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Agreed. Was not given.
Old 06-02-2009, 01:35 PM
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Doug Siegel
 
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Would changing the ring and pinion create more power all over and be advisable compared to just changing 1st gear?
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88' blk/blk 930: Haltech EFI, Twin Plug, Pauter Rods, Nascar Bearings, custom crank work, dowel pinned case, ported manifold and heads, Kokeln I/C, SC Cams, Turbonetics ball bearing 62-1, BB headers, RARLYL8 Zork, additional 993 oil filter, plx/inyourface gage, RS style coilover, Fikse FM10-17 wheels, TIAL 46mm 1 bar. (where the heck did all my money go?)
Old 06-02-2009, 02:42 PM
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[QUOTE=dsiegel360;4695819]I've got a twin plug, efi, sc cam, elec ignition with 18* advance at idle (I think)QUOTE]

Really?(sorry for the hijack on this thread). Wow, that's a lot of advance. She doesn't miss when cruising no-load (some people have found that much beyond 12 degrees BTDC you start having running issues). Just curious, since I'm in the the process of "optimizing" my timing.
Could be a totally different story with your Halltech EFI for all I know.
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Old 06-02-2009, 03:05 PM
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Doug Siegel
 
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Mark,

Not sure. But, with the Dizzy and boost retard, it's tricky.

I have no issues with missing during cruise.

The EFI and programmable ignition is a different ballgame.
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88' blk/blk 930: Haltech EFI, Twin Plug, Pauter Rods, Nascar Bearings, custom crank work, dowel pinned case, ported manifold and heads, Kokeln I/C, SC Cams, Turbonetics ball bearing 62-1, BB headers, RARLYL8 Zork, additional 993 oil filter, plx/inyourface gage, RS style coilover, Fikse FM10-17 wheels, TIAL 46mm 1 bar. (where the heck did all my money go?)
Old 06-02-2009, 03:11 PM
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Quote:
Originally Posted by dsiegel360 View Post
Mark,

Not sure. But, with the Dizzy and boost retard, it's tricky.

I have no issues with missing during cruise.

The EFI and programmable ignition is a different ballgame.
Yeah, it's kinda like comparing the first stone wheel made by prehistoric man with today's modern tires. I dream of EFI and programmable ignition...
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Old 06-02-2009, 03:35 PM
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Doug Siegel
 
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I'm not really an authority on the issue. As far as maximizing your set up, Chis....356-930 is the man.

By setting the advance the way you would like, at 3000 rpm off boost your headers will be glowing and detonation will probably occur. Thus you can advance it only slightly but on boost retard a bit more so to compensate for your advance.

I know exactly what your question is, since I had your set up B- EFI, but I never really set it up since I had no proper knock sensing ability.
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88' blk/blk 930: Haltech EFI, Twin Plug, Pauter Rods, Nascar Bearings, custom crank work, dowel pinned case, ported manifold and heads, Kokeln I/C, SC Cams, Turbonetics ball bearing 62-1, BB headers, RARLYL8 Zork, additional 993 oil filter, plx/inyourface gage, RS style coilover, Fikse FM10-17 wheels, TIAL 46mm 1 bar. (where the heck did all my money go?)
Old 06-02-2009, 03:57 PM
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Doug Siegel
 
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Would changing the ring and pinion create more power all over and be advisable compared to just changing 1st gear?
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88' blk/blk 930: Haltech EFI, Twin Plug, Pauter Rods, Nascar Bearings, custom crank work, dowel pinned case, ported manifold and heads, Kokeln I/C, SC Cams, Turbonetics ball bearing 62-1, BB headers, RARLYL8 Zork, additional 993 oil filter, plx/inyourface gage, RS style coilover, Fikse FM10-17 wheels, TIAL 46mm 1 bar. (where the heck did all my money go?)
Old 06-02-2009, 03:59 PM
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gears

Yes. Changing the ring and pinion would lower all the gears relative to the reduction of gear ratio through the ring and pinion.
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Old 06-02-2009, 05:12 PM
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Originally Posted by gtu935 View Post
Yes. Changing the ring and pinion would lower all the gears relative to the reduction of gear ratio through the ring and pinion.
How strong is the gear in a reduced final drive like 8:39 or 8:41 versus the stock diffy set of 9:39?
I heard that the diff gears get weaker when you go away from stock set, and it is better to change the 1-4th gears for strength/longevity.
Looking for experience other than the advice of the tranny builders who may be intersted in maximizing profit.
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, k27S turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),stock 4spd tranny
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Old 06-03-2009, 07:04 AM
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Fred,

If you think that a 10% or less profit margin on race parts and a New York Metro area labor rate of $102 per hour (cheap) against the cost of Payroll, cost of leasing a building, Workmans comp ins. Garagemans Liability ins, electric, water, Alarm co, etc, etc a "maximizing profit" opportunity, You may want to re-think your position as do it your selfers will usually fail first and succeed later and maybe then even wind up at a professional shop spending three times the money they should have.

You want also want to educate yourself on the stock gear ratio of a turbo 4 speed and look at that in relation to doing just ring & pinion change which would keep the stock set, where the stock first would be ridiculously low. The turbo would still quickly fall off boost between gear changes due to the huge RPM drop.

Regards from the "Big Apple"
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Old 06-03-2009, 07:24 AM
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Doug Siegel
 
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GTU935 has set up my gears so that when I shift at hi rpm, I remain in the power band. It certainly works wonders at the track. Before he did the tranny, he made it clear that no matter what I do to this tranny, a 5 speed is better. So, making the best of the 4 speed is a subjective question. Figuring out the perfect solution so to make it street and track worthy is....well....A 5 speed.
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88' blk/blk 930: Haltech EFI, Twin Plug, Pauter Rods, Nascar Bearings, custom crank work, dowel pinned case, ported manifold and heads, Kokeln I/C, SC Cams, Turbonetics ball bearing 62-1, BB headers, RARLYL8 Zork, additional 993 oil filter, plx/inyourface gage, RS style coilover, Fikse FM10-17 wheels, TIAL 46mm 1 bar. (where the heck did all my money go?)
Old 06-03-2009, 07:50 AM
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Quote:
Originally Posted by gtu935 View Post
Fred,

If you think that a 10% or less profit margin on race parts and a New York Metro area labor rate of $102 per hour (cheap) against the cost of Payroll, cost of leasing a building, Workmans comp ins. Garagemans Liability ins, electric, water, Alarm co, etc, etc a "maximizing profit" opportunity, You may want to re-think your position as do it your selfers will usually fail first and succeed later and maybe then even wind up at a professional shop spending three times the money they should have.

You want also want to educate yourself on the stock gear ratio of a turbo 4 speed and look at that in relation to doing just ring & pinion change which would keep the stock set, where the stock first would be ridiculously low. The turbo would still quickly fall off boost between gear changes due to the huge RPM drop.

Regards from the "Big Apple"
Hey no need to slam me, I meant no direction at you when I said looking for advice other than tranny rebuilders. This forum is for everyone to give feedback. IF I had a problem with you or your shop I would have said so. You have to understand my position when getting info from outside suppliers which could be a conflict of interest. AGAIN I WAS NOT LOOKING TO SLAM YOU, WHICH IT APPEARS YOU MAY HAVE INFERRED FROM YOUR RESPONSE here.
Let me tell you about educating myself about the tranny ratios of the 4 speed. I am very qualified to understand this as I am a degreed engineer and have in fact been working for a transmission company- ZF.
I was just saying that I was told by a big tranny rebuilder that the aftermarket diffy was not as strong as the stock diffy gear set and that should be considered versus changing the entire gear set. I was hoping to gain outside opinions based upon experience because this is a much bigger expense versus the ring and pinion alone and should be justified.
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, k27S turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),stock 4spd tranny
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 06-03-2009, 08:28 AM
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Two more cents worth :

Custom gearing choice takes some one that knows what they are doing (not me), an understanding of how a motor produces its power, and an understanding how the owner is most expecting to enjoy there car.

A street sport box in the USA would have likly have a first gear low enough for decent street starts but not so low that it burns through its power band like an explosion. It would also have a fourth steep enough to support proper RPM's at freeway speeds. In between these two goals, comprimizes have to be made. Do we go for factory style progressive spacings, or do we make it a close rato for the first gears for max acceleration up to 100 plus MPH and then live with a larger rpm drop into our overdrive fourth.

A general DE track box might start with a top speed desired for the tracksone expects to run and set the fourth gears rate. Then close ratio gears would be built under it to ensure there is a minimum of power drop off between gears. First would likly be on the high side and set low enough for good accel out of the slowest corner. This box would probably not be fun on the freeway unless you drive at over 160 on the track. Further trying to start from the stop light would be a real pain as boost would probably not come in untill one is over the neighgorhood's legal speed limits.

These two extreams are at odds with each other. Even a 5 speed box will suffer comprmizes.

Fornatuatly a 930 has a huge amount of mid range torque increase and a very broad on boost power band.

For most 930 owners, it is cheaper to just drop in a lower ring and pinion. This will drop the effective gear ratio from a stop and will feel like a major improvement. The MPH splits between gears will also narrow to a lesser degree for some improvements in power between gears. Freeway cruse will be at a higher rpm but will often put one closer to being where boost can be made instantly to reduce the need to shift down into third all the time. It wont be the ultimate 4 speed box but of good value and a proven solid improvement.

Just droping a lower R&P in the above box car may improve first gear starts but may also create or manify other issues.

Gear ratios really need to be digramed and compaired against the HP curve of a motor and built for the type of driving planned.

I am not a transmission expert, just what I think I have learned so far.
Old 06-05-2009, 01:40 PM
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To gain quicker spool, you can dump ignition couple degrees between 90-110kPa / 3000-4000 RPM (or wherever turbo starts to spool). This means that you will get less torque prior to boost but boost will hit quicker. It's a tradeoff for a track where you don't spend much time at low load.

(There are further tricks to gain full boost between shifts, but it's really race-only and not kind on equipment. For example installing magnetic solenoid that bypasses the throttle which is activated on <60kPa between 3000-6000RPM, together with -20 deg ignition and enriched fuel maps = lot's of bangs between shifts, glowing headers on engine brake and zero lag)
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Old 06-05-2009, 02:25 PM
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Doug Siegel
 
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I've been drawing graphs to maximize my tranny. Yup, it is difficult. I'm currently out of town and busy till next week. Next week I will chart my current set up. I'm guessing, shorter 1st and 2nd. Leave 3rd and 4th. (In my already altered gear box).

I've got to check my 65mph and 80mph rpm's in 3rd and 4th. Which is a big deal on highway runs.

Thanks 911st.
More soon.
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Last edited by dsiegel360; 06-06-2009 at 06:53 AM..
Old 06-05-2009, 02:30 PM
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Quote:
Originally Posted by beepbeep View Post
For example installing magnetic solenoid that bypasses the throttle which is activated on <60kPa between 3000-6000RPM, together with -20 deg ignition and enriched fuel maps = lot's of bangs between shifts, glowing headers on engine brake and zero lag)
I think you can do almost the same thin by dumping a compressor bypass valve to atmosphere on a CIS car which makes the AFR spike rich. Our de-acceleration valve then adds the air by bypassing air around the throttle plate between shifts. This can turn your Turbo into a turbine jet motor between shifts.

Or, I used to have my adjustable Compressor Bypass Valve ridged so it stayed open on idle and cruse so the turbo would spin faster when vac was present in the intake manifold. Then it would slam closed only when vac went away with acceleration. Instant .5 bar boost on the freeway with acceleration. This also reduced the exhaust back pressure some as the turbo did not have to push so hard against the turbine wheel at cruse.

I added to this an drop and catch strategy where bypassed Control Pressure around the WUR and to the metering arm / plate drop significantly with acceleration. Then I would bring it back to maintain near perfect AFR's through out the RPM/load range with CIS (Andial Fueler valve w custom AIC driver). These two things reduced my lag significantly.

Fun stuff.
Old 06-05-2009, 03:10 PM
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911st,

I'm confused about this "adjustable compressor bypass valve."

I think that it would work well to have the turbine spinning faster at idle and cruise. Can you give

further explanation? My Blow-off valve currently goes to atmosphere. Is this part of the equation?
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Old 06-06-2009, 06:51 AM
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If I had and EFI turbo I would go for it.

My car was CIS. Any air that comes through the metering plate has to be accounted for and thus much be returned to the area before the turbo with the CBV.

If you are runing a MAP or a referance system you can vent to atmosphere if you do not mind the noise.

On my C2T I sourced an aftermarket metal CBV to replace the plastic Bosh CBV. It was a pistons style w a spring that pushed against the piston. The piston size in the upper chamber was large than the bottom and had about 3 times more surface area. The spring was adjustable as to pressure.

I reveresed the CBV's orintation so the pressure in the intercooler area was pushing agains the botom of the CBV's piston instead of agains the side of it. This would thus have the turbos pressure trying to push the CBV open.

As you know the small tube to the CBV is hooked to the area after the throtle plate. As such there is a vac on that line at cruse and idle. Thus, I had the boost in the IC pushing the CBV open as well as the manfold vac.

When the throtle is opened vac goes away and at some point boost starts to build in the manfold that starts to presserize the top of the pistion that has more surfice area in the CBV. This increased area would alow the boost pressure in the upper chamber of the CBV to over come the boost pressure in the bottom section to asist in closing the valve.

The adjustable spring was used to tune when the CBV would close. With out the spring, boost would have to become pressent before the valve would close. Put enough spring tension in top of the CBV's piston and it would keep is closed. Set is at the righ level and the CBV will close as soon as the manfold vac disapears.

Again, doing this gave me on my car instant .2 bar boost of idle and .5 bar at freeway speeds. Bypassing air pressure around the Turbos compressor valve at idle and cruse may even lower the exaust back pressure and increase VE a bit.

I did this about 6 years ago. There is a company that has of late designed a boost valve that works on the same principle. I just do not recall the name of it.

Hope I discribed it clearly.
Old 06-06-2009, 07:44 AM
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As to compression and boost levels, there is a formula in Bruce Anderson's book on modifying Porsche's for computing approximate effective compression ratio of a motor on boost. For a supper charged motor with little or modest inter-cooling they suggest keeping the effective CR under about 11.6/1. It is interesting to me the factory on there NA 993's went to 11.3/1.

It comes out at the about the following limits.

6.5/1 at 1.2 bar
7/1 at 1.1 bar
7.5/1 at 1 bar
8/1 at .8 bar
9.5/1 at .45 bar

It may be possible to go past this with extra fuel, pulled back timming, and an extra efficient inter-cooler but I do not know how that works or is possable???
Old 06-06-2009, 08:01 AM
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Below is an interesting uTube video on that Compressor Boost Valve mentioned above compared to a normal blow off valve.

The BOV only opens to release boost on overrun to keep the compressor from dammage.

The other valve stays open and only closed with acceleration to keep the turbo spinning in reserve when not accelerating.

This is what I did on my C2T by changing the orientation of an adjustable CBV and playing with the spring tension. Mine was actually much faster acting but smaller. There might be an advantage to the new system with the amount of air if may flow. My set up fit the standard Bosch CBV fittings which is about a 1" hose in and out of the CBV.

http://www.youtube.com/watch?v=gvnBDlXyheI
Old 06-06-2009, 08:08 AM
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