TheSamba.com :: View topic - Puzzling combination of Type IV issues

Fri Jun 07, 2019 6:26 am

Nitramrebrab72 wrote: And if your compression is down, compensating by increasing timing is an old trick..
Just as high compression ration engines need to be retarded.
The compression ratio is down so much its normal you have to advance timing.

I'm late looking at this thread.....but your point is spot on.....and for whatever reason whether its the exhaust manifold design, head design....whatever.....I have found that type 4 engine of any configuration....bus, 411/412 or 914....are some of the most sensitive engines I have worked on.....with regard to compression changes.....MOST ESPECIALLY....lowered compression.

The lower the compression....the less efficient the burn (and a lot of that greatly depends om how it is lowered).....and the less efficient the combustion....the more dead on all of the supporting mechanisms need to be....initial timing, advance and fuel mixture.

Years ago Jake Raby had some long threads that put it very well. As compression on the CS engines he was building increased.....ignition advance could and should be reduced.

Its a common habit of a lot of owners and especially higher performance builds...to start increasing advance. At some point you are starting the combustion so early with the piston so far down in the bore still ...and the gas expansion rate becomes so high that it is expending almost as much extra energy fighting the rising piston as it produces with the advance. Its a diminishing return.

As compression and efficiency on his CS builds increased.....he found that advance could drop back to right around what VW started with.....27 BTDC or even a bit less.

As you were commenting about what waw done with the 914.....yes.....some of that same experimentation was done in the 1.7L engines for 411/412.....especially for higher altitude and specific locations. Mostly it was done......as is going on here......by increasing initial at idle timing to give more advance off the line.....which also produced higher total advance at high rpm.....and because vacuum advance can partially reestablish at high rpm part throttle openings......you saw mostly on 1.7L 914....and some 2.0L 914....and even on some 411 and 412 1.7L....the installation of an advance can with arm #917 that had a factory adjustment limiter screw for vacuum advance.
When this vacuum can is used....since they are usually setting the idle timing higher by about 5+ degrees.....it was no longer critical to have as much vacuum advance immediately as the throttle cracked open.

Very different engines than the bus......but some of them are instructive for a lot of the same reasons.
With the 1.7L in 411/412 and 914......as compression dropped across various apppications....proper fuel mixture tuning became more and more difficult. Driveability suffered and head temps went up.

Back to the bus engine at hand.....I would not be surprised to find that you are one tooth off on the cam. That could easily explain the need for a good deal more of inital timing.

However.....SGKent made a very good point early in this thread about the cam. The bus engines had notoriously large deck volumes......a combination of piston dish and actual deck. They needed this set up....but it made the combustion a bit less efficient.
But.....if you add in a new camshaft.....whose overlap and duration greatly change the dynamic compression......without first fixing or changing that inefficent deck volume equation......your dynamic compression can be way down......requiring a whole lot of initial timing advance to start the mixture early enough to get compression efficiency back up.......and these type of engine combos almost always run hot......and are peaky and difficult to tune the fuel mixture for.
Ray

Fri Jun 07, 2019 6:31 am

skills@eurocarsplus wrote: asiab3 wrote:

Oh no, not another one…………………

I agree. I just did car/rotor/points/condenser on a 2004 Audi 1.8T. it's sooo buttery smooth when you dial in the dwell

Personally, I don't notice much of a difference. The Pertronix never failed me, but since I swapped out the points for troubleshooting purposes, I'll probably just leave them in there. But that's not related to this engine's current issue.

Fri Jun 07, 2019 7:11 am

Slip356 wrote: I didn't read your entire post but have you checked the vacuum advance? I found the T in the vacuume line goes to the air cleaner, to a diaphragm for pollution control was shot so had no vacumadvance. Bentley has a neat chart showing total advance, cetrifigal and vacuum for different distributors.
I had no difference hose on or hose off. Vacuum can on distributor was good so I eliminated the T and got full advance per Bently
Bus runs cooler with better power.
Bus is 78 FI stock except pertronix
Hope this helps.
Slip

Thanks, good suggestion but I checked that and I have good advance hose off, and more with hose attached.

