Car sales in August (4,873) were up 32% on August last year.
So far this year, 89,279 new cars have been sold, an increase of 30% on 2013.
The increase in registrations in July and August alone generated an additional €68m for the Exchequer, which brings the total for the year from new car sales to €720m.
In addition, SIMI says 4,200 new jobs have been created this year as a result of the success of the dual registration plate and the overall increase in business.
Alan Nolan, Director General of SIMI, said: "The dual registration plate has really helped in spreading the sales through the year, which was the intention.
"But the real driver in increasing the registrations has been the level of growth in consumer demand, which has not been seen in the industry for some time.
"The continued strength of commercial vehicle sales underline the improvement in commercial activity in the economy this year."
Although down by 32% (63 units) in August, new heavy commercial vehicles remain ahead of last year by 30% (365 units).
New light commercial vehicles are up 54% (441 units) for August and 47% (4,196) for the year to date.
Nolan continued: "Vehicle sales have a direct impact on employment in the sector and it is great to see the number of people working in the industry beginning to rise again.
"By the end of this year, we predict new car registrations will exceed 95,000. While this is very positive, we are still in the very early stages of recovery, having moved from 45% of normal sales volumes last year to about 60% this year.
"Next year, new car sales have the potential to generate a further €100m for the economy, on top of this year's growth, and create 1,500 more jobs.
"However, it is crucial that this growth is not stalled by any negative decisions made in this year's Budget."
