Need a plan - component selection for restoring 68 340 that runs on 91 oct
- Thread starter Hank’sFS
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Ok, here is what I'm thinking tonight and then a few comments.
I'm mulling over some possible pairings:
KB243KTM pistons with a Hughes SEH1620AL-12 cam
L2316F pistons with Comp Cams 268AH-10
Or a bit more aggressive
Same pistons with Lunati 10200702 or Comp Cams XE274H or Hughes SEH2024AL-11
And some comments - from all the digging I have done, I haven't seen anything that actually defines the original 340 4-speed cam beyond the basic specs. So that gives me some wiggle room. But I still want to run on 91 if possible. I assume everyone who stated use the stock cam means something close to the original numbers but doesn't really know every metric used for a modern cam or do you?
Here are the numbers I did find: PN 2899205 advertised duration 282/292, @0.50" 214/221 , lift .445..455 , lobe centers 114 & ???.
Back to my premise and some notes on why: The engine on the outside must look stock because well see below about why I bought the car 30 some years ago. I'd like some performance but a couple of things. First, it is a A-vert, not a notch or fastback. When I bought the car in the 80s it had a MP purple and was 0.20 over, stock manifolds, carb and exhaust. I swapped a MSD for the dual point (still have original), added some octane boost and it did just fine. But even then you could stand on the brakes, punch it and see the car twist a bit. Why? Well I think cause it is a convertible and has less structure to fight the twist induced by the torque. And yes, before you wander off, it is a CA car and has almost no rust and the structure is unbent. It was and is really quite nice. So, putting 450HP and pile of torque into this car seems like going too far, even if I could do it so you could not tell by looking. On the other hand, I also don't want to dummy it down in performance just because I can't buy decent fuel. I will use octane boost if necessary but have asked you to help me come up with something that works well with the gas I have and the desire to keep it looking original. Why? I bought the car realizing that though the engine was worn and once rebuilt, the car was in fact a Formula S 340 Hurst 4-speed vert and even in the 1980s I knew this was a very rare A-body. So, I haven't tub it, or cut sheet metal or done lots of other things that would have Sox and Martin proud. IMHO this isn't the car for that. I think it should be restored as best possible so folks can see and hear a small bit of 1968 Americana.
I'm mulling over some possible pairings:
KB243KTM pistons with a Hughes SEH1620AL-12 cam
L2316F pistons with Comp Cams 268AH-10
Or a bit more aggressive
Same pistons with Lunati 10200702 or Comp Cams XE274H or Hughes SEH2024AL-11
And some comments - from all the digging I have done, I haven't seen anything that actually defines the original 340 4-speed cam beyond the basic specs. So that gives me some wiggle room. But I still want to run on 91 if possible. I assume everyone who stated use the stock cam means something close to the original numbers but doesn't really know every metric used for a modern cam or do you?
Here are the numbers I did find: PN 2899205 advertised duration 282/292, @0.50" 214/221 , lift .445..455 , lobe centers 114 & ???.
Back to my premise and some notes on why: The engine on the outside must look stock because well see below about why I bought the car 30 some years ago. I'd like some performance but a couple of things. First, it is a A-vert, not a notch or fastback. When I bought the car in the 80s it had a MP purple and was 0.20 over, stock manifolds, carb and exhaust. I swapped a MSD for the dual point (still have original), added some octane boost and it did just fine. But even then you could stand on the brakes, punch it and see the car twist a bit. Why? Well I think cause it is a convertible and has less structure to fight the twist induced by the torque. And yes, before you wander off, it is a CA car and has almost no rust and the structure is unbent. It was and is really quite nice. So, putting 450HP and pile of torque into this car seems like going too far, even if I could do it so you could not tell by looking. On the other hand, I also don't want to dummy it down in performance just because I can't buy decent fuel. I will use octane boost if necessary but have asked you to help me come up with something that works well with the gas I have and the desire to keep it looking original. Why? I bought the car realizing that though the engine was worn and once rebuilt, the car was in fact a Formula S 340 Hurst 4-speed vert and even in the 1980s I knew this was a very rare A-body. So, I haven't tub it, or cut sheet metal or done lots of other things that would have Sox and Martin proud. IMHO this isn't the car for that. I think it should be restored as best possible so folks can see and hear a small bit of 1968 Americana.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Usually
The bigger the cam, the lower the cylinder pressure will be, and the less likely to detonate the engine will be. But this comes with a penalty, the softer the low-rpm take-off will be. And that leads to a higher stall TC to get off the line, and bigger gears to continue the acceleration.
