Did dyno @ Marko's Supercar Tuning Center on a stock LS1 motor, with cats left in place and has BBK A.B.

First installed his STC clutch ... to hold the power to the rollers. Ran a number of pulls @ various boost levels. Car had the Predator tune ... things were not optimal with it. After much earlier fiddling with the Predator, I punted the tune job to Marko.

We found the Predator tune was pig rich @ 9.5 A/F levels ... baseline dyno results were poor. RWHP and TQ were only in high 300's.

Willem did a MAF Tune next. Got A/F to 11.5, timing advance set to 15, and disabled the GM computer "learning" program (very important step).

Now @ 5 lbs (stock boost) ... we got HP 416 and TQ 437.

Next, adjusted electronic boost controller (A dial) to 7 lbs ... and RWHP went to 472 with TQ @ 495.

Finally we set B dial to 8 lbs boost ... and RWHP was 474 and TQ went to 534.

We briefly raised boost to 10 lbs ... during several experimental runs ... but, stopped the dyno prematurely when we saw the boost gage hitting the 10lb+ range early in the pulls. Didn't want to blow the beast .. or take any chances til we saw what 8 lbs would do for us.

Marko should be able to post the 3 dyno pulls later today here @ FI section. We noticed that consistently at 5500 RPM ... regardless of boost level ... we got a significant dip in HP/TQ. It would recover by 5750 RPM's and pull on back to redline.

Willem has some ideas about what is occurring at the high RPM's .. but, when the dyno's get posted .... I'd like to hear what you experts think the problem is.

Car now drives great. Much smoother during boost ... and much stronger than before. Clutch still getting broken in ... too early to say how it will work ... but, it needs only light foot pressure. Feels like my stock one. No chatter noted during dyno pulls ... but, I've yet to hammer it on street or track.

 

what are you running for a fuel system?

what boost controller?

 

Stock valve springs are hitting a resonance at that rpm, going ape sh*t.
Common problem from what I hear.

 

WF: would 918's be a good replacement for the stockers? I'm simply looking to swap springs to avoid this 5500rpm nonsense...

What about the factory springs that come on 6.0L heads? I have a complete set of those at home and I could simply swap heads to drop the CR and fix the spring issue at the same time

 

Kudos to Warp Factor. You nailed it. There is a term for it ... when seen on a dyno chart. I forget what Willem called it.

Exactly what they think. The fix: install dual springs .. each with different tensile strengths .. different harmonic characteristics. Would cost about $200 for springs and $300 for installation.

I'm wondering what risk I take of breaking a valve spring ... if I don't fix it right away .... and run engine to redline alot?

Apparently the LS6 engine has different springs ??? And its not seen on dynos of that engine ???

 

I think they call it spring surge, hope that’s your issue as it is a easy fix.


Mike

 

i know the LQ9 heads are similar to the LS6 heads... so if the springs on the LS6's will work, the LQ9's might as well.

 

M,
This is a real possibility. It could be something else. See if the sensor on the rear of your manifold is oiled.
B

 

what sensor?

 

Don't know, man, I'm tapped out. That info came from my Guru during an "LS1 for boneheads" lesson when I picked up my car. He says you can tell without a dyno when an engine is doing this because it sounds different in that rev range, even if it's not bad enough to feel the power sag. For some reason, my engine doesn't do this, or doesn't do it yet.
You could try PMing RoadRebel for a spring recommendation, or maybe he'll show up here.

 

93 pump gas. BC is the EVC Easy 2. Its same system Marko uses in his 1500 HP Supra Blower car. Hides away inside ashtray compartment out of view. Can turn it off ... and have the stock 5 lbs of boost. Turn it on and you have two adjustible boost control *****. I've set A for 7 lbs ... and B for 8 lbs. Depending on weather conditions and what boost gage shows .... one can easily finetune the boost while looking at your boost gage.

IMO ... its the only way to safely do a B.C. I first tried the manual STS controller ..... mounted under the hood. It is not reliable or sensitive enough. Only a tiny twist of **** and you go from 5 to 10 lbs boost. Can't see the boost gage when doing it ... so its a PITA to try to use. I think its asking for trouble to rely on it for adjusting the boost.

With the EVC ... each click on **** is good for approx 1 extra lb of boost. Its back lit ... so is visible for night driving.

 

Valve float is a common issue on LSX engines. It essentially is a condition when the push rods can no longer follow the camshaft lobe.
The mass of the valve-train (mostly rocker arm) and the valve spring rate are the biggest contributors. The stock single beehive spring is adequate for certain changes but often run into this condition at a certain frequency. This harmonic is usually around 5350-5550rpm on stock hardware.

Their are plenty of replacements available. I think the best bang for the buck for you application would be the PRC spring kit from Texas Speed. The complete kits is less than $300 with everything you will need.

Phil

 

It the sensor all the way in the back of the manifold.

 

Phil, you changed your Avitar again.
Kind of miss the old one.......
What the heck is it?

 

Haha, Ninja kitty..there is a video on the net floating around..about a year old..kinda funny...

Phil

 

yes, but what sensor are we talking about ? I still don't know...

 

MAP or manifold absolute pressure, don’t think that’s it, they would have seen it while tuning.


Mike

 

lets guess what it is then.........oily....hrmmmm ....back of the manifold......

 

wow those #'s are low...valve springs or not...

 

A few things can affect low dyno numbers, particularly on an STS kit:
1. The kit is rear mounted, so the entire system, including exhaust needs to be up to temp prior to doing any pulls. If the system is not up to temp, boost will build slower.
2. The air is drawn from dual air filters placed behind the rear lights. STS recommends removing all 4 rear lights on a dyno to get fresh air. When driving, the car is moving so fresh air is not a problem.
3. If the wastegates is dumping externally, exhaust gases will deflect and go into the air intake. STS recommends fabbing up a pipe past the bumper to avoid this.
4. Generally, turbos produce boost under load. This load is not simulated on a dyno.

My STS car feels fast on the street. It will nice when the weather gets nice to see some STS 1/4 mile times posted to see what the kit can do.