Big Bore Kits for Harley

Question I have a 1994 Dyna Wide Glide I’m customizing this winter. I want to rebuild the 1340 Evo engine. I’ve been looking at big bore kits for Harley, a friend of mine has an 06 deuce he put a big bore kit in it. His stock engine should’ve been 14th cc I think. Would the jugs and pistons work on my 1340 evo? I appreciate your time and input on this. Thanks, Paul

Answer Paul, there are big bore kits offered for your Evolution motor. The kits usually require that your crank cases be honed to accept the larger cylinders. That makes the job a bit more involved than your buddy’s Twin Cam kit.

S&S offers their classic Sidewinder package. Check that out. Here’s a link:

A big bore kit is not the only way to gain significant horsepower.
Consider Screamin Eagle heads with a more aggressive cam.
A Thunderheader, or Supertrapp exhaust also aids a performance package/combination.

Choose a cam that reflects your riding style.

The Evo has been around for three decades now. People have figured out a lot of different combinations for creating more horsepower. Do your homework. Search on line to see what others have done. Read reviews of kits & combinations that have been tried. Find something that fits your budget.
Don’t rule out Nitrous. That is a lot of fun too!
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19 Responses to “Big Bore Kits for Harley”
  1. Chuck

    I too have a 1994 evo. Wouldn’t a big bore kit most likely cause the crank case to crack? I thought the evo’s susceptible to that.

    • Dennis Santopietro
      Dennis Santopietro

      Hi Chuck, Some of the casting were not as good as others. When we modify from original, we go away from the engineered spec and yes issues arise.

  2. Jon

    I have an s&s ground pounder 06 the evo has been bored to 130cc it is carved with check buttons on heads when I crank bike I am loosing compression on front lift rod and shooting fire from head ring will this be a major job or not

    • Dennis Santopietro
      Dennis Santopietro

      Hi Jon,

      Thanks for the comment: It depends on what you consider major. You have a blown head gasket. You need to strip the motor back down to the base gaskets and see if anything, other than the head gasket, is damaged. Also, you need to diagnose why this head gasket failed.

  3. geo rubino
    geo rubino

    i bought a bolt on kit, Wiseco 10:5-1 pistons and the jugs were bored .020″. by the way it’s a 1996 evo1340cc, so the cases don’t have to be split and no machining required. just have to set ring end gaps and put it back together..

  4. Andrew T
    Andrew T

    Hi Chuck. I ride an 87 FLHTC. When I hit the 100,000 mark it needed a freshen up. The cylinder base gaskets were weeping and a little oil consumption over normal. It was a stock engine to this point. I did a rebuild performing the following upgrades. Bored the cylinders by .010″, New Weisco .010 over flat top pistons. This way didn’t need to modify the cases. We did however split the cases to check a suspect crank bearing. So while in there had the crank balansed and new bearings done. We rebuilt the oil pump. Added an Andrew’s EV27 cam, and Jims breather gear. Did head work consisting of a valve job, and had the heads ported, polished, flow tested. The carb, I upgraded the old Kehin with a ’93 and newer 40mm CV. The carb was jetted slightly, and fitted with a needle from and ’98 Sportster (find articles by Joe Mitton on this in American Rider magazine). I already had the hi-flow air breather kit and Kerker slip-on mufflers. At the end of the rebuild the bike went onto the dyno. It turned out a very respectable 95 ft/lb torque, and 88 hp. My bike gets 180-200 miles per 5 gal tank of fuel. I currently have just over 200,00 on it and still as reliable as the day after the build.Honestly, my only regret is the porting/polishing and flow. Although the bike produces good solid power, it is now a lot more suseptable to bad gas and knocks and pings if I get some. I fell the head work did not quite produce the bang for my buck. when building a motor you gotta consider how you ride the bike. I can’t match the performance of my friends on new Twin Cam rides when the ride pushes past legal limits, but When on a tour it is just fine, and remains dependable. Good Luck. Andrew

  5. Andrew T
    Andrew T

    Hi again Chuck. I realized a typo. The needle for the carb was from a “1989 Sporty”. The reason is the diameter, and taper of that needle provide improved fuel delivery during the throttle range. You will get the same result from “Thunderjet Kit” however you will most likely find a dramatic drop in your fuel economy.

  6. Richard

    Back in 1988 I used a Sputhe Big Bore Kit. Turned a stock 80″ into a 95.5″ and with a 4 5/8″ STROKE 107″. You really have to cut the cases to fit these cylinders. Would I do it again, NO! The best bang for the the buck I’ve seen over the years is a 4 5/8″ stroke with stock cylinders 89″.

  7. Jarry

    What do you think is better for all around riding, no racing or high rpm’s, a remap from Harley, or an after market cobra F.I. Computer kit for a 103 engine, circa 2013 or 2015, along with pipes and free flowing air filter.

  8. keith

    Chuck I have a 1981 FX stroked and big bored to 93″ using all S&S parts, After sitting over winter when I start oil is coming out the vent hose that come’s out of the S&S oil pump? Any ideals?

  9. Andrew T
    Andrew T

    Hi Keith. That oil burp is no big deal. We refer to it as morning sickness. During the riding season, and when your bike is running it typically has 1/3 of a quart or so circulating through it at any given time. When your ride is shut down for extended period of time (ie; winter). Oil from the reservoir can settle from the tank into the motor caseing. When you fire things up for the 1st time of the season some of this excess oil simply burps out the vent tube of the engine. Next fall, check the oil level on the dip stick when you store the old girl. Then before firing her up in the spring, check the oil level. You will notice a difference. After you fire up the motor, check the level again. You should notice that the oil has come back to the reservoir. Except of course what has burped out. This is also partially why you want to run a motor with a remote oil reservoir prior to changing the oil. So there is no excess oil trapped anywhere in the system, the correct amount of oil is in the engine, and the reservoir. Hope this helps.

  10. Jerry

    I’ve got an anniversary ultra classic. I’m going to put a big bore kit, 6 speed xmsn and high performance pipes in her. Are there any other components I should buy to go along with this upgrade?

  11. Wayne shelton
    Wayne shelton

    I. Have. A. 2012 wideglide. 103cub inch. Can. I. Change out. The. Stock carb. An put. On. S&S. In. It’s. Replacement? Thanks. Bro

  12. robert cunningham
    robert cunningham

    I had my ’98 dyna rebuilt a year ago and added domed pistons for more compression. big mistake. It pings under load, especially when hot. I live in AZ it’s always hot. I have a S & S 520 cam in it right now. I’m considering a 85″ kit and more cam. I would appreciate your input.

    thanks, robert

  13. TheMaddYooper

    I had to go back and look. I just got this discussion in Apr of 19. The comments are from 2015.
    Any way the first thing I ask myself and anyone else wanting to do a build is how much money do you want to spend?
    Then how much can you afford to spend? These are questions that the individual needs to answer for themselves.
    After that is how do you ride?
    If you don’t or can’t answer those questions it is way to easy for the average guy to get in over his head and end up with a very expensive law ornament.
    Having said all of that I like S&S products I have never been disappointed with them.
    Nitrous is horse power smart. It isn’t combustible it produces power by rapid thermal expansion. So you get power without additional heat. Always a plus.
    One last thing, I don’t believe in cutting corners. It costs more to dothese things but in the long haul you will be better served.
    Have fun I know you will.