Author Topic: Ironhead on the dyno  (Read 401 times)

0 Members and 1 Guest are viewing this topic.

Offline JW113

  • Full Member
  • Posts: 1661
  • Country: 00
  • San Jose, California
Ironhead on the dyno
« on: May 29, 2019, 02:30:26 PM »
I've been working with my local shop to dyno tune my '78 XL. Have to say, am not real happy or impressed with the results. The bike:

Mostly stock 1978 XLH
S&S Super B with Thunderjet, and S&S and air cleaner
MAC dual shorty exhaust
Stock P cams

I don't know what is supposed to be typical for a 70s stage 1 Ironhead, but does 38HP sound about right to you guys? I was thinking it should be up in the low 50s or so, but maybe that is just wishful thinking.

What really through me was the A/F ratio plot. Down blow 3500, it was getting up above 15:1. That ain't good for old iron with no-quench hemi heads, is it?

I'll post the dyno chart when I can scan it. Not allowed to post in the AFR zone, they did not record the results the way that I had asked.

-JW
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

Offline guppymech

  • Full Member
  • Posts: 253
  • Country: us
Re: Ironhead on the dyno
« Reply #1 on: May 29, 2019, 06:29:49 PM »
I think low to mid 50's is right where it should be.  What was the AFR above 3500 rpm on the main jet?  15:1 on the intermediate jet,  I think you need to go to a one size larger jet to richen it up a little.   How many turns out is your idle mixture screw?
Linky to some IH dyno runs and discussion:

http://xlforum.net/forums/showthread.php?t=951664&page=2
'84 FXE, '02 883R

Offline JW113

  • Full Member
  • Posts: 1661
  • Country: 00
  • San Jose, California
Re: Ironhead on the dyno
« Reply #2 on: May 29, 2019, 07:08:30 PM »
Yeah Gup, that was basically what I was expecting to see. Not the case, so it looks like I have a lot of work to do. And the starting point is, find somebody that actually knows how to tune an Ironhead! I might know a guy down in San Jose, he loves Ironheads, but is a bit of a pain in the ass to deal with. As long as the results speak for themselves, probably worth the pain.

Dyno sheet attached, sorry for the lousy picture qualtiy. I doctored it the best I could, the orignal was quite pale.

I think the number one concern is how the torque starts off OK, then quickly falls past 3000. And thus, so too will the HP. Real lean below 3500, but OK after that. So where is the power going?

-JW

  [ You are not allowed to view attachments ]  
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

Offline guppymech

  • Full Member
  • Posts: 253
  • Country: us
Re: Ironhead on the dyno
« Reply #3 on: May 29, 2019, 07:19:29 PM »
On the one run it looks like the main jet is too rich, maybe go down one size or turn off the Thunderjet.  Hows the engine health? Done a cranking compression test lately?  What kind of baffles do the MAC mufflers have in them?  You're a pretty savvy guy, I would think you could tune it yourself.  The S&S Super B manual and Mikuni HS40 manual have some good tuning info in them.
*edit* Are you running E10 fuel like we have to use in the midwest?
« Last Edit: May 29, 2019, 07:54:15 PM by guppymech »
'84 FXE, '02 883R

Offline JW113

  • Full Member
  • Posts: 1661
  • Country: 00
  • San Jose, California
Re: Ironhead on the dyno
« Reply #4 on: May 30, 2019, 07:52:19 AM »
Actually, I think I'm going to start with going back to a CV. Yes the Super B is stylish, but sure comes with some baggage. I'm not sure what baffles are in those MAC mufflers, they're not exactly quiet so likely not that restrictive. So the journey begins...

-JW
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

Offline Burnout

  • Full Member
  • Posts: 1131
  • Country: us
Re: Ironhead on the dyno
« Reply #5 on: May 30, 2019, 11:42:29 AM »
The pipes don't look bad on the dyno. No ~3000 rpm dip

++ on the CV much better for the street.

Best is a Mikuni VM39 with a branch kit.
(no butterfly and shaft in the way provides more flow)
And the slide gives you a Variable Venturi at the fuel discharge port for better atomization.

And Dual plugs....
They don't call me Ironhead Rick just because I'm "hard headed"

Offline JW113

  • Full Member
  • Posts: 1661
  • Country: 00
  • San Jose, California
Re: Ironhead on the dyno
« Reply #6 on: May 30, 2019, 12:54:05 PM »
No dip, but that steady downhill decline after 3000 is a problem. Even stock P cams ought to be holding torque out past 4500. Something is wrong, I just need to figure out what. Timing?

I love the look of the Super B, but a really hate how twitchy they are just off idle. As in, when downshifting, and reaching for the clutch level and you move the throttle ever so little, and the motor surges. Hate that. CVs don't do that at all, in fact one of their "drawbacks" that I find a positive feature is the damping effect from the slider. They don't respond to minor movement on the throttle due to that slight delay in response. Much better street behavior if you ask me.

What is really strange, is that the behavior of the bike out on the road does not really correspond to what the dyno chart is saying. It actually runs quite nice, does not seem short on power at all, and pulls fine up to 6K. I'm tempted to go somewhere else and get a baseline on it before changing anything just yet, and this time with SAE correction.

-JW
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

Offline kd

  • Site Supporter
  • Full Member
  • *****
  • Posts: 6608
  • Country: ca
Re: Ironhead on the dyno
« Reply #7 on: June 02, 2019, 07:34:04 PM »
What gear was that run in?
KD

Offline JW113

  • Full Member
  • Posts: 1661
  • Country: 00
  • San Jose, California
Re: Ironhead on the dyno
« Reply #8 on: June 02, 2019, 07:36:45 PM »
4th.

-JW
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber