[Nabush]

Hello Guys,

Posting here, because it is an LT1 and I also have an 17' SS 1LE ...

So my AutoX/Roadcourse C7 GS...

Previously had :

- AFE CAI
- ARH Long tube headers 1 7/8
- Catted X pipe
- MSD Intake manifold
- Ported TB
- Hp tuners tune (I tune myself)

Was making 455-458WHP/420 WTQ on a Mustang dyno

With all the same parts but a TSP Stage 3 cam, C5R timing chain, PRC dual valve springs, DOD delete etc

508 WHP/424 WTQ on the same Mustang dyno.

In both case Pump gas 91

We can assume Dynojet numbers would have been 530-540WHP

I precise I did the whole job myself as well as the tuning. Fairly big job to do a cam.

But....Power under the curve is shitty. I tried everything on the dyno to gain but no luck. Timing/SOI/Fuel/TQ management. No luck. There is an airflow resonance/issue between 3000-4400 rpm.

Car drive great (spend 10h tuning on the road before the dyno and MAF calib and volumetric efficiency are spot on), definitely not a tuning issue.

I took the car appart a second time to recheck my timing and even put a new cam phaser and still the same. I initially thought that the cam could have been installed retarded somewhat but no...

The only difference I see with other TSP Stage 3 cam dyno I saw if that I'm using stock OEM heads. Pretty sure my issue is coming from there.

With the ported heads I see 400 WFT/Lbs from 3500 rpm (on a dynojet though) when in my case I'm at 350 WFT/Lbs

I don't think here people have a lot of experience with this subject (tuning and cam) but I wanted to share my thoughts. Waiting on a answer from TSP about the heads being possibly the issue.

Unless it is the MSD Manifold (which is known to loose torque down low, but I already had it prior to the cam)

In red FBO in black FBO cam



PS : second time I did the cam it took me only 1 week end on a C7 (which is more work than a Camaro)

[Nabush]

I can upload my tune and logs if someone thinks he has an idea other than heads

[oldman]

I would caution you on racing dynos, you can't assume what a dynojet would do.

Second, you are approaching a 10% correction factor already i.e. your car is making a whole lot less HP than this dyno shows.

Third, you are on 91 octane, I guess you can get away with this at your attitude, but it is very low. I don't know the effective dynamic compression (download cam doctor), at your altitude you could be like dunno 10.5 or something? i.e. you should have a stage 1 cam.

Fourth, AFAIK all TSP cams can take a cam phaser limiter of 20 degrees, don't know about their big stuff, you can get some of this midrange back by advancing the cam say 6 degrees till 4500 RPM, TSP should be able to give you general guidelines. IMO with fast ramp profiles, the factory phaser is not able to handle (there is dynamic walk).

Fifth, what is a catted X pipe? I also have an M6 and with factory suitcase, there are strange harmonics that lead to all kinds of issues including false knock.

Your header tube size is too small for size of cam.

I would port the heads and mill, you probably need to notch the pistons. Looking for dunno say 12.3 static. thinner head gasket too? Stock head ports flatline above .550 lift and actually flow less at higher lifts, so all that valve lift is just losing HP and torque from flow (as well as dynamic compression).

https://www.enginelabs.com/engine-te...-lt1-di-heads/


Drop the cam size to a stage 2 that works at 2000+ ft.

eliminate the cam phaser

bring tube size to 2"

ported 95mm TB or 103 TB

All of the above assuming you can get 93 octane.

On 91 and 2000 plus feet:
stage 1 cam, ported heads, maybe a slight mill to 11.75 CR.

Full disclosure I live near sea level and 93 octane my whole life.

[Nabush]

Originally Posted by oldman

I would caution you on racing dynos, you can't assume what a dynojet would do.

Second, you are approaching a 10% correction factor already i.e. your car is making a whole lot less HP than this dyno shows.

Third, you are on 91 octane, I guess you can get away with this at your attitude, but it is very low. I don't know the effective dynamic compression (download cam doctor), at your altitude you could be like dunno 10.5 or something? i.e. you should have a stage 1 cam.

Fourth, AFAIK all TSP cams can take a cam phaser limiter of 20 degrees, don't know about their big stuff, you can get some of this midrange back by advancing the cam say 6 degrees till 4500 RPM, TSP should be able to give you general guidelines. IMO with fast ramp profiles, the factory phaser is not able to handle (there is dynamic walk).

Fifth, what is a catted X pipe? I also have an M6 and with factory suitcase, there are strange harmonics that lead to all kinds of issues including false knock.

Your header tube size is too small for size of cam.

I would port the heads and mill, you probably need to notch the pistons. Looking for dunno say 12.3 static. thinner head gasket too? Stock head ports flatline above .550 lift and actually flow less at higher lifts, so all that valve lift is just losing HP and torque from flow (as well as dynamic compression).

https://www.enginelabs.com/engine-te...-lt1-di-heads/


Drop the cam size to a stage 2 that works at 2000+ ft.

eliminate the cam phaser

bring tube size to 2"

ported 95mm TB or 103 TB

All of the above assuming you can get 93 octane.

