Lets Talk HP numbers / Engines
 

Ok... So, Ive got a very nice 71 targa w/ recent rebuilt 2.4 and a little hotter cams.. the car is a Blast to drive! but... as always.. Everyone wants MORE HP.. OH, Its mated to a 915 box.. which is also breaking in Nicely!

So Ive decided that If I were to rebuild another engine I would like to have in the upper 200 HP area... I figure that would be "Enough"

So, What are Good possibilites to start w/ and type of engine work needed to get this as a Daily driver?

Whats your budget?

Depends what you want from the car are you happy to have a modern looking engine in the back if so I would agree with noah 3.6 conversion would be easiest route into upper 200hp numbers. If money is not an issue and you want a somewhat stock ish looking motor then I would go with a 3.2SS. This engine is based on a 3.0 case and crank but using 98mm P&C's with some hot cams high CR twin plug and 46mm PMO's you would be seeing the high 200hp numbers. Cost wise ???? not cheap

Steve

Ok.. Lets talk about the 3.6 for a minute.. doesnt this swap require Lots of mods compared to the 3.2 ? Whats the stock 3.6 produce?

A 964 produces around 250ish? while a 993 I belive has 265 I think alot of the differance came from the exhust so by running the 993 he's on a 964 you would get similar numbers. As for the conversion theres not alot of differance between the two as far as wiring goes the extra work is in the flywheel and clutch to get it to work with a 915. Patrick motorsport sell most of the conversion stuff I belive. Then theres a few other bits on the 3.6 to mod such as blanking off the powered steering pump. Do a search theres many threads on this. A 3.2 swap is simpler but it isnt going to get you the higher 200 numbers without extra work a stk ROW 3.2 was only 235?? Also you mag 915 wont stand up well to these sort of hp numbers with its 7:31 ring and pinion.

Steve

Stock SC motor with carbs and exhaust will yield 220-240 and bolt right into your car. Minor changes for carbs and ignition are all you would need. A 3.0 with euro pistons and 39mm ports can put out 245 with 46mm carbs and good exhaust.

-Andy

What Andy suggests above has the obvious advantage of being far simpler to fit to an early car than the later 3.6 engines and wouldnt be too far from your goal HP in your early car this would still be lots of fun. This is prettmuch the route im going for my 72, 3.0 with 9.8:1 cr pistons, dc 20 cams mine will be twin plugged however and run on MS EFI.

Steve

B/n the 3.2 and 3.6 which one is more Cost effective? I've looked into a 3.2 before and found one for 5500 w/ the DME and complete Engine. I found that to be very affordable .. now keep in mind it is Fuel injected... so W/ this type of setup what kind of HP ?

Here a chassis dyno run of my car. HP at the rear wheel. It's an 88 3.2 with DME, still the STOCK chip in it. The only mod done to it are a set of Bursch headers with a custom muffler with dual outlet. On the intake side there is a K&N cone filter mounted directly to to the air flow meter. Everything else so far I know is stock. A custom chip can probably bring the HP up as it is running fairly rich at higher RPM.
If a chip can bring about 10hp that will put it close to 240hp at the crank.

http://forums.pelicanparts.com/uploa...1198776031.jpg

Pat, I bet your car pulls pretty strong , ehh?

Lets turn the page a bit... What can be done to a 76 2.7 carrera engine? I belive this engine is stock w/ 180HP .....

Or take a 3.2 core and enlarge to 3.4 with 993 ss cams - still motronic (so keeps it driveability) the 993ss cams act like an early s car (power at the top end - comes on in a rush) flat torque curve - You don't have quite as much low end torque of the 3.6 (which should put less strain on your 915)

It's often cheaper to drop in a stock 930 motor than lots of custom motor work.

They're fairly simple to wire in, and the 930 mates straight up to a 915. There's a Sachs competition pressure plate rated @ 350 ft/lbs which will deal with it just fine. (The Power Clutch is borderline, at best).

A stock US 3.3 930 (265 HP) or a RoW one (300 HP) both make enough torque to turn a mag-case 915 into soap. But a later 915 will live if you beef it intelligently and don't just mash the loud pedal at really low RPMs...

