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I have a sock VW 1600 cc air cooled engine with 2 cylinders

reading 160 PSI compression(at operating...
I have a sock VW 1600 cc air cooled engine with 2 cylinders reading 160 PSI compression(at operating temp).Is that too high for a proper compression ratio?The same engine has the folowing readings for valve timing.

#1 Intake closes at 75 degrees exhaust open at 95 (140 PSI)
#2 " " 110 " " " " 85 (160 " )
#3 " " 90 " " " " 110 (150 " )
#4 " " 110 " " " " 85 (160 " )
Does this look right?It has a calibrated front pulley.
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Answered in 22 minutes by:
6/26/2010
Jan Andersson
Jan Andersson, ASE Master Tech
Category: Classic Car
Satisfied Customers: 834
Experience: 20 years of car repair & modification, I love classic cars and have owned several, still do.
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Hi,

 

VW says maximum compression pressure for your engine would be between 114-142PSI. Warm engine, all plugs out, full throttle, full battery, turn engine over with starter.

 

Your compression pressures do sound a little high, maybe the heads have been flycut/shaved to increase compression or to fix a problem. Or maybe they came from an engine that had a bigger cam in it and needed higher compression ratio.

 

To really know what you are dealing with, you should pull the heads off and measure a few things. Are you planning to go that far? Or are you just running some tests with teh engine installed in the car?

 

Do you have any driveability problems? Overheating, knocking, dieseling after shut-off?

 

What is the valve clearance set to?

 

 

You can install cylinder base shims to increase the deck height, to bring the compression down. That's the most common way anyways.

The BEST way is to optimize the deck height to 1.1-1.3mm and modify the cylinder head to achieve the volume you need, for the compression ratio you want.

Let me know how mechanically inclined and equipped you are, and I can tell you everything you ever needed to know about rebuilding and modifying these engines. I have built countless of them for race and street use, as well as stock rebuilds, for the past 20 years. These cars are my passion. I still have a 68, with a little overXXXXXengine, at around 150hp :)

 

If you pull the oil pump out, you can examine the end of the camshaft. If there are numbers stamped on the end of it, they would tell you what aftermarket cam it is. If it's blank, its' either a stock VW cam or possibly one that was reground to some other specs.



Edited by Jan Andersson on 6/26/2010 at 5:17 PM EST
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I should add that almost every compression test gauge will show different numbers, they aren't generally calibrated very well, if at all. :) The important thing is that all the cylinders are close to each other.

Your compression pressures are at the higher end of the spectrum even if your gauge read a little too high. Some stock engines show 150PSI on some gauges easily.

If you have no driveability issues, I wouldn't worry about it. These engines can stand more compression than stock. You can try to see if a tank of high octane makes the engine behave better, get rid of high load noise (pinging/detonation). Pinging is not always audible, but when it is it's at high throttle openings, low to mid rpms, high loads. It would sound like someone left pennies or keys in the engine and they are rattling around in there :)

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Customer reply replied 7 years ago
I may be pulling off #1 and 2 head because of the 20 lb difference between the two.For some reason there is oil seeping from the head to barrel surface.(both cylinders)The motor does'nt smoke so I d'ont know how it gets there.The only drivability problem is some ocassional sneezing through the carb from #1(dificult to set the mixture scew).It has a stumble due to the 009 distributer.Somebody told me to use a vaccuum advance distributer.This would require drilling a hole in all 4 intake manifolds and running them into a reservoir for vaccuum.Does this make sense?It has a mild scat cam(the mildest one they have).I have the specs.

Ahh so we are not talking about a stock engine here.

 

What carburation and intake are you running? and if you have the cam manufacturer name and grind number, I would like to see those too. I have the specs if you have the grind number.

 

The oil leak is pretty common. You can have oil weeping past the cylinder head and cylinder sealing surface (poor seal, loose head studs) or through the rocker assembly studs... those go through the heads and often leak oil through to the other side, where it would appear to leak from between the head and the cylinder.

 

If you want I can help you sort the carbs out and reduce that famous 009 stumble too.

 

Your idea for vacuum would not work. You can't take distributor advance vacuum from the intake manifold, it HAS to be taken from the carburator body, right where the throttle valve is. Also a vacuum "reservoir" won't work, the signal has to be instant coming on as well as going off. A reservor would leave it "hanging" until it was depleted, and possibly slow to respond until it was "full". Hmm. That's weird. How can anything be "full" of vacuum... lol but you get my point hopefully :D

 

If your carbs have a port for vacuum, you can use a vacuum advance distributor. But mind you, you need a distributor that has BOTH mechanical and vacuum mechanisms. Not just a vacuum distributor. What you need is referred to as an SVDA distributor (Single Vacuum, Dual Advance).

 

It will buy you much beter driveability and better fuel economy, and better throttle response. Better in every way than the 009. Your best source for one is www.aircooled.net ask for John Connolly, the owner, to explain it to you. You will need to tell him the application too, what kind of engine and carburator setup. He will then be able to choose the right model SVDA for you, already tweaked to suit your engine. Tell him Jan sent you :)

 

if you want to get the 009 working the best it can, I can walk you through but it will take a little more correspondence back and forth.

