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Old 11-25-2009, 09:52 PM
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SBC circle track engine plan.......

We're planning a new "bullet" for next years dirt track(3/8 mile)season.
Need to stay "sorta" legal. The cu. in. rule is 350+60. This is were it gets a little crazy. Thinking about a 400(4.125bore) block with a 327(3.25 stroke)crank. Should equal out to 348+ cu.in. Would a 6" rod(illegal,but..) make a big difference in torque? Anybody got any experience with this set-up? We figured the power of a big bore and the RPM's of a short stroke.No double humps or Vortec heads. We got a set of 040 heads. 1968/327 heads. SUPPOSE to flow like the humps but without the marking! Any suggestions on cam and carb ? How about "covert" work on the heads? Any guess on HP and Torque?
Thanx
6sally6

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Old 11-25-2009, 11:08 PM
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any cam restictions? suppose you ran a 502 cam ? octane restrictions?
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Old 11-26-2009, 05:27 AM
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What does the car weigh? tight or wide corners? Lowest rpm off corner ? max at end of chute? Carb?
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Old 11-26-2009, 07:42 AM
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SBC circle track engine

Quote:
Originally Posted by mean machine
any cam restictions? suppose you ran a 502 cam ? octane restrictions?
Race fuel(110 octane) allowed. Only cam restriction is lift....500.Solids allowed. Car is a 70's Nova weight?? 2800lb. can't remember. Any carb/intake combo! No 6" rods.....no double hump heads....is how they keep the power down, somewhat.They only flow so much. NO Vortec heads. Fairly wide turns....rpms in turns...approx.2000/2500rpm...rpm out approx.6000/6200rpm
Anybody EVER try this combo?!
6sally6
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Old 11-26-2009, 09:09 AM
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At the low rpm you are turning and with the head restriction you will not see the gains that this combo could produce. It only shows it's big bore strengths with a large valve (2.10" or bigger) that are shrouded in a 4" bore block, and real high rpm(8000) at the end of the straight. It only really starts to take off at the rpm you are calling your limit(6000-ish). No sense reinventing the wheel here, it will just cost you more with little to no gain. The money would be better spent on a professionally built carb or into the chassis because of your head restrictions. Thats my 2 cents
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Old 11-26-2009, 01:09 PM
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With those restrictions and that rpm range you could use a 307 block and 400 stroker crank to pump up the torque, jump off the corners, OR just build a 350. Either would be a lot cheaper than a de-stroked 400.
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Old 11-26-2009, 01:37 PM
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I think the loss of some low end could actually benefit the deal- this IS a dirt track. I'm a little surprised that the revs go so low in the turns, I'd expect wheelspin to keep them well up in the band.

Anyway, I would consider building it- but not w/6" rods. Why crap the bed at tear down (if you win, BET YOUR ARSE you'll get protested), the sound alone will have guys wondering w tf is up w/you anyway, don't give them anything that will get you disQ'ed.

BTW, I had a set of the 040's from a '68 327. They are similar to the fuelies, but had 1.94" valves, no acc. holes and pressed studs. Nothing too special about them, IMO.
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Old 11-26-2009, 02:29 PM
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It's been done lotso times. If you went 358 CI, 4.155 and 3.25 stroke, you'll need to turn it at least 9200 to make use of all the RPM potentional. The long rods will hurt lower speed power where most dirt track passing is done, corner entry or off the bottom on corner exit. You'll need 6:50 or :70 gears and that may not be available in you current rear axle configuration too. To get back some of that torque you lost with long rods to save from pulling out he piston pins, you'll need 16 to 17:1 compression and that means more head work then you really want to spend. I don't think you can get your current head chamber that small. 38cc or so. I think you are better off a 355, a name brand carb, and good shocks and tires. Learn to keep the car tighter on the throttle on corner entry with the brakes will get you through the center with more momentum negating the need for more engine.
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Old 11-26-2009, 08:57 PM
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Would the tech man miss the fact that it is a 400 block? I realize you are speaking of cubic inches but I am sure the rule states 350 and not a destroked 400.
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Old 11-27-2009, 09:41 AM
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SBC Circle Track Engine.......

Quote:
Originally Posted by cobalt327
I think the loss of some low end could actually benefit the deal- this IS a dirt track. I'm a little surprised that the revs go so low in the turns, I'd expect wheelspin to keep them well up in the band.

Anyway, I would consider building it- but not w/6" rods. Why crap the bed at tear down (if you win, BET YOUR ARSE you'll get protested), the sound alone will have guys wondering w tf is up w/you anyway, don't give them anything that will get you disQ'ed.

BTW, I had a set of the 040's from a '68 327. They are similar to the fuelies, but had 1.94" valves, no acc. holes and pressed studs. Nothing too special about them, IMO.

