plastic manifold on a SC

[trond]

Hello forum

Considering my next move with my SC I took out the engine last week to re-install the 98 mm cylinders, that came back from re-plating. They are 10.5 CR but I measured 10.2 or so when cc ing which is better considering fuel availability. I have dual spark CDI, and for now SSIs,. And I have some nice cams also on the shelf. GT2-108s and also a set of new webcams 464/465. I have not decided which way to go...

I am thinking about moving away from my 42 mm Triumph ITBs I ran previous season because of noise and hassle with synchroniation. They work well apart from those issues but I really don’t enjoy the suction noise they make

Now a 993 plastic inlet manifold may be available locally. But how to install on my small port 3.0 heads ? I found some fairly expensive adapters in Australia. Beautiful but so expensive I am hesitating… They have 2 bolt adapaters for both 34 mm and 39 mm ports and I think maybe the 39 mms would be good, and enlarge/port heads accordingly

Is there are better way ? A 3.2 manifold would be easier certainly…

[winders]

Rothsport has built a bunch of 3.0L engines for racing using a 3.0L engine and the 993 plastic intake. They use their own ITBs for this I believe.

A similar build here:

Rothsport ITB 3.2 new build

[Peter M]

trond,
I go through similar thoughts every twelve months or so and last time I investigated the Adapt Motorsports intake adaptors were the only ones I could find that are currently readily available. Seems like a number of people have supplied them in the past like Turbokraft, Rothsports and the odd eBay vendor but there was no evidence on their current websites that I could see.

I also noticed that others have used an aluminum adaptor plate to convert our 2 bolt mounts to the standard 3 bolt 964/993 manifold adaptors. These look reasonably easy to make out of plate around 10 to 15mm thick with the plate held to the heads using countersunk set screws and the holes for the adaptors drilled and tapped into the plate.

Would you use your ecm to drive a single electronic throttle body and a resonance butterfly?

If you find a cheaper alternative I'm all ears!

[mikedsilva]

I'm no expert...

But I think moving away from ITB and to a single throttle/plenum, may restrict what camshafts you run.

[Peter M]

Mike,
I'm no expert too but I think EFI opens up a whole lot more possibilities that we never had with the standard SC CIS or the C3.2 air flow meter.

John Dougherty recommended his 993SS cams (242/228 duration @50thou and .490"/.455" lift with 114 lope centres) as the practical maximum for an air flow meter equipped 3.2. I see the Webcam's 464/465 is not a huge step further on. (Web Cam Inc. - Performance and Racing Camshafts / Porsche 911 SOHC 12v Timing Card )

However possibly more importantly, I recall Steve Weiner cautioning the use of cams hotter than 993SS cams in street 3.2's with standard gearing due to the loss of bottom end torque that he has found to come with these cams. I'll try and find the reference but it certainly helped make my mind up with the cam going into my EFI single throttle body 3.4 build. I can certainly confirm that mine is pretty underwhelming under 3,500rpm!

Unfortunately I haven't seen any posts previously describing the build trond is proposing (and I've been looking for years!) so am keen to see how it works out and learn a few things!

[Peter M]

Rothsport ITB 3.2 new build

Link to Steve Weiner's comment on 993SS cams and possibility of too big for street 3.2's.

[Jeff Alton]

Rothsport uses Jenvey throttles on these applications. With some other proprietary bits....

[stownsen914]

Another option - put a plenum on top of your ITBs. It would quiet them and if done right give you a boost in midrange.

If you switch to a single throttle body, you'll want cams with less overlap. Your GT2-108s may be good, the other ones if on narrow lobe centers possibly not so much.

[trond]

I would not be using air flow meter, but MAP or TPS as with ITBs. Is the geometry of a 3.2/964/993 manifold an issue with say the 464/465 cam ? Without the airflow plate entirely... Or do they require ITBs ? Just want a break from the ricer noise for a while. Driveability with the ITBs is excellent but I could see from color in exhaust ports I had not managed to get them perfectly synchronized.

