3.2 crank in a 3.0 - good or bad
 

I've collected most of the bits for my next engine. a 3.2 stroker. I like big torque more than high end horsepower so my intention is to use a 3.0 case, a 3.2 crank, and JE 95mm 9.5:1 pistons.

anyone have any thoughts on this? the 3.2SS seems more popular but I like big bottom end grunt. any downside to using my setup? any assembly issues or is it a straightforward assembly.

thanks, Don.

It is a straight forward build but you also need the 3.2 rods to get the full stroke and the rod small ends are a different size than the 3.0 so you effectively have a 3.2.
The late 3.0 were built on the 3.2 cases.
Bruce

There are no real reasons not to, as long as you accomodate the weak points of the 3.2. The biggest issue is the stock rods, which use 9mm bolts, compared to 10mm for the 3.0L. With stock rods, anything more than 6500 RPM is unwise. In this case, your best bet are aftermarket rods.

Most go to 98mm P/Cs in your case with the original 70.4mm crank to get to 3.2SS since it is easier and generally more cost effective since opening the case isn't required, but you're already in there and sounds like you already have the crank.

Not sure that the longer crank will add any more grunt than a displacement bump through piston diameter. I haven't seen any dyno sheets that support this.

One downside is that a longer crank doesn't like to rev like a shorter one, but since you are looking for gruntiness, it doesn't sound like you are planning to spin the motor hard anyway.

The biggest question is what are you doing for P/Cs? Another downside is that SC P/Cs will see a big drop in CR on the longer crank, a poor choice. If you are buying P/Cs to accomodate, why not just get some 98mm units and use the old crank for a 3.2SS or use the 3.2 crank and get 3.4L? THAT'S grunt!

my thinking was that the longer stroke would give better torque down low. I have the 3.2 crank, 3.2 rods, ARP rod bolts, and JE 95mm X 23mm 9.5CR pistons. I could go to a 3.4 but not sure it'e in the card$$$.

regarding the CR, with a 3.2 crank and rods, and 3.2 pistons. shouldn't the CR be approx what the piston spec is? ( allowing for JE's variances in this area).

You'll be just fine with that combination since you're not going to turn the engine very hard.

As long as your JE's were made for the 74.4mm crank and rods (23mm pins), you should be OK, BUT I would strongly recommend measuring the CR to confirm everything. Mistakes have been made in this regard depending on where the piston set came from.

I had a dyslexic moment - the stock SC Mahle pistons would have higher CR on the longer crank. Since you are using JE, you can just spec them for the crank you are using.

yes, I did that with my current engine and JE's, and will do so with this one. if I fall over a good deal on 98 p&c's I'd jump on them, but for now I'll stick with what I have. this engine's going MFI, just to make things more interesting. :rolleyes:

http://forums.pelicanparts.com/uploa...1277312708.jpg

74.4 mm stroke
127mm rod length
95mm diameter
23mm pins

I don't expect a redline over 6500, with the configuration there wouldn't be much point anyway. similar cams to the ones I used here.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/449608-dougherty-racing-cams-my-experience.html

engine results using said cams

http://forums.pelicanparts.com/porsche-911-technical-forum/502996-3-0-dyno-day-pleasant-surprise.html

on this one I'm hoping to hit 300 hp and 275 ft/lbs. I'll be running 36mm intake ports. I could pick up a set of big-port heads but I'm afraid of killing the bottom end and moving the torque curve/hp peak to high up the rev range.

As a data point, we recently did a SS 3.2 for a customer that made 263BHP with single ignition using Mahle MM P/C's, 9.6:1, Mod-S cams, big-port heads, 46mm PMO's, SSI's and a stock, OEM muffler. With a Sport muffler, it made more; a little over 270BHP. :)

It was VERY torquey but still ran to 7K (with the Sport muffler).

Remember, everything must work together: cams, intake system, head flow, and the whole exhaust system. If you want an honest 300BHP from your 3.2, you may need to change your configuration,.... :)

Steve, Would that motor have made more power if it was twin plugged? What if it had headers and the sport muffler? Guestimate?

IMHO, getting to 300HP on a 3.2 w/ a 6500 RPM redline is impossible unless you are running crazy compression and C16 race gas or using nitrous.

well thanks for all the help guys. as far as hp, it is what it is. gonna build it and see what happens. I guess 300 was optimistic but I never expected 250 from my current 3.0 either. 300 is probably too much for a SWB anyway.

all input much appreciated, Don.

MFI motors are just supposed to be spun. :)

At least to the S redline of 7300.

As Mark Donohue said: "I will never have too much horsepower until I can spin the tires down the whole straightaway in every gear."

He came close with the 917.30. :)

Yes, but only with double-relief pistons. :)

The MM wedge-dome pistons were designed and optimized for single-plug operation and there is no real gains with twin-ignition.

Larger headers and a good sport muffler would have made more power, but at the expense of low-end torque and the customer wanted lots of bottom end, without a compromise in up-to-7K capability.

This engine, with the sport muffler, really wanted to sail past 7K on the dyno (we saw 272+), however he wanted quiet so he chose the OEM version. Regardless, it runs VERY good in his 2200 lb car. :) :)

No "guesstimates" from me,............"Just the facts, man". :)

Would using JE Pistons @ 9.5CR necessitate twin plug ignition or would the results be the same?

For what is is worth 300 HP at 6500 RPM = 242 Ft/lbs. Not impossible but not easy. Yes you would need to make everything play very nice to get there. The longer stroke would be your friend for that plan. The low compression may not be your friend.

If you believe dyno sheets I just looked at a 300 HP RSR and PK TQ was 227@ 5200, fell to 200 Ft/lbs at 6500. This from 10.5 compression and RSR cams.

Drop the overlap on the cam a bunch still not sure but I do believe it is possible with all the right parts. a blower would get you there.

PFM