Thread: High volume oil pump

Why we need more oil in the top end when we put a big bore kit?

One of the main purposes of oil is heat transfer for cooling purposes and the bigger bore will create more heat. Thus the more oil you flow, the better cooling on the top end you will get and the engine will last a lot longer. If you are going to a big bore, don't try to save a few pennies and skip the larger oil pump. You will regret it.

The reasons are twofold.

Improved cooling becomes an issue when hotrodding a 72cc engine that began life as a 50cc unit. An engine must burn more fuel to make more power and more fuel burned equals more heat generated. Since we're talking about an air cooled design, cooling capacity (finned area, oiling system) remains unchanged resulting in higher engine temps. Once you have enough power to reach 50mph (roughly 300% of a stock 50cc motor), an oil cooler is needed also. Typically, a basic 85cc bore-up will take a 3-speed CT70 to about 45mph with no other changes. The added displacement will produce more torque, but not a lot more hp without cam, carb and head changes. Motor oil is only good to about 240F; beyond that point it breaks down and your motor becomes an expensive paperweight in short order . You might be surprised to learn how hot a stocker runs just cruising along at moderate road speeds. Oil temps in the 220-230F range aren't unusual.

The second issue is rpm. Operational loads increase geometrically with increased rpm. Running an engine designed for 8000rpm as high 10,000rpm or more (very easy to do, with these little motors) requires a lot more oil flow to maintain adequate lubrication.

Now then, just in case you're scratching your head & pondering the sanity of building-up an engine , you can rest assurred that these little motors hold up amazingly well, even when tuned for 60mph+ power levels. Start with the larger oil pump & a dipstick oil thermometer, they're cheap insurance and all you're likely to need with just an 85cc bore-up (no cam or head changes). If the oil temp runs consistently above 220F, then add an oil cooler; it'll cost about the same as the other 2 items, but is still a helluva lot less costly than an engine rebuild...and about all that's needed to allow a highly-tuned motor to live a long time. Keeping engine temperatures under control can also result in slightly more power output. Transmissions shift better when not overheated, as well. It just doesn't pay to "penny-wise & pound foolish".

I am convinced. Going to order a high volume pump right now

Dave

any one know if the finned cam sprocket cover and valve covers help much lowering oil temps ?

They look nice but probably don't do much. The only way to significantly increase cooling is with an external oil cooler. Mounted in a location that sees good ariflow, these can lower oil temperatures by 20-40 degrees, maybe more depending on the specifics.