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Old 10-04-2006, 09:17 PM
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Small Block Chevy 400

I am currently in the planning stage of building a 400 sbc.

The motor will live in an '84 Chevy 1/2 ton 2wd pickup w/ 3.08 gears and an overdrive transmission.

The plan so far is to run the factory bottom end setup and heads. Compression will likely not be over 8.5 to 1. Itll have headers. Emissions are not a concern.

Would a standard 'white box' cam be best in a stocker rebuild such as this? Or should I look into a RV type cam?

Would an Edelbrock 1406 on top of a performer manifold be better than a Quadrajet on a factory manifold?

Im not looking for huge power numbers, just a good compromise between ample torque and fuel efficiency. The pickup is driven daily. 12mpg town and 15 highway would be good.
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Old 10-04-2006, 09:31 PM
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cool

this one I have done recently 400 sbc flat top pistons rpm cam wiend stealth intake 650 dble pumper carb (demon) with 1inch spacer 76 cc smoger heads mild port job headers 2.5 exhaust from headers into flow master exhaust scavenger into 3" single pipe into 3" 40series muffler beat a 96 vet hands down man it was fun haulin lumber
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Old 10-05-2006, 01:21 AM
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The biggest factor (other than driving style) in MPG is cam timing. Less overlap uses less fuel. There are two ways to limit overlap; reducing duration, or increasing lobe separation angle. The first tends to shift the torque peak left on the graph, meaning where the torque peaks will be at a lower RPM. The second tends to move the hp peak down; that is to say, the RPM where it peaks remains the same, but it will suffer a bit.

In your application I would probably keep a 112 LSA and shoot for duration that looked like 212/218. I've built that one a few times before for trucks with a mild pocket porting and it provides a dead flat torque curve that stays just above 400 lb-ft all the way to 4000 RPM. HP peaks at about 340 at 5000. Absolute torque monster. You won't set any records for MPG, but you'll at least not waste any more than a stock setup.

Here is a look at what your power curves MIGHT look like. This is a dyno simulation using 8.5:1 compression, pocket ported stock heads, small headers with exhaust, and a 212/218 cam with a 112 LSA at about .5" lift. Disregard the graph higher than 5000. Redline here is 5200 tops, but I'd shift at 5000.
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Old 10-05-2006, 01:27 AM
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I also want to add that you absolutely won't do better than the factory Qjet for mileage, streetability, and accurate metering. They are by far, hands down, the most accurately metering carb ever built, and that is independent testing, not just my opinion. They are loved by those who understand them, but hated by those who don't know them. If you think about it, the same carb was used on 455 buicks in 1970, as well as smog-choked 140-hp Olds 307s in 1989. They were also used on some V6s. They are a wonderful carb, but not easy to tune for the new user.

Edelbrock intake, definitely. But I'd rather see you use the Qjet. Better throttle response, mileage, and aftermarket support. Its also best to match the intake with the carb. Qjets use the spreadbore intake; edelbrock carbs use the square bore intake. They can be adapted to each other, but the results are never as good.
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Old 10-05-2006, 07:37 AM
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Small Block Chevy 400

I wouldn't recommend stock cam, they are outdated. I have a RV cam in my '85 Chevy, 1/2, 3.42s, 400ci, 4x4, close to the same set up you have and it works great for torque and hp without haveing to rev the het out of it.
Good Luck
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Old 10-05-2006, 06:58 PM
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Id wanted to mention one more thing. With the 3.08 gears and the overdrive, the engine is only turning a little more than 1500 rpms at 60mph.

Will a cam as large as the one you suggested be inefficient at that engine speed?
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Old 10-06-2006, 12:55 AM
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Depends on your tire size. If you're turning that low an RPM, then it might be on the low side of where it would be most efficient. The OD should be .7, right? We're talking about a 700r4?

Well, I would say that 1500 is definitely lugging for even a bone-stock engine. I think the mismatch there is factory gearing and tire size, so I don't think any cam would be really "matched" to it. I guess that leaves you a couple choices; a 3.42 rear, smaller tires, or going back to a stock engine where the lugging would be minimized.... but I digress... these are very fine points of tuning to the last ounce.

I would say that 3.23 or 3.42 would be a better match in this case, but there is enough torque available from 1500 rpm that (while not optimal) probably won't upset things in the MPG category. I'm having trouble with desktop dyno so I can't see VE numbers right now, but I strongly feel that unless she's shifting in and out of OD all the time I wouldn't worry about it.... and if you ARE shifting all the time, 3.42 truck axles are very easy to find and bolt in.
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Old 10-06-2006, 10:46 AM
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The tires are 28 inches tall and yes the transmission is a 700R4 with a .7 OD.

The 305 currently in the pickup has to work pretty hard at 1500 rpms to pull that aerodynamiclly challenged truck at 55mph.

The 3.08 gear is sweet on the highway at 75mph, I have gotten 19.1 mpg with the current setup but I agree a 3.23 or 3.42 gear would be much better. Most of the miles are town miles or hauling light loads on the farm.

Thanks for the help!
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