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Discussion Starter · #1 ·
I've been struggling with my current setup & wanted some input to validate what I'm seeing is OK.
My boost seems too low for the pulley sizes & engine mods.
This is my first roots build that wasn't an aftermarket bolt-on style kit.

Base info:
LS3 with stock LSA charger
Boost control solenoid is not used.
ZL1 lid
218/232 Cam
Stock heads
92mm cable throttle body
4" intake
Killer chiller intercooler with no HX
1-7/8" headers & dual 3" cutouts

Initial testing was to confirm basic functionality:
Using a 10% lower with no cooling, I was getting 160kpa boost & 160deg temps on a short burst.
Cruise air temps were 20deg higher than ambient before any heat soak.

Once I got the chiller functional, I was able to safely make some longer test runs.
The boost was typically 150-152kpa maximum with it peaking at my 6500rpm shift point.
There consistently seems to be a 1-2kpa bump at peak rpm.
IAT readings in the lid were starting in the mid 60's & finishing in the upper 80's
The cold water seems to be reducing the boost.

The latest is with a 22% lower & stock upper pulley.
Air temps went from 64-104 in 1/4 mile.
The max boost is still only reading 170kpa.

I removed the air filter to see if it was a restriction with no change in boost.
I assumed a slipping belt or inlet restriction would cause a drop on the top end.

I have a 100lb injectors hitting 70% duty cycle at 11.3:1 AF ratio on 93.
Traction is currently a problem in lower gears so I cannot get a good ET, but it accelerates from 100-125 in 3.2 sec according to my data log.
 

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Doesn’t a chiller lower boost pressure?

Fwiw, mine peaks over 210 kpa.


Sent from my iPhone using Tapatalk
Yes, when air is cooled, air molecules shrink and take up less space.
 
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Killer Chiller have many issues, cam on the small side but with a 9.5" lower I would expect to see 12-13 psi
I am thinking that the OP should look into a high quality intercooler.
 
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Discussion Starter · #8 ·
Doesn’t a chiller lower boost pressure?

Fwiw, mine peaks over 210 kpa.
Yes, it should it theory, but in that case my boost should also rise with an air temp increase through the 1/4mile...
Going from 60-100F, it should rise 12kpa, but it doesn't. It only rises 2-3kpa.

Killer Chiller have many issues, cam on the small side but with a 9.5" lower I would expect to see 12-13 psi
Yes, I expected more boost.
10-11 was my goal with the factory 10.7 compression.
... I know, E85 is in my future.

Cam is small, but I originally planned for a Pro-charger & this is my daily driver when the weather is dry.
I have other radical cars that are not considered long distance drivers, so I kept this one mild since I'm 32mi from work.
I like idling through town at 900rpm in 6th gear.

I am thinking that the OP should look into a high quality intercooler.
Yes, I've heard of many issues.... so, I built my own lines, fittings etc. with a universal kit.

I cannot complain about the cooling.
From my testing, the IAT is approximately 10 deg hotter than the return water temp... limited by the HX efficiency.
I routinely see low 40 deg return water in the tank with low 50 deg IAT's.
I do not have a convenient way to measure temp to the charger as my IR heat gun reads too wide of a pattern to reliably get the fitting temps.

This week with weather in the 80's I was cruising around at 53 Deg IAT.

I still need to insulate the lines & fabricate an airbox to keep hot air from the filter.
Air at the throttle body is typically 20 deg hotter than outside at cruise & it climbs in traffic.
On a 92 deg day, I had 62deg IAT's & 73 with the AC in cab on full tilt.
I plan to put a smaller orifice tube in the evaporator as the in-cab cooling is still excessive... this will gain a few more degrees of water reduction.

My biggest regret is too small of a storage tank. I only had room for 1 gal under the hood.
With the AC compressor kicking out at 5500rpm, the temp climbs during a pass.
Not sure where the AC compressor flies apart.
I wanted a 5 gal tank under the truck, but getting lines to the rear is about impossible unless running over the engine, which adds a lot of heat.
I may add another gallon under the front bumper in the future.
 