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Customer reply replied 7 years ago
Its a Scat cam grind #C20.I'm running Webber IDF (Empi) knock offs.They were ordered from C1P and are suppose to be set up for a stock engine.I've reamed out the main jets from the stock .115 size to .121 That seemed to help the stumble a bit.Currently I have a 205 S distributer(Porsche 914 1.8 liter).It seems to work better than the 009 but the vaccuum advance is not hooked up.The carbs have a brass pipe coming out the side.They are capped with a screw one on each carb about 3/4 of a inch from the base plate.They are not drilled though to the carb body.Not sure if they are above or below the throttle plate.

Yea that's a mild cam. It cantolerate just a little higher compression RATIO than stock, and depending on the rest of your build details, a slightly higher copression pressure won't hurt the engine either. The more you can compress the mixture before igniting it, the more power you get. As long as it doesn't pre-ignite on it's own.

These are the Empi HPMX carbs I think. They come with vacuum ports ready for the distributor vacuum. Run a vac hose from both through a T fitting into the distributor. The fittings SHOULD be drilled through, but the hole is supposed to be very, very small. Look closer or check with a vacuum pump.

These carbs come set up for a stock 1600, which is close to what you have. What kind of exhaust do you have?

And have you synchronized the carbs properly?

You didn?t tell me what your valve clearances are. What kind of pushrods? Stock aluminum rods or steel rods?b
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Customer reply replied 7 years ago
<p>This engine is on a trike.There are 2 seperate exhaust pipes and the muffler part comes up above the engine.Not much back pressure on these so I do get a bit of rumbling when decelerating.I have a syncroniser and I set the idle with the linkage disconnected etc.The mixture scew on #1 seems to have little effect and that's the one that sneezes through the carb.I read that I need to change the idle jets because the mixture scews set up 2.5 turns out (too much?)The valve lash is set at .001 clearance with steel push rods.I was told to retorq this head due to the oil leaking and the 20lbs difference betweem #1 and #2.What do you think?</p>
Customer reply replied 7 years ago
Not sure if you got my previous reply?

You may have dirt in the idle jet or idle passage on #1. Clean the carb real good, take the jet out and blow the passages clean with air - from a small distance, don't pressurize the passage.

 

Double check your valve clearance on #1.

 

I haven't worked on the HPMX carbs yet, I try to stay away from them after reading lots of negative feedback on the early batches of the carbs. The later batches may have had some improvements incorporated into them.

You can also further improve them by using genuine Weber add-ons or upgrades, I can tell you more if you want.

 

Mixture screws generally should be out 1.5 turns, and you choose the idle jets so this is possible. It's just a rule of thumb to get you close. If you have to turn the mixture screws out much more than 1.5 turns, it is an indication of too small idle jets.

 

Bigger idle jets would help with the off-idle stumble and flat spot. Idle jets are in play up to 2500rpms, not just at idle. Then you start using main jets and idles together, until the rpms climb higher and the main jets take care of most of the mixture and percentage of idle jet flow gets real small. At the high rpm range, air correction jets come into play more and more, taking part of the role of the main jets.

 

 

if you do take the head off, you have an opportunity to do some measuring and learn more about the engine. I would fabricate pieces of metal pipe or a plate that allows you to clamp the cylinder down against teh case, imitating a cylinder head. Then you can accurately measure deck height, which would be VERY nice to know, letting you calculate the compression ratio. You would also need to measure the volume of the combustion chamber, cylinder bore and stroke. (Bore you can read from the top of the piston, should be stamped there).

Make your cylinder clamp downs in such a way that you can lay a metal straight edge across teh two adjacent cylinders, to check that the tops of the cylinders are exactly level with each other. One cannot be sitting higher than the other, or you will have sealing problems and head warping.

 

Before removing the head, go ahead and check the head nut torque on all 8. It's usually the lower 4 that get loose, being in consrtant oil bath more or less.

 

On reassembly, remember to replace the o-rings on the rocker studs before putting the rocker assembly back on. Use sealant under the washers on the lower 4 head studs. These are common places for oil leaks in the area you describe, looks like it's coming from between the cylinder and the head.

 

If the head to cylinder mating surface looks iffy, you can use valve grinding compound to lap the cylinders into the heads a little. Do it on both cylinders on one head so they remain even. No gasket, but you can use a very thin coat of some high temp sealant. I use Mahle cylinder sealant but people in the know recommend Yamabond or Hondabond too, from Yamaha or Honda motorcycle dealers. Aviation permatex has also been mentioned. RTV Silicone is not a good sealant here. I would only use it between the cylinder and the case, in place of the paper gasket. It has no other place in a VW engine because it's too thick for most purposes. (I don't use it at all)

 

 



Edited by Jan Andersson on 6/28/2010 at 11:24 PM EST
Jan Andersson
Jan Andersson, ASE Master Tech
Category: Classic Car
Satisfied Customers: 834
Experience: 20 years of car repair & modification, I love classic cars and have owned several, still do.
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Hi,

 

I mentioned the Weber update kit earlier, here's a link to it:

 

http://www.cbperformance.com/catalog.asp?ProductID=508

 

That SHOULD also work with the HPMX knock-offs. I am not 100% sure, so you should try to confirm it before buying.

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Jan Andersson
Jan Andersson
Jan Andersson, ASE Master Tech
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