A man has admitted his involvement in the theft and sale of $2 million of V8 engines and other parts from Holden's Adelaide plant.

Former courier driver Richard Andres Jorquera, 27, was among seven people arrested in July last year.

Police alleged 140 V8 engines and 175 high-powered transmissions disappeared from the Elizabeth plant over two years.

In the District Court, Jorquera pleaded guilty to two counts of theft.

The court was told he was paid $30,000 over about 18 months to use his courier van, taking 60 engines and 78 transmissions - two or three parts at a time - for sale by another person for more than $5,000 per item.

It heard the thefts were not detected despite regular inspections and the scheme had been operating for some time before Jorquera got involved.

The prosecutor said Jorquera had breached the trust of his employer and of Holden and should be jailed.

Jorquera is to be sentenced later in the month.