should you build a 350 or a 383 SBC COMBO

[grumpyvette]

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

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.
it helps a great deal if you take the time and effort to find a trust worthy and reasonably priced local machine shop , and trust me when I say this is critical, and yes, the machinist will seem to point out endless things that should be done to increase durability, or just allow proper component function,and a good machinist will try to guide you in component selection to help avoid mis-matched parts and low quality parts being used, yes quality parts and machine work, ALWAYS COST more than you may expect them too!

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.

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

upgrading SBC crate engine heads

Will L 98 ,58cc, 160-165,cc port alum heads (14101128)help performance on a 290hp small block thank you pete. you may find info in links you can use else-ware in many threads https://garage.grumpysperformance.com/index.php?threads/bbc-related-links-and-useful-info.17140/ as compared to...

garage.grumpysperformance.com

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

calculate the intake port size in your intake and in your cylinder heads to match the engine intended power band and operational rpm range


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



http://www.hotrod.com/articles/1206phr-383ci-small-block-chevy/

http://www.superchevy.com/how-to/76178-chevrolet-ht-383-engine/

http://www.enginelabs.com/news/dyno-video-qmp-builds-500-horse-383-stroker/

http://www.chevyhardcore.com/tech-stories/engine/building-the-little-383-small-block-that-could/

http://royalpurpleconsumer.com/wp-c...-block-in-six-easy-steps-hot-rod-magazine.pdf

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





rebuilt or new chevy 350 crank
https://www.speedwaymotors.com/Speedway-Chevy-350-Crankshaft-Two-Piece-Main,8682.html

https://www.amazon.com/Scat-Crankshafts-9-10442-Crankshaft-Chevrolet/dp/B003N2RRTY

http://www.northernautoparts.com/Pr...=20&product_ecat_engine=1386&btnSubmit=Search


rebuilt or new chevy 383 crank
http://www.superchevy.com/how-to/project-cars/sucp-0706-small-block-chevy-stroker-kit/

 

[grumpyvette]

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
you may or may not have SCAT provide an internally balanced, 383 sbc ,
I would certainly suggest , 6" connecting rods with 7/16" ARP rod bolts,
but thats not mandatory
but Id suggest you buy the flywheel and damper separately as you have more control on the QUALITY of the components,
a billet flywheel is a huge step up in strength over a cast OEM flywheel.
http://garage.grumpysperformance.com/index.php?threads/selecting-a-flywheel.1042/#post-1969

http://garage.grumpysperformance.co...e-a-clutch-in-a-c3-corvette.15034/#post-85152

and of course, by now you might realize I post related info for the hundreds of members,
that may read through the thread in months or years yet to come
read through all links and sub-links
be aware that a 168 tooth flywheel will not fit in every bell housing design,
but it allows a much better choice in clutches and in many cases better quality clutches.
always ask questions before spending cash
http://garage.grumpysperformance.com/index.php?threads/harmonic-balancer.3554/#post-53706

http://garage.grumpysperformance.com/index.php?threads/168-or-153-flywheels.3951/#post-67681

http://garage.grumpysperformance.co...pes-of-crankshaft-steel.204/page-2#post-46231

http://garage.grumpysperformance.co...ing-rod-strength-h-vs-i-beam.1168/#post-40253

http://garage.grumpysperformance.co...nk-durring-short-blk-assembly.852/#post-39417

http://garage.grumpysperformance.com/index.php?threads/what-damper-flywheel.6026/#post-21582

http://garage.grumpysperformance.com/index.php?threads/selecting-a-flywheel.1042/#post-1969

http://garage.grumpysperformance.com/index.php?threads/don-t-beat-that-damper.83/#post-14101

http://garage.grumpysperformance.com/index.php?threads/damper-honing.4975/#post-13912

http://garage.grumpysperformance.com/index.php?threads/damper-tool.223/#post-8024

https://www.dieselarmy.com/engine-tech/engine/how-it-works-viscous-dampers-a-k-a-harmonic-balancers/

https://www.dragzine.com/tech-stori...ers-are-crucial-to-the-health-of-your-engine/

http://www.laskeyracing.com/shop/harmonics.htm

https://fluidampr.com/how-a-fluidampr-works/

http://garage.grumpysperformance.co...r-seal-crank-in-1-piece-block.301/#post-31934

http://www.dieseltechmag.com/2009/02/dt-tested-fluidampr-performance-damper

https://motoiq.com/project-golf-r-mkvii-fluidampr-test/3/

http://garage.grumpysperformance.com/index.php?threads/cheap-damper-ballancer-source.279/#post-1673
like I stated many times,
its the combo of the engines,
compression,
displacement ,
cam timing
and the exhaust scavenging,
and the intake manifold design,
NOT the intake port cross sectional area,
that are the most critical factors, in the engines lower rpm and mid rpm torque.
but for damn sure an intake runner port can be small enough to noticeably restrict upper mid range and peak power significantly,
For 5 decades I've heard endlessly about how installing larger free flowing cylinder heads would devastate the engines ability to make any low or mid rpm torque.
especially when Id suggest using a set of smaller 300cc-320cc, aluminum,rectangle port heads on a 496 BBC, or 200 cc-210cc heads on a 406 sbc, I was asked to build
yet on every engine I've ever had built or had some guy ask me to look at, to see why it ran a great deal less impressively than he expected it too,
they brought into my shop its was very obvious (at least to me) that it was the combo of low compression, too little displacement, with too much cam duration ,
a restrictive exhaust or some guy who was trying to save money and continuing to use a stock stall speed torque converter, or retain a badly mis-matched 2.87:1-3.08:1 rear gear ratio,
with an engine that he miss matched components by slapping a large carburetor , and a single plane intake on,an engine that will rarely exceed 6000 rpm, that was the major reason.
if you want an engine combo to run your first step is to logically match the list of components you,ll use to the application,
and that requires you stop, engage the brain and think things through carefully,
and the most common way to screw up the process is to over cam a low compression engine,
have a restrictive exhaust or mis-match the drive train gearing to the engines power band.
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

http://garage.grumpysperformance.com/index.php?threads/383-build-for-a-friend.14273/

viewtopic.php?f=52&t=727

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

try for .060 CLEARANCE, there are connecting rods designed for increased clearance in a sbc stroker application

the cam rotates while indexed by the timing chain at 1/2 crank shaft speed , there are connecting rods designed to provide additional clearance.

