LS7 FAST 102 running out of steam?
LS7 FAST 102 running out of steam? I have an LS7 with MAST Motorsports heads on it. It is Naturally Aspirated. It is hitting 575 rwhp @ 6,500 rpm through 4.10 gears in a M6 GTO.
At 6,600 rpm it goes real rich and starts to stumble. We think the FAST 102 intake is choking itself out at that point.
We initially thought it may have been spark related, so we changed plug wires, then coils.
We also originally thought maybe valve float, but the springs have 460 lbs of open pressure.
What do you think?
At 6,600 rpm it goes real rich and starts to stumble. We think the FAST 102 intake is choking itself out at that point.
We initially thought it may have been spark related, so we changed plug wires, then coils.
We also originally thought maybe valve float, but the springs have 460 lbs of open pressure.
What do you think?
Last edited by Marble_Sharp; Nov 18, 2010 at 09:47 PM.
What type of intake piping do you have in front of the throttle body? It may not be that the intake is running out of steam, instead it could be that your intake piping could be running out of steam.
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From personal experience I don't believe his intake is a restriction depending on who it was ported by. On my own personal car there was no kpa loss on a 441 LS7 with All Pro Heads and an extremely healthy cam (more than likely larger than the OP's) although I have 4" piping from the throttle body down to the filter on my C5.
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From personal experience I don't believe his intake is a restriction depending on who it was ported by. On my own personal car there was no kpa loss on a 441 LS7 with All Pro Heads and an extremely healthy cam (more than likely larger than the OP's) although I have 4" piping from the throttle body down to the filter on my C5.
I have the stock intake duct on my car, wonder if it's holding me back? FWIW I think you might be right.
From personal experience I don't believe his intake is a restriction depending on who it was ported by. On my own personal car there was no kpa loss on a 441 LS7 with All Pro Heads and an extremely healthy cam (more than likely larger than the OP's) although I have 4" piping from the throttle body down to the filter on my C5.
Christian
I have an LS7 with MAST Motorsports heads on it. It is Naturally Aspirated. It is hitting 575 rwhp @ 6,500 rpm through 4.10 gears in a M6 GTO.
At 6,600 rpm it goes real rich and starts to stumble. We think the FAST 102 intake is choking itself out at that point.
We initially thought it may have been spark related, so we changed plug wires, then coils.
We also originally thought maybe valve float, but the springs have 460 lbs of open pressure.
What do you think?
At 6,600 rpm it goes real rich and starts to stumble. We think the FAST 102 intake is choking itself out at that point.
We initially thought it may have been spark related, so we changed plug wires, then coils.
We also originally thought maybe valve float, but the springs have 460 lbs of open pressure.
What do you think?
Christian
Launching!
Joined: Dec 2003
Posts: 251
Likes: 2
From: Portland OR
If the dropoff comes on suddenly at 6,600, it's not an intake problem. Intake dynamics don't change that quickly with RPM.
Valve float - or valve bounce - actually doesn't have that much to do with spring pressure. If you have a strong enough harmonic somewhere in the valvetrain - spring harmonics, pushrod flex, etc - you'll get bounce with almost any amount of static spring pressure.
Valve float - or valve bounce - actually doesn't have that much to do with spring pressure. If you have a strong enough harmonic somewhere in the valvetrain - spring harmonics, pushrod flex, etc - you'll get bounce with almost any amount of static spring pressure.
The FAST 102 has been opened up to 107mm and "massaged" heavily by VA Speed - much more than a simple port matching or porting.
Mine looks almost identical to what WKMCD posted and on my 11.2:1 compression nitrous motor made ~615whp at ~6300 and carried it out to 6900.
If the dropoff comes on suddenly at 6,600, it's not an intake problem. Intake dynamics don't change that quickly with RPM.
Valve float - or valve bounce - actually doesn't have that much to do with spring pressure. If you have a strong enough harmonic somewhere in the valvetrain - spring harmonics, pushrod flex, etc - you'll get bounce with almost any amount of static spring pressure.
Valve float - or valve bounce - actually doesn't have that much to do with spring pressure. If you have a strong enough harmonic somewhere in the valvetrain - spring harmonics, pushrod flex, etc - you'll get bounce with almost any amount of static spring pressure.
Thanks, and thank you WKMCD for posting the pic. I guess I'll need to address that at some point. It also looks a whole lot better than my stock junk.
Teching In
Joined: Nov 2009
Posts: 5
Likes: 0
I will look up valve size when I get home. I can say that the valves are the hollow stem steel variety from MAST, and the springs are their top of the line.
As far as coil bind, the springs were set-up by the shop that did the heads to match the cam.