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Join Date: Mar 2000
Location: St Charles Il
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head for a turbo

Mine is coming apart this winter/ spring What should I do (while I am there $$ ) to the heads.

I figure to face off 1mm per BA and then?
I looked over the port numbers from BA

carrera I 40 E 38

3.0 turbo I 32 E 36

3.3 turbo I 32 E 34

3.0 934 w CIS I 41 E 41

935's I 41 E 41

81 935 I 43 E41


With the success of the 3.2 conversions I am thinking maybe 40/40 or 39/39. At this time I am sticking with CIS (thinking of Imagine Auto CIS mod).

I like the 934 CIS but think I should go a little smaller so my power band is not all the way at the top, 4-6K full tilt would be fine with me.
I am already running SC 330 cams.


Any experiences or input would be helpful. And how much is it going to hurt $$$$
Old 11-27-2004, 12:35 PM
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how does inlet/exhaust dimentions affect power? im in a bit of a corner over buying some modded 3.3 turbo heads (36 inlet 32 ex, new valves and guides, twin plug, ) I want to get to at least 400 horses with efi, twin plug, sc cams, 7.5 (maybe 8) to 1 comp, .9 bar, posh head studs, arp bolts. how will these heads affect any future plans to increase hp?

Andy
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1980 SC soon to be big hp 3.3t powered 73RSR Replica (well, I'm keeping the engine but everything else is going )

Last edited by adomakin; 11-30-2004 at 01:15 PM..
Old 11-30-2004, 01:10 PM
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As far as I remember, 934 had twin CIS just to keep it breathing.
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Old 11-30-2004, 02:04 PM
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The bigger the exhaust port the more turbo lag you will have. High velocity small ports spool the turbo faster. The downside to the small port is at a certain RPM it can stop flowing or it can overspeed the turbo(causing the turbo to stop flowing).
Increasing the intake port volume should push up the powerband. It can also reduce the amount of boost the engine sees.
(Less restriction for the turbo to work against) You will also lose "off boost" driveablity with bigger ports.
It really depends on the entire combination, compression ratio, displacement, Cam selecton, style of turbo etc.

How about a 3.2 with 40/38 ports, 8-1 c/r , k27-7200 and 964 cams?
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Old 11-30-2004, 02:33 PM
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If you are going to stay with CIS, you should stay with the stock heads. The CIS system restricts the cams and defeats the need for bigger ports. As stated above, smaller exhaust ports speed velocity which helps the turbo spool quicker. Larger intake ports kills these motors on low-end power. If you look at some of the other turbo sites, you will find a couple of well built CIS cars putting out over 400 rwhp with stock heads and SC cams.

If anything, bump the compression to 8:1 and buy a good turbo - K27 high flow. This will give you good low end and big power on top. This is also the cheapest way to go with CIS if you are going to pull the heads.
Old 11-30-2004, 03:13 PM
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Small intake ports do not help turbo spool quicker in any direct way.

Strangled intake ports merely raise gas velocity trough the ports which helps cylinder filling at low revs, which in turn raises low-end off-boost torque somewhat. That lower end torque might and might not help spin the turbo sooner...I believe difference is diminutive. It also chokes the engine at high end.

So it's not the turbo lag you'll be feeling if using bigger ports but less torque while off-boost. Turbo itself will probably spin up just where it used to.

If you plan using CIS then it's too much job to open them up, as they won't match with intake runners and phenolic injector blocks so you won't win anything in the end.

If you plan to fit Carrera plenum and EFI then it's perfect time to sell whole enchilada to somebody who believes that everything that says 930 is good

Carrera plenum will fit perfectly in Carrera heads (of course) and provide really good base for hi-power motor.
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Old 12-01-2004, 02:06 AM
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goran, what do you think of these set of heads that im looking at. they are 930 heads with 36 inlet and standard exhaust, twin plugged, new aase srpings, titanium retainers, new guides. my engine bits list is 7.5 (maybe 8) to 1 comp, je ceramic/dry filmed pistons, shot peened 930 rods, arp bolts, supertec head studs,.9 bar, sc cams, sds efi,carrera inlet, k27 high flow and some headers. im looking for a good 400 hp and the car is going to be a street missile with some (but not much) track time. are these heads a suitable combination or would i just be better off with standard twin plugged carrera heads?

Andy.

P.S. sorry to hijack the thread!
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1980 SC soon to be big hp 3.3t powered 73RSR Replica (well, I'm keeping the engine but everything else is going )
Old 12-01-2004, 02:34 AM
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Adomakin:

Only thing to worry about with those heads is match-porting to accept Carrera 40mm intake flange.

I've already posted pics of what kind of job is waiting for you in case you go with 930 heads.

#1 has to be enlarged to look like green gasket in #4. As 930 head has little less material than Carrera head over right stud it can be solved by filling it with Epoxy or by welding extra material on it.

It's all matter of what's easiest/cheapest for you. If it's cheaper to keep your 930 twin-plugged heads, port them to 40mm, put some epoxy filler and mate them with Carrera-intake than go for it. If not, you can sell them to somebody who want's to build twin-plugged CIS 930 engine, buy Carrera heads and machine them to accept second row of spark-plugs. It's your call.



(Remember, 930 exhaust ports are 34mm and Carrera are 38mm...so 930 headers might not fit Carrera heads perfectly in case you want to use 930 heat-exchangers).

Hope it helps.
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Old 12-01-2004, 07:11 AM
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I think you're going in the wrong direction here. It is important to remember that the 934 only had CIS on it to comply with racing restrictions that the car resemble the production model. CIS is not a performance injection system, and cannot be used with aggressive cams. The CIS system on the 930s should have been scrapped (in my opinion) in 1984 when Porsche introduced Motronic. However, I doubt they sold enough Turbos to justify the costs of redeveloping that engine's injection system.

-Wayne
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Old 12-01-2004, 09:42 PM
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Thanks Guys. I reread through BA's bible and he suggests opening the intake side to 36mm. I also found this thread
best way to 400 (reliable) hp

Dave from TRE mentions going up to 36. There are two stage 3 imagine CIS cars too. In one build sheet/ parts list porting and polishing is mentioned but no details are given.

Any more ideas? Any one with some first hand experiences?

david 89 turbo cab
Old 12-02-2004, 01:47 PM
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Hi Dave, have you made any more decisions?

Andy
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1980 SC soon to be big hp 3.3t powered 73RSR Replica (well, I'm keeping the engine but everything else is going )
Old 12-07-2004, 11:39 AM
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