On 91 and 2000 plus feet:
stage 1 cam, ported heads, maybe a slight mill to 11.75 CR.

Full disclosure I live near sea level and 93 octane my whole life.

Hi,

I'm at 2800-3000FT elevation hence the 9%+ SAE correction factor. But SAE correction factor is fairly accurate.

Real power the car makes at those 3000FT is 455 WHP yes. Altitude sucks.

This does not change the power curve though. There are no reasons that the car should loose torque between 3300 and 4000 rpm. There is definitely and air flow issue. Power loss with altitude is pretty linear and can be simulated at sea level with partial throttle.


I have a 0 Deg lock on my cam phaser. TSP Stage 3 cam does not take partial lockout. Also there is cam phaser "float" at high rpm because of lift and duration if I were to partially lock it. Already contacted TSP about that..

I took a Catted X pipe for smell... I agree with the false knock because of harmonics though...Something I saw since I have headers. Thouse are 100 cells cats though. Pretty free flowing

I completely agree about the heads. I think most of my issue comes from that. I will give it a try after this coronavirus deal is taken care of (hopefully in a few months)

My cam is 235/239, .645"/.635", 116 LSA 112ICL so it lifts way over 0.550....

I also agree I think I need a bigger TB. The stock ported one is probably too small.

The exhaust size not so much. 1 7/8 can be used on Z06 with much more exhaust gas flow and is perfectly fine for NA IMHO. Moreover my issue is not top power. Bigger exhaust tubes loose power down low.

As far as fuel, 91 is the best I can get, though I can get E85 in 1 or 2 gas stations.

[oldman]

Originally Posted by Nabush

Hi,

I'm at 2800-3000FT elevation hence the 9%+ SAE correction factor. But SAE correction factor is fairly accurate.

You can't "correct" dynamic compression.

Originally Posted by Nabush

Hi,
Real power the car makes at those 3000FT is 455 WHP yes. Altitude sucks.

Yep sucks even more on large cams and poor octane as dynamic compression goes down and you can't mechanically compensate because you need octane. Hence all piston-engine aircraft worth anything are FI and run av-gas.

Originally Posted by Nabush

This does not change the power curve though. There are no reasons that the car should loose torque between 3300 and 4000 rpm.

Please re-read my post, a large cam reduces dynamic compression, altitude reduces dynamic compression. lifts above .550 reduce flow (stock head) which not only reduces HP and torque, it has the double whammy of reducing dynamic compression. Then throw in the trifecta of less VE due to a short runner intake and a large cam / overlap presto you are down midrange torque.

Originally Posted by Nabush

There is definitely and air flow issue. Power loss with altitude is pretty linear and can be simulated at sea level with partial throttle.

Even at sea level and with a CR that could support the cam say 12.5. There would be midrange loss with your setup (assume). mainly becuase the stock head flows less air above .550 and you have a .634 cam with a fast ramp.

Originally Posted by Nabush

I have a 0 Deg lock on my cam phaser. TSP Stage 3 cam does not take partial lockout. Also there is cam phaser "float" at high rpm because of lift and duration if I were to partially lock it. Already contacted TSP about that..

roger that.

Originally Posted by Nabush

I took a Catted X pipe for smell... I agree with the false knock because of harmonics though...Something I saw since I have headers. Thouse are 100 cells cats though. Pretty free-flowing

Yeh, not a flow issue, it is a harmonic, IMO it is worst as most / all aftermarket X pipes remove the two factory flex coupler. I'm having that issue right now. I was interested in the mfg of the pipe..

Originally Posted by Nabush

My cam is 235/239, .645"/.635", 116 LSA 112ICL so it lifts way over 0.550....

The tight LC should help mid-range torque, but that is assuming dynamic compression is correct. That cam must be loope...duppe (I like big cams myself). 116 is on the loose side BTW

Originally Posted by Nabush

The exhaust size not so much. 1 7/8 can be used on Z06 with much more exhaust gas flow and is perfectly fine for NA IMHO. Moreover my issue is not top power. Bigger exhaust tubes loose power down low.

As far as fuel, 91 is the best I can get, though I can get E85 in 1 or 2 gas stations.

You might have to mix on E50 is you can bump the CR to 12.5... all issue IMO go away.

I like you argued for a while that 2" will make less torque and depending on the build less HP, dyno after dyno show that at WOT form stock to wild the engine likes 2". I run 1 and 7/8 for clearance and heat, my rides makes more than enough power.... and yes 2" on stock engine makes more torque at WOT over the entire power band... I know

[Nabush]

Originally Posted by oldman

You can't "correct" dynamic compression.



Yep sucks even more on large cams and poor octane as dynamic compression goes down and you can't mechanically compensate because you need octane. Hence all piston-engine aircraft worth anything are FI and run av-gas.






Please re-read my post, a large cam reduces dynamic compression, altitude reduces dynamic compression. lifts above .550 reduce flow (stock head) which not only reduces HP and torque, it has the double whammy of reducing dynamic compression. Then throw in the trifecta of less VE due to a short runner intake and a large cam / overlap presto you are down midrange torque.




