info on n/a engines what cam
03-13-2004, 12:29 PM
#11
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Hey jdcna1:
I was told years ago that when you read the RPM range that Crane or anybody else lists for their cams you should adjust by the ratio of CID.
For example, if the cam book says 3800 - 7000 for 454 CID then that cam would run between 3000 - 5500 in a 572 CID. I think this assumes that the same heads are being used, so air velocity in the ports, at any given RPM, is higher due to the greater displacement being filled.
Same heads and same cam means the same HP, just at a lower RPM. If you use bigger ports on the bigger engine then RPM goes back up, and with it the HP.
That's what I was told. Does this sound right in your experience?
I was told years ago that when you read the RPM range that Crane or anybody else lists for their cams you should adjust by the ratio of CID.
For example, if the cam book says 3800 - 7000 for 454 CID then that cam would run between 3000 - 5500 in a 572 CID. I think this assumes that the same heads are being used, so air velocity in the ports, at any given RPM, is higher due to the greater displacement being filled.
Same heads and same cam means the same HP, just at a lower RPM. If you use bigger ports on the bigger engine then RPM goes back up, and with it the HP.
That's what I was told. Does this sound right in your experience?
03-13-2004, 03:14 PM
#12
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Tomcat;
That is correct from my experience, but my experience comes from large CID and SOLID ROLLERS....Hydralic has to behave similar but I don't have any hands on experience from that side...just witnessed what friends have done and seen from the result side. As you know, if you want to make power there is no substitute for a solid roller. My 632 makes peak power @6300 running a 280/288 @.050 115 CL .730/.730. The cam before that was a 272/278 @.050 114 CL...that was out of power @6000 these cams would obviosly never work in a 454 or 502 but really aren't that big for a 632" motor. Going up 10 degrees picked up power by 40HP. This is on a 10.5:1 93 Octane motor; TR with Fully ported Dart 360 heads.
IMO you need as big of a hydralic roller as there is made in engines 572" and larger. A better route would be a "mild" solid (250-260ish duration .700 lift) which would still make more than a "radical" hydralic. Put a set of Jesel rockers on and lash rarely needs to be set. I think the lifters would live nearly as long with this set-up as with the radical HR set-up. Again, these are just my assumptions.
That is correct from my experience, but my experience comes from large CID and SOLID ROLLERS....Hydralic has to behave similar but I don't have any hands on experience from that side...just witnessed what friends have done and seen from the result side. As you know, if you want to make power there is no substitute for a solid roller. My 632 makes peak power @6300 running a 280/288 @.050 115 CL .730/.730. The cam before that was a 272/278 @.050 114 CL...that was out of power @6000 these cams would obviosly never work in a 454 or 502 but really aren't that big for a 632" motor. Going up 10 degrees picked up power by 40HP. This is on a 10.5:1 93 Octane motor; TR with Fully ported Dart 360 heads.
IMO you need as big of a hydralic roller as there is made in engines 572" and larger. A better route would be a "mild" solid (250-260ish duration .700 lift) which would still make more than a "radical" hydralic. Put a set of Jesel rockers on and lash rarely needs to be set. I think the lifters would live nearly as long with this set-up as with the radical HR set-up. Again, these are just my assumptions.
03-13-2004, 05:46 PM
#13
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i want to make power and torque wanting a good all around engine...i'm planning on setting the msd chip at 5500 for most times... but maybe 6000 now and then for a hot run...
Don
Don
03-15-2004, 07:08 AM
#15
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Just something to keep in mind when selecting a cam for your motor.
This is a common problem with high HP motors;
If a motor produces it's max HP at 6000 rpm and say the peak torque is at 4800 rpm you can't decide to run the motor with a WOT rpm of 5400 to save the motor. It has to be propped out with the WOT rpm at least 1000 above the peak torque rpm, preferably 1200 - 1400 above peak torque. If you look at most dyno numbers that's about where peak HP is anyway.
The problem comes in when the boat is propped out 500 - 600 above peak torque. The drive train becomes torque loaded and requires a large pitch prop, this in turn lifts the stern of the boat which results in a large prop slip. Which requires an even higher pitch prop which lifts the stern even more, it's a no win situation.
It's OK to set the rev limiter at a lower rpm like chromecat was talking about but ti still needs to be propped out so it could run at the higher rpm if the rev limiter was not there.
Just trying to save someone a lot of headache in the future.
This is a common problem with high HP motors;
If a motor produces it's max HP at 6000 rpm and say the peak torque is at 4800 rpm you can't decide to run the motor with a WOT rpm of 5400 to save the motor. It has to be propped out with the WOT rpm at least 1000 above the peak torque rpm, preferably 1200 - 1400 above peak torque. If you look at most dyno numbers that's about where peak HP is anyway.
The problem comes in when the boat is propped out 500 - 600 above peak torque. The drive train becomes torque loaded and requires a large pitch prop, this in turn lifts the stern of the boat which results in a large prop slip. Which requires an even higher pitch prop which lifts the stern even more, it's a no win situation.
It's OK to set the rev limiter at a lower rpm like chromecat was talking about but ti still needs to be propped out so it could run at the higher rpm if the rev limiter was not there.
Just trying to save someone a lot of headache in the future.
03-15-2004, 04:04 PM
#17
MarineKinetics
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The 651 is the correct cam for this engine, however 8.8:1 is not the correct compression ratio. The 572 certainly has the displacement to support the 306*/318* duration of the 139651 cam, but the 8.8 static compression ratio/late IVC and the resulting low cylinder pressure will significantly degrade performance. The 86* ABDC intake valve closing angle will bleed off a great deal of cylinder pressure on the compression cycle, killing torque in the process. In the current configuration will have a DCR of 5.8:1 with cylinder pressures in the area of 115 lbs. The Canfield Aluminum heads are good for a point more CR than iron heads and can easily support 10.25:1 on 89 octane pump gas. Keep the ICL @ 109*, as retarding it to 112* will delay the intake closing further bleeding of additional cylinder pressure and elevating the tq/hp curve. The minimum recommended CR by Crane for this cam is 10.5:1 - 12.5:1.
Bob
Bob
