Cam Timing

When setting cam timing, is it best to go by what the cam manufacturer recommends or would a better procedure be to set it at the best cranking compression obtained?

 

timming

If the cam was made for what your combo is, start it out with what the manf. ground it to If after you make all your tune-up changes and you want to try something go right ahead. I am a great one who thinks they know what the pro's, don't and everytime they prove me wrong. Don

 

Timing

Are you saying that the cranking compression is irrelevant?
If I start out using the manufacturers spec and have 160 psi cranking pressure and then advance the cam 2° and now have 190 psi is this better because I should then have more cylinder pressure or will the engine become less efficient at higher RPM.
We tried this on a friends Big Chief Chevy -- 1/2° retarded to start with 150 psi. Then 3° advanced and had 210 psi. The engine sounded totally different and throttle response was better. What had noticeably changed was the pressure coming out of the zoomies! It now would sting your hand if held a foot away.
Maybe the only way to find out is to test? In my class we just don't have many opportunity's to run multiple laps under the same conditions. Just trying to optimize what I have.

 

I would either run it at where your cam manufacture says to, or install it slightly forward. I am not a fan of retarding camshafts. Just remember to check your piston to valve clearance.

 

camtiming

i have a lencodrive psi c brad 5
cam in at 33 deg and 10.4 comp 4.150x4.467
it likes to flood cyl 1 and 2 out when in gear
and when stageing takes too long
it takes 1 -1.5 seconds to get back to 800deg
then its 1150 at end of a run
idle is .7 gpm with cyls 700-800
ive tried clearing it out befor dropping it into gear
and that makes it recover sooner but its still kills cyl 1 and2

since i cant test much
i was wondering if raising compression to 10.9 and advancing cam from
33 deg to say 35 would help this flooding issue

it runs good now but if the cyls were firing at the hit it would run better
and more consistant

thanks for any help and sorry for posting on your thread

 

Installing the cam retarded takes away power down low and provides more power in the 8-10,0000 RPM range. I also run a Lencodrive/PSI/BAE combe and we have the same problem of cylinder(s) out at the hit, ours is usually/almost always #1. We've tried putting a blank in the dribbler etc, it doesn't seem to make much difference. Even with that cylinder(s) cold, it's still got timing out to keep wheelspeed under control, we are recovered by .2 or .3 into the run. If you aren't leaving with max power as it is, why not retard the cam a bit, get the tuneup closer, and have more power at the top end....of course like mentioned above, the ptv clearance is a must check.

blwnapex - do you run something like a 296/300 114C w/ 478 int.? I don't think moving the timing will do much, seems to be a universal problem with the converter.

Brandon Booher
NHRA TAD #34

 

Remember one thing about the cranking compression theory;
Air does not move in and out of the engine at 8,000 rpms and 200mph like it does on stands testing cranking compression.
You can see the difference on the dyno making more power where the less cranking compression is, and if we could run dynos in a wind tunnel, then we could really see it.
But I will say, I have never seen a pair of spread ports that runs better with the lobes advanced. Of course, most of my testing is on naturally aspritated junk.

 

mine is 292 / 296 .4700 x 2 @114 Just drops #2 when I run it real fat. Don

 

my cam

my cam
i-290/500
e-296/510
118 cl
in at 33deg

my cyl1 go dead even with no hose on port reving past popet(4500)

does the cam really make a big difference 477 to 500 lobe or is it more
where you degree it

and yes we take 8-15 degree out till about .6 and start back in depending on track

thanks

 

increase idle rpm should help cylinder temp recover faster