Questions about C/R and ignition timing for high octane fuel.

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Knotical

Knotical

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Howdy everyone, when running high octane fuels on these engines, do y'all have a method for advancing ignition timing or are you simply increasing compression ratios?

I've got a secondhand 5T 2.0 with a bad G320 that I'm looking to rebuild. I have 100 and 110 octane available without too much issue. I see thinner copper head gaskets online calling for 95+ octane, but if there's timing adjustments I could use to either utilize the available octane I'd love to hear about it.

Not necessarily interested in the cost effectiveness of this, I just love tinkering with engines and am curious about the options out there.

Thanks!
 
I'll give you my two cents. Higher octane fuel used in an engine that does not have the compression to support it does nothing to help performance ; it actually makes less power. Sounds strange but it is true.

Timing can be set anywhere you want , just remove the flywheel key and throw it over your shoulder. Despite what some may tell you the key is there for alignment only and not to keep the flywheel from rotating. A proper fitting flywheel that is lapped to the crankshaft with a properly torqued nut is all you need.

Yes you can run a thinner base gasket or even delete it but keep in mind this also alters port timing.

Save your money on expensive race gas . A good non ethanol fuel around 94-95 octane rating is all you need.
 
Agree 100 % .Can't see any reason to alter timing especially with a basic stock engine. Have a bartalone pipe on mine and in my opinion more than adequate!!!! Proper 2 stroke mix and carb adjustments will bring much performance out of that engine. I run maxima castor 927 and a bit of vp racing madative . Use same jug of fuel for 5t and 2 raminators ,one with taylor 5o. All trucks usually pop after 2 pulls with choke on and fire 2nd pull with choke off. Don't think I ever touched carbs except for initial idle speed adjustments. If it ain't broke don't fix it......... k.i.s.s. principal, keep it simple stupid , has gotten me a long way.......
 
Most of us playing with ignition timing are also playing with different cylinder heads which means the coil is bolted to a custom bracket or the fan cover. TS used to make an adjustable fan cover coil mount, they can still be found used, but expect to pay a premium.

I do not recommend running no key because I've sheared a flywheel key before. Although in smokinwheel's defense, the flywheel nut could've used some loctite, and the coil also came loose and hit the flywheel .

Alternatively You can get an offset key for mini-bikes and grind them to fit or machine the flywheel.

You can also change the heat range and the resistance of the ignition system through resistive wires and different spark plugs.
 
Higher octane fuel won't yield more power output for all the reasons stated above - because our 2 stroke engines don't have variable timing or knock sensors.

Higher octane fuel takes more compression before it explodes. This is desirable in high compression race engines that can exploit this higher compression and prevent detonation by the use of knock sensors and change the timing accordingly.

In the UK, our petrol is E10 - it's 10% ethanol and a bit crap. It's 95 Ron and equates to US Pump 91

Screenshot_20250306-063942.webp

E10 with it's alcohol content is not great for our engines or the carbs unless they have newer alcohol resistant bulbs and o-rings.

Using the higher octane version of fuel, such as V-Power, or Premium 99 - has the distinct advantages of a) containing less ethanol and b) has detergents for keeping engines cleaner. I only use this fuel for my Baja 5B. Not for performance necessarily, but for longevity.

25:1 is often the recommendation for 2 stroke and in my experience this is far too oily.

32:1 is a much better choice on decent 2 stroke oil. I use Silkolene Pro 2.

My Baja 5B on 18 year old CY Fuelie 26cc Engine:

Screenshot_20240714-174211.webp

0-40mph:

Screenshot_20240714-174628.webp

Whilst this is purely my personal preference/opinion, I believe my experience and results lend some weight to it. My engine porting experience is limited to nitro and whilst I have improved my CY engine, I haven't attacked it with a Dremel (yet!). 😅

It's still good for 19300rpm. Part of this surprising longevity I put down to the 'right' fuel choices.

PXL_20250518_151438111.MP.webp
 
Thanks for the replies guys. I think I'll start with getting the thing rebuilt and running with a decent pipe for now. I found an old comment from DDM when the G320 first came out saying they weren't really seeing gains from advanced timing anyway.
 
I kind of understand the science behind why there is no real power advantage in running high octane race fuel in these little motors, although it is above my pay scale. But come on!! CAM2 or VP smells so good, thats got to be worth a few hp..🤪
 
Since this state has no pump gas without corn fuel in it I went to VP small engine fuel, it is 94 octane with no alcohol. I run this fuel in all my 2 stroke stuff.
 
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