From the cam info sheet on the grind I picked.

Valve Timing Information
Engine: Set (2) Porsche 928 SOHC 16v - Hydraulic
Grind # 552/553

Intake Exhaust
Valve Lash 0000 0000
Valve Lift .506 .462
Duration 266º 240º
Duration @ .050 244º 222º
Lobe Center 110º 110º
Intake Opens 12° Before TDC
Exhaust Opens 41° Before BDC
Intake Closes 52° After BDC
Exhaust Closes 1° After TDC

Mike - did you find out exactly what the room is in the lfter for additional lift? You said in your first post that you think its okay, but have you checked? I'd like to do something similar, but I only know for a fact about the 4V lifters. Not the larger 2V.

Your stated numbers compile to 1.397mm decrease in base circle. Thats seems relatively tame and within the specs of the lifters.

I bought two sets of 944 turbo springs, have the first, waiting on the second to arrive, then I start measuring etc. I am not 100% sure yet which lifters I will be using, used factory, new factory, coated used factory, or yipes.

WebCams said they have had trouble in the past with some of the INA light weight lifters, and that was my original plan.

Yes, there have been issues on the INA stuff, at least for the larger 2V ones.

Hi Mike
With 15 degrees of overlap you may get some reversion back into the MAF at idle ? Do you intend to raise the idle speed to get out of the zone where the MAF is confused by the back pulse ?

Good question. You'll need to find a balance with the overlap. Carbs don't care much, but injection fussy. Hmmm....

How did you calculate valve to piston clearance for the higher lift cams?

Dennis

Late on a Friday I was exchanging technical information with Jim, Tom, and Mark at 928Intl, and Tom started talking about Mark's last 16v motor and what a screamer it was. Carefully built from hand selected parts, (Tom scrounged the junk bin) with the biggest cam that would fit through the bearings. Next week I dropped off my cams to be made to what I "thought" was the same grind as Mark, but later found out maybe he used different ones.

I am concerned that any kind of calculation or planning may reduce the educational value, so I am winging it, periodically asking questions. Pistons will be fly cut to accommodate the needs of the valves. I just noticed the overlap the other day.

Overlap are these two numbers right?
Intake Opens 12° Before TDC
Exhaust Closes 1° After TDC

Duration is 266, duration at 0.050" is 240, thats 22 degrees below 0.050, guessing half opening and half closing, so how bad is the overlap functionally with the lift so low?

OTOH at idle manifold vacuum is pretty high, looks like a great educational opportunity for me. ;)

The overlap won't affect valve to piston clearance but, as mentioned earlier, it will affect vacuum. I did notice you are getting new valve springs which will reduce the likelyhood of valve to piston contact. If you are having the pistons recut a good/safe amount would be equal to the amount of additional lift on the new cams.

Dennis

I got a 1.62mm difference. What am I doing wrong? Either way I would think the stock lifters could handle 1.5mm with better springs.

Question is the benefit of just reducing the base circle with out adding weld on a Euro S cam? About $700 cheaper and would give close to same results. Changing the base on a Euro S 1mm, lift should go from .471" lift to .512", 1.5mm would net a .531 lift.

Is my math wrong? Base circle reduction is added directly to lift as cam center point is unchanged.

That makes sense to me. I would think you could change the ramp and center line some also. This could change the duration. The ramp speed could be really fast or you could slow it down. Makes my head spin...

So..... I have these euro "S" cams on the shelf... Hmmmm...

I think Carl's cams have about a .5mm base circle reduction along with more meat on the lobe. Diffefent ways to achieve the same max lift.

If you plot valve open time verse distance opened, the plat under that graph gives you how much air it could suck in. A reduced base circle cam that gets to max lift quicker has a larger area under the curve and therefor a tiny bit more power. However it is much harsher on components.

Here's how I see it. Over-exagerated but green line notes both cams have same total lift. Lift on second cam is a combination of lobe lift plus reduction of base circle allowing lifter close point to be higher up. Example would reflect more of a .25" reduction but you get the point.

Fixed pic to show offscenter cam center point. This is what base circle reduction really does.
http://forums.pelicanparts.com/uploa...1233180505.jpg

Base circle is the diameter, valve movement is works from the radius which is 1/2 as much.

I started with a base circle of 1.410", on a factory cam ;
173/174 246 241 .396 .350 I HYD. E HYD 1980-2 MODEL.

Base circle was reduced to 1.390" initially, but the peak of the lobe would not fit through the bearings, and it was reduced to 1.360", which is 0.050" and half that is 0.025" or 0.635mm.

*** note factory spec is 1.415", but mine measured 1.410".

Using the US 80 cam starting at .396 lift, and reducing base circle by 0.050" would end up with a .421 lift.

Using the Euro S cam starting at .474 ends up with .499 lift, no clue on other details.

Hey maybe you already know this, but here's my .02. I've talked to web and that coating is there for break in. The big problem for anyone with non-rolling lifters is that zinc-phosphate has been removed from oil for emissions reasons. It's about the biggest help in preventing lobe and lifter wear. You can buy it in additives, and I believe (for now) the shell diesel oil still has it. Here's a good article about it enginebuildermag.com/Article/3100/performance_oils_and_additives_got_zinc.aspx . Also for your lifters, ask the woman who always answers the phone at web (can't remember her name), there's a shop in new york that does diamond like coatings (dlc) on about anything and it's supposed to help tremendously and long term with friction.

as I understand this:

reducing the base allows for the lifters to pump up more (fully) before they actually start up the ramp. this effectively adds lift/duration that would not normally be there with the stock stick. reducing the base circle on the ramps (up or down) causes the valve to open/close faster.

with the 16V you can only get so much lift (from the centerline of the cam) due to loading the cam into the camtower from the end (through the bearing hole).

therefore, if you reduce the lobe diameter (base circle) with respect to the cam centerline, you can get more lift/duration with all other things being equal.

I disagree with the CompCams diagram as it only shows removing material from the ramps. not the base diameter (circle) of the cam lobe. (it's a lousy diagram)

I believe you have to think of the lobe's relationship to the valve with respect to the cam's centerline. Just offsetting the the lobe will not give you more lift.
removing material from the areas on the ramps as pictured will not give you more lift.

remember, the maximum lift is the greatest measurement you can install with respect to the camtower bearing hole entry--what ever that measurement is. the maximum lobe lift will be the radius of the camtower bearing hole, less the radius of the stick itself. example: if the hole is 3 inches, and the stick (not the lobe area) is 1 inch, then the maximum lift can be no more than 1 inch.

the real question is, how much plunger travel is in the cam bucket itself? if there is say, .250 inch travel in the bucket, then there is a lot of room to work with. I do not have any info to accurately judge this, may be others can provide this. (collapse the lifter plunger, install in camtower, install camtower on head, pre-oil engine (full oil pressure), then tear down to see just how far the plunger has moved?--do not rotate crank or cams while doing this)

in conclusion--

if you remove material from the diameter (base circle) of the lobe, it allows the lifter to pump up more creating maximum lift and duration. Duration dims can be increased, much like the NHRA/IHRA "stock" class cheater cams, but these tend to be very undesire-able for street engines (little vacuum, choppy idle, etc).

the only other way to get more lift with the 16V is to cut up camtowers and machine cam securement using clamps over the cam bearings, and then fab up remove-able tops for the camtowers----basically making valve covers for the cam towers. if someone was crazy enough to do this, then cam dims could be increased significantly.







--Russ

one word of caution Mike....

winging it is dangerous. be sure to have your lifters pumped up (pre-oil the engine) and then check valve to piston clearance for the entire rotation of the lower assembly.

a good clearance figure would be .100" valve/piston.

you can use putty to check this, while being sure to properly torque the heads before and after.

it's a lot of work dong this, but it's worth the effort to prevent bent valves.






--Russ

Funny thought on the cam towers. I've wondered about boring out the cam tunnel and having custom cam blanks ($$$$$) with bigger bearing diameters. Better yet (I'm dreaming) bore the tunnel out signifigantly if it permits, install roller bearings (I've seen it done on endurance racing pushrod engines) and run the bigger bearings. Actually, with roller bearings having such low friction you could have the bearings welded up and ground pretty easily.

You know if their were two piece cam boxes for these engines how easy it would be to shim up solid lifters?

either way, you're on the right track.

I'm pursuing the custom blanks question.

Jesel may have some answers with their 9310 cores. how about cam needle bearings? they offer them as well. we'll see......







--Russ