What are the negatives to using a 7.5 advanced gear? Do dyno results exist? How does deciding to use one effect your decision on which cam and rear axle ratio to use?
Moves the power range to a lower RPM. More grunt starting out and less top end.
If you're buying a new cam from Chaffin's, his new 280 already has the advance built into the cam. In that case, an advanced gear would likely be too much.
My car has a 3:1 rear end so it really needs the torque band moved down since its RPM is lower. I am running an advanced gear with a 290 regrind. Don't worry about the top end either. My car (27 touring) will top 55 MPH with this combination. I run a Z head as well.
If your running basically stock duration cam, the gear is a blessing at low RPM. This is one of the cheapest mods you can do and if your gear is still good it can be redrilled and remarked to get the advance for basically the cost of a gasket to pull the front cover. Level of difficulty = 1 beer.
The 7.5 deg advanced cam gear is a good idea for a stock or Stipe cam. Our new 280 cams are already advanced, so don't advance them anymore. We are now advancing our reground Driver cams, so don't advance them either.
Glen, are your camshafts marked in some way to show that they are advanced? Might help to avoid some confusion in the future if they changed hands and the new owner didn't know what he had. Dave
Gavid, No they are not marked. No cam is marked with specifications. They are easily checked with a degree wheel. Our cams are computer optomized for street use, not racing. We have designed them for both a very good low end and a very good high end. We have no unhappy customers.
If I have one of your advanced cams and also have a 7 1/2 advanced gear, what's going to be the result? Good, bad, same? Because me thinks that is what I have on one of the cars.
Glen, When did you guys start making the regrinds with the 7.5 degree advancement? I have one of your 270 driver cams and wonder if it is advanced or not. Got it within the last year.
Glen, I'm not talking about specifications as such, just if the cam is marked as a 7 1/2 deg advanced or not. Not everyone has a degree wheel, or know how to use one. I for one would not want to use one if I didn't have to. Just as Tom Moorehead just posted, there could be some confusion if the cam isn't marked. It just seems to me that a simple stamp on the camshaft one way or the other might help solve some problems for a future owner. JMHO. Dave
If you re-read Glen's first post in this thread he said his "new 280 cams are already advanced, so don't advance them anymore."
Kevin, We advanced the 280 cam in March 2011 and the Driver Cams in April 2015. David,I don't think that the advanced cam gears are marked either.
So if I have a cam you supplied me in 2015 as a regrind performance, is it advanced or not? I am using a 7 1/2 advanced gear. Is that the best set up?
Sure would have been nice to know that the cam I bought in Nov 2015 was advanced, especially since the description in the catalog and on the invoice don't say it. That probably also explains the following:
-The cam was $150 rather than $95 as listed in the catalog.
-I can pull the spark lever down and not notice much change after the first couple of notches.
At the same time I got a 3047BR bronze timing gear (also no mention of advance in the catalog). Is that advanced also? That sure would stink since I got the engine back in the truck and all buttoned back up. I agree with Tom and David, wouldn't hurt to stamp the cam and gears the cam was already stamped with the initials of who re-ground it and the date of regrind anyway.
Now a question for those of you smarter than me... With the cam being advanced 7.5 degrees and assuming the cam gear is stock. When setting the timer using one of the TW gauges that measures off of piston position, should I manipulate that setting any or stick with the 15 degrees after TDC like the book says? From the sounds of it if in fact the bronze gear is advanced also I get the joy of pulling my radiator and timing cover back off then?
Cam timing and ignition timing are two separate things. Cam timing is determined by whether you have an advanced cam grind or cam gear. Ignition timing is set with the piston slightly past TDC and the spark lever all the way up. Cam timing determines when the valves open and shut. Ignition timing determines when the spark occurs.
Also, Nathan, if you are using a Chaffin cam, I believe they recommend not setting the valves by piston position, but set the lash at their recommended value instead.
This is an area I don't know a lot about, so please bear with me. I always thought a stock cam began to open the intake valve just after TDC and seated it just before BDC. Conversely, I always thought the cam began to open the exhaust valve just after BDC and seated it just before TDC.
Having said that (and understanding my thinking may be slightly flawed), what exactly does a 7.5 degree advanced cam do? Does it change the lift but still use the same opening and closing time relative to piston position or does it cause the vales to open and close differently relative to piston position (sooner or later)?
I'm guessing that based on the above posts, since the "7.5 degree advance" can be accomplished with the cam or the cam gear, it changes only when valves open and close, not lift or duration.
I'm interested in knowing exactly what it does, what results it produces and why. I know, a lot of technical information but I'm an old dummy who'd like to know more.
If we advance or retard the dowel pin holes on one of our cam gears, that information is clearly marked on the center hub of the gear.
Glen, see what I mean? Seems to me there could be a lot of confusion in the future if things aren't marked as to what they are. Seems like a simple fix to me. JMHO. Dave