Ralph:
Sent you a PM.
J.P.

Ralph:
PM waits for you.
J.P.

This evening Steve and I got to work a couple of more hours with the rain pounding outside. I got the new oil pressure relief guide and installed the vertical assembly in the case. One less thing to worry about.

Then it was time to install the ARP head studs into the case. After Steve took a die and cleaned the threads in the case (there was a ton of gunk in there), he turned me loose with a little Loctite 262 and said get going. With the threads chased, the studs went in beautiful. Here is a pic of the head studs installed:

http://forums.pelicanparts.com/uploa...1098155601.jpg

Measured that they were in far enough but not too far and then double checked by loosely fitting a cylinder and head with head stud nut and washer. Looks good to go.

While I was doing the head studs, Steve was beginning to figure the compression ratio by cc'ing one of the twin-plug heads.

http://forums.pelicanparts.com/uploa...1098155895.jpg

Head CC is 91.8ml. Steve used a concoction of WD-40 and oil. Thick but not too thick that it takes forever to fill the combustion chamber of the head (and later piston/cylinder).

Time to test fit a piston/cylinder to check deck height as well as get the measurement when the piston is dropped enough that the dome is below the top of the cylinder. Since all I had were .25mm base gaskets in my gasket set, a single .25mm gasket is what we started with. Deck height is not where we want it to be at .5mm. Going to have to get a thicker base gasket(s) to get the deck height up to 1mm where Steve wants it.

Here's a pic of the piston/cylinder temporarily installed:

http://forums.pelicanparts.com/uploa...1098156510.jpg

Here's a pic of Steve filling up the cylinder:

http://forums.pelicanparts.com/uploa...1098156661.jpg

The cylinder CC is 71ml. We can start to plug the numbers into the formula. Not the result I was expecting, it looks like the measured CR is going to be 9.6:1, alot lower then the claimed 10.3:1 of this piston and cylinder set.:(

Steve had the same problem with his 3.4L motor. He ended up with 9.2:1 initially (same 10.3:1 was quoted) but took some more material off the heads until he settled for 9.4:1. He also says that it is common for the CR to be alot lower then advertised. I can't speak for other's Porsche motors, but the water-cooled VW motors are notorius for having inflated CR's. The Mk2 GTI's 1.8L were rated 10:1 from the factory and were more like 9.2:1. Same with Mk 3 GTI 2.0L's, stated CR was 10.5:1 but in reality more like 9.5:1.

Anyone else measure a different CR (lower or higher) then what the piston/cylinder set was rated on their 911 motor? Anyone know if US spec Carrera's are actually 9.5:1 and not lower? I would speculate that they are.

Have a couple of choices to make. Can send the heads back to Ollie's to take some more material off the heads or can also let them play with the rods a bit to increase the CR. Since my motor does not have a knock sensor, will run in a warm climate and has to drink 91 octane, I think that I may leave it alone unless you guys can convince me otherwise. Anyone?

Ralph

I'd run more comp. since it is twin-plugged. Comp. = power. The "safe" guideline is 10.5:1 for twin-plugs. But ask around in SoCal -- your gas may be different there.

In fact, I know it is different -- let me mod. that stmt: the gas may sufficiently different there to make you run a different CR.

Wow, great hands on pictures. Keep 'em coming.

I have heard that the 'lower than stated compression ratio' is pretty common with Porsche factory engines. My 993 engine is 11.3:1 - it is probably more like 10.5:1.

Ralph,
You can't mess w/ the rods to increase CR if you've already hit the limit on deck height. (If your deck height was too much, you could lengthen the rod by boring the small end off center). I have a similar motor but w/ an SC crank and J&Es. I think I measured my twin plug 3.2L heads about the same as you. I will check tonight and post. My J&Es came out very close to the 10.5:1 I specd. I gave them my head volume though. I distincly remember the EBS guy thinking my heads were a little "large" on the volume side compared to a regular 3.2 head. The twin plug dimple, 100mm chamfer, and any valve job will yeild more volume. (FWIW, Having the carrera valves sit just 1mm further down in the seats will yield 2.7cc more!) Mine have had at least one valve job.

SMD

Yes, you're right. These are off the shelf Mahle units, not custom made JE's so I think I may be stuck. The 9.6:1 is even going to come down a bit more with a thicker base gasket, I'll run the numbers again and double check.

Looking at the heads closely, I can see that Ollie's already has removed some material, I don't want to remove too much. Thanks for the input and I would be interested in seeing what your head volume was (and others).

