3.2 to a 3.4?

[rdane]

I'm thinking about adding 98mm P&Cs to a 3.0 case with a 3.2 crank to end up with a 3.4. Since the original 98mm conversion doesn't need twin plug why would the 3.4 in this case? 9.5 or 9.8 :1 compresion is what I am looking at.

I am thinking the combustion chamber on this would be the same @ 3.2 or 3.4 and leaving off twin plugs would be more than safe enough running 92 octane with a reasonable compression ratio in the mid 9s.

Did I miss something?

[dd74]

I thought you were selling your 3.0, you capricious devil you?

I've wondered this too, not that I've asked this same question directly to anyone.

But often, when I have spoken to various wrenches about a 3.4 conversion on a 3.0, twin-plugging was not mentioned.

Do you think the bang is worth the buck?

[rdane]

Do you think the bang is worth the buck? [/B]

Depends I quess. I am adding Ti valve spring keepers and some head work while it is apart. Including the mill work for twin plugs in case I decide to throw in another $2000 down the road If it comes in under $15000, which it looks like it will, then yes. I think it is a better value than the 3.6 conversions people are quoting at 20K+ for an unknown engine.

It isn't a race engine but it should be a good street engine with lots of toque and a good bit more than a Carrera 3.2 and pushing a C2 with the difference between power to weight ratios.

I'll let you know. Dropping the engine next week to get started.

[ChrisBennet]

There is no denying that making something yourself is more fun but I think you are mistaken if you think it will be more cost effective than a 3.6 conversion. A 3.2 crank if you can find one is going to be over $1000. I bought one a few years ago and it was $1100 then.
Unless you bump the compression to 10.3-10.5:1, I think the twin plug option is a waste of money. To put it another way, if you decide to do the twin plugs you would need to change your pistons at the same time to get any real benefit. I don't want to talk you out of what sounds like a fun project, just look at the costs first.
I did a 3.4 from a 3.2 and it was fun and much cheaper than your project proposal but I wouldn't say it was as big a bang for the buck as a 3.6.
-Chris

[Bill Verburg]

Don't forget that w/ the 964 3.6 you also get a sophisticated twin plug setup and knock sensor package. The improvements get even better w/ the 993 3.6. If you don't trust the motor (yes, they are alll getteing a bit old now) then just rebuild the 3.6. Most of us have belly button cars(everyone has one) and swapping in a different engine isn't going to hurt its value appreciably. I would always want to start from the most advantageous point.

[rdane]

If I were doing all this myself the number would be under $10K....
I already have the crank so that is no big deal.

Lots of opinions on compression, 3.4 and bigger displacement when twin plugs enter the picture.

I am going to stay under 10.0:1. Thanks for the comments. No question a late 993 is the engine to get but I am not willing to get in that deep.

[ChrisBennet]

True/measured 9.8:1 is generally the limit on high octane pump gas. The factory compression numbers actually measure out to less so don't use them as a basis for comparison. I.e. 3.6 compression is 11.3:1 but if you actually measure it you get 10.4:1.
-Chris

[rdane]

I'm going to a measured 9.5 Chris so I should be OK. But thanks! Not everyone's choice in an engine....but it will be my engine

[Superman]

Not a bad choice at all. In fact, that little thing on your "airport gear" transmission is going to feel like a cannonball. It should be very delightful. Very spirited. And no, if your compression ratio is reasonable, you don't need two plugs. You'd only need two plugs if you went in there and replaced pistons.

[Craig 930 RS]

A few observations/my philosophy behind my 3.2 to 3.4 conversion within the next month:

My engine:
3.4 P&Cs @ 10.3:1
964+ cams
Twin plug$
Extrude hone manifolds
Ti retainers
Aase valve springs
Cross drilled and edged crank
RSR pressure plate/flywheel/clutch package
Ye Olde port & polish

A 3.6 is approx 11-12k --- and you have an engine with unknown history; ie what were its last moments in life like before it was removed?

A USED engine to boot. Perhaps 1/3 to 1/2 of it useful life already have passed. A 3.4 is essentially NEW - with 100% known running life span.

