Reducing compress ratio with shorter con.rods!
12-01-2006, 12:38 PM
#31
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That was done by the previous owner so no way of knowing. I had run that setup upto 1 bar but is currently running at .8 bar because the factory 968 MAF canot support more.
I ran it with a APE MAF and I didn't have such restrictions. I was running a 2.7 head and 951 electronics while now it runs 968 electronics.
Raj
I ran it with a APE MAF and I didn't have such restrictions. I was running a 2.7 head and 951 electronics while now it runs 968 electronics.
Raj
12-02-2006, 03:44 AM
#33
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Originally Posted by hally
Hi AL I see that that Mazda engine uses direct injection. (have been eyeing off the cx-7 which just got released here). I vaguely understand this to allow higher compression ratios / boost...maybe someone can elaborate on this direct injection topic.
Hi Hally,
Direct injection is not new. But lately it's been improve for automobile use. In principal, it works just as a diesel engine does. It make for a very efficient combustion, witch gives you better power and economy. The reason Mazda uses DI on this engine is because it can run a high CR with a very high boost pressure. As the air is been compress inside the cylinder, the high pressure fuel is release and this has a cooling effect on the mixture. This helps with preventing Knock, and to produce more power and torque. Even the new BMW 335I turbo runs DI with a CR of 10.2:1.
Regards,
AL
12-02-2006, 10:05 AM
#34
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Raj, what I understand your car is running 8 valve head? Why did you remove any material from the pistons? If you bolt 8 valve head to S2 or 968 engine then compress ratio is down anyway to 9's. If you remove some material from burn chamber its as down as 8.5:1
Me I am planning to use 16 valve head and that means at least 3mm material removal..
As far as doing this I was thinking to use fully automatic computer controlled machine for that to be 100% sure that all the pistons will be EXACTLY the same. I was also thinking that maybe after material removal would be nice to ceramic coat them from top to add that extra strenght to them.. has anyone tried to ceramic coat stock pistons?
And the plan is 1.3-1,4 bar of boost! 550 hp
Me I am planning to use 16 valve head and that means at least 3mm material removal..
As far as doing this I was thinking to use fully automatic computer controlled machine for that to be 100% sure that all the pistons will be EXACTLY the same. I was also thinking that maybe after material removal would be nice to ceramic coat them from top to add that extra strenght to them.. has anyone tried to ceramic coat stock pistons?
And the plan is 1.3-1,4 bar of boost! 550 hp
That was done by the previous owner so no way of knowing. I had run that setup upto 1 bar but is currently running at .8 bar because the factory 968 MAF canot support more.
I ran it with a APE MAF and I didn't have such restrictions. I was running a 2.7 head and 951 electronics while now it runs 968 electronics.
Raj
I ran it with a APE MAF and I didn't have such restrictions. I was running a 2.7 head and 951 electronics while now it runs 968 electronics.
Raj
12-02-2006, 11:11 AM
#35
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Still
Does anyone have picture of 968 pistons and con.rods?
Can someone confirm that they are foged not cast?
What is the story with factory 968 turbo piston rings, why you have to use those?
I am not planning to rev the engine more then 6700 rpm, will stock rods holds in my goals of 550 true hp on engine?
Markus
Does anyone have picture of 968 pistons and con.rods?
Can someone confirm that they are foged not cast?
What is the story with factory 968 turbo piston rings, why you have to use those?
I am not planning to rev the engine more then 6700 rpm, will stock rods holds in my goals of 550 true hp on engine?
Markus
Last edited by Markus951; 12-02-2006 at 11:47 AM.
12-02-2006, 03:01 PM
#36
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Originally Posted by AL951
Hi Hally,
Direct injection is not new. But lately it's been improve for automobile use. In principal, it works just as a diesel engine does. It make for a very efficient combustion, witch gives you better power and economy. The reason Mazda uses DI on this engine is because it can run a high CR with a very high boost pressure. As the air is been compress inside the cylinder, the high pressure fuel is release and this has a cooling effect on the mixture. This helps with preventing Knock, and to produce more power and torque. Even the new BMW 335I turbo runs DI with a CR of 10.2:1.
Regards,
AL
Direct injection is not new. But lately it's been improve for automobile use. In principal, it works just as a diesel engine does. It make for a very efficient combustion, witch gives you better power and economy. The reason Mazda uses DI on this engine is because it can run a high CR with a very high boost pressure. As the air is been compress inside the cylinder, the high pressure fuel is release and this has a cooling effect on the mixture. This helps with preventing Knock, and to produce more power and torque. Even the new BMW 335I turbo runs DI with a CR of 10.2:1.
Regards,
AL
The high pressure fuel released does not help cool the mixture to prevent knock.... at least not like that.
The fuel is released just a hair before desired ignition. Of course spark plugs are still used, but basically whether it knocks or has proper ignition the same end effect is achieved. Knock is your friend in an engine like that because it's not really knock anymore
I do not know the full setup of the cx-7, but if they are taking cues from diesel engines then it is possible that they have removed the butterfly in the throttle body and run constant boost from the turbo like diesels do. This would do wonderful things for it's fuel efficiency since the engine is no longer working to create constant vacuum.
12-02-2006, 04:44 PM
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Originally Posted by Markus951
Raj, what I understand your car is running 8 valve head? Why did you remove any material from the pistons? If you bolt 8 valve head to S2 or 968 engine then compress ratio is down anyway to 9's. If you remove some material from burn chamber its as down as 8.5:1
you can just get an s2 or 968 and use a 2.7 head, and your done, or maybe a slightly thicker cometic head gasket just to be sure.
