L8 APEKS

Hey guys,

The beast is finally back on the road again! Still have some fine tuning to do before a dyno is possible, but she's running and driving pretty well (aside from the blown front shocks...ugh!).

Installed a new waterpump to replace my old noisy one (thanks Julie and Eyal!), new cap/rotor, and the adjustable cam gear. My head was shaved .030", and from what I've been told by 944 engine gurus, that equates to roughly ~3 deg. of timing retard at the cam. The only way to get that back is with an adj. gear, and the only guy that sells them (that I could find) was Mr. Lindsey!

The gear allows for a range of -4 deg through +6 deg (one tooth on the stock gear is 18 deg). I set mine at +4 deg, which I figured would net me about 1 or 2 deg of actual advance. All I can say is...WOW!!! Now I can feel the higher compression, that's for sure!

Before the gear was installed, my car was slower at 11.1 CR than it was at the stock CR. I knew this was from the timing. She didn't really start to pull until about 5k RPM, and was a pig at anything less.

Now, she actually breaks the tires loose (I'm on 16's...Michelin GTXV4's or something like that) at ~80% throttle in 1st, and grabs good rubber going into 2nd. I know this is a bad way to judge power gains, but before installing the gear, she wouldn't come close to losing traction at all.

So...while it WAS expensive, it most certainly did it's job. I'm happy with the purchase as my car has finally woken up again!

Eyal 951

I've been meaning to do that, but maybe I really need to. I milled .050 off my head!

josephsc

I was wondering what was going on in your sig! 11:1CR, huh? not bad....

Skunk Workz

...you could just have asked..

Oddjob

I would be very interested in seeing or hearing how shaving 0.030" off the head will change the cam angle 3.0 deg. Im a little skeptical of that number - it seems really high. And for the stock cam sprocket to be 18 deg per tooth, that would mean there is only 20 teeth on the sprocket - I dont have one in front of me, but I recall there is more than 20 teeth on it (?).

This topic comes up periodically when guys talk about shaving the head. It concerned me, since I have shaved heads on 4 different motors w/o ever being concerned about altering the cam timing. So I made some calcs and CAD drawings to estimate the change in came angle relative to the crank, when shaving the head.

Ballpark numbers I found were:

shave____________ change in cam angle
0.010"-------------------0.25 deg
0.020"-------------------0.51 deg
0.030"-------------------0.76 deg
0.040"-------------------1.01 deg
0.050"-------------------1.27 deg

If you look at cam timing relative to crank angle - meaning the crank has to move so many additional degrees to bring the cam to the same position (after shaving the head), take my cam numbers and multiply them by 2. I believe this is the common convension when referring to cam timing, so 0.030" would equate to approx 1.52 deg change in cam timing with respect to the crank.

If anyone has some math/geometry that shows 0.030" equates to 3 deg, I would like to see how it was determined, because I cannot match or reproduce numbers that are close to that.

At the time, when I made the above calcs, I pretty much dismissed this as being an issue. I had only shaved 0.020" off my heads and I did not think that 0.5 (1.0 crank) degrees of cam timing was enough to be concerned about. My guess is that under varying load/rpm/age/tension conditions, the cam belt stretches enough to alter the cam timing by a greater amount than shaving a couple thousands off the head.

Am I missing something on this?

EDIT: And let me add, Sean, Im not doubting that you noticed an improvement in performance, but it might be that you are advancing your cam timing more than you first thought; by 2-3 degrees instead of 1 (if my numbers are correct/close to accurate).

GlenL

That Lindsey gear looks nice. For $300, though, not a bargain.

I adjusted a cam sprocket on my 928 using a $7 offset Woodruf key.

https://rennlist.com/forums/928-forum/170346-78-79-easy-cam-sync-advance-retard.html

If you're thinking "but I've got the rectangular key" then that's OK. I mistakenly thought I did too (early 928s do) but ground down the Woodruf key to fit. It was the right width, just had to take the round back off.

theedge

I got one too. Only thing that annoyed me about it was the assine little bolts. I went all over looking for an 8MM 12 pointed socket, in 1/4" drive. Its some sort of fabled Unicorn socket I guess. I gave up and bought four little allen bolts.

GlenL

Is the offset key approach well known in 944 circles? I thought it would get some comment.

Oddjob

Glen,

Not that Im aware of, Ive never seen it discussed here before.

Also, what did you notice (performance wise) when you changed the cam timing on your 928, and why did you decide to try it?

GlenL

Jim,

After I rebuilt the engine I noticed that one bank of the cylinders posted compression numbers consistently higher (~5psi) than the other. The high bank cam was right on at TDC and the low bank was a half-tooth off. Adding the key brought the low bank up and now they're all about even at 155-160 psi with no side-to-side bias.

Haven't dyno'd the engine to get "after" numbers. Does feel smoother, though.

L8 APEKS

Sorry for the mistake! It should be 9 deg. per cam tooth...18 deg per *crank* tooth (the crank rotates 2x for every 1 rotation of the cam).

Whatever the total amount of cam retard from the headwork, it was certainly noticeable...and it's certainly gone now! The nice thing about the adj. gear is that it takes only a couple minutes to tweak the timing across a range of 10 deg. of timing...I can mess with the settings and go back to stock with ease. You can't do that with the woofruff key trick, so I thought the gear would be a nice thing to have.

And yes, that dastardly 8mm 12pt is IMPOSSIBLE to find!!! They are ARP bolts, though, so that's a plus. You know they're strong.

EYAL, you really need to do something about your timing if you took .050" off the head!!!

MM951

URIN2ND -- I like your setup on the N/A. Did you lighten the stock flywheel? I'm assuming that because the Findazas are ~6lb. I'm doing that when I do the clutch job -- would you say its worth it? Any comments on it? Must be fun having an N/A that can spin @ 80% throttle. Mine hardly makes a chirp shifting hard into 2nd...

L8 APEKS

Thanks! So far the mods have worked well together. I'm contemplating a chip next.

Yeah, I lightened the stock unit. Although, if I had the money I would have gone with the Fidanza. There have been no ill effects from the 10 (actually I think it was like 10.6) pound fly. Just quicker accel through the gears from less rotating mass. Combined with the high compression and now the adjusted timing, it revs up pretty damn quick. Basically, I will NEVER drive a hi-performance car with a stock flywheel ever again. This is the 5th car in a row I've done it, and every time I've been pleased as punch with the results.

She seems quick for an N/A...I am planning on a baseline dyno before the end of the month. I'm having some weird fuel problem though so I hope I'm not leaning out too much. The car stumbles every now and again like it loses fuel for a second, then lunges back into action abruptly. It also shuts itself down once in a while, and then I have to crank it forever to get it to start again.

I see no reason why she shouldn't be making above 130 whp, as long as the fuel stays in the green. Need to get an A/F meter...

david fracolli

I had the head on my N/A milled .l035 as that was the maximum I could go with the aftermarket canm i was running and still maintain proper piston to vale clearance. When I checked my cam with a degree wheel it was between 2.5 and 3 degrees retarded.

josephsc

I hadn't heard of it either, but it's worth investigating. Thanks for the link!