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Wayne 962's Avatar
Quote:
Originally posted by TonyG
I don't know if the 39mm ports are too big, but I do know that the 34mm ports are not too small.

I got 200RWHP on a 3.0SC with 34mm ports, 20/21 cams, and 40mm PMO carbs with SSI's.
The GE40 cam is a quite a bit more hotter than the 20/21 cams, if memory serves me correctly. You're also talking about a short-stroke engine (higher revving) and an increase in displacement.

34mm for the short stroke will indeed have some impact on performance. How much, who knows? But it is small for that much air going through the engine...

-Wayne
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Old 12-26-2004, 12:24 AM
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Actually Wayne, without looking at the specific acceleration rates of the two cams, they are pretty similar. The GE40 has intake durations of 256 I/ 248E and the 20/21 had durations of 258 I / 246 E. The GE40 has lifts of .470 I / .440 E while the 20/21 has lifts of .485 I / .458 E. So the 20/21 has about 3% more intake lift then the GE40. I'm not sure if I'd call that "quite a bit hotter", although you are welcome to.
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Old 12-26-2004, 06:19 AM
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John, dont the closer lobe centers of the GE40 (102, IIRC) create more overlap and make the GE40 similar to an S and not suitable for CIS?
Old 12-26-2004, 06:22 AM
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Right Sherman. The GE40 has about 48 degrees of overlap while the 20/21 has about 8 degrees. And so you're right, the GE40 is better for a carb'd or MFI'd engine while the 20/21 is optomised for CIS or EFI with a common plenum.

My brain's running a little slower after eating so much over the last couple of days.
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Old 12-26-2004, 10:59 AM
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Quote:
Originally posted by jluetjen
My brain's running a little slower after eating so much over the last couple of days
Indeed, mine too. That is why I put "if my memory serves me correctly." Call me too lazy to look it up.

The 20/21 cam is a good one for CIS-style engines (not too hot). I think it's about on par with the 964 cams? All of the GE cams are hotter, performance cams, with the higher the number, the hotter the cam (in general).

-Wayne
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Old 12-26-2004, 01:25 PM
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One thing to point out... is that with the addition of closer lobe centerlines (more overlap), the worse the idle, the lower the vacuum signal, and typically, when you move the lobes closer together (more overlap, you move the torque peak upward (peak power coming in at a higher rpm), and typically, lower and midrange power suffer.

It's always a trade-off with cams. When in doubt, choose the smaller...

The 34mm ports can quite easily support 235Bhp. And, I'm quite sure that I can get the same combo upto at least 250Bhp... all with the peak Hp coming in at 6000rpms (which is very good for a true daily driven street car).

TonyG
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Old 12-26-2004, 01:54 PM
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Quote:
The GE40 has intake durations of 256 I/ 248E and the 20/21 had durations of 258 I / 246 E.
The GE40 numbers are given at .050" valve lift. These 20/21 numbers are given at some other valve lift spec which is unknown.

The 20/21 cam at .050" Valve lift is 238/226 degrees according to WebCams page.
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Old 12-26-2004, 02:01 PM
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Quote:
Originally posted by TonyG
The 34mm ports can quite easily support 235Bhp...
Are you saying 235 bhp With CIS?
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Old 12-26-2004, 06:36 PM
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dd74

>>>Are you saying 235 bhp With CIS?<<<

No. 3.0SC engine, 20/21 cams (fairly "mild" cams BTW), 40mm PMO carbs, SSI heat exchangers, and 2in/2out muffler with the distributor converted to 100% mechanical advance). Basic bolt-on goodies.

But the point is that the 34mm intake ports didn't limit the power up to 235Hp. That power figure was with the carbs installed out-of-the-box with no jetting corrections as well as the timing not as advanced as it could have been at the time of the dyno session, and the car not quite getting full throttle.

With some more fine tuning, I'm 100% certain that this combo can be easily good for 250Hp-260Hp still using the 34mm intake ports (stock cylinder heads, no porting, stock valves, stock pistons, etc...).

So, are the 39mm ports too big? Probably not since the '78/'79 SC's had them from the factory. But are the 34mm ports too small? Definitely not up to the 250+Hp range with typical bolt-on mods, and with a powerband that's 100% perfect for street/everyday driver usage.

TonyG
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Old 12-26-2004, 08:29 PM
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>>>Those are some big numbers - I might have some doubts about the accuracy of that dyno run...<<<

I love it. Now the excuses come into play. "The DynoJet 224X was not comparible to a DynoJet 248...

