New Slant Heads for 80cc's: Compression Boost!?
- Thread starter europorsche914
- Start date
Pablo
Master Bike Builder & Forum Sponsor
Seems fine to me - save money and hassle. I may switch back, just to see. No squish band though, but at least you keep the hemi.
Pablo
Master Bike Builder & Forum Sponsor
.020-.022" works well.
I dont exactly understand what you are asking? should the spark plug be perpendicular to the motor?
If thats what your asking then no.
You should have the exposed end of the spark plug pointing towards the rear of the bike, instead of out the front towards the exhaust like how I always see them mounted. The point is to run the intake side hotter, and let the exhaust side run cooler. You get a more ambient (and lower) cylinder temperature.
I finally got my chambered exhaust installed. I took a short test ride and you can definately notice a difference. The bike pulls better and runs a bit smoother. Next is the 36 tooth sproket. I'll keep you posted. Also, you can see on on of the pic that I have an extra thick amount of gasket material. I believe I have more than needed. I did this to fix the piston slap problem I got when I first installed the slant head. I will probably reduce the thickness as much as allowable to increase compression. Do you have your slant head facing back?? foximus.
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Pablo
Master Bike Builder & Forum Sponsor
I can tell you guys in practical terms on my bike it makes zero difference. I (like many/most folks) run with my plug forward now, but I was running with the plug slanted back. No difference. Plus I really doubt fins in front make the cylinder temp cooler - in fact, maybe the opposite.
FileStyle
New Member
I know , that I have a friend who has a "80cc" slanthead and that motor runs good! it can almost keep up with mine. did you notice I said almost. but it runs really good, I have ordered a "slant head" head for a next build. to see what difference if any, my motor already runs good. just on a quest for speed! and then about plug open end pointing torward intake, would that be indexing the plug? and where do you get the correct plug washers to properly get your open end torward the intake?
Spark plug indexing washers
Here
CSR Spark Plug Indexing Washers - SummitRacing.com
Here
B&B 30510 B&B Spark Plug Index Washers
and here!
YourOilShop - Spark Plugs and Indexing Washers
After riding the bike around today, I found that it now has an extreme amount of viabration at higher rpms and that it cuts out at high rpms due to lack of fuel. The high rpm harmonic viabration is so bad, that it not only makes it extremely uncomfortable to ride, but it shakes loose all the bolts on the bike causing a major ongoing maintenance issue around tightening bolts and nuts all over the bike. I tried to make it richer with no success. I adjusted the float as much as possible with out it flooding, and again no luck. It still acts like it is starving for fuel and cutting out at the upper end of the rpm band. Remember, this bike is ported as well. With these problems persisting, I will have to go back to the stock exhaust. Anybody have any suggections?
bare bones
New Member
Has anyone ever compared compression before and after they put on their slant head? I just got my slant head in the mail. I have a compression gauge. I think I am going to compare the stock to the slant and see how much more the slant head adds.
Very first indication something was different was noticing rear wheel had a tendency to skid when starting. Sometimes I have to pull in the clutch and try again. This with 2 gaskets. :0
Dan
Staff
Very cool BB. Looking forward to your findings. Is really great that you are taking the time to research and share your findings. Keep us posted!
I have been wondering about the long term effects. Would seem there has to be some, but dunno
bare bones
New Member
I did the compression test and here are the results:
Normal stock Grubee Skyhawk: 95psi
Slant head from Boy Go Fast: 180psi
I expected more compression but WOW!
Normal stock Grubee Skyhawk: 95psi
Slant head from Boy Go Fast: 180psi
I expected more compression but WOW!
Seriously? That seems a bit extreme. I just got a slant head and installed it yesterday. Since the weather has not cooperated, I've only been able to go around the block. I didn't notice a difference at all. Starting seemed the same and did not notice an increase in pull up the hill. I'll play with it more when the weather clears up. I have a compression checker as well and If i recall, I was in the mid 90's with a standard head Grubee 66cc.
Pablo
Master Bike Builder & Forum Sponsor
First thing is to make sure that thing is not leaking. They pretty much all do.
Believe me, I have thought of that but just have not taken the time to properly troubleshoot. I used a new head gasket and tightened the head bolts, ran for 10 min and tightened everything again.
It seems some think the slant head makes a world of difference and others don't think it offers alot. Dunno....
It seems some think the slant head makes a world of difference and others don't think it offers alot. Dunno....
bare bones
New Member
I didn't believe it either at first. I tested and retested around 6 times each and came up with those readings consistently. I'm with Pablo. Yours may have a leak. What does your slant head read with the compression checker?
Great for you. 2x compression reading! That is amazing. I would expect an increase but not to that magnitude.
Even though its still raining, I ran a compression check. About 95+ for the slant. Its a cheap test so the readout isn't very precise. This is in the neighborhood of the test I ran on the regular head.
I pulled the slant head and noticed that the rear ward side of the gasket didn't seem to have a good seal. I didn't see blow by but it wasn't as defined as the front side even though all of the studs were equally tight. I reset the head and we'll see if there is better weather tomorrow.
Did you use a torque wrench or just go reasonably tight?
Even though its still raining, I ran a compression check. About 95+ for the slant. Its a cheap test so the readout isn't very precise. This is in the neighborhood of the test I ran on the regular head.
I pulled the slant head and noticed that the rear ward side of the gasket didn't seem to have a good seal. I didn't see blow by but it wasn't as defined as the front side even though all of the studs were equally tight. I reset the head and we'll see if there is better weather tomorrow.
Did you use a torque wrench or just go reasonably tight?