The on ramp challenge
#1
09-13-2018, 07:56 PM
Join Date: Jun 2008
Location: So Cal
Posts: 1,352
The on ramp challenge
Looking to run a stock displacement Klx250s with an aftermarket exhaust, dj 2206 jet kit against a mcm modified Klx250s with similar mods.
Let’s actually see how it plays out!
Let’s actually see how it plays out!
#2
09-13-2018, 08:15 PM
I'll bring my 351 with stock exhaust, better make sure you guys have it tuned up with a new plug!
I want to warn you too, mine will have dirt on it!
I want to warn you too, mine will have dirt on it!
Last edited by durielk; 09-13-2018 at 09:38 PM.
#3
09-13-2018, 11:40 PM
Have the rider on the MCM bike ignore the tach and ride it like an off roader - aka shift when it quits pulling strong. None of that ten grand crap. The HP peak is around 8600 rpm on both bikes.
#4
09-14-2018, 02:57 AM
Exactly Mark !
To expand that thought a little, max accel would require a timed trial and error session for each rider and each bike - the extent of delving into over-rev before shifting is dependent on the TRQ curve of the over-rev and the desired RPM after the shift - which also depends on the TRQ curve... All I can offer is that the MCM bike has an extremely gentle/shallow over-rev power drop off and significantly better TRQ curve below 6500 rpm.. The non-MCM bike should never be allowed to dip below 6500 rpm after a shift as the TRQ for such bike below 6500 rpm is far below even the levels produced from a stock KLX !
My knowledge and information in this matter concerns two KLX's with lidless airboxes, proper CVK setups, full FMF exhaust systems, with one having the MCM and one not..
To expand that thought a little, max accel would require a timed trial and error session for each rider and each bike - the extent of delving into over-rev before shifting is dependent on the TRQ curve of the over-rev and the desired RPM after the shift - which also depends on the TRQ curve... All I can offer is that the MCM bike has an extremely gentle/shallow over-rev power drop off and significantly better TRQ curve below 6500 rpm.. The non-MCM bike should never be allowed to dip below 6500 rpm after a shift as the TRQ for such bike below 6500 rpm is far below even the levels produced from a stock KLX !
My knowledge and information in this matter concerns two KLX's with lidless airboxes, proper CVK setups, full FMF exhaust systems, with one having the MCM and one not..
Last edited by Klxster; 09-14-2018 at 02:59 AM.
#5
09-14-2018, 03:17 PM
This is the key, period. More power at any given rpm below 6500, where the engine is used the most. You don't find that value on some drag race comparison anywhere. You find it when off road, especially when riding in sand or slow maneuvering on tight difficult trails or going up rough hills. Places where the bike is working from 5000 rpm to 8000 rpm.
#7
09-14-2018, 04:44 PM
Very true. Even multiple runs could vary significantly. I had a friend who was drag racing a 57 Chevy with 4.11s a hi-rise and four barrel running e.t. brackets. He was ultra reliable, since the Power Glide wouldn't spin the tires, shifting out of low at 7000 rpm. When he got up in the rounds he got all excited and ran it to 7200 rpm and broke out. Two hundred rpm made the difference. So even a slight difference in shifting can make a difference in results.
I'm thinking dyno runs use fourth gear, probably to increase the time it takes to reach peak enough to increase the delivery of data to plot it accurately. If done in one of the first three it would be too easy to have the tire spin on the dyno or have it rev up so fast as to make too few data points reducing accuracy. Heck the data is all about statistics and if you don't have enough points of data the statistics are less reliable. Going above fourth is not needed, probably doable, but not needed.
But I could be wrong... and it wouldn't be the first time.
I'm thinking dyno runs use fourth gear, probably to increase the time it takes to reach peak enough to increase the delivery of data to plot it accurately. If done in one of the first three it would be too easy to have the tire spin on the dyno or have it rev up so fast as to make too few data points reducing accuracy. Heck the data is all about statistics and if you don't have enough points of data the statistics are less reliable. Going above fourth is not needed, probably doable, but not needed.
But I could be wrong... and it wouldn't be the first time.
Last edited by klx678; 09-14-2018 at 04:47 PM.
#8
09-14-2018, 06:11 PM
Join Date: Jun 2008
Location: So Cal
Posts: 1,352
The simple nature of this is to see which machine gets up to speed the quickest.
Nothing more nothing less. Let’s actually see if this mod does what people say it does.
Cause I actually called an engine building company and they said it’s all a compromise. You trade one for the other. Adjustable cam gears have been tried before, this isn’t the first time someone retimed a cam. Impressive gains have been claimed before....
So I could bring bills big bore #87 along too, but not trying to compare displacement increases. Just the mcm modded vs another similarly modded klx250s. Like I said simple. Kiss. Keep it simple sxxxxx.
Nothing more nothing less. Let’s actually see if this mod does what people say it does.
Cause I actually called an engine building company and they said it’s all a compromise. You trade one for the other. Adjustable cam gears have been tried before, this isn’t the first time someone retimed a cam. Impressive gains have been claimed before....
So I could bring bills big bore #87 along too, but not trying to compare displacement increases. Just the mcm modded vs another similarly modded klx250s. Like I said simple. Kiss. Keep it simple sxxxxx.
#9
09-14-2018, 06:23 PM
Join Date: Jun 2008
Location: So Cal
Posts: 1,352
So my friends ‘12 klx250s (search ‘Another klx250s mod thread’) has only bolt on modifications. Nothing internal was done to the motor. Slip on fmf q4, dj jet kit, airbox lid removed to be exact. And piloted by a girl even....
Last edited by RaceGass; 09-14-2018 at 06:46 PM.
#10
09-15-2018, 12:23 AM
Is she lighter than the other rider? Re: Shayna Texter or Angele Sampey.
By the way, this is all in fun. Regardless of any outcome, for me it isn't any big deal. It's like shop talk. Fun! I'm waiting for the outcome, regardless and really just wish I could be a participant, just for the BS session before and after.
By the way, this is all in fun. Regardless of any outcome, for me it isn't any big deal. It's like shop talk. Fun! I'm waiting for the outcome, regardless and really just wish I could be a participant, just for the BS session before and after.
Last edited by klx678; 09-15-2018 at 12:26 AM.
