the 305 and 307 sbc engines are far from the ideal starting points for a performance engine build-up.
but they are far from being a total lost cause, EITHER!
EXAMPLE pay attention to the bore stroke ratios, a 307 with its greater bore and shorter stroke , and slightly ;larger displacement and less valve shrouding should ALWAYS show a slight advantage in performance over a similar smaller bore longer stroke 305
Chevy V8 bore & stroke chart
Post by RebStew on Fri 08 Feb 2008, 3:28 pm
CHEVY SMALLBLOCK V-8 BORE AND STROKE
262 = 3.671" x 3.10" (Gen. I, 5.7" rod)
265 = 3.750" x 3.00" ('55-'57 Gen.I, 5.7" rod)
265 = 3.750" x 3.00" ('94-'96 Gen.II, 4.3 liter V-8 "L99", 5.94" rod)
267 = 3.500" x 3.48" (Gen.I, 5.7" rod)
283 = 3.875" x 3.00" (Gen.I, 5.7" rod)
293 = 3.779" x 3.27" ('99-later, Gen.III, "LR4" 4.8 Liter Vortec, 6.278" rod)
302 = 4.000" x 3.00" (Gen.I, 5.7" rod)
305 = 3.736" x 3.48" (Gen.I, 5.7" rod)
307 = 3.875" x 3.25" (Gen.I, 5.7" rod)
325 = 3.779" x 3.622" ('99-later, Gen.III, "LM7", "LS4 front wheel drive V-8" 5.3 Liter Vortec, 6.098" rod)
327 = 4.000" x 3.25" (Gen.I, 5.7" rod)
345 = 3.893" x 3.622" ('97-later, Gen.III, "LS1", 6.098" rod)
350 = 4.000" x 3.48" (Gen.I, 5.7" rod)
350 = 4.000" x 3.48" ('96-'01, Gen. I, Vortec, 5.7" rod)
350 = 3.900" x 3.66" ('89-'95, "LT5", in "ZR1" Corvette 32-valve DOHC, 5.74" rod)
364 = 4.000" x 3.622" ('99-later, Gen.III, "LS2", "LQ4" 6.0 Liter Vortec, 6.098" rod)
376 = 4.065" x 3.622" (2007-later, Gen. IV, "L92", Cadillac Escalade, GMC Yukon)
383 = 4.000" x 3.80" ('00, "HT 383", Gen.I truck crate motor, 5.7" rod)
400 = 4.125" x 3.75" (Gen.I, 5.565" rod)
427 = 4.125" x 4.00" (2006 Gen.IV, LS7 SBC, titanium rods)
Two common, non-factory smallblock combinations:
377 = 4.155" x 3.48" (5.7" or 6.00" rod)
400 block and a 350 crank with "spacer" main bearings
383 = 4.030" x 3.75" (5.565" or 5.7" or 6.0" rod)
350 block and a 400 crank, main bearing crank journals
cut to 350 size
given a choice a 383 or 396 stroker combo built on a 350 block is a FAR BETTER starting point than what most guys refer too as a crummy 305,or 307 sbc with its limitations,
but there's dozens of guys stuck with those 305s and 307 sbc engines due to economic or lack or easily accessed basic engine core,reasons so I figured Id give them some useful info!
the standard VORTEC heads , with some basic port and bowl clean-up and better valve springs are about the best, available and most cost effective OEM sbc heads available for the smaller bore SBC builds
http://www.summitracing.com/parts/SUM-151124/
in salvage yards for those low budget engine builds, and a decent vortec intake
http://www.summitracing.com/parts/EDL-7516/
matched to those heads goes a long way to allowing the smaller engines to breath, if matched to a decent cam with about a minimum of a 220-225 duration at .050 lift and a .460 lift at the valve, and about a 9.5:1 compression ratio is where youll want to start.
while its not reasonable to start at a disadvantage then try to overcome it, before building an engine , you need to realize that many guys feel they must work with what they currently have,personally Ive always found it advantageous to build a second PERFORMANCE engine in the garage and swap it in,after its complete with the correct parts for the application, rather than constantly doing minor mods to a street engine! the advantages are many! but the main one is that you can drive the car within the weekend should the performance engine fail, by swapping back too or swapping in the standard engine, if the other one has problems so your not stuck more than a weekend without dependable transportation.!
keep in mind a 350 block is NOT generally all that hard to locate or expensive
https://secure.pawengineparts.com/shopp ... catid=1477
maybe this INFO BELOW will be of interest
http://www.chevyhiperformance.com/proje ... index.html
http://www.carcraft.com/howto/854/
http://www.hioutput.com/tech/400hp/400hp.html
viewtopic.php?f=52&t=1070&p=2051#p2051
http://www.popularhotrodding.com/engine ... index.html
http://www.goingfaster.com/spo/praisetbi.html
if your thinking the only difference between the 305-307 and a 350 is the displacement advantages...
