kt100 header and flex length suggestions

Dan Brown

Dan Brown

Member
Hi again guys. Getting ready to hit the track this weekend for the first time this season, getting new ( to me ) Margay's ready to go. I am running an RLV A3 pipe to start with , and I am looking for flex suggestions. The header I have is 3 3/4" long from the exhaust flange to the end ( I have other length headers if this one isn't the best option). Home track is relatively small and twisty, baseline gearing for pipe class is 10T drive, 87T driven. Any suggestions on a baseline flex length that will produce good mid-range torque ? I have a Digitron with rpm, egt and cht to help with tuning. I also installed a brand new Steel Nytro clutch and checking the engagement on the stand with the brakes locked it was around 7500 rpm. I think I should be closer to 9500. Any thoughts? Thanks.
Dan
 
Hi Dan,

Do you happen to have an A2 or L2 pipe ? The A3 is more of a mid range - upper end pipe. The A2/L2 would be better suited for the small twisty type of track. We ran the A3 pipes on street courses and usually had the flex around 9 5/8 to 9 3/4. I think we were closer to 10,100 on clutch engagement.

The exhaust gas temp is great for watching to see if the low speed is too lean at clutch engagement. I have one on my son's kart and have taught him how to watch the egt temps and tune his low speed. It makes a big difference for sure.

Hope that helps,
Chris
 
I have an A4 pipe which is more top end. I had an A2 but it was in rough shape, sold it with my Tony Kart. I can buy a A2 or an L series pipe, wanted to try the A3 first since it's basically new and I already had it.
 
Header measurements are always from the piston face to the start of the 1st cone. From the piston to the header flange is right at 2 inches. If you go to the RLV website they may have header length information there.

I always set the clutch at 10,300 when I tested it the way you described. A little less is okay, but not much. We always set our carburetor at 2 to 2 1/2 on the bottom and 1/4 to 1/2 on the top. It won't idle in the pits but it does work fine on the track. If you hear something that sounds like rocks rattling in the pipe, that's detonation and you need to make the carb a little richer.

If you can buy a compression test gauge, you should see about 160 psi. That's with the carb wide open. You want a cold plug.
 
This engine is a fresh out of the box stock kt100 that came in a team buyout I purchased. I plan on running as many laps as possible this year , gonna put some time on this stocker as a practice engine. I have always believed in seasoning an engine before blueprinting it. So I need to break it in, haven't checked the compression on it, I will after this weekend when I get the rings seated in. I will swap out to my race engine on race days . I run AR51 plugs with pretty good results so far. I set the carb to Steve Oharas easy idle settings, thought I would try it for practice days, have another carb with low pop off race settings on my Haddock race engine. I will check the RLV site.
 
The proper "flex lenght" for A series pipes is 7 3/8 to 7 5/8 inches from the piston face to the end of the added piece of "FLEX" pipe.
 
I was looking on the RLV site Jack, and it shows a slightly longer header that states it works well with the A series pipes and gives improved bottom end. Unfortunately there isn't any length measurements listed with the headers, and the headers I have do not have any identifying numbers on them. It makes it kinda tough to figure out which combo to run. With the 3 3/4" header installed, and an A3 pipe, if I set the flex at 7 1/2" the pipe almost touches the back of the header, there is only about 1/4" between them. That is how I set it up today, unless someone tells me I did it wrong I am going to run it this weekend and see how it performs. I have longer and shorter headers, but to set the flex at the measurements Paul gave me a longer one won't work. I can always go shorter if I need too.
 
"L" and "A" series headers and FLEX lenghts are the same.
I also looked at the RLV site, and I conclude that the long header actually has the flex built in. Note in the picture an additional short piece of "PIPE" to be used for fine tuning.
 
Funny how the recommended flex lengths differ, I think the A and L series measure from the block face, not the piston. Also I'm quite sure that the exh. port measures 2" from piston to outer surface.
 
jack burroughs said:
Funny how the recommended flex lengths differ, I think the A and L series measure from the block face, not the piston. Also I'm quite sure that the exh. port measures 2" from piston to outer surface.
Click to expand...
If that is true Jack then I will be 2" short on my flex length, as I am measuring from the piston. I think I will give RLV a call tomorrow and see if I can get a clarification on this, 2" short is obviously going to create all kinds of issues.
 
Paul Ahrens said:
"L" and "A" series headers and FLEX lenghts are the same.
I also looked at the RLV site, and I conclude that the long header actually has the flex built in. Note in the picture an additional short piece of "PIPE" to be used for fine tuning.
Click to expand...
Most of the headers I have are a female end facing the pipe, and the pipe has a matching female end, with the flex length being male both sides. I do have a longer header that appears to be the same as the one on the RLV site, which has a male end facing out. I also have several short pieces of pipe with it, ranging from around 1/8" to about 5/8". So I think you are correct, the flex is built in and it is fine tuned with the short pieces. I am going to give RLV a call and see what they say.
 
DB if your is a tapered long header that what you want ultimately for a tight corner track , but a short taper would be next best (I have PM me). I just sold my last long tapered.

