valve shims vs performance cams

[manoa matt]

Has anyone added thicker shims to give higher lift or longer durration vs new performance cams. Mark, I seam to remember when I visited you that your car was set up with .014" clearances on either the intake or exhaust, can't remember which one.

Some one school me on the theory.

[So Cal Mark]

I set mine up at either 010 and 012 or 008 and 010

[manoa matt]

Correct me if i'm wrong, just thinking out loud, so: With the stock cams and tighter clearances the lobe profile stays the same obviously. The tighter clearance means the valve bucket/shim will contact the lobe sooner and start to open the valve sooner. Conversly the valve will also close later, hence longer durration that the valve is open. Tighter clearances will also mean that the valve will be depressed further into the cylinder by a few thousanths. All that taken into consideration will result in more valve overlap OR to say it differently: Both valves will be open at the same time for a longer period than would with stock clearances.

Question: I thought the idea was to close the intake valves sooner to build up more pressure, and open exhaust valves sooner to maximize the scavenging effect.

Do your tighter clearances produce more power? "I set mine up at either 010 and 012 or 008 and 010" Always tighter on the intake side right?

[ventura ace]

Matt,
I have the PBS 40-80 camshaft on my intake (300° duration). I set my intake valves to the PBS recommended clearance of .010" (see http://www.pbseng.com/camdata-124.html), which does indeed give a duration close to 300° (more like 294°) for this particular design camshaft. Actually, I shimmed more to achieve equal balanced duration for all 4 cylinders, as opposed to shooting for equal valve clearance on all 4 cylinders, so the clearances range from .009" - .012" to obtain the desired equal duration accross all 4 cylinders. This is a little more involved, requiring an accurately marked degree wheel on each camshaft, rather than just measuring the cam circle spacing with a feeler gauge. I also use adjustable cam pulley wheels, to give more control on the phasing of the opening and closing in relation to piston TDC, but I must admit that I still haven't optimized and tested with a good measuring stick, such as dynamometer testing.

I did experiment with setting the intake valve clearances to the .017" that Fiat specs out for the standard camshaft, and found that the duration decreased as expected, to around 285° or so, and noted that the cylinder compression changed accordingly.

Camshaft design is more than just duration, though. The ramp ange, lift angle, and total lift have a big influence on the air flow into and out of the cylinders, also. You may want to experiment with changing your duration (by shimming), and monitor the change in compression and your perceived change in performance. Keep us posted of your results!

Alvon

[wmausbach]

Alvon,
Setting the valve clearance with a degree wheel is interesting. I'm starting on a high milage project for my every day driver. I using the theory that race engines are very efficient when running in a "economy" mode. My project will be to build an old 1438 cc engine with performance and economy using as much race technology and Fiat parts as possible (Higher gear ratio,Blue printing, HC,coatings,F.I.,Adjustable Cam wheels, Ford Edis igintion system, plus very precise tuning).

My targets are 100 hp (stock 90 hp)and 50 mpg highway milage on my 1981 Spider.

What kind of degree wheel did you use ? I would like to know how you rigged the micrometer etc.

By the way I really enjoyed being your co-pilot (even though I got us lost) during the FFO drive. Your car is awesome and now I know one of your "secret tweeks".

Ciao
Wayne in Houston

[ventura ace]

Hello Wayne, and Happy New Year!
I enjoyed having you along for the ride at FFO, and Maureen was happy to give up her seat (after sitting in it for the last 4500 miles) and relax in the spa back at the hotel. Now listen up Denise and Bernie -- you heard Wayne admit that he got us lost on the drive, so you can quit ragging me about it! Actually, I probably distracted Wayne by talking too much . . . so I'll share the blame, Wayne.

Now, back to your question. It's been 3 years since I built the engine, so I forget some of the details.

The Degree Wheels. I just made them myself. You can Google "Degree Wheel", and find several offers for downloadable pictures that you can print out on paper. This is what I did, then used a copy machine to resize the paper degree wheel to the same size as my crank pulley and cam pulleys. Next, I cut them out and taped them to the pulleys, and for a pointer, I clamped a stiff wire to handy place on the engine nearby. This smaller hand-made version is probably not as accurate as using a nice professional 10" or 12" diameter degree wheel, but you can easily get within 1°, which is close enough. I used a dial indicator to determine the lift and profile of the cam lobes, and used a similar set up to determine piston TDC very precisely.

