964 C2 3.8 Build Thread - Page 3 - Rennlist - Porsche Discussion Forums

Notices
964 Forum
Sponsored by:
Sponsored by:

964 C2 3.8 Build Thread

Reply

Old 03-11-2017, 06:59 PM
  #31  
Sire
User
 
Sire's Avatar
 
Join Date: May 2004
Location: Netherlands/ The Hague
Posts: 276
Default Bore

Originally Posted by Juha G View Post
Slip-in = the cylinders "slip" into the engine case. Cylinder bottom sealing is done between the flanges. (this is as original street engines).

Bore-in = Engine case needs to be machined (borred) to fit the cylinders. Sealing by O-rings which requires further machining of the case for the O-ring grooves. Sealing between the flanges is not possible because there is just not enough surface area on the flange for proper seal after machining.

The original case has cylinder openings for the 3.6 cylinders. The 3.8 cylinders are bigger in diameter so you can either have same outer diameter (=slip in) with thinner cylinder walls or original thicker cylinder walls which require enlargening the case openings (=bore in).

All the racing engines had the thicker cylinder walls. I think any of the top end engine builders will advice to go with the thicker cylinder walls. It will cost more because of the machining work needed but it is the right way to do it.
Both slip in and bore in cylinders are available for the engines.

I went with the Mahle "bore in" / Motorsport cylinders in my "RSR" build. Here are some photos: https://m3supercar.1g.fi/kuvat/993RSR/Winter16/
thx for the education, bore in is the way to it correct.
Sire is offline  
Reply With Quote
Old 03-11-2017, 08:06 PM
  #32  
eddieb4
Addict
Rennlist Member
Thread Starter
 
eddieb4's Avatar
 
Join Date: Feb 2014
Posts: 987
Default

It debatable ... talked to George at Midwest Eurosport and he recommends sleeved. I can have him weigh in.

Newly powered coated engine bits.

Pic of old 3.6 jug and piston- if you look closely you can see that there is no groove for gasket and you can see oil residue where is was leaking out on the face of the jug. As I understand it, only a small percentage of "ringless" actually leaked at this junction. Mine was one of the small percentage of engines that leaked at the base cylinder area.

Next pic: New Mahle 3.8 jug ... you can see the groove.
Attached Images      

Last edited by eddieb4; 03-12-2017 at 03:40 AM.
eddieb4 is offline  
Reply With Quote
Old 03-12-2017, 02:10 PM
  #33  
onevoice
User
 
Join Date: Dec 2014
Location: N. Ala
Posts: 126
Default

Originally Posted by eddieb4 View Post

Pic of old 3.6 jug and piston- if you look closely you can see that there is no groove for gasket and you can see oil residue where is was leaking out on the face of the jug. As I understand it, only a small percentage of "ringless" actually leaked at this junction. Mine was one of the small percentage of engines that leaked at the base cylinder area.

Next pic: New Mahle 3.8 jug ... you can see the groove.
Interestingly though, the gasket was a crutch to stop the wetness, not the reason for it. The earlier 3.2 engines, and turbos, didn't have head gaskets, and weren't known to leak. I would hesitate to even call it a leak, because there is no oil there to leak, the combustion chamber side of the piston is never really wet with oil. Henry (from Supertec) says the design of the head causes it to warp somewhat from the clamping force of the head being torqued. So the wetness isn't really an oil leak, it is combustion byproducts, oily water and probably fuel from cold starts when the aluminum hasn't reached operating temp. Unless an engine has a serious problem, it is unlikely an engine will ever have enough leak there to ever cause more than wetness, not a drip.
onevoice is offline  
Reply With Quote
Old 03-12-2017, 03:13 PM
  #34  
John McM
Addict
Rennlist Member
 
John McM's Avatar
 
Join Date: May 2001
Location: Auckland, New Zealand.
Posts: 11,555
Default

Originally Posted by onevoice View Post
Interestingly though, the gasket was a crutch to stop the wetness, not the reason for it. The earlier 3.2 engines, and turbos, didn't have head gaskets, and weren't known to leak. I would hesitate to even call it a leak, because there is no oil there to leak, the combustion chamber side of the piston is never really wet with oil. Henry (from Supertec) says the design of the head causes it to warp somewhat from the clamping force of the head being torqued. So the wetness isn't really an oil leak, it is combustion byproducts, oily water and probably fuel from cold starts when the aluminum hasn't reached operating temp. Unless an engine has a serious problem, it is unlikely an engine will ever have enough leak there to ever cause more than wetness, not a drip.
I need to read more about this, but I recall reading a view that adding a gasket to early 964 engines was no longer an automatic choice. I think it was Perelet on Pelican
John McM is online now  
Reply With Quote
Old 03-12-2017, 04:24 PM
  #35  
eddieb4
Addict
Rennlist Member
Thread Starter
 
