987 2.7 vs 986 2.5 review

[pothole]

Originally Posted by runjmc2

My understanding is the 2.7 is not a bored 2.5, rather it has a longer stroke (3.07in vs. 2.83in). All things being equal the shorter stroke 2.5 would have a lower piston speed (FPS) and allow for a higher red line than the 2.7.

Are all things "not equal" in this comparison, e.g. the design/materials on the crank/etc of the 2.7 better and allow great piston speed than the 2.5.....or is the 2.7 just rated at a higher redline "less conservatively" than the 2.5? Sure this has been covered, just have not come across it.

Question being does the 2.7 really have greater RPM capability over the 2.5 or is it a spec illusion?

Good questions. Yes, the 2.5 is shorter stroke. But it's a fact that the 2.7 has a higher rev limiter and produces peak power higher. You could, of course, fairly easily tweak the 2.7 with a lower rev limiter and to produce peak power lower down.

God knows if the 2.7 has a better crank, I doubt there are dramatic engineering differences. The difference in peak revs isn't huge anyway.

Neither engine is terribly stressed, if you ask me.

[southernstar]

Pothole, you are suggesting (without any evidence) that Porsche changed the gearing on the 2.7 to improve fuel economy at the expense of performance. My point about the 981 was that, yes I agree that Porsche has made some changes in the Boxster for the purpose of improved fuel economy - e.g., electric steering and start/stop technology in its most recent model, and they have acknowledged that this was the principle reason for those changes. But I thought we were talking about changes made to the 986 Boxster series, where they made no such claim about the changed gearing that came with the introduction of the 2.7.

What is interesting about the gear ratios on the 2.5 as opposed to the 2.7 is that, while the ratios for the the first three gears are identical, the ratios for fourth and fifth gear are actually closer in the 2.7 than the 2.5. I assume you will agree that for the purpose of performance driving, a close-ratio gearbox is generally considered better (after a shift, it enables one to keep the engine RPM's in the sweet spot in the middle of the power band). Put in practice, a shift into fourth from third, or fifth from fourth in the 2.7 will drop the rpm's less than in the 2.5.

It is obvious that we will never agree on this point and that's fine. You say that Porsche changed the gearing solely for the purpose of improving fuel economy. You say that in spite of the fact that Porsche never made such claims and indeed, you offer no fuel consumption figures to prove that there was any such improvement. I say that Porsche introduced that 2.7 and 3.2 in order to improve performance and thereby address the biggest criticism of the 2.5 - that it was lacking in power, torque and flexibility. I am saying that Porsche altered the gearing in order to match and optimize it with the improved peak torque and horsepower as well as the flatter torque and horsepower curves that came with the increased displacement and improved fuel injection in the new engine.

While it is unclear whether Porsche improved fuel efficiency with the 2.7 (and I suspect they did not), it is clear from Porsche's own figures and from comtemporary tests that it did improve performance over the 2.5.

Cheers!

Brad

[paintboy]

Experts like Pete Townshend, Tim Curry and Paul Williams all agree that the 2.5 is the engine to own. Many 911's have had their new motors replaced with 2.5s that have upwards of 100k miles on the clock. A spokesman for NASA, B. J. Smegma, stated that if the 2.5 was available in the 1960s, it would have powered the Apollo rockets into space, instead of those silly American made Saturn 5 things. And had 2.5 been available to the German war machine in WWII, who knows how things would have turned out....a Tiger tank doing 0-60 in six seconds would have been unstoppable.....

[southernstar]

Thanks Paintboy - you have brought us back to earth! While much less interesting and fun than contemplating the world order if the Germans had the 2.5 in WWII, I just checked the EPA site re: the fuel economy numbers for the 1999 2.5 versus the 2000 2.7:

1999 Boxster 2.5 manual: 17 MPG city, 24 MPG HIghway, 20 MPG combined
2000 Boxster 2.7 manual: 17 MPG city, 25 MPG Highway, 20 MPG combined

Wow, if Porsche changed the gearing on the 2.7 for the purpose of improved fuel economy, they failed dismally! The combined number is identical and the 1 MPG improvement on the highway cycle could probably be explained by anything from varainces in individual cars to the improved fuel injectioin system. Even worse, while trying to improve fuel economy at the expense of performance, they actually by their own admission in the brochures (and as confirmed by contemporary tests) IMPROVED performance. Porsche got it all wrong!

Brad

[recycledsixtie]

I have not read all the responses in this forum but I understand that the 2.7 Boxster base(2001) does 0-60mph(0-100kph) in 6.5 seconds. So what is reported time for the 2.5 litre engine?

[southernstar]

Porsche 0-60 Times & Porsche Quarter Mile Times | Porsche 911 Carrera 0-60, 944 Turbo, GT2, Boxster S, Cayman R, GT3 and Porsche Cayenne 0 to 60 stats!

The above site posts 0-60 and 1/4 mile times for various cars, apparently based upon averages from contemporary magazine tests. They show the following:

1999 Boxster 2.5: 0-60 6.3 seconds, 1/4 mile 14.8 seconds
2000 Boxster 2.7: 0-60 6.0 seconds, 1/4 mile 14.5 seconds

http://www.howstuffworks.com/porsche-boxster-history4.htm

The following is a quote from the above web page in connection with 0-60 times:

"Porsche pegged the 2000 base Boxster at 6.4 seconds in the benchmark 0-60 dash, a modest .3 seconds up on the 2.5 litre original. The real-world time was probably more like 5.9...."

The actual times vary, although it would seem clear that the difference in 0-60 times is at least .3 seconds as between the 2000 2.7 and the 1999 2.5. I don't have my brochures here with me (and I don't have one for a 2001 Base which was a bit heavier than the 2000 due to the lined top and cupholders), but the 6.5 second figure you refer to may reflect 0-100 kph (which is actually a little over 62 MPH), or it may have increased slightly due to the additional weight.


Brad