Supercharged Stock 1600 DP

[Dan Dryden]

If I remember correctly, reducing the size of your air corrector jets will help richen up your mixture at higher rpm. So may be worth considering going smaller. What you describe about it falling on its face when you blip full throttle points to your enrichment circuit, so I would check out the accel pump jet size first before messing with the air correctors.
Keep up the good work, I'm enjoying this thread!

[T-34]

The fuel is pretty new (well new to the bus at least) - I filled up just before the weekend. Also - I always use 98.

gearheadgreg - Interesting comment. I think I agree that it would make no difference in this case if one jet was larger then the other but there's just something about having odd sized jets that doesn't seem right - just like wearing odd socks - they do the job but you're gonna get ridiculed about it

Did a bit more reading last night. (http://ozgemini.com/forums/tech/viewtopic.php?t=19014) has got some good info on how the mains / airs work, plus a nice little diagram to show idle / moderate throttle / full noise. The thread gives some suggestions about sizing but nothing directly applicable (it's mostly twin carb stuff + different capacity).

There's also some useful info here - http://www.s262612653.websitehome.co.uk ... llorto.htm This same info can be seen repeated around the web, again some useful info but not necessarily directly applicable.

I also read somewhere (cannot find / remember where) that the idle jets are generally in play up to about 2500 rpm before the mains kick in (wasn't necessarily a VW application) and that most driving was therefore actually done on the idle jets. Obviously this engine speed is largely dependent on the carb setup but this would be consistent with what I have experienced. Low down it is okay, but higher up the revs the engine is dying (even on a slow opening throttle).

I'm going to try another jet size (or two) and see how this effects the drivability - I can easily solder them up again.

The carby that I have is an emissions model, it has more progression holes than a normal DHLA and so from what I am led to believe may be a little harder than normal to dial in. I'm still confident that I can get it to the stage where it is drivable, and figure if I make small incremental changes to one thing at a time I should eventually be able to get it figured out.

Thanks for the the continued input. Will get back out to it this arvo. For now I need to track down some more drills.

Mick.

[T-34]

Okay, next size drill I could get was 1.75 so drilled the mains out to this. It will now run higher up the rev range and has a little improvement from before so I'm guessing that the mains are now working / starting to work however, it's still pinking on a high load / low throttle and still stalling on a fast opening throttle. Not sure I want to go any further than 1.75 as from what I have read this seems to be getting on the large size so I think my issue may be elsewhere.

As things have improved and I have been able to make longer runs, one thing I have noticed is that the exhaust temps seem to be quite high - I'm now wondering if the idles are too lean. I've currently got the idle correctors wound all the way out (7 turns ). There is also no noticeable change from the base setting of 2.5 turns to 7 turns whereas everything I've read indicates that I should first see a slow rise in revs followed by the engine stuttering as it goes too rich.

I checked the pump jets - these are 42's I'm not 100% sure that this equates to physical size on Dells (hole looks tiny 0.42mm maybe??)

At the moment I'm toying with the idea of opening up the idle jets and seeing what this does. I've also measured up for the new belt route so will go grab a belt whilst I ponder what to do. (hopefully someone will post up some insightful info in the mean time).

I haven't tried with the vac disconnected yet so will also try this before drilling anything else.

Mick.

[T-34]

Got the new belt but found that the new route clashes with the throttle cable so need to do some rework there - maybe a longer throttle cable.

Just necking a coffee and going to get back out to it.

Mick.

[T-34]

Okay tried with the vac disconnected - no difference so I'm guessing the vac port is in the right place.



Opened idles up to .6mm
Huge improvement on partial throttle. Less pinking under load still some on heavy load tho


Opened idles up to .65mm
Again a massive improvement, still stalling on a fast throttle but nowhere near as bad as before. Slight pinking under heavy load


Opened up idles to .7mm
Again much better, does not pink under heavy load but does sometimes under full throttle ( accel jets?) was hunting a little indicating too rich so wound idle circuit in until hunting evened out. its now sitting at 1/2 a turn so could probably go down to a 68 idle.

Still a bit of pinking / hesitation when opening the throttle fast so now looking to open up the accelerator jets a little. Will measure what they are (I'm guessing .42) and then go to .5 s this is the next drill size up that I have.

Will report back my findings.

[T-34]

The accelerator jets were indeed .42mm so I opened them up to .5mm However, this seemed to make no difference at all. Not sure if this is because the change was not significant enough or if this simply isn't the cause.

Went for quite a drive to see if I could figure things out. Still getting pinking - in fact probably worse than before, so I wound the idles back out a little (now sitting at 4 turns). Pinking reduced but engine now running hot again.