NOT REALLY!
the 350 has several other advantages other than the increased displacement
it can use larger valves and clear the bore, it has less valve shrouding even if the same valve size is used,thats easily a 5% increase in breathing potential alone for the 350, vs the 305, if both use the largest valves that will clear the bore wall its has the extra 45 cubic inches of displacement as mention but it gets that from a larger bore so a side benefit is the larger surface area of the piston, that allows more total effective pressure, against the piston even if they are exactly the same peak pressure in the cylinders, resulting in more torque,
youll have a much harder time getting over 400hp with a 305 than a 350, using just the port flow rates alone as a guide
then lets assume you get 1.2hp per cubic inch from engines using similar parts
305=366hp
350=420, add the extra 5% breathing potential and your at 440hp , a significant advantage if the larger valve heads are used with the larger bore
now add a 3.75" stroker crank and a .030 over bore and build a 383 and you can easily add an additional 35-40 hp and ft lbs of torque over the similar 350, now 450-475 hp is well within the engines potential if its correctly thought thru and built.
COMPRESSION ratio increases generally give a 3% average boost in torque for each point gained in compression in the 8:1-11:1 range
if both a 305 and a 350 have true flat top pistons and lets assume a 68cc average combustion chamber size , a .018 head gasket and a .023 deck height the 305 will have about a 9.5:1 cpr and a similar 350 would be at about 10.3:1, or a 2% increase in torque from that factor alone across the usable rpm band., you could used dished pistons and drop the ratio but the difference in cpr will be similar if both engine use similar piston designs
305 = 3.736" x 3.48" (Gen.I, 5.7" rod)
350 = 4.000" x 3.48" (Gen.I, 5.7" rod)
13% more surface area on the bore diam.on the 350.
13% more displacement for the 350
1.84 valves on the 305
1.94 valves on the 350
5% more curtain area for the 350 at any valve lift
slightly less valve shrouding on the cylinder wall to valve tangent area in the combustion chamber for the 350.
if you can fill the combustion chambers with a 5% lower flow restriction,thru the use of slightly larger valves, and you burn approximately 13% more fuel/air mix per power stroke and apply that extra force over a 13% larger piston surface area, you get a noticeable advantage
IM not saying you can,t get decent power from a 305, but anything a 305 can do a 350 can do noticeably better, when the criteria you judge by is the power produced
add to that the fact that you can find 383 stroker kits, and 350 rebuild kits at the same or lower price in some cases to 305 parts, that will add an additional increase in displacement and you've got a significant reason to build with the larger bore combos.
BOTH the 305 and 350 have the SAME stroke and rod length
the larger surface area and larger displacement DO make a difference
a 305 has a piston dome area of about 11 sq inches, a 350 with its larger bore has a piston dome area of about 12.59 sq inches, if both have a peak cylinder pressure of 600psi that 6600 pounds of force exerted, for an instant or two on the 305 and 7550 pounds of force exerted pounds of force exerted, for an instant or two on the 350 piston
typical high performance pressure curves
305 = 3.736" x 3.48" (Gen.I, 5.7" rod)
350 = 4.000" x 3.48" (Gen.I, 5.7" rod)
if your thinking the increased power is all the result of the increase in displacement alone,
again, comparing apples/oranges the displacement went up about 13% due to an increase in bore diam of about 13%, but the stroke remained constant, between the two engines and the torque did go up as did the hp. even thou the stroke remained a constant, torque went up mostly due to the larger bore, and the resulting increase in displacement ,hp went up, due to the higher torque at any given rpm.
now a more reasonable comparison to show the effective result of increasing the bore but keeping the displacement nearly constant would be to compare the 305 with its 3.736" bore to a 302 with its 4" bore
305 = 3.736" x 3.48"stroke (Gen.I, 5.7" rod)
302= 4" bore x 3" stroke(Gen.I, 5.7" rod)
what you find is the larger bore and the shorter stroke , but nearly equal displacement move the power curve up about equal to the change in piston speed
at 3000FPM in piston speed a 305 is turning 5172rpm
at 3000FPM in piston speed a 302 is turning 6000rpm
or about 800 rpm faster, if both make the same 300ft lbs of tq at the same piston speed you get
305 is turning 5172rpm x the same 300ft lbs of tq =295hp
302 is turning 6000rpm x the same 300ft lbs of tq=343hp
which shows the advantage of the same displacement but a larger bore and shorter stroke at similar stress levels
as you can see in this chart most of the stock heads don,t flow as well as the AFR 195cc heads and there ARE better flowing heads
now some guys are required to maintain the stock block, or basic displacement, and in those cases you might also want to think about supercharging the engine, its no big trick to install a decent supercharger on your basic 305-307 and make 400-450 plus hp either
but they are far from being a total lost cause, EITHER!
