FrontEngineDragsters.Org Forum
Technical => Spud Miller's Cave => Topic started by: FEDNV on February 10, 2016, 04:48:29 PM
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First let me start by saying I have a BBC 565, with around 15:1 compression and currently running around 38 degrees and car is running good and have good heat on the plugs.
I have read on another site that a lot of guys with my similar setup are running as low 30 degrees but most in the 32-34 range, but others say you need to run more timing with injected alcohol than with gas.
I know there are a lot of variables such as the cam and compression but what are your thoughts or findings on this? Is there a general rule or just tune your car to what it likes?
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Bottom line is that I would give it what it likes and no more. Run the least amount of timing you have to for the best performance. It's pretty typical that a Chevy on methanol likes about 38 degrees.
Gas is a dry mixture, is very easy to light and fast burning so less timing is needed. Also, it detonates much easier and ignition timing aggravates that.
I'd just keep doing what you're doing :)
Spud
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I never ran that much compression but on my 14-1 SBC I ran the same timing. Probably ran to much timing on gas....
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38 degrees on 15:1 methanol 467 BBC and 38 degrees on 505 BBC on 30%. Never ran gas on a big block.
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Thanks so much for the info, love this site and the quality input compared to some of the other sites.
Guess we will just keep doing what we are doing.
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I have not raced a BBC since my blown gas dual engine Top Gas Dragster in 1972, but what I've learned racing my SBC NA on alky is timing seems to depend on combustion camber design. My 23° raised runner iron SBC likes 29° to 34° [ racing at 4400'] mostly I run 30°. Now other racers run different timing, like 36-38° for non-raised runner 23° iron heads. I helped a Jrfuel team at Bowling Green once where the grains of water where 154, so to try and keep up to the changes of water in the air I keep adding timing, and at 44° and still no signs of enough heat on the plugs on his non-RR SBC, you can't burn water. Now this is all about trying to run faster, not racing index where racers are running a set ET.
I agree with Spud, run the timing your motor wants. Read your spark plugs, I perfer reading cad plated NGK, because the NGK's will burn off some of the plating, and discolor the ground strap. I also make sure I have at least one new plug for each run, when I'm looking for changes. If the weather has not changed and i'm running the same tune-up I'll keep the same plugs in her for a few runs. When i've had racers ask about tune-ups, I recommend they run one new plug every run, that way you can see whats going on with your tune up. What I suggest is put a new plug in #1 cylinder for the 1'st run on the week-end #2 cylinder in the second run, etc. If i'm looking for signs of timing I look close at the ground strap, ie discolored all the way to the base of the plug, but also looking for signs of detination ie black or silver spots. When I do run into spots i'll either back off on the timing or change the tune-up to run richer.
Keep in mind I'm always trying to run as quick as I can in my all iron SBC, and my early all iron early Hemi, running low 7.0's and high 6's on alky. That's with the 400 ci SBC running over 10,000 rpm, but not that high with the 409ci Hemi.
BTW, I have also learned the alky burns better with engine temps at 180° to 200° at the start line, with a water filled SBC, and 150-160° with the block filled Hemi. Alky burns better when hot. Thats why I don't get anybody running a cooling systems when burning Alky.
I hope this helps.
Jon, 805-444-4489
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SBC Chevy heads (ALU) when a blower is used bennifit from water cooling in the heads(only) to stabilize temps in the area between the 2 center exhaust valves.
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On my SBC I was told to run it at 38* and it ran okay. I even tried it as high as 41* timing and did not have any problems. but when I put it on the dyno we found it liked 28* and it was easier on motor to. Most of the information out there for my heads still says 36* to 38* timing and that is way too much. It only picked up about 10 Hp if I remember right when we dropped it to 28* but it came in earlier and stayed later and easier on motor to. That may not be enough to tell a difference on the track but it could mean the difference between hurting parts.
I think many people are running way more timing than actually needed. The best way to know for sure is dyno it, you can find out best timing and get your fuel curve perfect in half a day and a few hundred dollars. That would take you thousands of dollars and a month of track tuning assuming you did not hurt anything.