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Eye of the Toiger
 
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Turbo Charging 78 3.0 SC

I there,

I have a 3.0 SC motor 8.5:1 CR and one of my friends has an aftermarket turbo charing system that bolts stright on to CIS system and manifold.

the turbo has a banjo fitting for oil of the oil line were the chain tensioners get fed, the plumbing is all crome, and it has headers that feed into the the turbo, which he thinks is a Garrett 26, the guy he bought it of had it on a 3.0 and said it went hard.

There is only some minor mods to engine tin to get it to fit.

Now my question is do I need to lower CR for a bolt-on system or can I run a turbo on a stock SC with lower boost. The 3.3 Turbos have 7.7:1 CR so my engine is not to far of the mark in terms of CR.

What kind of grunt can I expect? I run a 915 box that has a wevo bearing retainer plate, so it's strong, my engine is new (recent complete re-build).
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Old 11-21-2007, 01:08 AM
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I never heard of "Garrett 26". Are you sure itt's not KKK K26? That's pretty small turbo. 3.3 Turbos had C/R of 7.0:1, not 7.7:1. I guess you can run low boost with 8.5:1 C/R but you need to be sure fueling is allright. Also, without intercooling, amount of boost you will be able to run won't be much.
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Old 11-21-2007, 02:14 AM
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I am "guessing" you could run .5bar without an IC at that CR.

You will only need to lower the CR if you want to increase boost and get higher bhp no.s which I wouldn't recommend with a 915 even with that retaining plate.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg

Last edited by NathanUK; 11-21-2007 at 02:35 PM..
Old 11-21-2007, 02:10 PM
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you can do it

Hi
I will do that in the future. Check the forum. Patkeefe and mb911 have done it and also another guy can't remeber his name, he did it back in the 80's I think got lots of miles on it since. also rarly9 (sorry RarlyL8)has got a lot of knowledge on the subject there are lots of other guys can't remeber their names, but the expertise is here. good luck, post pictures on the progress.
Jesper

Last edited by jsveb; 11-25-2007 at 07:25 AM..
Old 11-21-2007, 02:28 PM
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one of the great unwashed
 
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Quote:
Originally Posted by matty74 View Post
aftermarket turbo charing system that bolts stright on
Do not be decieved by nor take lightly what your friend describes as bolt on

You can get at least 250 RWHP from this. Leave the CR as is. I have a lot of stuff posted on this subject, if you search my user name. There are many people on this board that can answer questions, help out and provide moral support.

Pat
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Old 11-21-2007, 02:40 PM
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Everything you could ever want to know is here...


911SC Turbo
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Old 11-21-2007, 05:47 PM
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RarlyL8 - Rarely Late

The 915 should be fine in your application. It'll take up to 350 ft/lb torque if you don't beat on it. I have the WEVO plate in mine as well. NICE unit.
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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 11-21-2007, 07:15 PM
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So I need to ask a question here.

Miata's have a Compression Ratio of 9.5:1. They are routinely turbocharged and intercooled with a minimum net increase in HP of about 60%.

Honda S2000's have an 11:1 CR. They are routinely supercharged to provide a net increase of 35% in HP.

This is done with no internal engine modifications.

Now, there are two differences. First, the head designs on both the Honda and the Miata are far more advanced than our antique p-cars and second, the computer engine management is much more advanced as well. As they ought to be given 20 some odd additional years of progress.

So here's my question. Even with the above limitations in head design and engine management: why would we ever have to decrease the compression ratio just to turbocharge the motor. Seems to me that if I turbocharge my 3.2 Carrerra motor, I should expect to be able to get at least 60% more HP like on a Miata. The compression ratio on my 911 is waaaayyyy lower than the Miata.

That would be, lessee 241*1.6=385hp? Yeah. That'd do me.

Let's be less aggressive and use the Honda numbers, 241*1.33=321hp. That'd work just fine also.

Am I missing something?

Hal
Old 11-22-2007, 09:09 AM
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The Hondas and Miatas are also water cooled.

You need to consider the dynamic compression ratio, how effectively you can fill the cylinders with charge, what RPM range you want the optimum power and torque, and a few other things. Don't imagine the head design of a Porsche is inferior, it really seems to me to be quite effective in ventilating the combustion chamber; it's limitation in my mind is the flame front propagation, which is why twin plugging is necessary.

Compare to a 930, which is more apples to apples. They use a lower static compression ratio, evidently because the factory wanted more power in the higher RPM ranges. They also have much higher boost limitations than you would get from a converted n/a engine, but the air cooled powerplants also have heat rejection limitations. So, depending on cams, fuel, intercooling, etc, there may be times when you might have to decrease the compression ratio of a 3.2 n/a engine to make it work for your application.

Bolt on turbocharging is basically a compromise, but it is relatively cheap HP in the Porsche world. I get 251 RWHP from my 3.0 CIS SC engine, and it is just like a plain old SC engine to about 3000 RPM, then it picks up a bit of power. It is quite streetable, and runs well on the track, which is what all Porsches should be capable of. I run the static 8.5:1 CR, and 6 PSI boost. I think I calculated my BMEP to be around 210, IIRC, which is not bad.

Previous posters in this thread are in my opinion some of the sharpest guys on this subject, maybe they will chime in further on this.
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Old 11-22-2007, 09:55 AM
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The watercooling is what makes the big difference.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 11-22-2007, 02:26 PM
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Don't forget engine management. The new cars have precise engine control that will allow running boost at higher mechanical compression ratios. They are also capable of pulling down the timing when sensing detonation.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 11-22-2007, 03:13 PM
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Quote:
Originally Posted by NathanUK View Post
The watercooling is what makes the big difference.
Yup. It's the heat rejection and the ability to precisely retard timing to avoid detonation. That didn't occur to me until you guys said it.

I'm still not buying that our antique old Porsche heads - advanced as they were for their time - are anywhere near as efficient as a modern head.

I'd like to see flow numbers for comparison.
Old 11-22-2007, 06:23 PM
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It's not just flow numbers. It's also combustion chamber geometry and head temperature.

While being quite OK for a 2-valve design, aircooled 911 heads just aren't most optimal for turbocharging. This is the reason Porsche left aircooling and went water alltogether.

With other words, just beacuse you might get away with turbocharging a Miata w/o lowering C/R, it doesn't mean it will work on 911. There is no moderating effect of watercooling, there is no pentroof design, the distance that flame propagation front has to take is quite big, no knock-detection etc.

So yes, you can probably survive with boosting stock SC engine with 8.5 C/R but you have to be careful. Also, forget about linear raise in power just beacuse you boost 1.6 times the ambient pressure. VE just isn't there and turbocharger and CIS inefficiencies will eat a great deal of power.

With other words, IF you chose to turbocharge a stock 3.0 SC engine with stock CIS, you have to be very careful with fueling and temperatures.

I suggest intercooling, low boost and AFR logging run to begin with as you have no safety features.
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Old 11-23-2007, 05:57 AM
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I had no problem running 8lbs on my non intercooled 79 SC engine at 8.51.
I did use a 7th injector and retarded the timing using a MSD BTM as a safety measure.

Go back and read through Thad Suters thread, all is explained.

http://forums.pelicanparts.com/showt...0&pagenumber=1
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Old 11-23-2007, 06:34 AM
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