Jussi

I'm building my 993TT engine with new 3.8 ltr P/C kit.
Cylinders are Nickies and Pistons JE.
Is it reasonable to make P/C kit so that compression ratio is more than original 8:1?
Bigger ratio should give better torque values but how about heat and reliability..

Few examples with higher compression ratios:
RS Tunings BiTurbo: 3.6ltr 8.4:1 535hp/754Nm
Eurotech Twin-turbo 993: 3.6ltr 9.0:1 530hp/620Nm

Jean

Juha

You will find a lot of good advice from our gurus here, in my opinion, with the single-plug 3.8 P&C and higher compression ratio, you will need to keep your boost levels at or below 1Bar otherwise you will end up with massive amounts of heat, which in turn will affect your performance as knock sensors pull your timing.. You will also want to use race fuel most of the time while you are still with single plug.

One has to question why you want to do it. As you said, normally the bump in compression will increase responsiveness to your engine while off boost, and provide you with better torque, which you are now getting with the 3.8 displacement bump.

The 533hp RS engine you are mentioning, I believe was based on a N/A twin-plug engine, not a TT engine.
I would stick to stock compression, especially with the P&C you chose to use (non Mahle).
Jean

Geoffrey

You can go to a higher compression ratio, but you will need to run lower boost levels. This is primarily a function of cylinder head temperature more than anything. At 8.0:1 and 1 bar of boost, you are going to be running near 210 degrees C. I like to keep the cylinder head temps below that number when used in a racing environment. On the street you may be able to run a little more boost since full boost, full throttle applications are few and far inbetween compared to a engine used on the track. If you run the higher compression ratio, I would suggest also going to twin plug. As you begin to have a piston with a dome, you loose the squish area and the combustion chamber becomes less efficient and will requie more ignition timing. This is not a desirable scenario.

Kevin

I caution anyone that builds a 3.8 102mm engine and going over 1bar.. Extensive welding patterned after the EVO engine builds and installation of stepped flame rings are in order. It is also foolish to build such and engine without adding the dual plug arrangement as Geoffrey mentioned.

Jussi

Jean:
That RS Tuning BiTurbo is twin-turbo conversion from 964 Carrera 4. I couldn't find any mention from twin plug system. Story says other things like forged pistons, bigger valves, special profile camshafts, modified combustion chambers. Top speed is unbeliavable 220 mph / 355 km/h ! (source 911&Porsche World No 51 1998)
Are you running standard 8.0:1 compression with your 3.8TT conversion?
You must also use much more boost than 1bar when you achive that massive 700hp. What are maximum bar?

Also that another example which use high 9.0:1 compression says that the fires are still lit by the standard 993 twin-distributor set-up. What is that, is it twin plug system?

When I set my question about higher than 8.0:1 compression, I mean just little more compression. Like 8.1:1 or 8.2:1 or 8.3:1. Has anyone tested these kind of compression. Engine would be more responsive, more torque, better fuel economy etc.

I'm not gonna use my car in race track. Just "normal" street and traffic lights race - sometimes
and also in special 1/4 mile and top speed days which are just few times per year.

Jean

Juha
The Carrera 4 engine is a twin-plug, it has dual distributors and 12 spark plugs.

https://rennlist.com/forums/993-turbo-forum/237044-rs-tuning-tuned-tt911-article.html

As I mentioned earlier, heat will be your ennemy to performance by going this route with 3.8 and single plug, and you will have to limit your boost, but you can have an American muscle V8 like acceleration from 2k RPMs between red lights, if this is what you would like.

You need to make choices. Check out user "edpurplett" on this board and his higher compression 3.8TT for more info. That car has very extensive work done on it.

For your 520HP, 12k Euro objective, I would definitely keep the 3.6 even if you need to buy P&C anyway. Unless your tuner knows how to calibrate a Motronic for twin plug usage.

To answer your question, my engine is not a typical TT engine, it is based on pressure sensing, uses a Carrera Motronic, has Garrett turbos, has almost not exhaust restriction, modified intakes, etc.. It "showed" 700hp on the engine dyno at 1.14 Bar and race fuel, but I would expect to be running around 600+ on the road in its current configuration at 1 Bar. Then again, the budget is not the same.

Please keep in mind that I am not a mechanic, nor tuner nor professionally related at all with engines or Porsches so take my POV with a grain of salt.

Jussi

That twin-plug system seems to be necessary when using higher than 8.0:1 compression. How much these cost and who sell these?

Because I have now limited 12k budget, is it possible first convert engine to 3.8TT with 8.5:1 compression & 0.9 bar boost
and later, just change this twin-plug system and reprogram motronic again with 1.1 bar without changing any already converted parts?
I mean that I'd buy the right parts now for future needs, so I can minimize cost when stepping forward to "stage 2".

That 3.8 ltr Nickies/JE set will come with CMW flame rings and Pistons with special coatings.

Thanks for your help
-js

Kevin

I'd recommend purchasing Mahle 102mm pistons and liners... (strongly recommend it)

Have you received a labor estimate to rebuild your engine/topend?

In order to go back in to install twin-plugged heads you are spending alot of labor (twice)

The twin plug option is very reasonable.

You will have to reprogram when you step up to the 3.8ltr regardless.

