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  1. #16
    casual poster JaseQ314's Avatar
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    Quote Originally Posted by EH179 View Post
    I have information from BP stating that 10:1 is the highest we should run on BP 98...howboutdat!
    The funny thing is some standard engines these days have that or more on regular unleaded. The original LS1's were around 10.2-1, the later stuff up as high as 10.7-1 from memory.

  2. #17
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    If I have learned one thing in this hobby it is that some engines can run 10+ CR all day on 98 & others with lower CRs will detonate on 98.

    Many factors seem to be involved: quench distance, engine's cooling system, does it have cold air induction,cam specs, are the exh overs blocked...& probably a few other things like mixture atomisation, even the oiling system. A friend was getting detonation with a 9.5:1 455 Pontiac. Tried various fixes; what finally fixed it was an engine oil cooler.

    Back to the reason I started this thread. Checked with the owner & the heads are the 58cc chamber version & the pistons are flat tops for a 347, 4.030 bore, 3.400" stroke. So CR should be ~ 10.5:1.

    So what should the total timing be at WOT? I am guessing, in the 28-34* range.

  3. #18
    Do you ever leave? EH179's Avatar
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    If it's a true flat top piston, you will be at 11.3:1, so to get ~10.5 the piston needs 6 cc dish.

    With the little Hyd ft cam in there, i would start conservative @ 28-30*

  4. #19
    Do you ever leave? paulzig's Avatar
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    Quote Originally Posted by GtoGeoff View Post
    If I have learned one thing in this hobby it is that some engines can run 10+ CR all day on 98 & others with lower CRs will detonate on 98.

    Many factors seem to be involved: quench distance, engine's cooling system, does it have cold air induction,cam specs, are the exh overs blocked...& probably a few other things like mixture atomisation, even the oiling system. A friend was getting detonation with a 9.5:1 455 Pontiac. Tried various fixes; what finally fixed it was an engine oil cooler.

    Back to the reason I started this thread. Checked with the owner & the heads are the 58cc chamber version & the pistons are flat tops for a 347, 4.030 bore, 3.400" stroke. So CR should be ~ 10.5:1.

    So what should the total timing be at WOT? I am guessing, in the 28-34* range.
    Yeah thats it closer to the higher end...

  5. #20
    Do you ever leave? EH179's Avatar
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    Quote Originally Posted by paulzig View Post
    Yeah thats it closer to the higher end...
    Straight to 34*- you say?

  6. #21
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    Quote Originally Posted by EH179 View Post
    Straight to 34*- you say?
    Yeah, smash it up ... Timing, fuel, RPM my answer to everything... You'd be surprised how many times it fixes issues...

  7. #22
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    Quote Originally Posted by TRIKHQ View Post
    Alot of this depends on engine combo, cam etc, I run 12:1, have 205lb cylinder pressure and run 98 just fine. Duno made 642HP, I got dynamic comp of 8.81.

    Built a 347 Windsor with alloy heads a little while back with 11:01CR. Dynoed fine on 98.

    Cheers
    Yep, fair comment. I probably made a bit of a blanket statement there as there are many variables.
    Iíve got a 355 with 11:1 compression with cast iron heads, yet Iíve got a few mates with alloy headed Holdens and Chevs with over 11:1 running well with no detonation. You can definitely go a bit higher with the alloy heads if needed.

  8. #23
    Do you ever leave? TRIKHQ's Avatar
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    Quote Originally Posted by GtoGeoff View Post
    If I have learned one thing in this hobby it is that some engines can run 10+ CR all day on 98 & others with lower CRs will detonate on 98.

    Many factors seem to be involved: quench distance, engine's cooling system, does it have cold air induction,cam specs, are the exh overs blocked...& probably a few other things like mixture atomisation, even the oiling system. A friend was getting detonation with a 9.5:1 455 Pontiac. Tried various fixes; what finally fixed it was an engine oil cooler.

    Back to the reason I started this thread. Checked with the owner & the heads are the 58cc chamber version & the pistons are flat tops for a 347, 4.030 bore, 3.400" stroke. So CR should be ~ 10.5:1.

    So what should the total timing be at WOT? I am guessing, in the 28-34* range.
    The 347 I did with 11:1 comp went to 28 deg on the dyno, It had just a tad over 200lbs cylinder pressure hyd roller, made 450 HP

  9. #24
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    The pistons have valve reliefs of 6-7cc. Thanks for the replies.

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