Predator Rocker Arms

I totally forgot you had both of these engines Gordy. There is absolutely no rush at all in doing this for me. I won't do anything with this information till summer. Wait till it warms up and you have some free time. I know how busy you are. I was just thinking this would be a $17 performance upgrade if it works.
 
That was the same video I watched. At the 3:53 minute mark , I feel he has them backwards, and to me they don't look the same. The adjusting nut would have to be the same for both engines also. If you measure the distance from the stud to the pushrod, with clearance on the valve, that should tell us. Check the distance from the stud to the valve stem also.

The other strange point is..........why did this guy use two different ratios? From looking at the head the piston to valve clearance is the same for both valves.
 
michael whiteman said:
That was the same video I watched. At the 3:53 minute mark , I feel he has them backwards, and to me they don't look the same. The adjusting nut would have to be the same for both engines also. If you measure the distance from the stud to the pushrod with, clearance on the valve, that should tell us. Check the distance from the stud to the valve stem also.

The other strange point is..........why did this guy use two different ratios? From looking at the head the piston to valve clearance is the same for both valves.
Click to expand...
With intake, if you want performance it needs to breathe in easier with enough swirl, however exhaust side you need scavenging, so timing is super important.

My guess is the exhaust with 1.3R allows the valve to open too much for efficient scavenging, and possibly becomes a waste of energy because exhaust is pressurized, intake is not (unless boosted) no reason to open the valve that much.
 
Wyvern said:
With intake, if you want performance it needs to breathe in easier with enough swirl, however exhaust side you need scavenging, so timing is super important.

My guess is the exhaust with 1.3R allows the valve to open too much for efficient scavenging, and possibly becomes a waste of energy because exhaust is pressurized, intake is not (unless boosted) no reason to open the valve that much.
Click to expand...
That's a good guess. I have never seen (nor did we ever build) a high performance engine that did not use the same ratio on the intake and exhaust valves. These changes are made with a custom ground cam having specific duration and overlap profiles. Higher ratio rockers simply open the valves farther. Why would you not want to scavange the exhaust out of the cylinder a quickly as possible?
 
michael whiteman said:
That's a good guess. I have never seen (nor did we ever build) a high performance engine that did not use the same ratio on the intake and exhaust valves. These changes are made with a custom ground cam having specific duration and overlap profiles. Higher ratio rockers simply open the valves farther. Why would you not want to scavange the exhaust out of the cylinder a quickly as possible?
Click to expand...
It's actually pretty common in the hot-rodding community.

Same reason you don't want a wide open exhaust on a N/A engine, scavenging also works on exhaust back pressure waves and timing them with the valves is tricky business.
 

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