Cylinder Head Oil restrictor

[rjaxe]

I am in need of some guidance, I have read somewhere that an orifice is or can be fitted in the cylinder head oil supply to restrict this flow and bias it more to the crank.
I cannot find any reference to it in the manual or the parts catalogue so am a bit in the dark on the issue.
Can anyone confirm if this is a standard fitment or a desirable mod that should be incorporated.
If it should be fitted where does it go and where can one be obtained?
Your help will be appreciated

[ringe]

Richard,

it's not a standard part AFAIK.

Dave Bean's catalog lists two diameters
0.090 in (racing only)
0.120 in

The oil restrictor is also mentioned in this article:

http://www.lotuselan.net/publish/twink_rebuild_1.shtml

Matthias

[types26/36]

Fitting an oil restrictor is not a standard fitment but can to be done on the preX flow ,X flow and twin cam, it involves fitting a restrictor (usually brass with a 90 thou hole )in the block where the oil is fed up to the head. It prevents the head being flooded with oil with prolonged use of high rpm.
Here is a pic of one I fitted in my Seven TC, its easy enough to make up if you have access to a lathe.

[CBUEB1771]

it's not a standard part AFAIK.

Cosworth did it as a standard fitment for the BD series of engines.

[rjaxe]

Many thanks for all your help, I will need to remove the cylinder head on my Plus 2 in the near future this will give me an opportunity to fit an orifice.

[rgh0]

With a normal oil pump and within spec cam bearing clearances you do not need a restrictor and it would potentially give you a problem with inadequate oil flow to the cam bearings and cams

In a race engine with a high pressure / high flow pump and potentially loose cam bearing clearances and maybe inadequate sump baffling so its vulnerable to any lowering of oil level. You can end up with all you oil in the head and none reaching the oil pick up in corners. So people put a restrictor in either the head or block.

Easier to put the restrictor in head unless the block is totally stripped.

But it is really hiding other problems if you need one I believe. None of my race engines have ever needed a restrictor but then I build my engines to spec bearing clearances and dont put in used cam bearings despite the cost of new ones which are not cheap.

Cosworth put them on their BD series I suspect because the cams run direct in the aluminium carriers and hard to control cam bearing clearances overtime compared to replacing with new bearing shells.

regards
Rohan

[rjaxe]

It is a good point you raised about the cam bearings, I don't know their condition but can check when I strip the head.

[types26/36]

Although my Seven is fitted with a modified oil pump I have fitted restrictors to standard T.C. and Xflow engines without having a problem.
I dont think Dave Bean was refering to racing engines when he recommended fitting a restrictor quote:

"Bean also recommends an additional modification to improve the performance of the oiling system. A restrictive plug with a 0.090-inch-diameter hole can be installed in the block to reduce the flow of oil to the head. In a Twin Cam, the valve train receives a disproportionate flow of oil when the engine runs at high revs, causing a build-up of oil in the head. Reducing the oil flow to the head allows more oil to be retained in the sump, and also provides additional flow to the crank and rods."

[bill308]

So maybe a 0.100-0.120 restrictor delivers meaningful benefits without without concern for the top end? Oil flow to the head should be roughly proportional to the flow restrictor diameter, squared.

Bill