Fri Jun 07, 2019 7:23 am

raygreenwood wrote:
Back to the bus engine at hand.....I would not be surprised to find that you are one tooth off on the cam. That could easily explain the need for a good deal more of inital timing.

Good points, but I did eliminate that possibility:

Fri Jun 07, 2019 7:33 am

FWIW we did a lot of dyno tuning on Fiat 124 1608 dual over head cam racing engines in the late 1970's. It was #2 in its class (FP) in the late 1970's. I took the lessons from that engine tuning and created a 1438 dual over head cam for GP that created more power than the 1608. One thing we learned from dyno tuning, There is no sweet spot on air to fuel or timing. What I mean by that is once you are close with the timing or the air to fuel ratio, the power and torque changes very little, at least on those engines. Moving the timing 2 or 3 degrees made no difference in measureable power. If it ran well at say 38 BTDC then making it 36 or 40 didn't change anything except that the 40 took you closer to detonation on a cold morning. If a mixture of 14.2 made you a lot of power, going to 14.4 didn't cause a huge drop or gain. Once the engine is close to the proper settings the power will be there if everything else is working. On my 1977 FI bus, I get slightly higher head temps at 32 BTDC full in hoses off than I do at 29 BTDC, When I say slightly i mean 3 to 5 degrees F. AT 28 BTDC full in I can feel a slight drop in power but it is barely discernible. You would not know it was different unless you were looking for it. At 26 BTDC there is a noticeable loss of power but think about it - that is 9 degrees off where VW set the engine up to run. If someone cranks in 10 - 20 degrees of additional advance then they are only asking to melt a piston. In 1976 I melted a hole in a 1600 piston running 34 - 36 degrees BTDC full in. Took about 10 miles on a cold night climbing a grade at Box Springs in Riverside CA. Dealer gave me the number because that is what they were setting beetles at.

If the camshaft has too much overlap the power will be gone at the low end. That is how single profile cams work. In addition the FI system relies on vacuum to open the AFM flap. If it is too closed the mixture will be too lean at the low end. Close the bypass screw down to lessen the amount of vacuum lost at low RPM and raise the idle speed just shy of the advance coming in. Be easy on the clutch when engaging. See if that helps. It is a workaround if the camshaft is too much for the L-jet FI. Even the stock 142 solid lifter Webcam sells is based on a proflle used in the 100 HP GA 914-4 and 912E engine. It has more duration than the stock bus cam (and HP) and results in lower vacuum at the low end but performs well.

Fri Jun 07, 2019 7:34 am

I ordered a LM-2, and I'm looking forward to getting into another level of engine understanding, which I kinda dig. I'm a pilot, and live gauges, numbers, and limitations, so establishing KNOWN fuel/air settings, rather than tuning by ear, is right up my alley.

It will be a few weeks till get home and am able to weld on the bung and get tuning, and I have much to learn in the mean time. If anyone has a good thread or website reference for working with the LM-2 on type IVs, I'd love to have it.

I sure do appreciate all the input, I'm confident I'm on my way to giving this engine "what it wants".

Fri Jun 07, 2019 9:37 am

When I got my LM-2 I also ordered the tailpipe piece. Makes that nice when I am getting the rest of my cars ready for smog check.

Pay attention to the LM-2 handling instructions! There are a couple of warnings about set-up that must be adhered to.

Another thing that helps me out is I made up a ‘battery extension cord’ which is two giant alligator clips, a 15’ length of 12 AWG two conductor wire and ends with a cigarette lighter socket. You probably won’t need that for the bus, but it’s super helpful for the Vanagon and some of this other junk I have. It gives me a lot of flexibility with where the LM-2 can be handheld.

Fri Jun 07, 2019 11:25 am

Fixed it for ya... :lol: That is bad ass! :twisted:

Squeeze Cheese wrote: Good points, but I did eliminate that possibility... because I don’t mess around! I will dig deep to find the truth!

