What boost pressure can 2nd gen 3sgte handle before valve float occurs

**Howieau** · 28-10-2007, 10:02 PM

Hey at what boost psi do the stock valve springs on a 2nd gen 3sgte begin to float does anyone know?

**MS-75** · 29-10-2007, 02:10 PM

It can actually have lots to do with boost dude.

Boost induced valve float is very common.

**jezza323** · 29-10-2007, 02:17 PM

correct, the more air pressure on the backs of the valves the more resistance there is to the valves closing. this can be caused by higher air speed, or by higher air pressure, or both

**Norbie** · 29-10-2007, 02:27 PM

What they said. If you have 40 lb/in seat pressure and the boost pressure exerts 20 lb/in on the back of the valves, your effective seat pressure has just halved and valve float becomes a very real possibility.

**Howieau** · 29-10-2007, 03:39 PM

Ah ok mixed answers. I thought it wasnt boost related based on the answers I was given at MR2OC
http://www.mr2oc.com/showthread.php?...04#post2867704

Cheers, back on topic then.

**JustenGT8** · 29-10-2007, 03:47 PM

I have run as high as 19psi at the track with no issues with a Gen III 3SGTE. I can't recall the spring rates off the top of my head but not much different (if at all) to a Gen II. This was with Blitz 264 cams that have a 1mm or so more lift than stock.

**MS-75** · 29-10-2007, 04:45 PM

I can't see that board as I'm not a member-but nonetheless, it can be a problem quite often.

Different engines suffer from it a different points, but it is also strongly affected by turbo choice.

Generally, the compressor to turbine backpressure ratio in a car is 2:1 or greater. What this means is that most of the time, it is the exhaust valves that begin to bounce first, and not the inlet valves.

Obviously, the bigger the turbine, the lower the ratio, with small turbine set-ups being able to reach 4-5:1 turbine/comp pressure ratios when running high boost. (not very efficient obviously).

The last time I encountered it was when my 1FZ started to valve-bounce at 20psi and anything over 5500rpm, where as XR6 turbos hit the limit at around 14psi from memory.

I can't tell you what the limit on a 3S is specifically, but as a rough guide, uprated springs when running over, say, 17ps is a pretty good idea.

**Joshstix** · 29-10-2007, 05:46 PM

The fact that a nice set of upgraded valve springs from Performance Springs who sponsor the club were $80 last time I bought a set make the question pretty much redundant I reckon. If you're concerned about floating the valves get some better springs.

**Norbie** · 29-10-2007, 06:07 PM

Agreed. I recently bought a set of Performance Springs for my 2JZ, it was a no-brainer at $200 but for $80 you'd have rocks in your head to not do it.

**The Real Roadrunner** · 29-10-2007, 06:47 PM

Originally Posted by JustenGT8

I have run as high as 19psi at the track with no issues with a Gen III 3SGTE. I can't recall the spring rates off the top of my head but not much different (if at all) to a Gen II. This was with Blitz 264 cams that have a 1mm or so more lift than stock.

just wondering what revs? i had probs with mine floating above 18psi and 7300rpm.

cheers
linden

**JustenGT8** · 29-10-2007, 08:19 PM

Power FC had rev limit set around 7800rpm, never had an issue.

With Jack's 22 we were running 18psi thru the big TO4 and the car spent most of the lap bouncing off the rev limiter which was 8000rpm i think?

again, never saw any float and that was a stock Gen II.

I can see it happening, especially with worn springs just never had a prob myself. Maybe i'm just lucky? the TTUZ is certainly doing more than you would reasonably expect