Lot of talking here??...944fest '09
01-14-2009, 03:19 PM
#211
Addict
Rennlist Member
Rennlist Small
Business Sponsor
Rennlist Member
Rennlist Small
Business Sponsor
Power is created by pressure in the cylinder, so on an ‘average’ basis with the number of cylinders being equal the pressure per square inch of piston crown (cylinder head is pretty close) will also be equal (the smaller cylinder diameter will have to run at a higher pressure to be equal in total power output).
That being said the smaller diameter cylinder can have less flex due to the closer proximity of the head studs.
One other point is that the ignition curve can have a dramatic effect on the peak cylinder pressure – to aggressive a curve will give you head lift due to pressure peaks too close to TDC. Pre ignition will give you a ridiculous pressure peak (that’s what does the damage).
I am guessing the ST did some timing adjustments to make his earlier head lift problems go away….
That being said the smaller diameter cylinder can have less flex due to the closer proximity of the head studs.
One other point is that the ignition curve can have a dramatic effect on the peak cylinder pressure – to aggressive a curve will give you head lift due to pressure peaks too close to TDC. Pre ignition will give you a ridiculous pressure peak (that’s what does the damage).
I am guessing the ST did some timing adjustments to make his earlier head lift problems go away….
01-14-2009, 03:32 PM
#212
The Impaler
Rennlist Member
Rennlist Member
Power is created by pressure in the cylinder, so on an ‘average’ basis with the number of cylinders being equal the pressure per square inch of piston crown (cylinder head is pretty close) will also be equal (the smaller cylinder diameter will have to run at a higher pressure to be equal in total power output).
That being said the smaller diameter cylinder can have less flex due to the closer proximity of the head studs.
One other point is that the ignition curve can have a dramatic effect on the peak cylinder pressure – to aggressive a curve will give you head lift due to pressure peaks too close to TDC. Pre ignition will give you a ridiculous pressure peak (that’s what does the damage).
I am guessing the ST did some timing adjustments to make his earlier head lift problems go away….
That being said the smaller diameter cylinder can have less flex due to the closer proximity of the head studs.
One other point is that the ignition curve can have a dramatic effect on the peak cylinder pressure – to aggressive a curve will give you head lift due to pressure peaks too close to TDC. Pre ignition will give you a ridiculous pressure peak (that’s what does the damage).
I am guessing the ST did some timing adjustments to make his earlier head lift problems go away….
01-14-2009, 03:34 PM
#213
The Impaler
Rennlist Member
Rennlist Member
Not compression ratio, cylinder pressure. Read chris whites post above
In really simple terms you could say that "X" type of motor is going to run into problems with head lift around "Y" horsepower.
Isn't the amount of boost/compression a direct proponent to head pressure?
I think a large motor easily making 500hp would have a LOT less head/cyl pressure than a smaller motor making a lot of head/cyl pressure and only making 300hp.
I.e.
Large motor @ 9:1 = 500hp
Small motor @ 12:1 = 300hp
Which one is going to be more likely to have head lift?
In that example hp would not be the issue, head pressure/cyl compression is.
I think a large motor easily making 500hp would have a LOT less head/cyl pressure than a smaller motor making a lot of head/cyl pressure and only making 300hp.
I.e.
Large motor @ 9:1 = 500hp
Small motor @ 12:1 = 300hp
Which one is going to be more likely to have head lift?
In that example hp would not be the issue, head pressure/cyl compression is.
01-14-2009, 03:46 PM
#218
Race Car
Join Date: Sep 2005
Location: TEXAS
Posts: 4,247
Likes: 0
Received 0 Likes
on
0 Posts
I'm going to just jump right out here and say this. I think you guys are giving way too much credit to the 8v head. No matter how much porting and valving and shaping you do.
- Stating specifically the 2.5 Porsche motor against the 3.0 Supra motor.
8v head Vs. hemispherical chambered style 4 valve. DUAL Overhead cam that they rev to 10K.
HUGE difference.
