Can't figure out this timing issue

[dj_ender]

So as some of you know I rebuilt my F22 back in November, it's running good and strong. In the past month or so I have figured out my TPS was set wrong and affecting my MPG's. It is now set correctly and MPG's are way up. I recently took a trip to Seattle, WA and on one tank of all highway miles I got 420 miles, averaging about 28/29 MPG. The issue Im having is that when I set my timing to 15 BTDC it acts like it's advanced, I have plenty of power up to, and beyond redline. But if I advance it I notice no real difference, possibly even a slight loss. Now when I retard it 2 degrees it acts like it's at 15 BTDC, losing top end power around 5500/5800.

I forgot to ask the machinist how much he took off, but now I'm starting to wonder if he took off a bit. When I got my head back there were machining marks on the bottom of the head casting beyond the head surface, specifically on the underside of the coolant neck thats next to the dizzy. And you can see some of that here in the pic as well. The spot in the upper left coner, looks like an upside down U, and at the bottom in the middle, looks like a U. You can see they are freshly machined. I didn't think much of it, but I kinda had a suspicion is wasn't normal.



So, I'm starting to wonder if he took off enough to affect my timing. I have checked the physical timing about 4 or 5 times, both by eye, with the timing window cover off and the VC off. And I have checked with a dipstick in the number 1 cylinder to verify TDC. Timing is dead on. So any input would be greatly appreciated.

[SOHC-FTW]

Look's like it's been milled a good amount as it's into the CC's. Milling also retards timing which is why you have to advance it beyond BTDC to have decent pull.

[dj_ender]

But Im not advancing it...

[SOHC-FTW]

BTDC is no longer BTDC.

[dj_ender]

Right, when I get it to 15 BTDC using the flywheel, it acts like it's advanced 2 degrees.

[SOHC-FTW]

"Now when I retard it 2 degrees it acts like it's at 15 BTDC, losing top end power"

You are going to have to find what timing works best for the engine, i know it runs way worse retarded an at BTDC i've seen it (Maybe look into an adjustable cam gear). You should have asked the machinest how much he took off to start with.

[dj_ender]

You should have asked the machinest how much he took off to start with.

I know... I don't know why I forgot to ask.

[SOHC-FTW]

Mine had .035 taken off, i had to advance about a tooth on the cam gear and play with the distributor aswell.

[reklipz]

Mine had .035 taken off, i had to advance about a tooth on the cam gear and play with the distributor aswell.

I hate to take this OT, but wouldn't advancing the timing belt a whole tooth completely (well, one tooth...) throw off the valve train timing? Assuming each tooth is 1/4 inch (+ 1/4 inch gap), that's 0.50 in/tooth * 112 teeth, giving 56 inches. 0.080 inches (0.035 * 2 +0.01; 0.01 for some trig, and x2 for up and down of belt) / 56 inches, gives less than 2 tenths of a percent (0.14%) difference in distance.

Is the whacked valve train timing really worth the gained ignition timing (assuming it was necessary in order to achieve proper ignition timing, as you state)? I realize that you can tune for a different valve train timing, so if you have done this, then bravo; ignore my post. But, please clarify!

[SOHC-FTW]

You are not advancing the entire timing belt just the cam gear to get it back to or as close to BTDC.You can play about 30 degrees out with the distributor.

Grand old question of any modifications done.... is it worth it?

Jason on the other hand didn't do it to bump a tiny static amount, he just wanted a flat surface.

[reklipz]

You are not advancing the entire timing belt just the cam gear to get it back to or as close to BTDC.You can play about 30 degrees out with the distributor.

Grand old question of any modifications done.... is it worth it?

Right, but advancing the cam gear advances the valve train by the same amount. Unless you tune for this, you risk ruining performance, etc.

Jason on the other hand didn't do it to bump a tiny static amount, he just wanted a flat surface.

Yeah, it looks like there has been quite a bit taken off. I've been looking for photos of a stock head to compare to, but that's apparently easier said than done.

[dj_ender]

My old, stock, head.

[reklipz]

Hmm, not as bad as I was expecting. It looks like the chamfers around the valves extend all the way to the edge of the chamber, even beyond in some places. You're certain that was stock?

[dj_ender]

Pretty sure, when i disassembled said engine everything was original.