eddieb4's Avatar
 
Join Date: Feb 2014
Posts: 987
Default

Originally Posted by onevoice View Post
Interestingly though, the gasket was a crutch to stop the wetness, not the reason for it. The earlier 3.2 engines, and turbos, didn't have head gaskets, and weren't known to leak. I would hesitate to even call it a leak, because there is no oil there to leak, the combustion chamber side of the piston is never really wet with oil. Henry (from Supertec) says the design of the head causes it to warp somewhat from the clamping force of the head being torqued. So the wetness isn't really an oil leak, it is combustion byproducts, oily water and probably fuel from cold starts when the aluminum hasn't reached operating temp. Unless an engine has a serious problem, it is unlikely an engine will ever have enough leak there to ever cause more than wetness, not a drip.
Thanks for the education.
I made some uneducated assumptions and stand corrected ... I'm not going to quit my day job to become a mechanic that's for sure.
It's fun leaning though because what you say makes perfect sense!
eddieb4 is offline  
Reply With Quote
Old 03-13-2017, 03:55 AM
  #36  
Juha G
Addict
Rennlist Member
 
Juha G's Avatar
 
Join Date: Aug 2006
Location: Finland
Posts: 2,506
Default

Originally Posted by eddieb4 View Post
It debatable ... talked to George at Midwest Eurosport and he recommends sleeved. I can have him weigh in.

Newly powered coated engine bits.

Pic of old 3.6 jug and piston- if you look closely you can see that there is no groove for gasket and you can see oil residue where is was leaking out on the face of the jug. As I understand it, only a small percentage of "ringless" actually leaked at this junction. Mine was one of the small percentage of engines that leaked at the base cylinder area.

Next pic: New Mahle 3.8 jug ... you can see the groove.

????

Your photos show the top of the cylinder. There is no oil that can leak there. The base seal is on the bottom of the cylinder.

Also, I'm really curious to hear in what way a thinner walled slip in cylinder is better than one with original cylinder wall thickness (cost put aside)?
Juha G is offline  
Reply With Quote
Old 03-13-2017, 08:56 AM
  #37  
eddieb4
Addict
Rennlist Member
Thread Starter
 
eddieb4's Avatar
 
Join Date: Feb 2014
Posts: 987
Default

I've got it wrong ... I'll get down to the shop and be more thorough.
eddieb4 is offline  
Reply With Quote
Old 03-13-2017, 03:42 PM
  #38  
AVI_8
Addict
Rennlist Member
 
AVI_8's Avatar
 
Join Date: Aug 2014
Location: Prestwick Scotland
Posts: 47
Default

Originally Posted by Juha G View Post
????

Your photos show the top of the cylinder. There is no oil that can leak there. The base seal is on the bottom of the cylinder.

Also, I'm really curious to hear in what way a thinner walled slip in cylinder is better than one with original cylinder wall thickness (cost put aside)?
It's not better other than cost.
But as far as cost goes, where do you stop?, I would have presumed that the OP sat with his engine builder and agreed a specification fit for the type of driving that the engine will be exposed to.
Fitting the best of the best of everything can turn a 12K rebuild into a 25k rebuild which would be overkill on a road engine with occasional track use.
Wouldn't it be great though money aside!!
AVI_8 is offline  
Reply With Quote
Old 03-13-2017, 09:01 PM
  #39  
onevoice
User
 
Join Date: Dec 2014
Location: N. Ala
Posts: 126
Default

Originally Posted by Juha G View Post
????


Also, I'm really curious to hear in what way a thinner walled slip in cylinder is better than one with original cylinder wall thickness (cost put aside)?
Like a lot of things in Porsche-world, the real answer is probably "it depends". IIRC it is only a 2mm difference between the two, which is 1mm of wall thickness, or in numbers my brain calculates in, about 0.039". Enough to make a difference, maybe, but you are also weakening the case by the same amount. I have seen engine builders say they have seen large leakdown numbers using slip fit cylinders in as little as 10k miles, but that doesnt make a lot of sense to me. Nothing much is happening at bottom dead center in the cylinder, and leakdown numbers are done at top dead center. Why would the cylinder get out of shape at the top from a missing 0.039" at the bottom? Especially when the bottom is so lightly loaded?

Not saying it isnt the BEST way to do it, but does it really make a difference in the real world in a non-racecar?
onevoice is offline  
Reply With Quote
Old 03-14-2017, 03:06 AM
  #40  
JV911
Super User
 
JV911's Avatar
 
Join Date: Oct 2006
Location: Sydney, Australia
Posts: 3,449
Default

subscribed
JV911 is offline  
Reply With Quote
Old 03-15-2017, 04:34 AM
  #41  
Michael D'Silva
User
 
Join Date: Apr 2013
Posts: 120
Default

Originally Posted by onevoice View Post
Interestingly though, the gasket was a crutch to stop the wetness, not the reason for it. The earlier 3.2 engines, and turbos, didn't have head gaskets, and weren't known to leak. I would hesitate to even call it a leak, because there is no oil there to leak, the combustion chamber side of the piston is never really wet with oil. Henry (from Supertec) says the design of the head causes it to warp somewhat from the clamping force of the head being torqued. So the wetness isn't really an oil leak, it is combustion byproducts, oily water and probably fuel from cold starts when the aluminum hasn't reached operating temp. Unless an engine has a serious problem, it is unlikely an engine will ever have enough leak there to ever cause more than wetness, not a drip.

