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Manifold Comparison VCTS, Flat Top, Skunk 2

Manifold Comparison VCTS, Flat Top, Skunk 2

Old 01-12-2019, 07:13 PM
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Default Manifold Comparison VCTS, Flat Top, Skunk 2

I know this topic has been covered in at least two other threads, however, I have not seen a thread with comparison of these three manifolds on the same turbocharged car.

My car had a VCTS manifold with the tumble generators removed and the holes filled with JB weld between the cylinders, an NPT plug to the outside and a great deal of smoothing of the finish inside. However, I was stubborn, blaming every other part of my car on the lack of top end power, like the old BEGI intercooler and 2.5" exhaust. During all this trial and error was also dealing with leaking valve stem seals. Specs of the car are as follows:

Engine built by McCully Racing Motors (McCully Racing Motors- There's no Replacement for Displacement.) 2002 VVT engine with the following parts:
Manley Rods
Supertech 84mm pistons
BE oil pump
SuperMiata damper
Supertech Inconel +1mm Valves
Supertech double valve springs 74lb, titanium retainers
Combustion chambers and area behind the valves cleaned and smoothed
EUDM flat top manifold
OEM throttle body
Oil squirters retained
9.4:1 effective CR

Turbo kit:
FMII, GT2560
Hydra 2.7 ECU Hydra EBC controlling the boost at 16psi.FM 3.0 downpipe and Exhaust, 200 cell cat

The red trace is the best I could get out of the car with all the parts shown above, except for the intake manifold. The red trace is with the VCTS manifold. The blue trace is the results of the flat top manifold with the ECU tuned for it. Boost in both plots is electronically controlled by the Hydra ECU at 16psi. The engine is knock limited in both runs. I was able to run between 3 and 7 degrees more advance through the RPM range with the flat top manifold. Fuel requirements increased roughly 7% above 5500RPM. I was hoping for 300HP, but fell short. 299.56hp will have to do.

Besides the improvement in ignition advance, the EBC settings had to be changed quite a bit. The base duty cycle went down and the amount of additional duty cycle to maintain 16psi was hugely reduced. In short, the turbo made this boost pressure and power at a slower turbine speed. I am really happy with the top end power the engine has now. The engine pulls hard all the way to 7000RPM, just like a sports car should deliver its power.

I have a Skunk 2 manifold with a spacer on the way to me. When i get that installed, I'll be back at the dyno to measure the results. Again the ECU will be tuned for whatever the manifold needs and the boost pressure will be at 16psi.
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Old 01-12-2019, 07:25 PM
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Dramatic results. I must say though, something isn't adding up to me. I would think you would need more than 7% fuel to account for the difference, even with the timing. I also need to ponder the change in EBC DC a bit. What is your WG configuration?
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Old 01-12-2019, 07:44 PM
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glad it went as discussed and your car definitely loved the flow increase
thank you for sharing results too
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Old 01-13-2019, 06:17 AM
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for sharing data; waiting on the Skunk2 update. Are you gonna test this with and without the spacer?
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Old 01-13-2019, 09:56 AM
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Interested in the skunk results, but I'm lazy and doubt I'll change my setup
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Old 01-13-2019, 12:27 PM
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Poscat for the data! It is awesome to see a clear comparison. I hope for similar results once I get my square top on.
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Old 01-13-2019, 01:52 PM
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I'm glad you achieved such great results. But I don't believe that any correctly functioning VTCS manifold would stomp your power by 75hp. I am more willing to believe that all of your mods to that manifold screwed it up.

