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Old 01-17-2013, 04:31 PM
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Originally Posted by F-BIRD'88 View Post

Your cr counds out the 11.48:1 but I have reservations on some of the stuff.
Like how you got valve to piston clearance with a tiny single valve relief of 1 cc.
Some of it seems od to me..

Any idea on the fuel specs beyond "98 octane" rated.

Here , our fuel is rated as a average of the two different bench tests.
R and M... Motor octane is always lower and emulates a engine more accorratly under load in the car.

We do have a 98 octane R+M/2 pump gas here at some limited gas stations.
Sunoco GT-98. It generally is good for a 11.5 to 12.5:1cr engine if the tune and conditions are good. It is not readily available.
Here we also have a 100 R+M/2 octane unleaded sold at very limited locations some stations.
Delta Sonic---- it is Sunoco GT-100 sold as "CAM2" Its good stuff.

Our 94 octane premimum is quite good. I cannot tell you the absolute cr limit.
Some people get in trouble around 10.00:1 some have better luck with a bit more cr up to around 11:1. Beyond that it is real hit and miss. Depending on daily conditions and tune up.

many many stations in the US in particular sell very inconsistant fuel quality and octane. Many epople have touble even at les than a 10:1 ratio their local pump premimum gas. Especially in the Mid West states.

I do know that your fuel is rated differently than ours. And that generally the European fuel and oil quality standards are higher
than North America.

Having been there done that... I always warn people to take all this DCR stuff with a grain of salt when planning a engine build for pump gas for true street driven use.

Had a friend here that bought into the DCR stuff hook line and sinker and even after ignoring my warning and explaination of the hows and whys,,, destroyed two perfectly good 350's @ 10.70:1 cr. What happended was exactly what I predicted would happen. We rebuilt them with 9.8:1 and all was good..

I built on a t 12.65:1 with plenty of cam etc etc.. it went fine for a while on 94 with conservative (reduced) timing, but really liked and wanted 110 unleaded.
Came unglued on me one day when I forgot to reduce the timing for 94 pump gas use. Never heard a thing.
Broke a ring land. But it was fun. ( On this one I knew perfectly well that the 94 octane fuel was not going to be enough for this engine so no surprise) Like said it really liked and need the 110 octane unleaded. Went like a raped ape....

I suggest you tread lightly on it with pump gas. (watch the water and engine air inlet temperature)
stay off the throttle or reduce the timing a bit if when conditions are not optimum.
As the engine ages the octane requirement will go up. (carbon buildup- oil consumption, deposits in the combustion chamber)

Do you have any way to detect detonation @ WOT? "engine ears" or a knock detector?
I built my own amplified "engine ears" for under $50. Unfortulatly on that day I smoked that 350 I did not have my "ears" on.
F'BIRD-88, thank you for that advice. I'm working away from home ATM so I can't check my notes, but from memory, I think I had .080" inlet and .120" exhaust clearance. I'll check my notes ( if I can find them, I couldn't find them last time I looked) when I get home and post the specs.
Lift is .525" by the cam card, once again I'll have to find my notes to see what the actual lift is with my 1.5:1 scorpion rockers, I think it might have been a tad more.*
*I was always puzzled by the octane ratings between AUS and USA until I noticed in one of your posts that we use RON here and you use R+M / 2
and that cleared it up for me quite a bit. The fly cuts are quite minimal in my pistons. The diameters are not much more than necessary to clear the valve. 1cc pretty much covers it in terms of volume.*
I positively HATE detonation. I hammered an engine to death many years ago. I cannot detect and pinging with this engine, that is that's audible to my ears. I like the sound of that amplifier that you built. I would hate to think I was having detonation issues without knowing about it!
Don't know much more about the 98 octane fuel that I'm using except that it's caltex and that I get it from a high turnover gas station that all the gear heads here say has the best gas*
I can get 100octane, but it contains ethanol and my old ****box has steel tank and lines etc, so no good for me.*
Compression gauge shows bang on 200psi per cyl. Actually one is 198 and one is 203 the rest 200psi
I'll post again when I get home.*

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