oil restrictor to Heads

[Brian Coombs]

does anyone fit oil restrictors in their engines to reduce the flow up to the rockers?

I have heard of people doing this to keep more pressure for the crank and cam?

if so please can someone tell me what size of restrictor they are using and where they have fitted it?

thanks,

Brian coombs

 

[Dave Wood]

If you are referring to FE engines, I always put restrictors in. I take a little different approach, but 20+ years of doing it haven't created any problems. Instead of restricting oil between the block and head I do it at the feed hole to the rocker shaft. I fit a hex piece (like an oil pump drive) rod that is just the size of the hole. I round off both ends and make sure that it doesn't interfere with the rocker stand, and then set it in. The reasons are many that I do it that way. If the restrictor should get plugged,it is easy to remove and clean, but that hasn't ever occured. I also believe that the hex allows more area for oil to flow than does a small restrictor hole and is less easily plugged with any small material that may find it's way in to the oil system. Although I used the oil pump drive reference to illustrate the shape, I never use a hardened metal, and the fit within the hole is important to keep it from moving around under pressure and creating metal fragments. Others put a small orifice in the block feed hole to the heads. I would suggest that either one is O.K. however, I use my method because it has served me well. When you build engines for others, it sometimes takes unique solutions to old problems that make them long lasting and trouble free.

 

[speed220mph]

Brian: Be careful when installing such restrictors. First, they are typically installed in the lifter oil galleys. Such restrictors are not to ensure the crank and rods get oil, but to reduce the amount of oil dropping on the crank and rods from the top end, which causes aeriation and hp loss from the oil being whipped up into a milkshake. Further, the practice of doing this, even on all-out race engines, is not being done as much starting with early 2007. For sure, never restrict oil-galley passages when using a flat tappet cam. A lot of oil is needed to keep the followers alive. The latest flat tappets are drilled at the foot to provide direct oiling to the lifter/lobe interface. This practice was first used with billet cams in NASCAR Cup engines. As for roller followers, many are being drilled similarly to lube the roller bearings. This also requires full oil pressure to the lifters. So first check with your cam manufacture to make sure. As woodz428 says, he does it at the rocker shaft. But this is for an FE engine. If yours is a small-block, you'll do it at the two lifter oil galleys. Again, check first.

 

[Jac Mac]

Brian,
Since you have a SBF use stand pipes in the 4 center valley drains and screens over the two rear drains & single large hole by the dist gear. DONT restrict the lifter galleries and either buy lifters with face / pin oilers or cut oiler grooves in each lifter bore as per Comp Cams article.
Use stand pipes at each end of cyl heads to raise running oil level in heads up to bottom of PC type stem seals ( drill small 0.060" hole at base of these stand pipes to allow drain back at shutdown ).
The stand pipes in valley force oil to drainback at rear & via timimg chain cavity to reduce windage.

Jac Mac

 

[BruceA]

Jac. Can you explain a bit more what you mean by 'stand pipes'? Are these actually tubes placed in the valley drainback holes? If so where do they extend to? Back through the crank to the oil or something else?

 

[speed220mph]

Stand pipes prevent oil from draining from the top end directly onto the crank. They are available from Stefs. Again, check with your cam supplier to see if restrictors are needed.

When prepping Boss 302s for TransAm racing we installed external drain-backs to the sump with AN hoses plumbed from the ends of each head. Doing this is a bit much for your application, but it sure kept the crank dry for our situation. Wet sumps were required by SCCA.

 

[speed220mph]

I forgot to add the picture. Notice the vents/standpipes in the lifter valley and screens in the corners for oil drain-back on this block prepared for Busch racing. The photo is from page 144 in "The Racing Engine Builder's Handbook".

 

[Rick]

Why the hex plug in the rear corner?

 

[Jac Mac]

Busch cup car -only turns left, therefore preferred drain is to RR corner, road race application would probably use both rear drains.

Jac Mac

 

[speed220mph]

Jac Mac: Correct. I neglected to mention that little detail. As for Busch cars only turning left, they do run a few road courses, so different engines are usually used. Another detail of interest to note are the Jesel Dogbone roller-lifter guide-plate studs and spacers between the lifter bores.

 

[BruceA]

I assume the standpipes are hollow? Is this to aid crankcase breathing?

 

[speed220mph]

They are hollow, otherwise we would've just plugged the drain holes.