Regards,

Ralph

Ralph,
looking through my notes, my heads came out to 92cc. My J&E domes were 43cc, and I ran the clearance right at 1mm which gave me a CR of ~10.7:1. I remember the tighest spot was NOT at the very edge, but just on the inside of the chamfer of the 95mm part.

FWIW, at these settings a 1cc head or piston change makes a 0.17:1 CR change. A 0.1mm clearance change makes a 0.13:1 CR change.

SMD

Are these Mahle 'Sport' RSR type pistons, designed to accomodate high lift/overlap cams (and milder cams, of course)?

Hi Ralph:
From what I've been reading; are you stuck with a 9.5:1 comp. ratio for your engine?
Regards,
J.P.

Maybe I missed this but what head studs are they?

SMD, thanks for posting your info. My 9.6:1 ratio is with a .5mm deck height (using a .25mm base gasket) which obviously won't work. Got a set of .5mm base gaskets from Andial this afternoon (ouch! pricey!) to help get the deck height closer to 1mm. Dieter at Andial recommends a deck height of .8mm to 1.2mm. I will be somewhere near the tighter clearance but since I am using relatively docile cams I don't think (or is it hope?) it will pose a big problem.

J.P., the problem is even 9.6:1 is now optimistic. I ran the numbers again, and with a .75 deck height, the CR is 9.13:1. Now can you guys see why I am crying in my beer?

Kobalt, yes these are the carb/mfi type "hemi" piston rather then the stock wedge dome type. Their design lends itself better to twin-plugging then the wedge dome type which is also one of the reasons (others as well) why they are rated with a higher CR. I also spoke with Pete in parts at Andial while paying for my base gaskets and he says they don't sell many of the 98's or 100's of this type with the 23mm pins anymore but has heard through the grapevine that this is a problem with these particular sets. Steve's motor confirms this, as his 3.4L uses the same piston carb/mfi type and he ended up at 9.2:1 before milling the heads to end up with 9.4:1. The compression ratio of both of these sets is not the claimed 10.3:1! I guess I am learning the hard way.:(

If I look on the bright side, my motor with twin-plugs will run on water, right? Joking, only joking.

The Motronic wedge dome 98's and 100's are apparently very close if not spot on to the claimed CR of 9.8:1. Who would have figured that these pistons would actually have a higher CR than the hemi style???

Bill, head studs are ARP. You know something that may be of use? I am getting desperate.

Steve suggested and I decided to have the heads milled. This evening, I disassembled them (yes, I labeled the heads, valves, springs, retainers and shims where they came from) and tomorrow my buddy Eric at PMNA will remove .015" from them to try and get back some of the compression. Steve says .020" can be safely removed but it is better to be able to remove more material if required but you can't put it back if you go to far!

For reference, here is the PMNA way of calculating the compression ratio:

1) Figure area of bore and divide by 1000
2) Measure volume of cylinder head. This is "Head CC" (A)
3) Write down final deck height
4) Drop piston enough to get dome below top of cylinder and write down the distance
5) Add item 3 to item 4
6) CC the cylinder and write down this number
7) Multiply item 5 by item 1
8) Subract item 6 from item 7. This is "Dome CC" (B)
9) Multiply item 1 by the crank stroke. This is "Swept CC" (C)
10) Multiply item 1 by item 3. This is the "Deck CC" (D)
11) Compression Ratio:

C + A + D - B divided by A + D - B

Will get the heads back in a day or two and then check everything again. In the meantime, this is my motor hibernating:

http://forums.pelicanparts.com/uploa...1098246435.jpg

Word to the wise: Don't assume the CR is what is claimed and don't buy the carb/mfi Mahle sport 98's or 100's for the Carrera if you want to have a high compression ratio.

Ralph

Craig, based on the above, what is your guess now?SmileWavy

Ralph

Thanks, Ralph. This line of pistons definitely look different depending on the B&S dimensions plus head cc they are designed for.

I'm sorry to say I don't have any groundbreaking ideas for you. Unfortunately you're not the first to find a mahle set measuring out to below CR spec, which you already knew.

I recalculated - my guess is now.........255 rwhp......my 'official' (final) guess. Gonna be one hell of a motor no matter the compression!

Way to go !

Hell of the project.................. Great R&D:)

Just shim that bad boy up and turbo charge it with that compression ratio - then you really will end up with a beast!

If not then at least you will not be sweating it if you get some crummy gas...

Guys keep them coming... I am learning so much from these threads.
I am still on the fence on rebuild vs 3.6 Vario swap. I just bought Wayne's and BA's book on the 911 engine. But this forum is incredible!

