MOPAROFFICIAL
If it has tits, it's a liabilititty.
Yep, about 8 -10 degrees cam adv and it'll be breathing fire. To hell with mileage, but it will be a nasty ****.
what solid cam is equivalent to a hyd 268 ?
- Thread starter stroker402
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nothing wrong with solid, but if you wanted to go hydraulic, a set of rockers and pushrods would be almost free as they were spread like honey on bread on small blocks from the late 60's to the early 90's. Not recommending anything, just say'n....
Too much for street? I would say so.
The 268 is a popular small block cam. Works great with a mild 340/360. Works well in 318's too but that cam in a automatic is borderline too big with a stock converter. It has been done but tuning is tricky. Your 273 2 barrel is easy to over cam and if you do there goes your bottom end. Good you have a 4 speed so you don't have to mess with torque converters.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Heres some math;
3.65bore x 3.315 stroke gets you swept of 568.4cc
the .028 is about 6.3cc
-.020 deck is 3.4cc
heads could be 60cc or maybe 57cc
eyebrows maybe 7cc
that works out to an Scr of 8.41 to 8.71
If the deckheight was only -.010, then the numbers are 8.58 and 8.89
So the range is 8.89 to 8.41
and none of these, NONE, will get you 160psi with that cam installed at 107 or 102 or any other reasonable number........... until the ICA gets down to 45* with the highest likely 8.89 figure, to 31* with the smallest likely 8.41 figure.
If you want to be most optimistic and go with the 45* ICA
Then a solid cam with a 45* ICA NET after lash, might have an advertised ICA of say 51*, and the single pattern solid cam,that carries that, could be a 262/262/108+3........................could be
And if OP had such a cam, he sure woulnd't be complaining about a soft bottom end, nor that it takes forever to get to the power.
So, that's why I'm having trouble believing his compression tester. I've almost never heard anybody complain about soft bottom-end when he has 160psi. This is a very good number.
But everybody who has only 112psi, is guaranteed to complain about something,lol! Anything less than 135 on the street, IMO, is already getting soft, certainly,too soft for me. And less than 120 might work for a DD, but really that's sad...cuz it will suck gas big time, especially in city driving.
Anyway it's just math.
BTW
OP, advancing that cam to 102 will increase your cylinder pressure, guaranteed. But I foresee a couple of possible issues
1) if you really do have 160 and it is possible, say with leaky rings on a 10/1 piston, then you may need to run a higher grade of gasoline due to detonation setting in.
2) if you do have hi-compression pistons in there, then you better check your piston to valve clearance, at the new installed centerline.
3) IMO, the increase in cylinder pressure will not be significant enough to spend all this time on.
4) I like that cam. It just needs a lot of compression,and a lot more rear gear. But IMHO, it is too big for your combo.
5) I like a lotta cams with matching compression and gears.
6) if the 160psi is wrong, then I don't think a 268* cam is gonna be the answer. Certainly it will be better, than the current cam, but it too will want more rear gear.
7) the Isky looks about right
8) but I wouldn't do anything until the cylinder pressure is verified by a second gauge. And if it too says 160, the I would be doing a Leakdown test.
3.65bore x 3.315 stroke gets you swept of 568.4cc
the .028 is about 6.3cc
-.020 deck is 3.4cc
heads could be 60cc or maybe 57cc
eyebrows maybe 7cc
that works out to an Scr of 8.41 to 8.71
If the deckheight was only -.010, then the numbers are 8.58 and 8.89
So the range is 8.89 to 8.41
and none of these, NONE, will get you 160psi with that cam installed at 107 or 102 or any other reasonable number........... until the ICA gets down to 45* with the highest likely 8.89 figure, to 31* with the smallest likely 8.41 figure.
If you want to be most optimistic and go with the 45* ICA
Then a solid cam with a 45* ICA NET after lash, might have an advertised ICA of say 51*, and the single pattern solid cam,that carries that, could be a 262/262/108+3........................could be
And if OP had such a cam, he sure woulnd't be complaining about a soft bottom end, nor that it takes forever to get to the power.
So, that's why I'm having trouble believing his compression tester. I've almost never heard anybody complain about soft bottom-end when he has 160psi. This is a very good number.
But everybody who has only 112psi, is guaranteed to complain about something,lol! Anything less than 135 on the street, IMO, is already getting soft, certainly,too soft for me. And less than 120 might work for a DD, but really that's sad...cuz it will suck gas big time, especially in city driving.
Anyway it's just math.
