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Old 12-04-2004, 11:58 PM
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Please critique this 408

Am rebuilding my 408 again. It will have Scat internally-balanced 3.75 cast crank, Scat 6" I-beam rods, KB 2-valve flat-tops with C&A 1/16" rings, Comp 230/238 .510/.520 hydraulic roller, Summit Engine Shop prepared Sportsman II's (2.05/1.6, 69cc chambers, 200cc intakes matched to a 1205 gasket), Edelbrock Performer RPM gasket-matched to a 1205 gasket, Demon 750VE carb with 14x6 K&N air cleaner, Petronix Flamethrower HEI that be 12 degrees initial and 20 degrees mechanical, Flowtech Afterburner 1 5/8" headers with 3" Flowmaster 40-series mufflers. Behind this will be a TSI 2800-3200 stall into a turbo 350 turning 4.11 gears and 33" tires. I run mostly 150' mud drags and 200' mud bogs that I did very well last year in pretty well the same combo except with stock S/R torquers w/ bigger springs, Weiand X-celerator and TSI 2200-2400 stall. Also if someone has a desktop dyno, could you run this? The only thing I couldn't find was the flow specs on these heads since they are about 7 years old.

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Old 12-05-2004, 12:05 AM
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That will be very similar to my engine combo.

I would run 18o intial and 16 distributor. That is where I am at with mine. I am at 11:1. If I could, I would run even more timing, but my compression won't allow it.
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Old 12-05-2004, 01:03 AM
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I was at one time running 18 degree initial and 15 mechanical but in the last post I had about breaking the ring lands, I had a member say: (Your initial timing was probably a big factor, along with the ring gap, in breaking the ring lands. Try 8-12 degrees intital and 20-24 mechanical. It might help the pistons live a little longer). I am planning to gap the rings at .035 instead of the .019 that the 1st Keith Blacks had. I figured if I went with less initial and more mechanical along with a .002 bigger gap than recommended, I could keep this engine alive a lot longer than 9 months and 2500 miles. I have always used forged pistons before and this is my 1st engine with KB's so not that familiar with them. Just don't want to do this again
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Old 12-05-2004, 01:28 PM
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Apparently KB recommends a larger than usually gap. I have never run them personally. .035 is alot for an NA engine, but will definately not butt together. I dont think that your timing had anything whatsoever to do with the ring lands breaking UNLESS the engine was detonating at part throttle or something.

Chris
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Old 12-05-2004, 03:11 PM
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"Also if someone has a desktop dyno, could you run this?"

Using my non-ported Sportsman II file DD2000 says 398 hp at 4500 and 514 ft-lbs at 2500. The torque curve is almost completely flat until 4000. It says 195 hp and 511 ft-lbs at 2000. It also indicates that the dual plane is better for all RPMs with this combo.
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Old 12-05-2004, 03:26 PM
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Quote:
Originally posted by tornado-tech
I was at one time running 18 degree initial and 15 mechanical but in the last post I had about breaking the ring lands, I had a member say: (Your initial timing was probably a big factor, along with the ring gap, in breaking the ring lands. Try 8-12 degrees intital and 20-24 mechanical. It might help the pistons live a little longer). I am planning to gap the rings at .035 instead of the .019 that the 1st Keith Blacks had. I figured if I went with less initial and more mechanical along with a .002 bigger gap than recommended, I could keep this engine alive a lot longer than 9 months and 2500 miles. I have always used forged pistons before and this is my 1st engine with KB's so not that familiar with them. Just don't want to do this again
That is not the case. The ring land broke because the rings weren't gapped correctly.

If you hear detonation you can reduce the initial a little. But, with moderate compression you can really benefit from higher initial timing.
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Old 12-05-2004, 04:35 PM
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I used this guide to decide on which ring gap to go: http://kb-silvolite.com/article.php?...=read&A_id=32. I thought the towing at .008 or the mud bog at .009 would both work since I do stress the motor so I took the average at .0085. This figure of .0085 times the bore of 4.165 equals .0354 ring gap. Last year I turned appr 5300rpm for about 45 sec-1 minute in mud bogs going through 24"-36" deep pit. I ran 92 octane with a can of 104 octane boost last year and never heard any denotation and that was with 18 initial and 15 mechanical with no vacuum advance.
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Old 12-05-2004, 04:42 PM
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If you are sure there is no detonation, keep your initial high. I wouldn't run an excessive ring gap. Just run what is recommended.

Don't waste your money on the octane boost any more. It is another "snake oil".
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Old 12-05-2004, 05:14 PM
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Ok thanks. I will take your advice and run with my original setting of 18 initial and 15 mechanical. Also Lluciano77, what type of fuel do you run with your compression at 11:1 with the KB's you have? I am looking very hard at mixing 92 octane with Sunoco 110 instead of the 104 boost.
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