Turbo a 10.5:1 compression engine
 

Hey all,

I have seen a lot of talk about turbocharging (light boost) a 3.2L Carrera engine with 9.5:1 compression, but what are your thoughts on turbocharging 3.2L engine with 10.5:1 compression? Should you just change out the pistons for the US spec ones? Would the engine be that much closer to detonation at .5 bar? If another thread has already been started concerning this, please post the link. Thanks guys!

Could be done on E85, using twin plugs.

See it often on newer cars - aftermarket supercharging/turbocharging with higher compression.
5 lbs boost seems to be the limit on these factory cars (with no TP or other mods)

Well SAAB 9-5 Aero boosts 1.2 bar on 9.3:1 ex factory.

Also, factory C/R figures for Carrera mill are a bit ambigous. Lot's of people cc-ed the chambers and got different numbers.

I say a guy running whooping 1 bar of boost on 10:1 Alfa Romeo V6, using E85. I believe it was 2v/cylinder engine. I believe it's doable to have quite high boost on ROW Carrera mill, but not on what passes as fuel in US. E85 or shaving the pistons is the melody...

You have to remember all these newer generation cars which run higher C/R and higher boost are watercooled and have much more advanced engine management systems than the archaic Motronic DME's and also have knock sensors etc :(

If I were you, I'd slip in 9.5:1 pistons and whilst you've got the top end apart, put on some C2T head gaskets to drop the C/R even further to ~8.8:1 and you will be able to run 0.85bar (intercooled) all day every day for ~485 crank HP :cool:

I agree w/ WydRyd, any cars running that much compression with boost are much newer, advanced EFI systems, some are even using direct injection. You will surely have trouble with detonation i'm afraid. Even if you manage it well at first, with a fresh engine, as soon as you start to get carbon buildup, which you will when those valve guides get a taste of the extra heat that comes with boost, things will change. I'm currently experiencing detonation with a RUF RCT engine in a '94 RS America. A friend of mine bought one from an older gentleman in Illinois and it has terrible detonation at random times. Mostly at the torque peak, with some heat in the motor. It also consumes a fair amount of oil which is most likely taking up permanent residence in a new form in various parts of the combustion chamber. We've tried various fuel cleaners and it actually seems to amplify the problem. I guess they "soften" up the carbon and make more little "glow plugs"?? It has 70K miles on 94 valve guides and only runs .77bar with 8.5/1 and still makes at least 385hp-actually 365 to the wheels on a dynojet recently (it took 11 pulls to start detonating, AFR stayed perfect) BTW It has twin knock sensors w/ RUF EFI Just my $.02 good luck!!!

I have to agree with the gang. For example, I recently dyno tuned a couple of 2.4 liter Pontiac Solstices with aftermarket turbo kits ($4500+install). They are 11:1 and as such can only run 6-7lbs boost AND you have to pull so much timing to eliminate most of the detonation to run that power output is only 185whp on a Dyno Dynamics(so about 215 on a Dynojet). Even then the ecu is still pulling timing in certain instances. Throttle response sucks too. Rebuilds on our engines are just too expensive to play with detonation, a good used solstice/HHR long block is under a grand. Lower compression is the way to go, you may be able to machine the piston tops, I know it's done on the 3.6 NA pistons for turbo/supercharging.

The turbo and supercharger kits makers will tell you it won`t work,don`t do it. Yes it`s true that some modern turbo engines have high static compression ratios but the 3.2 Porsche at 10.5 is just not suited for it. You COULD run very low boost with the right chip and boost cooling but if you have the funds available by all means install the lower compression pistons,turbo gaskets and stronger rod bolts.As Wydryd says a reliable 500 HP is just around the corner with some simple mods and you`ll have no regrets doing it right...

Its not a 3.2L but a 993 with a stock 3.6L ( 11.5 comp) with 6psi of boost... its puting over 400hp at the wheels.
http://www.6speedonline.com/forums/s...ad.php?t=93992

So it can be done with a good EMG and tuning.

AHHHH, that's a different story! I thought you were referring to the 3.2 CARRERA motor!

Anyway, yes, it can be done on a 993 with the right changes to engine management. I believe the system running on that 993 is a Protomotive system. Protomotive have built their reputation on developing aftermarket kits for the naturally aspirated platforms and know their ***** when it comes to aftermarket turbocharging. Send Todd Knighton an e-mail... top guy ;)

I'm doing all of this in stages as I don't have all funds right away. I've just started the valve job, so I don't have a clear idea yet of how much I am going to be spending on parts. The compression and leak down test numbers were very solid when I had the tests performed last summer, so I don't suspect any surprises.

I have the 9.5:1 compression pistons in right now, and I'd rather not lower the compression yet as I don't know how long it will be until I actually get the turbo in there. Where should I spend my extra cash (between $1500-2000) to prepare the engine for turbo charging? From what I've read and heard from you guys, I'm thinking about installing raceware head studs and rod bolts. Any suggestions?

Definately do the bolts at the very least for starters and either use the 9.5 pistons and some turbo gaskets or get the lower compression pistons. On these motors even 9.5 compression with turbo is pushing it,why restrict your available boost even more? you`ll see no reliable performance gains using the high comp pistons.
lf you`re not sure when you can swing the turbo conversion don`t sweat it, running low comp pistons for a while won`t be as bad as you think.l ran a turbo motor on straight fuel injection for a while and it didn`t kill me,it was still fast enough to have fun in. Good motivation to complete it also..