12-02-2006, 06:38 PM
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Hi Zero,
What i describe above was one method of DI. What your are describing is call lean-burn mode. again another way of using GDI. Most car makers, like Mitsubishi, BMW,VW/Audi, GM, and Isuzu, agree that one of GDI benefits is the cooling effect it makes inside the chamber. GDI is very flexible. I hear toyota is going to make an engine with two injectos per cylinder. one inside and one in the port. anyway GDI is a perrty cool technology, I am shure it's going to cotinue evolving.
Regards,
AL
What i describe above was one method of DI. What your are describing is call lean-burn mode. again another way of using GDI. Most car makers, like Mitsubishi, BMW,VW/Audi, GM, and Isuzu, agree that one of GDI benefits is the cooling effect it makes inside the chamber. GDI is very flexible. I hear toyota is going to make an engine with two injectos per cylinder. one inside and one in the port. anyway GDI is a perrty cool technology, I am shure it's going to cotinue evolving.
Regards,
AL
12-02-2006, 06:43 PM
#39
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Originally Posted by Zero10
I hate to side-track this thread any further, but I feel the need to add to what was said here.
The high pressure fuel released does not help cool the mixture to prevent knock.... at least not like that.
The fuel is released just a hair before desired ignition. Of course spark plugs are still used, but basically whether it knocks or has proper ignition the same end effect is achieved. Knock is your friend in an engine like that because it's not really knock anymore
I do not know the full setup of the cx-7, but if they are taking cues from diesel engines then it is possible that they have removed the butterfly in the throttle body and run constant boost from the turbo like diesels do. This would do wonderful things for it's fuel efficiency since the engine is no longer working to create constant vacuum.
The high pressure fuel released does not help cool the mixture to prevent knock.... at least not like that.
The fuel is released just a hair before desired ignition. Of course spark plugs are still used, but basically whether it knocks or has proper ignition the same end effect is achieved. Knock is your friend in an engine like that because it's not really knock anymore
I do not know the full setup of the cx-7, but if they are taking cues from diesel engines then it is possible that they have removed the butterfly in the throttle body and run constant boost from the turbo like diesels do. This would do wonderful things for it's fuel efficiency since the engine is no longer working to create constant vacuum.
The main DGI advantage now is improved part throttle fuel economy accomplished by running very lean, which again is problematic for the typical catalytic converter. Gasoline requires the AFR to be within +-20% of stoichiometric to create stable combustion, but by stratifying the fuel in the combustion chamber, there will always be a layer that has the right AFR, even if there is an excess of air. Unfortunately the net AFR flexibility is not enough to eliminate the throttle plate, as BMW has done with their variable valve timing and lift.
A new Lexus will have both port and direct injection, so there may be some downside to the direct injection to make the added cost worthwhile. Another novel feature of that car is an 8-speed automatic gearbox.
Laust
12-02-2006, 07:22 PM
#40
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Originally Posted by 944CS
why are we talking about removing material from pistons?!! You want to more than double the horsepower of the engine, yet make the piston weaker??
Jeez!
Raj
12-05-2006, 03:40 PM
#43
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Can anyone confirm that 968 pistons are forged?
If they are how to identify that. It could be similar story with S2 engines where some pistons where forged and some cast units..
Does any of you have a shot of them?
markus
If they are how to identify that. It could be similar story with S2 engines where some pistons where forged and some cast units..
Does any of you have a shot of them?
markus
12-05-2006, 03:50 PM
#44
Originally Posted by Markus951
Can anyone confirm that 968 pistons are forged?
If they are how to identify that. It could be similar story with S2 engines where some pistons where forged and some cast units..
Does any of you have a shot of them?
markus
If they are how to identify that. It could be similar story with S2 engines where some pistons where forged and some cast units..
Does any of you have a shot of them?
markus
Check out this site, I know this guy did some investigation about this some years ago.. http://www.944968.com/
12-05-2006, 04:01 PM
#45
Former Vendor
Oh well, here we go...
I just did a search with " forged connecting rods" and found this and that, also a claim about 968's rods being forged. While I don't say anything about those, I do have something to say about 944 con rods.
According to PET ( which should be quite reliable source ) there are three different connecting rods in whole 9442 ( '85.5-91, all engine sizes and cylinder heads ) family. These are:
944 103 001 00 turbo con rod '85-'88, NLA, replaced with 944 103 008 00
944 103 008 02 all others
Only forged one is 944 103 001 00. There are other series of numbers in con rods themselves, but these are casting numbers...like those numbers on aluminium suspension arm. Forged rod is replaceable with cast one and vv. If, for a reason or another, someone has had been forced to order "a short engine" from the factory in the nineties, the innings might have had those rods mixed....please do not ask how I know. And this is the answer I got today from Porsche Centre Helsinki and their head of service.
I might admit that I'm wrong, but only after very good and reliable evidence...
I just did a search with " forged connecting rods" and found this and that, also a claim about 968's rods being forged. While I don't say anything about those, I do have something to say about 944 con rods.
According to PET ( which should be quite reliable source ) there are three different connecting rods in whole 9442 ( '85.5-91, all engine sizes and cylinder heads ) family. These are:
944 103 001 00 turbo con rod '85-'88, NLA, replaced with 944 103 008 00
944 103 008 02 all others
Only forged one is 944 103 001 00. There are other series of numbers in con rods themselves, but these are casting numbers...like those numbers on aluminium suspension arm. Forged rod is replaceable with cast one and vv. If, for a reason or another, someone has had been forced to order "a short engine" from the factory in the nineties, the innings might have had those rods mixed....please do not ask how I know. And this is the answer I got today from Porsche Centre Helsinki and their head of service.
I might admit that I'm wrong, but only after very good and reliable evidence...