EXAMPLE pay attention to the bore stroke ratios, a 307 with its greater bore and shorter stroke , and slightly ;larger displacement and less valve shrouding should ALWAYS show a slight advantage in performance over a similar smaller bore longer stroke 305
Chevy V8 bore & stroke chart
Post by RebStew on Fri 08 Feb 2008, 3:28 pm
CHEVY SMALLBLOCK V-8 BORE AND STROKE
262 = 3.671" x 3.10" (Gen. I, 5.7" rod)
265 = 3.750" x 3.00" ('55-'57 Gen.I, 5.7" rod)
265 = 3.750" x 3.00" ('94-'96 Gen.II, 4.3 liter V-8 "L99", 5.94" rod)
267 = 3.500" x 3.48" (Gen.I, 5.7" rod)
283 = 3.875" x 3.00" (Gen.I, 5.7" rod)
293 = 3.779" x 3.27" ('99-later, Gen.III, "LR4" 4.8 Liter Vortec, 6.278" rod)
302 = 4.000" x 3.00" (Gen.I, 5.7" rod)
305 = 3.736" x 3.48" (Gen.I, 5.7" rod)
307 = 3.875" x 3.25" (Gen.I, 5.7" rod)
325 = 3.779" x 3.622" ('99-later, Gen.III, "LM7", "LS4 front wheel drive V-8" 5.3 Liter Vortec, 6.098" rod)
327 = 4.000" x 3.25" (Gen.I, 5.7" rod)
345 = 3.893" x 3.622" ('97-later, Gen.III, "LS1", 6.098" rod)
350 = 4.000" x 3.48" (Gen.I, 5.7" rod)
350 = 4.000" x 3.48" ('96-'01, Gen. I, Vortec, 5.7" rod)
350 = 3.900" x 3.66" ('89-'95, "LT5", in "ZR1" Corvette 32-valve DOHC, 5.74" rod)
364 = 4.000" x 3.622" ('99-later, Gen.III, "LS2", "LQ4" 6.0 Liter Vortec, 6.098" rod)
376 = 4.065" x 3.622" (2007-later, Gen. IV, "L92", Cadillac Escalade, GMC Yukon)
383 = 4.000" x 3.80" ('00, "HT 383", Gen.I truck crate motor, 5.7" rod)
400 = 4.125" x 3.75" (Gen.I, 5.565" rod)
427 = 4.125" x 4.00" (2006 Gen.IV, LS7 SBC, titanium rods)
Two common, non-factory smallblock combinations:
377 = 4.155" x 3.48" (5.7" or 6.00" rod)
400 block and a 350 crank with "spacer" main bearings
383 = 4.030" x 3.75" (5.565" or 5.7" or 6.0" rod)
350 block and a 400 crank, main bearing crank journals
cut to 350 size
given a choice a 383 or 396 stroker combo built on a 350 block is a FAR BETTER starting point than what most guys refer too as a crummy 305,or 307 sbc with its limitations,
but there's dozens of guys stuck with those 305s and 307 sbc engines due to economic or lack or easily accessed basic engine core,reasons so I figured Id give them some useful info!
the standard VORTEC heads , with some basic port and bowl clean-up and better valve springs are about the best, available and most cost effective OEM sbc heads available for the smaller bore SBC builds
http://www.summitracing.com/parts/SUM-151124/
in salvage yards for those low budget engine builds, and a decent vortec intake
http://www.summitracing.com/parts/EDL-7516/
matched to those heads goes a long way to allowing the smaller engines to breath, if matched to a decent cam with about a minimum of a 220-225 duration at .050 lift and a .460 lift at the valve, and about a 9.5:1 compression ratio is where youll want to start.
while its not reasonable to start at a disadvantage then try to overcome it, before building an engine , you need to realize that many guys feel they must work with what they currently have,personally Ive always found it advantageous to build a second PERFORMANCE engine in the garage and swap it in,after its complete with the correct parts for the application, rather than constantly doing minor mods to a street engine! the advantages are many! but the main one is that you can drive the car within the weekend should the performance engine fail, by swapping back too or swapping in the standard engine, if the other one has problems so your not stuck more than a weekend without dependable transportation.!
keep in mind a 350 block is NOT generally all that hard to locate or expensive
https://secure.pawengineparts.com/shopp ... catid=1477
maybe this INFO BELOW will be of interest
http://www.chevyhiperformance.com/proje ... index.html
http://www.carcraft.com/howto/854/
http://www.hioutput.com/tech/400hp/400hp.html
viewtopic.php?f=52&t=1070&p=2051#p2051
http://www.popularhotrodding.com/engine ... index.html
http://www.goingfaster.com/spo/praisetbi.html
if your thinking the only difference between the 305-307 and a 350 is the displacement advantages...
