AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
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forphorty
Well when you advance a 110 cam to an installed of 106 what are you doing? You are effectively giving up power stroke for compression stroke. and killing the overlap in the process. and skewing exhaust duration. Why do you do that? Cuz it's the wrong cam for the application. So why not just get the 106 cam in the first place and run it straight up?
Well partly because of the tranny in the combo.
The regular autos have very wide powerband requirements. 59% and 69%. That is to say, if you outshift at say 6200, the Rs will come in at 3670, and 4280, making the powerband requirements; 2530 and 1920. So your cam is gonna have to cover that at the top of the curve. As you probably know, the typical aftermarket cam in a 6200 engine will not have that wide a powerband. Rarely do they exceed 1500 rpm. So that means you have two options; namely short shift and climb up the bottom of the curve, or rev well past the powerpeak, and come in at a higher power level, to increase your average hp
Now the 4 speed has a much smaller powerband requirement; 72/73% . So again shifting at 6200, the Rs will now fall to about 4500, on all shifts, making a powerband requirement of 1700.
So why in the world would you put the same cam in both engines? Easily the 4speed could have 4 less degrees on the LSA.
Now My combo has just a 78% split, so this is a pb requirement of just 1360 rpm, when shifted at 6200. So if you look at the typical dyno curve of a 380hp engine, what do you see? A long, almost flat power curve up there, and a full generous amount of power leading up to it. That's great......for an automatic, cuz it has to spend a lotta time down there. But a 4-gear with a performance gear, passes thru that zone just once, and then lives from the torque peak to the powerpeak, and a bit beyond..... But how is that you might ask? Well with say 3.55s and an automatic, the first gear road ratio is 8.70; whereas the 4-gear makes 9.44. To break even the TC would need to make an average of 8.5% TM internally, throughout the Rs. But first isn't where it's at; second is. Here the auto posts 5.15 to the stick's 6.82. Now the TC would have to make up the 32% shortfall; that ain't gonna happen without a lot more stall. And then you run into a problem at the other end; with 5 to 8% or more TC slip, she's gonna want to be shifted a few mph sooner than the manual, and then the Rs fall into the basement, and with the same cam,right off the power curve. That's partly why the autos typically had more LSA than sticks. The wide LSAs brought the average performance up on them, and the average down on the sticks.
At the track it makes little difference with the proper TC, cuz you never go thru that sub 4500 zone, or at least shouldn't. But a streeter lives there,95 or more%, (guessing),of the time.
So My thought is a 360 has already got more bottom-end than it can possibly use, so why not sacrifice some of it, and make a nice spike up top, using the overlap in our favor?
And in my case, splitting gears, I'm gonna be aggressive about that, cuz the splitter comes with an overdrive. But this time I don't want a 7000 rpm cam. That means the 292/284,even 276 cams are out for me. That 292/108 cam had 76* of overlap, and when that 367 of mine wound up, I could really feel that surge. The 223/110 had none of that, but it could sure make the MPGs. The current 276/110 has just 61* of overlap, and I sure miss that 76* lol.
So then the 268/276/104 cam, in straight up, would give me 64* of overlap, and let's see what the headers do with that. Meanwhile the 268 intake duration is, IMO a near perfect street cam. The exhaust duration at 276, for Eddies and dual 3" pipes wouldn't need to be there.. but I need it to be, to get the overlap started early. That leaves the compression and power events which total 240, and straight up, it would be 124 for compression and 116 for power. The 124 will give me an ICA of 56* and that will make mountains if power, while the 116 is a really long power event, and if I can keep reversion at bay, I know I can tune that for plenty of point-to-point mpgs.
Since I already have a three-cam experience with this engine, with overlaps of 53,61, and 76; I already know what I didn't like.
Since I already know what the power stroke did at 102 to 114, I already know what sux gas.
Since I already have experience with compression events of 110 to 119,and the accompanying cylinder pressures, I'm gonna shoot for more.
So I'm just gonna marry what I think will work, based on my experiences, all on the same cam. I would put it on a 102, if I was a wee bit braver. As it is, it's a big step from a 108 to a 104. I've got to leave a little bit for next time,lol.
>I map all my cam experiments on little circles, that I divide into 5 quadrants, representing the 5 events of a performance cam. Top and bottom of the circle are TDC, and the East/West axis is BDC. I put compression in the bottom left, power in the bottom right, exhaust in the top right, overlap splitting the Top TDC line and intake in the top left. In the very center I draw another small circle just big enough to write in the LSA. Then I work out the durations and pencil those in,and from those I determine the various opening/closing degrees, and pencil those in. I droop the East/West lines for a better visual representation.
