setup for avgas needed

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fred
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setup for avgas needed

Post by fred »

poped up to kemble tower today to see if i can get any avgas .which i can.i'le be having the barrels of and rebuilding with the best matching barrels and pistons i have.standard head.going the 2 f3 + 2 standard valves setup. Is it mainly just with the jetting so i can go down a few sizes ? It wont be mixed with pump fuel apart from whats in the float bowls
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JanBros
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Post by JanBros »

I don't understand this : you are going to run a standard engine with full avgas ? what's the point ? what benefit's/gains ? I only see trouble ...
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fred
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Post by fred »

it aint standard yan .and you did'nt answer the question .rate can i run a motor at a event then change jetting for everyday use? Only building it for a sprint .
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scooble
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Post by scooble »

so has the CR been raised?
Luders
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Post by Luders »

Fred the problem here is you started by saying the head is standard.

It doesn't matter what flow or port work has been done on the engine, if you haven't raised the compression ratio and set your squish, it's as good as a standard motor for the purposes of running avgas which is what Jan means and sees.

In answer to your question and based on my experience, you can normally get away with being a jet size too lean running on avgas, probably because of the lead content.

This is the difference when racing of having a blown motor and not though and if you're not racing I would not advise leaning your mixture down to the degree to which we do.

In this case it's probably best for you to tell us what you were hoping or trying to achieve.
fred
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Post by fred »

ahh ,i see now . The head thats on there at the mo has been skimmed.and i have 3 heads on the bench.2 with damage that i can machine. I can make a flycutter for the mill to reprofile the squish (1/2 a degree more than the angle at the edge of the piston) then skim the head .ile have a look for recomended cchamber volumes.
If i can't set the engine up to run on blue avgas ,then another day run on pump fuel i wont bother,i was just looking for a easy gain in performance
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Post by Luders »

If you are running a higher compression ratio and set a larger squish band at around 0.7, that should give you the performance gain.

The avgas is then a requirement, because you are asking more from the motor and the only thing we gain from running avgas is to help the longevity of the motor, not soley for performance.
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Post by dave32 »

For what its worth,
As i have to run Avgas (100pc) on my TZ and RS,so already have it,ive run it on my KR and RG5 when im at a trackday,
Both engines are tuned but not specifically modded for leaded/AV (they run fine on superunleaded).
You WONT cause any harm running AV (straight) but i found NO noticeable GAIN or LOSS in performance,the only change needed was in the mid range (i had to lean the needle a clip) as the AV made it run a bit richer out of slow corners (the main/top end was fine).
what i would say is that i managed well over 10 trackdays in a year and what had to be over a thousand road miles and still the pistons were in good condition,for some reason parts were more lubricated upon stripdown whereas when ive had to run Unleaded (with the same oil and mix) parts were noticeably "dry".
The head on the KR is fairly standard and squish is a very conservative 1mm,im pretty sure going from what i run on the TZ and RS you could reduce this to 0.7 and have better performance.
Interestingly when i recently stripped another one of my B2's down the other week that has had alot of work done (not by myself) the squish was 0.6 one side and 0.75 the other,turns out the new Mitaka pistons have varying crown height.
This engine was used at Mallory and Donnington last year and ran straight super unleaded,no sign of detonation and it ran great but a noticeable difference in piston crown deposits.
So IMO if you want to run AV then its fine,but dont drop MJ sizes before determining that you actually NEED to,best just start off with the stock unleaded setup THEN change anything if its running rich,you cant guess jetting.
HTH
ATB
Dave
OH and a very good oil to use would either be ELF HTX 906 or castrol A747.
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Post by fred »

cheers for all the info i realy appreciate it as what i thought was way off the mark :oops: apologies jan
so when people run pump and avgas mixes is it more of a protective measure :?:
rebuilt today ,just changed the pistons for the best i have at the mo (mitaka)
got the squish from .68 to .77 and did a quick compression test straight away even tho it was cold ,both barrels even but need to calibrate n check this tester i rigged up once i get to grips with it ,will warm it up a few times tomoro when ime doing brake seals ,go for a run then check again
Image
oil wise the motul 800 is nearly used up,on pump in the cold it`s doing its job
are ELF HTX 906 or castrol A747 ok on pump :?:
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Post by Luders »

A747 is definitely not pump suitable.
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JanBros
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Post by JanBros »

fred wrote:cheers for all the info i realy appreciate it as what i thought was way off the mark :oops: apologies jan
not accepted for little stupid misunderstandings like this :lol: :wink:
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Post by dave32 »

No NEITHER of them oils i mentioned would be suited to the pump,i had the feeling you were running a race bike/track use setup in which case you would be running premix.
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Post by TwoStroke Institute »

In warn climates/weather castor/synthetics are fine to run through oil pumps. Heard of quite a few people doing this in summer in Europe. They buy another oil tank to use.
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