Stock IC vs 1 bar boost spring

[cellison]

does a stock IC work with a 1 bar spring?

[911nut]

The bigger question is does running the stock turbo at 1 bar put the compressor into the "choke" region of the map? If it does you will be pumping superheated charge air into the engine that the small stock i/c won't be able to cool.

[Ronnie's.930]

As 911nut indicates above, and many here agree with, that is a real gamble.

Something to think about - 7:1 static compression ratio with .8bar boost = 12.52 effective compression ratio . . . make that 1.0bar boost and now you are at 13.9 ECR . . . that is a significant bump in ECR . . . that bump will increase combustion chamber temps, so it is a good idea to lower the incoming charge air temp, with a better than OEM intercooler and/or water-methanol injection, in order to offset that increase (helps to lesson the likelihood of detonation).

[klefroid]

Originally Posted by Ronnie's.930

As 911nut indicates above, and many here agree with, that is a real gamble.

Something to think about - 7:1 static compression ratio with .8bar boost = 12.52 effective compression ratio . . . make that 1.0bar boost and now you are at 13.9 ECR . . . that is a significant bump in ECR . . . that bump will increase combustion chamber temps, so it is a good idea to lower the incoming charge air temp, with a better than OEM intercooler and/or water-methanol injection, in order to offset that increase (helps to lesson the likelihood of detonation).

What is ECR?

[smurfbus]

I would guess effective compression ratio

[Ronnie's.930]

Originally Posted by klefroid

What is ECR?

Originally Posted by smurfbus

I would guess effective compression ratio

Yep.

[TurboKraft]

While your ID says you're in GA, so you get 93-oct instead of our junk 91-oct, and you have a 1979 which has the higher flowing Euro-spec CIS... it's still a gamble. Those stock intercoolers heat soak pretty easily.

[Speedy Squirrel]

The compressor outlet temperature will increase about 18 C when going from 0.8 bar to 1 bar. This is a fairly big jump, and is due mainly to the increase in pressure. The compressor efficiency for the stock "3LDZ" only looses a couple of points going to 1 bar.

The "effective compression ratio" is not a factor. The final temperature at the end of the compression stroke is strictly a function of the temperature of the mixture in the cylinder at the beginning, the compression ratio, and the ratio of specific heats.

[Ronnie's.930]

Originally Posted by Speedy Squirrel

The "effective compression ratio" is not a factor. The final temperature at the end of the compression stroke is strictly a function of the temperature of the mixture in the cylinder at the beginning, the compression ratio, and the ratio of specific heats.

Speedy, so the increased effective compression ratio does not increase the possibility of detonation?

[oz 930 turbo]

Is there any noticeable gain from installing a 1.0 bar spring?
I've had one lying around ready to install for a while but have always had doubt about its effectiveness. I'm running a K27-7200 rebuilt through turbokraft with a Kokeln intercooler.

[quattrorunner]

Originally Posted by oz 930 turbo

Is there any noticeable gain from installing a 1.0 bar spring?
I've had one lying around ready to install for a while but have always had doubt about its effectiveness. I'm running a K27-7200 rebuilt through turbokraft with a Kokeln intercooler.

Do that and you tell us what you think?
It's easy and your turbo and inter cooler could cope I'd say.

Quick answer is yes. Effective? Yes.

[oz 930 turbo]

Thanks for the reply quattrorunner it's that "could" or "should be ok" caveat that keeps me wary. These engines are getting on for 30-35 years old and I wonder if its worth the risk of pushing them harder than they were originally designed for

[timspu]

i expect one consideration would be ambient temperature. If you are standard day temps 15C then i expect it is not an issue, but if you are at 25 c plus then maybe the adiabatic heating will be an issue and a larger cooler needed.
I ran a 3ldz with 1 bar and standard cooler with no issue. But we don't get hot in the south west of England.

It makes a real improvement on the 3LDZ.

[911nut]

Originally Posted by Speedy Squirrel

The "effective compression ratio" is not a factor. The final temperature at the end of the compression stroke is strictly a function of the temperature of the mixture in the cylinder at the beginning, the compression ratio, and the ratio of specific heats.