When you do it like that, you can easily see all the events, and instantly compare one to another, and how advancing and retarding a cam affects all the other events.
>My favorite example is my first cam the Mopar 292. I installed it straight up, giving 38* each to intake and exhaust, thus getting 76* of overlap. But this only gives you 106* each for compression and power.That means you need a lotta compression ratio, for a modest effective compression. And if you don't have it, the bottom goes seriously soft. Meanwhile, with just 106* of extraction, there is still a lot of energy at the end of the tailpipe. Energy that didn't move the car. Energy that I paid for, just to heat up the environment, and create neat little tornadoes on gravel roads. Yeah, no that wasn't working for me. So I retimed the cam to 104* .. Well that stole 4* from the power stroke and gave it to the compression side, making the power-extraction side worse and the compression side a teensey bit better. But it also screwed up the overlap!
Being a glutton for punishment, I stepped up to an install of 100; stealing another 4 from the power side, giving it to the compression side.So now I was up to 114* compression,98* power, and a thoroughly messed up overlap. It was more driveable, but the power was down. It was the wrong cam for me and I got rid of it right quick.
The next cam was a 270/276/110. In straight up, it had 116* compression, up two from the very advanced 292. And it had 111* power, so plus 13* over the very advanced 292. And it had 53* of overlap, almost equally split.Which altho mathematically was 23* less overlap, You'd almost not know it in the power delivery , except because I had run the 292 straight up and felt the power-surge, that the smaller cam just did not have.But yeah, it was down on absolute power, cuz a 270 is after all , 3 sizes smaller than the 292. So I bought some 4.30s, and an overdrive, and started splitting gears; problem solved.
But the amazing thing was that 111* of power extraction. That combo got great fuel mileage, which became tremendous with the overdrive .
That cam died an untimely death, and is sorely missed.
The last cam, a 276/286/110 has compression,power, and overlap events,about right up the middle between the previous two
And the next one will capitalize on what I learned.
I just wouldn't recommend a 104 cam for an automatic,lol.
>But you gotta keep in mind that a streeter is basically a 1.5 to 2 gear car, so you don't have to optimize it for the quarter mile, and first gear is going up in smoke at WOT, no matter what. So, on second thought.......For myself, I would try it,lol,in a 904.
So that's my thinking.
Well when you advance a 110 cam to an installed of 106 what are you doing? You are effectively giving up power stroke for compression stroke. and killing the overlap in the process. and skewing exhaust duration. Why do you do that? Cuz it's the wrong cam for the application. So why not just get the 106 cam in the first place and run it straight up?
Well partly because of the tranny in the combo.
The regular autos have very wide powerband requirements. 59% and 69%. That is to say, if you outshift at say 6200, the Rs will come in at 3670, and 4280, making the powerband requirements; 2530 and 1920. So your cam is gonna have to cover that at the top of the curve. As you probably know, the typical aftermarket cam in a 6200 engine will not have that wide a powerband. Rarely do they exceed 1500 rpm. So that means you have two options; namely short shift and climb up the bottom of the curve, or rev well past the powerpeak, and come in at a higher power level, to increase your average hp
Now the 4 speed has a much smaller powerband requirement; 72/73% . So again shifting at 6200, the Rs will now fall to about 4500, on all shifts, making a powerband requirement of 1700.
So why in the world would you put the same cam in both engines? Easily the 4speed could have 4 less degrees on the LSA.
Now My combo has just a 78% split, so this is a pb requirement of just 1360 rpm, when shifted at 6200. So if you look at the typical dyno curve of a 380hp engine, what do you see? A long, almost flat power curve up there, and a full generous amount of power leading up to it. That's great......for an automatic, cuz it has to spend a lotta time down there. But a 4-gear with a performance gear, passes thru that zone just once, and then lives from the torque peak to the powerpeak, and a bit beyond..... But how is that you might ask? Well with say 3.55s and an automatic, the first gear road ratio is 8.70; whereas the 4-gear makes 9.44. To break even the TC would need to make an average of 8.5% TM internally, throughout the Rs. But first isn't where it's at; second is. Here the auto posts 5.15 to the stick's 6.82. Now the TC would have to make up the 32% shortfall; that ain't gonna happen without a lot more stall. And then you run into a problem at the other end; with 5 to 8% or more TC slip, she's gonna want to be shifted a few mph sooner than the manual, and then the Rs fall into the basement, and with the same cam,right off the power curve. That's partly why the autos typically had more LSA than sticks. The wide LSAs brought the average performance up on them, and the average down on the sticks.
