Another FI Cam Suggestion Thread
04-25-2007, 10:07 AM
#1
Another FI Cam Suggestion Thread First, I don't like search engines on all forums. Most of the time they don't answer my questions. So now that is out of the way, here is what I have:
402 Iron Block Stroker
Dart 240cc ported by TEA 8.7CR
F1R Procharger with A2W IC and W/I
Up to 20psi of boost and 7000rpm redline
Current Cam TSP Giant with CompCams "R" Lifters and Aluminum Roller Rockers
OK, here is the deal. I was going to order my Dart heads from TEA. I was talking to Mike at TEA telling him about the above setup. He told me that with the strongest valve springs for hydraulic roller lifter would be 160-lb seat and 460-lb at .600". With 20psi of boost on the back of a 2.08" intake valve I would lose 68-lbs of spring pressure. He asked me what were the lobe patterns on the Giant cam at which I had no idea. If the lobe ramps are too aggressive, that 92-lb seat pressure would cause valve float. I sent an e-mail to TSP about the camshaft design, but no response yet. If I have to, I will get a camshaft that is more suitible to use with higher RPMs and boost. I would like to hear about some proven camshafts with valve spring specs that fit my setup.
BTW, I don't want to go with a solid roller because of the added maintenance with valve lash and spring replacement as well as the knock sensors needing to be de-sensitized for the lash.
402 Iron Block Stroker
Dart 240cc ported by TEA 8.7CR
F1R Procharger with A2W IC and W/I
Up to 20psi of boost and 7000rpm redline
Current Cam TSP Giant with CompCams "R" Lifters and Aluminum Roller Rockers
OK, here is the deal. I was going to order my Dart heads from TEA. I was talking to Mike at TEA telling him about the above setup. He told me that with the strongest valve springs for hydraulic roller lifter would be 160-lb seat and 460-lb at .600". With 20psi of boost on the back of a 2.08" intake valve I would lose 68-lbs of spring pressure. He asked me what were the lobe patterns on the Giant cam at which I had no idea. If the lobe ramps are too aggressive, that 92-lb seat pressure would cause valve float. I sent an e-mail to TSP about the camshaft design, but no response yet. If I have to, I will get a camshaft that is more suitible to use with higher RPMs and boost. I would like to hear about some proven camshafts with valve spring specs that fit my setup.
BTW, I don't want to go with a solid roller because of the added maintenance with valve lash and spring replacement as well as the knock sensors needing to be de-sensitized for the lash.
04-29-2007, 12:28 PM
#3
FormerVendor
Originally Posted by Gold Phoenix
OK, here is the deal. I was going to order my Dart heads from TEA. I was talking to Mike at TEA telling him about the above setup. He told me that with the strongest valve springs for hydraulic roller lifter would be 160-lb seat and 460-lb at .600". With 20psi of boost on the back of a 2.08" intake valve I would lose 68-lbs of spring pressure.
Well, fwiw I ran a lower rate spring to achieve 200lbs seat pressure and 425 over the nose with comp stock replacement lifters for thousands of miles and no problems to date.
Also, I don't believe it's accurate to say that "X" amount of boost equals "X" amount less spring pressure because to make that calculation you need to know the pressure on the other side of the valve as well. When the intake valve is open pressurized air is flowing into the cylinder, so their may be a pressure drop across the valve of a few psi but it's not like their is 20psi boost at the back of the valve and zero psi in the cylinder.
Now, when the valve is closing the piston is on it's way back up the cylinder (the cylinder that is also pressurized). The instant the valve closes the compression cycle starts and pressure in the cylinder immediately eclipses boost pressure on the backside of the valve. Again, their is going to be a pressure drop across the valve but if a few psi pressure differential puts you into loft your springs were marginal to begin with.
I think the only real area of concern as far as spring pressure and forced induction is the exhaust side of a turbo motor as the valve is usually trying to close against double the pressure of the intake manifold, during overlap.
04-29-2007, 12:58 PM
#4
On The Tree
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Last edited by Rusted40; 04-29-2007 at 01:11 PM.
04-30-2007, 11:27 AM
#5
Originally Posted by INTMD8
Well, fwiw I ran a lower rate spring to achieve 200lbs seat pressure and 425 over the nose with comp stock replacement lifters for thousands of miles and no problems to date.
Also, I don't believe it's accurate to say that "X" amount of boost equals "X" amount less spring pressure because to make that calculation you need to know the pressure on the other side of the valve as well. When the intake valve is open pressurized air is flowing into the cylinder, so their may be a pressure drop across the valve of a few psi but it's not like their is 20psi boost at the back of the valve and zero psi in the cylinder.
Now, when the valve is closing the piston is on it's way back up the cylinder (the cylinder that is also pressurized). The instant the valve closes the compression cycle starts and pressure in the cylinder immediately eclipses boost pressure on the backside of the valve. Again, their is going to be a pressure drop across the valve but if a few psi pressure differential puts you into loft your springs were marginal to begin with.
I think the only real area of concern as far as spring pressure and forced induction is the exhaust side of a turbo motor as the valve is usually trying to close against double the pressure of the intake manifold, during overlap.
Also, I don't believe it's accurate to say that "X" amount of boost equals "X" amount less spring pressure because to make that calculation you need to know the pressure on the other side of the valve as well. When the intake valve is open pressurized air is flowing into the cylinder, so their may be a pressure drop across the valve of a few psi but it's not like their is 20psi boost at the back of the valve and zero psi in the cylinder.
Now, when the valve is closing the piston is on it's way back up the cylinder (the cylinder that is also pressurized). The instant the valve closes the compression cycle starts and pressure in the cylinder immediately eclipses boost pressure on the backside of the valve. Again, their is going to be a pressure drop across the valve but if a few psi pressure differential puts you into loft your springs were marginal to begin with.
I think the only real area of concern as far as spring pressure and forced induction is the exhaust side of a turbo motor as the valve is usually trying to close against double the pressure of the intake manifold, during overlap.
That is a REALLY GOOD point. I was wondering why other have more aggressive lobe profiles were no having problems. Thanks.
