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Old 03-28-2010, 10:51 PM
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New to BBC's need some suggestions

Hello everyone and sorry about the long post. Well...not really

I have had only small blocks in the past and finally figured it made more sense to make a mild BBC than a wild SBC to make the power I want in this car. I assume the BBC will last longer, be more fun and more streetable in the 500hp/tq range.

I nabbed my first big block. Its a 454 casting number 361959 and has 781 heads on it. Stole it for $400. Its in running condition but I would rather do a rebuild and have some piece of mind it will last a while before installing it. Its going in my 87 caprice (4700lbs) that has a built t-56 six speed.

While its apart I would like to raise the compression and just wake it up a little bit, making it a lot more fun that it would otherwise be in stock form.

This is my daily driver and its intended purpose is for street only. Horsepower isnt as important to me as torque and I would like to have around 500-550tq and a pretty flat curve. If 500-525 hp is achieved in the process I promise I wont complain about it. This is going to be on a budget.

From my research I gather the 781 heads are great factory heads and with mild porting and bowl blending and possibly larger valves will be sufficient for my power goals. This is good if thats the case because I cannot afford aftermarket heads at this time.

Would the resident experts care to chime in and suggest a cam and a rebuild kit with dome pistons that will get the compression up. What compression do you guys recommend? 9.0, or 9.5? I want to use pump gas, 87 octane if possible. What type of cam do you guys recommend? stick with flat tappet(puke)? Hyd Roller? Solid Roller?

I would kinda like a solid roller or is that not recommended for street?
With my 0.62 sixth gear ratio, 3.90 gear, and 27" tire diameter my cruising rpm is 1900rpm at 65mph. Should I choose a cam with the power range that falls within the 1900rpm? I dont plan on spinning the motor past 6k. It may never see 6k but if it does it will be rare since this may be a 2bolt main(havent looked yet). Are two bolts strong enough for my power goals? I have a mighty demon 650cfm carb and an old Qjet, the large cfm qjet according to cliff's highperformance(popular qjet builder) is the 650 demon too little? Are edelbrocks any good?

Intake manifold recommendation? carb spacer? I already have a 1-1/8" spacer with heat insulating gaskets for the demon.

Is dialing in the quench important with a bbc as it is with an sbc? On to the exhaust. I currently have 2.25" dual exhaust with an H-pipe and 2 chamber flowmasters. Is this sufficient or should I go 2.5-3" with an X-pipe? Flowmaster or spintech mufflers? Any preferences? Right now the exhaust exits right behind the rear tires with slash cut chrome tips. Lots of people have recommended I cut the exhaust and weld turndown tips on the end of the mufflers and dump them right before the axle and a slight angle to make it sound better. Is this true and will it make any diff in performance? I dont know if longtube headers will fit. Are block huggers ok or will I lose low end with them? 1-3/4 or 1-7/8 primaries? I have an msd 6al ignition, what do you think my timing should be, just ball park setting to get me started and any ideas on where to start with spark plugs?

I will be adapting my SBC serpentine belt setup to the big block with an adapter kit ive found so I assume i will need a reverse rotation water pump. What vehicle/year should i specify when I go the parts store so I get the right one. I have a 3-row radiator is this sufficient?

I know this posts questions were all over the place but this is all new to me and the questions just kept popping in whats left of my mind. Im very excited about this. Wont it be cool to have a 6speed coupled with a 454 in a full size chevy sleeper that was never offered a manual trans? Most all of these were equipped with 305's too so its a big change. Ive got a digital dash and new scat/procar elite black leather bucket seats. Torq thrust II 17" wheels. All upgraded suspension courtesy of spohn racing, hotchkis and energy suspension. I just cant wait to stuff this big block in it and put a smile on my face.

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Old 03-28-2010, 11:33 PM
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I would run atleast a 750 carb. Camshaft would be a hydraulic roller if not the flat tappet. Do not need a solid roller in this application. Intake would be an Edelbrock Performer RPM Air Gap. Every bit of porting you can afford to do will be worth it. What I do on these are gasket matches and blend about 1" into runner, 3 angle valve job, and I pay alot of attention to the bowl and throat area under the valve. Piston I would run is the basic LS6 piston. With large chambers you will be in the 9's in compression, I like to hover in the 9.75 area which will need a 113cc head with the right quench and this piston. 87 octane is out unless you want to kill your power and trque with 8.1 compression. Run the 93. Quench is very important on any engine, so I would aim for getting the piston .005" in the hole and run a .039" gasket for .044" quench. Headers, a 1 7/8" is fine. Exhaust should be 2 1/2". I have made over 500 ft lbs with these, with a broad curve, but hp will be down due to the cylinder head. I would say in the area of 450hp. This same combination with Edelbrock heads at 10.1 makes 550+hp and trque. What you will have is a maintenance free torque monster that should be alot of fun on the street.

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Old 03-29-2010, 01:15 AM
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750 Q-Jet
1 7/8" long tube headers
9.1:1 static compression ratio w/119cc heads
0.010" deck, 0.040" gasket, 0.050" squish
2.19"/1.88" valves, bowl blending, 3-angle job, 30 degree back-cut on valves.
Install 2 degrees retarded. (intake centerline 108).
Clicks off like a switch at 5600
2000 175 461
2500 221 465
3000 281 492
3500 350 525
4000 411 540
4500 459 536
5000 492 516
5500 496 473
6000 441 386
Peak volumetric efficiency 91.6% @5000
Peak BMEP 176.7 @4000 Should sing happily all day on junk pump gas.

VERY STRONGLY SUGGEST not using a flat tappet cam in a BBC.
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Old 03-29-2010, 10:52 AM
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I hear a lot of people like running mechanical flat tappet. With oils nowadays do I have to run an additive in my oil or what is the problem with running one in a BBC. If it is the oil is there an off the shelf oil that is still good for flat tappet cams? Rotella maybe? What compression ratio is the cutoff for 87 octane? I can run 91 but we have no 93 octane around here. Again should my cams power range fall within my 1900rpm cruising speed? If i cruise at 1900 and have a cam that starts making power at 2000 or 2200 is that a bad thing? reduced economy at cruise or what? Going to look at some headers today, will block huggers be ok for street or do you recommend something else?

Thanks for the info so far fellas. Keep it comin if anyone has anything to add. I had a lot of questions in there.
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Old 03-29-2010, 01:50 PM
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The magnum 280hr cam you suggested Techinspector looks nice. Do you think a dual pattern cam would work better for factory 781 heads?
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