The big advantage of the 930 approach is when you dial in the suspension, brakes, tranny etc. get bored with 300HP and decide you want to add another 50, 100, 150HP - that particular route is relatively cheap, easy and well-travelled - to say nothing of being mostly bolt-ons...

Paradoxically, most 400-500HP 930's are easier to drive than the stock 930. With good headers and turbos, you lose the turbo lag and the sledgehammer-to-the-chest effect and end up with a tractable car instead...

I've got 9.3:1 95mm pistons, PMO 40s, SSI, M&K for a total ouput of 204 HP and 214 lbs. trq. at the flywheel. :confused:

I am considering a shortstroke rebuild and want to limit my power to 240 ft lbs or so because I actually like the 901 shift pattern. Keeping the rear wheels planted on a light weight narrow body with power closer to 300 HP will be your next challenge.

I agree with the others that a turbo or 3.6 is the least expensive way for a big power upgrade but the trans will need to be upgraded too.

Of all the money I spent, my vote for best "bang-for-the-buck" goes to the asymmetric lockup diff.

I already had 21/30 TBs, but the LSD makes a very useful difference under power, decelerating and through corners. Pretty much everywhere except cruising, really :)

[QUOTE=joetiii;3668614]I've got 9.3:1 95mm pistons, PMO 40s, SSI, M&K for a total ouput of 204 HP and 214 lbs. trq. at the flywheel.

The small ports are probably hurting you the most. I also have an M&K muffler and I suspect it is costing some power as well. You have really good torque. You may also be able to run more ignition advance. I'm running 30 degrees total but some of our guys are running more. I don't know what the safe limit is. Our spec class has found that the big port motors have more power even with the stock 8.5 pistons than the small port motors.

-Andy

With those pistons you are up to euro compression and should have 204 hp with the stock exhaust and CIS.

Euro or rather ROW CR is 9.8:1, his engine will also be suffering from the small ports on the late US SC engines.

Steve

Your right about the compression, but the ports are equally small on the euro.

GotaT,

Sorry if this thread is heading in a "how to get to 250 HP" direction. We can start a new thread. Spuggy is correct in that you will want to add some type of limited slip differential in a 8.3:1 915.

Andy, when the car was on the dyno, we advanced the timing to get these results, though I do not know what the final timing number is. I recocnize the later SC engine is more of a torque motor w/o the big port heads. I first considered hogging out the smaller intake and adding 964 cams but then I would be in the same boat as GotaT... I would be searching for more power a short time later.

GotaT - bumping power by over 35% in a 2400 lb car will make a huge differrence. I was thinking my measely 50 hp increase (25%) would be significant. :)

I Know in the rebuild book it states that the ROW post 79 SC's had small ports but in reality I dont think they did. I have stripped both a 83 and an 81 SC engine last year as well as my current 79 SC engine all three were ROW and all three had the large 39mm ports. These were not engines that had been retrofitted with early heads as the date stamping matched. Someone with more experiance may chime in but im pretty sure all ROW SC engines had 39mm ports.



Steve

Yep, Steve is right, all ROW SC's had the large ports .

Allright, news to me. Happy to learn something new today!

what does the LSD do to whilst cruising?

Well, to put it another way, if you can tell the difference between an open diff and a limited slip one whilst pottering about gently or cruising on a fixed throttle, you're a more sensitive driver than I am. :D

There are situations where it's obvious there's an LSD in the tranny, but it's completely undetectable to me in the above two.

Even kicking it hard in a straight line, there's no hint there's an LSD in the mix unless one (or both) wheels break traction.

please expound!

Joe, sent you a PM.

The debate about HP and which transmission to use is interesting.

Surely it is torque that breaks transmissions rather than HP and I would be interested to know what torque figures are considered sensible for the various different boxes taht are used in early cars.

I wouldn't like to use a 901 with much more than around 180 lbsft.

The 7:31 used in the 915 also seems to be an issue but is this due to the amount of correction needed to obtain 'smooth' running with only 7 teeth on the pinion or due to gear case stiffness with mage cases?

Any thoughts?

Agreed.

This is probably the definitive "beef up my 915" thread:

http://forums.pelicanparts.com/porsche-911-technical-forum/250779-how-beef-up-915-thread-parts-costs.html

Hayden says that controlling the differential and the two gear shafts are critical for the 915. WEVO sell a billet replacement diff cover that uses a 930 diff carrier bearing, and a one-piece intermediate bearing retainer plate.