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Your wrote:
"Base info:
LS3 with stock LSA charger
Boost control solenoid is not used.
ZL1 lid
218/232 Cam
Stock heads
92mm cable throttle body
4" intake
Killer chiller intercooler with no HX
1-7/8" headers & dual 3" cutouts

Initial testing was to confirm basic functionality:
Using a 10% lower with no cooling, I was getting 160kpa boost & 160deg temps on a short burst.
Cruise air temps were 20deg higher than ambient before any heat soak.?"

--------------------------------------------------

Is this a 376 CID LS-3 Engine?

What are the pulley sizes?
What engine rpm are you shifting at?

Is timing being pulled at 160° F?
Yes, I understand that you have now reduced that number.. :giggle:

--------------------------------------------------

You have stock, non-ported heads. . .Correct!
Your camshaft, along with a 2.165" Intake Valve, is only good for ~6,300 to maybe 6,400 rpm.

So then. . .
=> (376 * 6350 / 3456)= 691 CFM, which will only support 463 fwHP. . .
'Plus' whatever increase in Density Ratio your simple 'Roots Blower' can supply.

Since I can't calculate what your specific density ratio is,
we can still plug in two typically seen values, high to low. . .

=> (691 * 1.75)= 1209 CFM. . .Or 810 fwHP, or a %VE, of ~108%
=> (691 * 1.41)= 974 CFM. . ..Or, 653 fwHP. or a %VE, of ~87%

And a simple fact, regarding an LS-3, 376 Engine, having a stock 2.165" Intake Valve,
should produce around 650 fwHP, to maybe 675 fwHP, on gasoline.

--------------------------------------------------

Boost is simply a restriction to airflow within an engines induction system. . .
Small camshafts, and stock cylinder heads, provide a restriction to airflow.

Now, with all of the above in mind; what bothers me is that with stock heads,
and the 'smallish' camshaft, why is your boost so low?

Cheers
 

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Discussion Starter · #10 ·
Is this a 376 CID LS-3 Engine?
Yes, a stock LS3

What are the pulley sizes?
It is a 9.6" (22%) Powerbond lower & stock 2.95" upper

What engine rpm are you shifting at?
Spark based rev limiter set for 6700
Currently the shift light is set for 6400 & my datalogs typically show just under 6500 on the shifts.

It will rev higher but power does definitely start to taper off.

Is timing being pulled at 160° F?
Yes, I understand that you have now reduced that number.. :giggle:
I only had 10 deg in it for that test, but now run approx. 15 deg timing, with 1 deg timing being pulled at 130 & 1 more for every 10 deg above up to be safe.
Still being conservative in the tune.
--------------------------------------------------
You have stock, non-ported heads. . .Correct!
Your camshaft, along with a 2.165" Intake Valve, is only good for ~6,300 to maybe 6,400 rpm.
Stock LS3 heads, not LSA heads with intake guide vanes.

So then. . .
=> (376 * 6350 / 3456)= 691 CFM, which will only support 463 fwHP. . .
'Plus' whatever increase in Density Ratio your simple 'Roots Blower' can supply.
For reference, my NA tune showed peak flow of 368 gm/sec at 6600rpm

Since I can't calculate what your specific density ratio is,
we can still plug in two typically seen values, high to low. . .

=> (691 * 1.75)= 1209 CFM. . .Or 810 fwHP, or a %VE, of ~108%
=> (691 * 1.41)= 974 CFM. . ..Or, 653 fwHP. or a %VE, of ~87%

And a simple fact, regarding an LS-3, 376 Engine, having a stock 2.165" Intake Valve,
should produce around 650 fwHP, to maybe 675 fwHP, on gasoline.
Now I'm tuned for speed density only & my VE table is 99% to hit the desired AF ratio.
My odd issue is that the VE does not taper off at high rpm... I expected the need to pull fuel at peak RPM.
My 100lb injectors are currently hitting 70% duty cycle.

--------------------------------------------------
Boost is simply a restriction to airflow within an engines induction system.
Small camshafts, and stock cylinder heads, provide a restriction to airflow.

Now, with all of the above in mind; what bothers me is that with stock heads,
and the 'smallish' camshaft, why is your boost so low?

Cheers
Yes, confirming my original question.... I do not see the cold IAT's being totally responsible for this.
I expected 10psi with a 10% lower, & now only see this with the 22%.