I would tend to agree that ECR won't help us make a judgement in this case but it gets us into the ballpark. It's more about temperatures and efficiencies. The stock turbo and intercooler aren't winners. As soon as Porsche could go to more efficient components, they did (the K27 and full bay intercooler of the 965).
ECR is a theoretical term that's not unlike horsepower. It is a design tool. It keeps people from making stupid mistakes like spec-ing out an engine with an ECR of 21, for example.

[RarlyL8]

All the above statements are to be considered.
To boil it down, you live in GA (I am in AL). In the winter you can run 1bar on the street using the stock IC with no issue. In the summer I would not. The ambient temperature keeps the inlet temperature too hot for the little IC to cool anything down. Even a giant IC cannot cool the intake temp down to the level you get in the wintertime starting with such low ambient temperatures.
If you do not wish to run a bigger intercooler I would suggest a boost controller that will allow use of the stock spring in the summer (or during hard use) and allow you to delay the boost signal to 1bar when the temps are lower.

[Robbbyg]

I think for every .1 bar added equals 10hp

so 1.0 over 0.8 = 20hp gain.

Having said that.

Im curious about the charge pressure and temps,,

Example
A Factory NON IC Euro 1977 930 with 260hp running stock 0.8 bar spring
(made just before Intercooler introduction)

Then
If FACTORY 930 IC is added along with 3.3 intake manifold and 3.3 BOV assembly and MSD Ignition, MSD Blaster coil and Tial 46
and running 100 unleaded premium petrol here in OZ not sure what that is in the US

How high a boost spring can one put in with no worries?

[911nut]

Originally Posted by Robbbyg

I think for every .1 bar added equals 10hp
so 1.0 over 0.8 = 20hp gain.?

Problem is, as you approach the choke point of the compressor, the extra heat being put into the charge air drops efficiency. So with the stock turbo and i/c, an extra .2 bar might look like 5 hp gain.

[9Thirty]

Originally Posted by Robbbyg

I think for every .1 bar added equals 10hp

so 1.0 over 0.8 = 20hp gain.

Having said that.

Im curious about the charge pressure and temps,,

Example
A Factory NON IC Euro 1977 930 with 260hp running stock 0.8 bar spring
(made just before Intercooler introduction)

Then
If FACTORY 930 IC is added along with 3.3 intake manifold and 3.3 BOV assembly and MSD Ignition, MSD Blaster coil and Tial 46
and running 100 unleaded premium petrol here in OZ not sure what that is in the US

How high a boost spring can one put in with no worries?

I think the issue then becomes the capability of the CIS. You will run lean (13 afr or above) which will cause detonation over a period of time once you get over 1 bar.

[cellison]

Here is my reason for asking. it the April Panorama i just received, a question was posted in the TECH QA on page 125 about the1 bar boost spring in an 82. in answering the question, there was comment about a stock intercooler isn't really big enough to accommodate 1 bar spring. nothing mentioned about the turbo itself.

my set up:
1 bar spring
stock IC
k27
headers
open dump pipe
964 cams

this is how i bought it but wonder why the PO didn't put on a larger IC.

i don't really drive it much in the summer heat as i rotate to the 88 cab and pull out the tr6 to beat around in. the 930 is more of a fall/winter/early spring car. i don't track it but do run it when i drive it.
I'm fat dumb and happy the way it performs and sounds, mostly the 60-120mph passing sprints on GA 400.

[RarlyL8]

Your exhaust system and turbo reduce back pressure over stock so the heat of the 3LDZ/
J-pipe/OEM muffler are irrelevant. For this setup you can expect ~15hp/0.1bar. AFRs at redline should not be a problem if the WUR is fresh. They should be verified anytime performance adders are in place.
If driving the car on the street and not in the summer you should be OK at 1.0bar with the OEM intercooler, premium grade fuel and conservative timing. If you get into traffic and heat soak the IC needs time to recover. Adding a good intercooler is free HP and insurance so worth consideratin.