Rat Patrol
Well-Known Member
Gary, can you expand on Barton's comments? Did he think that a lot of tuners run too much timing, or too little?
5.7L Hemi, 1968 Barracuda.. Opinions.
- Thread starter orange68cuda
- Start date
-
Gary, can you expand on Barton's comments? Did he think that a lot of tuners run too much timing, or too little?
garyfish340
Well-Known Member
He was actually putting forth a rhetorical question. He was talking about Apache cylinder heads, because I was dead set on up grading from stock. I was telling him of all the different set ups I've read about, and he was asking me, " Do you know that what you have right now is optimized ? "
I kind of understand where he's coming from, in my own naive sense of things. With the old distributer engines you were sort of stuck in a set linear dimension. I suppose if you're good you could play with springs, and the slots, and stuff. With computer ignitions for instance, you could remove a bit of advance until you pass TDC, then quickly bring some back. ( correct me guys if I'm wrong ) With aluminum heads and 10:1 compression, you might ask why. If you know how to build a timing curve correctly, than you can have a custom cam ground. Unshackling yourself from generic of the shelf stuff. In my case with a carb, I could change the overlap of the cam, and build cylinder pressure. Which would make my combination think it has more compression than it actually does, or more dynamic compression. ( For those in the know ? am I correct ?) My reply to Ray was, I used the CD that came with the Hemi 6 to get a timing map by description. It runs super smooth, and doesn't knock, or ping. I tune my carb with a combination of a vacuum gauge, my ear, spark plug color, and the seat of my pants. To this great wisdom he replied, " It's lunch time." and I said ok, and he said, " No, I mean leave, go home." I think he found me tiresome.
I kind of understand where he's coming from, in my own naive sense of things. With the old distributer engines you were sort of stuck in a set linear dimension. I suppose if you're good you could play with springs, and the slots, and stuff. With computer ignitions for instance, you could remove a bit of advance until you pass TDC, then quickly bring some back. ( correct me guys if I'm wrong ) With aluminum heads and 10:1 compression, you might ask why. If you know how to build a timing curve correctly, than you can have a custom cam ground. Unshackling yourself from generic of the shelf stuff. In my case with a carb, I could change the overlap of the cam, and build cylinder pressure. Which would make my combination think it has more compression than it actually does, or more dynamic compression. ( For those in the know ? am I correct ?) My reply to Ray was, I used the CD that came with the Hemi 6 to get a timing map by description. It runs super smooth, and doesn't knock, or ping. I tune my carb with a combination of a vacuum gauge, my ear, spark plug color, and the seat of my pants. To this great wisdom he replied, " It's lunch time." and I said ok, and he said, " No, I mean leave, go home." I think he found me tiresome.
Rat Patrol
Well-Known Member
I dont want to hijack the thread suffice to say you'd probably find some chassis dyno time very "revealing".......not so much as far as making huge hp increase from timing adjustments....but the AF mixtures might yield some interesting results.
BTW ..that MSD "base tune" is a little suspect I reckon.
They have the MAP chart pulling timing off the mechanical total timing when MAP reaches 11 psia.
I understand the principle of the MAP adding timing at low pressure and reducing as MAP increases under Wot.....like a vacuum advance........but I dont get why the MAP chart goes into "retard" at 11psia.
In my mind it should just "zero" ....at high MAP.....not start yanking timing out of full mechanical advance.
Check it out on you PC ...you'll see what I mean....
BTW ..that MSD "base tune" is a little suspect I reckon.
They have the MAP chart pulling timing off the mechanical total timing when MAP reaches 11 psia.
I understand the principle of the MAP adding timing at low pressure and reducing as MAP increases under Wot.....like a vacuum advance........but I dont get why the MAP chart goes into "retard" at 11psia.
In my mind it should just "zero" ....at high MAP.....not start yanking timing out of full mechanical advance.
Check it out on you PC ...you'll see what I mean....
garyfish340
Well-Known Member
Unfortunately a dyno probably wouldn't teach me much. I'm thick, so a qualified person would need to show, and teach me, before I could grasp anything. As far as timing by MSD's set up. In my case it had to be changed. Because when we got the 1st intake manifold 4 or 5 years ago, it was unknowingly cracked under the plenum by a pipe fitting, and had a vacuum leak. I was alone doing this, and couldn't get it to idle well at all. when I shut the engine down, it ran on. Out of panic, and frustration, I touched stuff I shouldn't have, having zero knowledge of what I was doing.A friend of mine reset stuff up, because I was bitching like a little girl, and tweaked a few thing, as if to say " I was here." And it runs good now I have tens of thousands of miles on it.
I remember these guys coming into a shop I worked at. They would race A Body cars at Englishtown in stock classes. These rules are supposed to dictate that if you have, " say " a 360 LA, with 8.8:1 compression, and a given lift on the cam, you were supposed to abide by that. A lot of the new guys ( who didn't know how to cheat ) played by those rules. and they still broke into the 11 seconds. A 1975 360 only makes 245 BHP. Over hearing people talking they would blueprint the engine to the max allowable spec, and than mess with cam duration, cam and spark timing to build cylinder pressure. At the same time they needed to avoid detonation. The jeep guys do the same thing sort of. Because of the poor combustion chamber in the 4.0, the engine detonates with a very low static compression. So they play with different timing, and temperature equalization tricks to try to get the most for off roading. Even though Jeep 4.0 only has say 320 lbs torque. they get the curve very broad, like off idle to 4800. That's what Ray was saying optimize. If you know about the stuff I'm writing, than you're way ahead of me, and you know I'm leaving out a lot of the ingredient, just by simply being novice.
I remember these guys coming into a shop I worked at. They would race A Body cars at Englishtown in stock classes. These rules are supposed to dictate that if you have, " say " a 360 LA, with 8.8:1 compression, and a given lift on the cam, you were supposed to abide by that. A lot of the new guys ( who didn't know how to cheat ) played by those rules. and they still broke into the 11 seconds. A 1975 360 only makes 245 BHP. Over hearing people talking they would blueprint the engine to the max allowable spec, and than mess with cam duration, cam and spark timing to build cylinder pressure. At the same time they needed to avoid detonation. The jeep guys do the same thing sort of. Because of the poor combustion chamber in the 4.0, the engine detonates with a very low static compression. So they play with different timing, and temperature equalization tricks to try to get the most for off roading. Even though Jeep 4.0 only has say 320 lbs torque. they get the curve very broad, like off idle to 4800. That's what Ray was saying optimize. If you know about the stuff I'm writing, than you're way ahead of me, and you know I'm leaving out a lot of the ingredient, just by simply being novice.
Rat Patrol
Well-Known Member
Don't underestimate yourself...you seem to have grasped the concept of cylinder pressure and overlap pretty damn good!
-
