cam questions...

[joosep]

could anybody help me with cam questions? Sorry because the car is liquidcooled but old 8v vw engine.
Engine management - VEMS
We are looking for missing power It´s under 2 litre engine and used to make 153kw from wheels but after melting and rebuilding they don´t get it eaven close. (only 100kw from wheels)
Engine owners know nothing abut engines and specs of it.
*I started checking with valve caps....they seemed to be normal (0.2-0,3mm)
*Then I checked the compression and it was massive....18-20BAR
*Then I cheked the valve and piston leaks....zero valve leak.
*Then I measured the cam and it was ~11mm lift 300degree exhaust end 320 degree intake. - quite impressive. (from zero opening)
I noticed a thing I´m thinking about now. I know nothing about this engine but I thaught that maybe the cam is abit late because lobes are not in same angle when I look intake and exhaust in first cilinder with piston in TDC...is it possible? actually I wasn´t sure about it by looking it but it seems like that after measuring.
Exhaust starts opening 120 degrees after TDC
Exhaust closes 60 degrees after TDC
Intake starts opening 35degrees before TDC
Intake closes 75 degrees fefore TDC
If I´m not mistaken the difference in lobes angle is about 25 degrees ?
Thanks for your help

[Marc]

By convention, valve events are usually expressed as Intake Open => degrees before TDC and Intake Close => degrees after BDC; Exhaust Open => degrees before BDC and Exhaust Close => Degrees after TDC.

Translating, you have I.O at 35° BTDC and I.C. at 105° ABDC...total duration of 35+180+105 = 320°

E.O. is at 60° BBDC and E.C. at 60° ATDC...total duration of 60+180+60 = 300°

It's not impossible that there'd be that much difference between intake and exhaust, but it'd be worth taking another look - especially since your numbers, as you suspect, also indicate MAJOR cam retard (like, two teeth off).

Due to differences in the lengths of the "clearance ramps" it's not very meaningful to use raw duration data when comparing cams. Your data would be more meaningful if you were to note the valve events at the point of .050" lift.

If you want to know the lobe separation angle it'd be wise to note the crankshaft position at the point of maximum lift (it can be deduced from the valve-open and valve-close events, but only if the assumption is made that the lobes are symmetrical).

Typical LSA (commonly but inaccurately referred to as "lobe center" will be between around 106 and 112° on an ACVW.

Here's a typical cam card (chosen because it has a gross duration of 320°, so it should be somewhat close to yours) as an example of how these are normally marked.

In this example, the nose of the intake lobe is at 106° ATDC (½ of 276 = 138, 138-32 = 106) and the nose of the exhaust lobe is at 110° BTDC (138-28 = 110°).
106+110=216, then divide by two because up until now all events have been expressed in crank degrees, but LSA is expressed in cam degrees and the cam moves at half crankshaft speed: 216 ÷ 2= 108.
This cam has 2 crankshaft degrees of advance "built in" to the grind compared to the classic "split overlap" method of determining when a cam is "straight-up" - that's evident because of the 4° difference between the I.O and E.C. numbers, and the E.O. and I.C. numbers (the difference is again divided by two).

Rerun your checks at the .050"-open point, and also take note of the crankshaft degrees at the point of maximum lift for both intake & exhaust.

[joosep]

Thanks for your response, it is really helpful. Thank you
What do you think to which way is it usually safer to turn? I mean is it usually safer to turn cam earlyear or later and how it affects?

153kw from wheels it pulled up to 8000 nicely.....now we didn´t let it so high because power started dropping earlier.

[Marc]

The dominant valve event is the point of intake closing - the earlier that happens, the sooner pressure starts to build in the cylinder. BUT at high speeds it can be beneficial to let it stay open longer to take advantage of the inertia of the incoming charge to fill the cylinder further.
Short answer is, advance to enhance low RPM and retard to enhance high RPM - but if you need to mess with it by more than about 3° either way, IMO you have the wrong cam.

Also bear in mind that changing the camshaft timing will also affect your valve-to-piston clearance - advancing will reduce intake clearance, retarding will reduce exhaust clearance - so you can get into trouble by changing it too much.

[joosep]

Thanks again. I´ll do my best to get most out of it with safety. It has to qualify only one event this year and goes to bigger 16v or 20v or eaven turbo engine next year because there is no engine limits in icerace events and there is no reason to keep it so high performance engine.

[joosep]

Tryed to measure 1mm opening degrees (Noticed that most european cam specs use millimeters as I prefear)
Why, didn´t I do that on a first time it was alot easier to measure that way....the result was always the same and quite different difference between intake and exhaust duration.