Interestingly, he also cites a limited slip as a durability item by preventing radical rotational speed differences within the diff that breaks the gears on an open diff..

For track use, controlling oil temperatures (cooler) is essential. Ensuring oil gets where it needs to be (spray bars) intuitively seems good.

Mag-case 915's aren't strong. The alu units are stronger (and heavier) and got stronger again when the factory switched from the 3.0 SC to the 3.2 Carrera. Eventually, of course, the factory decided not to use the 915 for the 3.2.

That said, Jack O has a tweaked, mag-case 915 in BBII with the 3.6, and if I'm reading his response to "how long has it lasted" right, it's been in there for 5 years and countless track days...

Hayden's rule of thumb for a 915 with appropriate modifications is apparently 350 ft/lb & 5,000 RPM. In other words, if you make more than 350 ft/lb at less than 5,000 RPM, the 915 is just not going to last.

He also says that there is no guaranteed way to make a 915 live at these power levels. You can drive carefully around the limits and get good usage from the 915 for years, but you can also break it almost at will. And it probably doesn't much matter what you do to it internally either - it'll still break if abused.

"Sensible"? LOL

Well the 914 guys who run small-block V8's with the 901 joke about changing them out with the clutch. Except they're probably not joking...

In that application, they either remove 1st completely or use 1st for moving around the parking lot only, and strengthen what they can.

They do prefer to build high-revving, low-torque motors for that application, but "low-torque" in the context of an SBC lump is, uh, considerably in excess of 180 ft/lbs..

The 7:31 is apparently an issue for any motor significantly more powerful than the one it was originally shipped with, and I understand that that is entirely down to the strength of the crown wheel and pinion itself.

It's not usually advised for a 3.0, much less anything with more grunt than that.

I had a Mag case 915 with 7:31 for many years with my 3.2 with no problem. Doing track and AX with it.
Nothing special was done to it. I rebuilt it with new synchro and some bearing but that was before the 3.2 went in it. The dyno chart that I show up earlier in this tread was done with that tranny. I now got an 84 or 85 Alu. 915 with the 8:31 in the car. With the size tire that am running with, the 7:31 was too short gear, I was on the rev. limiter in 5th at VIR and Road Atlanta, not that fun. With the 8:31 I still got some room left in 5th, and during AX I don't need to go in 3rd that often anymore. Having an Alu. 915 now give me the possibility of making some change to the 3.2 to have more HP and still be on the safe side of the tranny.

My belief on the 901 trannys comes from local race experience.
I'd agree that its probably more a question of torque than hp.
but the local 914 race shop believes that 225-250hp is the max for a 901

this was based completely on cost effectiveness.
it became more expensive to rebuild 901's over a course of time than to convert to a 915 at the 250hp mark.
(this was an observation based on approximately 8 cars)

also these are high rpm race motors with out the torque of a V8.

I use an "F" first gear ratio in my 901/914 box and these have proven to be good up to 200hp, but again thats a high rpm race motor that is not built for torque.

the 914 guys commonly believe that a 901 will survive to 300hp on the street
(and I believe 250 in track conditions)

torque and heat are what kills a transmission, besides run of the mill negligence

what a trans will take for a short period of time is inversely proportional to what it will take for a long period of time due to the above factors.

that said factory ratings for a warranted trans are
sand cast case 901 used thru B series MY69 -138 ft-lb
die-cast & later mg case 911 used on C & D series MY 70-71 - 148.5 lb-ft
die cast mg case 915 used on E, F, G series MY72-74 181 lb-ft(for racing where durability isn't an issue & w/ cooler - 275 lb-ft)
mg die cast case 915 used on H, I series w/ 8:31 200 lb-ft
al die cast case 915 used on J - K series 225 lb-ft(250 lb-ft w/ cooler)

For street driving torque is everything, for race torque at high rpm w/ proper gearing is half the battle.

a 250 hp 3.0 isn't going to be as accomodating on the street as a 250 hp 3.6 because of the torque characteristics of each engine, gearing can trade revs for either accelration or speed but not both at the same time.