[trond]

I expect some loss of torque with the hotter of these cams but issue is cylinder pressures are too high already with 98 mm & 10.5CR and engine tended to overheat with stock cams. I got the 464/465 cams on advice from William Knight as they should reduce heat issues. For my use of the car I really should go with less compression. But I enjoy what I am doing and will make one or two more attempts with cams and these p&cs. If the GT2-108 still have heat issues and/or don't work with single throttle body I will try with ITBs. Driving style has mellowed over the time I had the car too and I seem to enjoy purring as much as screaming these days. Maybe go for the 464 cams and ITBs before I am too old, then stepping down can be my next step. Will toss a coin. Meanwhile there are enough parts in my basement to keep me busy the next 10 years...

[Peter M]

By saying overheating did you actually mean detonation?

[stownsen914]

Also curious what overheating you would like to fix with cam choice.

Interesting about using TPS or MAP with the single throttle. I’m sure someone here has experience with that and may be able to comment.

[rdimarco]

I run 464/465 Cams on a 3.2 manifold/single throttle body. EFI needs to tune with TPS (poor MAP signal at lower rpm). Very happy with this setup. Torque curve is reasonably level from 4000-6200 rpm. Peak HP @ 6500.
I believe the overlap/longer duration is less prone to detonation.

[trond]

are you on 3.0 or 3.2 capacity ? What CR ?

I have been running with MAP based tune since 13 years, even with ITBs but not with hotter cams.

Originally Posted by rdimarco

I run 464/465 Cams on a 3.2 manifold/single throttle body. EFI needs to tune with TPS (poor MAP signal at lower rpm). Very happy with this setup. Torque curve is reasonably level from 4000-6200 rpm. Peak HP @ 6500.
I believe the overlap/longer duration is less prone to detonation.

[trond]

by overheating I mean engine getting hot, as indicated on oil temperature. Running 10.5CR 98 mm p&c on stock cams I had issues with high engine temperatures summertime. Hotter cams with more overlap give lower cylinder pressures (except at torque peak)

Originally Posted by stownsen914

Also curious what overheating you would like to fix with cam choice.

Interesting about using TPS or MAP with the single throttle. I’m sure someone here has experience with that and may be able to comment.

[Peter M]

Originally Posted by trond

by overheating I mean engine getting hot, as indicated on oil temperature. Running 10.5CR 98 mm p&c on stock cams I had issues with high engine temperatures summertime. Hotter cams with more overlap give lower cylinder pressures (except at torque peak)

During normal street driving in? Was that assessment based on the dash gauge or your ecu datalogging?

Do you have a trombone or a C3.2 style fender oil cooler?

No issue with detonation experienced once you sorted out the tune? (BTW What RON fuel are you using?)

[trond]

assessment made based on dash gauge going to and into the red, reinforced by dropping oil pressure and also checked on TunerStudio CLT sensor. On sustained 80 mph+ driving on autobahn. Have only trombone cooler. No issues with detonation. 95 octane RON

Originally Posted by Peter M

During normal street driving in? Was that assessment based on the dash gauge or your ecu datalogging?

Do you have a trombone or a C3.2 style fender oil cooler?

No issue with detonation experienced once you sorted out the tune? (BTW What RON fuel are you using?)

[Peter M]

Originally Posted by trond

assessment made based on dash gauge going to and into the red, reinforced by dropping oil pressure and also checked on TunerStudio CLT sensor. On sustained 80 mph+ driving on autobahn. Have only trombone cooler. No issues with detonation. 95 octane RON

trond,
I think there is some other reason for your high engine temperatures unrelated to your current cam and compression ratio choice.

Sorry, I don't know what that is but I assume you have checked all the obvious stuff!

[stownsen914]

If you're not seeing detonation, it could just be the trombone cooler isn't sufficient for your engine. I don't see where you mention what temps you're seeing. Some say that 250+ degrees F is acceptable, but I'd prefer lower personally. You might just need more cooler capacity. The trombone has low heat shedding capability.

[rdimarco]

Originally Posted by trond

are you on 3.0 or 3.2 capacity ? What cr ?

3.5L 10.5cr