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91' Turbo Rebuild...Help the Newbie please

Hello everyone, Have been reading many posts and learning, great site
I have a 91' Turbo with 79K miles that frankly runs fine but that's never stopped me before with other cars
Basically, I am very mechanically inclined with my garage/shop fully tooled for this project (lifts, air tools, etc..) and I have rebuilt motors on some of my other cars albeit, old detroit muscle (Mopars)...OK got that out of the way.

After researching, I have come to the conclusion I am going to run EFI, nice header/exhaust combo and an upgraded Turbo and top-notch ARP head studs, etc. I have no intention of racing/tracking this car, basically I want a really fun occasional weekend car built right.

Here is where I really need some direction:
I would ultimately like to do a major top-end overhaul, My first thought was to Bore out the existing cylinders however I am not sure as to How much I can or if it's just a "bad idea" on these motors altogether. In a perfect world, a bore to 3.6 would be great however I do not know if that's realistic. I have looked into the "Nickies" cylinders and while they are nice...very expensive too. I am taking the approach the cylinders are going to need some type of bore so I am obviously trying to get more power at the same time too, don't need to push anything to extremes. As for the bottom-end, I will split the case if advised however i really don't want to change the crank if possible, not sure what the "weak link" in the bottom-end is so any advice would be greatly appreciated.

Heads: OK, I know You can do the twin-plug mod to the heads and honestly I do not know exactly if I would need this or not and that is about all I know Not sure if their is specific porting/polishing that can be done to increase flow, etc...

Cams: Big shocker here...clueless ! Are the stock cam grinds decent? Any alternatives that are possibly a bit more aggressive to match a bore/headwork?

Sorry for the long posts everyone, I LOVE this car and really want to do it right so I am taking time to learn long before I dig in to anything. I can pick out a parts combination for a V-8 engine without hesitation so I am obviously using the knowledge I have with these engines as a starting point....Oh, I also know these motors are much more $$$ to play with and I am not in a rush so that is fine. Hopefully someone that really likes to Typing will read this post LOL
I need some hand holding, Happy Holidays and Thanks in advance for any help.


Last edited by Barracuda; 12-24-2007 at 05:57 AM.. Reason: Forgot something
Old 12-24-2007, 05:52 AM
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Oh, I should add this, I have the Factory Manuals too for reference
Old 12-24-2007, 06:02 AM
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Right on! I was a mopar guy as well. The engineering and design of Porsche engineers is amazing. A top end is a lot of work on a Porsche, and lost of $$. Typically these engines will run 200,000 miles before a rebuild. If I were you I would hold off on the rebuild till it is leaking or consuming lots of oil, or a loss of power. If you take the car to the track it shouldn't take to long to get to that point.

Twin plug is required when running high compression like in my NA 964 motor 11.3:1 CR.

Upgrading the turbo, and everything that you stated above will cost a lot of money. I don't know what type of performance benefits this can have.

I think if you upgrade to a more aggressive cam profile then you might have trouble passing smog, if that is a concern.

I am by no means a Porsche expert. This information is just based on observations I have made on this forum and through my experience rebuilding (currently in process) my 3.6l motor.

Hope this helps,
Emerson
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2003 996TT Basalt black
Old 12-24-2007, 12:24 PM
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One doesn't generally bore Porsche cylinders like in the V-8 world. Most cylinders are aluminum with very hard coatings applied to the bore rather than cast iron or iron sleeved, so if they are bored you must re-plate them. Sometimes the machine work and plating is more expensive than buying a piston and cylinder set once you've factored everything in. Porsche's Nikacyl coating doesn't really wear out, usually the cylinders become out of round with age and heat cycles.
There are almost an infinite number of cam grinds available, the limiting factor is valve/piston interference. You can relieve the piston tops to make room for the additional valve lift, but there are more aggressive than stock cam profiles that will work without any extra machine work. We are lucky that several bona-fide Porsche experts post regularly here and I'm sure that you can call any of them and get lots of info about which cams will work out of the box.
I'm not aware of any legitimate bottom end weak points except for the magnesium cases and several different head stud issues, under about 7200 RPM's, none of which should affect you particular application necessitating splitting the case.
In my limited opinion, you can probably achieve what you desire with a cam change, some better exhaust, and some boost control.
Old 12-24-2007, 01:13 PM
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If the crank is fine, no need to change it, but changing the rod bolts to the ARP 9mm is pretty much mandatory.

If you're going to change pistons/cylinders, your best option is probably 98mm (1mm overbore) replated nikasil (Mahle) cylinders and JE pistons. Boost the compression a little, 7.5:1 on single plug, perhaps 8.0:1 or a tad more if you get twin plugs. =3.4L

For twin plugs, about $300 to machine/drill the heads, and who knows how much more, depending on your setup. If controlled by EFI or Motronic, perhaps less than a full crankfire system...then again you wouldn't need the distributor with crankfire.

Port the heads; usually 36mm works well for mildly modded 930s, using stock (machined larger) injector blocks. If you get custom/billet Al injector blocks, 40mm intake ports may not be uncommon for wild 930s. Perhaps 34-36 or similar on the exhaust ports.