Craig, will you be my dyno operator?:D I think you are way optimistic with your revised quote but I thank you for your positive outlook! I am going to venture a guess in the 235 rwhp range.

Not much more of note to report. The heads will be cut down tomorrow and measured to make sure they are even in an attempt to try and get back some of the compression. Steve will then CC a head or two and I will plug the value into our formula. Steve is optimistic we can get back to 9.5:1 which is the stock 3.2L US spec CR but short of the 10.3 "advertising" of the Mahle set. We will also have to check the piston to valve clearance with the Web 20/21 cams that just arrived.

I had a nice talk with Dieter on the Andial side after dropping the heads off to my buddy at PMNA across the courtyard. He said that Andial NEVER, EVER builds a pre-964/993 street motor with more than 10:1 CR. He doesn't feel that a higher ratio is compatible with 91 octane. He also has told Mahle countless times that their "CR claims" are inaccurate on some of their sets but it has apparently fallen on deaf ears. He is positive though that the new 10.7:1 98's for SC & Carrera race applications that are in their new Excellence ad are indeed accurate because he did the development work on them.

He also says not too worry about the lower compression, I am giving up at most 5 horsepower. He says I should be able to get away with more ignition advance to help compensate and Mr. Wong can help me there.

Didn't do much tonight, just installed the oil thermostat I finally got as well as checked the ring gap on the pistons and all are between .010" and .012". Here is a pic of a 100mm piston with a cylinder that has been "mooned" by Ollie's:

http://forums.pelicanparts.com/uploa...1098419292.jpg

Also took apart the chain tensioners, idler sprockets, idler arms, tensioner sprockets, etc for cleaning. The sprockets should all be looked at for wear, but don't necessarily need replacing. Mine look fine and will be reused, saving some money (about $150) on the rebuild. YRMV.

img]http://forums.pelicanparts.com/uploads4/IMG_08581098419496.jpg[/img]

Will update again when we have the CR finalized and we can proceed further.

Ralph

Sorry, here is the pic:

http://forums.pelicanparts.com/uploa...1098419848.jpg

Have a good weekend all!

Ralph

Ralph, sorry to here you are having a little trouble with the C/R. It will still be a fine motor though. Good luck. I think you will be safe with the .80ish deck height with those pistons. And with the .015 off the heads, things should be just fine. Just remember, There are a very few things that a couple of pints of Granville Island's finest can't cure!!

Cheers, Jeff

Hmm...I don't know much about about this, but why bother with Mahle's at all when you can order custom forged JE pistons in almost any dimension/shape you want? They are lighter to boot...

Mahle rules.

Well I understand that we have huge purist population here with lot's of myths, legends and history floating around but frankly, Mahle doesn't rule any more than 80's KKK K27 turbochargers compared to modern Garretts...

It's 2004 for god's sake...there are better pistons to be had than some shelved "gold plated" pistons from 20 years ago.

JE's are stronger and lighter than 20 year old Mahles, and probably priced the same or less. I don't see the point of building low comp race motor just to say it "has Mahles in it"...it doesn't show when you look at the engine.

There is lot's of mumbo-jumbo around which piston-design to use, but my anectdotal expirience is that JE'swill withstand more horsepower than OEM ones in most cases. I have a friend with 680 dynoed HP from a 2L engine, using JE pistons.

Wayne:
http://forums.pelicanparts.com/911-engine-rebuilding-forum/161373-je-pistons-vs-mahle.html?highlight=forged

You guess 235 rwhp?? You are LOW!:)

A friend has a 3.2 that has been chipped, cam timing advanced, your headers and a Flowmaster - 213 RWHP. Stock cams. Do a rough projection to 3.2 liters and viola, 234 hp - WITHOUT your internal mods and internal attention to detail!http://www.pelicanparts.com/support/smileys/smash.gif
(Guy working)

Mahles/JEs:

This is so controversial.....
My 2 cents, no comments on this plz, just a data point:

Mahles are proven and rarely have problems; JEs have had some weird issues in the past with reliability in 911 engines.

FWIW. And from what I've read on this and the Rennlist boards.