http://www.scatcrankshafts.com/index.htm
don,t forget to verify the cam to connecting rod clearances
a cams VALVE LIFT is determined by the DISTANCE the lifter moves as the cam rotates under the lifter base as it moves from the cam lobe base circle
(the closest the lifter comes to the cams center line)
up to the cam lobes ramp to the lobes peak,
(the furthest the lifter up off or from the cams center line)


your cams lift, is the result of the lifter movement, or distance it travels from the cams base circle, where the valves seated, to the point in the cams rotation where the lifters moved along the ramp surface fully up on the nose of the cam lobe where the valves at full lift.
example
lets say in this case we compare two imaginary cams
a standard cams base circle is 1.125" and
your cams running on a .900 base circle
both cams have a .560 valve lift and run with 1.5:1 rockers
so both cams will need to move the lifter .374"
that means the standard cam lobe will be 1.125"+.374" or 1.499" from the cams base to the cam lobe nose
that means the small base cam lobe will be .900"+.374" or 1.274" from the cams base to the cam lobe nose
which is significantly smaller,
small base circle cams are generally only used when connecting rod clearance necessitates there use

the BASE CIRCLE IS NEVER A CLEARANCE ISSUE, its the cam LOBES that can potentially contact the edge of the connecting rods or bolts, this is why the rods or rod bolts are machined for additional clearance for the cam lobes as you rather obviously CAN,T machine the cam lobes themselves without destroying their function.
now think about it for a few seconds
the cams lobe lift and the cams LSA or LOBE SEPARATION ANGLE
both have an effect on the cam lobes potential interference with the connecting rods

notice how the rod bolts come close to the cam bearings as the pistons reach top dead canter in the bores

RODS WELL AWAY FROM CAM LOBES

RODS CLOSE TO CAM LOBES

WITH THE CORRECT SOFT WARE BOTH THE PISTON TO VALVE CLEARANCE AND CAM TO ROD CLEARANCE CAN BE CALCULATED
BUT ANY COMPETENT ENGINE BUILDER WILL PHYSICALLY VERIFY CLEARANCE

http://garage.grumpysperformance.com/index.php?threads/virtual-dyno-software.2301/#post-53646

http://www.auto-ware.com/software/eap/eap.htm

rods designed like the 3 SERIES generally won,t work with stroker cranks while the 2 series usually will

the connecting rods you sellect make a huge differance in the rod to cam lobe clearance, even a small base cam won,t clear some designs, it should be obvious that the connecting rod with the thru bolt has a great deal less cam lobe clearance potentially than the cap screw design next to it., and the cap screw rod probably clears the blocks oil pan rail area easier also


YOULL OBVIOUSLY NEED TO DO SOME MATH AND CAREFULLY PLAN ANY COMBO,EXAMPLE

Grumpy? I'm doing a rebuild on my low mileage 383. My question is if 10.3 compression is too much for xe 268 comp cam which I have already? The motor has kb 197 dish pistons, .025 down, .015 shim head gasket, TFS 195 heads with 64 cc chambers. Edl RPM airgap, Demon 750 dp and 1 5/8 headers. It's going into a 83 chevy wagon with 200r4, 2200 stall and 373 rear gears. Do you think this combo will work with 93 octane, or do i need to lower the compression ?

ok lets look at the math a bit,
youll generally be fine with 93 octane fuel and using aluminum cylinder heads if you keep the engine coolant temps under about 215F
and the DYNAMIC compression under about 8.2:1 ,
dynamic compression is based on where in the crank rotation the valves both close as the piston can,t compress anything until the valves seal.
the charts based on iron cylinder heads and yours are aluminum which will generally allow about a 1/2 point in dynamic compression higher without issues.
your pistons are listed as having a 12cc dish volume, and being .025 down the bore adds about 5.6 cc more
https://www.summitracing.com/parts/UEM-KB197-030/
thus you have about 10.25:1 static compression

the math shows your dynamic compression will be near 9.5:1 which is a bit too high for reliability without an additional octane booster

if we look at your cam we see it is listed as having 224 duration on a 110 lsa


http://www.compcams.com/v002/Pages/388/XE268H-10.aspx

if we look at this chart we see that your intake valve closed at about 38 degrees after bdc.

you might want to read thru these link's carefully
http://victorylibrary.com/mopar/cam-tech-c.htm

http://members.uia.net/pkelley2/DynamicCR.html

http://www.wallaceracing.com/dynamic-cr.php

http://www.projectpontiac.com/ppsite15/compression-ratio-calculator

OK, first fact! the piston can,t compress anything being trapped in the cylinder by the piston compressing it as it raises,until both valves seat & seal

http://garage.grumpysperformance.com/index.php?threads/dynamic-vs-static-compression.727/

http://garage.grumpysperformance.co...-calculators-and-basic-math.10705/#post-46768

http://garage.grumpysperformance.co...octane-for-compression-ratio.2718/#post-35581

http://garage.grumpysperformance.com/index.php?threads/crowers-valve-timing-charts.4299/

http://garage.grumpysperformance.com/index.php?threads/how-to-read-a-cam-spec-card.1477/#post-3329