Good informative post.
I totally agree with this.. I have always asked where the oil comes from between the bottom of the head and the top of the cylinder...
My 964 motor had similar "leakage" to yours.. but I also had leaks at the base of the cylinders.. so did a full re build.
Michael D'Silva is offline  
Reply With Quote
Old 03-15-2017, 11:41 AM
  #42  
[email protected]
Basic Sponsor
Rennlist
Site Sponsor

 
Alec@Fabspeed's Avatar
 
Join Date: Nov 2006
Location: Fort Washington, Pa
Posts: 4,418
Default

I am officially addicted to this thread. Subscribed and looking forward to seeing how the build turns out Ed!
__________________
Alec Acuff
Porsche Performance Specialist
[email protected]
267-742-3047

Fabspeed Motorsport USA
155 Commerce Drive Fort Washington, PA 19034
www.Fabspeed.com

Ultimate quality T304L Stainless Steel Exhaust Systems, Carbon Fiber Air Intakes and ECU Tuning for Exotic Cars
Alec@Fabspeed is offline  
Reply With Quote
Old 03-15-2017, 02:35 PM
  #43  
ezinternet
Addict
Lifetime Rennlist
Member
 
ezinternet's Avatar
 
Join Date: Mar 2006
Location: Chicago, IL
Posts: 236
Default

Hi Ed

I had a similar bit of work done by George at Eurosport Racing in 2010 (time flies!) on my '91 964.

3.8 Mahle p/c, ARP bolts, ported head, 993 RS valves, Ti retainers, custom cam ... trans rebuild w a few new synchros, LWFW, RS clutch, JRZ ... I'm sure I'm forgetting some things.

I put on the Fabspeed exhaust w/heat. Great sound, and a modest drone that went away with time. I don't get enough heat from those small sized heat exchangers to drive in the winter in Chicago.

I also sourced a 964 Euro RS ECU. I recall George did some extra dyno work and replacing the pressure regulator to maximize that benefit.

The car is at Autobahn in Joliet if you'd like to see it or give it a listen/drive when next you're down there.

Can't say enough good things about George and his team, as I'm sure you know. You're in good hands.

Dyno results attached ... YhpMV ... I'm sure you'll love it

Best,
Ez
Attached Images  
Attached Images
File Type: pdf
EG Graph.pdf (981.1 KB, 37 views)
File Type: pdf
EG Data.pdf (1.22 MB, 154 views)

Last edited by ezinternet; 03-15-2017 at 02:40 PM. Reason: trying to make graph smaller
ezinternet is offline  
Reply With Quote
Old 03-15-2017, 07:20 PM
  #44  
Bill Verburg
Addict
Rennlist Member

 
Bill Verburg's Avatar
 
Join Date: May 2001
Posts: 10,548
Default

Originally Posted by ezinternet View Post
Hi Ed

I had a similar bit of work done by George at Eurosport Racing in 2010 (time flies!) on my '91 964.

3.8 Mahle p/c, ARP bolts, ported head, 993 RS valves, Ti retainers, custom cam ... trans rebuild w a few new synchros, LWFW, RS clutch, JRZ ... I'm sure I'm forgetting some things.

I put on the Fabspeed exhaust w/heat. Great sound, and a modest drone that went away with time. I don't get enough heat from those small sized heat exchangers to drive in the winter in Chicago.

I also sourced a 964 Euro RS ECU. I recall George did some extra dyno work and replacing the pressure regulator to maximize that benefit.

The car is at Autobahn in Joliet if you'd like to see it or give it a listen/drive when next you're down there.

Can't say enough good things about George and his team, as I'm sure you know. You're in good hands.

Dyno results attached ... YhpMV ... I'm sure you'll love it

Best,
Ez
Curious as to why you bought a 964RS DME?

Is that data flywheel or rear wheels?
Bill Verburg is offline  
Reply With Quote
Old 03-15-2017, 08:21 PM
  #45  
ezinternet
Addict
Lifetime Rennlist
Member
 
ezinternet's Avatar
 
Join Date: Mar 2006
Location: Chicago, IL
Posts: 236
Default

Originally Posted by Bill Verburg View Post
Curious as to why you bought a 964RS DME?

Is that data flywheel or rear wheels?
Hi Bill -

- At the time I was collecting bits and pieces for this C4 project, and I had thought that the RS DME would be a shortcut to a faster tune. I realize the ECU are functionally identical except for the chip/maps. Digging into my notes I see the ECU may of had or come with an AmD chip. I was hoping to avoid the LWFW stalling issues others had reported. After the dyno work I had a customized map anyway.

- The data is flywheel. The car was over there, and the engine over here.

Last edited by ezinternet; 03-15-2017 at 09:15 PM. Reason: correction
ezinternet is offline  
Reply With Quote

Thread Tools
Search this Thread
Quick Reply: 964 C2 3.8 Build Thread


Contact Us Advertising Cookie Policy Privacy Statement Terms of Service

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: