All of my Base Circles are Reduced

[Danglerb]

Originally Posted by entropy

The big problem for anyone with non-rolling lifters is that zinc-phosphate has been removed from oil for emissions reasons.

I run non synthetic Shell Rotella T for that very reason. I am thinking seriously on coating the lifters as well, but DLC is insanely expensive, so likely something else.

ZDDP is low due to issues with the newest types of catalytic converters, thats the cover story, really its to destroy all old cars.

[Danglerb]

The main issue as I understand it with our lifters is that reducing the base circle makes the lifters go higher in the bore and that can cause trouble with supplying oil to them. The secondary issue is how much the lifters can pump up, but if needed shims from some 911 are supposed to work fine.

This is a hybrid motor, starting with 32v pistons and cutting new reliefs to match whatever the 16v heads require. Claying the pistons, isn't that a sign of being chicken? Don't worry, I'm be plenty chicken.

[Danglerb]

I'm having fun pursuing what can be done with the 16v, but this isn't a problem I think should have a lot of money thrown at it. The point of diminishing returns isn't much beyond what I am doing.

[rich]

I wouldn't think you even need to silly putty the piston tops. The stroke remains the constant, the heads are euro "S" and we have a known lift height for the stock "S" cam. We have a piston in the 4.7L euro "S" engine that is already notched for clearance for the existing valve and stroke distance. That all remains a constance. The only thing your changing is the bore to 5.0 and some added lift on the "S" valve.

You should be able to figure out the depth and location of the notch by measuring the 4.7L euro "S" piston. When setting up the drill press you could even use one to get the proper angle and notch location. Then add depth to the cut for the added lift.

I built a franken engine for one of my BMW 2002's A machine shop F'd' up the head while plaining it. It ended up shaped like a wedge from front to back. I brought it to a second shop and had it plained square. By the time they were done with it, it was .111 over the maximum allowed cut. JUNK! unless I could figure out a way to use it....

I ended up trying it on the car. I had big time valve to piston issues. I took an old head and made a cutter out of a chevy valve. I installed the head on the engine, and rotated the piston to top dead center. I connected a hand drill to the valve stem and used a stop on the stem for depth. I cut the notches in the pistons without tearing the engine down. Sounds cheesy but all the notches were in the correct position and all were the correct depth.. Yankee engineering wins again. That engine is still running and sounds like a SBC on Riods! Just goes to show, you can get by using your head and not your wallet.

[entropy]

If you check the clearance with clay or something you may also want to experiment with slightly different cam timing incase you ever change it in the future. I've seen motors clear with the say...the cam straight up...or only retarded, but not clear at another timing.

[Danglerb]

Three flavors of clearance; ok with correct timing, ok even a few teeth off, and ok with a broken timing belt. A factory Euro S motor is ok even with a few teeth skipped, and despite the higher lift I think my cam would be as well.

Our heads have the valves up in a pocket, exact depth I'm not sure of, but enough that with the early pistons and cams it was non interference, ie valves could be at full lift and with a broken timing belt the crank could still turn and never make contact. Early cam is .396 lift, and my cam is .506, 0.110" more. Peak lift happens with the piston down in the cylinder, so doesn't really matter. I need to look at some calculated numbers, but pretty sure the valves are up in the pocket before that piston is close to TDC, how much and how close will decide how far the timing can be off before it smacks.

Down sides to cutting the piston, lowers compression, cut too far and its a vented piston, and combustion related issues.

I'm not going to cut the pistons unless I see good reason to do it, beyond everybody does it.

[N2O-SHARK]

Originally Posted by Danglerb

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

Duh... I was using that "new math"

So if you reduce the base circle 1.5mm you'd effectevly add 0.75mm of lift or .503" lift on a Euro S cam.

I know the 944 specs may be slightly different than the 16v valves, but JME starts using longer valves or lash caps at .526 with just better springs required from .503" They don't show any grinds in between .503 and .526 so it's not noted where the lashcap would be needed first. Carl is at .506 so I would assume you're safe to that point at least.

