15:1 compresion on methanol

Here's a photo of Roberts 920cc monster sidecar rig running 15:1 CR on Methanol. I wasn't sure if Nortons could even run that high a CR and survive. I know he had to use special ARP through bolts for the cylinders because the SS bolts that came with the 920 cylinders failed.

Do you know who supplied the 920 cylinders and bolts?

Ken

jseng1 said:

Here's a photo of Roberts 920cc monster sidecar rig running 15:1 CR on Methanol. I wasn't sure if Nortons could even run that high a CR and survive. I know he had to use special ARP through bolts for the cylinders because the SS bolts that came with the 920 cylinders failed.

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A lot of (car) drag racers are using E-85 with higher 14.5:1 CR.

Monster is right. That CR combined with a methanol/02 charge? That is getting into top fuel drag racing formulas.
I wouldn't want to be hanging onto that beast if it decides to let go...Impressive that all the parts are still attached.
Nice work to make it work.

The highest comp. ratio my brother and I have used with methanol was 17 to 1 in a Jawa two valve speedway motor which was of 600cc capacity. Steve Oszko ran his 500cc Manx at 14 to1 comp. He used to make his own pistons. At 14 to 1 comp., he used to retard the ignition about 2 degrees. Strange things used to happen - the pistons started to collapse below the inlet valve. At high comp. the motor tends to use more fuel, so theoretically it should give more power. I suggest the theory does not always represent what actually happens. Methanol can give excellent power at comp. ratios as low as 7 to 1. I suggest many people do not know how to tune their carburetors - so jet too rich. The difference in jetting between fast and slow when using methanol is almost nothing. With petrol as fuel, it is twice as bad because methanol jets flow twice as much when compare with petrol jets. Methanol will always give more power than petrol, because it hides-up the tuning errors. But to get the best out of methanol, it needs to be jetted so lean that the motor almost begins to miss.
Compression ratio, ignition advance and jetting are in balance at optimum power. If you change one, the other two are affected.
With lower compression, it is likely similar power can be produced as when running high compression, by adjusting ignition advance and jetting.
If you raise only the comp. ratio and gain more power, it is likely that you were previously jetted too rich.

I suggest the Amal methanol needles have tapers which are too rapid. However if you use leaner needles, there is a likelihood that you will jet off the needles instead of the main jets at full throttle. When racing the main jets need to be a bit rich, so the motor is not run too lean at high speed. it is possible to recess the needle jets, so the restriction is lower down and the tip of the needle is still retained by the needle jet. If a slide hangs-up, you might make a fast exit.
With my bike, I feed the throttle on slowly, as you would with a two-stroke. It is faster that way. If you whack the throttle open and the motor gets mixture which is slightly too rich, your bike will be much slower. - It makes a lot of difference.
HAVE FUN !

I make my own needle jets out of brass hex, using a mix of metric and number drills to get the sizes. You need to go in half thou steps.
The common methanol needle jet at 12 ro 1 comp. is 0.120 . At 9 to 1 comp. , mine are 0.1165 . I started with 0.117 because I knew the size from experience. My needles are 6D Mikuni.

That is a really slick looking outfit. Anyone have any links to more technical details? I couldn't find anything by searching.

Ken

Lineslinger said:

Monster is right. That CR combined with a methanol/02 charge? That is getting into top fuel drag racing formulas.
I wouldn't want to be hanging onto that beast if it decides to let go...Impressive that all the parts are still attached.
Nice work to make it work.

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Last I heard it had 97 races and counting on the same light domed pistons. But he did lose a set of cases when the cylinder through bolts snapped.
He's using Tri-Fluted ARP bolts now.

It's an impressive setup. Looks like or is the one you posted info about a while ago.

Are the fluted APR through bolts yours or just similar to yours?

I've got your ARP through bolts in the Molnar barrels. Not even a hint of a leak at the base, but I lowered the compression to around 9.5:1 from a little over 10:1. I can't imagine 15:1. Could just be my limited imagination though.

I’m running JS Tri fluted ARP head fasteners on a 1007. Good stuff.

Schwany said:

It's an impressive setup. Looks like or is the one you posted info about a while ago.

Are the fluted APR through bolts yours or just similar to yours?

I've got your ARP through bolts in the Molnar barrels. Not even a hint of a leak at the base, but I lowered the compression to around 9.5:1 from a little over 10:1. I can't imagine 15:1. Could just be my limited imagination though.

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I agree, it is our imagination. In particular, I can't imagine starting a motor with 15:1 compression!!

I also can't imagine keeping the head joint sealed for any length of time at that compression, especially for racing. The stock Norton setup likes to let go at 8.5 to 1 cr and sustained 6200 rpm. My 850 lasted about 20 minutes at that rpm and then the studs pulled out, oil everywhere.
This engine must use some tricks that I'm not aware of.
Big bronze inserts likely help.

