100mm yes or no

[Rich Buckner]

OK. It is decision time. I have a set of new 100mm Mahle cylinders that I bought for a 930 rebuild project. I have been advised by several reputable engine builders NOT to use these cylinders because it is a one way street. Once the spigots are bored, there is no way back.
Here is the question.
Can a 3.5 be built without having concerns about reliability. I plan on going to an EFI system and using 8:1 JE pistons at 1 bar.

Who can point me in the right direction?

[935TURBO]

Yes....you must machine the engine case for a bigger diameter....105 mm.....that's what I am doing on my TT project.......as follow......

[SCHNELE]

Serge, is there a crack in the case or is that a casting mark?

[935TURBO]

Originally Posted by SCHNELE

Serge, is there a crack in the case or is that a casting mark?

...of course...casting work....it would be such a pity if it has been a crack.....my original cranck case......

[gumba]

I had my 3.5 rebuilt a few years back by Jerry Woods. They didn't feel there were any reliability issues. They used 7.1 Mahles. This is a street car that will see some track use at some point.
'79 930/DP935

[Rich Buckner]

Gumba,
What kind of pressure are you running? Did Jerry Woods add a CE type head gasket? What type of horse power are you generating?

[gumba]

Mine is a conservative smog legal motor. Didn't use CE type head gasket. 400 f.w.h.p. @.9 boost.
3.5 twin plug (distributor), SC cams, CIS, stock heads, K27 turbo, SSI's, DP muffler, 46mm tial w/g, DP 3/4 bay intercooler.

[911nut]

Originally Posted by Rich Buckner

I have been advised by several reputable engine builders NOT to use these cylinders because it is a one way street. Once the spigots are bored, there is no way back.

I think that once you drive a 3.5 turbo engine you won't want to go back

[voitureltd]

Originally Posted by 911nut

I think that once you drive a 3.5 turbo engine you won't want to go back

I also have one with a 3.5 and that you cannot go back is a option you will not want to exercise.

[Rob Channell]

"400 fwhp"

gumba,

Man, that is one nice looking motor. I missed the fwhp meaning, though. All I can think of is "front wheel horsepower" and how that motor would look funny in the front of a Honda.

[Helmsy]

fwhp I presume would be fly wheel hp and I likey the DP intercooler

[gumba]

Yes, flywheel h.p.

[Reaper930]

I say go for it, I'm running a 3.8tt and when I talked to the shop about reliability etc. they said that at around 1-1.2bar its a non-issue, but as a race motor they don't live very long. But as long as you're not going for a straight up club racer you'll be just fine.

The most important thing is the quality of the parts going into the motor, especially the oiling system & fuel delivery. Go EFI and don't look back.


Serge, you're going twin turbo?!?!?!?!

[osiris2600]

if one gets 98mm piston with a 3.6 RSA crank will that amount to a 3.5? Likewise if one has 100Mm pistons with 3.6 crank the displacment will be 3.6?

[gumba]

Rick,
Is this a street or track motor? If it's for the street I'm pretty sure/positive that efi won't pass the visual smog test.
Someone else on this board is building an efi motor and plans to swap it out every two years with cis.

[SCHNELE]

I am just curious as to what takes place on the visual inspection in CA, I mean you guys are saying that some state employed lackey is going to be able to discern the difference between CIS and EFI????

[gumba]

Most turbos are going to need some type of adjustment, usually by an independent shop to pass. Most shops I know won't try and sneak it by the smog place. Even if you adjust it yourself there's also a chance the smog guy will notice. If you fail (I think twice) then you need to take it to a state smog station, they will definitely notice.

If you are fortunate enough to know a smog guy who will pass it by various means, then go for it. I'm not saying it can't be done, it's just gotten a lot harder.

On the other hand I had a smog guy think the blower fan on my 3.2 was a turbo. This is one of the few times you look for an inept mechanic.

[Rich Buckner]

So far, my experience here in Thousand Oaks, CA has been this:
1. A visual inspection that determines if all of the stock components are in place. This included the air cleaner, smog pump, injector tubes, crank case ventilation, catalytic converter with censors, distributor and distributor vacuum line.

2. Actual smog test which is run on a chassis style machine.

The only thing that I think might cause a problem is the stock air cleaner. Everything else I have covered. I plan on using to different maps for this car. One for the smog test and one for the fun test (daily driving).

So far, I have had the car smoged twice without incident. And this is with 964 cams, K27-7006 turbo, Kokeln Intercooler, Zuc Z headers, Euro CIS system and a (temporary) stock 930 catalytic. I run a GHL muffler after I leave the smog station. One thing I do is turn back the enrichment screw slightly to lean it out for the test only.

Thank you to everyone out there for your input.

[HotRod]

So, did you go for it with the 100mm cylinders?