OMG 5 minute performance upgrade YES IT WORKS!

Discussion in '2-Stroke Engines' started by Skyliner70cc, Mar 19, 2009.

  1. Skyliner70cc

    Skyliner70cc Active Member

    I hereby on penalty of perjury do hereby attest to the following fact:

    The "80cc" slant head does increase compression and engine performance noticeably.

    I live in Colorado at an altitude of about 6500 feet and ride up to 9900 feet on rides. One thing that really sucks is the 3% loss in horsepower for every 1000 ft in altitude. Couple this with a carb that runs super rich, power is down probably even more.

    I just found the solution and IT WORKS! I bought a high compression slant head from a vendor.

    Here are my observations:

    1. I can no longer pedal start with my centrifugal clutch engine with SBP shifter kit. The engine compression is so much greater that I think I broke something in the auto clutch when I tried (maybe the one way bearing failed?

    2. I used to be able to pull start the engine with 2 fingers. I now have to use a significantly more force to pull start the motor. The difference is incredible and I have to get off the bike now to start it using my dominant right hand. Before I could just flick start it with my left arm while sitting on the bike.

    3. Power: Before I could only climb the steep hill by my home in 1st gear which is a 34 tooth mega gear. Now I can climb the hill in 3rd gear from a dead stop at much faster speeds. In fact, my centrifugal clutch started slipping real bad under the load and couldn't keep up with the engine. I did not attemnpt to determine if there was any change to top speed. I'm more concerned with hill climbing torque and am happy chugging along at 20mph.

    Interesting twist: One thing I should mention is that my original head gasket was 3 times the thickness (it was stock) of the usual head gaskets I've seen on the 100+ HT engines I have installed on bikes. I do not know how much of the increase in compression is due to the thinner replacement head gasket I used with the new head or the new head itself. The new head does have a significantly smaller squish volume and I was worried that my plug top with smack the piston cylinder but it doesn't. Please check your stock head gasket especially if you have a BGF engine. This BGF engine's headgasket is crazy thick and replacing it would help performance a bunch but the slant head is definitely a better improved product.

    Sorry, but the vendor I got these from is already out of stock and I wish someone else sold these.

  2. fenderhole

    fenderhole New Member

    yep, i love my slant head too. best money i ever spent!
  3. Skyliner70cc

    Skyliner70cc Active Member

    Fender, please comment on performance improvement over stock flat head. I can honestly say that my performance at my altitude is now equal to that of being at sea level. I rode several hundred miles in Florida last summer and there is an appreciable difference in power between sea level and over 1 mile high.
  4. aksteverobert

    aksteverobert New Member


    Skyliner, Is it possible to get a thinner head gasket. Seams like the one on my motor is like .100 thick aluminum. Also do you have a pull start on your two stroke motor.
  5. DIYMark

    DIYMark Member

    Could someone PLEASE post a pic of the underside of the slant head either for the 50cc or the 66cc - what I want to see is the squish band so I can decide between buying this head for machining my own (**** if i can just buy one like I want ill do that :) )
  6. DIYMark

    DIYMark Member

    lol it wont let me write h3ll
  7. fenderhole

    fenderhole New Member

    here's what i posted about the head on the vendor's forum-

    "so i got the upgraded replacement slant head for my pk80 yesterday from zoom and installed it today. the first thing i would like to mention is the combustion chamber is ALOT smaller than the original. this has to jack the compression to around 9:1(i've heard 10:1 but 9:1 seems a more reasonable assumption). power has dramatically increased across the entire rpm range. it now has bucket loads of low end torque and i gained 7 mph on my top end. the engine runs much smoother and seems to be alot happier. do yourself a favor and get one of these on your motor asap, you'll definitely be glad you did!"

    and yes they do make a thinner head gasket, sick bike parts has them. here's what i copied off the webpage-

    Head Gasket for 67cc-"80cc" Chinese Engine with 8mm studs
    Aluminum head gasket, .025" thick.
    The gasket is thinner than the stock and will increase your compression ratio and increase horse power.
    This will fit the 67cc, 69cc, 70cc and the so called "80cc" engines with 8mm studs.

    1 Head Gasket $4.99
    Item # SBP-HG698
    Last edited: Mar 19, 2009
  8. Skyliner70cc

    Skyliner70cc Active Member

    Yes, it just keeps on getting better as the rings on my engine are beginning to seat. One of the biggest improvements is the low end'carburation is much better because its no longer rich on the low end.

    I'm also finding myself having to bump up the octane from 85 to 87 due to some minor pinging occuring under heavy engine loads at full throttle. Starting the engine with my pull start is a bear. I've got a bad shoulder and the extra compression is noticed when pulling ;-)
  9. impression

    impression Member

    i hope these come to AUS soon, really wanting on :D
  10. linnix13

    linnix13 Banned

    replace head gasket?

    if i buy the slant head(which is currently out of stock) do i need to replace the head gasket or will the old one still work?
  11. azbill

    azbill Active Member

    head gasket should still be good
    they don't torque down tight enough to give any probs re-using my experience :)
  12. Skyliner70cc

    Skyliner70cc Active Member

    If I reuse a head gasket, I usually flip it over. No leaks yet!
  13. impression

    impression Member

    i would like to run with no head gasket, just for that 1mm more less volume ;)
  14. Pablo

    Pablo Motored Bikes Sponsor

    I'm going to get in line and order one!
  15. impression

    impression Member

    why do you have such low fuel there, here lowest is 91octane and goes to 100octane ( not counting meth or alco fuels)
  16. Pablo

    Pablo Motored Bikes Sponsor

    Our fuel is rated differently R+M/2. I believe yours is just R.

    Your 100 is roughly our 91.
  17. impression

    impression Member

    may i ask what the r and m stand for ?

    and shouldn't it be (R+M)/2

    as 4+2/2 = 5 vs (4+2)/2 = 3 the placement of brackets can mean success or failure :S
  18. Pablo

    Pablo Motored Bikes Sponsor

    Of course you are correct on the math. I was just using so called "internet shorthand" :jester:

    R = research
    M = motor

    This is an interesting reference:
  19. impression

    impression Member

    ah so our 91 is your 87 and our 98 is your 93 and our 100 is your 95 :) cool.
  20. Skyliner70cc

    Skyliner70cc Active Member

    Normally aspirated engines work great (if not slightly better) with lower octane fuels at high altitude. If I recall correctly, you can drop 1/2-1 point in octane for every 1000 foot gain in altitude. Our regular gas in Colorado is 85 octane, not 87 like most parts of the country.

    I once used 79 octane in an overseas mountainous country and it worked great except when driving to lower altitude areas.