I have 2 gallons on mine. Definitly a decent motor. JP1 pipe. Good stable/progresive power from bottom and it screams on top even with the JP1. My racing partners run Nova P5x and a REX. Very comparable. I know it is a Picco base, but looking at the porting, its not the exact same as the P7r. For the money also consider the STS MKII. Its new and it has very impressive bottom and top with a JP1. My friend has it in his Mugen and I can't pull him at any section with the Jammin motor. Nor can the Nova's pull on me with the exception of sub 7000rpm, but that is only on a super high traction clay track. Outside when traction is not insanly good they are equal, as all these motors today make so much power they easily overpower the tires grip anyway. I recomend the Jammin and the STS .21 MKII equally. MKII is 30-40 bucks less too. STS also provides super support for their porducts. They sent me 2 rebuilt motors when my engine case failed at the mounting points on both my .21b and .21t motors. STS is first rate in customer support. You can get the STS mills here:
http://www.stsmicroengines.com/ or check for RC/mall on ebay for even lower prices. They are less but shipping is 2 weeks as they come from Taiwan.
I also run an STS .21T and an RB WS7II.