A 3.4 engine is just plain fun to watch the build process. One has a 'hand' in creating it.

My builder will be close by so I can stop by and check on the process.

Above all -- this stuff is about passion -- otherwise we would drive Geo Metros and have zero fun. For me a well-built 3.4 is about as custom as you can get. I expect close to 290hp - for me this is pretty heady stuff for a 2600 lb car.

Pwer to weight ratio? The SAME as an M3. Objective numbers for fun?
Not a straight line racer by any means but.....0-60 in 5.0, 1/4 in 13.5.

I'll be spending a bit less (approx 2k) than a late 964 or 993 3.6 conversion.

We go 'round once in life. Have fun the first time!

[ChrisBennet]

I would be really surprised if you got a true 290hp out of a 10.3:1 3.4 without going to aftermarket EFI.
-Chris

[rdane]

My engine:
CIS 3.0 case
98 Mahle, Max Moritz CIS P&Cs @ 9.8:1
Pauter rods
APR studs
3.2 Carrera crank
20/21 cams
Magnecor wires
powder coat valve covers and sheet metal bright yellow
polish the heads
Ti retainers
Aase valve springs
Sachs power clutch and a light fly wheel
SSIs and 2in/2out
Should be around 250/60hp @ crank and 200/210 on torque

I am 215 @ the crank now and 170 on torque

Ya never know till you run it on a dyno though

[emcon5]

Originally posted by RennStore
3.4 P&Cs @ 10.3:1
964+ cams
Twin plug$
Extrude hone manifolds
Ti retainers
Aase valve springs
Cross drilled and edged crank
RSR pressure plate/flywheel/clutch package
Ye Olde port & polish

Just a few observations:

It looks like you are doing all the hardcore spin-it-real-fast bottom end and valvetrain stuff, but I question if your cams will breath well enough for the engine to benefit from it. Spinning the engine to 9K RPM really doesn't help if the engine stops making power @ 7K. There is some discussion of this here:
Can a 3.0 safely rev to 7,000 RPM on a consistent basis?

Does Motronic have the same limitations for cams as CIS? If so, is there is anything you can do about it? That engine would be awesome with early S cams, if the pistons you are planning on using have enough clearance (and if the induction system can handle it).

Some of the Mahle 98mm 10.3:1 RSR pistons are only 10.3:1 with smaller volume RSR heads. On my 90cc 911SC heads they measure to right at 9.8:1. You may want to ask about this.

My engine has these pistons, with 964 cams, twin plug and SSIs. I used ARP rod bolts, and new stock springs. I haven't been to a dyno yet, only 400 miles on the engine. I am thinking it should be in the 215-220HP ballpark.

We'll see.

Tom

[rdane]

My engine has Mahle 98mm 10.3:1 RSR pistons, (actual compression of 9.8:1) with 964 cams, twin plug and SSIs. I used ARP rod bolts, and new stock springs. I am thinking it should be in the 215-220HP ballpark.

Did you use the original Motronic?

As a reference Noah's 3.0 Carrera engine has, "CIS, SSI's, 9.5:1 compression (no idea what the compression actually is) , and 964 cams. His dyno showed 203 at the wheels and 175.4 in Torque. That makes it 240 crank if the numbers are correct.

A 3.4 with 9.8:1 and dual plug should push you very close to 220 @ the wheel, 260 crank, I would think and a bit more. I am very interested in seeing your dyno numbers.

[emcon5]

Originally posted by rdane
Did you use the original Motronic?

Nope. (muhahahaha)

As a reference Noah's 3.0 Carrera engine has, "CIS, SSI's, 9.5:1 compression (no idea what the compression actually is) , and 964 cams. His dyno showed 203 at the wheels and 175.4 in Torque. That makes it 240 crank if the numbers are add up.

A 3.4 with 9.8:1 and dual plug should push you very close to 220 @ the wheel, 260 crank, I would think and a bit more.

