Well, I have been working on an RC car project that requires me to send and receive data simultaneously. As I read from other topics, you can do this with one module but you can't do it simultaneously(it has delays between transmitting and receiving.). But I need the data to be constantly sent 
. I have been ripping my hair off for weeks to find out how. So I decided to create this topic for me and other people that need to do this. ;D
What are you sending data to? What data?
What are you receiving data from? What data?
You don't need more than one nRF24 module on your Mega.
If you need more than (say) 5 messages per second then there is something serious wrong with the design of your system.
Have a look at the second example in this Simple nRF24L01+ Tutorial. It will do a round-trip message and reply in a few millisecs so you could probably do 50 per second. But I don't see any need for that for controlling a single car.
...R
An acknowledged message is unlikely to hold up your Mcu for more than 5ms.
If you really need simultaneous transmitting and receiving, the Rf24Network library supports dual head mode, where 1 radio is Tx and the other is Rx. Both radios share MO, MI and SCK pins but have unique CE and CS pins.
Hi,
What you are looking for is FULL-DUPLEX operartion, this can be extremely difficult to do as the uplink and downlink need to be operating on widely different frequencies.
We need to know the reason for such high spec linking.
What is your application?
Thanks.. Tom.. 
TomGeorge:
We need to know the reason for such high spec linking.
Agreed. The standard nRF24 transmit/acknowledge process is so fast that it will appear like full duplex.
...R
yigit:
RC car project that requires me to send and receive data simultaneously.
If this really were true, using the AckPayload feature of the NRF24L01+ would be the best solution. IMHO