Cams timing and all that

[Fitzgearld, Fredric]

WOW, I think I can actually contribute something, here.

It is true that advancing the cam will give you more "Grunt".  It's a 
common thing to do for those of us that are "Rock Crawlers".  The whole 
power/torque band of the engine moves down the RPM range.  And that's 
fine for us because we rarely see anything over 4500-5000 RPM.

Now, we get to the argument: how much is too much?  I personally have 
run some cams as much as 8 deg advanced.  Generally, 4 deg is the agreed 
maximum.  But then again, it depends on the cam, and the application. 

I haven't had that much experience with boosting, but I suspect that you 
will have a big problem getting any usable torque from off idle to about 
1500-2000 rpm.  Then again, you may not care about that range.  If you 
have a torque converter with a stall for 2K you'll never see that range, 
anyway.  

But then again, What do you want to do with the vehicle???  If it will 
see a lot of street use, you may want to reconsider building the engine 
for the 5K-7K RPM range.  If your hiway RPM is about 2700-3200 RPM, and 
you have a 2000-2500 stall, the tranny will be slipping the whole time 
you're on the hiway.

One other thing, Some of ht after-market, stockish, timing sets have 
built it cam timing that has been retarded for emissions.  To really set 
the cam timing you will need to find TRUE TDC and use an index wheel.  
But then you probably knew that.

With what I know about boosting, which is not too much, I would get the 
engine set up to run in the RPM I want, then try to add more boost to 
the lower RPM range to cover the "void".  Then again, it all depends on 
what the engine is used for.

Then again, Maybe I can't help at all.   :)

FEF
___________________ Reply Separator _________________________________
Subject: Cams timing and all that
Author:  Robert Humphris [SMTP:r.humphris at indigo-avs.com]  at MSXGATE
Date:    3/27/98 6:37 AM


Some while back someone wrote that advancing cam timing improved low end
response.

Now I know that this will result in loss at high end, probably peak
torque will move down the rev range please could someone confirm this?

The crux of the matter is this:  I am gonna run my engine at 7.5:1 as I
want to run silly ammounts of boost.  To help eliminate lag, I was
thinking of running a whole load of ignition advance, and advancing the
cam to give me a tractable ammount of low end off boost.  No I know that
a gain in one area comes with a fall in another... so what pit fall am I
going to get here?
Is the engine going to get upset with the cam timing and refuse to rev
above a certain level? or is there something I just cannot see yet?


Rob Humphris