In a message dated 7/4/2014 1:57:58 A.M. Central Daylight Time, johnxxxxxxxxxxxxxxx writes:
sorry to bother you with our Euro problems, I´ve a good friend how does hillclims with an Alfa GT 2000. He´s also a good mechanic but he made the same mistake all people around here make, he bought Catcams for he´s engine development, the 1030243 Catcam, I attach the data sheet of those cams. The problem, as allways, is that both cams are the same and what is happening is that the Ex valves are touching the pistons slithgly.
I told him many times to buy cams from you, but he forgot about that when he made the purchase (stupid him). I also told him about this problem that the valve will hit the piston due to to much overlap and lift on the Ex side and sugest him to use the C&B AR.120.292.S with 292º and 12mm of lift on the Ex side that he has.(no money left)
Some data of the Engine:
The usuall stuff, bottom end balanced, head ported & blueprinted, etc.......
Measured 10,5:1 CR (head was milled to get to the CR target)
Running with 48 DCO´s
Please would you recommend me LC´s to have a starting point to work with?
Many thanks for your time and regards.
If you look at not just the data but at the graph of the lobes you can see that at the lash setting which is .20mm (.008) the valve events have at least 75-80 degrees of overlap.
Far to much even for a race engine as all it will produce is very high RPM power.
Two things can be attempted to improve the setup so engine is better timed as to valve events and clear the internals.
First increase lash from .008 (.2mm) to .012 int (.25mm)and .014 exh.(.28mm) this will get the off the seat opening farther up the opening ramp and reduce the overlap.
Secondly, open the Lobe centers from 105 to 108 intake and 110 exhaust. This will improve both the excessive overlap and increase the Lobe Separation Angle to better match Alfa`s intake runner length.
It also advances the cams "centerline" improving mid range output. This could be done before taking the effort to change lash just to see the difference in output with only this change
The only way to really make improvements economically is to use a true exhaust design cam to correct valve timing events to make more torque and power.
His application requires a broad torque curve not peakey hp. These cams are not going to provide what he needs.
In a message dated 7/7/2014 1:35:43 A.M. Central Daylight Time, john.xxxxxxxxxxxxxxxxxx writes:
Thanks for that Richard!!
We´ve still the same problem, we can not go on the Ex cam to 110 LC because the valve touching piston, the pistons are Motronics but the valve pockets havent been worked (deepened) so they are still standard height, we have try lash of .50mm on the EX side and still touching so we are forced to go back to the C&B AR.120.292S on the Ex side (less lift).
So, having to use this combo, In Catcam & Ex C&B, should we start from the same set up? IN 108LC & EX 110LC??
John, you are doing it incorrectly if you are having P to V issues at 110 LCs.
On the intake side LC marks are Before Top Dead Center "BTDC" . The larger that LC (110 opposed to 102) the more RETARDED is the camshaft. (Cam is rolled counter clockwise to increase LCs(as viewed from in front of the engine). Valve clearance relative to the piston is increased.
On the exhaust side LC marks are After Bottom Dead Center (ABDC) the marks will increase on the exhaust side of the cap. (Not the intake side of the cap as on the intake)
Increasing the LC to 110 ADVANCES the cam (clockwise) so that the valve closes earlier and increases P to V clearance.
As to using another old high overlap on the exhaust side you wont get much performance benefit, but set the LC at 110 initially but close both based on info below.
Below is the short version of some of my setup info:
Initial timing and valve piston check:
This is very important as when cams advance the piston clearance reduces dramatically.
Set Intake and exhaust cams at initial LCs as indicated by provider set up instructions, and lash
By running the .050 plastic wire-tie between the Intake valve & piston, and .100 (or .080 ) on
the Exhaust side you can check if there is any interference and see that you have adequate
clearance between piston & valve. If by turning motor over by hand you feel some interferance
using a .050 thick wire-tie, (or .080 on Exhaust) but the motor continues to roll through, you are
at the limit! YOU MUST ROLL THE MOTOR OVER OVER BOTH FORWARDS &
BACKWARDS TO BE SURE THERE IS CLEARANCE AT THE LIMITS!! WHEN OFF
THROTTLE CHAIN TENSION REVERSES!!
If it locks up, retard the cam(intake side, (however you would advance the exhaust cam a degree or more to
get more clearance) a degree (or a couple of degrees) and try again until the clearance is found.
I suggest as a test to find this limit, you advance the intake cam until you do, and permanently
mark that point on the cam cap. That will be the point where the cam must NOT be advanced
Then do the same with the exhaust only retarding it until the limit is found.
Timing initially is dependant on design of cam lobe, & internal (pistons) components. Aggressive large duration cams will be more retarded.(intake) and advanced (exhaust) because of ramp & valve lift.
Tighten and instal lock nut on intake and bolt through sprocket and cam nut. Inspect carefully.
Roll the crankover by hand to verify timing.
When the intake cam is at the limit, or LC setting whichever is less advanced. You are there! That`s as good as it can get with your combination of components.