Intake opens 1mm @ 20 degrees before TDC
Intake closing 1mm @ 65 after BDC
= 265 degrees opening more than 1mm

exhaust opens 1mm @ 48 before BDC
exhaust closes 1mm @ 34 after TDC
= 268 degrees opening more than 1mm

I think that 3 degrees is because of my measuring problems.

difference between E clossing and I opening was 14 crank degrees and I thaugt that its a bit too much turned the cam and measured all again:


Intake opens 1mm @ 27 degrees before TDC
Intake closing 1mm @ 58 after BDC
= 265 degrees opening more than 1mm

exhaust opens 1mm @ 56 before BDC
exhaust closes 1mm @ 26 after TDC
= 268 degrees opening more than 1mm

I checked that there is atleast 1mm between valves and pistons ( I put 1mm welding wire between lifter and cam and turned the engine 2 rotations with my hand.

I think I put this car back to dyno and look for any difference....

[Marc]

Yes, European convention is to use 1mm rather than .050" - that's fine, so long as you aren't trying to make direct comparisons of two camshafts using numbers attained by different methods. Measured at .050" your cam would probably come up around 257° (somewhere between Engle's W-120 and W-125) which implies that it's well past its peak by 8000.

I get 265° intake and 262° exhaust @ 1mm.

Interesting that your exhaust duration was 20° less before and close to the same now - evidently the ramps are shorter/quicker on the exhaust giving it more "seat time" for the valve heat to transfer to the head.

If we assume that both lobes are symmetrical it looks as though you've now got it quite close to "straight up" per the split-overlap criteria, where before it was retarded ~7½° - I would expect to see a noticeable gain in torque at the lower end now. The top-end horsepower may be down some, of course, but I suppose that's not a big issue on ice.

[joosep]

I finished this car for this time
I took all out of it what was possible. There is some problem with compression ratio because major problem is that piston hits the plugs and after that there is no plug gap at all depends at what angle is the plug.
I put some extra shims under plugs to avoid it When I measure compression its seems to be over 20BAR now but my gauge doesn´t show more. Guy who put this engine together didn´t measure or calculate CR.

There is alot detonation when I go over 28 degrees with ignition.
102 octane gas (made for airplanes)

every detail (plugs, mixture, ignition, cam, ITB lenght) gave me only 3-5kw and 5-6NM
I hoped that cam would change a lot but it didn´t

I changed 7 NGK heatrange plugs to 6 - Is it riski business? there were a lot of black on the edge with 7

Highest pull - 126kw / 220 NM @ wheels

maximum kw@ 6450 rpm max NM @ 5200

I´t will be 16v for nex season. I´ll try to measure CR when the head is down one day.

Last year the owner of the car qualified as a most fastest man on ICE (Here in Estonia ofcourse) . This year never get higher than 4th place with 100kw from wheels...This car uses special ice tires and need some more power https://www.upload.ee/image/1143747/piik.jpg


Thanks for your major help

[Marc]

That much cranking compression, and the fact that the pistons need notching for the sparkplugs, tells me your C.R. is probably up in dedicated race-fuel (or alcohol) territory. AvGas is intended for relatively slow/steady-speed engines and even though the octane number looks impressive it may not be the best for you.

I once ran a 12½:1 1285cc (heads had to be flycut clear to the edge of the sparkplug hole to get that out of a 1300 with flat-top pistons) and class rules did not allow racing fuel, only "pump gas" or methanol (and octane "boosters" weren't regulated). I used a 50/50 mix of leaded AvGas and unleaded Premium (91 to 93 R+M/2) with about 10% methanol, using a recirc pump at the tank to keep it from stratifying. Octane boosters may or may not have been desirable on top of that, but I stopped using them because they made plug readings difficult and I never found any detonation damage upon teardowns. That witch's brew did the job for me, but then that engine was rarely turned over 5500 RPM, in deference to the non-counterweighted stock crankshaft. The combination of high static C.R. and a relatively low-duration cam (mine was 246° @ .050") pushes the peak cylinder pressures to extremes; one of my competitors back in the day had an amusing term for such an engine: "muscle-bound"

File a small notch in the hex on your sparkplugs that's in line with the tip of the electrode so you can easily see how the plug is indexed from outside (a felt-pen mark will do in a pinch); indexing washers of various thicknesses are available for correcting that (or you can stack an extra used/flattened gasket between the plug and the new gasket.) But add only what's necessary, exposing the last thread of the head to the chamber can create a hot spot. You can make a tool from a gutted sparkplug body and a bolt with cutting teeth filed into the head which you can use to clearance the piston tops; I suppose one could even do that on an assemble engine if airflow was maintained through the chamber to keep chips from piling up.