Sooo... you can tell if someone is running a 6" rod set-up just by the different sound it makes?! I'm still learning alot on this subject.
Looks like ...TO EVEN HAVE A CHANCE of building a winner...it should be built to live at 9000+RPM?! Sound$ like alot of forged part$ may be needed!
What about a 383 using a stroked 350 block and the short 400 rods?! Taking a chance on not being torn down?! Maybe sandbag and just "barely" pull into the lead on the final lap(Occasionally!) type trick? Still trying to "fish" for ideas here!
Thanx,
6sally6
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Old 11-27-2009, 10:18 AM
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Quote:
Originally Posted by 6sally6
Sooo... you can tell if someone is running a 6" rod set-up just by the different sound it makes?!
lol No, more the RPM's and how quick it would rev would sound a bit different than a longer stroke.

Quote:
I'm still learning alot on this subject.
Looks like ...TO EVEN HAVE A CHANCE of building a winner...it should be built to live at 9000+RPM?! Sound$ like alot of forged part$ may be needed!
What about a 383 using a stroked 350 block and the short 400 rods?! Taking a chance on not being torn down?! Maybe sandbag and just "barely" pull into the lead on the final lap(Occasionally!) type trick? Still trying to "fish" for ideas here!
There is more to winning than HP- handling will get you to the front as fast or faster than all the HP out there. 9K RPM will COST! I'd rather see a dependable (and more affordable) 6500 RPM engine tune to begin with.

If you're relatively new at racing, try to keep the set-up simple and don't over-spend. Practice will get you faster, faster lol.

I really doubt any amount of cheating will get you to the winners circle quicker than a good handling legal (within reason, that is ) set-up.
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Old 11-27-2009, 01:01 PM
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Stick with the 350, your heads, intake, exhaust & other mechanical restrictions will not benefit the destroked 400.

If you are new to racing, everyone knows it. The way you arrive at the track, when you line up for heats and how you drive. No offense intended. So, even if you happened to fall somewhere in the top 3 and magically win, the engine's coming apart- especially if there's a car that usually wins there and believe me, every track has one in every class. Stock 8 or late models.

There is more to learn about weight distribution, tires, spring rates, and handling setups than just about anything else and this will determine how good you can be. The engine is 2nd to this.

When you start getting a handle on the track, then worry about finding power and spending money on engines.

By the way, the rpm drop you mentioned in the turns (2,500rpm) no way that should be happening, even with a poorly prepped car in sweeping large turns, heck, probably not even at a paper-clip type short track.

Best of luck- but stick with a good 350, torque is your friend when learning.
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Old 11-27-2009, 08:06 PM
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I agree with the other posters that your time would be better spent figuring out roll center and other characteristics of handling than trying to recreate the wheel or in your case, engine.

Learn to win within the rules and you will gain alot more respect. I realize alot of drivers spend alot of time in the "grey" area of the rules, but there are some that use their brain and learn what it takes to be truely fast the right way.

Yes I am a tech guy at a circle track and that 400 block wouldnt make it to see its first race at our track because we do check casting numbers among other things.

Check out this site,,,, lots of good info there. Dirt Forum

Last edited by SNTGreg; 11-27-2009 at 08:11 PM. Reason: forgot to add link
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Old 11-29-2009, 06:38 PM
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SBC dirt track bullet......

I appreciate alot of the good advice, but I guess I wasn't too clear. My fault. This is the 4th year my pal and his two guys have been racing at the local dirt tracks. Last year and the year before they raced the "crate-motor" late model class(asphalt too). They have the handleing,chassis set-up,driving, etc. down pretty well. They are just dropping back to a more interesting class to race in. They started out in this class 4 years ago.
Anyway....this will be the third engine I have built for them(with their money...and help) One engine won a race and finished in the $$ a half dozen times...the other engine...catasrophic disaster...A .25 roll pin sucked thru the carb can do ALOT of damage!!!
Sorry to be so long.
I'm just looking for "a little edge" in building this next engine. We got the racing part down!(IF anybody can honestly say that?!)
Sounds like STROKE is where the torque is...moreso than big bore. Any gains in running a 6" rod with a 350 engine?! OR just put a 383 together and just "barely" pull into 1st or second place?
Any ideas men??!
Thanx,
6sally6

Oh...I was off about the RPM's coming out of the turn. I don't know for sure. I DO know going into the turns it tach about 6300RPM according to the tattle-tale tach.
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Old 11-29-2009, 06:55 PM
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My opinion, as an engine builder and a tech man, stay in the rules.
Don't worry about the 6" rods, it's been beat to death and even if you agree with the pro's of them being able to produce more power, it isn't much, and certainly not worth the risk of being forever labeled a cheater, and it won't matter if the illegal part isn't "much" advantage. For instance, I dq'ed a guy for .003" too much cam lift, not enough to make any sort of difference on a dirt track but he was illegal and forever be remembered for that.
Do it right, and get the handling down. The money you'd spend on 6" rods would not improve your lap times as much as a new set of tires would.
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