Author Topic: Compression vs. head mill vs. fuel octane  (Read 641 times)

Hoatso

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Compression vs. head mill vs. fuel octane
« on: June 12, 2019, 03:01:40 AM »
I’m putting together my 3XV1 with Wossner pistons. I just got my cylinders o-ringed using jsnook’s tooling (thanks!).

I checked the squish to make sure that eliminating the head gasket still left the minimum 0.7-0.8mm as recommended on this forum. My squish measured 1.3 mm. Anybody know what octane fuel is required for this?

I have a spare set of cylinders and heads that I got on eBay from the UK. One cylinder was trash, but I wanted a spare plus spare heads.

I cleaned up my lathe, chucked up a spark plug to use as a mandrel fixture, and figured I would cut 0.5 mm off. Then, I noticed that my spare heads already had 0.5 mm cut. I checked the squish on them and read .85 mm. Perfect. What octane is needed to run this? I run 100 avgas for ping safety and purity (no ethanol), so I’m probably safe.

What if I took off another 0.5 mm from the gasket surface and from the squish? What octane would I need? I could switch to 108 if it pings.

I’m going to get head and cylinder cc measurements. From this, I can calculate compression ratio. But, the port timing affects real compression, so this may or may not help me understand.

There is an old 2T race mechanic in my town that says a compression reading can give me an idea of what octane is required.

Anybody have experience with this?

vinny

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Re: Compression vs. head mill vs. fuel octane
« Reply #1 on: June 12, 2019, 09:16:41 AM »
I asked this question myself a few years back as i had no experience with tuneing tzrs only gp bikes .
i kinda worked it out myself .
I just used my own judgement/experience  in the end .
Personally I wouldn't go too radical on the lathe 0.8 is a nice safe squish .
Lots of things affect how much you can tighten your squish or raise the compression.
Is this for the track ?
Are the tracks  tight and twisty or more open ?
How often do you plan on rebuilding the top end /crank ?
How many miles will you do in any given year ?
What sort of ignition do you use ?
It all has a bearing on how highly you want to tune ?
You are using Avgas that's good for tuneing it's very forgiving. 😀
« Last Edit: June 12, 2019, 11:33:20 AM by vinny »

Hoatso

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Re: Compression vs. head mill vs. fuel octane
« Reply #2 on: June 12, 2019, 04:14:48 PM »
I use the bike on the street. I’m looking for torque and zippy midrange, and don’t need super high rpm. I run a 5 mile loop out through the country a couple times a week.

I like 2-strokes. The TZR is light weight and seems to have good handling and brakes. I put SP forks and an Ohlins shock on it. A little overkill considering that I hardly have any street experience, but I’m 6’4” tall and 250 pounds, so I needed stiffer springs and damping both ends just to be safe.

I have a dirt bike that was professionally tuned to run 108 octane leaded fuel (VP C12) with only a head mod and was super impressed with the improvement in power throughout the rpm range. So, I figure that the TZR might like the same treatment.

I just rebuilt the engine with a new SP crank and Wossner pistons.

What combustion chamber cc’s do TZ’s run?

tasswipe

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Re: Compression vs. head mill vs. fuel octane
« Reply #3 on: June 12, 2019, 08:25:37 PM »
My 96 4-tw has 8cc heads as stock
Manual says use a minimum of 100 ron leaded

tasswipe

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Re: Compression vs. head mill vs. fuel octane
« Reply #4 on: June 12, 2019, 08:28:51 PM »
I’ll add that it’s running 0.81/0.83 squish has kit porting and makes 82 ponies on brands dynojet in anglesey

Scotty4321

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Re: Compression vs. head mill vs. fuel octane
« Reply #5 on: June 12, 2019, 08:37:18 PM »
Now you have O ringed the barrels and don't have to buy head gaskets, you can adjust the squish by changing the base gasket thickness. Dan (Maccas) can sort you out. I think I went for 0.75mm squish and head cc around 10.1
but I just use super plus unleaded petrol which is around 95-98RON.
I had a lot of fun with my bike as it had a 5KE TZ con rods put in it and so the piston heights were changed. I have aluminium spacers and base gaskets to get the piston heights right to the cylinder tops. Cheers Scotty

vinny

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Re: Compression vs. head mill vs. fuel octane
« Reply #6 on: June 12, 2019, 09:28:26 PM »
What scotty just listed is exactly the kinda setup I would go with for a road bike .
I'm using the following in my race bike
0.8cc  volume heads and
a 0.6mm squish
with a bit of advance on the ignition.  (4mm I think )
 im using elf 102 race fuel .
The bike is quick and reliable but it's  too high of a tune  for a road bike in my opinion.