Mine is now 3.2, with slightly higher compression than Noah, but the same cams. He has larger ports, but a lighter crank. My gut feeling is that Noah's dyno was a little optomistic, mainly because historicly Porsche never left that much power on the table. However Noah had a 200HP engine to start with, so adding a full compression point (8.5 - 9.5:1), better exhaust and getting a fattter torque curve from the cam may make his numbers add up. If his engine is honestly putting out 240 at the crank, that is a 20% improvement over stock. That is huge for the relatively small changes he made, especially when you consider that a 964 is only 10HP more with much larger displacement and much higher compression.

The one unknown here is where Noah timed his cams. If he retarded them slightly, it could explain the more power he has on top, but that is usually at the expense of torque. Looking at his dyno sheet, that probably isn't it. His torque curve is remarkably flat, and and ~10 ft-lbs more than any other CIS 3.0 chart I have seen.

There is a dyno chart in Bruce Anderson's book of a SC engine with a "bolt-on 3.2 liter conversion" with and without SSIs. Looks like peak power is in the 185-190 range. It isn't noted, but I assume this is at the wheels.

I am very interested in seeing your dyno numbers.

Me too

Tom

[rdane]

OK, my confusion, I thought you had built a 3.4L. You have a 3.2 short stroke based on a 3.0 SC case correct? Add a simple 7% for displacement on Noah's engine and you should be 220 at the wheels.

I do know of a 3.2 Carerra with Varioram induction that was dyno'ed at 220RWHP.

I agree Noah's numbers are unique. But I don't understand the comments on a 964 cam's "flat" torque curve. In this case it isn't.

Noah's dyno


This is the normal 20/21 cam "V8" torque profile from my experience.



"There is a dyno chart in Bruce Anderson's book of a SC engine with a "bolt-on 3.2 liter conversion" with and without SSIs. Looks like peak power is in the 185-190 range. It isn't noted, but I assume this is at the wheels."

I am running a 3.0 with 180 rwhp, 215 crank on SSIs. Add 7% for a 3.2 and you'd have 192rw or 225 crank. Plug 10hp on for compression increase and another 10rwhp from the better combustion of twin plug and and you should clear 215rwhp is my guess. Just as you said

[emcon5]

The scale for torque is different on Noah's, and is shown on the right. Because the scale is expanded, the small variations are exagerated on the graph. If you compare the numbers, the shape is not that far off of yours, with 2 peaks @ ~4200 and ~5200, and a loss of ~15-18 ft-lbs between ~5200 and redline.

Not quite as flat as 20/21, but much more so than a stock 3.0, which only has one torque peak at ~4200, and loses ~30 ft-lbs between it's much earlier peak and redline. Here is DD74's run from the Reseda dyno day (stock SC w/ early exhaust):



Tom Tweed's chart which you posted in the other thread, the torque dropoff after peak is even more pronounced, losing ~50 ft-lbs.

Noah really needs to come up with a better scan of that chart.

Tom

[rdane]

These are a better perspective on several different stock 3.0 engines.





SUPERMAN's is another with 20/21s, 'pre '74 exhaust, triad muffler and torque equal to Noah's

[dd74]

BTW: since the Reseda dyno run, Tyson's done some tweeks to my engine (retarded it back to factory spec), so I suspect my hp should be a little higher - maybe 195 at the crank.

What's appealing about the 20/21 cams to me shows up in Dane's torque curve. Because I have a 7.31 r/p and 50-series tires, everything is already very responsive from about 4,000 to 6,000+. Plus, I'm verging on being about 200 lbs lighter than most SCs out there.

Nonetheless, I'd love to see the same cam mods reflected on a dyno as what Dane has, but on a small port 3.0 ('80-'83), before I start boring my heads and fitting on early CIS injection.

Superman has these mods on his '83. I don't remember seeing his dyno sheet, though. Jim, if you're out there, can you scan and load it up?

Again, Noah's engine has differences, albeit small, compared to standard SC engines. I don't think comparing his to ours is entirely accurate.

RPiper's SC engine is a better comparison IMO.

[dd74]

More insight: on the thread I started asking if a 3.0 can safely rev to 7,000 RPM, Superman stated that there is not much difference between a small port 3.0 and the earlier large port 3.0, which gives me hope to save about $2.5K in modification costs.