580 rotary valves

[george]

I'm trying to make sense of the specs,
1990 sp 132 deg
1991 xp 132 deg
1991 sp 147 degree

I'm putting a 90 sp intake (single carb) on what I think is a 91 xp
short block. What valve should I use? (I need to buy a new one in any case.)

By the way are the single/twin carb rotary valve covers the same?
(The manifold is a seperate piece on these motors if anybody thinks that a silly question)

[Bill O'Neal1]

Re: 580 rotary valves

No, the intake manifolds and RV covers are different. There is one set for single carb setups, and a different set for twin carb setups.

132 degrees would be the closest, as I think the early 580 rotary valve is set to 115 degrees, but I'd have to check my manual to be sure.

I think I have some single and dual RV covers, and maybe even an intake manifold at my shop if you are interested in buying used parts. 626 914 9509 after 9am PST.

[Technical Support]

Re: 580 rotary valves

91 SP is not 147. See our rotary valve timing article for all the correct numbers.

[Bill O'Neal2]

Re: 580 rotary valves

Let me make this as simple as possible to time a rotary valve.

No matter which valve your motor came with orginally, if you have that orginal valve the closing timing wiil be set correctly at 65 degrees plus or minus 5 degrees. All Rotary valves get set at 65 degrees closing timing. The other end will be correct no matter what motor you are working on if you have the correct valve for the motor.

Align the 360 degree mark on the degree wheel with the top of the front intake port when the front (mag side) piston is at top dead center. Reading the degree wheel, you will see the 65 degree mark below the front port. Align the rotary valve with the 65 degree mark.

Note. The rotary valve is asymetrical. Flipping it over may make the RV come closer to the 65 degree mark.

[Mark914]

Re: 580 rotary valves

I am doing the same thing with a 91 xp. I am using the intake and rotary cover from an sp. I ordered the stock 132 degree valve for an sp and setting opening timing at 115 per the tech article. My xp had a 147 degree valve in it when I bought it, but apparently was changed by a previous owner.

[george]

Re: 580 rotary valves

TS your "how to time" article gives the timing angle but not the
valve opening. Am i looking in the wrong place? Can you infer the valve opening from the timing setting?
Anyway I got those numbers off some other web site and I thought they looked odd thats why I asked...

[Technical Support]

Re: 580 rotary valves

115 times are a 132 valve. 129 and 130 times are a 147 valve. 147 times are a 159 valve.