To do it all requires a very careful co-ordination of parts. So if the rear gears have to stay then you sorta have to build around them. If the TC has to stay, then you really have to be careful. After that the Cylinder pressure and camshaft have to be friendly one towards the other, or it all goes sour in a hurry.
Best advice I got is to forget that 2899205. That cam scrubs pressure from a build with too much, and leaves you with a pretty small .050, yeah just try spinning tires with that in an 8/1 engine. You're not at that point,yet
For a nice torquey 340, Ima guessing a 218/222 intake duration at .050, and 9.6 Scr , will have a lotta potential. The lower your rear gear is, the higher your stall will need to be. If you need a hiway gear like 3.23s, then you might like a 2800TC. If you have 3.91s then you could probably use a stock teener TC.
With the Go-To 3.55s, the factory TC is a good starting point.
The 220ish cam is not a high rpm-powerhouse. What it is, is a low to mid rpm torque booster, just right to get a 3.23geared A-vert motoring, with the right TC. And just right for cruising 60~2400 depending on tire diameter. Its also pretty good on the 2-1 downshift at 30/35 mph. And not too bad in the Zero to 60 dash, hitting about 6200 at the top of first gear, yeah a little out of the power, but second is worse topping out at 3700.
So that if that sounds pretty good then you just have to marry the Scr to the ICA, for the gas you wanna burn and yur done.
And that's where the trouble starts.......And so; there are a few ways to skin this cat.
First.....Your engine will fall together at a certain to be determined Scr. That is to say a cheap build; no deck machining, no head shaving nor intake machining etc, Cheap. When you get that final Scr number, then you go try to find a 220ish cam with the required ICA, to keep the pressure as high as possible and yet not detonate..... that is the problem.
oh yeah sure , you can guess 10 psi low and pump up the TC and it works because you can just give it more gas and away you go........ until you run out of gas-pedal and it's too slow for you; THEN WHAT?
Well then it would have been better to guess that extra 10 psi and just either delay the power timing, or start injecting anti-detonant.
Second..... If you choose the cam first, then you engineer the Scr around a known ICA, and don't have to guess. But it usually costs more, cuz there may be machining required.
Third..... You go find somebody who has already built the combo you want and get the skinny from him
Fourth..... You call the man with all the cam experience of a lifetime and tell him what you wanna do, and he tells you, and you just go do it.
Fifth..... That guy is watching, and waiting, and ready to jump in.
Sixth..... I'm out of ideas, but there has gotto be a sixth; there's always a sixth, I just know it's gotta be here somewhere. Wyrms, help me out, wouldjah
But first you gotta make some decisions, like
what gear are you gonna run, cuz that will determine some upstream decisions. And be honest about your application;
if it's gonna be a streeter,any 340 combo will do, unless you really screw it up. So forget horsepower numbers, they are practically meaningless in this instance.
And what gas are you gonna run. This is a big deal, because each grade isabout a 5 psi cylinder pressure difference. And pressure is performance......... and economy. A 220 cam with max pressure, and a hiway gear can bring in some really good MPG numbers.
Now I just guessed at the 220*@050 cam size based on my experience. It's an all round do-everything pretty good cam.
If you want to bias for torque or economy, go down one size.
For a lil more power, go up one size.
But the rest of the package still has to be optimized for the new ICA.
And if you optimize for one size cam, it might be hard to just swap cams nexy week!, so choose wisely .
With open chamber heads and no Quench, if you optimize for mid grade gas, then you should be able to move up or down one cam size, using the gasket thickness to compensate for the pressure change.That's what I did, but I guessed low on the pressure on the initial build. That's OK, my 367 went 93 in the 1/8th on 87E10,lol
Happy Happy HotRodding
The bigger the cam, the lower the cylinder pressure will be, and the less likely to detonate the engine will be. But this comes with a penalty, the softer the low-rpm take-off will be. And that leads to a higher stall TC to get off the line, and bigger gears to continue the acceleration.