Fri Jun 07, 2019 1:24 pm

skills@eurocarsplus wrote: asiab3 wrote:
We don't need any more threads about this shit.

yea, I feel the same way about this one

https://www.thesamba.com/vw/forum/viewtopic.php?t=720140

more threads about what? about how fantastic points are vs quality electronic ignition?

when you buy a PicoScope and look at how dirty the signals are let me know and we can compare notes...

lol 1.8t sludge= people that had no clue how to own/maintain a turbo car.

That would be nearly every original buyer/leaser of that engine.........

Fri Jun 07, 2019 2:01 pm

I love Robbie and Skills both for what they bring to this site, but man, Skills, that was a sick burn. :shock:

Fri Jun 07, 2019 3:18 pm

Thats an AFR meter? I don't know if the timing is not factory it will function correctly. As its based on a widband oxygen sensor. It measures the oxygen after the burn. And not fuel and air masses before. I hope I`m wrong. You see by increasing the advance on a too rich setup it gives the cycle time enough to fully burn and give a normal O2 reading. Im really not sure

Fri Jun 07, 2019 4:07 pm

By looking at the left over oxygen you can tell if you are too lean or rich. Lots of left over O2, too lean. No left over O2, too rich. What one wants is just a tiny amount of O2 left. There are charts that show O2 to A/F ratios. Timing plays a part because for example late timing will extend the burn which could leave high HC and O2. So you set your ignition dwell and timing up first. Then idle CO, then read 15 and 25 mph. What you see at say 2,000 RPM in neutral will be close to what you will see at 15 and 25 so you can get close before a drive. If the AFM has never been played with you set the A/F by the slider screw. If the AFM has been monkeyed with then you set the door tension first then use the slider to trim it. Then you can monkey with the spring tension to change the curve.

Frankly with the cam you have I think you will always notice a little loss of power on the low end so you will need to gear down sooner than someone with a cam with less overlap. Your peak will be 600 - 700 RPM higher than a stock engine IMHO. I hope you put good bearings in it and get good oil pressure because if you are going to be pushing it then you'll want the best there.

Sat Jun 08, 2019 9:45 am

If you want a permanent installed AFR gauge here is my thread

https://www.thesamba.com/vw/forum/viewtopic.php?t=676774&highlight=

Sun Jun 30, 2019 8:03 pm

Hello all, I’m back with an update. The short story is that the bus is drivable but not sustainably so. I’ve reached the point of making adjustments to optimize the engine running as-is, but I’m at a decision point. I think I’ve conclude what that decision should be, and I’d like to know if the expertise agrees.

Recap so you don’t have to reread three pages...

Engine:

78’ Westy Type IV stock 2.0L except Web Cam 107i and hydraulic lifters (255 Duration, .430" Lift)

Stock L-Jet fuel injection set to run pre-rebuild totally stock 2.0L engine.

Mahle P&Cs. HAM heads with both coatings.

Compression Ratio 7.6:1 (7.75-8.25:1 recommended for the 107i cam)

Timing set to 28 BTDC max advance hoses off and plugged.[/list]

Condition after install, before any adjustments:

500 RPM idle speed cold and 700 RPM warm, barely running, with the throttle body idle speed screw all the way out.

380-410F CHT in stop and go (less than 45MPH).

Very slow acceleration and low HP.

What I did next:

Verify no vacuum leaks, all four firing, timing notch correct, cam indexed correct, valves set and pumping up, pertronix not at fault.

Checked AAR and Decel Valve operation.

Checked fuel pressure.

Compression test 85-90 PSI. Leak-down test <20% and no sign of compression leak.

Advanced timing to an unsustainable 40 BTDC before it seemed to run better.

What I’ve done since my last post:

Acquired a LM-2 in hopes that the AFM was way off. I went back to 28 BTDC and found that 1000 RPM AFR was around 13.2 and 60MPH AFR was 12.8. Not overly lean, yet CHT 420 at 60MPH.

