hey GRUMPYVETTE??
"
i have a real 265 race engine in my '56 Nomad. i am ready to change cams and wonder how much overlap is just right for this small engine.
rpm range is 5 to 7K 5.67 gear, 12 1/2 comp.
the current cam has 21 degrees and makes no top end HP. this is not a killer motor but not a streeter either."
Ill be glad to work with you as Ive got several software programs and tons of notes from many years of engine builds, but I need to know more info, TO MAKE A VALID SUGGESTION,
ARE YOU RUNNING 1/8TH OR 1/4 MILE TRACKS
car weight?
transmission USED?
LAUNCH RPM?
STALL SPEED IF ITS AN AUTO TRANS?
HEADER DIMENSIONS?
ARE YOU RUNNING OPEN OR FULL EXHAUST?
COMPRESSION RATIO?
HEADS USED?
GOT ANY FLOW NUMBERS?(OR AT A MINIMUM,CASTING NUMBERS)
INTAKE AND CARB USED?
TIRE HEIGHT
RPM THRU THE LIGHTS
AND ANY OTHER INFO YOU CAN SUPPLY
answers by ?'s asked
1. 1/4 mile. [normally 'vegas @ 2200", sometimes phoenix @ 1100".]
2. 3560 with me in seat.
3. 2.64 low 4 speed [wide ratio] 5.67 rear
4. usually 5400 launch.*see last comment
5. 12 1/2 [rated for the 265 with old power pac heads, i have no idea what the cc's were on those heads] with 65 cc heads measured, [old 64 cc's with age {ie valve jobs} and polish]
6. 1.94 x 1.5, three angle with 30 back cut
7. 461 or 462 [old age-sorry]
8. 600 Holley DP + Holley 300-1 [early low single plane]
9. 28.5"x 9" phoenix
10. with a cam [#1] i no longer own 7000, cam #2 6800, current cam [#3] 6600.
additional info.
with cam #1, i could leave at 4400 and cross the line at 7K in low 13's. cam #2 leave at 5200 and cross line at 6800, mid 13's. cam #3 leave at 5800 cross line at 6600 low 14's [ugh] note i still have cam #2 [on shelf] and #3 is in engine.
cam #3 is 244/255@50 and 510/533" net.with 21 degrees overlap.
cam #2 [257/270@50 & 470/488" net] has 39 degrees overlap, [however it lacked lift. current cam #3. has lift but hacks overlap.]
only specs on cam #1, 272 @50 and .558" net lift.
headers have a merge collector with a goilet and a megaphone exit.
i ran this engine for some time with a dual plane and a 750DP, the car preformed very well [generally 13.40's and 105].with #2 cam.
when i changed to #3 cam [looking for more lift], with the dual plane and it wouldn't go then i added the single plane. i almost believe it got worse.
thanks for your time and effort. await your reply.
rod in AZ.
read this first
keep in mind you can,t use .050 lift duration specs to calculate overlap
and to maximize the results youll want to use a compression ratio in the 10.5:1-10.8:1 range, and an intake like the RPM AIR GAP , with a 2" 4 hole carb spacer MAY HELP, due to the smaller displacement
.
thin head gaskets, milled heads,domed piston will help
If the seat to seat opening and closing times are not known, the overlap can be calculated using the advertised duration and the Lobe Separation Angle (LSA). This formula works for both single and dual pattern cams.
Add the intake and exhaust adv durations
Divide the results by 4
Subtract the LSA
Multiply the results by 2
Using the example cam above:
268+280=548
548/4=137
137-110=27
27*2=54
The overlap is 54º
Here's another example:
Comp Cams XE294H
Adv Dur: int 294º, exh 306º
110 LSA, 106 ILC (4º advance)
Valve timing @ .006"
Int opens @ 41º BTDC
Int closes @ 73º ABDC
Exh opens @ 87º BBDC
Exh closes @ 39º ATDC
Adding the int open and exh close times (41+39) the overlap is 80º
Using the formula above:
294+306=600
600/4=150
150-110=40
40*2=80
The overlap is 80º
read thru these links
viewtopic.php?f=52&t=480&p=1666#p1666
viewtopic.php?f=52&t=1070&p=2051#p2051
my computer says you want this crower cam i linked below,
Ill save you the math, its got 77 degrees of seat-to-seat overlap, yes you want the wide lsa as it traps cylinder volume and results in more high rpm tq
http://www.crower.com/misc/cam_spec/cam ... &x=47&y=11
crower 00323 with 1.6:1 rockers, verify clearances and geometry as that results in a .563/.581 lift, you may want to use the 1.5:1 ratio if clearance is an issue as the gains with the higher ratio are not large,and a rocker stud girdle seems like a good idea for valve train stability
as the ratio of displacement to valve diam. is reduced the lsa needs to get wider to maximize cylinder fill efficiency
or put a different way, as the valve size is limited in a 265 to about a 1.90 valve ,by the small bore,and as the displacement is reduced by the short stroke the wider lsa improves high rpm cylinder filling
http://www.popularhotrodding.com/tech/0 ... index.html
"
i have a real 265 race engine in my '56 Nomad. i am ready to change cams and wonder how much overlap is just right for this small engine.
rpm range is 5 to 7K 5.67 gear, 12 1/2 comp.
the current cam has 21 degrees and makes no top end HP. this is not a killer motor but not a streeter either."
