Originally Posted by Tom Mobley
skip the 112 version, that's like a blower cam or something. you can give the 108 a try, but it might not make it. You need to be looking at modern, aggressive lift rate cams. see what you can find with 110 or so, with less difference between seat timing and 050 timing. the seat timing will affect your idle quality and vacuum readings at low RPM. Look for cams that have no more than 50* spread between the two duration figures.
Say, you know there's no way for them to tell you're running Rhodes lifters...... really help with the vacuum. Do they check after the race? When the oil is really hot?
I don't understand the "50deg spread thing, could you explain??
I highly doubt you will make the vacuum with that 108 cam. In fact I can almost guarantee it.
The first one on a 110 would probably make it if the seat timing isn't stupid long.
I used a hyd cam similar to that a few seasons ago & it worked very well but don't remember the vacuum.
You need some duration to fill the cylinder & the only way to get vacuum is to widen the centers & kill some overlap
Vacuum is not just related to seat timing, it is also directly related to overlap as is idle quality.
And do not believe you can't make power with a wide lobe separation.
I have a "few" restricted 2bbl engines with 180 cranking compression 14" vacuum rules & one in particular has reset the track record twice this year along with winning the championship & generally ****in off most of the other drivers in the class.
To the point I have gotten a number of kinda rude phone calls about my "cheated up" engines"
This is with a 114 separation.
BTW, these same lobes went from 110 to 112 to 114 & the car lost nothing according to the driver, just got faster. The engine was within 6 or so HP with the 110 & the 114, this I know for a fact,,, can't tell you the vacuum at 1200 though as we had to make it at 850.
It did lose some mid range torque but this I think actually made the car better off the corner due to tire rules & made the thing a bear down the straight,,,
Go figure,,, Gotta love restricted racin',,,,
Also, you are restricted to the 882 head but is there a cranking compression or compression rule?
The heads can be brought down to the mid 60cc range without too much work. About .100" angle mill will do it.
Flat top .010 out with 65cc's is about 10.3,,,
You can get more with attention to detail.
While I am not a fan of Rhodes lifters most of the time, this is one place where they are a win-win deal & as Tom said, try to make sure the oil is hot like 200 at least if possible & run a lighter grade oil like 15/40. Don't use crap oil, use a race oil or one of the good synthetics like Amsoil or what ever you like except Mobil 1 shelf stuff. The race stuff is ok but the shelf stuff has the Zinc & prosperous either removed or lowered a bunch just like all the "for gasoline engines only' dino oils or anything with the Starburst on the container.
If you want to run Mobil 1 or cheap oils add some GM EOS or Crane Break-in lube every other change or so,,, it has lots of the 'good stuff" in it,,
Also, do not restrict yourself to just the hyd lobes.
There are a number of solid lobes that work very well with .002-.006 hot lash.
Your rule states hyd lifters,,,,
no one said you had to know how to adjust them,,,