should you build a 350 or a 383 SBC COMBO



should you build a 350 or a 383 SBC COMBO

Postby grumpyvette » December 18th, 2012, 6:10 pm

I get asked if guys should you build a 350 or a 383 SBC COMBO, in my opinion a great deal depends on your goals and what your starting with in parts and your budget and mechanical skills. these engines have been worked on, and tested for decades, theres lots of parts available and with the correct heads and roller cams well over 600 hp is potentially possible, even without a turbo, or super charger.
soft ware dynos can be rather useful at predicting potential power ranges but obviously the better the soft ware and the more exact the input data the more likely your results will reflect reality.
I will point out a few facts
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notice how the longer crank stroke effects the piston stroke distance in the bore, both at the lower and upper end of the cylinder
first critical piston speed is about 4300feet per minute with very good quality components and most hydraulic lifter valve trains will dramatically loose power at or above about 6300rpm, so you should think seriously about researching your options and perhaps using solid lifters if you intend to exceed that rpm level.

a 350 has a 3.48" stroke so your looking at about 7350 rpm as a max peak rpm.
a 383 has a 3.75" stroke so your looking at about 6800 rpm as a max peak rpm.

with either engine size youll need to match the compression ratio, cam duration and port sizes to match the intended power curve.
if your starting from scratch, Id strongly suggest the 383 is the better option.
but remember the cars rear gear ratio and transmission gearing, ETC. must match the intended power band.

the extra displacement of the 383 will almost always result in an extra 35-40 extra foot labs of torque in the most effective part of the power band and at least 20-35 foot lbs more than a similar 350 over most of the lower and mid range rpm band.
carefully read thru the links then do more research, if you do the research youll save a good deal of time and money.

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heres a few general tips, and related linked info, to read thru

youll need too, calculate the required static compression to match the required cam duration matching your intended power band so the dynamic compression falls close to 8:1 , the more duration in the cam, the higher the static compression required to keep the engine torque fairly reasonable, remember the piston compresses nothing until both valves are seated

viewtopic.php?f=52&t=727

http://www.youtube.com/watch?v=aATDsYVVcRM

if the cams duration at .050 lift is under 235 degrees youll almost always do better with a dual plane intake manifold, and as both lift and duration increase your need to check valve train geometry and piston to valve and valve train clearances and spring load rates also becomes mandatory
Longer rod ratios have a longer dwell at TDC ,
In theory thats more high rpm tq for the 6" rods due to more efficient use of cylinder pressure at those high rpms but cam timing, scavenging and compression ratio must match to get the benefits, and detonation could be slightly more common
MATCHED ,CAM TIMING, PORT CROSS SECTION AND LENGTH< <COMPRESSION< AND EXHAUST HEADER CONSTRUCTION, DESIGNED TO MATCH THE LONGER ROD DWELL TIME IS REQUIRED TO ACCESS THE POTENTIAL BENEFITS, FAIL TO DO THAT CORRECTLY AND YOU LOOSE THE SLIGHT POTENTIAL GAINS

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calculate the intake port size in your intake and in your cylinder heads to match the engine intended power band and operational rpm range
viewtopic.php?f=55&t=624

http://www.wallaceracing.com/runnertorquecalc.php

http://www.wallaceracing.com/lpv.php

http://www.chevyhiperformance.com/tech/ ... ewall.html

match the drive train gearing and converter stall to the engines intended power band
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RELATED THREADS, it might take you several hours to read thru these but you'll save a lot of time and money doing so! rather that just buying parts first

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viewtopic.php?f=52&t=181

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viewtopic.php?f=44&t=38&p=26432&hilit=+known+engine+combo#p26432

viewtopic.php?f=55&t=624&hilit=port+cross+section

viewtopic.php?f=51&t=125

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viewtopic.php?f=52&t=5078

viewtopic.php?f=69&t=2301&p=23315&hilit=dyno+software#p23315

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viewtopic.php?f=69&t=519
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: should you build a 350 or a 383 SBC COMBO

Postby grumpyvette » February 8th, 2013, 12:39 pm

GRUMPY ? What does the increased cubic inches have to do with what octane fuel you use?


If we were to assume you were to build very similar engines differing only in the stroke and piston pin height and you built either a 350 or a 383 engine were built with a flat top piston that reached TDC and had the pistons top surface equal in height to the blocks deck height, and both were built using a .042 thick head gasket and a 67cc combustion chamber cylinder head, you would have markedly different true static compression
you would have about 10.5:1 with a 350 but closer to 11.4:1 with a 383, theres 43.75 cubic inches of volume in a 350s cylinder and 47.8 cubic inches of volume in a 383s cylinder.
it should be rather obvious that increasing the compression changes the fuel octane requirements

http://www.kb-silvolite.com/calc.php?action=comp

viewtopic.php?f=55&t=2718&p=12119&hilit=calculate+octane#p12119

viewtopic.php?f=50&t=208&p=16848&hilit=calculate+octane#p16848

viewtopic.php?f=52&t=4081&p=10861&hilit=calculate+octane#p10861

viewtopic.php?f=44&t=38

viewtopic.php?f=52&t=727
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keep in mind theres sometimes mechanical clearance issues to deal with in stroker combos
viewtopic.php?f=44&t=38
viewtopic.php?f=50&t=428


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try for .060 CLEARANCE, there are connecting rods designed for increased clearance in a sbc stroker application
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Site Admin
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Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida


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