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Old 11-08-2002, 01:12 PM
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Question 11:1 compression

I'm preparing to build my first 350. It is for a '68 chevelle that I using on the street. It will not be a daily driver, so I want to have a lot of horses. It is my understanding that 11:1 puts out the most power for a sbc. What is the downside of this. Do motors with this compression hold up well? What other components are needed to run this compression? I have a weiand dual-quad for it as well. I desire a really lopey idle...what's kind of setup do you guys see here? <img src="graemlins/mwink.gif" border="0" alt="[mwink]" />

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Old 11-08-2002, 01:25 PM
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Say there servant, bout how much $$$ had you planned on investing in this lil' 350 setup (if this is even an item)? 11:1 would be squelchin a whole lotta' ponies outa that little 350 (and I do take it this is going to be a Chebby 350, yes?), and getting there will hardly be an affordable venture. And on issue of reliability, if you honestly plan on pumpin' 11:1 comp. outa a 350 motor, you're reliability's just gone out the door,...but then you said this won't be a daily driver, right? Tell us exactly what you're expectations are, what you have to spend, and what applications and abuse this engine will experience?

My 2 cents; 350's, both Chebby and Olds make great street cars, but if you're looking for max hp and max torque, for the sake of reliability, durability, and of course $$$, a big-block would be your best bet. Now, locating and building up a 350 might be an easier jaunt, but just how long do you think you can expose that stout 350 to that kind of abuse?

My 2,..3 cents,
~John~
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Old 11-08-2002, 01:28 PM
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Oh yeah, I'm going to use the first camel hump heads, the 2461: 62cc chamber, 2.02 intake, 1.61 exhaust.
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Old 11-08-2002, 01:37 PM
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Thank you John, see, this is what "preparing" is for. I like these questions...'cause they make me think about what the hell I really want to do. I do not want to pull out the motor and rebuild it every 6 months...that's for sure. I do want something that it driveable on the street and will also rock whenever I desire. To be honest with myself, I will not me hummin' up around 9,000 rpms every other drive. Considering that I already have my intake, carbs, running 350, headers, and heads(I will keep the head-work cost out of the motor contributions), I wouldn't want to spend more than say...$1,000 or so. I would go a little higher if absolutely necessary for an excellant setup.
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Old 11-08-2002, 01:45 PM
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Hmm, sounds like a good stout setup ya got there, but what about those pesky downsides? Most big-block motors are high comp. engines to begin with (factory), so naturally they are going to hold up much better than a maxed out SB with equally matched comp. (hence why I said your best bet would be a BB for durability and reliability purposes) Now, if you have your heart set on a maxed SBC 350 that you intend on running 11:1 comp with, ............i'll get back with ya on that at. I gotta go! (the wife's home!)

Good Luck,
~John~
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Old 11-08-2002, 01:49 PM
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Stick w/ no more than 9.5:1 if you plan on paying for 92+ octane, otherwise stick w/ no more than 9:1 and maybe you can get away w/ regular unleaded. 11:1 compression, 300deg cams, 1200cfm Dominator carbs on a Victor manifold all sound sexy but for a street engine they will result in a disappointing parked car.
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Old 11-08-2002, 02:55 PM
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10:1 compression with aluminum heads and 9.5:1 with iron heads is the rule of thumb. To get 11;1 to run on the street is just about impossible. You will have to retard it so much that you will probably dip down into lower power than you would have if you had a well tuned 9.5:1 motor. Further more, the increase in compression ratio will not add that much power. Put your money into the best set of heads you can afford, that is where the performance comes from.

Those double hump heads were the hot ticket in their day, but do not lay a candle to a set of Air Flow Research or similar performance heads.
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Old 11-08-2002, 03:14 PM
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Some smallblocks came factory with 11:1 and werent what I would call radial.By todays standards,you wil have to watch for detonation.I did a 355 a while back that was real strong,and dead relaible,and after making over 500 hp with it for 3 seasons of racing I intentioanlly killed it after I had finished my even better engine.I started with a factory 2 bolt early block and nodular crank.I had the block bored .030 over and the crank turned,I had a set of factory X rods resized with arp bolts in them.I then ran stock replacemnt 1970 LTI pistons and pressed fit the pins onto the stock rods.I topped it off with a set of 461 heads that had 2.02/1.60 valves and a bowl blend job.I ran a flat tappet solid cam that was actually a circle track grind from a company named reed cams.It had 258 intake duration and 265 exahust duration at .050" with 292intake and 300 exhaust advertised,with .518intake and .532exhaust lift and a 106 lobe seperation.I ran a single 750 double pumper on a holley strip dominator intake,and used hooker 1 7/8" headers.I ran this setup in my 3400# 1973 firebird with a th350 trans and 3500 stall convertor and 4.10 gears with 30 inch tall tires.I shifter it at 7000 rpm and the car went 11.80's at 112 mph crossing the finish line at the top of second gear.I added a 125 shot of nitrous to it and ran 11.20's with it.I ran the snot out of it and drove it all over on the street{with mufflers of course}After I finished my new motor,I put the 400 hp plate that I had bought for the new motor onto the old 355 and set it to 250 hp and went 10.60's a few times and then cracked a head between the valves.In 3 years of running the other setup I had no problems so this failure was totally dues to my greed for power.I drove this engine on the street on 93 octane pump gas with 32 degrees total timing but used race gas when I shot the nitrous.The "new engine" was a smilar 355 with a steel crank,and 4 bolt mains and a set of ported dart 2 heads and a 7500rpm roller cam.I ran that setup into the high 10's on motor{with 5.13 gears and 5000 rpm stall} and low 10's on a 200 shot,it also ran on pump gas on the street,but that setup was really about 10.25:1 because I had to flycut the pistons for the cam and I ran a flepro type head gasket.If you can use a big cam and a loose convertor,that setup will live on th street.Good luck
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