986 2.5 underdrive pulley dyno graph
 

i have just installed the RSS underdrive pulley and had gotten it dyno tested today. The car is a 97 boxster 2.5L. I think some people will be interested in the results. it started at 199hp for the first run. they had pulled it 5 times and every time i had gotten about 1-2hp more. i called it after the fith pull because it was starting to get hot. the final result was 206.5. When it was stock i had dyno tested at 200.9-201.1hp.

[IMG]IMG]http://i899.photobucket.com/albums/ac197/transtlye/1271541660420.jpg[/IMG][/IMG]
http://i899.photobucket.com/albums/a...1541645936.jpg

nice results. I have my pulley sitting in a box for my 3.2, waiting for a nice day to install it.

RSS also makes a harmonically dampened underdrive pulley, designed for the M97 3.8 motors, that fits just fine on any of the rest, provided you use the longer bolt.

Seems like a pretty good idea to me to get some damping onto the crank in these things.

"RSS also makes a harmonically dampened underdrive pulley, designed for the M97 3.8 motors, that fits just fine on any of the rest, provided you use the longer bolt. Seems like a pretty good idea to me to get some damping onto the crank in these things."

would this help those of us with lightweight flywheels to dampen some of the harmonics normally handled by the DMF?

Ed

:)

Yes. Hence why it's on my motor :)

Cloudsurfer, what are your driving impressions with the harmonic RSS unit?

Not sure yet, I'll let ya know once I get the car running again!

Ed,

What clutch did you use with the LW flywheel? I opted for the Sachs 6 spring clutch to (hopefully) mitigate possible harmonic issues.

kj

Not bad - Note that Dyno Dynamics dynos tend to read 10 - 15% lower than Dynojet dynos, which most aftermarket manufacturers use to make their dyno claims.
Dyno Dynamics are excellent for real-world tuning.

SPEC Stage 2 (sprung center) with Aasco flywheel.

Continually we see exactly 12-15% variations between either of my engine dynos with the same engine installed into the vehicle and evaluated on our dyno-jet chassis dyno. This is the same differentials with either air-cooled or water cooled Porsches.

I am less concerned with actual peak numbers than most any person you'll meet. Our dynos were bought to be developmental tools so repeatability trumps any peak number.. Last week I did 5 runs back to back on the dyno jet and attained less than .75 HP of differential across the entire average RPM range. That repeatability is whats necessary to do the level of developmental comparison that I am interested in.

a question for Jake regarding harmonic issues.
 

Jake,

I was very interested on installing the LWFW along with the Sachs spring clutch disc but got cold feet after reading one of your posts where you mentioned that the dual mass flywheel cancels the harmonic issues and that there were several engines that failed because the dual mass FW was replaced with a LWFW.

Do you think that would be safe to install a LWFW (AND) an underdrive crank pulley with a harmonic balancer?

I saw an ad from a company called ATI Racing and they told me that it was possible to manufacture an underdrive pulley with a harmonic balancer.

However, I was not aware of the RSS UDP until this post, but the ones from ATI seem beefier.

Somewhere I read that some of the older Porsche engines had a harmonic balancer build into the crank pulley as well, but I am not sure if these would fit or if they would do the job once done by the dual mass flywheel.

What do you think?

Regards,
Gilles

PS, this is the link to ATI:

http://www.atiracing.com/products/dampers/damper_tech.htm

.

ATI makes great stuff, unfortunately they do not have any applications that would benefit us, hence why I went with the RSS unit.

I have been developing a harmonically dampened UDP for over two years now.. As soon as I saw the other companies making similar companies I halted the development because theirs is cheaper and few people buy "better" these days.

aint that the sad truth

So, overall for the 986... What would be the pros/cons now, choosing between the RSS pulley with the harmonic balancer versus the 4" Pulley from Raby/Amond?

Would the extra weight of the dampened unit be a disadvantage, or is it mostly the size/diameter of the pulley that is more of a factor in its effectiveness?

Jake,
Do you think that would be OK to install a LWFW (with a Sachs spring disc) as long as a harmonically dampened UDP is used as well?

I'll certainly take the damping effect over saving a tiny bit of weight.

I'm also really interested to get some quality feedback on clutch/flywheel upgrade ideas and what is good vs what is asking for some kind of problem..I too have read those threads on people putting in LWFW and then having some kind of motor failure.... My car is approaching 80k and I can feel some vibration when I engage the clutch...the grab is still okay, but not as good as it used to be, so I know a clutch is in my future.. not sure if the flywheel has to be redone, replaced, or what when my clutch is replaced.

putting in a LWFW *and* an underdrive pulley would be anice way to make my 2.7 more peppy....but I don't want to do something that makes the car likely to have any major failures....

what is the consensu on these parts...particularly teh LWFW?

I'm not trying to be critical or anything, but a max 5.5 HP gain (less than 3%) does not seem worth the effort/cost. Do you feel there is a noticable difference in the seat of the pants? I was thinking about a Raby UDP but am hesitant based on these results. Any encouragment to offer??