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Torque EFI vs. Transmission

I want to get more low end torque. I have a '91 965 w. the following engine mods:
8:1 compression pistons
B&B headers & muffler
EBC currently set at 0.7 bar
Twin plug w. crank fire
DWUR
Cold air intake

The new pistons have improved low end torque quite a bit, but it's still not good enough.
  • Does EFI improve low end torque?
  • How much of a difference would it make to put in a 993TT transmission?

I don't want to spend the money on doing both. Which one would give the biggest increase in pre boost torque?

Cheers.
Old 01-31-2010, 06:12 PM
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I know that the transmission will not improve torque, but it should improve drivability.
Old 01-31-2010, 06:14 PM
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The stock G50/50 has a pretty tall first gear. Those that have changed to a 6 speed seemed quite happy with there choice and even reported it transformed the car. However, you will need to get a limited slip added. Changing out 2-5 can make a significant speed potential but not low end.

Still, it dose not cure the real issue.

EFI dose allow for more ideal AFR's, which can make a difference.

What it dose best is to get the restrictive metering plate and assembly out of the way.

This dose for the intake side of the turbo what removing the cat and adding a straight through muffler dose for the hot side.

Thus, boost onset will come sooner and there will be less lag (time between boost onset and full boost).

The compression bump was equal to about 5% more pre boost power. Twin plugs about the same amount, making it a 3.5 adds about 6%. If you still have the stock clutch, a cup style unit removes a lot of mass for quicker response.

Cams and a different turbo can have an effect to.

Basically, a good efi conversion w the right cams, a bit larger intake ports, and the righ turbo will make a significant difference. With that your trans will seem near perfect.

JMO.

Last edited by 911st; 01-31-2010 at 08:53 PM..
Old 01-31-2010, 08:51 PM
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You do not list what turbo you have. If stock 7200 11/11 you can switch to a K27S an knock off another 300rpm of threshold which will move the torque curve and help driveability.
Optimizing spark and fuel will significantly improve driveability.
SC cams will move the torque band lower and fatten it up.
If wanting to spend big money swap in the G50 from an '89 930 as they have lower gears.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 01-31-2010, 09:11 PM
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Does the 993tt transmission come with limited slip? Do you know how much of an improvement this would be over the G50/52?

I am still running the stock turbo. I have read mixed reviews about the HF and HFS turbos. Can you shed some light on this?
Old 01-31-2010, 10:43 PM
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Quote:
Originally Posted by Pinsko View Post
I want to get more low end torque. I have a '91 965 w. the following engine mods:
8:1 compression pistons
B&B headers & muffler
EBC currently set at 0.7 bar
Twin plug w. crank fire
DWUR
Cold air intake

The new pistons have improved low end torque quite a bit, but it's still not good enough.
  • Does EFI improve low end torque?
  • How much of a difference would it make to put in a 993TT transmission?

I don't want to spend the money on doing both. Which one would give the biggest increase in pre boost torque?

Cheers.
What does your ignition curve look like? What type of crankfire ignition you running, Electromotive? Are you using the vacuum advance feature?
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'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P
Old 02-01-2010, 06:53 AM
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Quote:
I am still running the stock turbo. I have read mixed reviews about the HF and HFS turbos. Can you shed some light on this?
If your wish is to move the torque range to a lower rpm level then you do not want a HF or HFS but a K27S. The same power level and capability are retained with an addition of lower threshold.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 02-01-2010, 09:38 AM
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There are a couple of things you might try in the mean time.

Did you change out your Wast Gate spring for a lower boost spring? If not you have a .8 bar stock spring and the EBC is not doing a thing for you. If you set the EBC at just a little over the WG it will keep the WG closed a little tighter as you get near full boost. Thus it should help you at about 3000rpm a bit.

I see you have a D-WUR. I made my own 7 years ago and used it to adjust my AFR's so I was 14.5 at idle, droped with any acceleration to 13/1 untill boost came on for max power.

I also used what I called a 'drop and catch' strategy. I started by noting my manfold vac at idle and freeway cruse. In the program cells just out side that I dramitically lowered control pressure. This got the metering plate moving as fast as it phylicall could with acceleration. Then after a manfold vaccum started to recover I rased control pressure only as much as I needed to maintain normal AFR's and keep it from going to rich.