BTW
OP, advancing that cam to 102 will increase your cylinder pressure, guaranteed. But I foresee a couple of possible issues
1) if you really do have 160 and it is possible, say with leaky rings on a 10/1 piston, then you may need to run a higher grade of gasoline due to detonation setting in.
2) if you do have hi-compression pistons in there, then you better check your piston to valve clearance, at the new installed centerline.
3) IMO, the increase in cylinder pressure will not be significant enough to spend all this time on.
4) I like that cam. It just needs a lot of compression,and a lot more rear gear. But IMHO, it is too big for your combo.
5) I like a lotta cams with matching compression and gears.
6) if the 160psi is wrong, then I don't think a 268* cam is gonna be the answer. Certainly it will be better, than the current cam, but it too will want more rear gear.
7) the Isky looks about right
8) but I wouldn't do anything until the cylinder pressure is verified by a second gauge. And if it too says 160, the I would be doing a Leakdown test.
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MOPAROFFICIAL
If it has tits, it's a liabilititty.
Buying the 268 would be like buying another cam thats still too big "for a stock 273 automatic trans car" ...get a cam with an advertised 256 or 260 duration tops. Probably been said, I saw isky mentioned in here by rusty I beleive.
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No, that was not mine. I had Barracudas, 64, 66, and a 68 383. Still have all but the 64. There is a thread about a lot of cams in a 273 Commando/Charger with quarter mile times, mph, and impressions. 69 440?
stroker402
1968 dart GTS convertible
Ok, I thought it didn't sound quite right.
here are the correct results of compression test.
compression tester starts out at 35#'s. " JUNK"
minus what I have on the previous results. engine cold and carb butterflies open
125 range +or - .
sounds more realistic now doesn't it ?
here are the correct results of compression test.
compression tester starts out at 35#'s. " JUNK"
minus what I have on the previous results. engine cold and carb butterflies open
125 range +or - .
sounds more realistic now doesn't it ?
MOPAROFFICIAL
If it has tits, it's a liabilititty.
Cold sweep should be 90+ psi
Throw that tester away!
stroker402
1968 dart GTS convertible
yep, got that right !
stroker402
1968 dart GTS convertible
well where do I go now knowing there is not much compression, mill the 920 closed chamber heads/ intake or smaller cam?
pistons are out of the question.
pistons are out of the question.
I used Egge HP pistons, milled my 273 heads, used the thinnest gasket I could and still only got 9.6/1 static. With the Isky E4 advanced a few degrees, it runs good and doesn't ping.
I have a friend who just Dyno’d a 273 with .030 over 2 barrel pistons, OEM rings, 920 heads, Isky E-4 cam, 340 valve springs, original intake, Edelbrock 650?, made 266 HorsePower up to high 5K. I think, Commando Distributor, but not sure. The point is your cam is pretty big for a street 273. Next 273 I build will have a Racer Brown ST-1. I would not worry about compression, it is what it is, just maximize your tune. You have nice even compression, so the 273 seems sound. One thing that might be holding you back is the distributor. My 64 273 had a 284 duration solid cam and a 600 cfm Holley for a couple years. It ran strong, but not as strong as the E-4 and OEM AFB. I vote for a smaller cam.
stroker402
1968 dart GTS convertible
Let me run this by you guys >>>>>>>>>>>>
I may have access to a 68 318 . I believe that is a 9.2 compression flat top engine from the factory . What if I installed my closed chamber 920 heads and my big erson cam with 8* degrees advance in that 318 ? I read here that installing those 920 heads with a .028 head gaskets on a 318 would bump the compression up almost 1 point that would be somewhere close to 10.1 compression. and installed my ld340 and 650 dp with headers . what do you think of that combo? I have so many more option with a 318 or 340 engine than my 273 .
Or , if someone has a 340 short block or complete 340 , no 360's though. they want to sell close to wisconsin I may have to upgrade to that.
let me know what you have .
I may have access to a 68 318 . I believe that is a 9.2 compression flat top engine from the factory . What if I installed my closed chamber 920 heads and my big erson cam with 8* degrees advance in that 318 ? I read here that installing those 920 heads with a .028 head gaskets on a 318 would bump the compression up almost 1 point that would be somewhere close to 10.1 compression. and installed my ld340 and 650 dp with headers . what do you think of that combo? I have so many more option with a 318 or 340 engine than my 273 .
Or , if someone has a 340 short block or complete 340 , no 360's though. they want to sell close to wisconsin I may have to upgrade to that.
let me know what you have .