I ran level road 60 MPH tests with progressive richening at the AFM cog (dynamic) to see if I could find a mixture setting that would at least make highway driving possible. I had to go +12 cog teeth rich before I could achieve 390 CHT, abnormally rich at 10.9 AFR. But the rich setting made idle 500 RPMs and still the marginal performance. So I progressively advance the timing and had to reach 34 BTDC before it would idle, although still 700RPMs at best, which also produced my lowest 60 MPH CHT, 385.

That far advanced, power is pretty good, of course. But that far rich MPG is 8, of course, and the plugs show it. And it still won’t idle cold, barely when warm, with the throttle screw all the way out, and the AFM idle mixture screw making no difference. So, drivable but not sustainable.

My conclusion, and this is where I’m asking for consensus or not, is that I assembled the engine with a too-low compression ratio (7.6:1 with a cam that “works best with 7.75-8.25:1”) and that is the cause of symptoms such as high temps, low power, low idle, low compression test numbers 85-90PSI – and that my attempts to adjust mixture and timing will never fix the underlying flaw. So I should pull heads and have Len fly cut to increase CR.

If I’m way off base, I welcome any suggestions?

Sun Jun 30, 2019 8:49 pm

it all works together. I would go with a stock cam personally. Ljet is fussy enough and gets angry with funky cams. imho, that compression is way low, really. when I pulled Ride-On's engine before a conversion, the compression on that was like 140-150 iirc

EDIT:

skills@eurocarsplus wrote: well, took the bus for a ride today pre swap. I have to say this thing runs GREAT!

so, before it's difficult to do, I went and took some compression readings before we pull it. it will be listed for sale here in a bit, but I just have to post these results...

mind you, this was with a cold engine. no smoke, no mirrors no bullshit...this was a DRY compression test

and according to the book, WELL within specs

goodbye old friend...you'll be missed (for about 1/2 a minute)

and that was a well cared for, but used engine. so...you built a pig honestly. with compression numbers that low...its a wonder it runs a bus down the road really.

you could bump the compression, but I really have to wonder about that cam. if it were really built foe low compression trying to bump it up solely by cutting the heads would be a waste imho

Mon Jul 01, 2019 4:44 am

skills@eurocarsplus wrote: I would go with a stock cam personally. Ljet is fussy enough and gets angry with funky cams.

I agree with Skills.

I had a situation very much like yours and it was all about the "performance cam" not playing well with the stock FI. I really wanted to keep FI so I went so far as to split the case and replace the cam.

Mon Jul 01, 2019 7:01 am

SqueezeCheese, have you performed a vacuum gauge test?

Did you calculate the piston dish (15cc) into the combustion chamber volume?

I stuck some Len Hoffman heads on my '77 Westy June 6th in NY, now at 2,000 miles here in Minneapolis, running 17 mpg, 410* highway, compression 130/140/130/135
Colin

Mon Jul 01, 2019 7:21 am

I tend to agree.

No matter exactly how you got to this point.....the fact that I mentioned earlier is that even though you want to keep compression sane on a bus.......like every other type 4 engine it does not appreciate or work well with EXCESSIVELY low compression.

And....what is considered excessively low.....varies with the exact engine combination, the powerband its designed to run within, the vehicle type and gearing.

For example.....the 7.6:1 compression you are running....would run exactly like what is happening to you....but far worse and with a short, hot life.....in a 914 or a 412.

That cam....the 107i.....is a waterboxer cam pattern. Different and better ignition on the WB.....and liquid cooled engine. It can get rid of the extra heat.....and the vast majority would be running near the TOP of the 8.25:1 spec.....not near the bottom.

See....this....in my opinion.....is a common problem that many make with a whole lot of tolerances when rebuilding ACVWs in general....and type 4s specifically.

They see a tolerance range listed in the book.....and their parts are not perfect....but in their mind.....as long as the parts or spec is falling within the "range" listed in the book....they figure they are ok. And even worse.....if they fall very slightly below minimum tolerance....they figure its so close that its close enough.