I know the 114 LSA cam is not ideal, but it still has 2 deg negative overlap at .050", so I do not see it blowing the boost out the exhaust.

I had blamed the air filter, but testing revealed it is not the issue.

Throttle is wide open.

I checked the boost actuator & adjusted the stop with lid off to be sure it was fully closed.

I am happy with the performance at the moment & am not trying to push it to spit parts due to the stock bottom end.
Just trying to maximize what I have.
Mostly, I just want to understand the boost discrepancy.
 

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Yes, a stock LS3

"Your wrote:
"I am happy with the performance at the moment & am not trying to push it to spit parts due to the stock bottom end.
Just trying to maximize what I have.
Mostly, I just want to understand the boost discrepancy."




It is a 9.6" (22%) Powerbond lower & stock 2.95" upper



Spark based rev limiter set for 6700
Currently the shift light is set for 6400 & my datalogs typically show just under 6500 on the shifts.

It will rev higher but power does definitely start to taper off.



I only had 10 deg in it for that test, but now run approx. 15 deg timing, with 1 deg timing being pulled at 130 & 1 more for every 10 deg above up to be safe.
Still being conservative in the tune.
--------------------------------------------------


Stock LS3 heads, not LSA heads with intake guide vanes.



For reference, my NA tune showed peak flow of 368 gm/sec at 6600rpm



Now I'm tuned for speed density only & my VE table is 99% to hit the desired AF ratio.
My odd issue is that the VE does not taper off at high rpm... I expected the need to pull fuel at peak RPM.
My 100lb injectors are currently hitting 70% duty cycle.

--------------------------------------------------


Yes, confirming my original question.... I do not see the cold IAT's being totally responsible for this.
I expected 10psi with a 10% lower, & now only see this with the 22%.

I know the 114 LSA cam is not ideal, but it still has 2 deg negative overlap at .050", so I do not see it blowing the boost out the exhaust.

I had blamed the air filter, but testing revealed it is not the issue.

Throttle is wide open.

I checked the boost actuator & adjusted the stop with lid off to be sure it was fully closed.

I am happy with the performance at the moment & am not trying to push it to spit parts due to the stock bottom end.
Just trying to maximize what I have.
Mostly, I just want to understand the boost discrepancy.
If everything indifferent from the Blower 'Is' Okay, I would be led to believe that
you have a blower issue, or something simple, such as a slipping pulley etc.

Also, your pulley ratios will only supply sufficient air, to fill the 376 CID Engine
to 100% VE%, with the stock 1.9L Blower.

And the 218° duration intake lobe, will only yield about a 10% increase in HP. . .

But if your happy with the performance, then I am happy..lol
 

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Discussion Starter · #12 ·
The engine only has about 3000mi on it, so I have no desire to rebuild it.

The blower was a low mile warranty unit I bought from a friend of mine.
It's spotless inside with the rotor coating looking like new.

Drive system is an LSx Concepts manual tensioned setup which maximizes the belt wrap.
Belt was tightened with a tension gauge & even what I consider a bit too tight & it made no change.


Yes, I'm happy for now (relatively speaking) but I get bored easily.
I keep telling myself to be content with it running instead of turning it up until it breaks.
Being the truck is only 3500lb, it does pretty well.

This is already installed but I must resist hooking a nitrous line to it for the time being.
Red Gas Font Electronic device Auto part


Has anyone detected a substantial drop in boost from cutouts or open headers?
I have seen this in the past, doing some Procharged 4th gen Camaro builds, with adding headers/exhaust & losing 2 lbs of boost.

If I remember correctly, after doing a friends ZL1 with headers, stainless works duals & a 22% lower it still made 12-13#.
WeaponX claimed a 1.5lb boost reduction from adding a chiller.
 

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I mean, boost is a measure of restriction, right? Free up the exhuast, and you will see boost drop (even though you'll probably end up making more power at the same time.)
 
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I mean, boost is a measure of restriction, right? Free up the exhaust, and you will see boost drop (even though you'll probably end up making more power at the same time.)
^^^ (y) (y) (y)

Boost is the delta between two pressures:
That delta is seen between the intake manifold and the tailpipe outlet.

If the intake manifold pressure rises, or the pressure seen at the tailpipe is reduced, then performance will rise. . .
 
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