Timing With Rv Cam

Just wondering how an RV design cam will affect timing. My OF 231 runs an RV cam and I'm wondering if perhaps the cam would require a timing adjustment from the stock specifications.

Other engine mods are modest. No other major head work. Over bored cylinders but I forget how much with stock design dished pistons. Headers. 2 bbl carb.

Didn't really know what I was doing when I had this built many years ago. Don't know much more now except that I would do a few differently.

So, timing adjustment from stock......????

 

Every engine is a bit different depending on variances from original. The factory spec for things like timing are a good baseline to start from. A mild cam won't drastically affect timing.
After the engine is up and running, I usually start tweaking fuel mixture and jetting. I also start playing with timing by advancing it a degree or two more than factory spec, then drive it, listening for pinging, also called power tuning. For maximun performance, just a touch of pinging under heavy load, then back off a degree or two to be safe. Also, make sure it isn't too far advanced to cause hard starting. Then I go back and see where the timing ends up. It should be within a couple degrees of factory spec, probably on the advanced side. Are you running a stock distributor, with the stock advance curve? Another variable. I expect the HEI has a little different curve than stock. Does the advance mechanism in your distributor still work, both centrifugal and vacuum?
When you installed the aftermarket cam, there are usually three positions for the crank sprocket, assuming the chain set got replaced too. Stock position, or advanced or retarded can alter where the power comes in. This also can affect how the engine is timed. There are lots of variables, so power tuning is the best final adjustment.
-Donny

 

Thanks Donny. I'll put the light on it sometime this coming week, I hope and see where it's at now. I have no idea where the engine builder positioned the cam when he assembled it. I didn't know to ask.

The HEI distributor seems to be working well. Has an Accel super coil on it.

This all started with discovering very low vacuum with a gauge, a while back. I sprayed some carb cleaner around the intake and carb areas and had no noticeable changes in idle. So, I started thinking maybe the timing was off. Today, I sprayed some starting fluid around the same area, with the air cleaner off as before, and noticed the idle pick up when I sprayed it around the carb base......actually the base of the adapter plate for the Holley.

I think I'll start with taking the carb off and checking out the adapter plate and gasket. See what I turn up there. Then recheck the vacuum reading. And forward to timing check after that.

 

Donny is spot on. Most of the off shelf grinds you will degree in like factory. IME the 231 with it's small valves will take a fair amount of duration as long as the intake opens early. You won't lose the bottom end or get lumpy that way. Over something like .427 lift requires guide milling ( mine are with a way too big old Crane grind) I find that the odd fire purrs like a kitten with HEI and upwards of 14° advance with some reasonable gas at 800 rpm idle .

 

Fino, thats exactly what I meant in my reply above. You need to get out and drive it to fine tune the timing. Under heavy load, you should be just get a hint of ping, then back off a degree or two. The same engine may got a slight ping on 87 octane, and be fine on 89 octane. Significant elevation change can affect timing too.
-Donny

 

Starting fluid is not ideal for this purpose, it's too volatile. You were probably getgetting some sucked down the carb.

 

Yea, I was kinda wondering about that. Maybe I'll try the carb cleaner again.

 

A propane torch works well for checking for vacuum leaks also.

 

Sea Foam works for that test.

 

As far as timing goes mine likes to run at 13 degrees advanced, (Blueprint 225), I'm running a DUI-HEI distributor with a total of 23 degrees of advance curve. The cam was set at the advanced setting, I believe its about 6 degrees. I always question how far advanced it is but it likes it and runs great with a an idle set at 750 rpm's.

 

After looking at my notes from Terry, the cam is only advanced 2 degrees.

 

Sorry, I just have to say the idea of an 'RV cam' in a 231 implies that there was a 231-powered RV which is pretty amusing.