I'm a little confused about the conflicting signs - temps hot indicating too lean yet engine hunting indicating too rich.

I think tomorrow I will continue opening up the idle jets some more and see what happens. Opening these up to their current setting (.7mm) whilst having the adjusters wound out to 7 turns has given me the best gains so far. Perhaps the hunting is a bit of a red herring or maybe it's some weird effect caused by the supercharger. Not really sure on that one so guess I will need to keep investigating.

All thoughts / input / advice welcomed

Mick.

[andy198712]

this is a brillent progressive thread, great job, you'll get there!

[T-34]

Been looking at pulleys.

Belt slip is still an issue so looking to see how much it would cost to swap out all the pulleys to gates style micro-vee pulleys. Stumbled across this...

[spoonerdtg]

For 22deg on pulley from tdc notch measure 33.6mm to thr right

Arc distance= 2x3.1416 x 87.5 ( radius of 175diam pulley) x 22 deg÷360 = 33.597

[gearheadgreg]

Went for quite a drive to see if I could figure things out. Still getting pinking - in fact probably worse than before, so I wound the idles back out a little (now sitting at 4 turns). Pinking reduced but engine now running hot again.

I'm a little confused about the conflicting signs - temps hot indicating too lean yet engine hunting indicating too rich.

OK - my opinion (and that is all this is, I'm no expert) on this is ignition timing. Think about it this way - would you run different ignition timing on identical engines if one was running 7.0:1 compression, and the other was running 10:1 compression (assuming the same octane fuel)?

Yes. The faster burning 10:1 compression needs less lead, or advance to the spark event than the lower compression engine. By *not* retarding the timing under boost, you are likely causing some of the pinking and getting much higher cyl head temps than would otherwise occur. Just a guess. There's a reason that most boosted setups retard ignition timing proportionally according to boost.

[Steve Arndt]

Once you detonate hard on a set of plugs it will continue to do so easier and easier. I would try some new plugs, and go one heat range colder as well.

[T-34]

Went for quite a drive to see if I could figure things out. Still getting pinking - in fact probably worse than before, so I wound the idles back out a little (now sitting at 4 turns). Pinking reduced but engine now running hot again.

I'm a little confused about the conflicting signs - temps hot indicating too lean yet engine hunting indicating too rich.

OK - my opinion (and that is all this is, I'm no expert) on this is ignition timing. Think about it this way - would you run different ignition timing on identical engines if one was running 7.0:1 compression, and the other was running 10:1 compression (assuming the same octane fuel)?

Yes. The faster burning 10:1 compression needs less lead, or advance to the spark event than the lower compression engine. By *not* retarding the timing under boost, you are likely causing some of the pinking and getting much higher cyl head temps than would otherwise occur. Just a guess. There's a reason that most boosted setups retard ignition timing proportionally according to boost.

The temps were okay when I had the idles wound out 7 turns. The temps only rose up again when I reset them after drilling out the idle jets the last time. I feel that this was my mistake as I misread what was happening with the engine. I also broke my own rule and made more then one change at a time. I'm pretty sure if I wind the idles back out to 7 turns the temps will be back to normal. Tomorrow I plan on going up another size on the idles and trying to reset them again. I was convinced the engine was running rich due to the hunting but I now feel that I was wrong.

I did try retarding the timing but it did not help the issue. Timing at the moment is set at 22 overall. I retarded it until it the engine was just starting to stumble at idle to see what effect this would have on the behaviour at full advance but it did not make any difference. I recon this was possibly retarded by 10 degrees, this plus the 8 it was already retarded gives an overall of 18 degrees.

You are of course right, I'm sure that boost referencing the timing is the best thing, but this would require another dizzy / retard unit and add to the cost. Others have been successful in doing a similar thing without resorting to boost referenced timing and from a commercial standpoint I really would like to do the same.

I have a nagging suspicion that my pulley ratios are wrong (currently a 3.75:1 ratio - the pulley was supplied with the charger and wasn't my preferred size). I wanted to see how much boost the setup was making at this ratio (the blower is maxed out at about 16,000 rpm when engine is at 4800rpm) and then adjust the size accordingly, but it is almost impossible to measure what the boost is as the engine dies before it can produce it. So far I have seen a maximum of about 8psi on the gauge but this is not constant, I recon that if I can give it enough fuel it will go even higher.

I will carry on with my current line of testing but I think that what I really need to do is to swap out the pulleys and try setting it up with a lower boost. Maybe I have just crossed the line with the current configuration? Or maybe I simply need to work through this in baby steps - get it working at a lower boost and then incrementally increase it.

Once you detonate hard on a set of plugs it will continue to do so easier and easier. I would try some new plugs, and go one heat range colder as well.