2mm reduction would net .513 and require the lifters to handle an additional 1mm.

Seems like base circle reduction would be much cheaper though the cam profile would not be as ideal as a true weld and grind. However just reducing base circle elimates the worry about fitting throguh cam journal bearings.

[Danglerb]

I may have this wrong, but I suspect welding needs to go all the way around the lobe, not just part of it, so the lobe would be ground to less than final spec, welded to beyond the spec, and then ground down to spec.

[N2O-SHARK]

If you went too far in base circle reduction for the lifters to keep up wiht, why couildn't you just put a .5mm shim washer between the spring and bucket?

[rich]

Originally Posted by N2O-SHARK

If you went too far in base circle reduction for the lifters to keep up wiht, why couildn't you just put a .5mm shim washer between the spring and bucket?

You can, they call them lash caps.

[2Quick4u928]

Very informative, thought I was back in school again....this site is great. Thanks for taking the time with this detailed info Mike ( You also Mr. Mike S.) hehe.

Myself, will be contacting Carl at 928 Motorsports this weekend as I now have 100% of the costs for these 32V cams he is asking (Round #2 for me for regrinds). Thinking very heavily also about the total electronics upgrade he is offering for $2700. May be the first 928 here in Europe with the upgrades hehe.

Keep the information coming Mike, is much appreciated!!

[Danglerb]

Making SLOW progress, two steps forward, then question those steps.

I now have two sets of used 944 turbo springs, but I may end up buying all new springs. Several people have wagged fingers at me saying you can never know if a used valve spring is any good.

I haven't gotten any smarter on lifters either, except I am thinking more about having them coated or surface treated.

I have been schooled a bit more on cam timing, so now I am a bit concerned by the overlap, but until the motor is together and running it may be hard to judge the seriousness.

Next task is to send the heads out for a valve job, then I want to gasket match port them myself, and I think at that point I will decide about lifters and springs.

[rich]

Mike, I would suggest doing your porting before the valve job. I built a BMW 2002 franken engine several years back. I ended up missing one little fleck of aluminum and it ended up on the seat when the valve closed. I needed to pull the head and lap the valve back into the seat.

[Danglerb]

Rich, I will have the heads cut for the valves, but won't assemble the heads until the porting is done. I think there is a reason for this sequence, but I don't know what it is.

[rich]

Cool, There may be a reason. Be careful not to hit any of the seats with the shaft of the die grinder. I use a couple layers of masking tape on the seats. Others may have much better ideas. I'm looking forward to watching your progress.

[rhjames]

Originally Posted by Danglerb

Rich, I will have the heads cut for the valves, but won't assemble the heads until the porting is done. I think there is a reason for this sequence, but I don't know what it is.

make sure you give your machine shop (the one that's porting the heads) the valves to work with as well.

recommendations are:

measure the intake outlets--increase the intake port to match (yep, port matching, but also taking the port diameter all the way to the valve, at a minimum)

Same for exhausts.

Don't get crazy bout opening up the ports--go too big, and it will affect low /middle rpms, where most of your driving is (?)

5 angle valve seat grind, blending the bottom cut into the ports.

Valve guide at port end should be blended to a point--increases flow.

unshroud the valves--you will need to supply a head gasket for this (5.0L hybrid will need a 5.0L head gasket for this. you can unshroud the valves a bunch with a 5.0L gasket compared to using 4.7L or 4.5L gasket.)

clean up the combustion chamber--only remove enough material to prevent detonation.

piston tops should be smooth with no sharp edges--again, only enough to prevent detonation.

make sure the head/block mating surfaces are straight and true. if you have to machine either, make sure you only take enough material to get the straight. removing large amounts of material affects CR and cam timing.

and above all, be consistent with all cylinders--do the same thing for each of them. if your shop has access to CNC headwork, that's the ticket. an engine that is uniform for all cylinders will out perform one the isn't.

--Russ