To do it all requires a very careful co-ordination of parts. So if the rear gears have to stay then you sorta have to build around them. If the TC has to stay, then you really have to be careful. After that the Cylinder pressure and camshaft have to be friendly one towards the other, or it all goes sour in a hurry.
Best advice I got is to forget that 2899205. That cam scrubs pressure from a build with too much, and leaves you with a pretty small .050, yeah just try spinning tires with that in an 8/1 engine. You're not at that point,yet
For a nice torquey 340, Ima guessing a 218/222 intake duration at .050, and 9.6 Scr , will have a lotta potential. The lower your rear gear is, the higher your stall will need to be. If you need a hiway gear like 3.23s, then you might like a 2800TC. If you have 3.91s then you could probably use a stock teener TC.
With the Go-To 3.55s, the factory TC is a good starting point.
The 220ish cam is not a high rpm-powerhouse. What it is, is a low to mid rpm torque booster, just right to get a 3.23geared A-vert motoring, with the right TC. And just right for cruising 60~2400 depending on tire diameter. Its also pretty good on the 2-1 downshift at 30/35 mph. And not too bad in the Zero to 60 dash, hitting about 6200 at the top of first gear, yeah a little out of the power, but second is worse topping out at 3700.
So that if that sounds pretty good then you just have to marry the Scr to the ICA, for the gas you wanna burn and yur done.
And that's where the trouble starts.......And so; there are a few ways to skin this cat.
First.....Your engine will fall together at a certain to be determined Scr. That is to say a cheap build; no deck machining, no head shaving nor intake machining etc, Cheap. When you get that final Scr number, then you go try to find a 220ish cam with the required ICA, to keep the pressure as high as possible and yet not detonate..... that is the problem.
oh yeah sure , you can guess 10 psi low and pump up the TC and it works because you can just give it more gas and away you go........ until you run out of gas-pedal and it's too slow for you; THEN WHAT?
Well then it would have been better to guess that extra 10 psi and just either delay the power timing, or start injecting anti-detonant.
Second..... If you choose the cam first, then you engineer the Scr around a known ICA, and don't have to guess. But it usually costs more, cuz there may be machining required.
Third..... You go find somebody who has already built the combo you want and get the skinny from him
Fourth..... You call the man with all the cam experience of a lifetime and tell him what you wanna do, and he tells you, and you just go do it.
Fifth..... That guy is watching, and waiting, and ready to jump in.
Sixth..... I'm out of ideas, but there has gotto be a sixth; there's always a sixth, I just know it's gotta be here somewhere. Wyrms, help me out, wouldjah
But first you gotta make some decisions, like
what gear are you gonna run, cuz that will determine some upstream decisions. And be honest about your application;
if it's gonna be a streeter,any 340 combo will do, unless you really screw it up. So forget horsepower numbers, they are practically meaningless in this instance.
And what gas are you gonna run. This is a big deal, because each grade isabout a 5 psi cylinder pressure difference. And pressure is performance......... and economy. A 220 cam with max pressure, and a hiway gear can bring in some really good MPG numbers.
Now I just guessed at the 220*@050 cam size based on my experience. It's an all round do-everything pretty good cam.
If you want to bias for torque or economy, go down one size.
For a lil more power, go up one size.
But the rest of the package still has to be optimized for the new ICA.
And if you optimize for one size cam, it might be hard to just swap cams nexy week!, so choose wisely .
With open chamber heads and no Quench, if you optimize for mid grade gas, then you should be able to move up or down one cam size, using the gasket thickness to compensate for the pressure change.That's what I did, but I guessed low on the pressure on the initial build. That's OK, my 367 went 93 in the 1/8th on 87E10,lol
Happy Happy HotRodding
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AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
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Now How in the world did I miss that!!,lol.Wait what thread am I in. You have the A-vert as you say,an original FormulaS car right? Lemmee go check........