Ill be glad to work with you as Ive got several software programs and tons of notes from many years of engine builds, but I need to know more info, TO MAKE A VALID SUGGESTION,
ARE YOU RUNNING 1/8TH OR 1/4 MILE TRACKS
car weight?
transmission USED?
LAUNCH RPM?
STALL SPEED IF ITS AN AUTO TRANS?
HEADER DIMENSIONS?
ARE YOU RUNNING OPEN OR FULL EXHAUST?
COMPRESSION RATIO?
HEADS USED?
GOT ANY FLOW NUMBERS?(OR AT A MINIMUM,CASTING NUMBERS)
INTAKE AND CARB USED?
TIRE HEIGHT
RPM THRU THE LIGHTS
AND ANY OTHER INFO YOU CAN SUPPLY
answers by ?'s asked
1. 1/4 mile. [normally 'vegas @ 2200", sometimes phoenix @ 1100".]
2. 3560 with me in seat.
3. 2.64 low 4 speed [wide ratio] 5.67 rear
4. usually 5400 launch.*see last comment
5. 12 1/2 [rated for the 265 with old power pac heads, i have no idea what the cc's were on those heads] with 65 cc heads measured, [old 64 cc's with age {ie valve jobs} and polish]
6. 1.94 x 1.5, three angle with 30 back cut
7. 461 or 462 [old age-sorry]
8. 600 Holley DP + Holley 300-1 [early low single plane]
9. 28.5"x 9" phoenix
10. with a cam [#1] i no longer own 7000, cam #2 6800, current cam [#3] 6600.
additional info.
with cam #1, i could leave at 4400 and cross the line at 7K in low 13's. cam #2 leave at 5200 and cross line at 6800, mid 13's. cam #3 leave at 5800 cross line at 6600 low 14's [ugh] note i still have cam #2 [on shelf] and #3 is in engine.
cam #3 is 244/255@50 and 510/533" net.with 21 degrees overlap.
cam #2 [257/270@50 & 470/488" net] has 39 degrees overlap, [however it lacked lift. current cam #3. has lift but hacks overlap.]
only specs on cam #1, 272 @50 and .558" net lift.
headers have a merge collector with a goilet and a megaphone exit.
i ran this engine for some time with a dual plane and a 750DP, the car preformed very well [generally 13.40's and 105].with #2 cam.
when i changed to #3 cam [looking for more lift], with the dual plane and it wouldn't go then i added the single plane. i almost believe it got worse.
thanks for your time and effort. await your reply.
rod in AZ.
read this first
keep in mind you can,t use .050 lift duration specs to calculate overlap
and to maximize the results youll want to use a compression ratio in the 10.5:1-10.8:1 range, and an intake like the RPM AIR GAP , with a 2" 4 hole carb spacer MAY HELP, due to the smaller displacement
.
thin head gaskets, milled heads,domed piston will help
If the seat to seat opening and closing times are not known, the overlap can be calculated using the advertised duration and the Lobe Separation Angle (LSA). This formula works for both single and dual pattern cams.
Add the intake and exhaust adv durations
Divide the results by 4
Subtract the LSA
Multiply the results by 2
Using the example cam above:
268+280=548
548/4=137
137-110=27
27*2=54
The overlap is 54º
Here's another example:
Comp Cams XE294H
Adv Dur: int 294º, exh 306º
110 LSA, 106 ILC (4º advance)
Valve timing @ .006"
Int opens @ 41º BTDC
Int closes @ 73º ABDC
Exh opens @ 87º BBDC
Exh closes @ 39º ATDC
Adding the int open and exh close times (41+39) the overlap is 80º
Using the formula above:
294+306=600
600/4=150
150-110=40
40*2=80
The overlap is 80º
read thru these links
viewtopic.php?f=52&t=480&p=1666#p1666
viewtopic.php?f=52&t=1070&p=2051#p2051
my computer says you want this crower cam i linked below,
Ill save you the math, its got 77 degrees of seat-to-seat overlap, yes you want the wide lsa as it traps cylinder volume and results in more high rpm tq
http://www.crower.com/misc/cam_spec/cam ... &x=47&y=11
crower 00323 with 1.6:1 rockers, verify clearances and geometry as that results in a .563/.581 lift, you may want to use the 1.5:1 ratio if clearance is an issue as the gains with the higher ratio are not large,and a rocker stud girdle seems like a good idea for valve train stability
as the ratio of displacement to valve diam. is reduced the lsa needs to get wider to maximize cylinder fill efficiency
or put a different way, as the valve size is limited in a 265 to about a 1.90 valve ,by the small bore,and as the displacement is reduced by the short stroke the wider lsa improves high rpm cylinder filling
http://www.popularhotrodding.com/tech/0 ... index.html