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that 9.2 compression is closer to 8.4 and its still to big I have used that combo with a similar cam and it still had no bottom end but the whiplash cams did surprise me with good bottom end 280/475 lift but the idle was rough and sounded like a racecar everything is a trade off.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Here is a snapshot of your 273 engine with the 286cam, indicating the reason for your poor low-rpm performance; notice the VP of 82
base) Static compression ratio of 8.5:1.
Your dynamic compression ratio is 6.77:1 .
Your dynamic cranking pressure is 128.43 PSI.
V/P (Volume to Pressure Index) is 82 ....................................... 82 .
Here it is with a 99* install
Static compression ratio of 8.5:1.
Your dynamic compression ratio is 7.15:1 .
Your dynamic cranking pressure is 138.04 PSI.
V/P (Volume to Pressure Index) is 93, and 93/82=.................... plus 13%
read about VP here
V/P Index Calculation
A) If I recall correctly that 69 -318 already has closed chamber heads.and so, with the 286cam in at 99*
Static TRUE compression ratio of 9.2:1.
Your dynamic compression ratio is 7.68:1 .
Your dynamic cranking pressure is 151.60 PSI.
V/P (Volume to Pressure Index) is 118, and 118/82= ............... plus 44%
To give you an idea of what this means, imagine your engine just got 44% more torque at about 1800 rpm. This is a huge improvement, also akin to increasing the rear gear by 44%..
Now, changing the ICA to 99* will really mess up your overlap period and wreck the whole point of having that cam, which is the 72* of overlap, which, with properly working headers, will make a nice little power boost somewhere around 5200/5400 rpm. With a 108 install, your split overlap will be 8* advanced, meaning the intake valve will now be opening at 8* sooner and the exhaust closing also 8 degrees , sooner. The net result of that is a serious loss in the power-spike, and probably a rougher lower-vacuum, idle.... IMHO it's too much.
B) however, you now have a few more cubes,318, so you could back the 286 up to 104, and get
Static TRUE compression ratio of 9.2:1.
Your dynamic cranking pressure is 145.95 PSI.
V/P (Volume to Pressure Index) is 110 and 110/82 is..................... plus 34%
but before you get too excited, recall that this is with a true 9.2 Scr.
C) But that 9.2- 318 will run pretty good with a 268*FTH cam
Static compression ratio of 9.2:1.
Your dynamic compression ratio is 7.68:1 .
Your dynamic cranking pressure is 151.60 PSI.
V/P (Volume to Pressure Index) is 118 .and 118/82 is..................... plus 44%
This cam has 52* of overlap, not even close to the 72 of that 286* cam,
BUT that 286 in at 99* only has an effective overlap of 56*anyway, so you haven't really lost anything there.
and recall that this is still at a true 9.2Scr
D) With the 318/268cam at a more likely
Static TRUE compression ratio o,f 8.8:1
Your dynamic compression ratio is 7.35:1 .
Your dynamic cranking pressure is 143.13 PSI.
V/P (Volume to Pressure Index) is 111 .This is now 111/82=............. plus 35.4%
E) But if you boost the 318/268 to ;
Static TRUE compression ratio of 9.9:1.
Your dynamic compression ratio is 8.14:1 .
Your dynamic cranking pressure is 163.52 PSI.
V/P (Volume to Pressure Index) is 125 . and 125/82=........................ plus 52*
F) And finally the 273 @.020 o/s, the 368 cam, and bumped to
Static compression ratio of 10.0:1
Your dynamic compression ratio is 8.22:1 .
Your dynamic cranking pressure is 165.61 PSI.
V/P (Volume to Pressure Index) is 111. and 111/82=.......................... plus 35.4%
G) But guess what,with the compression now up,
the 273/286cam could look like
Static compression ratio of 10.2:1.
Your dynamic compression ratio is 8.19:1 .
Your dynamic cranking pressure is 164.83 PSI.
V/P (Volume to Pressure Index) is 106, and 106/82=..................... plus 29%
H) And the 318/286 cam, at 3.94 bore
Static compression ratio of 10.1:1.
Your dynamic compression ratio is 8.11:1 .
Your dynamic cranking pressure is 162.74 PSI.
V/P (Volume to Pressure Index) is 123 and 123/82=..................... plus 50%
This is only a tiny loss from the 268, with a huge increase in peak-power,
plus you get to keep the power-spike and the nasty idle.
Now compare the H) combo here at 10.1Scr,
to the B) combo at a true 9.2.