HYUP there it is right n post #1,lol
In that case you are gonna have to be more careful than ever with co-coordinating the combo, cuz the clutch does not have any built in Torque Multiplication;whatever torque goes into it, about the same comes out of it.Further the 3.23s call for a torquey engine because the available TM is just
3.23x2.66=8.59... and with 26.5" tall tires, this gets corrected to 8.59x12/13.25=7.78 .......
which is pretty flipp'n dismal, lol. It would be all too easy to fubar this combo up with a long slow lazy cam like that 2899205
So now I have to re-guess that the 220 cam is probably one size too big ..... depending on the design. A fast-rate 220 will still be OK, but a slowrate 213 could be worse.
See a fastrate 220 could be 260 advertised, and a slowrate 213 could be 257. Then you factor in where they ACTUALLY, REALLY REALLY, close, and you find out they are both 265s or 268s who knows. The thing is both will make similar pressure, and could idle similarly, yet the bigger cam might make 15 or 20 more horsepower..... with no penalty in fuel economy or low-rpm torque! Winner!!
BTW
You don't want a 114LSA cam; those are designed for the wide ratio Torqueflites, and are pressure bleeders. Nor do you want a 112,or even a 110. In your application with about a 1500 rpm powerband requirement and one gear to 60mph, Ima thinking even a 108 could be a skip-over. And that means that you can step up a size in cams to about 225/108, or a 230/106 fastrate.
Lets have some fun; To recap
>that 220 fast rate could be a 260 advertised, and an actually not leaking intake at 265, so lets call it a 265/273/110 ok ,that, at split overlap, would have an ICA of 60 and overlap of 49*
> now the slow one could be exactly the same
> next How about that 225/108 cam. That could be a 267 advertised, but no longer bleeding at 272, so lets call it a 272/280/108. Ok again at split overlap, the ICA would be 62*and overlap of 60*
> finally the biggest, the 230. This could be a 275/283/106 And again at split overlap the ICA would be 64*and overlap of 62*
Now lets check this out; The ICAs vary from 60 to 64, so basically they could all be installed at 62*!!! Lets say the rest of the engine can keep up, and then
the 213/110 makes 285hp. And lets say then maybe
the 220/110 makes 300hp,and
the 225/108 makes 325hp,and
the 230/106 makes 340hp;Jus saying.
Ok so with the same ICA of 62*, they are all gonna want the same Scr, surprise #1.
Next the cams with less overlap will make better city mpgs, than those with the more.
On the hiway the difference is much less.
So pick your poison; 285hp,300hp,325hp,or 340hp.......................Boy I wish it was that easy
HYUP there it is right n post #1,lol
In that case you are gonna have to be more careful than ever with co-coordinating the combo, cuz the clutch does not have any built in Torque Multiplication;whatever torque goes into it, about the same comes out of it.Further the 3.23s call for a torquey engine because the available TM is just
3.23x2.66=8.59... and with 26.5" tall tires, this gets corrected to 8.59x12/13.25=7.78 .......
which is pretty flipp'n dismal, lol. It would be all too easy to fubar this combo up with a long slow lazy cam like that 2899205
So now I have to re-guess that the 220 cam is probably one size too big ..... depending on the design. A fast-rate 220 will still be OK, but a slowrate 213 could be worse.
See a fastrate 220 could be 260 advertised, and a slowrate 213 could be 257. Then you factor in where they ACTUALLY, REALLY REALLY, close, and you find out they are both 265s or 268s who knows. The thing is both will make similar pressure, and could idle similarly, yet the bigger cam might make 15 or 20 more horsepower..... with no penalty in fuel economy or low-rpm torque! Winner!!
BTW
You don't want a 114LSA cam; those are designed for the wide ratio Torqueflites, and are pressure bleeders. Nor do you want a 112,or even a 110. In your application with about a 1500 rpm powerband requirement and one gear to 60mph, Ima thinking even a 108 could be a skip-over. And that means that you can step up a size in cams to about 225/108, or a 230/106 fastrate.