I'd be happy to ship my stock VTCS to you for a dyno run if you'd be interested in trying it out. I ran that exact turbo/manifold setup (VTCS, 2560 turbo, etc) and never saw such a dramatic falloff in performance.
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Old 01-13-2019, 02:45 PM
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I mean, I appreciate Ken for his hard work comparing the manifolds, but he's in no way alone with these results. Top end performance tanks both naturally aspirated and turbocharged with those manifolds, I've experienced it numerous times and I would put dollars to doughnuts there's an issue with your setup that's causing it not to drop off on the top end, which when fixed would showcase the VTCS manifold's downfalls easily.
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Old 01-13-2019, 03:56 PM
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Curly - can you clarify what you said

"causing it not to drop off on the top end, which when fixed would showcase the VTCS manifold's downfalls easily."

You are saying there WAS something wrong with my VTCS that caused it to NOT drop off on the top end. And that if I had simply fixed it, I too would be able to enjoy shitty performance at the top end?

I must admit ignorance on this subject, as I've only used a VTCS and VICS. If I can get 75hp from a flat top or skunk, I'll buy one tonight.
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Old 01-13-2019, 04:26 PM
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Originally Posted by Mudflap View Post
I'm glad you achieved such great results. But I don't believe that any correctly functioning VTCS manifold would stomp your power by 75hp. I am more willing to believe that all of your mods to that manifold screwed it up.

I'd be happy to ship my stock VTCS to you for a dyno run if you'd be interested in trying it out. I ran that exact turbo/manifold setup (VTCS, 2560 turbo, etc) and never saw such a dramatic falloff in performance.
I picked up only 19hp. The improvement to me is the extension of the torque curve out to redline. The engine pulled great up to 6 grand were the party was over and time to shift. Now, the engine pulls all the way to redline, which is really want I was searching for. The hp numbers are nice, but the flat(ish) torque curve out to 7000RPM was my goal.

My engine has a CR of 9.4:1 which is higher then optimal. With the VTCS manifold I was limited to 10 degress of advance at 16psi which caused the rapid fall off in torque above 6000RPM. I'm now running 13 degrees in the mid-range raising up to 17 degrees at 7000RPM. A huge improvement.
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Old 01-13-2019, 04:33 PM
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Originally Posted by Ted75zcar View Post
Dramatic results. I must say though, something isn't adding up to me. I would think you would need more than 7% fuel to account for the difference, even with the timing. I also need to ponder the change in EBC DC a bit. What is your WG configuration?
Ted, I have attached the injector on time delta between the VTCS manifold fuel table and the flat top fuel table. Most of the changes are above 3000RPM so that is what I'm showing. Also i only tuned in boost on the dyno. I'll let autotuning figure out non-boost rows for the next 300 miles or so, then import the changes.

For boost control the EBC output is in %, with 100% being wastegate fully closed and 0% the wastegate fully open. With the VTCS manifold, the EBC output was 70% at 3000RPM and 80% at redline. With the flat top, the EBC output was 41% to 77%. Still about the same at the top, but much lower down at 300RPM.
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Old 01-13-2019, 04:44 PM
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Thanks for the reaponse Ken.

I see 14%, am I mis-reading? What AFR do you target up there (scaled to lamda = 1 @ 14.7 for alternative fuels)?

did you by any chance get a new alternator or solenoid? What WG spring do you use?

I also assume you are using a simple WG/solenoid configuration.
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Old 01-13-2019, 05:41 PM
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The top two rows are tuned for 11.2:1.
I am using a new wastegate actuator with the same 10psi level of boost. The alternator and MAC EBC valve are still the same.
Yes, I'm using a simple single port Tial internal wastegate actuator with a 3 port MAC valve, with the third port to atmosphere. Nothing unique
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Old 01-13-2019, 06:37 PM
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Ahh, ok. New actuator, and presumably a change in pre-load. If it were me, that is all I would need to know WRT the change in commanded DC.
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Old 01-17-2019, 03:14 PM
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I received my Skunk2 manifold and plenum spacer yesterday. Unfortunately, we are supposed to get hit with snow this weekend in S.E. PA. I will get it installed in the next few days, but my car does not go out on salt covered roads. I'm also traveling for work the first week of February, so I will not make it back to the dyno until the middle of February at best. I'll post up results when I have them.
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