And I get 123/110= plus 11.8 from compression alone, and recall that this is low-rpm performance only,
also compare H to E
And then is the cost;
How much for the cam kit installed, versus
a set of high compression pistons installed in either engine.
base) Static compression ratio of 8.5:1.
Your dynamic compression ratio is 6.77:1 .
Your dynamic cranking pressure is 128.43 PSI.
V/P (Volume to Pressure Index) is 82 ....................................... 82 .
Here it is with a 99* install
Static compression ratio of 8.5:1.
Your dynamic compression ratio is 7.15:1 .
Your dynamic cranking pressure is 138.04 PSI.
V/P (Volume to Pressure Index) is 93, and 93/82=.................... plus 13%
read about VP here
V/P Index Calculation
A) If I recall correctly that 69 -318 already has closed chamber heads.and so, with the 286cam in at 99*
Static TRUE compression ratio of 9.2:1.
Your dynamic compression ratio is 7.68:1 .
Your dynamic cranking pressure is 151.60 PSI.
V/P (Volume to Pressure Index) is 118, and 118/82= ............... plus 44%
To give you an idea of what this means, imagine your engine just got 44% more torque at about 1800 rpm. This is a huge improvement, also akin to increasing the rear gear by 44%..
Now, changing the ICA to 99* will really mess up your overlap period and wreck the whole point of having that cam, which is the 72* of overlap, which, with properly working headers, will make a nice little power boost somewhere around 5200/5400 rpm. With a 108 install, your split overlap will be 8* advanced, meaning the intake valve will now be opening at 8* sooner and the exhaust closing also 8 degrees , sooner. The net result of that is a serious loss in the power-spike, and probably a rougher lower-vacuum, idle.... IMHO it's too much.
B) however, you now have a few more cubes,318, so you could back the 286 up to 104, and get
Static TRUE compression ratio of 9.2:1.
Your dynamic cranking pressure is 145.95 PSI.
V/P (Volume to Pressure Index) is 110 and 110/82 is..................... plus 34%
but before you get too excited, recall that this is with a true 9.2 Scr.
C) But that 9.2- 318 will run pretty good with a 268*FTH cam
Static compression ratio of 9.2:1.
Your dynamic compression ratio is 7.68:1 .
Your dynamic cranking pressure is 151.60 PSI.
V/P (Volume to Pressure Index) is 118 .and 118/82 is..................... plus 44%
This cam has 52* of overlap, not even close to the 72 of that 286* cam,
BUT that 286 in at 99* only has an effective overlap of 56*anyway, so you haven't really lost anything there.
and recall that this is still at a true 9.2Scr
D) With the 318/268cam at a more likely
Static TRUE compression ratio o,f 8.8:1
Your dynamic compression ratio is 7.35:1 .
Your dynamic cranking pressure is 143.13 PSI.
V/P (Volume to Pressure Index) is 111 .This is now 111/82=............. plus 35.4%
E) But if you boost the 318/268 to ;
Static TRUE compression ratio of 9.9:1.
Your dynamic compression ratio is 8.14:1 .
Your dynamic cranking pressure is 163.52 PSI.
V/P (Volume to Pressure Index) is 125 . and 125/82=........................ plus 52*
F) And finally the 273 @.020 o/s, the 368 cam, and bumped to
Static compression ratio of 10.0:1
Your dynamic compression ratio is 8.22:1 .
Your dynamic cranking pressure is 165.61 PSI.
V/P (Volume to Pressure Index) is 111. and 111/82=.......................... plus 35.4%
G) But guess what,with the compression now up,
the 273/286cam could look like
Static compression ratio of 10.2:1.
Your dynamic compression ratio is 8.19:1 .
Your dynamic cranking pressure is 164.83 PSI.
V/P (Volume to Pressure Index) is 106, and 106/82=..................... plus 29%
H) And the 318/286 cam, at 3.94 bore
Static compression ratio of 10.1:1.
Your dynamic compression ratio is 8.11:1 .
Your dynamic cranking pressure is 162.74 PSI.
V/P (Volume to Pressure Index) is 123 and 123/82=..................... plus 50%
This is only a tiny loss from the 268, with a huge increase in peak-power,
plus you get to keep the power-spike and the nasty idle.
Now compare the H) combo here at 10.1Scr,
to the B) combo at a true 9.2.
And I get 123/110= plus 11.8 from compression alone, and recall that this is low-rpm performance only,
also compare H to E
And then is the cost;
How much for the cam kit installed, versus
a set of high compression pistons installed in either engine.
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stroker402
1968 dart GTS convertible
So , are you saying this will be an improvement to what I have now ? A 318 with my erson cam with 8* advance will be way better?
the compression ratio is up to 151#'s and the cam advanced 8* will help breath and exhale more efficient .
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4spdragtop
Well-Known Member
I have that exact cam the 270S from Comp. It's in my 273, LD48 stock stall 904, stock 323 SG. It's a dog off the line. I sit ported the stock heads. No noticeable change. The 273 best be pretty stout for the 270S cam.
My 273 is coming out and 340 going in this spring. I'l[ probably swap cam and lifters into 273.
Good luck.
QUOTE="Marcohotrod, post: 1972025213, member: 40408"]adjustable rockers can be used with hydraulic lifters, probably need different length pushrods. a good solid is 20-246-4, 270*/270*, 224*/224* at .050", .468"/.468" and 110* lobe seperation , Comp cams[/QUOTE]
My 273 is coming out and 340 going in this spring. I'l[ probably swap cam and lifters into 273.
Good luck.
QUOTE="Marcohotrod, post: 1972025213, member: 40408"]adjustable rockers can be used with hydraulic lifters, probably need different length pushrods. a good solid is 20-246-4, 270*/270*, 224*/224* at .050", .468"/.468" and 110* lobe seperation , Comp cams[/QUOTE]
stroker402
1968 dart GTS convertible
Found this .......... says 68 318 has 675 open chamber heads probally with 8.8 compression or so 9.2 ?? I thiknk it's a flat top piston also.
sooooooooooooo...................... if I put my 920 closed chamber heads on this 318 what will be the compression ratio?
Small Block Cylinder Heads.
CC's /Port Volume / Size / Flow
1968 - 1974 {273 & 318} Casting #2843675
Open-Shaped Combustion Chamber
Factory CC Level.........................67.0 - 68.5 CC's
Recommended Minimum CC's.....60.6 CC's
Intake Gasket Size....................1.05" x 2.07"
Exhaust Gasket Size..................1.14" x 1.59"
Intake Valve..............................1.78"
Exhaust Valve............................1.50"
Intake Bowl Size.......................1.53" {86%}
Intake Port Size........................127 CC
Exhaust Port Size........................61 CC
Intake Flow...............................160 CFM @ .450" Lift...........162 CFM @ .500" Lift
Exhaust Flow.............................107 CFM @ .450" Lift...........109 CFM @ .500" Lift
Intake-to-Exhaust Flow......................66.8%...................................67.1%..........
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stroker402
1968 dart GTS convertible
Just trying to see if I can bump the compression ratio up where my erson cam will like . need lots compression for that erson .
I read here from someone that installing 920 closed chamber heads on a flat top 68 318 the ratio would jump 1 pt. making it 10.2. sound right ?
I read here from someone that installing 920 closed chamber heads on a flat top 68 318 the ratio would jump 1 pt. making it 10.2. sound right ?
Too much for todays fuel unless AJ thinks that top fuel cam you have will bleed off compression. LOL
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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VP is a Measure we use to compare low-rpm improvements and NOTHING more.
You are comparing the base combo to the A combo, and the math for a TRUE 9.2 318 shows it to have a low-rpm improvement of Plus44%
But with the 318/286 at a true 9.2,(Combo B) you can install the cam properly to and still have a plus34% improvement, and get back the power spike at 5200ish.
AND, with the 318/286 at 10.1 (combo H), you can get an improvement of plus50% !
I like combo H because pistons are available from KB to do it, and you get to keep that wicked cam. And with 50 more cubes, and 3.91s it will be dynomite.
If you were to build combo H, you would have to check the piston to valve clearance, and if insufficient, the piston tops would have to be machined, at added cost. And you would also have to check the piston to head clearance and try to keep the Q in a decent working range. There is only a 6% difference from a TRUE 9.2 to 10.1, so I'm not sure if it's worth pursuing from a VP-only standpoint.
K) But if the TRUE SCR of the 9.2 318 is actually 8.7, that's a hard hard hit
Static compression ratio of 8.7:1.
Your dynamic compression ratio is 7.32:1 .
Your dynamic cranking pressure is 142.37 PSI.
V/P (Volume to Pressure Index) is 112
This still with the 286 cam. Compare this with the H combo at 123VP
Now you're falling back to 112/82= 36.6%
So if you measure the 318 at under, say 9.0, then to me the 10.1 Scr IS worth doing, not only for the Low-rpm improvement, but for the across-the-board power increase,and for superior driveability, and for the potential for improved fuel economy ........ cuz according to the numbers, that cam has gotta suck gas pretty hard.
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