Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > 911 / 930 Turbo & Super Charging Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
rsrmike's Avatar
 
Join Date: Jan 2008
Location: Birmingham, AL
Posts: 538
3.6 Pistons 8.5-1 comp. ratio

I was wondering what some of you thought about machining stock 3.6 NA pistons down to from 11.3 to 8.5 to 1? How common is this? Does anyone have much experience with it?

I did a search as I'm sure it's been discussed but I was hoping to start a new discussion about turbocharging NA 3.6 engines. Primarily want to talk about pistons and the different options...

Any thoughts? Thanks,
Mike
Old 02-29-2008, 06:24 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
930gt-40r's Avatar
 
Join Date: Jan 2007
Location: Boca Raton, FL
Posts: 2,063
Set of stock 993 turbo pistons/cylinders is perfect for this application. I know more than a few people that make 700+ on stock 993TT pistons and they are probley best for the street for expansion purposes.
__________________
Kris @ Tech9
86' 930/GT-40R Sold
94' Rustang GT daily (long gone)
2008 C6/Z51 Corvette
Old 02-29-2008, 09:20 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
 
copbait73's Avatar
 
Join Date: Nov 2003
Location: Chesterfield IN
Posts: 1,316
Garage
Quote:
Originally Posted by rsrmike View Post
I was wondering what some of you thought about machining stock 3.6 NA pistons down to from 11.3 to 8.5 to 1? How common is this? Does anyone have much experience with it?

I did a search as I'm sure it's been discussed but I was hoping to start a new discussion about turbocharging NA 3.6 engines. Primarily want to talk about pistons and the different options...

Any thoughts? Thanks,
Mike
Mike I have the same interest.
Not sure about machining stock used pistons. Maybe there is an answer out there. Also, I have not pursued the option of finding used or new factory TT pistons. I just assume they are rare and expensive.
However, just this week I contacted JE Pistons. They replied they can supply 8:1 or 8.5:1 C.R. pistons. Cost is $175 each with pins, locks and rings, 4 week leadtime.
Old 03-01-2008, 06:34 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
930gt-40r's Avatar
 
Join Date: Jan 2007
Location: Boca Raton, FL
Posts: 2,063
Don't get me wrong, JEs are bad@ss, but are they really safe for street use?
__________________
Kris @ Tech9
86' 930/GT-40R Sold
94' Rustang GT daily (long gone)
2008 C6/Z51 Corvette
Old 03-02-2008, 06:41 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
Join Date: Jan 2005
Location: Western Canada
Posts: 2,058
Quote:
Originally Posted by 930gt-40r View Post
Don't get me wrong, JEs are bad@ss, but are they really safe for street use?

why wouldnt they be?? Just wondering
Old 03-02-2008, 06:48 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
rsrmike's Avatar
 
Join Date: Jan 2008
Location: Birmingham, AL
Posts: 538
I'm curious about the J&E pistons as well, how well do they really work with the nikasil? Do you need more clearance? Do they make noise when cold?
That seems pretty reasonable if they just "drop in"

As far as 993TT goes, What would you have to do to fit these?

I know the top of the piston extends past the top of the cylinder, do you need the TT heads too or can you machine this clearance in a NA head??!!

I guess I should fess up what started this...

I just tore down a RUF RCT for a valve job expecting to see all sorts of neat stuff in the motor (it made 365 whp @ .77bar)

Well, it appears to have stock pistons with the tops machined off!! ( I could be wrong)

Needless to say, I was a little surprised at first, but my wheels got to turning pretty quickly... It even uses stock NA heat exchangers, there is a K27 where the CAT used to be. The NA cat is moved to where the pre-muffler used to be. Imagine that, 400hp through a stock C-2 CAT.

Long story short, I was wondering how many people were into machining 3.6 pistons for lower compression or if it's been one of those best-kept secrets, until now...

Thoughts?