Headers!! GHL or something quality. A stock '91 Turbo (KKK K27) works well for mildly modded cars. A K27S for a bit more, K27-HF (High-Flow) for a wild 930, perhaps even a K29 which is bigger and spools slower. Personally I like the K27S series usually, on 930s, that is, unless you go to twin turbines . Other brands like Garrett work as well, look into some of the compressor maps. Maybe a T-04E 54 trim?

Cams: 911SC cams are good for the street. If you go to the track perhaps even C2/964 cams though I personally find there's not enough bottom end torque with much more than a stock pair of 3.0/3.2 SC/Carrera cams. The stock 930 cams leave a lot of power on the table.

If you are a car nut, you might like a Zork tube by Fabspeed, or buy some flanges from TIAL and make your own. (NO Muffler! )

TiAl 46mm wastegate..

3.2 Carrera intake manifold if you start pushing 400+ rwhp, otherwise 930 manifold works OK

AND, Head studs. Supertec or ARP Head Studs are pretty much mandatory for doing anything like this on a 930.

Here's a 3.4 930 motor I built for a customer (he wanted to finish out the EFI, turbo, etc. himself)

930 Twin Turbo 3.4 Project...commencing...

The specs.
3.4L built on stock '89 930 case
stock crank, balanced and magnafluxed
ARP rod bolts
Supertec Head studs
Balanced and shot-peened rods
JE pistons, 98mm cylinders, ~7.7:1 compression
Twin plug heads, 40/38mm ports (I used the heads from a Carrera 3.2, no porting required...because this car was going to use a 3.2 Carrera intake manifold anyway, w/ custom injector blocks)
The cams are pretty radical, for track, 993-GT2 "Evo" cams
Twin K16 Turbines from a '96 993 Turbo
Monster intercooler

Now pushing over 550hp at the flywheel @ 14psi!

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Last edited by YTNUKLR; 12-24-2007 at 07:27 PM..
Old 12-24-2007, 07:23 PM
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Thanks everyone for the feedback...I willl have to look into the mahle rebored Jugs, where are they purchased from? Mahle direct?

As for the intake, seems the 3.2 is the way to go as I have also read on other posts but I am a bit confused on the heads, Are you saying to scrap the sstock turbo heads and replace w/ 3.2 heads ported/polished and twin-plugged?

Already have the Tial 46mm wastegate so good there...

The rest of the motor You described seems pretty much on target for my goals however...No twin screws for me Just one nice Turbo will do, as for the cam, I will look into the SC cams as I have also heard the stock 964 Turbo cams are a bit docile too. Anymore tips, plz keep them coming.

What year(s) 3.2 intake work on my motor?
Old 12-25-2007, 09:05 AM
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You want to spend a big chunk of money just to rebuild a perfectly working 79k 3.3 engine? OK, it's your call

I'll give you a few hints:

First and foremost, you don't "bore" the cylinders. You replace them alltogether. You cannot bore them as they are thin and plated with exotic stuff.

Second, 3.3 930 heads (which you have) are made of aluminium alloy which is slighly better at withstanding temperature than Carrera heads. They also have more narrow passages and injector notch is different between Carrera and 3.3 heads.

Personally, I believe that propper money-efficient way of chasing big HP numbers is by selling your existing non-fiddled 3.3 motor and buying a N/A 3.6 one and doing turbo-conversion. Amount of job and money you'll spend on tweaking a CIS 3.3 to say 500hp is double it will take 3.6 to get there (especially once you deduct money you get for your 3.3 mill).

If you still want to go with tuning 3.3 engine with EFI and all you can try something like this:

H-beam steel rods (option, if you want to run at higher RPM's)
SC cams for better breathing (or GT2-EVO cams for some more)
Bigger jugs and pistons for more displacement (option, bigger jugs need new pistons as well)
Twin-plugged OEM heads, intake ports enlarged to accept Carrera intake (there will be extra job to mate flange pattern between, as injector notch is dissimilar)
Carrera intake (will make fitting OEM intercooler problematic, so you'll need new intercooler as well)
SS headers of some sort.
Garrett GT35R turbo or bigger/smaller depending on needs (needs Garrett flange, KKK K7200 if you are conservative)
EFI with built in ignition controller (this is not as critical as most of them will do. Even Megasquirt II. Pick one that you or your tuner understands the best)
WBO2 logger (critical)


In the end, you'll be between 10 and 20k poorer (depending on how good you are doing things yourself) and be able to achieve something like 400-500hp.

3.6 path is slightly easier. Swap out the pistons to 993TT ones + some steel rods, slap a turbocharger (or two) No need to twin-plug (it's already twin-plugged), port the heads (it already has big ports), swap the cylinders (it's already 3.6L) etc. You'll need aftermarket intercooler and EFI to go though.

It's possible to get big power from 3.3 but not as cost-efficient compared to 3.6.

Regards,

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Last edited by beepbeep; 12-26-2007 at 04:01 PM..
Old 12-25-2007, 09:30 AM
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