Here are a few pics showing a bench set up I used to map out the cam profiles (click to enlarge). I took lobe lift measurements at every 1°, and entered the data in an Excel spreadsheet. Having all this info available in the computer, I could easily play around with the numbers and see the effect of valve clearance on total lift and duration.





I used a similar set-up on the engine, to check the relation between valve events and piston events. These pictures are from when I had fixed cam pulleys. Later, I installed adjustable pulleys from our buddy Jason Miller there in Texas, and used the degree wheels again to play with changing the overlap of the 2 cam shafts.







You don't really need a dial indicator to determine duration or valve lobe peak lift angle. All you need to do is check the wheel degrees at the point where the lobe just starts to hit the valve shim (use your fingers to rotate the shim back and forth -- when the lobe touches the shim, you can't wiggle it any more), then continue rotating engine and check the wheel degrees when the lobe is again off the valve shim. Duration is the angle difference between the 2 readings and the lobe peak lift should be halfway between the 2 readings.

When using a dial indicator (or any device) to check TDC of the pistons or peak lift of the cam lobes, it's difficult to determine exactly where the peak is since the lift changes a very small amount per degree of motion at this point. It's more accurate to check the angle at .010" or .020" off the peak in both directions, then use the halfway point as your peak.

Good luck with your project, Wayne!

[wmausbach]

Alvon,
Thanks that is exactly what I wanted. You are an inspiration and I hope to drive to the next FFO . A group of us drove to FFO-05 but it was only 1200 miles. Your drive this year was really a motivation for me.
Jason is part of our Houston group and a great kid. We are fortunate to have him to machine all our little projects here.
Ciao
Wayne

[mdrburchette]

So Wayne...you're the one that got us lost? You're off the hook. I'd much rather blame Alvon.

[baltobernie]

Alvon & Wayne; “Ego Absolvo te”
Maybe I can come up with a route in Chester County for this year, and return the favor

[ventura ace]

Hey, that's great! Bernie's taking us out for eggs and tea . . . I think?? Must be some kind of Northeast omelette.

[baltobernie]

Leggo my eggo!

Here's another one for you, slick. I plan on leaving the timing cover off after my rebuild, now that I no longer wear a necktie. What do you use for a pointer against the balancer? Or could I put a mark on the intake cam wheel to line up with the reference alignment pointer, once I get the engine dialed in?

[So Cal Mark]

timing off the cam would be a very inaccurate way to set ignition timing. Either use one of the late pointers that mount on the right side or make your own pointer.

[ventura ace]

Bernie,
I put the cover back on to set ignition timing, and read the mark on the crankshaft pulley. Actually, I have the cranksaft pulley marked every 2° from 0° to 50°, and I know just about where the zero reference is by lining my line of sight up with the fender and the aux shaft center bolt, so I can get fairly close without having to install the timing belt cover.


I don't know if you can see it in this picture from my owner's manual, but the 10° mark on the cover is just at the lower edge of the aux pulley center bolt. That's my reference. if the lower edge of the bolt lines up with my TDC (0°) mark on the crankshaft pulley, then I'm at 10° advance.

I'm keeping my eye out for a spare cover so that I can cut off the lower part and just attach it to the block whenever I want to check timing. But, as Mark suggested I could just make some kind of a pointer.

When I was checking valve phasing to the crankshaft phasing, I had fashioned a rigid wire pointer to read the degree wheel that I had attached to the crankshaft pulley. I did the same for degree wheels that I had installed on the camshaft pulleys.

[ga.spyder]

If you guys could have just kept up with me and the Canadiens,you wouldnt have gotten lost at all. My navigator(my son Geoff) is going to accompany me to our first rally in May...the famous Moonshine Rally in N.C.
Craig

[mdrburchette]

Oh goodie! I'll make sure you don't get the directions that have been 'modified'. I hope Geoff is up to it...there have been drivers lost in the mountains with no word of whether they've been found or not.