Last edited by rsrmike; 08-04-2008 at 08:53 AM..
Old 03-02-2008, 07:05 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
930gt-40r's Avatar
 
Join Date: Jan 2007
Location: Boca Raton, FL
Posts: 2,063
I bet that motor is really cool and has boat load of little tricks that are not so apparent.
The JEs are slip fit into the cylinders and I believe that they make up for the tolerences by simply machining the pistons smaller. But at cold startup, there has to be a level of slap- because the pistons are machined smaller for room to expand due to the fact that they are forged, and the fact that they are for an air cooled application. So think of the scenario on a street car when you are late to go somewhere and dont have time to let the engine get to running temp before driving... I dont know, I dont have any experience with forged pistons on a street car.
I would be cautious when machining the tops of the stock pistons off, I would worry about heat quenching ability.
__________________
Kris @ Tech9
86' 930/GT-40R Sold
94' Rustang GT daily (long gone)
2008 C6/Z51 Corvette
Old 03-02-2008, 07:19 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
7.0:1 > 11.3:1
 
Join Date: Oct 2003
Location: Calgary
Posts: 1,895
Garage
Granted this appears to have been done on the RCT, someone should measure the dome/crown thickness of the NA piston because this sounds like a huge CR drop (11.5 down to 8.5). Perhaps someone can do a mathmatical calc based on the cross section bore area and determine the needed reduced dome height.

Years ago I messed with turbo Datsuns and toyotas, on one application we machined the dome for reduced compression height and the piston eventually split across the crown. It was however a cast piston, and by comparison the 3.6 pistons may be forged or cast with different metalurgy.

Another trick with Datsuns was to install shorter rods from another Datsun motor. Is there any possibility that some of the other Porsche rods have a slightly shorter beam and retrofit into the 3.6?

Back in the 80s JE had huge expansion factors but I've read that their metalurgy is far improved since then. I'd be inclined to ask what clearance they spec for the turbo 3.6 bore. For my Datsun race motor they specified 8 thou on a 96mm bore, but again, this was 20 years ago. Not streetable at all.
Old 03-02-2008, 08:33 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered User
 
rsrmike's Avatar
 
Join Date: Jan 2008
Location: Birmingham, AL
Posts: 538
Interesting point Jim, in fact, that's the very same train of thought that kept me considering it. Nice work by the way, I checked out your EFI conv. The manifold blocks were very trick. I have great respect for attention to details like that.


I would expect the exhaust valves are sodium filled. Do those come in NA 3.6's? I know they are in the turbo. These valves have 964 p/n's, I took one head apart to confirm the guide were in fact worn out.

I'd like to try to cc the combustion chamber volume and try to figure the comp ratio if possible. I've never done this before and would like a little help I didn't have time to play before shipping the heads out to Ollies to get freshened up but perhaps when they come back..

The rods are absolutely not stock 3.6 rods though...

I might add that part of the reason we took this thing down is it had a bad random detonation problem and some oil leaks. Not to mention it burned 2 qt's of oil in less than 1Kmiles.

It also had massive carbon build-up from the oil consumption which I assume contributed to the detonation. I dyno tested it before teardown to see if it would detonate and if so what the AFR was when it did. It took 11 pulls before even a hint of detonation. But it's easy to make it do it at 4,000 rpm in 3rd on the highway. I suspect the MAF may be going bad. It has one similar to a mid '90 VW/Audi When my friend bought the car a few months ago I discovered the airfilter element wasn't installed quite right and there was lots of dirt on the MAF. I cleaned it and it seemed to help for a short time.
I dunno, hopefully it won't detonate when I put it back together with no carbon and less oil in the air/fuel mix.

This just seems like a cheap way to go for guys looking to turbo their C-2's like many of you 3.2 guys are doing right now.

I also know of several supercharged 3.6's in desperate need of lower compression...

Anyone willing to donate an unusable 3.6 piston to the cause for a little disection?
The machine shop next door has a great bandsaw...