Even at sea level and with a CR that could support the cam say 12.5. There would be midrange loss with your setup (assume). mainly becuase the stock head flows less air above .550 and you have a .634 cam with a fast ramp.



roger that.



Yeh, not a flow issue, it is a harmonic, IMO it is worst as most / all aftermarket X pipes remove the two factory flex coupler. I'm having that issue right now. I was interested in the mfg of the pipe..



The tight LC should help mid-range torque, but that is assuming dynamic compression is correct. That cam must be loope...duppe (I like big cams myself).



You might have to mix on E50 is you can bump the CR to 12.5... all issue IMO go away.

I like you argued for a while that 2" will make less torque and depending on the build less HP, dyno after dyno show that at WOT form stock to wild the engine likes 2". I run 1 and 7/8 for clearance and heat, my rides makes more than enough power.... and yes 2" on stock engine makes more torque at WOT over the entire power band... I know

So overall you agree that the TSP 360 CFM ported heads should help in my case ?

Honestly I did not try 2" headers, so I can't really confirm or infirm if 2" are better for NA applications... Just remember a post from ARH saying 2" was a bit too big for NA application but good for FI

Don't know if you do your own tuning like myself, but with my current setup my cylinder airmass decreases between 3300 and 3800 rpm. Cylinder airmass is a calculation made by the ECM from the MAF or VE tables (depending on the mode) and rpm /load...

This means that in this RPM range my engine sucks less air per revolution...Like if there is a flow/backflow issue in the heads/intake/Intake manifold...

[oldman]

hmm, lets just address the air mass:
1) the MSD has a know flat spot in this area.
2) the heads flow LESS at lift above .550 and you have a fast ramp .645
3) torque mgt tables? Check to if TB is WOT the whole time
4) collapse CAT (backflow issue)
5) don't know how good the AFR CAI is try the stock on again?
6) port the MSD (remove flash neer the port exits)

Maybe a dynamic that I is unique to the combination and the altitude; because 50 HP gain from cam is NOT bad with stock heads, especially a cam that is WAY too big and way too much lift (head flatspot in flow).

[6spdhyperblue]

It’s is a head scratcher why they don’t have low lift options even in stg 0 and stg 1

[oldman]

I designed my own cam and it is .596 lift

[oldman]

I was thinking and this is simple. The engine is effectively 9% smaller or 5.6 liters. The cam is simply too large for head flow and engine size. This is causing flow stagnation and probably some reversion into the intake ports. Look the piston is only moving down the bore for 180 degrees, all the rest of the filling is because of dynamic flow. The cam is too big, engine too small to allow for this to happen. Ported heads will NOT fix this. You need to pick a cam that will work with a 5.6 street engine and this ain't it. Stage 1 is good.

[Nabush]

Originally Posted by oldman

hmm, lets just address the air mass:
1) the MSD has a know flat spot in this area.
2) the heads flow LESS at lift above .550 and you have a fast ramp .645
3) torque mgt tables? Check to if TB is WOT the whole time
4) collapse CAT (backflow issue)
5) don't know how good the AFR CAI is try the stock on again?
6) port the MSD (remove flash neer the port exits)

Maybe a dynamic that I is unique to the combination and the altitude; because 50 HP gain from cam is NOT bad with stock heads, especially a cam that is WAY too big and way too much lift (head flatspot in flow).

I'll try the ported heads no matter what.
My TB does not close, this is one of the obvious stuff to check when you tune.
I did not check my CATS. Had a weird vibration noise yesterday, I may have an issue with a broken cat. Need to check.
Porting the msd is an option.

[95 imp]

Originally Posted by oldman

I was thinking and this is simple. The engine is effectively 9% smaller or 5.6 liters. The cam is simply too large for head flow and engine size. This is causing flow stagnation and probably some reversion into the intake ports. Look the piston is only moving down the bore for 180 degrees, all the rest of the filling is because of dynamic flow. The cam is too big, engine too small to allow for this to happen. Ported heads will NOT fix this. You need to pick a cam that will work with a 5.6 street engine and this ain't it. Stage 1 is good.

This.

And porting the heads will make it worse.

[BlackbeastSS2]

Let’s compare a small change the LT2 did in its camshaft to roughly increase from
455/460 hp and 460/465 lb-ft in the LT1 to 490/495 LT2. (Corvette)

“The camshaft’s intake lobes remain the same as the LT1’s, but lift on the exhaust lobes is slightly increased. The LT2’s cam phasing, which alters intake and exhaust timing together, is about the same as before. The rest of the valvetrain is carryover from LT1 as is the LT2’s rev limiter, which remains at 6600 rpm.”

Bigger isn’t always better. But in reality is I worth the excess money to gain that extra 35-50 HP to the fly. I did it before on my other build and it can be overwhelming to choose the right path.

[KingLT1]

Have you had somebody else look over the tune? I don't see a cam with 5 degrees of overlap causing that kind of torque loss even on stock heads if everything is sorted correctly in the tune.