Ain't that the truth! All I will say on the matter is many of the most respected engine builders and machine shops here on the West Coast use Mahle products exclusively for their street engines. The ones that I am familiar with are Andial, Vision, Rennsport Systems and Ollie's Porsche machining. Steve Weiner from Rennsport has posted on these forums many times why he doesn't use JE's in a street application. Do a search as there is plenty of info, you just have to decide for yourself whose opinion you trust. I defer to the experts above who do these motors on a regular basis. If I am a sheep for blindly following then so be it.:)

Just for the record, there are also many tricks available to further raise up the compression ratio. Unfortunately, you start spending serious money on custom machine work and you can open up a whole new can of worms with respect to the width of the motor and potentially having to use custom sprockets, chains, etc. For a basic street motor, I don't feel it is worth the extra effort. We'll mill the heads .010"-.020" and whatever the CR ends up being after this work will be what we run.

My problem with Mahle is that they advertise one CR (and know it is wrong) when in reality it is something completely different.

Jeff, thanks for the vote of confidence. Steve feels the same way. I miss sitting on the couch on Saturday nights watching HNIC with a GI in one hand and some Indian Candy in the other.SmileWavy Damn NHL.

Ralph

What is the main difference between the Mahle US version and Euro version? Why can you acheive 10.3 CR with a Euro stock 3.2l set up and only 9.3 (or close) with a US set up? I know PAG originally did it because of the lower quality/octane fuel avaliable in the US.. But I am wondering why Ralph is having trouble acheiveing a 10 CR with Mahle pistons.

Ralph:
Do the chain sprocket boxes have to be machined with the cylinders to keep the cam line in sync??
Regards,
J.P.

Don't confuse the original Mahle 95's found in the US and Euro spec 3.2L engines with what I have. Those CR are supposed to be pretty accurate.

The problem seems to be with the 98's and 100's carb/mfi type pistons that Mahle Motorsports makes for the 23mm wrist pin. Someone at Mahle must have measured something incorrectly when these sets were designed or produced. From what I understand, the Motorsport 98's and 100's that retain the original wedge dome top for Motronic are accurate with their stated 9.8:1 CR.

Ralph

In my particular instance, no. In other situations depending on the massaging done then yes other factors can come into play. This is what I want to avoid at all costs (figuratively and literally).

The width of this motor really is not changing much where I will have these additional worries. Ollie's opened up the spigot bore but didn't really remove any material from the case that would make the width narrower. Machining the relatively insignificant amount of material from the heads also narrows the width somewhat (which increases the compression), but that will be compensated for to a degree with the thicker base gasket to get the deck height in spec (which will lower the compression).

It truly is a game, isn't it? Trying to increase compression without ruining the deck height or losing proper piston to valve clearance or having to modify other parts.

At this point, I just want to compromise and get back to a stock 9.5:1 CR without custom machine work that will affect other components. At the end of the day, it is still a street motor.;)

Ralph

"Someone at Mahle must have measured something incorrectly ..."

- That is not possible. They are German!

Let's hope that it is them that has miscalculated and not me! Anyone want to double check my math?

The heads were milled .020" and we are using a .5mm base gasket for a final deck height of .75mm. Here are the numbers for the CR formula listed above in a previous post:

1. 7.85
2. Head CC is now 88.8
3. With .5mm base gasket, deck height is .75mm
4. 5
5. 5.75
6. Cylinder CC is 71
7. 45.14
8. Dome CC is 25.86
9. Swept CC is 584.04
10. Deck CC is 5.89
11. CR is:

584.04 + 88.8 + 5.89 - 25.86 divided by 88.8 + 5.89 - 25.86

Compression ratio is now the original 3.2L US spec 9.49:1. You can see that milling the heads changed the head cc volume a full 3 ml from 91.8 to 88.8 and gained back .36 in compression.

I'm happy, would have liked to had it up a bit higher but not willing to go through additional gyrations to make it happen. The CR is conservative enough that I won't have any problems with 91 octane and it won't potentially knock itself into a million pieces next summer when things heat up again.

Not much else to report tonight. The cylinder heads were obviously reassembled since they had to be taken completely apart to be milled. I also loosely assembled the conical bolts and nuts on the rocker arms and installed the RSR o-rings onto the rocker arm shafts in preparation for the coming nights. Organized the cylinder deflectors and sheet metal and brought home all the old parts that I will not be using but may need for something or someone else down the road.

If everything goes according to plan, the pistons & cylinders, heads and cam towers will all be fitted tomorrow night. We hope to have the longblock fully assembled by Thursday night or Friday night at the latest. Next week will be the electrical and injection components put back on and routed nicely and then it should be ready to go back in the car. Will have to install the Andial signal splitter under the seat next to the DME unit, install Steve Wong's new chip and install a bracket to hold both ignition coils.