I suspect that your plug color isn't due to too cold of a plug (I ran B8HS on mine) - NGK 6 is probably going to cause some preignition. File the electrodes back something like this:

There's no ice-racing around here but we used to have some Canadians who would come down to invitational pavement races and tell us about it - those guys had the best damn rain-driving skills ever Back home they didn't even have any engine rules, classes were determined solely by the stud count/design of the tires. Yours would qualify for what they termed "unlimited".

[joosep]

Interesting reading again Thanks.

Unfortunately I have not enough skills with reading plugs and with naturally aspirated engines. I boost engines for living and usually they are old cheap m50 141kw BMWs in light third serie body and they ask for 300-400kw with stock internals but sometimes 500+ kw when we have some room to play with ethanol and some budget for chinese rods and better headgasket We gain the displacement up to 3.2 litre with diesel crank and 2mm oversize pistons from some another car like nissan or what ever we can find Thouse engines live nicely with cheap NGK7 but need 0.6mm gap and last maximum one season. We don´t read plugs and use only wideband and EGT sensor when needed.

Can you help me with reading heatrange from plug? (There were old plugs and when I was thinking that they are too cold then now Im little worried and not feeling comfortable to let this car out with 1 step hotter plugs,

Old bosch on picture (matches heatrange 7 with NGK)
I think I touched it too much because there is no black on the edge as it was before

[Marc]

Several challenges when reading plugs. First and foremost is getting a "clean shutoff" by switching off and declutching at the point of full-load. Any time spent under other conditions (i.e. idling) can change the look of the plug - typically that's where any black soot comes from on a healthy engine. Fuel additives can add coloration. To get a really good read you need to use a loupe and strong light to peer down towards the base of the insulator, the "color" there is more consistent/reliable than what you see near the end.
The plug in your photo looks pretty good to me, from what I can see of it.

http://mechanics.stackexchange.com/ques ... heat-range

The scariest thing you can see is tiny shiny balls (often with a purplish tinge) clinging to the plug, since those indicate preignition and imminent melting. Usually the cause is too lean of a mixture but detonation from any cause, including a too-hot plug, can be a factor. http://www.hotrod.com/articles/reading-a-spark-plug/


I assume you're aware that Bosch heatrange numbers run counter to those of many others, this is for the benefit of others reading this: http://www.leeroysramblings.com/OB%20im ... reange.jpg

[farmer]

Hello.
No wonder it doesnt make any power. The cam is on 104,5 LC. Then on top of that it is RETARDED about 7,5 degrees.
I seriusly doubt that it has ever made that kind of power. ´That´s simply wishfull thinking and/or a very optimistic chassis dyno. It takes a VERY stout 2 liter engine to produce 200 hp at the wheel (unless it is a 16 valve modern engine) Even 200 at the flywheel requires a well thought out engine combo.
I am almost 100% positive that the cam has been retarded 1 tooth during assembly.

T

[Marc]

...The cam is on 104,5 LC. Then on top of that it is RETARDED about 7,5 degrees...

His most recent numbers:
Intake opens 1mm @ 27 degrees before TDC
Intake closing 1mm @ 58 after BDC

exhaust opens 1mm @ 56 before BDC
exhaust closes 1mm @ 26 after TDC

[farmer]

Ahh, OK. That eliminates the retard. But still at 105 LC. That cam will never support that kind of power. 150-160 hp on the flywheel on a good day.

T

[Marc]

joosep never directly measured the nose degrees as I recommended, so we can only infer the LSA by assuming that his measuring technique is accurate and that the lobes are truly symmetrical - but 105.25° isn't that far out. Some 911 Porsche cams come on 97 or 98°!

I've run a Web 121 on 105° successfully on limited-carburetion circletrack engines and found it superior to the same grind on 108°. Just to experiment, I also had one done on 102°, and that was definitely too much of a good thing - it did sound badass with all that overlap, though

A tighter LSA will reduce top-end HP, but in exchange you can expect a higher torque peak and a narrower powerband which favors midrange.
Sig Erson's E746522 and E749422 grinds were both on 106°; the E749422 I used on a 1775 delivered on both counts compared to an Engle W-110 on 108°, although not surprisingly fuel economy suffered slightly.

Point being, a wider LSA will give you a broader powerband and most likely higher peak HP readings, but narrow LSAs can have their place too.