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Old 10-12-2009, 08:19 PM
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SBC 358 Build for Economy

I want to build a motor that will not only perform exceptionally well on the street but can also get me decent fuel mileage (around 20mpg). It will go into an 86 oldsmobile cutlass supreme with a 700r4 and 3.73s. I have some .040 pistons, 882 heads, and a TPI intake from an 86 camaro. What limitations am i looking at with this intake?

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Old 10-12-2009, 08:34 PM
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My ideal goal was to do the same thing with the same car and I did. Only, I didn`t have a 700r4, I had a TH350C and 3.23 posi.
I started with a 880 casting Vortec block. I had it decked .010.
The bore was good so we left it standard.
I used jet hot coated hooker super comp headers.
Dual exhaust, turbo mufflers, crossover pipe.
A comp hydraulic roller cam with .204 duration and .500 lift.
Crane OEM replacement roller lifters, comp heat treated push rods.
906 Vortec heads, springs, locks, retainers to match the cam.
KB Hyper 14cc D dish pistons checked at .015 below deck.
.028 thickness GM head gaskets, Quench distance set at .043
Stock Vortec windage tray.
Edelbrock performer Vortec intake.
K&N Air Filter, cold air induction.
SMI Rochester Quadrajet built to engine specs. Moroso 825 ohm spiral core plug wires, pertronix flame thrower cap and coil.
Cloyes Vortec street single roller timing chain (must be used on a Vortec block)
My idea was, maximize combustion efficientcy hence the use of Vortec heads. Use a Quadrajet for outstanding low end response, a small RV roller cam for less resistance.
A great tune up for a great spark. Tune it all in and see what kind of mileage I could knock off. The machinist screwed up the bore when he honed it, and me, being completely stupid didn`t check the bore clearence. Needless to say, it had piston knock like no tomorrow and didn`t seal up for very long, but for the short time it did, I went from here to Atlanta, all interstate, 70 mph, it knocked off 18 MPG, impressive for a car with a TH350 with a non working lock up tranny and a 3.23 rear. It had outstanding low end torque and throttle response as sensitive as fuel injection. As for your combo, I think the losing factor will be the large chamber heads. They aren`t very efficient.
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Old 10-12-2009, 08:39 PM
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hmmm i was worried about the wedge style chambers and how much it would affect the build. I was thinking going with just a flat tappet cam.
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Old 10-12-2009, 08:46 PM
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hmmm i was worried about the wedge style chambers and how much it would affect the build. I was thinking going with just a flat tappet cam. Did you use the stock pistons from the vortec block?
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Old 10-12-2009, 08:49 PM
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Nope, 14CC D-Dish KB hypers which I still have on PM Rods. The stock Vortec pistons required metric rings that are 80 bucks a set, plus, the full concave piston design would give no Quench, the 2 very reasons I went with D-dish pistons. Small chamber heads with a tight quench and a D-dish makes for excellant combustion efficientcy, the very thing I was targeting. The trick to MPG is cruise RPM, if you can keep it around 1800 at cruise speed, with a RV style cam your in it`s torque band so the engine has enough torque to keep you going without lugging the engine. The TPI don`t flow much but works outstanding for low end torque. My plan was to use a 700R4, but after I had invested that much in it already, I couldn`t afford to get it rebuilt. I was shooting for the best MPG I could get with great low end torque by targeting less engine resistance and combustion efficientcy, it worked for a little while. Had it sealed up good and I later added a 700R4, I`m sure I could have knocked off over 20 MPG.
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Old 10-12-2009, 08:56 PM
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When I finally got all the kinks worked out on my SBC build:

86-95 350ci, one piece rear, roller cam block, 4 bolt mains, bored .040" over
Vortec 906 heads
LT4 Hot Cam, Proform 1.6 roller rockers, Comp 26918 beehive springs
Professional Products Crosswind (Dual plane, Air gap)\
Balanced ZZ4 rotating assembly, H345NCP-40 pistons, 10.3-1 compression
Edelbrock 600cfm
34 degrees max timing all in by 3200rpm, 91 pump gas

This was in front of a PCM controlled 4L60E with a 3200rpm lockup converter and 4.10-1 rear gears with 30.4" tall wheels on a 4,380lb pickup

Around town I only got 12-14mpg, but on a few road trips from Prescott Az to Phoenix, I got 23-25mpg on the way down the hill and 16-18mpg up the hill.

Since than a few things have changed and I'm not pulling nearly that kind of fuel economy, but I didn't build it to save on gas

Last edited by 04SilveradoMykk; 10-12-2009 at 09:01 PM.
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Old 10-12-2009, 09:00 PM
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The only reason i am considering the 882 heads is because the intake bolt pattern is designed for earlier heads. I have a set kicking around, and i have flat top pistons which would yield about 9.0:1 compression. Maybe some small chamber 305 heads with 1.94x1.5 valves will work better but then i will have to get different pistons. 70mph should be about 2200 rpm is that a good cruise rpm.
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Old 10-12-2009, 09:38 PM
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Maybe this will help you out some. I have a 350 0.04 over with flat top pistons and stock 882 heads. This engine came with the car (81 corvette). It has the th350c auto trans, 287 stock rear gear. I have installed long tube headers 2 1/2 dual pipes with magna flow mufflers. Cam shaft unknown. 600 cfm edle carb and edle performer intake. The engine runs great but no way a powerhouse. I get 12mpg hot rodding around town and the best on the highway was 17-18mpg. IMO the 882 smog heads are junk. Either for performance or gas milage. Cant wait for winter tear down and new top end build
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