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Crotchety Old Bastard
 
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GT2 Cams - what is the power band?

We're looking at cams that will support 500whp and give up as little low end as possible. GT2 are in that range. What are the real world driving characteristics?
Thanks -

Old 10-17-2014, 01:04 PM
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I'm guessing this will be with EFI, right?
A CIS mechanical airflow meter probably wouldn't get along with the intake pulses from the intake and exhaust valve timing overlap during low rpms. I'm just going on hearsay and havn't tried it though.. and I don't know if anyone actually has.
Old 10-17-2014, 02:15 PM
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Crotchety Old Bastard
 
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Nope, CIS.
Good point about the pulses and metering plate. That is a problem with the 911 but I don't know if it would be with the 930. I need to research the cam profiles used on the 934 to help answer that question.
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Old 10-17-2014, 02:54 PM
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I assume with the erratic pulsing would cause the injectors to inject erratic too?

Or is there hysteresis built in?

When I had old school low impedance injectors with EFI, I had a hard time tuning idle and low speeds due to this same situation.

If this is the case, I'd avoid at all costs?

Second, won't 964's get you there?

Third, just run more boost until you achieve 500whp.

Old 10-17-2014, 02:59 PM
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Just to chime in, when I ran big cams in my 16V Scirocco (Schrick 276s on CIS-E) the bouncing fuel plate due to intake pulses was a very real and very annoying problem. Car was annoying and nasty at low speeds and with static throttle input below 2400-2500 rpm. Flat out though it pulled to the moon and that idle.....oh man....loved that lumpy idle.

Interesting side note when I went to research the problem most of the info I found was about 930s with big cams.
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Old 10-17-2014, 03:20 PM
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Doesn't look like big cams are a problem for the 930. I found several examples. Now I need to narrow the search. I need the biggest cams that do not require valve reliefs as the pistons must stay stock.
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Old 10-17-2014, 06:28 PM
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The GT2-EVO cam will not clear the exhaust side on stock 3.3 pistons. Tried it.

Ended up with 964 grind.
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Old 10-17-2014, 06:37 PM
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Quote:
Doesn't look like big cams are a problem for the 930. I found several examples. Now I need to narrow the search. I need the biggest cams that do not require valve reliefs as the pistons must stay stock.
I personally don't think you need big cams to make big power, you need a big turbo with higher than 1-bar of boost until desired hp level.
Old 10-17-2014, 07:12 PM
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Quote:
The GT2-EVO cam will not clear the exhaust side on stock 3.3 pistons. Tried it.



Ended up with 964 grind.
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Old 10-17-2014, 07:13 PM
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Quote:
Originally Posted by Tippy View Post
I personally don't think you need big cams to make big power, you need a big turbo with higher than 1-bar of boost until desired hp level.
Wouldn't that be extremely difficult to do with K-Jet/CIS? I guess if you modify the fuel head accordingly you could run big boost, but of course, there is still no knock detection and active timing adjustment with that system.
Old 10-17-2014, 08:46 PM
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Quote:
Originally Posted by Ronnie's.930 View Post
Wouldn't that be extremely difficult to do with K-Jet/CIS? I guess if you modify the fuel head accordingly you could run big boost, but of course, there is still no knock detection and active timing adjustment with that system.
A J&S safeguard would fix the knock protection issue and allow better timing control. That's how mine is set up. With more fuel im sure its doable.
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Old 10-17-2014, 09:01 PM
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Just use 934 cams, they hit 500whp.
Of course, they also had crap low speed driving characteristics, and single digit mpg.

GT2 cams are not high rev cams, not part of the GT2 engine strategy. Decent midrange torque. Will need either/or head and piston preparation to make work on a 3.3L.
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Old 10-17-2014, 09:29 PM
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Cam logic

Dear fellow Pelicanites,

the cam is an essential part of the package.

To make this package most efficient and most harmonic as well the core components should work on a synergetic way with each other.

First comes the analysation about the specific application.

Cam choice starts with the view on the static compression ratio, next comes the valve train background and the peripheral situation around inlet plenum, exhaust and turbo.

On the turbo mostly the hot side must fit the cam in size.

The GT 2 evo cam is a good component but as all good parts it is made to fit into a specific concept of a specific application.

Knowing your concept and goal I would say that it is not the right cam for you.

When the lift in TDC grows the system gets more sensitive and more reactive - which helps us to generate much more power and torque then using restrictive catalytic converter smog test oriented cam profiles. A good cam will open up your engine drastically.

It is also the moment where the dynamics tell you if the inlet and exhaust parts fit to each other as they get more connected by the overflow and gas exchange.

In overlap, when both valves are open, the system must pump the right way.

Beside the fact that the GT 2 evo cam must be adjusted quite asymmetrical to work on a CIS and it is not a bolt on part then, it wants a cr of 8:1 better 8,5:1 to work properly in the low rev range.

As you are going with 3,3 l std pistons you will not generate the right cr.

Today's modern cam layout is using most possible lobe area, proper lift, good acceleration without doing harm to the rockers by a nice ramp design.

On this way you reduce duration and generate the best possible surface under the power and torque curves.

Good low end pick up combined with nice peak power numbers as a result.

Best reg.

Dirk
Old 10-18-2014, 03:33 AM
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Greater cam overlap flows more mass but requires a higher static compression ratio to gain back lost low speed engine performance. The problem is that on a turbocharged engine, there isn't much leeway on increasing static compression ratio without risking detonation.

Some of the loss can be gained back with a lightweight flywheel as the engine can get through the sluggish low speed zone quickly.
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Old 10-18-2014, 04:57 AM
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Low CR it's the bugaboo. Once I went 8.5:1, the world opened up. 993 Super Sport definitely won't clear stock pistons, either, though.
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Old 10-18-2014, 05:15 AM
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Balance

That's the point - more static cr needs more overlap to avoid detonation and vice versa.

If you go with a motivation cam you need some more static cr.

Port / valve seat design helps you to gain flow and velocity - a good header concept too.

Do not forget about squish band design also.

Bring it together and it runs as it should.

Best reg.

Dirk
Old 10-18-2014, 05:15 AM
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Here is my RWHP dyno run with GT2 Evo cams on a 3.4 Jarvis motor to get some break in time @ 11psi. Compression ratio is 8.25 JE pistons. Add 20% for crank rating.
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Old 10-18-2014, 06:57 AM
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I see what you have in mind, about time.
Old 10-18-2014, 09:34 AM
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I see what you have in mind, about time.
400 Ft lbs of torque @ around 2500 RPM even @ 11psi should give EVO GT2 cam users enough low end grunt . At 16-18 psi it should be a real stump puller.
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Last edited by voitureltd; 10-18-2014 at 10:39 AM..
Old 10-18-2014, 10:03 AM
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Quote:


Quote de Tippy



I personally don't think you need big cams to make big power, you need a big turbo with higher than 1-bar of boost until desired hp level.


Wouldn't that be extremely difficult to do with K-Jet/CIS? I guess if you modify the fuel head accordingly you could run big boost, but of course, there is still no knock detection and active timing adjustment with that system.
If you can squeeze 500whp out of CIS, it doesn't matter if its from 0.2 bar or 2.0 bar of boost.

It doesn't care.

Old 10-18-2014, 11:43 AM
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