Bee Jay

Thanks Larry, I'll pull the driver's side valve cover tonight while watching the UT game. Do you have any experience in degreeing a cam. The sprocket only allows +- 4 degrees. What if I need more adjustment than that. What does one tooth on the cam sprocket eqaul in crankshaft degrees? How bad can a GMPP factory cam be off?
Bee Jay

Bee Jay

The fuel injection has been on the car over a year and was pretty well dialed in. What I changed over the Holidays is the camshaft, the intake manifold, and the water pump.
Bee Jay

Bee Jay

OK, using the Quick and Dirty method, with #1 up at tdc, the exhaust is more open than the intake, in fact the intake is still closed and the exhaust hasn't closed yet. I guess the cam is retarded. The exhaust was closed and the intake had started movement less than 3/4" later on my 7 inch damper. Will advancing the cam 4 degrees fix this?
Bee Jay

larrywalk

I always degree every cam to avoid problems...

If the bottom cam gear doesn't put where you need to be, an offset bushing kit as used on the cam's location dowel usually offers +/- 6 degrees, therefore you can have up to 10 degrees of latitude when combined with the lower gear.

Since most lower cam sprockets have 22 teeth, one tooth off would be equal to 360 degrees divided by 22, or approximately 16.4 degrees.

__________________
1978 Corvette
406 SBC AFR heads Lunati roller Quadrajet TH-350 3.08
11.59 sec / 118.9 mph 1/4 mile

larrywalk

You are correct - can you estimate how far the exhaust was open at this point?

larrywalk

With the GM Hot Cam, the lobe separation angle is 112 degrees, and the duration is 218/228 @ .050. If both of the valves on #1 cylinder are equally open at TDC-overlap, the intake lobe centerline would be positioned at 109.5 degrees which will work very well.

This assumes that you have a solid reference for TDC of course, but if you're unsure whether or not the balancer may have slipped, remember that the TDC mark should be 10 degrees counterclockwise from the keyway slot.

Bee Jay

I got home today and put the garage tv on the Texas/Bama game, and start tearing the front of the engine apart. Once I get the pulleys, damper, water pump, and timing cover off, I find this:

The UT Quarterback gets knocked out of the game, and I find that the cam gear is off one tooth. How the hell did that happen. I took a picture of the setup just before I buttoned it up, or did I? I do not remember taking the cam gear off for any reason after taking the picture of the timing marks lined up perfectly. Damn.
Well, after reading David Vizard's book, I had regreted not putting the cam in 4 degrees advanced, so I'm doing that now.

I am really bummed right now because of this game and this major screw up on my part. Sorry guys.
Bee Jay

Matt Gruber

i missed a clue too. that it liked 50* timing at idle was a clue for a retarded cam.
No real damage, and it will now run great!
what is the comp. now? 180?

Gordonm

Keep digging and you will find the culprit which you did. It can now be fixed and it should run very well now. Its not the first and won't be the last something like this happens. At least you found it. Let us know the results.

73'Vette

I have a LT4 hot cam in my crate engine (Year One 400+ HP engine), and 12 in. sounds correct. My brakes and headlights work fine with that amount of vacuum.

Bee Jay

I don't know yet, I have to get a timing chain gasket today and put it all back together. I hope the cranking compression will be higher than my dumbass IQ. UT lost. Now I have to go to work, pay off my bets and be subject to humiliation. I look forward to getting home and getting my baby running.
Bee Jay

Bee Jay

I put everything back together tonight and meausured my cranking compression. It is now 150 lbs on all cylinders, with the cam advanced 4 degrees. Not the 175-185lbs I'm used to, but much better than 120-130 lbs. It's late, I'll crank it in the morning and see how it runs.
Bee Jay

Bee Jay

YEA BABY!
15" of vacuum and it running like a sexually violated semian (raped ape) again. I'm gonna wash and wax it and drive it like I rented it.
Bee Jay
note: If you use the one piece oil pan gasket, there is no way in heck to put the timing chain cover back in place without cutting that section of the one piece and installing a standard front oil pan seal in it's place. It is not leaking oil, but at some future date, I will drop the oil pan again and replace the one piece gasket......or not. It's not broke.
Bee Jay

cardo0

Man that's good to know the Hot Cam really makes 15" with 4* adv. I have looked at that Hot Cam for a long time and always wondered if it could pass CA smog. I was going to suggest u should ask the C4 section but now i see u have nailed it BJ. Really good reading helps the rest of us see how cam timing affects a lot of stuff.

cardo0

mrvette

Don't fix it, i'ts not broke....

I forget just how, but I modded a timing cover long time ago, to get it back in place with the gasket/pan there...used RTV for holding the gasket....

larrywalk

Way to go, Bee Jay!!!

Matt Gruber

sounds great!
maybe it can idle down to 700 ?

larrywalk

I just noticed the old manifold with the spread-bore mods...
Did you make these mods? I couldn't find any other intake manifolds (3917610) with dual bolt pattern.
I had thought about modifying my high rise aluminum manifold (3972110) for the dual bolt pattern. Do you have any comments how best to do it?

Thanks!

Bee Jay

I bought this manifold at the Pomona Swap meet. The vendor was really impressed when I did a double take. The LT1/Z28 manifold never came in the spread bore configuration. Someone carefully shaved off the top of this manifold, and welded a spread bore pad on. They did a good job too, because it looks like it was manufactured that way. It was a damn good manifold, but the Edelbrock guys at SEMA said that the RPM Air Gap would make more power. I don't run the Q-jet anymore, so I didn't need the spreadbore pad.
Bee Jay

Matt Gruber

Bee Jay
There is a C2 guy that advanced the cam 4* and went from 20 to 22 mpg! then he said he added another 4* and his cruise went up to 24!
So i was thinking 4 is easy but another 4 is gong to take some new parts.
So if 1 tooth is ~16, one could advance it 1 tooth, but use the 4* retard to get +12 without any new parts. Since you have been advancing cams i thought you might find the idea of 12* interesting, perhaps as a future experiment!