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Author
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Topic: How much difference could 4・make??
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 04-06-2002 11:01 PM
   
What would advancing the timing in a 500hp cleveland from 34・total to 38・total mean in HP??Paul
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Mpcoluv
Gearhead Posts: 1341
From: Charlotte NC usa
Registered: Apr 2001
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posted 04-07-2002 09:22 AM
quote:
Originally posted by Clevo377:
What would advancing the timing in a 500hp cleveland from 34・total to 38・total mean in HP??Paul
It could mean quite a lot. I know a guy who has an Aussie headed 400M in a ranchero. He picked up over 20HP with a 4 degree bump in timing. I just can't remember the exact timing figures however.
Why not try it?
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kid vishus
Gearhead Posts: 6590
From: middle of NC
Registered: Oct 2000
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posted 04-07-2002 09:49 AM
I'm not sure the actual amount it would make, but I do know it all depends on flame travel, burn rate, basically the efficiency of the combustion chamber. On my motor, I run 42* most of the time, and there's a big difference when compared ot 38*. Even when the motor was on gas, it ran better with around 42* of timing in it. I'm not suggesting you go that high, but 34* seems awfully low to me for a cleveland.
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 04-08-2002 01:05 AM
Thanks guys, I had the timing set at 10・(34 total) initially just to make sure there was no detination. Didn't have time to do any extra dyno runs with timing set higher so I was just wondering what to have expected. I have been running on avgas till now but now want to switch to pump gas. Our leaded pump gas here is 96 octane and you can get 98 octane unleaded. The avgas is only just over 100 and leaves a chalky paste residue in the carb??. So I want to stop using it. Do you think 11.9:1 compression is too high for 98 octane and 38・total?? Paul
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the last dive
Gearhead Posts: 147
From: sydney australia
Registered: Dec 2001
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posted 04-08-2002 07:48 AM
clevo.......im have a347 with 10.1comp and everybody i spoke to said 10.1is the limit for optimax and the the other 98 octane fuels i know a guy with a 393 clevo running 11.1 he has to run additives all the time
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 04-08-2002 06:52 PM
It seems to depend alot on heads, cam etc. I'll just have to give it a try!Thanks Paul
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 04-09-2002 11:20 PM
Was talking to the guy that did the welding on my heads and he said to stay away from Optimax. Apparently Shell is having trouble with it at the moment. Their is also a rumour that they are bringing out a 100 octane fuel at the pumps.Currently running a mix of 30% avgas 70% 96 octane (premium unleaded) at 38・- seems ok. When that runs out I'll try 100% 98 octane (Mobil) at 38・total. Paul
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Ron
Gearhead Posts: 137
From: Newcastle, Wa.
Registered: Feb 2002
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posted 04-10-2002 12:31 AM
Paul, 10 degree initial is way too low!
I would start out at 14 with 12 in the distributor.
You should be happy to have that high of pump gas where you live and I would not mix that one bit. you are not even gaining one point.
don't run avgas, its not formulated for automobile engines.The highest pump gas I can get here is 92, even with mixing that with VP I'm only gaining about 3-4 octane.
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 04-10-2002 01:24 AM
Ron, I was only running avgas initially to ensure there was no detination. Now I have a few miles under my belt I'm going onto pump. The reason I'm running a mix at the moment is just because there was some avgas left in the tank.
 Paul
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Alex
Gearhead Posts: 148
From: Melbourne, Vic, Australia
Registered: Jun 99
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posted 04-10-2002 02:28 AM
Paul,Our octane ratings are the RON scale, not the MON (?) scale used in the US. I think Optimax 98 RON is about what they call 92 in the US. I've got a 351 with 302C heads with just on 11:1 CR and a mild cam (222 intake) and can't go much higher than 30 degrees (crank). I've tried shell 100 and didn't find it much better (is illegal for street use now anyway??). Can't you wind it up 'till it rattles then back it up a little?
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 04-10-2002 08:23 AM
CAlex, that's what I'll end up doing. Did some reading and the US numbers are RON+MON/2. So our 96 is about equivelant to their 92.I've got 11.9:1 and 250・on the intake so I'm hoping I can get away with 98RON but if I have to add a booster then I will. It's only a weekend car anyway. Paul [This message has been edited by Clevo377 (edited 04-10-2002).]
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n2oMike
Gearhead Posts: 2831
From: Spencer, WV
Registered: Jan 2001
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posted 04-10-2002 08:52 AM
There's nothing wrong with Av-gas. It works just fine in engines that MUST be reliable (because breakdowns are deadly) and will power a hotrod around just fine. Engine dependability is NOT a concern with av-gas.That being said, Av-gas is not race gas. It is blended diefferently. BUT, neither is automotive pump fuel... and av-gas is 100 octane leaded. I've run TONS of it in the mustang, and in my tow vehicle. My tow vehicle likes to 'ping' under load, and long hauls towing the mustangs on hills are tough. BUT, adding five gallons of av-gas to each tank cures all problems. The mustang runs just fine on pump premium, but I'll often add a bit to the tank for the valve seats. (lead) As for cost... around here it costs around $2.00 a gallon, which isn't much more than pump premium. Small, local airports are the best place to get it. Most are happy to serve you, as long as you don't drag them out to the pump for 2-3 gallons. Be respectful and fill up at least a couple five gallon jugs. The guy at the local airport says he sells all kinds of it to the local dirt track racers, muscle car owners and Harley riders. It seems old shovelheads really like the stuff. It doesn't vaporize quite as easily as automotive pump fuel, (you don't want a vapor lock at 10,000ft) but this is not a problem in the summer. It -may- make the engine a little harder to start in very cold weather, but I've never had a problem with it. Blending with pump gas eliminates this potential problem entirely. If you run it straight, (and are extremely picky about the tune) jetting up one or two sizes may be beneficial. But for most cars, a 5 gallon jug (less, usually) per tank is more than enough for 'ping free' cruising. No rejetting required. I run straight race gas at the track (nitrous) but av-gas is a GREAT (and cheap) alternative for ping-free cruising on the street. I've got eight five gallon jugs, and make a couple trips a year to the airport to re-supply. Good Luck! ------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220 [This message has been edited by n2oMike (edited 04-10-2002).]
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 04-10-2002 07:28 PM
Mike, do you know anything about a chalky looking paste that builds up in the carb bowls when on straight avgas??Paul
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n2oMike
Gearhead Posts: 2831
From: Spencer, WV
Registered: Jan 2001
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posted 04-10-2002 08:12 PM
Never had a problem with that before... Never even heard of it.  Av-gas is some of the most precise fuel out there. The range of it's blended molecules is a lot tighter than auto fuel. It also lasts a lot longer without going 'stale'. ------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 04-10-2002 09:20 PM
A while ago we had some problems with our avgas. Perhaps this buildup is the remnents of that??Thanks for the info Paul
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