Last edited by rsrmike; 08-04-2008 at 09:12 AM..
Old 03-02-2008, 07:43 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Registered User
 
930gt-40r's Avatar
 
Join Date: Jan 2007
Location: Boca Raton, FL
Posts: 2,063
I think I got a "Detonated" 3.8 mahl piston laying around- you got to get me another nice ashtray and Ill let you get it.
__________________
Kris @ Tech9
86' 930/GT-40R Sold
94' Rustang GT daily (long gone)
2008 C6/Z51 Corvette
Old 03-02-2008, 07:52 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Registered User
 
copbait73's Avatar
 
Join Date: Nov 2003
Location: Chesterfield IN
Posts: 1,316
Garage
Mike:
A web search finds this Anderson review:http://www.911handbook.com/articles/f_rufcar.html
Does that engine have stock cams?
Article says 8.0:1 pistons, another article says 8.5:1 but they are said to be of of RUF source. What is the deck height?
Is the piston pin centered in the rod bushing or offset?
Look closely at the turbo, specifically does it have the same size turbine housing, compressor and turbine impellers? Article says the turbo configuration is unique to his spec.
Old 03-02-2008, 08:04 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Registered User
 
beepbeep's Avatar
 
Join Date: Jun 2001
Location: Sweden
Posts: 5,565
You are turbocharging a stock 3.6 N/A? go for 993tt pistons and H-beam rods. They fit the bill perfectly and I watched such engine produce way over 800hp.

Machining stock 11.3 (well I believe *real* C/R is more like 10:1) piston might leave the piston crown too thin and lead to crackning.

JE pistons are good too but aren't as metalurgically advanced so you'll have some piston slap when engine is cold. Not too dangerous but annoying.

As far as I remember, 993 engines with "dished" heads were produced for a year or too, and pistons were the same but jugs were shorter and heads were deeper.

A set of used re-ringed 993tt is probably the cheapest and best ticket here. They are made of tweaked alloy and will be quiet at startup. They are also tough as nails. Only problem with them is that they are somewhat heavy...so don't rev past 7000RPM (In turbocharged engine, this is usually not the problem as they tend to produce max power fairly low unless tuned to max).
__________________
Thank you for your time,
Old 03-03-2008, 05:58 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
Registered User
 
Join Date: Feb 2008
Location: Bayside Wi
Posts: 2,575
3.3 Mahle @ approaching 500 rwhp on dyno with fresh rebuild TT. Went to J E 3.4 on recomendation of race shop.

Last edited by voitureltd; 03-03-2008 at 06:54 AM..
Old 03-03-2008, 06:50 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #13 (permalink)
Registered User
 
copbait73's Avatar
 
Join Date: Nov 2003
Location: Chesterfield IN
Posts: 1,316
Garage
Quote:
Originally Posted by beepbeep View Post
You are turbocharging a stock 3.6 N/A? go for 993tt pistons and H-beam rods. They fit the bill perfectly and I watched such engine produce way over 800hp.

Machining stock 11.3 (well I believe *real* C/R is more like 10:1) piston might leave the piston crown too thin and lead to crackning.

JE pistons are good too but aren't as metalurgically advanced so you'll have some piston slap when engine is cold. Not too dangerous but annoying.

As far as I remember, 993 engines with "dished" heads were produced for a year or too, and pistons were the same but jugs were shorter and heads were deeper.

A set of used re-ringed 993tt is probably the cheapest and best ticket here. They are made of tweaked alloy and will be quiet at startup. They are also tough as nails. Only problem with them is that they are somewhat heavy...so don't rev past 7000RPM (In turbocharged engine, this is usually not the problem as they tend to produce max power fairly low unless tuned to max).
Goran, 930GT, Mike, glad to see you in this discussion. My 3.6N.A. (TT) will hit the street (planned this summer) with stock high compression then come down over the winter for C.R. reduction and or setup for E85. I really don't want much more than 400HP because it's in an RS flared '73, weight reduced to roughly 2000#. However, I want RPMs and would like a usable 7000RPM range and your reminder of component weight is a good one.
I'll watch out for 3.6TT parts.
Old 03-03-2008, 06:56 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #14 (permalink)
Registered User
 
Join Date: Jan 2005
Location: Western Canada
Posts: 2,058
Quote:
Originally Posted by beepbeep View Post
You are turbocharging a stock 3.6 N/A? go for 993tt pistons and H-beam rods. They fit the bill perfectly and I watched such engine produce way over 800hp.

Machining stock 11.3 (well I believe *real* C/R is more like 10:1) piston might leave the piston crown too thin and lead to crackning.

JE pistons are good too but aren't as metalurgically advanced so you'll have some piston slap when engine is cold. Not too dangerous but annoying.

As far as I remember, 993 engines with "dished" heads were produced for a year or too, and pistons were the same but jugs were shorter and heads were deeper.

