DTA
  • - Keep an eye on fuel pressure.
  • - Does the cars wideband match theirs
  • - Loose the closed loop

OK I'll report back with the results. ta
stevieturbo
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Re: Why's my beetle defying physics?

Post by stevieturbo »

This is the reason why insisting on TPS baffles me. Not only have you one map to contend with, but now you're trying to tune two 20x14 maps !! And still the numbers in front of you dont tell you actual timing you are using, nor actual pulse widths.

Of course TPS tuning does have it's place, but it really does make things more complicated.

I asked about the filter, as most units people use as a pre-filter for efi are woefully inadequate and will restrict flow and cause cavitation.
"12mm filter" is rather vague.

If you're only using 10psi, I'd say that 45degC charge temps...well they certainly arent anything to worry about, but they certainly arent great either.

Even on engines using 30psi boost, I wouldnt be overly happy with those sorts of temperatures unless it was for very short bursts only.

What sort of air temp sensor are you using ? Is it an open bulb thermistor ? ie fast acting ?

And turning closed loop on when you are having so many problems already, is just adding a further problem in the background.

Keep things as simple as possible until all problems are resolved. Only then can you safely consider messing about with other things.
Roverdose
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Re: Why's my beetle defying physics?

Post by Roverdose »

yet i use tps with map comps all the time without problems.

using 2 maps isnt the way forward. set the map comps to std, set ignition to degrees not %.
run 1 map, tune that one on the rollers.

Drew
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