Lets have some fun; To recap
>that 220 fast rate could be a 260 advertised, and an actually not leaking intake at 265, so lets call it a 265/273/110 ok ,that, at split overlap, would have an ICA of 60 and overlap of 49*
> now the slow one could be exactly the same
> next How about that 225/108 cam. That could be a 267 advertised, but no longer bleeding at 272, so lets call it a 272/280/108. Ok again at split overlap, the ICA would be 62*and overlap of 60*
> finally the biggest, the 230. This could be a 275/283/106 And again at split overlap the ICA would be 64*and overlap of 62*
Now lets check this out; The ICAs vary from 60 to 64, so basically they could all be installed at 62*!!! Lets say the rest of the engine can keep up, and then
the 213/110 makes 285hp. And lets say then maybe
the 220/110 makes 300hp,and
the 225/108 makes 325hp,and
the 230/106 makes 340hp;Jus saying.
Ok so with the same ICA of 62*, they are all gonna want the same Scr, surprise #1.
Next the cams with less overlap will make better city mpgs, than those with the more.
On the hiway the difference is much less.
So pick your poison; 285hp,300hp,325hp,or 340hp.......................Boy I wish it was that easy
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nm9stheham
Well-Known Member
The L2316F's and KB243's are interchangeable as far as compression ratio. So don't distinguish them from each other as far as cam selection.
The KB's are lighter than stock pistons and so require a crank re-balance; the 2316's are stock weights, so no re-balance is needed.
The KB's are lighter than stock pistons and so require a crank re-balance; the 2316's are stock weights, so no re-balance is needed.
AJ hell of a write up there. Seems the takeaway is you can get away with a lot by simply using the lower CR pistons as proposed and a lower LSA cam. If true, I will take another look at cams and throw another pairing out for comment.
Nm9stheham - thanks for the info, I did not know that. I’m using stock rods et cetera so not much point in lowering the weight of just he pistons. I’ll go with the 2316’s.
Nm9stheham - thanks for the info, I did not know that. I’m using stock rods et cetera so not much point in lowering the weight of just he pistons. I’ll go with the 2316’s.
Hi there
I'm new, but I have a 1969 gts 340 auto.
I put together my 340 last year also to run on 91.
It's taken a lot of trial an error to finally make it happy!
My combo:
72 .030 over. Stock deck height. Block
69 forged crank
Scat I beams
JE / SRP forged flat tops .010 below
Calculated static right at 9.5
Dynamic 7.5
JE plasma file fit rings
69 X heads no port work but hardened exh.seats. and guides cut for P/C seals and .500 + lift.
66 CC chambers
Fel pro .039 gaskets
Comp. XE 268h 224 / 230. @ 50
477 / 480 lift.
Installed 2* adv
Eddie air gap
Holley 670 sa (box stock)
Firecore vac. Adv. Dist.
Timing 18* initial
32* total mechanical
8* vac adv.
Mech. Adv all in @ 2400
Orange mopar ICU
340 hp.exh. Manifolds
2.5 tubing out the back
Dynomax ultra flo' s
I've tried about every spark plug for it.
It runs best with autolite 65's
I live in Phx. Az.
I drive my car every day and all summer at 110 to 115 *
It will not detonate on 91 with this set up.
But it is very sensitive to plugs and timing.
34* it will detonate, 32* is max
The rest of my drive train
998 with lower 1st an 2nd gear, with custom Hughes non lockup 2000
Stall converter
8.75 rear 3.23 clutch type sure grip.
This is a daily driver I take on the freeway too so it's pretty good all around.
Gets 16 mpg ave.
Would be more fun with lower gears though...lol
Good luck on your project!!
I'm new, but I have a 1969 gts 340 auto.
I put together my 340 last year also to run on 91.
It's taken a lot of trial an error to finally make it happy!
My combo:
72 .030 over. Stock deck height. Block
69 forged crank
Scat I beams
JE / SRP forged flat tops .010 below
Calculated static right at 9.5
Dynamic 7.5
JE plasma file fit rings
69 X heads no port work but hardened exh.seats. and guides cut for P/C seals and .500 + lift.
66 CC chambers
Fel pro .039 gaskets
Comp. XE 268h 224 / 230. @ 50
477 / 480 lift.
Installed 2* adv
Eddie air gap
Holley 670 sa (box stock)
Firecore vac. Adv. Dist.
Timing 18* initial
32* total mechanical
8* vac adv.