This made a significant difference in improving my pre boost response.

Again-- turbos do not like resistance after the turbine or before the compressor intake. This strategy reduces the intake restriction enough to be felt.

Your twin plug ignition curve may be suspect. Get the specs on it. Twin plugging on its own should make for a significant improvement off idle.

It really seems like you need someone that really knows what you are working with to get it all dialed in.

You have a great set up as it is and it should be a lot more responsive than a stock C2 Turbo.
Old 02-01-2010, 10:11 AM
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Iinstalled my EFI in two steps. First I installed the fuel system. This made an improvement in what I would call throttle response. The engine was more lively at part throttle. Then I installed ignition control. This made and even bigger difference. I would charaterize it as much more actual torque (and power). Finally, I installed my titanium aluminide turbo, still at 0.7 bar. This made a smaller difference, but noticable.
Old 02-01-2010, 12:50 PM
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1st gear always seemed way tall in the 930 box until I went with EFI (and a few other go fast parts). Now I'm only in 1st gear for a couple of seconds so any shorter and I'd be bouncing off the rev limiter faster than I could shift.
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Old 02-01-2010, 01:59 PM
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Quote:
Originally Posted by WERK-I View Post
What does your ignition curve look like? What type of crankfire ignition you running, Electromotive? Are you using the vacuum advance feature?
This is the primary way to improve torque - spark control. By managing spark and coordinating fuel delivery, you can get very good low end performance in these cars. The trick is not too much advance or you'll get killer detonation in these antiquated air cooled chambers. Before boost kicks in, I have around 36 degrees of timing with 8.0:1 CR pistons. This gives me 496 ft lbs of torque and 525 hp. If I was a bit more brave, I would try 40 degrees to eek out more low end - but I'm very happy where it's at. Most everything else mentioned here just helps HP.
Old 02-01-2010, 05:18 PM
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+1 ideal timing and AFRs.


FYI,

I do not think Don is running 36 deg on boost so please do not try it. This is probably at curse and after at least 2500rpm with very little load and is pulled back quickly with accel and boost onset.

I could be wrong.
Old 02-01-2010, 05:41 PM
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Keep in mind, this is a rather expensive upgrade if you want to do it to the same level as OEM.
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Old 02-01-2010, 05:46 PM
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Quote:
Originally Posted by WERK-I View Post
What does your ignition curve look like? What type of crankfire ignition you running, Electromotive? Are you using the vacuum advance feature?
I bought the crankfire kit from Clewett Engineering. The following is listed on the invoice: XDi-2 Ignition System dual plug, Rotary A/C pulley w. 2 bar map sensor

I don't know, what the ignition curve looks like and I am not sure, if I am using the vacuum advance feature. How can I find out about both and how should they be set? Can you please post your settings.

The WG spring is 0.6 bar (instead of the 0.7 bar as stated above) and the EBC is currently switched to the off position, which means that the solenoids are fully open. I haven't figured out how to set the EBC yet as I seem to be having issues reading the correct boost (see Blitz Boost Controller thread).

The engine was tuned to run rich under boost side since it needs to be broken in. It will go back for final tuning after the car has been driven for a few hundred miles. The car is still at the garage as I want everything to be sorted out before I pick it up.

I truly appreciate everybody's input as I am not familiar with the CIS system. Please keep the info coming.

Cheers,

Patrick
Old 02-01-2010, 05:57 PM
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Quote:
Originally Posted by 911st View Post
There are a couple of things you might try in the mean time.

Did you change out your Wast Gate spring for a lower boost spring? If not you have a .8 bar stock spring and the EBC is not doing a thing for you. If you set the EBC at just a little over the WG it will keep the WG closed a little tighter as you get near full boost. Thus it should help you at about 3000rpm a bit.

I see you have a D-WUR. I made my own 7 years ago and used it to adjust my AFR's so I was 14.5 at idle, droped with any acceleration to 13/1 untill boost came on for max power.

I also used what I called a 'drop and catch' strategy. I started by noting my manfold vac at idle and freeway cruse. In the program cells just out side that I dramitically lowered control pressure. This got the metering plate moving as fast as it phylicall could with acceleration. Then after a manfold vaccum started to recover I rased control pressure only as much as I needed to maintain normal AFR's and keep it from going to rich.

This made a significant difference in improving my pre boost response.

Again-- turbos do not like resistance after the turbine or before the compressor intake. This strategy reduces the intake restriction enough to be felt.

Your twin plug ignition curve may be suspect. Get the specs on it. Twin plugging on its own should make for a significant improvement off idle.

It really seems like you need someone that really knows what you are working with to get it all dialed in.

You have a great set up as it is and it should be a lot more responsive than a stock C2 Turbo.
I will forward the 'drop & catch' information to the dyno guys. Hopefully, they will know what to do with this.

Is there an 'optimal' ignition curve? I don't know, what mine looks like, but I will try to find out. Is this a print out similar to a dyno graph that I can post here?

Cheers.
Old 02-01-2010, 06:05 PM
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I'm running 34 degrees at 2500 so I'm a little more conservative than Don and it's still very snappy (for a 930.)
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Old 02-01-2010, 06:06 PM
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Quote:
Originally Posted by 911st View Post
+1 ideal timing and AFRs.


FYI,

I do not think Don is running 36 deg on boost so please do not try it. This is probably at curse and after at least 2500rpm with very little load and is pulled back quickly with accel and boost onset.

I could be wrong.
If I understand this correctly, the timing can be more aggressive with EFI than with CIS. If this is the case, what would be a safe level for my setup?
Old 02-01-2010, 06:11 PM
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Quote:
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If I understand this correctly, the timing can be more aggressive with EFI than with CIS. If this is the case, what would be a safe level for my setup?
If you wanted to spend the money on quality crank fire CDI ignition, you could get some great torque numbers with CIS. Despite some of its limitations, CIS is a great platform even 30 years later.

You really can't do too much to the stock ignition system and that's a big problem when tuning for peak torque and HP. Leave it stock unless you get a quality system. And although Richard Clewett is tops in the Porsche world, the wasted spark system that Electromotive builds is nowhere as good as the stock CDI - even though you can set a timing curve. Given the choice, I would always opt for the stock CDI system over a wasted spark because of spark energy and the quality of Electromotive.

And yes, my 36 degrees is up to about 3000 rpm. At WOT, its closer to 18 degrees.
Old 02-01-2010, 07:02 PM
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Quote:
Originally Posted by DonE View Post
If you wanted to spend the money on quality crank fire CDI ignition, you could get some great torque numbers with CIS. Despite some of its limitations, CIS is a great platform even 30 years later.

You really can't do too much to the stock ignition system and that's a big problem when tuning for peak torque and HP. Leave it stock unless you get a quality system. And although Richard Clewett is tops in the Porsche world, the wasted spark system that Electromotive builds is nowhere as good as the stock CDI - even though you can set a timing curve. Given the choice, I would always opt for the stock CDI system over a wasted spark because of spark energy and the quality of Electromotive.

And yes, my 36 degrees is up to about 3000 rpm. At WOT, its closer to 18 degrees.
Ouch. I thought that I had bought the good stuff. Wayne even recommends the Clewett system in his book. So, my new twin plug crankfire system is worse than the stock system?
Old 02-01-2010, 07:17 PM
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I wouldn't sing praises for CIS, but I wouldn't say it is junk either. I will say that getting rid of the flapper does make the throttle responsiveness like a modern car.

CIS = tap the throttle, throttle opens, air flows in and pushes plate, plate moves control piston, fuel flows into pressure balance chambers, fuel goes down long tubes and squirts into engine.

EFI = tap the throttle, TPS sensor signals ecu to increase pulse width, injector squirts in more fuel.

'nuff said about that. I would also say the ignition curve is not as important as the ability to modify it for current intake conditions. I have a lot of timing on my base timing map, and I use the MAP and MAT modifiers to back it off as required. This is the real "secret" to making a lot of power with EFI in my view.
Old 02-02-2010, 12:13 AM
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