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Old 08-01-2012, 10:41 PM
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400 sbc build. mpg and 1/4 guesses

Okay I am building a 400 sbc for my nova. Big upgrade from the 307. I have a stock 400 am swapping in a 488/510 hyd flat tappet. 750 quadrajet edelbrock rpm or airgap intake(don't kno which one) and keeping the powerglide(rebuilt) with 2.73 gears.

Can anyone make a good guess to how much torque or horsepower this might make. How many mpg should this thing make and what might a 1/4 mile look like. Anyone had a setup kinda close?

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Old 08-02-2012, 12:57 AM
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should run high 13s or low 14s. a 3 spd and 3.36 gears would drop you into the low 13s or high 12s if you hook well.HP maybe 335 to 350,need more info.torque hopefully over 400.
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Old 08-02-2012, 11:03 PM
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2.76 gear stock head 400sbc is going to get into the 14's, no way. Not with a cam bleeding off his low end. No stall compensation will complete that result.

Did you mention 13's, are we on the same planet?
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Old 08-03-2012, 12:17 AM
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just for spin,rofl.
I posted before about a 400 I built for a friend Mike.1978 monte carlo,,,rebuilder long block 400 from bond mechanical,bone stock,sig erson TQ-20 camshaft,street master manifold,750 carter carb,1 5/8s tube headers,2 1/2 inch dual exhaust. car ran 14,1s. over 20/mph,273 gears,installed used posi carrier,rebuilt turbo 350 with shift kit and rebuilt stock stall convertor. nothing else!!!
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Old 08-03-2012, 08:00 AM
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My freind craig, has a 71 boat tail riviera 455 with a 2.76 gear. Performer intake, 850 carb dialed in, mild cam and stall. He is in the low 15's . He did beat a 86 mustang gt 5.0 5 spd that ended with a 15.30's best.

We are not on the same planet.
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Old 08-03-2012, 08:36 AM
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71 boat 455 running 15s,thats probably a good time for that car,congrats.I had a 67 chevy 2 with a 250 inline 6 with a 3 spd auto...and it ran 17.7s
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Old 08-03-2012, 10:27 AM
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Op, thats a horrible combo (no offence). You need more gear and a higher stall tc. And you need to do something with the heads, stockers are no bueno. That cam doesnt do anything below 3k rpm, you'd need a converter. Also, the stock heads won't handle that much lift
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Old 08-03-2012, 10:40 AM
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400s make great torque and are economical 13 second motors.That cam is not that big for a 400 but less would be better with no stall
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Old 08-03-2012, 03:53 PM
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A stock 400 with that cam will be a dog below about 2800rpm's. No way it will hit even high 14 sec. in the 1/4, especially with those tall gears and the tall 1st gear in a powerglide trans. I'd bet money it wont do better than 15's in the 1/4. Might not even get into 15 sec. in the 1/4!
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Old 08-03-2012, 04:13 PM
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why would a car that has .500 lift be a dog under 2800RPM? LS-3 engines have 550 lift and they make power from idle.
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Old 08-03-2012, 10:51 PM
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Sad , but what is a LS 3 . Is that something like a LS1. Those are port fuel injected, with the canted injector misting the correct ammount of fuel down the valve at the best angle possible. A computer controlled system beyond the carburetors ability. You can have a decent ammount of roller lift without to much loss.

A carburetor needs the rpms generate velocity to pull the fuel through the valve.

I hate explaining anything. Why should I , nobody is gonna agree with me anyway.
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Old 08-03-2012, 11:41 PM
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Quote:
Originally Posted by vinniekq2 View Post
why would a car that has .500 lift be a dog under 2800RPM? LS-3 engines have 550 lift and they make power from idle.
You have to look at duration too. If the whole engine is built to work with the cam then i would say ok, but he want's to put a big boy cam in a completely stock engine. It will turn out horrible. The drivability will be terrible and combined with his stock converter, 2 speed powerglide, and highway gears he will have no power. He's going to be pulling first gear all the way down the track and it wont get in to the cams rpm range til like 40mpg or something stupid. It's just a terrible combo and needs to be thought through.
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Old 08-04-2012, 01:02 AM
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Im not familiar with bigboy brand cams,so how about a little Howards roller hydraulic for the girls ???
113215-10 CL113215-10 270 278 217 225 .495 .500 110 106 Hyd. Hyd. 1,2
1300-5500 Good idle, Street Performance. Strong lower mid range. Stock converter OK.

wow? stock converter and power starts at 1300RPM
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Old 08-04-2012, 01:07 AM
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201020 Z-20 2000-6000 .448 .018 268 228 112
SOLID .448 .018 268 228
I would use this cam for a first timer wanting a slightly stronger motor
Isky flat/solid
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Old 08-05-2012, 11:43 AM
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Don't be confused by lift alone. If it was as simple as just putting the max lift cam in an engine to make HP, then there wouldn't be so many choices from cam builders. Nobody makes a wonder cam that works with every SBC of the same cubic inch. Cams are designed to work with various engine builds, and putting a cam in with big lift and long duration only works if every other part in the engine is designed for that cam. Going big on the cam, and stock with everything else will result in less performance than a stock lift/duration cam for most of the RPM range.
I've had people bring a car by to see what could be done to make it perform after they decided a big old lumpy cam was the cure all, and would sound cool. I usually reccommend a cam with much less lift and duration, and if they suck it up and make the change they're always happeir with the performance gains.
The engine in question would be much better off with something around .450-.465" lift, and no more than 270 duration total. LSA should be around 108-110, depending on the converter. If the converter was "loose" enough he might even get away with 106 LSA, but with a stock converter that's too much lope. The rearend and trans complicate things even further, as the PG and high gears will make 1st gear wind out to over 70 mph easily, and it will take a long time for that cam to hit it's power band and start working with this combo. Then the shift to drive will drop it out of the power band and it starts all over again.
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