Since You want to avoid buying yet another pipe. You know your header measures 3 3/4". You know the piston side face to the outside engine surface is approx 2" +/- 1/8". You know L series and A series have the same 7 1/2" call out. You know the tiny flex gap between header & pipe to get 7 1/2" call out. You know your A3 series is mid range, but you need more bottom end. Do the math 2" + 3 3/4" header + 2" flex = 7 3/4" total which gives you 1/4" longer for more bottom end to compensate for the A3 vs A2 or vs L1. Per NIKE "Just Do It" and adjust from there. And yes it is fine tuned with short exhaust spacers. (perhaps short 1 1/4" axle spacers will work to save some money) JMHO
 
JB - I believe A & L series are their own animal with a 7 1/2" call out. JMHO

jack burroughs said:
Funny how the recommended flex lengths differ, I think the A and L series measure from the block face, not the piston. Also I'm quite sure that the exh. port measures 2" from piston to outer surface.
Click to expand...
 
Be assured that I know that, but isn't it funny that that measurement PLUS the 2" of exh. port length, equals the 9-1/2" I normally use? I also have 9 different headers that fit KT's and there isn't 1 I.D. mark on any of them.
 
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Jack is correct - measure from the face of the piston to the end of the flex. I just got home and checked - my '4' pipe is actually a Delta 4, not an A4. Sorry for the wrong info. We did run 9 5/8 on the Delta 4, not A4.
 
ENOUGH SAID PERIOD END
(see Art Verlengiere RLV quotes)

Bob's
Thread: Yamaha pipes
01-12-2014 03:41 PM
jack burroughs said:
TSOW, TSVX, L-2, RS-1 RS-2.Basicly run all my pipes @9-1/2".
Click to expand...
01-12-2014 08:17 PM
Taft Racing said:
Jack your flex is way to long on L2 pipe the rlv L pipes used 7 1/4 if I remember correct.
Click to expand...
Thread: RLV L-2 flex length
07-13-2014 01:16 PM
Paul Ahrens said:
7 1/2 inches--Paul
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07-14-2014 12:20 AM
racer_2828 said:
7.5 is right on
Click to expand...
07-14-2014 01:07 AM
arc100 said:
I assume measured from the piston to the start of the first cone
Click to expand...
07-15-2014 03:23 PM
jack burroughs said:
"L" series pipes are different., has to do with construction of the first divergent cone.
Click to expand...
07-18-2014 02:46 PM
snealon said:
ok engine builder got back to me 7.75" the 9.75 was a typo. I feel better now
Click to expand...


EKNClassic.com Forum Index -> 2-Cycle Racing RLV A2 Clutch Engagement & Flex Length

Sun Mar 07, 2004 12:44 pm Art Verlengiere RLV - Peter, the flex lenght is 7.25" to 8.00", depending on your weight Clutch should be set @ 10,200 to 10,400.

Posted: Sun Mar 07, 2004 8:23 pm Walt Gifford Post subject: RLV recomends 7.5" +or- .25" clutch 10,500 to 10,700 top rpm 14,600 to 15,600.

PostPosted: Mon Mar 08, 2004 6:47 am Walt Gifford Post subject: you can't go far wrong with the recomendations of the people who manufacture the pipe.

PostPosted: Mon Feb 20, 2006 5:32 pm Jim White Use the A2 for sure. Flex should be 7 1/2 inches from the back of the piston to the end of the flex for a good starting point.


EKNClassic.com Forum Index -> 2-Cycle Racing RLV A2 Flex pipe length question

PostPosted: Tue Feb 21, 2006 2:13 pm A Chad Landers - Laukaitis Racing Engines - little longer moves the powerband down, a little shorter moves it up some. The A-2 is more a bottom end pipe for shorter tracks and the A-3 would be for a little longer track. If you want more punch out of the corners lengthen the flex

PostPosted: Fri Feb 24, 2006 7:32 am John Wehrheim - FYI, you will never run below 7 1/4 from the back of the piston to end of the flex. Oh you could if you want to stick your motor. Probably the longest you'll go is 8 1/2 on a tight track. Also you stall speed should be in the 9,800 rpm to 10,100 rpm.


EKNClassic.com Forum Index -> RLV "L" Series Header

Posted: Fri Feb 17, 2006 5:25 pm Art Verlengiere RLV - Still the same story the "L" and the "A" series headers are the same. The reason for the two sets of pt#'was we went to print with a new catalog before the header testing was done on the "L" pipes. After testing header ideas we decided to stick with the same header, hence the two sets of pt#'s. Art V



Yeti Racing said:
DB if your is a tapered long header that what you want ultimately for a tight corner track , but a short taper would be next best (I have PM me). I just sold my last long tapered.

Since You want to avoid buying yet another pipe. You know your header measures 3 3/4". You know the piston side face to the outside engine surface is approx 2" +/- 1/8". You know L series and A series have the same 7 1/2" call out. You know the tiny flex gap between header & pipe to get 7 1/2" call out. You know your A3 series is mid range, but you need more bottom end. Do the math 2" + 3 3/4" header + 2" flex = 7 3/4" total which gives you 1/4" longer for more bottom end to compensate for the A3 vs A2 or vs L1. Per NIKE "Just Do It" and adjust from there. And yes it is fine tuned with short exhaust spacers. (perhaps short 1 1/4" axle spacers will work to save some money) JMHO
Click to expand...

; )
 
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