903 pump cam vs 901(160/175) pump cam

zachu812

zachu812

New member
I'm in the process of building a 13mm pump and trying to figure out what pump cam is best to use. I have good 901 cams laying around but the only 903 I have is beat up from my old 13mm pump. I've always heard people refer to the 903 as a "quick rate" cam and act like it's a must have but I've seen the 901 used in 13mm pumps with good results too. 903 cams aren't cheap or easy to come by. Does anybody know the actual difference between cams?
 
The lobe profile is a lot different. On the 903 you will see how quickly the tappet returns to the base circle, which allows for more fill time. If I don't have a 903 available I use the hamilton pump cams.
 
Discounting the backside of the cam and its quicker refill time, which is the quicker ramp up on the injection side?
 
We have a pump that we ran with both cams ,it was night and day difference adding the 903 higher rpm the fill time is important.. If it's any kind of competition aplication run the 903 . We also switched lately to a hamilton 2.75 in the same pump and seen great improvements over the 903
 
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I was expecting a bit of a different response, until recently I thought it had something to do with the injection side of the cam being slower as well as the refill side. I mapped both cams out recently and found that the injection side is pretty much identical, the only real change is the refill side. While the 901 cam dwells at .472 for 180* longer than the 903 cam, the steeper refill ramp along with the factory LPC settings from a 180 pump and a 160 pump means that the 160 pumps only have approximately 90* less fill time. Not something I'd want in a 13mm pump but with a 12mm pump and enough fuel pressure I feel like a 160 pump has almost the same potential as a 180 pump at a reasonable rpm.

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You can have a regrind done on your 901 for more fill time. That's what I did. With the 901 cam I couldnt make any power above about 2600-2800 rpm with my 13mm pump. My pump actually had less power and rpm capability with 13mm p+b than it did with 12mm and the 901 cam. Got a regrind done and my 13mm pump starting making tons of power and rpm like I originally expected.
 
Vincejax said:
You can have a regrind done on your 901 for more fill time. That's what I did. With the 901 cam I couldnt make any power above about 2600-2800 rpm with my 13mm pump. My pump actually had less power and rpm capability with 13mm p+b than it did with 12mm and the 901 cam. Got a regrind done and my 13mm pump starting making tons of power and rpm like I originally expected.
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Where did you send it for the regrind?
 
zachu812 said:
I was expecting a bit of a different response, until recently I thought it had something to do with the injection side of the cam being slower as well as the refill side. I mapped both cams out recently and found that the injection side is pretty much identical, the only real change is the refill side. While the 901 cam dwells at .472 for 180* longer than the 903 cam, the steeper refill ramp along with the factory LPC settings from a 180 pump and a 160 pump means that the 160 pumps only have approximately 90* less fill time. Not something I'd want in a 13mm pump but with a 12mm pump and enough fuel pressure I feel like a 160 pump has almost the same potential as a 180 pump at a reasonable rpm.

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Do you have a chart for the V2.75 vs the 903?
 
On a side note, the 903 cams are getting harder to come bye because Bosch discontinued the part. I talked with Hamilton at one point about doing a batch of 903 cams for the fuel shop I am employed at due to the lack of availability of both new cams and good cores. It didn't happen because the minimum order was larger than we required. So now for any high performance builds we try to use the v2.75 cams, which are similar to the 903 but with some improved characteristics.
 
The one thing I don’t particularly like about the V2.75 cam is how stiff of a spring is needed to keep the roller in contact with the refill side of the cam. If one could find a shop to cut the back side of a 901 cam to match that of a 903 cam for a reasonable price we’d be in business.
 
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