I'm definitely following you on the "why restrict your available boost even more?" mentality. So simply by changing to turbo head gaskets I could lower my compression ratio? Could you send me a link to some gaskets that you'd recommend?

.......and are we certain that these gaskets are viable, ie deck height etc?

I have no idea. That's why I'm in here asking.

What exactly would turbo head gaskets do for me? Does it affect the compression or does it just make the engine more capable of handling a turbo?

Question: How do the C2T gaskets drop compression? I had these fitted and my heads were cut to accept them?

Les

rasises the head off the cylinder making for larger CC heads so to speak.

Persoanlly I would try to limit Your CR to 8.5:1 maybe 9:1 then boost the rest of the way..

Mine works wonderful off boost at 8.5:1 so don't worry. if you choose the correct turbo you will never no the difference. My friend has a t3/t4 and you can't even really tell when its boposting as it is boosting from right off idle all the way up..

Totally agree -

Builders generally recommend 7.5 for CIS and 8.0 for EFI as the ideal CR for a 911 aircooled turbocharged engine.
BTDT. Researched and received this answer from the builders I hold in high regard.

What would the C2T gaskets lower the compression to on stock Carrera?

It sounds like the preferred solution is install lower compression pistons. Have you guys found it more cost effective to get your existing, high-compression pistons machined or to purchase lower compression pistons? How much does it typically cost in either case?

You have to be careful when machining high compression pistons for lower compression. It can cause some distortion in the ring lands based on forging stresses that may be relieved by the machining process. I know there isn't a lot of quench in our engines, but just throwing spacers under the cylinders to lower the compression ratio can make detonation and pre-ignition worse. A careful study of the piston shape and its interaction with the combustion chamber should be done to ensure optimal combustion chamber shape.

for example supertec does both but I would suggest new JE pistons over machining unless you have delusions of 200k engine then go MAhle's..

Could you send me a link to the pistons you'd recommend? I can't seem to find any lower compression pistons for a 3.2. Is it advisable to do the C2T head gaskets in addition to the pistons, even if I'm not planning on building a monster machine?

Call Henry@supertecperformance 760-728-3062 for correct pistons/cylinder combos.. I personally did not use c2 head gaskets

If I were to swap out to 3.3 or 3.4 L pistons & cylinders, would I have to get my heads machined and purchase new head gaskets? If so, how much would I be looking at to get the heads machined?

No head gaskets on the 3.2 to begin with but you would have to chamfer the heads to prevent detonation.. not sure on cost be fairly inexpensive

Hmmm,you seem set on using the high-comp pistons for some reason. l`m guessing you hope your off-boost performance will be better with the 10.5`s? On paper that may be true but the reality is that your car will be much faster when you can dial the boost up and that will only happen running a lower compression ratio. My 3.2 running stock pistons gets full boost before 2000rpm, l seriously doubt l could expect noticably better performance with the euro-pistons. l had a chance to buy a set of the 10.5`s and l passed for one reason- l intended to boost the car. lf you truly intend to turbo your car the bottom line is that 10.5 pistons are the worst choice you could make for the pistons.The stock pistons will work but why bother? you`ve got the motor apart ,do what any experienced builder would do when building a turbo motor: install FORGED turbo pistons with a lower compression ratio. The 3.2stock cast pistons tend to break the ring lands under excessive boost, a far greater fear with the euro 10.5`s. While you have pistons out send them to Swain-tech for coatings
http://www.swaintech.com/ you`ll be glad you did. l realize not everyone has $10-k laying around to spend on a motor which is probably the best reason yet not to use high-comp pistons in a turbo build. Some people report detonation using the euro slugs with our gas,imagine how they are under boost...

I'm sorry for the confusion. I have 9.5:1 pistons in my car currently. I was just initially inquiring about "what if you had 10.5:1 pistons".

I'm trying to decide whether to purchase new pistons & cylinders or to get my 9.5:1 pistons machined to a lower compression. I'm just considering all of the costs if I made the jump to turbo pistons & cylinders.

Ok, so if I were to get new P & C's for my 3.2L, it sounds like I should go with the fully finned cylinders from the 3.3L C2 Turbo. If I were to keep the heads from my 3.2L, I believe I need the following:

1. "chamfer the heads to prevent detonation" ~ Ben
2. 0.5mm head sealing gasket
3. o-ring that goes at the base of the cylinder

Am I correct about #2 and #3? If so, anybody have any idea on the cost for those parts? Please chime in if I need anything else. Thanks!

Hello, the project referred to in that post is in fact mine, here is a working link:
http://www.6speedonline.com/forums/showthread.php?t=93992

Todd K certainly does know his stuff, but there are no Protomotive parts on my car. ;) It is a completely custom setup I built myself, including an aftermarket ECU that is completely programmable (which I also tuned myself).

To the thread starter: As others have already said, having full control of ignition timing is key to keeping detonation at bay when running boost and higher CR. I am only running 6 psi on my setup, and I have to keep timing relatively low to run normal pump gas. If I run 110 leaded I can of course run more timing (and make a bit more power) without seeing any knock. Also, using an ECU that has knock feedback controls (such as the AEM I am running) can save you in case you have a bad tank of gas.

If you have any questions feel free to send me a PM. Good luck with your project. :cool:
Brett

I really like the extra large single turbo with stock C.R. When does your boost start coming on?