11-10-2013, 08:48 AM #1
Changing Blowers and the Expected Boost
I have seen actual data lately and want to share some of the data I have found about the blowers that are common and the resulting boost.
A little background. The boost that these motors make at WOT is very dependent on RPM. All of this data data assumes you have beat the stock speed limiters. HP is estimated using the formula MAP x RPM / 5100 to estimate HP
A stock blower on a 2013 RXPX at 8300 RPM will make 178 KPA or 11.3 lbs of boost for about 290 HP. Take that same motor to 8600 rpm, the intake will be at 186 KPA or 12.5 lbs of boost for about 317 HP. These skis typically run in the lower 70s when held to the 290 HP range.
A large blower like a Rude3 or an ET137 +4 will normally be installed with a 4" air intake with the screen in the intake removed. Note that most installs I see data from, have an aftermarket intercooler. The motors are getting at the same 8300 RPM, 192 KPA or 13.3 lbs boost producing about 313 HP. That is about a 27 hp increase or about +8% as you pull thru the acceleration part of the power band compared to the stock blower at the same RPM. Spin this same motor up to 8600 rpm and the blower will produce 198 KPA or 14.4 lbs of boost and be producing about 333 hp. These skis typically run in the high 70s when in this 333 HP range. Spool these motors up into the 9000 rpm range and you get in the low 80s
I am finding that when you get to these high levels of RPM and pressure for power with the large blowers, you need to be comfortable removing the head to have a look at the pistons fairly often. If you do not want to be in that situation, big blowers and high RPM may not be for you. Personally, I elected to stay with a 8300 RPM limit with a stock blower on my rec ski.
Have fun tuning
Last edited by whittlebeast; 11-10-2013 at 11:09 AM.
11-10-2013, 09:19 AM #2
andy 13+hp per lb boost is on the high side
I bet its closer to 11-12
the motor only with 8.5 pistons IMO is only 140+hp @ 8100
11 psi X 11hp/psi = 121 + 140 =261
7.5psi X 11hp/psi = 75 + 140 = 215
Last edited by skidoochris; 11-10-2013 at 09:37 AM.
11-10-2013, 10:19 AM #3
My point is expect overall reliability to go down at these power levels. Valves, pistons, rod bearings, valve springs, head gaskets, broken retainers, cam gear bolts, flywheel bolts......
Regarding HP, it is just a guess on the 5100 number. Pick whatever number you like. If the MAP x RPM goes up 30%, you better be able to increase fuel delivered thru the injectors about 30% I picked 5100 assuming the stock RPM and boost levels really does produce 260 HP.
11-10-2013, 10:34 AM #4
i get where your coming from with the thinking that increased power = shorter engine life. however there are many many people who have been running in the 14-16 psi ranges for way over 100 hours with no issues. for 6 straight seasons I ran a 2 rude over 14 psi on my old rxp. the engine that was in that rxp is still running today in a different ski. if its tuned right and its within safe limits they can be extremely reliable. on the other side of it, if the tune is no good and junk 87 octane gas is used then im on board with your first post.
11-10-2013, 11:06 AM #5
- Join Date
- Dec 2006
- Crest Hill, IL
Thanks for the info Andy
I will stress this, as this is what threw me off......is your reference to the STOCK blower. Even though it is stock, on this forum, its still considered an X-charger, which is standard on all 255/260 motors. Saying STOCK refers to the old 215 charger, because that size is still available in the current GTR.....So when doing searches for information on stock chargers, people can get confused........
Not being a pain, just trying to clarify for some people....
11-10-2013, 11:14 AM #6
I added bold letters to the original post.
My entire purpose of the thread is what is the effect of changing blowers and how RPM has a big effect on the boost numbers and the resulting HP. If someone ever asks "will changing my blower get me to X speed?", you have to include the RPM in the conversation. Fine tuning get involved real fast on this stuff.
11-10-2013, 02:21 PM #7
Very very good analysis of the potential these motors have.
Once you reach the higher rpms you've got to expect higher maintenance.
11-10-2013, 02:30 PM #8
11-10-2013, 02:39 PM #9
Removed my post to save everyone from a lot of profanity... Lets just say I can't change my rev limiter at this time
11-10-2013, 03:10 PM #10
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