Some good advice. Will pull the plugs tomorrow and take a look.

Mick.

[181]

Hi

Take a look at this calculator

http://performancetrends.com/Calculator ... ulator.php

I tried the following values

3.75 belt ratio
70% volumetric efficiency
70% blower efficiency
1.6 liter engine volume
0.5 liter blower displacement
14.7 psi barometric pressure.

calculated boost is.....hold on to your hat.....29.78 PSI

You are running way too much boost and I think this is your main problem. In my setup I will be starting with a 2:1 drive ratio. This ratio has the potential of producing around 8 psi.

I am getting my pulleys from here:
http://www.keicarshop.com/

I think also a good investment would be a wideband air/fuel meter. It will make jetting so much easier.

Good luck!

Alex

[T-34]

Hi 181, it's actually John who I got the original pulley from. I did have a chat with him at the weekend when I got it fired up but unfortunately he only has the one size. He said that most people size the bottom pulley to arrive at the required boost. With my configuration this is not possible without also changing the alternator / fan pulley.

My original calcs put the boost at approximately 10 PSI (http://www.vdubber.com/blogs/entry/supe ... ley-ratios) which is still too high but I figured it should run okay, although now I am beginning to wonder if my schoolboy mathematics was way off of the mark. Looking at the calculator in the link I haven't accounted for barometric pressure. I was hoping that VW's being a particularly inefficient design the actual boost would be somewhat lower than I had calculated. Wishful thinking I guess. (or dumb assumptions - take your pick )

Ironically I haven't seen over 7 / 8psi on the gauge, but this could be when the belt starts to slip. I find this quite interesting however, and perhaps a little telling. Maybe 7 / 8psi is a natural limit for the intake system? It doesn't matter how much I tension the belt this is all I see. I initially thought that this is what the system must be generating but it could simply be the equilibrium between back-pressure slowing the charger and grip of the pulley. Maybe it's possible to go higher if I sort the belt slipping issue, and perhaps subconsciously this is why I have left this particular problem alone, as the nagging voice at the back of my head is worried about what will happen if it gets full boost.

One thing I can now confirm is that it is definitely the blower pulley that is slipping as this is where the tell tale rubber dust is most prevalent. All of this leads me back to considering starting off setting up with a smaller boost and then slowly working up.

Been looking in the workshop to see what I could find in the way of pulleys. I have a stock VW A/C pulley (127mm) which according to the calculator in the link above this will generate 6.36 psi - a little on the low side from where I wanted to be but a good starting point. Only issue with this is that I will need to modify both the stand and inlet manifold to space the blower out enough (the A/C pulley is offset by 30mm).

I would prefer to keep the single belt setup and use a larger supercharger pulley so I think I will go to my local machine shop and see what they have.

I did some calcs using the calculator in the link above

Stock VW pulley OD = 178mm
Supercharger pulleys in range 60mm - 85mm

178:60 = 2.97 = 18.15 psi
178:65 = 2.74:1 = 14.88 psi
178:70 = 2.54:1 = 12.11 psi
178:75 = 2.37:1 = 9.8 psi
178:80 = 2.26:1 = 8.33 psi
178:85 = 2.09:1 = 6.1 psi
178:90 = 1.97:1 = 4.56 psi

First bold figure (60mm) is what is currently fitted - my initial measurement / ratio calcs were a little off
Second bold figure is where I want to be.

Guess I'm off to go find an 80mm pulley.

Will keep you posted

Mick.

[Humpty]

I hate to say it Mick..... But have you considered fitting a WBX crank pulley and a multi-groove alt and charger pulleys?.... I know you want to flog the OEM V belt horse, but to be honest you are massively limiting the safety and potential of the setup... Even the old school supercharged engines used more than one belt to gain the needed belt grip under load.... As you have pointed out.... Too much tension on the belt is bad for alt bearings.... The more load you put into the set-up, the more likely it is going to slip..... Logically, a multi-groove belt is way more effective in this sort of set-up, and really is a very small price to pay for reliability.... Another option is two belts..... One for the charging/cooling systems, and the other for the supercharger... This is the best option in my opinion.... V belts are not designed to run via complex tracts such as your project has... You are potentially limiting the life span of the belt as a result.... Yet another reason to consider a multi-groove belt.

Also.... Steve suggested a colder plug.... Very good advise there.... In my experience, our fuels here in Oz are pretty poop (I only run Caltex Vortex in the POS) compared to the rest of the globe... With my turbo engine, I have had to step down to a colder plug, to keep pinking under control.... And Steve's point about the plug pinking more easily once that state has occurred before is very true too.

And get a damn wideband in there will ya!?