This has the exhaust exiting further back and towards the centre of the car than Webber's newer design, with each one trying to harness the exhaust gases for a different aerodynamic benefit.
The team had always insisted that the newer one was a step forward, even though observers said it made the car look more difficult to drive, and the evidence of China suggests their data was right.
But Vettel said: "It doesn't feel right now to sit here and blame the car and the packaging.
"I was happy with the lap, it was not the best of my life, but it was pretty good. Overall, it is a long lap and we are not missing an awful lot.
Webber's guide to Shanghai track
"If you look at Mercedes pace in qualifying, especially [pole winner] Nico [Rosberg] in qualifying that was very strong. We could never have done that, but even if we are speaking 0.2-0.3 secs in Q2 it was exceptionally close."
He added: "Doing the same lap time three times in qualifying showed this was more or less it.
"It was not as if there was a 10th or a couple on the table. I don't think we missed out, it was just not quick enough at the time."
Webber's lap in final qualifying was actually slower than Vettel's best, but conditions had changed and the Australian said he had not been happy with his performance.
"The lap didn't come together, wasn't good enough," he said. "Shot our bolts. That's it."
Asked to explain the decision to run two different specifications of car, Webber said: "Seb was pretty keen to give it another crack. He had a pretty good winter with it.
"There was a collective decision from the team to gather more data with both situations particularly, giving us a bit of confidence I suppose for fresh tyre running.
DID YOU KNOW?
In finishing 11th in Malaysia, it was the first time in 27 races Sebastian Vettel had seen the chequered flag without picking up a point
"The car is pretty solid on used tyres in a grand prix, which we saw in Albert Park and in the limited running we had in Malaysia on slicks at the end of the race.
"So there was a collective decision made to bring it here on the Friday and see how that unfolded. They committed to running it for the rest of the weekend and investigations continue to go on.
"There are so many parameters go in, even more than previous years, to getting the best out of these cars. We're learning how we get the most out of the RB8.
"In previous seasons if you were missing 0.2-0.3 secs it maybe wasn't a big deal, but in 2012 it is. And it's a tight field because there are lots of competitive cars."
Chinese Grand Prix 2012, day two
Saturday 14 April: Qualifying replay 1300-1430 BBC Two and Red Button.
Chinese Grand Prix 2012, day three
Sunday 15 April: Race 0700-1030 BBC One, BBC Radio 5 live and live text commentary on BBC Sport website; Race replay 1400-1600 BBC1.
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