Engine out

Scott,
have you got the lash set to zero? The durations you measure will be short about 20 degrees if you don't....I fell for that too.

You don't want mis-matched cams, it will hunt the bottom end and add nothing on top. A bigger exhaust cam will also increase the blow-down you get when you add the blower.

 

you know i had thought of doing that, but was going by the 'book' WSM. the zero lash would work if the expansion of the parts reduced it to zero when at operating temps. i'll give it a shot and see what i get.

 

Yeah, there is a thread somewhere that talks about it...the WSM is more than a little confusing. The specs are at .020" lift, but it assumes zero lash. Just measuring the lash, say .006 and taking degrees at .014" valve lift doesn't work either....which I should have known I guess had I thought about before trying it.

In the end, after a lot of screwing around, I decided that what I actually cared about was lobe center. I found the lobe center by setting the lash to spec and using .050" of valve lift to to get off the ramps and onto the cam. Once I did that, I found that all the factory marks were pretty much right on...making me think the factory guys were probably doing something very similar.

 

i know it's now OHC but on my 512 (ford) i have solid lifters and you measure at zero there also, if you have hydrolic then you don't. but i was going by the WSM which leaves that detail out and stipulates the clearance so that would explain the problem.

 

okay, i started over and dug through the posts on degree'ing these buggers. brian crall had posted a great how to. basicly what you do is replace the intake and exhaust shims so that your clearance is now .05mm on cylinders 1 & 8. you can use a dial gauge or not i did. turn the crank until the gauge reads .002" from zero and check your degrees.

here's a couple questions.

doing it this way will net me the correct timing figures, but how does that translate when you go back to .2~.25mm shim clearance?

if i measure the cam directly i get the right timing events, but that gap once again changes what the valve sees so what is the expansion of the bucket assy? how much does the .2~.25 tighten up?

after all this the cap marks and notches all line up and the timing events are as they should be, well close one cam is off 1/2*.

I learn something new everyday....
last yr when i built the big block i sat and mapped the camshaft. every .005" i recorded the lift for the entire profile. then i put this into acad and have a nice profile for the cam. i just sat down and played with the profile moving it around and recording the degree events for each of the ways i tried these last two days. not surprisingly they all gave different events.

now i realize the profile isn't the same but the concept is. so i mocked up a bucket assy and measured the degrees the way brian had mentioned, then i went back and did it with the factory lash and zero assuming expansion from heat. the result?
bear in mind this is not a ferrari cam but it'll give a picture non the less. the first degree is where the cam touches the shim and the second is the degree at lift. zer o lash is the marker for 0*

zero lash + .02" lift : 0* ~ +18*
.25mm + .02" lift : +11* ~ +21.5*
.5mm + .002" lift : +18* ~ +19*

zero lash is close, but here's the 64k dollar question... why not use zero lash? why go to the trouble of re-shiming to .5mm?

 

Timing at low valve lifts means very very little. In the 60s when people first start to get that race engine used longer durations, the cam makers use mess with the start and end of the lobes adding say 10 degrees to each, and then claim the new cam had 20 degrees more duration. Technically it did, but efectively, it is exactly the same as before, but a touch less efficient. The US industry has standardized on .050" lift as a good point to spec events and talk about duration. Anything below that doesn't have much effect on the engine, and as you found, a slight lash adjustment makes a huge difference in timing, that matter very much.

 

alright more progress, got the covers and plenum redone. they were black and i wanted them red so now i'm happy

some more touch-ups and it's looking really nice, almost to nice to get dirty again. dupli-color make a great high temp aluminum paint 1615 i think. anyway it has just the right amount of mica in it to give it that cast look. helps on the areas that are to far gone from oxidation and heat.

it amazing the difference from when i pulled it out to now!
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login

 

Wow, that is one beautiful detail job!

I've been thinking of going black instead. Just the opposite, of course. I think black (rarely seen on a GT4 nowdays) was original at some point early on. Although I had considered the TR combo you did too. After seeing yours, maybe I'll rethink this again. Hmmm...

And I like the way you detailed out the lines. I didn't realize the double-line on the timing-chain cover matches up to the cam-cover double lines. Polishing them up really shows that off nicely. In spite of the fact that a purist will think otherwise.

I like it! Bravo!

 

thanks, i went through a couple options. the original i think was natural aluminum on the cam and valve covers and red on the plenum. the PO had it all black and that was boring to me.

i thought of aluminum with red lettering, or black with the aluminum highlights. then i decided on what i have now. it looks neat to me and the car is no longer original as it is, so the modification is on par with the car. besides it's paint, it can be changed again the next time around.