At the track it makes little difference with the proper TC, cuz you never go thru that sub 4500 zone, or at least shouldn't. But a streeter lives there,95 or more%, (guessing),of the time.
So My thought is a 360 has already got more bottom-end than it can possibly use, so why not sacrifice some of it, and make a nice spike up top, using the overlap in our favor?
And in my case, splitting gears, I'm gonna be aggressive about that, cuz the splitter comes with an overdrive. But this time I don't want a 7000 rpm cam. That means the 292/284,even 276 cams are out for me. That 292/108 cam had 76* of overlap, and when that 367 of mine wound up, I could really feel that surge. The 223/110 had none of that, but it could sure make the MPGs. The current 276/110 has just 61* of overlap, and I sure miss that 76* lol.
So then the 268/276/104 cam, in straight up, would give me 64* of overlap, and let's see what the headers do with that. Meanwhile the 268 intake duration is, IMO a near perfect street cam. The exhaust duration at 276, for Eddies and dual 3" pipes wouldn't need to be there.. but I need it to be, to get the overlap started early. That leaves the compression and power events which total 240, and straight up, it would be 124 for compression and 116 for power. The 124 will give me an ICA of 56* and that will make mountains if power, while the 116 is a really long power event, and if I can keep reversion at bay, I know I can tune that for plenty of point-to-point mpgs.
Since I already have a three-cam experience with this engine, with overlaps of 53,61, and 76; I already know what I didn't like.
Since I already know what the power stroke did at 102 to 114, I already know what sux gas.
Since I already have experience with compression events of 110 to 119,and the accompanying cylinder pressures, I'm gonna shoot for more.
So I'm just gonna marry what I think will work, based on my experiences, all on the same cam. I would put it on a 102, if I was a wee bit braver. As it is, it's a big step from a 108 to a 104. I've got to leave a little bit for next time,lol.
>I map all my cam experiments on little circles, that I divide into 5 quadrants, representing the 5 events of a performance cam. Top and bottom of the circle are TDC, and the East/West axis is BDC. I put compression in the bottom left, power in the bottom right, exhaust in the top right, overlap splitting the Top TDC line and intake in the top left. In the very center I draw another small circle just big enough to write in the LSA. Then I work out the durations and pencil those in,and from those I determine the various opening/closing degrees, and pencil those in. I droop the East/West lines for a better visual representation.
When you do it like that, you can easily see all the events, and instantly compare one to another, and how advancing and retarding a cam affects all the other events.
>My favorite example is my first cam the Mopar 292. I installed it straight up, giving 38* each to intake and exhaust, thus getting 76* of overlap. But this only gives you 106* each for compression and power.That means you need a lotta compression ratio, for a modest effective compression. And if you don't have it, the bottom goes seriously soft. Meanwhile, with just 106* of extraction, there is still a lot of energy at the end of the tailpipe. Energy that didn't move the car. Energy that I paid for, just to heat up the environment, and create neat little tornadoes on gravel roads. Yeah, no that wasn't working for me. So I retimed the cam to 104* .. Well that stole 4* from the power stroke and gave it to the compression side, making the power-extraction side worse and the compression side a teensey bit better. But it also screwed up the overlap!
Being a glutton for punishment, I stepped up to an install of 100; stealing another 4 from the power side, giving it to the compression side.So now I was up to 114* compression,98* power, and a thoroughly messed up overlap. It was more driveable, but the power was down. It was the wrong cam for me and I got rid of it right quick.
The next cam was a 270/276/110. In straight up, it had 116* compression, up two from the very advanced 292. And it had 111* power, so plus 13* over the very advanced 292. And it had 53* of overlap, almost equally split.Which altho mathematically was 23* less overlap, You'd almost not know it in the power delivery , except because I had run the 292 straight up and felt the power-surge, that the smaller cam just did not have.But yeah, it was down on absolute power, cuz a 270 is after all , 3 sizes smaller than the 292. So I bought some 4.30s, and an overdrive, and started splitting gears; problem solved.
But the amazing thing was that 111* of power extraction. That combo got great fuel mileage, which became tremendous with the overdrive .
That cam died an untimely death, and is sorely missed.
The last cam, a 276/286/110 has compression,power, and overlap events,about right up the middle between the previous two
And the next one will capitalize on what I learned.
I just wouldn't recommend a 104 cam for an automatic,lol.
>But you gotta keep in mind that a streeter is basically a 1.5 to 2 gear car, so you don't have to optimize it for the quarter mile, and first gear is going up in smoke at WOT, no matter what. So, on second thought.......For myself, I would try it,lol,in a 904.
So that's my thinking.
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