Hoatso

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Re: Compression vs. head mill vs. fuel octane
« Reply #7 on: June 13, 2019, 12:20:56 AM »
Thank you. I’ll let you know what happens.

Hoatso

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Re: Compression vs. head mill vs. fuel octane
« Reply #8 on: June 13, 2019, 08:28:43 PM »
Making shavings!


Hoatso

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Re: Compression vs. head mill vs. fuel octane
« Reply #9 on: June 13, 2019, 08:46:37 PM »
Squish angle is about 11.4 degrees.

For this test, I’m taking off 0.85 mm off the gasket surface total compared to stock. The heads had already been cut about 0.48 mm before I bought them used. After this cut, I’ll cut the squish deeper by about 0.37 mm to get .85 mm piston clearance.

I’ll check cc’s after this.

The new surface looks pretty smooth, but I may lap it on a surface stone to see how flat it really is.

I plan on radiusing the transition from the squish to the combustion chamber like stock to avoid sharp edges that may get hot.

In these photos, you can see that I’m using a spark plug as a mandrel. Once I chucked it up, I indicated off the gasket surface and adjusted the angle to get within a couple thousandths of inches.

I have not cut the squish deeper yet.

« Last Edit: June 14, 2019, 03:26:42 AM by Hoatso »

Hoatso

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Re: Compression vs. head mill vs. fuel octane
« Reply #10 on: June 13, 2019, 08:54:33 PM »
I’m running a Zeel. I highly recommend this. Especially if you have an early R model with mechanical oil pump and no power jets in the carbs. I think this is what the off-the-shelf tune was made for.

It runs great. The speedo and ignition restrictions are removed. Also the kickstand interlock.

I also swapped the stock exhaust for a JL stainless/carbon set. Beautiful, runs great, didn’t seem to affect jetting, and saved 16 pounds (7.3 kg).

Steveog

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Re: Compression vs. head mill vs. fuel octane
« Reply #11 on: June 14, 2019, 02:19:11 AM »
Hi, Hoatso. Who did this machine work for you? As a fellow Yank, if your source is local to you, I could save me shipping cost and time.

If you did your own work, are you available for other US 3xv fans?

I’m just finishing an 8 month build, but opinions for the future are always good.

JSNook has a man he recommends in the Florida and I’m pretty sure SeaRick could offer suggestions, too. But, Maryland is a lot closer to me than Tampa or Seattle. I could drive there.

Great Post. Thanks for any intel you can provide.

Steve
Brief, fleeting Glory. Which of itself cannot last, but while it does is the greatest game of all.

Hoatso

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Re: Compression vs. head mill vs. fuel octane
« Reply #12 on: June 14, 2019, 03:30:43 AM »
Jsnook mailed me his oring tooling and a couple cylinders. I found a local machinist to make an NC program and cut the grooves.

I cut the heads on my Chinese mini lathe.

I could get more cut if folks are interested.

Hoatso

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Re: Compression vs. head mill vs. fuel octane
« Reply #13 on: June 14, 2019, 03:54:05 AM »
One head done. Hope it doesn’t blow up. I think it will be OK.

If it pings on 100 octane, I’ll run 108. There is a shop in town that sells I think 112.

Hoatso

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Re: Compression vs. head mill vs. fuel octane
« Reply #14 on: June 19, 2019, 06:50:44 PM »
I got the bike running today. No leaks or noises. On the 1st test ride, I got a block away and it died. Turned out, I had the gas turned off. After that, ran fine. I have to take it easy for an hour or so to let the rings break in. I’m curious how much difference the compression makes.  It seems to be OK running 100 octane, so maybe I won’t need to run 108. Or maybe, I need to cut more metal off the heads?