I'm not sure why you'd have doubt unless you have experience comparing the DynoJet 248 to the DynoJet 224X on the same car in the same state of tune.

The dyno run was done on a DynoJet SAE corrected.

The SAE correction factors are listed on the dyno print out as was the temp/humidity/pressure conditions at the time of test and the smoothing factor.

Are you implying that DynoJet doesn't know what they're talking about when they say that their DynoJet 248 will produce the same results as their DynoJe 224X, perhaps you should contact DynoJet and ask youself since you have doubts.

The software used to display the results is comletely irrelevant, as I've test on many dynojet 248's with different software netting the same results (400+RWHP 944 turbos)

The shop that did the dyno test was DC motorsports which is a pretty big Dodge Viper tuning/race prep shop here in Los Angeles.

And according to DynoJet, the dyno that the test was pereformed (224X) on produces exactly the same results as the 248 DynoJet (larger older style dyno).


And... since I've been to the track, I can tell you first hand that I've pulled away quite easily at Willow Springs, down the straights from many 3.2 Carreras (stock or chipped, and 1 with a MAF kit, chips, and ARC2).


But if you can find a DynoJet 248 in Los Angeles within 40 miles or so, of Santa Clarita California, I'll be more than happy to back up the results there. Of course, I've played with the ignition timing and a/f ratios, the car is now getting full throttle, and the geometry of the throttle linkage has now been corrected, since then... and the car pull definitely stronger and much smoother now. :-)

It's a shame when there's "doubt" cast on hard work.

I guess I sound defensive... but I'm the first person to cast doubt when results are questionable. The question here is... why are these results questionable? I'd love to hear the answer.



TonyG
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Last edited by TonyG; 12-26-2004 at 10:33 PM..
Old 12-26-2004, 10:17 PM
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Tony, I dont think anyone is criticizing the work you have done. I think its exciting. Any scans of the dyno sheets? Maybe someone here has a sheet from the same dyno they can compare?

There are a lot of guys here who have put a lot of money in their 3.0s and cant match the dyno numbers you are quoting. Im too lazy to look it up right now, but I think 250-260 hp is 20hp beyond what Bruce Anderson says you can get with stock pistons, carbs, SSIs, and 20/21s in his Performance Handbook. 250-260 flywheel hp is high compression 3.2 or 3.4 territory

Last edited by Shuie; 12-27-2004 at 07:02 AM..
Old 12-27-2004, 06:55 AM
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Read the section in my book on dynos. The same dyno can give varying numbers on different days with the same car - sometimes 20% or more!

I was mostly thinking that you should be more cautious with your statement here:

Quote:
With some more fine tuning, I'm 100% certain that this combo can be easily good for 250Hp-260Hp still using the 34mm intake ports (stock cylinder heads, no porting, stock valves, stock pistons, etc...).
There are many people on this board with highly modified 3.0L engines who haven't reached this number. I'm not saying it can't be done, but not with some significant modifications.

-Wayne
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Old 12-27-2004, 05:59 PM
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Shuie

>>>There are a lot of guys here who have put a lot of money in their 3.0s and cant match the dyno numbers you are quoting. <<<

All the ones I've seen are using the CIS fuel injection... .which is probably why.

I'd be interested to see a similar 3.0 setup using carbs (dyno).

TonyG
Old 12-27-2004, 06:03 PM
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Quote:
Originally posted by Wayne at Pelican Parts
Read the section in my book on dynos. The same dyno can give varying numbers on different days with the same car - sometimes 20% or more!
I've read this section, and concur with Wayne. Also, there are some very knowledgeable individuals in the Porsche world who really don't give that much credit to dyno results. AFIK, a dyno is used for tuning, not necessarily to trumpet an engine's horsepower, though both are possible.

The only dyno of worth (to me) is the butt dyno: if you're squeezing your cheeks because your motor's strong, well then it probably is strong.

But if it's true that 34mm ports with CIS pistons and Webers can obtain 260 hp, then that must mean a lot of short stroke motors must be really putting out 280 hp.
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Old 12-27-2004, 06:36 PM
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IMO the drivetrain losses here are too high also. The original quote was 200 RWHP and that is not unreasonable. I think a realistic loss of 10 percent giving 220 at the flywheel and maybe 230 with the further tuning is more likely. This is about what my race group sees with carbed 3 liter engines and stock cams.

