What is the orifice diameter, 964 vs 993? Maybe the ticket is to buy the 964 sized restrictors and drill the hole to the larger 993 size?

I must admit after reading the various conflicting points of view, I wonder if the best answer is to drill a set of restrictors to be halfway between the two orifice sizes....

Dennis

that's what I did....

....did you just drill a diameter half way in between or did you drill so that the cross sectional area is halfway between (...you know, the pie are squared kind of thing)?

Dennis

diameter in between, I used a 4.5 mm bit.

Regarding the orifice size difference between 993 and 964 oil bridge pieces, also keep in mind that the 993 cam housing has different oiling requirements. The 993 housing was changed to accommodate the use of hydraulic valve adjusters.

Specifically the rockers are pressure-fed to both the hyd. valve lash adjuster and the rocker shaft. Also, the intake lash adjuster has an additional reservoir cast into the rocker to avoid starvation. That means intake and exhaust rockers are different & should not be interchanged. So, the 993 cam housing has additional oil passages in it to feed pressurized oil to the rocker arms. I suspect that's probably why they revised the orifice in the 964 bridge piece?

Kevin, I am not familiar with the 993 engine, but yeah, additional flow through larger (as compared to 964) orifice simply because there are additional oiling requirements. So I am back to the standard sized oil constrictors.

So should I do the oil restriction mod to the 3.2 engine I am rebuilding for my race car? it's legal, just don't know if it's a good idea!

Gary,

As you can tell from this thread, it doesn't make much difference. I tried them and took them out because my oil pressure was higher than I like when the engine was cold/cool. I've had several engine oil coolers leak and I hope the lower pressure will make the one I have now last longer.

Try them, you can always take it back out if you don't like the oil pressure you get. Another reason to use them is you might have better scavenging so are less likely to oil starve under braking.

-Andy

Yep, decided against it for my race motor, thanks Andy