GN1 on S2 - 22psi limit.

[Eticket]

To my amazement, I checked a couple of cylinder's valve spring installed height tonight and found them to be around 1.80 ish range. I was expecting 1.90ish range. If this is correct, it seems that I have plenty of valve spring ~ 260 lbs seat pressure.

Labor Day weekend, the car wouldn't climb RPMs at all.. took forever, almost down the entire 1/4 in 2nd gear. I decided to check my valve lash since I drive the car on the street. I found aweful valve lash adjustments, between .024 and .030+. At this time I was able to make as much boost as I wanted to but not any more power. Going from 22psi to 25psi didn't make much difference in 1/4 mile times or RPMs.

Resetting the valve train to .020 gave me power and rpm back. The cam card says .020, but doesn't say hot or cold. I did warm the car up to 160 deg idle but didn't see a difference in lash. Now the car will RPM just fine, but I can't get more that 22psi out of it.

I've checked the wastegate and it seems fine. Any ideas?

Do you think I should have driven the car and put more heat into the motor and "then" checked the hot lash? I wonder if the heat into the valves would then make them grow and I've just set my lash too tight?

I'm trying to get the car to the track this Sunday to get a 9.x pass out of it.

Thanks,
John Nguyen

 

[Alky V6]

In my experience the lash will grow as the engine warms. My cam uses a .020" lash and when cold it is .016". What is your redline with this engine? What is the A/R of the turbine housing? I am seeing a similar thing with my setup. I'm thinking that I've just reached the limit to what my T76 can put out.

 

[BlownV6]

I would say that by tightening up the lash you made the duration of the cam longer thus more air is moving through the motor and not being trapped in the manifold which would raise the boost but actually make less power. I have run mine at 0 lash cold to check if more cam works. but usually set mine at .010 to .015 because that is about as low as you can work with feeler guages and not bend them up !! thats my 2 cents!! mike

 

[Jeff Rand]

I once checked with Comp Cams and they said for aluminum heads to go
.006" less then the recommendation on the cam card for a cold setting.
Jeff

 

[EightSecV6]

How much overlap does the cam have?

 

[Eticket]

Guys, thanks for chiming in.

Here are the specs from Comp:
Part Number: 67-000-9
Cam Grind Number: BV67 276HER-2/276HER-2 SR112.0

Valve adjustment: Intake .020, Exhaust .020
Gross Valve Lift: I .545, E .545

With 1.55 Rocker Ratio
Duration @ .020 Tappet Lift: I 266, E 266

Valve Timing @ .050 Lift
Open 4 BTDC Close 48 ABDC
Open 4 8BBDC Close 4 ATDC

Specs with Cam Installed @ 112 Intake Center Line

Duration @ .050 232 232
Lobe Lift: .352 .352

Cam Ground with Lobe Center Separation of 112.0

Is that 8 deg or 96 deg of overlap? How is that calculated.

 

[Alky V6]

I once checked with Comp Cams and they said for aluminum heads to go
.006" less then the recommendation on the cam card for a cold setting.
Jeff

Each setup is going to be different. Mine was an iron stage II block with M&A heads. But, all the other components in the valvetrain are going to play a part also. I set the lash to spec when hot, let it sit overnight and checked it when cold. In my particular case I was .004" tighter when cold. You should be absolutely sure about this with your own setup and combination of valvetrain components. Set the lash hot, let it sit overnight and check it again stone cold. Once you are sure of the cold setting you can set the lash cold and not have to hurry with a hot engine setting the lash.

 

[Alky V6]

That would be 8 degrees overlap @ .050.
Depending on the aggressiveness of the lobe, around 56 degrees overlap from the seat.
A good midrange cam with a flat HP curve peaking at around 5,700 rpm. Torque peaking at around 4.200 rpm. A good shift point would be 6,500 rpm.
Power dropping off sharpest after 6,400 rpm.
Very little short circuiting betwen 4,000 and 5,000 rpm depending on your manifold tuning.
Watch for knock particularly around 4,200 to 4,500 rpm. Max cylinder pressure occurring there.
800 to 850 HP. Should be a mid 9s setup depending on your car setup.
Turbo still efficient at your airflow level. What is the A/R of the housing?
Keep your ignition timing conservative around peak torque.
Mach number really getting high after 5750 rpm.
BMEP and cylinder pressure numbers very manageable at 22 psi. Safe.

 

[Eticket]

Don, did you feed this through an engine software program?