NOT REALLY!
the 350 has several other advantages other than the increased displacement
it can use larger valves and clear the bore, it has less valve shrouding even if the same valve size is used,thats easily a 5% increase in breathing potential alone for the 350, vs the 305, if both use the largest valves that will clear the bore wall its has the extra 45 cubic inches of displacement as mention but it gets that from a larger bore so a side benefit is the larger surface area of the piston, that allows more total effective pressure, against the piston even if they are exactly the same peak pressure in the cylinders, resulting in more torque,
youll have a much harder time getting over 400hp with a 305 than a 350, using just the port flow rates alone as a guide
then lets assume you get 1.2hp per cubic inch from engines using similar parts
305=366hp
350=420, add the extra 5% breathing potential and your at 440hp , a significant advantage if the larger valve heads are used with the larger bore
now add a 3.75" stroker crank and a .030 over bore and build a 383 and you can easily add an additional 35-40 hp and ft lbs of torque over the similar 350, now 450-475 hp is well within the engines potential if its correctly thought thru and built.
COMPRESSION ratio increases generally give a 3% average boost in torque for each point gained in compression in the 8:1-11:1 range
if both a 305 and a 350 have true flat top pistons and lets assume a 68cc average combustion chamber size , a .018 head gasket and a .023 deck height the 305 will have about a 9.5:1 cpr and a similar 350 would be at about 10.3:1, or a 2% increase in torque from that factor alone across the usable rpm band., you could used dished pistons and drop the ratio but the difference in cpr will be similar if both engine use similar piston designs
305 = 3.736" x 3.48" (Gen.I, 5.7" rod)
350 = 4.000" x 3.48" (Gen.I, 5.7" rod)
13% more surface area on the bore diam.on the 350.
13% more displacement for the 350
1.84 valves on the 305
1.94 valves on the 350
5% more curtain area for the 350 at any valve lift
slightly less valve shrouding on the cylinder wall to valve tangent area in the combustion chamber for the 350.
if you can fill the combustion chambers with a 5% lower flow restriction,thru the use of slightly larger valves, and you burn approximately 13% more fuel/air mix per power stroke and apply that extra force over a 13% larger piston surface area, you get a noticeable advantage
IM not saying you can,t get decent power from a 305, but anything a 305 can do a 350 can do noticeably better, when the criteria you judge by is the power produced
add to that the fact that you can find 383 stroker kits, and 350 rebuild kits at the same or lower price in some cases to 305 parts, that will add an additional increase in displacement and you've got a significant reason to build with the larger bore combos.
BOTH the 305 and 350 have the SAME stroke and rod length
the larger surface area and larger displacement DO make a difference
a 305 has a piston dome area of about 11 sq inches, a 350 with its larger bore has a piston dome area of about 12.59 sq inches, if both have a peak cylinder pressure of 600psi that 6600 pounds of force exerted, for an instant or two on the 305 and 7550 pounds of force exerted pounds of force exerted, for an instant or two on the 350 piston
typical high performance pressure curves
305 = 3.736" x 3.48" (Gen.I, 5.7" rod)
350 = 4.000" x 3.48" (Gen.I, 5.7" rod)
if your thinking the increased power is all the result of the increase in displacement alone,
again, comparing apples/oranges the displacement went up about 13% due to an increase in bore diam of about 13%, but the stroke remained constant, between the two engines and the torque did go up as did the hp. even thou the stroke remained a constant, torque went up mostly due to the larger bore, and the resulting increase in displacement ,hp went up, due to the higher torque at any given rpm.
now a more reasonable comparison to show the effective result of increasing the bore but keeping the displacement nearly constant would be to compare the 305 with its 3.736" bore to a 302 with its 4" bore
305 = 3.736" x 3.48"stroke (Gen.I, 5.7" rod)
302= 4" bore x 3" stroke(Gen.I, 5.7" rod)
what you find is the larger bore and the shorter stroke , but nearly equal displacement move the power curve up about equal to the change in piston speed
at 3000FPM in piston speed a 305 is turning 5172rpm
at 3000FPM in piston speed a 302 is turning 6000rpm
or about 800 rpm faster, if both make the same 300ft lbs of tq at the same piston speed you get
305 is turning 5172rpm x the same 300ft lbs of tq =295hp
302 is turning 6000rpm x the same 300ft lbs of tq=343hp
which shows the advantage of the same displacement but a larger bore and shorter stroke at similar stress levels
as you can see in this chart most of the stock heads don,t flow as well as the AFR 195cc heads and there ARE better flowing heads
now some guys are required to maintain the stock block, or basic displacement, and in those cases you might also want to think about supercharging the engine, its no big trick to install a decent supercharger on your basic 305-307 and make 400-450 plus hp either
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