87 b6 head with the fms cam

[FestYboy]

it will change your dynamic CR, but not your static CR.

and blkford: the general rule is: more durration+more lift = more top end power.

[blkfordsedan]

I'm not sure how the rocker stands can be machined. The rocker shafts sit in a concave saddle that matches the radius of the shaft and they must be machined concave, straight and parallel with the camshaft. I don't know how they can do that, but they may be able to do it similar to the way they align bore main saddles or camshaft saddles. I'm not a machinist but maybe some one here knows how/if it can be done. You may also be able to have larger custom rollers made for the rockers (that would be expensive). The HLA's may be able to compensate, but I doubt it. It all depends on the increase in lift. None of this matters anyway if they weld up the lobes and don't touch the base circle. If they change the base circle, I would investigate the lash issue BEFORE having the cam ground.

As FestYboy said, the compression will not change but the cylinder pressure will decrease as the valve overlap increases. Aggressive cams use valve overlap to aid cylinder filling at high RPM. The overlap ( time when both intake and exhaust valves are open) creates a rough idle, kills cylinder pressure and consequently low end performance. That's why cam companies always specify a minimum compression ratio for most cam profiles. That's where the benefits of a roller cam really shine. The rollers allow for faster valve movement which allows the valve to spend more time at or around max lift (which is where maximum flow is). In a condensed version, a roller cam can achieve the same cylinder filling as a more aggressive flat tappet cam while using less lift, duration and requiring less overlap. This equates to better emissions, fuel efficiency and is especially advantageous in engines where flow is restricted by stock exhaust, intake, port flow, etc.. This is why most modern engines went to roller cam and can put out over 1HP per cubic inch while having a smooth idle and low emissions.
If you compare a roller cam and flat tappet cam of similar performance and RPM ranges you will almost always find the roller cam has less duration and often less lift.

Yes, as a rule of thumb, more lift does indeed mean increased flow. This is not restricted to any RPM range. However, many long duration, high RPM profiles have less lift because the length of time the valve is open becomes so short at high RPM. Maximum lift becomes less effective and valve control becomes an issue. They rely on overlap to help in cylinder filling. More duration moves the power band farther up the RPM scale. But if you are looking at two cams of same design (roller vs roller) and all else being equal (duration, overlap, lobe centers, etc.) the cam with more lift will make more power.

In the case of the Aspire vs Festiva cams, There are other issues as well. The Aspire roller uses a split profile design with the same lift as the Festiva on the exhaust and slightly less lift on the intake (assuming the rocker ratios are the same). This usually indicates an imbalance in port flow between intake and exhaust (weak exhaust in this case) and would make me think the engineers were paying closer attention to head flow when designing the camshaft. I don't know how the effective duration varies between them, but given the almost identical application I would say not by much. Considering the differences in basic design (roller vs flat), the split profile and the similar applications, the difference in lift or duration means very little. I suspect the roller would offer a very slight advantage in the smaller B3 if any at all.

If you want to investigate camshaft design more in-depth you can click on the link in my previous post. It will take you to the Circle Track home page. Just use their search function and type in "Camshaft design". Then click on "Camshaft Design Science-Matters of Control" listed under the Articles section.

[sasquatch]

I'm not sure how the rocker stands can be machined. The rocker shafts sit in a concave saddle that matches the radius of the shaft and they must be machined concave, straight and parallel with the camshaft. I don't know how they can do that, but they may be able to do it similar to the way they align bore main saddles or camshaft saddles. I'm not a machinist but maybe some one here knows how/if it can be done. You may also be able to have larger custom rollers made for the rockers (that would be expensive). The HLA's may be able to compensate, but I doubt it. It all depends on the increase in lift. None of this matters anyway if they weld up the lobes and don't touch the base circle. If they change the base circle, I would investigate the lash issue BEFORE having the cam ground.

As FestYboy said, the compression will not change but the cylinder pressure will decrease as the valve overlap increases. Aggressive cams use valve overlap to aid cylinder filling at high RPM. The overlap ( time when both intake and exhaust valves are open) creates a rough idle, kills cylinder pressure and consequently low end performance. That's why cam companies always specify a minimum compression ratio for most cam profiles. That's where the benefits of a roller cam really shine. The rollers allow for faster valve movement which allows the valve to spend more time at or around max lift (which is where maximum flow is). In a condensed version, a roller cam can achieve the same cylinder filling as a more aggressive flat tappet cam while using less lift, duration and requiring less overlap. This equates to better emissions, fuel efficiency and is especially advantageous in engines where flow is restricted by stock exhaust, intake, port flow, etc.. This is why most modern engines went to roller cam and can put out over 1HP per cubic inch while having a smooth idle and low emissions.
If you compare a roller cam and flat tappet cam of similar performance and RPM ranges you will almost always find the roller cam has less duration and often less lift.

Yes, as a rule of thumb, more lift does indeed mean increased flow. This is not restricted to any RPM range. However, many long duration, high RPM profiles have less lift because the length of time the valve is open becomes so short at high RPM. Maximum lift becomes less effective and valve control becomes an issue. They rely on overlap to help in cylinder filling. More duration moves the power band farther up the RPM scale. But if you are looking at two cams of same design (roller vs roller) and all else being equal (duration, overlap, lobe centers, etc.) the cam with more lift will make more power.

In the case of the Aspire vs Festiva cams, There are other issues as well. The Aspire roller uses a split profile design with the same lift as the Festiva on the exhaust and slightly less lift on the intake (assuming the rocker ratios are the same). This usually indicates an imbalance in port flow between intake and exhaust (weak exhaust in this case) and would make me think the engineers were paying closer attention to head flow when designing the camshaft. I don't know how the effective duration varies between them, but given the almost identical application I would say not by much. Considering the differences in basic design (roller vs flat), the split profile and the similar applications, the difference in lift or duration means very little. I suspect the roller would offer a very slight advantage in the smaller B3 if any at all.

If you want to investigate camshaft design more in-depth you can click on the link in my previous post. It will take you to the Circle Track home page. Just use their search function and type in "Camshaft design". Then click on "Camshaft Design Science-Matters of Control" listed under the Articles section.

thanks for the info