Mech. Adv all in @ 2400
Orange mopar ICU
340 hp.exh. Manifolds
2.5 tubing out the back
Dynomax ultra flo' s
I've tried about every spark plug for it.
It runs best with autolite 65's
I live in Phx. Az.
I drive my car every day and all summer at 110 to 115 *
It will not detonate on 91 with this set up.
But it is very sensitive to plugs and timing.
34* it will detonate, 32* is max
The rest of my drive train
998 with lower 1st an 2nd gear, with custom Hughes non lockup 2000
Stall converter
8.75 rear 3.23 clutch type sure grip.
This is a daily driver I take on the freeway too so it's pretty good all around.
Gets 16 mpg ave.
Would be more fun with lower gears though...lol
Good luck on your project!!
nm9stheham
Well-Known Member
Nice write-up. With your compression ratios, and the chamber sizes, you must have milled the heads about .030"..????
Pinging characteristics vs timing about as expected (at least based on my humble experience....) You might do better to have the mech advance come in more slowly.
OP, this illustrates very well what you need to think about, regardless if you end up with 9.5 or 9.2 static CR, and regardless of what cam (unless it is a big cam, which hurts low RPM torque and makes it not good as a cruiser/driver, 'specially with a manual trans, as AJ has been explaining). This is the detonation matter versus ignition timing that you need to get familiar with, with any significant compresssion (to match up to the original 340's character) and sticking with the open-chambered 340 iron heads. Moving to AL heads with closed chambers and achieving quench/squish helps that matter a LOT, but those heads are not at all original looking, so not an option for your original look.
Indy heads are closed chamber and at least are iron though the markings are not stock. That is another alternative. But that changes the pistons.....not sure if you want to go down that road at all. I don't mean to confuse things!
You may be able get quench/squish with different pistons and your stock heads to help in this matter, but that involves a fair amount of detailed measuring and machining work.
mderoy340
Well-Known Member
I would buy a set of IMM Indy LA X heads and grind off the Indy logo leaving the X in place. Use SRP forged flat tops -5cc, .040 head gasket to set quench, and a SFT cam [email protected] cam 3.91 gear. The closed chamber head has hardened seats and will perform better on today's pump gas without retarding timing ect.
Thanks
Hope that helps a little...
This is a Awesome web site!!
Hope that helps a little...
This is a Awesome web site!!
nm9stheham
Well-Known Member
FWIW.. I have run higher CR's (SCR and DCR) with iron heads, but with quench, but still had to keep ignition timing under control, even with 93 octane. So this is all within normal bounds of tuning. Was not a drag racer.... it all worked happily for my uses: horsing around on the street, commuting, towing a light rally car, etc.
I can tell you the combo I have.
.030 340 KB243 pistons, stock stroke, stock x heads, Lunati 703 cam, LD340 intake, 700 Holley carb.
73 Duster 4-speed 3.23 gears, 275-15 tires, stock manifolds with 2.5" duel exhaust.
Runs fine on hi-test pump gas.
But it is doggy just starting away in first gear, but pulls good after it is moving, and cruises nice.
I am used to just letting the clutch out, and the vehicle starts moving (jeeps trucks etc), the duster you have to give it a little gas.
I have deeper gears to put in it, will play with them at a later time, but the engine is what I expect out of it, a nice cruiser.
It ended up with static compression of 8.98:1, dynamic is 8.06:1 with 160 psi cranking compression.
I should put a little smaller cam in it to gain some torque back, but it is livable the way it is.
.030 340 KB243 pistons, stock stroke, stock x heads, Lunati 703 cam, LD340 intake, 700 Holley carb.
73 Duster 4-speed 3.23 gears, 275-15 tires, stock manifolds with 2.5" duel exhaust.
Runs fine on hi-test pump gas.
But it is doggy just starting away in first gear, but pulls good after it is moving, and cruises nice.
I am used to just letting the clutch out, and the vehicle starts moving (jeeps trucks etc), the duster you have to give it a little gas.
I have deeper gears to put in it, will play with them at a later time, but the engine is what I expect out of it, a nice cruiser.