It's getting closer!:p

Ralph:
With your final compression figure of 9.49:1, do you still need twin ignition with 91 pump gas? How much volume increase does the second spark hole add (cc's)?
Regards,
J.P.

As to the Mahle brand name controversy...

in all high-level ...or high quality...or "difficult" applications with "no worries"...I've seen only 2 brands consistently show up:

- Mahle
- Cosworth

OTOH......the west coast hot-rod sub-industry has ...over the years...produced some mighty fine stuff..and I always wondered, for example, when Porsche goes shopping world-wide for suppliers, why names like Carillo ( rods), ARP or Raceware ( bolting) , and such....don't figure into the equation. Some of this is indeed historical inertia....and some may be that these specialist suppliers may not be able to ( or want to) produce in the overall quantities necessary.

Wil

Ralph
Are you then saying that 3.5 mahle c.r. is allways low, but 3.4 will be close to 10.3? If you had know this before would you have gone to twin plug?

J.P.,

Yes and no. I still need twin ignition because of the high-dome piston design (see pics) and the fact that 100mm is a very large cylinder. If the above weren't the important facets, then no I would not need it for 9.49:1 because that is the same ratio as standard. I just wanted a higher CR to be able to kill two birds with one stone.

Unfortunately, we never cc'd a head with single plug for comparison. I have to go to Andial/PMNA again today and will ask but I am sure someone may be able to chime in here and provide the difference in cc from single to dual plug.

Ralph

I can only base this on my own personal experience, my friend Steve's 3.4 and from what I have been told by Andial regarding others. The 3.4 and 3.5 sets that use the carb/mfi piston type are indeed lower than claimed. Figure about 9.2:1 rather than 10.3:1 for these sets in twin-plug format.

From what I understand from them as well, is that the Motronic wedge dome shaped piston in 98mm or 100mm does indeed measure to the advertised ratio of 9.8:1. I do not know if the standard 95mm in 9.5:1 US spec and 10.3:1 Euro spec are completely accurate. Can anyone who has done a stock rebuild or upgraded to the Euro spec pistons confirm?

Interesting question that you brought up. I probably would still have proceeded along the same path, as I planned on twin-plugging regardless of using 98's or 100's as an extra safety margin with our poor fuel quality and hot weather. If twin-plugging, the extra machine work to bore the case spigots for 100mm is relatively inexpensive. I only ended up with 100's because they were actually much cheaper for me then 98's so it kind of made it a no brainer as far as I was concerned.

Ralph

Update for 10/26:

Made some good progress tonight. Steve and I were able to put pieces together in "chunks" tonight before things will slow down again.

We started by attaching the cylinder heads to the cam towers. We used Yamabond/3 Bond 1104 as the sealant.

http://forums.pelicanparts.com/uploa...1098844689.jpg


Completed assembly:
http://forums.pelicanparts.com/uploa...1098844781.jpg


We then sprayed/prepped the (6) .5mm 100mm base gaskets with Permatex High Tack Sealant in preparation for installing the piston/cylinders. Rod bolt torque (35 ft./lbs. per ARP) and bolt stretch (.0117-.0122 per ARP) was checked one last time before installing the pistons. The 3 oil ring gaps were lined up 120 degrees apart from each other before the ring compressor helped slide the pistons into the cylinders.

http://forums.pelicanparts.com/uploa...1098845245.jpg

http://forums.pelicanparts.com/uploa...1098845317.jpg


Next came the cylinder deflector tin, beautifully powdercoated semi-gloss black by Specialized Powdercoating in Huntington Beach, CA.

http://forums.pelicanparts.com/uploa...1098845407.jpg

Last, the oil return tubes and cam towers w/ the heads already bolted on were installed as a unit, leaving us with this:

http://forums.pelicanparts.com/uploa...1098845719.jpg

The ARP head stud nuts w/ washers are torqued down to 38 ft./lbs. per ARP's recommendation and will have the night to "settle". Steve likes to give them a night and then double check the torque before proceeding further.

To get an idea of how much time is involved, we have spent approximately 12 hours on the assembly since the parts came back from the machine shop. Combined with tear down time and cleaning/prep time, we are around 27 total hours right now. Many shops charge around 40 hours for a normally aspirated engine teardown/rebuild and I think that we will be close to that figure (either slightly higher or lower).

What do you guys think so far?:confused:

Ralph

It's a thing of beauty Ralph, I can't wait to see the article in European Car magazine. I subscribed when they did the early 911 series of articles and am glad to see they're doing more 911 articles. I'm thinking of building something similar eventually for my '72 911 "rsr" project, so I'm following this thread very closely!