Ezzy

Newb question. I thought the 993's 3.6 had twin plug heads. Is it the 3.8 watercooled motors that had the twin plugs? Maybe I'm confused because of twin distributers?
Thanks,
EZ

dbf73

Normally aspirated 993 3.6 has twin plugs. Twin turbo has single plugs.

Ezzy

Got it - Thanks.
EZ

edpurplett

Hola,

Just my few thoughts on 3.8's... I have approx 8.8ish static c/r... however I run .8 or .9 bar springs... about 600hp and 550 ft lbs....on 91 octane...(I run 94 Sunoco here vs Ca where the dyno is/was) as Jean says the big difference is insane torque low.... my car feels just like a 535 HP crate ford 460 in a five speed cobra with 3.36 gears..in 2400 lb car.... there is Nooo lag.... but again to Jeans point I can't even utter what an engine like this costs.... (with all the goodies to hopefully keep it together for a long time more importantly)

But the stock EFI MAF will only flow about 490ish HP....just as a case in point, assuming you have the turbos, ignition, twinplug, exhaust, fuel, ...

But a lot of this unfortunately is a moot point with the 12k... also what is your intended use.. I am mostly a street guy.. and as Geoffrey patiently points out :-)... if for track it's a little, if not a lot, different....

I and the others are absolutely not trying to discourage you, but trying to help you save money, time, and your sanity long-term.. and avoid a 'poof' in your future.... because as much as everyone thinks they can live with lower power the urge to 'turn it up' is sooo strong.... so...

Concerning twinplug...and the general 'upgrade' path issue.... JMHO, I am just a turbo nut and home wrench, caveats galore :-)...and sort of kevin's point.... you might be able to bare bones it and get a 3.8 for 12k, though th e P/C's alone are insane.... if you do not do the twin-plug, flame rings, better rods, welded heads, etc.... what will be your exact path to "stage 2".. this is more rhetorical....

There will be money 'respent' since you can't have 8.5+ cr , and then add alot more boost-HP...., and if the above mods are not done IMHO, the 'next level' will either get past your head seals, do in you rods, crack your heads, run your heads wayy too hot and cause myriad other issues etc....

the other issue is when do you need to add bigger turbos, headers, exhaust.. these things sort of work in 'logical groups'... there is the dependability issue which we have been addressing, but there are certain minimums for what you need just to produce X power.... (turbo sizings etc.) e.g. my Garrett Super 60's could NEVER reach 700 HP like Jeans engine.. conversely his larger turbos can't possibly spin up fast enough to produce 550 ft lbs by 3700 rpm... is this making sense?? Read Porsche phd's , Kevins, Geoffrey's , Viperbob and I'm sure others posts on HP and the parts required to make it....

unless you are a good boy :-) and keep the boost low.... kevin/Jean/Geoffrey/Viper may have a better feel at what the practical and safe limit would be on boost and CR without the mods... and then you could decide on when to step up to power and longevity mods.. I really dont see any other way... jsut my 2c...

I'm only rambling on since you mention 'monster' type of motors initially and big HP... HP is never cheap, HP and depandability are REALLY expensive.. :-)

ed

Jussi

Thanks a lot for your comments Ed and also others.

I like to specify my "Stage 1" parts (prices are in Euros):
- Carnewal LWF kit, 1400
- Nickies/JE 3.8 with special coatings and CMW flame rings, 4100
- ARP head studs, Pauters rods, Sport cams, 3000
- Complete gasket and bearing set + FPR 5bar, 1200
- Current turbo rebuild conversion to GT1 (K24wheel) and ECU reprogram, 1500
these makes total cost of 11k without labour costs.

So my questions is:
Is it reasonable now to choose these P/C kit so that compression ratio is 8.5:1 and tune ECU(timing,boost etc) to support this combination. Boost can be moderate 0.8bar.
And later step to "Stage 2" level which just consist of Twin Plug system without any other modification except ECU reprogramming to support full boost like 1.2 bar.
Does this make sense? or am I just dreaming

-Juha

Kevin

Have you seen a 993TT forged piston? Either 100 or 102mm? JE makes good pistons, however, they aren't in the same league that the Original Equipment Mahle's provide. Do you realize that the piston is designed to run into the cylinder head. Most engine designs have the piston stopping at TDC at or below the cylinder head gasket. But the 993TT extends past the gasket and into the heads.

I am writing all of this to say that you cannot beat the Mahle Pistons and liners for this application.

Jean

js

What Kevin said confirms what I had mentioned to you earlier. We are just highlighting what we know, the decision is your obviously.

You cannot do now the stage 1 and then go the twinplug route etc.. Rather, you can, but it will end up costing you MUCH more. Another serious problem youwill face is finding someone who will be able to reprogram your Motronic for a twin plug setup, if your local tuner tells you he should be able to do it, don't be so sure, only a handful can.

To close and in summary, I cannot recommend you to go with higher compression, nor with 3.8, nor with JE and nickies. I would keep it simple, buy a tested and proven package, or build it yourself but using tested and proven parts.
You will find dyno charts here for high compression and stock compression, Edpurplett had posted his chart and mine in the same thread not too long ago, made on the same engine dyno.

Cheers,
Jean