-Andy
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Old 12-27-2004, 07:53 PM
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Eagledriver

I would tend to agree with the losses. Years ago, we dynoed a bunch of stock 3.2 Carrera's. I don't remember the specific results, but backward calculating at the time (on a DynoJet 248) , we got about 12.5% drivetrain loss.. not 15%, probably because there's no driveshaft (guess).

I only used 15% because that's what everybody else on this board quotes, etc...

TonyG
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Old 12-27-2004, 08:56 PM
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I'm beginning to dip my toes in the engine puddle and I have some questions about this short stroke 3.2

-Is it a waste of time to make this engine run w/ CIS? I'm only wondering about cost savings. What about itb's? (I know those aren't cheap, but I'm not sure whether carbs or mfi aren't more costly)

-If it had CIS, would the 964 cams be a better choice?

-I know that in many build ups the CIS is the limiting factor, therefore avoided, but I'm really looking forward to the increased displacement over my T. Other than the CIS itself, would the fact that this setup was intended for carbs detract anything on account of the CIS?

Basically, I'm wondering about such a 3.2 while trying to limit some of my costs, while still enjoying a sizable bump in the output.

thanks.
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Old 12-31-2004, 04:42 PM
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The 3.2 short stroke, as I recall, started with CIS - in fact, it had to have started with CIS, since it was intended to boost the low-end and mid-range torque of a 3.0. Be that as it is, the 3.2 short stroke was a little-known modification started by some German tuners close to Porsche. Horsepower for the CIS engine when built off a late SC motor with 204 hp supposedly increased to about 220 hp. Bruce Anderson's Performance Handbook goes into a little more detail. But from what I recall, this modification was always originally intended for CIS-equipped 3.0 motors.

Of course, when a 3.2 short stroke has Webers, that offers up a whole new world of pistons, head port sizes and cam choices. Conceivably 250 hp could be obtained using the right combination. But originally, it was designed to boost the shortcomings of the 3.0 and the complaint Euro customers had with a lack of low and mid-range oomph. In my view, they probably just weren't driving the car hard enough.
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Old 12-31-2004, 06:19 PM
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I’m not an expert on this stuff at all. Hopefully nothing I’m about to type is too far off base.

Pistons:

The 98mm pistons are available in two different piston profiles. We'll call them RSR and Wedge Domed, a.k.a 'Max Moritz' pistons. Each piston profile can have a high (10.3:1) and lower (9.8:1) compression ratio.

The 9.8:1 wedge domed pistons were made as a direct bolt on upgrade to the CIS SC engines. These are great for single plug, but not so great for hot cams.

Both versions of the RSR pistons should be used with twin ignition since the shape of the piston splits the combustion chamber into two sections on the compression stroke. These pistons have large valve pockets, so they don’t require any extra machining for valve clearance with hotter cams.

Heres a pic of the wedge domed Max Moritz pistons on the left and rounded domed RSR pistons on the right





Cams:

Your cam choice will be limited by your piston and induction choices. Cams with high valve lift and long durations will obviously not work with pistons that don’t have the proper valve clearance. Cams with closer lobe centers (high overlap) will not work with a common plenum intakes like on CIS due to fuel reversion issues.

Don't focus on one component of the engine. You have to figure out what kind of motor you want/need and then pick an induction system, a piston, and a cam that will work well together.

Between the four different versions of the 98mm pistons, dozens of camshafts, and four different induction systems, there are tons of recipes for 3.2 short stroke engines. Here are my three favorites


Mild:

CIS induction
98mm wedge domed (Max Moritz) pistons 9.8:1
964 or 20/21 cams
single plug

while you could certainly run a different induction system, you may not gain a lot of performance due to cams and pistons on this motor
substitute the high compression Max Moritz pistons and twin ignition for more performance, but do not try to run a hotter cam with CIS or without machining the pistons for valve clearance


Hot:

40mm Webers, MFI, ITB
GE40 or S cams
98mm wedge domed (Max Moritz) pistons 9.8:1, relief cut for valve clearance with the cams
single plug


substitute high compression Max Moritz pistons and twin ignition for more performance. The limitation here is the pistons since they need to be machined for valve clearance with these cams. Forget about CIS with anything hotter than a 20/21 or 964 cam


Thai Hot:

MFI, 46mm Webers, or ITB
98mm RSR high compression pistons, 10.5:1
GE80, sprint, 906, or hotter cams
twin ignition

Last edited by Shuie; 12-31-2004 at 07:54 PM..
Old 12-31-2004, 07:18 PM
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