This is incorrect. With type 4 engines.....about every 0.2 of compression ratio...is a LARGE order of magnitude.....of tunability and running.....not to mention basic HP.

Keep in mind ....for instance.....that from the California version of a 411/914 motor at 7.3:1.....to the 49 states version.....at 8.2:1 compression.....is 69hp versus 82hp. Thats 13 HP.....and the CA version ran head temps equivalent to a bus....damn hot.
The bus 1700 version...or some of them...with a different cam, 7.3:1 compression, and different ignition....ran 63 and 59hp respectively with CB and CD series engines....and this was correct for the bus and gearing it was paired with.....but I am just illustrating what seemingly small differences in compression can make to a combo.
That is a LARGE order of magnitude.

I have not even looked at the profile of the 107i cam and calculated the overlap.....but I am betting it has a lot.

Bluntly put.....your compression is too low.....as others have noted. I think when you open this thing back up you are going to find any of these items or a combination of them.

1. Deck too large
2. The above issue coupled with a large piston dish
3. Possibly ring gaps too large....but uniform....because your compression from cylinder to cylinder seems pretty uniform.
4. All of this coupled with larger than necessary exhaust overlap (purely speculation from me).

If you are going to use this cam.....I would work to get compression up to the top of the spec.
Ray

Mon Jul 01, 2019 11:28 am

Amskeptic wrote: SqueezeCheese, have you performed a vacuum gauge test?

Did you calculate the piston dish (15cc) into the combustion chamber volume?

I stuck some Len Hoffman heads on my '77 Westy June 6th in NY, now at 2,000 miles here in Minneapolis, running 17 mpg, 410* highway, compression 130/140/130/135
Colin

Hi Colin, thanks for weighing in! This is my Dakota Beige 78' Westy that you helped me tune last year here in Marietta. It had a wrist pin work loose and gouge a cylinder wall, so I decided to do a full rebuild. Looks like I may have fallen for the "mild performance cam" marketing that goes something like "It's completely compatible with stock or aftermarket FI, and obviously a grind this mild is compatible with any carburetor system. This is fantastic with Automatic Transmissions too! This is a nice upgrade on stockish engines, it's an outstanding bus cam!"

I'm sure no one ever fell for that before. Should've listened to my gut and stayed stock. Damn.

Anyway, a vacuum test I have not done. At this point it seemed to me that if I don't increase compression, anything else is just symptoms of low compression. But I will do a vacuum check, and report back.

I had a reputable aircooled machinist calculate my CR based on the deck height I measured, maybe you can check the math? The email conversation went:

Steve (me): I got .028" all around, that's using the .009 metal case-to-cylinder gasket/shims that come in the gasket set. They are dished Mahle pistons.

Machinist: I come up with 7.45:1. You probably forgot to calculate the .8mm step in the heads which = 5cc's and figures as deck ht. If you remove the .009 gasket you get up to 7.6. That will leave you with a total deck ht of .047". A good spec.

Steve: So, to make sure I have this right, if I leave out the .009 gasket, (which means my deck measurement, not including the step, should be .018") - I'll have a CR of 7.6? But that's outside of the 7.75-8.25:1 recommended for the cam. Shouldn't I make an adjustment?

Machinist: At this point the only adjustments you can make will be to have us flycut the heads to reduce the chamber volumes, which would remove the coating, or have the jugs machined down .007' to get your total deck ht to .040" That would put you at 7.7. If it were mine I'd put it together just like it is.

So I left off the .009 gasket and put it together.

If the conclusion is to have heads cut to bring up CR I'm willing to do it. And although far from my preference, if the conclusion is that this cam won't work, I'll just have to bite the bullet and replace it...

What do you think?

Mon Jul 01, 2019 11:38 am

raygreenwood wrote: I tend to agree.

Thanks Ray, that's a lot of good info. The "slightly" low CR I have clearly makes a big difference.