I "figured" a 232-232 solid roller to be good to about 6800-7200. So that's where I've been shifting. The RPM climbs in 1st and 2nd gear have been steady, seems like, so thought the RPMs were justified.

Anothing thing that's interesting - that I dont' think has to do with this necessarily.. on the data log, the car is pretty rich in 2nd gear high rpms and then lean in hi rpms in 3rd gear.

Thanks,
John

Hope car runs 9.7's but weighs 3780 with me in it. Will be tough.

 

[Otto J]

If its gettin lean in high gear you may have a fuel delivery problem,Is this a f.a.s.t car? If so what is the duty cycle in high gear?

 

[Eticket]

KLHAMMETT

I believe the duty cycle is <80% ish? I'll check when I get home. The o2 correction is just a few percentages.

I'm using an Aeromotive pro pump brand new and have accidentally ran 30+psi one time (only 1/8th mile though, before tese valve lash adjustments) before and it was tuned rich.

I also figured that the lean looking problem was due to the lack of boost pressure being caused by something mechanical.

Thanks, John

 

[Alky V6]

How early have you been able to obtain full boost? What rpm?

 

[Eticket]

Donnie,

Seems like the car hits full boost around 5400 22psi.

I am just purely puzzled.

John

 

[Alky V6]

You're probably right about the weight of your car. I just threw some of your specs over my engine setup on my sim. Increased the stroke to 3.65", changed to your cam specs. Let me know if I guessed wrong on the stroke.
Do you know where the intake centerline was installed at? I would expect 5 degrees advanced?
Have you checked the turbo shaft by hand to see if there is any resistance to turning it or any contact going on?

 

[Eticket]

Donnie,

Mine's a 270" motor with 4" bore and 3.59" crank. Cam is installed as is. Not advanced or retarded I guess.

Have not checked the turbo shaft.

In talking with a buddy down here. It very well may be my lash setting? I set them a very snug .020. Most probably too snug, so who knows what they are. I'm going to relash to .025 and be sure not to have just a little resistance.

Right?

John

 

[Alky V6]

Donnie,

Mine's a 270" motor with 4" bore and 3.59" crank. Cam is installed as is. Not advanced or retarded I guess.

Have not checked the turbo shaft.

In talking with a buddy down here. It very well may be my lash setting? I set them a very snug .020. Most probably too snug, so who knows what they are. I'm going to relash to .025 and be sure not to have just a little resistance.

Right?

John

Do you know if any advance was ground into the cam? Did you degree it when you installed it?
Be careful increasing your lash. I know it's a tuning tool, but you could start beating up your valvetrain jumping over the clearance ramp of the cam lobe.
Do you have any flow numbers for your heads?
The A/R of your turbine housing?
Stock intake?
Typical aftermarket exhaust headers?
What exhaust system are you using after the turbo?
Intercooler size?
Converter type and stall speed?

 

[lazaris]

You said you went from 22-25 psi and did not go any faster. What rpm are you going through the traps? Another area to look would be your converter slippage.

 

[STP]

What rpm drop are you getting at the each shift? My car is doing the same thing if it makes you feel any better. No MPH change from 22-25psi getting anywhere from 4-600rpm drop at each shift.

 

[Eticket]

Lazaris,

The problem with no more power between 22-25psi was because the car didn't rpm fast at all. The car did pick up, but only .2 tenths or so. After resetting the valve lash... the car took .6 secound LESS to climb from 6200-7200 in second gear even with less boost.

rpms are dropping about 1000 or so between shifts. I think the valve lash is going to do it. I'll chime in Monday with some numbers.


Donnie:
Do you know if any advance was ground into the cam? Did you degree it when you installed it? No & Yes

Be careful increasing your lash. I know it's a tuning tool, but you could start beating up your valvetrain jumping over the clearance ramp of the cam lobe.

Do you have any flow numbers for your heads? All I know is that they flow good. Don't know the lift, but 258ish in the intake.

The A/R of your turbine housing? .85 3 bolt PTE
Stock intake? BGC intake

Typical aftermarket exhaust headers? ATR

What exhaust system are you using after the turbo? 3.5" DP and 2.5" duals
Intercooler size? CAS V1

Converter type and stall speed? Billet 9x11 approx 3300 stall I think.

I don't think any of these other things are issues. The only thing I did was reset the valve lash. Between being able to build a ton of boost or not. Makes sense that I did it too tight and the valves are staying open slightly?

 

[lazaris]

John,

How did you make out, find anything?