A set of used re-ringed 993tt is probably the cheapest and best ticket here. They are made of tweaked alloy and will be quiet at startup. They are also tough as nails. Only problem with them is that they are somewhat heavy...so don't rev past 7000RPM (In turbocharged engine, this is usually not the problem as they tend to produce max power fairly low unless tuned to max).

Hey goran,

So did you ever get your 911 running? Whats your website again?

What do you guys think of running a stock 993 3.6 with low boost? Theres a link to another site of a 993 with single turbo running a stock motor with low boost making 400Hp and it has been holdong up fine for almost 2 years .

What do you think
Old 03-03-2008, 09:07 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #15 (permalink)
Registered User
 
Join Date: Jan 2005
Location: Western Canada
Posts: 2,058
Another thing... can you use 993NA heads with the 993tt pistons+cylinders?
Old 03-03-2008, 09:12 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #16 (permalink)
Registered User
 
930gt-40r's Avatar
 
Join Date: Jan 2007
Location: Boca Raton, FL
Posts: 2,063
copbate- you could get 400 horse out of your motor with out breathing on it too hard with a low boost turbo setup- you may want to use a higher exhaust A/R in an attempt to keep the heat out of the combustion chamber. Also because you are high compression- the higher A/R wont kill you because you already make power N/A. Low boost/big volume I think is the key to not stressing the motor out- pressure usually finds the weakest point.

Herman maire- I believe that you can indeed use stock 993 heads (less exhaust valves maybe?) I would however check with a reputable Porsche machine shop. I also recomend machining for a ni-resist ring (I know there are head gaskets on these)
993 N/A head would be cool though- I think they have bigger ports/valves- but best of all they are already twin plug.
__________________
Kris @ Tech9
86' 930/GT-40R Sold
94' Rustang GT daily (long gone)
2008 C6/Z51 Corvette
Old 03-03-2008, 09:29 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #17 (permalink)
Registered User
 
beepbeep's Avatar
 
Join Date: Jun 2001
Location: Sweden
Posts: 5,565
It all depends on what do you want. A stock C/R 3.6 N/A engine won't take much boost before it goes completly out of whack regarding effective compression ratio so C/R will be a limiting factor.

You can relieve this soewhat by using E85 (cheap, needs roughly 40% more fuel flow for same lambda) or race fuel (fussy, expensive). My wide-a$$ed guesstimate is that you shouldn't try to boost more than ~0.5 bar on stock C/R and best petrol found in US...and you should keep your eye on ignition timing while doing that. But yeah, it can probably be done. Go on E85 and you could maybe extend that to 0.7 bar...which would provide some serious power.

About "having 7000 RPM usable range" with cheapskate turbo-conversion: I advise against reving it past 65000. A lighttly boosted stock C/R 3.6 would utilize smaller turbos and give you very nice and usable torque. I bet that such setup would give you max torque around 3500-4000 RPM and max power between 6000-6500 RPM. After that, the huffers would just fall flat on their arses and blow hot air. Your rod bolts will also have a field day and engine will produce more racey noise but not so much power.

It can be relieved by using hotter cams and bigger turbochargers but then you are out of "cheapskate"-range and into "buying expensive parts"-range. And if you are going to buy those, you might as well buy new pistons

So yeah, mildly boosted 3.6 running on E85, using stock cams and fitted into lightweight car will give very driveable and troublefree ride (as long as boost and fueling are kept in check).

As we all know, it's not the top horsepower figure but swept area under power curve that makes things accellerate faster.

So to round it off: if planning to do all this w/o lowering the C/R, concentrate on getting fueling (=lambda), ignition (not too agressive) and boost (not too high) right and don't hunt for expensive 7000 RPM noise-making setup. Chances are the car will be very tractive and torquey even w/o wringing the motors neck. Especially so if fitted in lightweight car.

P.S.
On such turboconversion, you should pay special attention to your ignition system, especially so if using stock distributors. Snapped dizzy sync-belt will leave only one row of plugs firing which might be very problematic when running high effective compression ratio (due to stock C/R and turbocharging).
__________________
Thank you for your time,
Old 03-03-2008, 09:30 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #18 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 01:44 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.