It ended up with static compression of 8.98:1, dynamic is 8.06:1 with 160 psi cranking compression.
I should put a little smaller cam in it to gain some torque back, but it is livable the way it is.
nm9stheham
Well-Known Member
Sireland67, may I ask how you come up with those numbers? Any particular calculator? <1 point spread between SCR and DCR is not normal with that level of cam.... (FWIW.... I get 9.5 and 7.8.) Just curious....
MOPAROFFICIAL
Oogliboogli
Just keep the dynamic compression "cranking" at or below 165 psi for a non quench open chamber 340 iron head.
autoxcuda
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You have some constraints I think you need to verify and/or clarify:
-Stock numbers 68 340 carb at 525-600 cfm with one idle screw (center) type
-68 340 hipo exhaust manifolds
- 340 X-heads open chamber
- stock 68 intake (a pretty good piece though)
- stock-ish sounding exhaust and idle.
- California emission spec 91 mtbe pump gas.
-Stock numbers 68 340 carb at 525-600 cfm with one idle screw (center) type
-68 340 hipo exhaust manifolds
- 340 X-heads open chamber
- stock 68 intake (a pretty good piece though)
- stock-ish sounding exhaust and idle.
- California emission spec 91 mtbe pump gas.
autoxcuda
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I’ve live and drive in So Cal. And have various older cars. And have to run our special California blend gas.
I’ve got a 416 4” stroker with actual 9.7:1 (fully measured). With closed chamber Al heads, 274S heads with combustion matched to bore, high spot polished down, .030 quench. Lots of careful stuff to prevent ping.
I’m like mopar69gts, my timings at 31 total. And it’s very sensitive to it.
I’d tell the original poster to run 9.5:1 max. But suggest closer to 9:1. And something like that XE268 to better match the OE carb and exhaust. And give it an egressive stock-ish sound.
Dropping in a cast scat stroker kit might give you more seat of the pants feel with torque with the constraints/requirements above.
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Auto X on your previous post, I think I have answered every question at least once and several twice (awfully long thread, I know). But to simplify, everything you can see is original or stock replacement and yes to everything on your list with a very small note that the AVS carb for the four speed is slightly different than for the automatic. Everything you can't see is up for change with the desire to run on 91 SoCal gas and try to get close to 1968 performance. Now will I cheat, yes but I will weigh the consequences. Will I add octane boost if that gets a significant improvement? Yeah but I will avoid it if I can. And it is likely I will do other things as well. For example, the exhaust will likely be stainless but it will have my original tips and of course look exactly original. I will avoid cutting, grinding or drilling anything that would make it really hard for someone to get the car back to original.
I used Wallace calculator.
nm9stheham
Well-Known Member
Roger. I'm gonna guess the .050" lift intake closing angle was put in. The 'advertised' intake closing angle needs to be put in for that calculator.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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And you might as well throw in some extra, to compensate for the time from advertised to no-longer bleeding-pressure, cuz .008, or .006 or .004 ain't closed yet. And few there are that know how much to add. I sure don't.........
I thought I was doing pretty good until Wyrmrider showed up. Of course I knew about that ramp, but I had no idea it was so large, nor varied so much. Yeah that was a humbling moment.
I first noticed the discrepency in 1999,by accident,during a LeakDown test. When the TDC piston flipped backwards and the pressure blew off,and the Leakpoint was way off scale. I reduced the test-pressure and snuck up on the advertised ICA. Crimminy, I thought, My cam is in wrong; how is that possible? It wasn't off.
But there is a silver lining to this.
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Wyrmrider
Well-Known Member
340 cam
There was a statement that there was not a lot of data on the 340 cam (true for the 68 4 speed cam)
Factory says 268 276 but that's using MOPAR way of measuring (same as way as MOPAR PERFORMANCE -AND very similar to Engle
however 268 MOPAR is much longer duration than a 268 Howard/ Lunati/ Comp Cams more like a XE274HL comp
Measured at the SAE method .006 at the valve or .004 at the lifter
429/444 (286/296 lobe lift)
279/289 (50 ovlp) 20 79 79 30 @.004 Intake gets to .004 79 degrees ABDC plug that into your dynamic compression formula
210/220 -8 37 46 -6 (-14overlap ) @.050
114 LCA 112 ICL 116 excl
TRW & Elgin -578-S` S644 SP-CS-644 Melling SPD-22 Crane 963901 Wolverine CS 4109
You can see why this cam is used to bleed of Dynamic compression in a High Compression Build
and why it does not build dynamic compression in a low compression build
you can directly compare with any 280 degree class from CRANE
such as
467/494 278/290 222/[email protected] 114LCA 2,200-5,200 Crane 693801 H278-2 HMV-278-2-NC
look at the difference in lift and duration at .050
here is a very similar cam with the lobe centers squeezed together to 112
420/443 278/288 27 71 76 32 204/214 5 29 44 10 112lca 107 in 117 excl Melling MTD-1l
this 204/214 was once very common here's Summits version
421/444 278/288 204/214 112LCA 1,200-5000 SUM 6900
here squeezed down to 108
421/444 (.281/.296) 278/288 (59) 204/214 -6 30 43 -9 (-15)112LCA 108 ICL 116 excl Elgin 937P (closes intake 3 degrees earlier @.004 than stock HP)
rearranging the deck chairs on the Titanic
here is a real mopar grind from Crane also at .004 so seat timing is comparable
480 [email protected] 220 136@200 61 Crane .903 H3 H-220/320
if you had the 200 data on the white box cams you would see that the Crane is much fatter at .200 and .035 more lift with less duration
So if you like the duration of the factory HP cam why would you leave Torque on the table?
Not building stock 340 compression or better? -factory HP cam, or any 280 SAE cam hurts
(lower gears, converter, gas blah blah blah)
next post we can talk about measuring at .006 and show how much longer the ramps are on the factory cams and why anyone recommending one with lower compression pistons is way beyond my pay grade
There was a statement that there was not a lot of data on the 340 cam (true for the 68 4 speed cam)
Factory says 268 276 but that's using MOPAR way of measuring (same as way as MOPAR PERFORMANCE -AND very similar to Engle
however 268 MOPAR is much longer duration than a 268 Howard/ Lunati/ Comp Cams more like a XE274HL comp
Measured at the SAE method .006 at the valve or .004 at the lifter
429/444 (286/296 lobe lift)
279/289 (50 ovlp) 20 79 79 30 @.004 Intake gets to .004 79 degrees ABDC plug that into your dynamic compression formula
210/220 -8 37 46 -6 (-14overlap ) @.050
114 LCA 112 ICL 116 excl
TRW & Elgin -578-S` S644 SP-CS-644 Melling SPD-22 Crane 963901 Wolverine CS 4109
You can see why this cam is used to bleed of Dynamic compression in a High Compression Build
and why it does not build dynamic compression in a low compression build
you can directly compare with any 280 degree class from CRANE
such as
467/494 278/290 222/[email protected] 114LCA 2,200-5,200 Crane 693801 H278-2 HMV-278-2-NC
look at the difference in lift and duration at .050
here is a very similar cam with the lobe centers squeezed together to 112
420/443 278/288 27 71 76 32 204/214 5 29 44 10 112lca 107 in 117 excl Melling MTD-1l
this 204/214 was once very common here's Summits version
421/444 278/288 204/214 112LCA 1,200-5000 SUM 6900
here squeezed down to 108
421/444 (.281/.296) 278/288 (59) 204/214 -6 30 43 -9 (-15)112LCA 108 ICL 116 excl Elgin 937P (closes intake 3 degrees earlier @.004 than stock HP)
rearranging the deck chairs on the Titanic
here is a real mopar grind from Crane also at .004 so seat timing is comparable
480 [email protected] 220 136@200 61 Crane .903 H3 H-220/320
if you had the 200 data on the white box cams you would see that the Crane is much fatter at .200 and .035 more lift with less duration
So if you like the duration of the factory HP cam why would you leave Torque on the table?
Not building stock 340 compression or better? -factory HP cam, or any 280 SAE cam hurts
(lower gears, converter, gas blah blah blah)
next post we can talk about measuring at .006 and show how much longer the ramps are on the factory cams and why anyone recommending one with lower compression pistons is way beyond my pay grade
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