the devil within......
11-28-2002, 09:25 PM
#11
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Originally posted by WETTE VETTE
Detonation!!! 9.9 to 1 compression with iron heads is gettin up there. Unless you are running a long cam and a fat A/F mixture my guess is even 93 octane is borderline. 32 degrees is fine if not a little low as far as ignition. What are your cranking cylinder pressures? Did you see any signs of small aluminum beads on the porcelins of your spark plugs when you were dialing in your motor? What are you running for spark plugs? On that motor MR43T plugs will burn real clean, but are really a little on the hot side which can lead to the big "D". My dad's 11:1 compression 355 was getting into light detonation on 110 octane fuel and we went to NGK R5673-8 spark plugs and haven't seen an aluminum bead on the porcelins since. If you still have the plugs take them to a good race shop and have them look at them umder some magnification to further analyze them. My guess is detonation.
It happens and thats racing!!!
Detonation!!! 9.9 to 1 compression with iron heads is gettin up there. Unless you are running a long cam and a fat A/F mixture my guess is even 93 octane is borderline. 32 degrees is fine if not a little low as far as ignition. What are your cranking cylinder pressures? Did you see any signs of small aluminum beads on the porcelins of your spark plugs when you were dialing in your motor? What are you running for spark plugs? On that motor MR43T plugs will burn real clean, but are really a little on the hot side which can lead to the big "D". My dad's 11:1 compression 355 was getting into light detonation on 110 octane fuel and we went to NGK R5673-8 spark plugs and haven't seen an aluminum bead on the porcelins since. If you still have the plugs take them to a good race shop and have them look at them umder some magnification to further analyze them. My guess is detonation.
It happens and thats racing!!!
Thanks for your help bro..
Travis
Last edited by traviss; 11-29-2002 at 08:11 AM.
11-28-2002, 09:27 PM
#12
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Originally posted by mopower
OK, The light just went on
. My buddy DID detonate a piston last year about an hour after we first took it out
.
Like you Trav , he only changed ONE piston
...I'll bet you this one was damaged but not visible
. The bad one was #4 last time so we could see it (same bank) when we had the head off. Maybe it would be a good idea to change the rest of them just in case
OK, The light just went on
. My buddy DID detonate a piston last year about an hour after we first took it out . Like you Trav , he only changed ONE piston
...I'll bet you this one was damaged but not visible . The bad one was #4 last time so we could see it (same bank) when we had the head off. Maybe it would be a good idea to change the rest of them just in case
Yes I think it was damaged at the same time, but we didn't take that head off. I am changing to a whole new setup so new pistons are a must
Travis
11-29-2002, 09:37 AM
#13
Wasn't the old theory on compression versus octane level 1:1.....and by that I mean, if you run 89 octane fuel, you cannot run higher than 8.9:1...or 93 octane....9.3:1
This theory has been around a long time and only with aluminum heads were you supposed to be able to go over those formulas but only by a tiny bit....Especially with the stress that the marine environment puts on engine components
This theory has been around a long time and only with aluminum heads were you supposed to be able to go over those formulas but only by a tiny bit....Especially with the stress that the marine environment puts on engine components
11-29-2002, 12:22 PM
#14
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Travis, just something to ponder. My 13:1 compression 496 has a cranking compression from 180 to 185. I run 110 octane leaded racing fuel. MY dads 11.25 compression 355 cranks at 190 to 195 and he runs 110 octane racing fuel. His cam is a solid roller with 246/254 at .050 and .565" lift on a 112+4. My opinion is if you want to run pump gas cylinder pressures should be no more than 175, and 155 to 165 is a nice number. Run a longer cam that bleeds it down a little and twist it 6000 RPM. My dads Alpha SS has been hammered on for the past 7 years which includes many nitrous blasts at 6500+ RPM with no problems and 6000 RPM is nothing for a forged component 4 bolt small block.
Later!
Later!
11-29-2002, 12:25 PM
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Originally posted by traviss
Yes I think it was damaged at the same time, but we didn't take that head off. I am changing to a whole new setup so new pistons are a must
Travis
Yes I think it was damaged at the same time, but we didn't take that head off. I am changing to a whole new setup so new pistons are a must
Travis
11-29-2002, 12:36 PM
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Geeter-B. Thats a theory we have never heard, but its nice to know it now
Wette vette.... We new it was on the ragged edge of just being to much, I just needed it to get me throught the season and that it did The new setup has aluminum heads and I think comp. ratio is gonna be around 9.5-9.7 this time. The only thing I am gonna use from this motor is crank, rods, roller rockers. Everything else is gonna be new again...
Hyperbaja.. Acutally I have 7 good ones.. But you don't want anything to do with these pistons LOL! They have had the life reamed outta them in onlya few months But they did the job
Talk to you guys ina few days Heading up north ..
Travis
Wette vette.... We new it was on the ragged edge of just being to much, I just needed it to get me throught the season and that it did
The new setup has aluminum heads and I think comp. ratio is gonna be around 9.5-9.7 this time. The only thing I am gonna use from this motor is crank, rods, roller rockers. Everything else is gonna be new again...Hyperbaja.. Acutally I have 7 good ones.. But you don't want anything to do with these pistons LOL! They have had the life reamed outta them in onlya few months
But they did the job Talk to you guys ina few days Heading up north ..
Travis
11-29-2002, 03:23 PM
#17
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travis,
was the failure in the same "hole" as the
one in july?
i'm on the DETONATION bandwagon too,
but curious if this the cyl. that failed before.
other 7 ok, if so, maybe a cooling issue pertaining to
that region?????
just curious.
jt
was the failure in the same "hole" as the
one in july?
i'm on the DETONATION bandwagon too,
but curious if this the cyl. that failed before.
other 7 ok, if so, maybe a cooling issue pertaining to
that region?????
just curious.
jt
11-30-2002, 11:57 AM
#18
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The piston in july was #1.. and get this the next broken one was in #2. Our buddie thought it was cooling issue, but it was never overheated and runs around 145--150 degrees. I was wondering if some how air was trapped or something..
Travis
Travis