Glen

When I was racing, my engine was running a measured 11.3 to 1 compression. Used Turbo Blue race gas, 110 leaded IIRC. I just used the standard head and cylinder hardware with no problems for years. Still being used as a LSR bike occasionally.

Running at a higher pressure causes jetting and ignition timing to be altered. The power result is probably not much different from running at a lower pressure. If you use more fuel, theoretically you should get more power, but what happens in pratice might not meet the theoretical expectations. Petrol has almost twice the calorific value of methanol. I suggest the problem with petrol lies in getting the jetting close enough to the optimum. With methanol half a thou of in inch in needle jet ID, is the difference between fast and slow - with petrol, that difference becomes a quarter of a thou. With normal carbs on petrol, the only way to achieve that might be to calibrate the needle jets usuing a gas flow-meter and a jeweller's reamer. If you are using wide ratio gears, the drop in revs at each gear change causes more throttle to be used, so quick taper needles richen the mixture more than might be lovable.
I only use Mikuni needles.
Manx Nortons had sodium cooled exhaust valves. Methanol runs cooler and has unlimited antiknock.

Steve A - yes they are my triangular bolt fluted on 3 sides so they stretch instead of pulling out the threads.

Worntorn - Yes some kind of inserts, hopefully steel time inserts. Triangular shank (reduced waist) so they can stretch throughout the bolts length like a rod bolt - evening out the stress and tension so its more linear from hot to cold - especially important for the head studs.

Many years ago I remember reading about English grass track side car racers running 12:1 C.R. on Methanol. Don't know the details.

My brother currently has about 3 speedway Vincents at home, they are all probably on 12 to 1 comp. ratio with methanol. In Australia, that used be normal for both speedway and road racing. Most people never bothered to find out what methanol was like at low compression. The only way I ever found out, was I ran a Triumph 650 on methanol a 7 to 1 comp. with race cams. It was quicker than many. In the old days, most of us got our tuning tips from 'Tuning For Speed'. Phil Irving said things in ways which lead to misinterpretation.
He said ' if methanol is run rich , it still gives good power'. He was correct, but that does not mean we should run methanol rich.

JIm, If you are going to put one of your motors on methanol, would you please do something for me. Before you raise the comression ratio get the motor going on methanol as well as you can at low comp. Then after you have raised the comp. ratio, do the same. I would really like to know if there is a substantial power difference in raising the comp.ratio.

acotrel said:

Running at a higher pressure causes jetting and ignition timing to be altered. The power result is probably not much different from running at a lower pressure. If you use more fuel, theoretically you should get more power, but what happens in pratice might not meet the theoretical expectations. Petrol has almost twice the calorific value of methanol. I suggest the problem with petrol lies in getting the jetting close enough to the optimum. With methanol half a thou of in inch in needle jet ID, is the difference between fast and slow - with petrol, that difference becomes a quarter of a thou. With normal carbs on petrol, the only way to achieve that might be to calibrate the needle jets usuing a gas flow-meter and a jeweller's reamer. If you are using wide ratio gears, the drop in revs at each gear change causes more throttle to be used, so quick taper needles richen the mixture more than might be lovable.
I only use Mikuni needles.
Manx Nortons had sodium cooled exhaust valves. Methanol runs cooler and has unlimited antiknock.

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It absolutely amazes me that you deny the irrefutable proof that increased compression makes more torque and thus more power across the RPM
range. Yes there are limits, but cam timing can reduce cylinder pressure at low RPM that is more than made up for from midrange on up. Increased compression is a win/win in that it not only increases power but also fuel economy. Why are modern car engines running over 11:1 static compression? The answer lies above. Granted, these high CR engines benefit from sophisticated fuel and ignition timing management, but there are still ways to mitigate pre-ignition in our primitive air cooled engines. My 10.1:1 static compression (7.4:1 dynamic compression) 850 engine is easier to start and so far has not exhibited any tendencies to spark knock under normal riding even when accelerating at WOT.

I like a bit of a compression bump as well. The calculators such as the Wallace racing calcs are based on a large number of actual dyno results.
According to the calculators, increasing compression helps but the benefit is on a diminishing scale as you go higher and higher.
For example, an 8.5 to one 50 bhp engine will increase to 51 bhp if the cr is boosted to 10 to 1.
Boosting further from 10 to one up to 11.5 to 1, the same size cr increase, raises output by an even smaller amount, giving 51.6 bhp.

When you get up around 15 to 1 adding a point of cr has negligible effect, according to these calculators, ( again, based on dyno results, not seat of pants)
Less and less of the cr is retained as ring blowby increases. One other factor is that more kinetic energy is used in compressing the mixture at these higher numbers.

10 to 1 seems to be working OK with my 920 and that is with the stock cam, which I would expect will be more likely to encourage pinking than a longer duration " hot" cam.
I have not yet taken it into the mountains on a hot day, that will be the acid test!

Glen