MTCFORUM
02-13-2002, 09:11 PM
I always throw out alot of thoughts that are going through my mind to bounch off some technical people. I'l try to share those here.
This post started from me working on a blown 2V GT. My friend built the motor and I do all the tuning on it. It's a '96 GT with a 2V with the newer heads and cam, forged pistons good rods, a Vortech with the Vortech aftercooler. With 13# of boost it made 400 RWHP (it's an automatic). We just turned the boost up to 17 PSI and it still makes 400 RWHP. It makes more torque up to about the mid 4000 rpm range, but no more peak HP.
Now that you are up to speed, he's my post from that board.Well, after talking to a few people, and a few experts, here is the theory.
The intake valve is open and the blower is stuffing in boost. You have valve spring pressure trying to close the valve and boost pressure trying to keep the valve open by pushing on the back side of valve. So you now have a balance between valve spring and boost. If the boost is high enough and the valve spring seat pressure low enough, you can blow the valve off the seat. Now, on a stock 2V there is like 60# of seat pressure so if you are running boost over 20 psi, you could blow the intake valves off the seat and lose power. I don't think that this is a problem with any of our cars.
But, when the valve is closing, before it's on it's seat, you have that balance of spring pressure vrs boost. You can slow down the closing of the valve right before it gets to it's seat. This will cause some loss of cylinder pressure as the piston is starting to move back up the cylinder and blowing past the intake valve.
Based on a quick model simulation that I had a friend run, the intake valve closing starts to slow down as low as 9# of boost, varying based on valve spring loads, rates, valve size variance, etc. If everything is nominal, the intake valve is slowing down a noticeable amount to cause power loss by 13#. So, the moral of the story is, you need better springs. The stock springs are basically junk and have a huge tolerance.
KD, could this be why, although the boost is a little high, you couldn't get past that magical 350ish RWHP range? Have you also noticed that some 4.6's with blowers make good power and some only make in the 350 range with all the same stuff?
One more thing to think about.
KD is a good friend, Kris Danner whose blown up about as many 2V motors as Dennis has 4V's. The last one you could see in one side the block and out the other side.
jerry
This post started from me working on a blown 2V GT. My friend built the motor and I do all the tuning on it. It's a '96 GT with a 2V with the newer heads and cam, forged pistons good rods, a Vortech with the Vortech aftercooler. With 13# of boost it made 400 RWHP (it's an automatic). We just turned the boost up to 17 PSI and it still makes 400 RWHP. It makes more torque up to about the mid 4000 rpm range, but no more peak HP.
Now that you are up to speed, he's my post from that board.Well, after talking to a few people, and a few experts, here is the theory.
The intake valve is open and the blower is stuffing in boost. You have valve spring pressure trying to close the valve and boost pressure trying to keep the valve open by pushing on the back side of valve. So you now have a balance between valve spring and boost. If the boost is high enough and the valve spring seat pressure low enough, you can blow the valve off the seat. Now, on a stock 2V there is like 60# of seat pressure so if you are running boost over 20 psi, you could blow the intake valves off the seat and lose power. I don't think that this is a problem with any of our cars.
But, when the valve is closing, before it's on it's seat, you have that balance of spring pressure vrs boost. You can slow down the closing of the valve right before it gets to it's seat. This will cause some loss of cylinder pressure as the piston is starting to move back up the cylinder and blowing past the intake valve.
Based on a quick model simulation that I had a friend run, the intake valve closing starts to slow down as low as 9# of boost, varying based on valve spring loads, rates, valve size variance, etc. If everything is nominal, the intake valve is slowing down a noticeable amount to cause power loss by 13#. So, the moral of the story is, you need better springs. The stock springs are basically junk and have a huge tolerance.
KD, could this be why, although the boost is a little high, you couldn't get past that magical 350ish RWHP range? Have you also noticed that some 4.6's with blowers make good power and some only make in the 350 range with all the same stuff?
One more thing to think about.
KD is a good friend, Kris Danner whose blown up about as many 2V motors as Dennis has 4V's. The last one you could see in one side the block and out the other side.
jerry