Off-Boost Torque & Big Cams Big Heads

[RarlyL8]

For you CIS guys with big cams and ported heads, how has this affected off boost performance?
The formula we use for our 400WHP builds is to go conservative with the cams and middle of the road with head porting. Result is excellent off boost performance and quick spool. The build I am looking at now is beyond all that, with big ports and big cams. I know there will be a performance loss down low but how much will it actually be noticed?
Any insight into real-world experience is appreciated.

[Black_Hat]

Mine is better than stock ...actually nice to drive off boost

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/767012-forced-deal.html

[RarlyL8]

Wow nice!
How do the cams you have compare to the 993SS grind?

[TurboKraft]

Those are cams provided by TurboKraft. They are very nice with stock 7.0:1 compression pistons and large ported heads, but the lift and timing of the camshafts requires small valve pockets be milled into the pistons for sufficient clearance.

We have a set of Edelweiss camshafts in stock as well, the most aggressive one can run with original 930 97mm pistons.

[911nut]

Interesting info.
So the anecdotal info that aggressive cams with CIS causes unstable idle isn't necessarily true or are 993 SS or Turbokraft cams not as aggressive as, say, an old "S"cam (the most aggressive cam I know of).

[TurboKraft]

IIRC 906 cams are about the most aggressive in regards to timing and overlap.

Those TK cams in Black_Hat's C2T have more aggressive timing than a GT2 Evo cam and emphasize midrange torque. We've used them in engines ranging from 3.2L to 3.8L and done as much as 420whp @ 0.9bar on a 3.3L CIS 930 and 600rwhp on a 3.5L EFI 930 with a flat manifold.

[kenikh]

I can tell you that using CIS and 8.3:1 compression, off boost response kicks my wife's SC's butt and gets better as revs climb (obviously). Really can't wait to get the EFI going...but that is going to be a while.

[RarlyL8]

I'll be using the 993SS cams and stock 7.0:1 C/R.
Just looking for real world info on what to expect off-boost. I know what they will do on-boost. How much will we be giving up compared to SC cams?

[Mr9146]

With a lightweight flywheel (and clutch if you want) you mitigate the slugishness of the low-compression/off boost performance of big cams and big ports.

It won't be N/A responsive but it won't be a complete dog, either. It'll be a nice, easy cruiser until you whack the throttle open.

[RarlyL8]

Didn't give the clutch and flywheel much thought, good idea. The clutch will be a KEP Stage II so don't know if that will help. I'll have to think about the flywheel, don't want the idle to stumble.

[jpnovak]

What do you consider big ports? How are they going to be shaped internally? If you are careful on the short side radius you can get excellent port velocity even with larger ports. the trick is getting airflow to adhere to the short side radius so that you get cylinder filling on that side of the valve. Get it wrong and the cylinder filling at low rpm, low lift really suffers. This is what gives you crappy off-boost response and overall driveability.

[kenikh]

Originally Posted by RarlyL8

I'll be using the 993SS cams and stock 7.0:1 C/R.
Just looking for real world info on what to expect off-boost. I know what they will do on-boost. How much will we be giving up compared to SC cams?

Dougherty explicitly told me not to use these cams with that compression. Which is why I bought pistons. Off boost dynamic compression of these cams is not conducive to good response.

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[Mr9146]

Originally Posted by RarlyL8

Didn't give the clutch and flywheel much thought, good idea. The clutch will be a KEP Stage II so don't know if that will help. I'll have to think about the flywheel, don't want the idle to stumble.

If you're running a turbo trans there's a kit to convert the clutch assembly to the 76/77 short bell housing setup. It's obviously "turbo approved", but it removes a ton of rotating mass and wakes up even a stock 3.3 car. Doesn't bug the idle one bit.

[RarlyL8]

there's a kit to convert the clutch assembly to the 76/77 short bell housing setup

This is intriguing, where do I find this kit?

Dougherty explicitly told me not to use these cams with that compression

Assuming that is true, and he didn't tell me the same thing, we have a problem.

[GJF]

I can't stress it enough. If you can, please upgrade the Pistons to higher compression. I know it is an extra expense, you will instantly think why it wasn't done long time ago. 7:1 was an old school bandaid when turbocharging was not really understood. It causes no low speed response due to non existing low speed port velocity. Excessive fuel consumption during low speeds. And it promotes lag. There is no win with 7:1.

[911nut]

Originally Posted by Mr9146

With a lightweight flywheel (and clutch if you want) you mitigate the slugishness of the low-compression/off boost performance of big cams and big ports.

It won't be N/A responsive but it won't be a complete dog, either. It'll be a nice, easy cruiser until you whack the throttle open.

+1
The LWFW transformed my car (My first iteration with SC cams and K27/K29 turbo had the stock DMFW installed, so that would be my A-B comparison). I get through 1st so quick that I hardly get into the boost. Second gear is outstanding. Third's nice too.
The LWFW cuts reduces inertial parasitic losses but the effect is less and less in the higher gears.

For you guys running aggressive cams: do you get any fuel smell from reversion on the cabin?

My other question is to kenikh: what boost are running with the 8.3/1 cr? Do you have any knock protection?

[Mr9146]

Originally Posted by RarlyL8

This is intriguing, where do I find this kit?

Nobody makes it in kit form, but you can build it yourself with these 5 pieces (available through the host):

930.116.081.11 T/O bearing
99.15.15.081 T/O extension sleeve
99.01.68.230 Ring gear spacer
930.116.014.02 Clutch disc
88.3082.999.594 Pressure plate (RUF BTR and Sachs Racing department)

I don't use KEP if I can avoid it ... factory parts whenever possible.

[smurfbus]

IIRC Patric motorsports have a kit too. I have this style setup with custom steel lwfw.

[kenikh]

Originally Posted by RarlyL8

This is intriguing, where do I find this kit?



Assuming that is true, and he didn't tell me the same thing, we have a problem.

You don't have to assume. We talked for an hour on the topic, as well as my calculations on dynamic compression for 5 different cams.

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[kenikh]

Originally Posted by 911nut

+1
The LWFW transformed my car (My first iteration with SC cams and K27/K29 turbo had the stock DMFW installed, so that would be my A-B comparison). I get through 1st so quick that I hardly get into the boost. Second gear is outstanding. Third's nice too.
The LWFW cuts reduces inertial parasitic losses but the effect is less and less in the higher gears.

For you guys running aggressive cams: do you get any fuel smell from reversion on the cabin?

My other question is to kenikh: what boost are running with the 8.3/1 cr? Do you have any knock protection?

My motor is set up for knock control, but isn't being used. Currently running low boost at .5 BAR with conservative timing until I can upgrade to AEM Infinity, which has 2 channel knock control.

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