Also 6 cylinder = spread pressure accross 50% more cylinders. Larger number of mains spreading out load on bearings.
That said. I think it might be possible. ......Once or twice.
I am still looking forward to 944fest.
- Stating specifically the 2.5 Porsche motor against the 3.0 Supra motor.
8v head Vs. hemispherical chambered style 4 valve. DUAL Overhead cam that they rev to 10K.
HUGE difference.
Also 6 cylinder = spread pressure accross 50% more cylinders. Larger number of mains spreading out load on bearings.
That said. I think it might be possible. ......Once or twice.
I am still looking forward to 944fest.
01-14-2009, 03:49 PM
#219
The Impaler
Rennlist Member
Rennlist Member
I'm going to just jump right out here and say this. I think you guys are giving way too much credit to the 8v head. No matter how much porting and valving and shaping you do.
- Stating specifically the 2.5 Porsche motor against the 3.0 Supra motor.
8v head Vs. hemispherical chambered style 4 valve. DUAL Overhead cam that they rev to 10K.
HUGE difference.
Also 6 cylinder = spread pressure accross 50% more cylinders. Larger number of mains spreading out load on bearings.
That said. I think it might be possible. ......Once or twice.
I am still looking forward to 944fest.
- Stating specifically the 2.5 Porsche motor against the 3.0 Supra motor.
8v head Vs. hemispherical chambered style 4 valve. DUAL Overhead cam that they rev to 10K.
HUGE difference.
Also 6 cylinder = spread pressure accross 50% more cylinders. Larger number of mains spreading out load on bearings.
That said. I think it might be possible. ......Once or twice.
I am still looking forward to 944fest.
I'm still looking for a 944S motor, and I want to do something different with the turbo placement. I have to wait until business picks up in the spring.
01-15-2009, 01:49 AM
#220
Formula One Spin Doctor
Rennlist Member
Rennlist Member
Wackypedia:
THE DYNO :
A Place ! Where all of the Mohammed I-Mark Bruce Lee Tuning Tips and VE Theories
Get F**k !
THE DYNO :
A Place ! Where all of the Mohammed I-Mark Bruce Lee Tuning Tips and VE Theories
Get F**k !
Last edited by A.Wayne; 01-15-2009 at 02:06 AM.
01-15-2009, 02:26 AM
#221
Rennlist Member
Give us the benefit of your viewpoint Mr W?
01-15-2009, 03:42 AM
#222
Race Car
Join Date: Sep 2005
Location: TEXAS
Posts: 4,247
Likes: 0
Received 0 Likes
on
0 Posts
I think he's trying to say that no matter what we say or theorize what may or may not be possible doesn't matter. It's whatever it ends up making.
BUT. I have yet to see an Dyno without some sort of correction tweak. So, I take many with just a grain of salt. But a dyno day that goes back to back without changing software settings all day. Good stuff.
Once again. I look forward to 944fest.
BUT. I have yet to see an Dyno without some sort of correction tweak. So, I take many with just a grain of salt. But a dyno day that goes back to back without changing software settings all day. Good stuff.
Once again. I look forward to 944fest.
01-15-2009, 11:10 AM
#223
Drive-by provocation guy
Rennlist Member
Rennlist Member
Join Date: Apr 2002
Location: NAS PAX River, by way of Orlando
Posts: 10,439
Likes: 0
Received 0 Likes
on
0 Posts
01-15-2009, 11:51 AM
#224
Formula One Spin Doctor
Rennlist Member
Rennlist Member
Most "headlifting problems" comes from poor management of the explosion , of course i mean after due diligence has been done if such an engine is prone to "headlifting" .
Alloy heads can also go "soft" , then there is nothing to do but get a new head , in the past Cryogenics has proven to be the best method in preventing this situation and going to tree stump size headbolts mean diddley if you are suffering from a soft head or poor explosion control .
Tune the engine not the Dyno ......................................
Alloy heads can also go "soft" , then there is nothing to do but get a new head , in the past Cryogenics has proven to be the best method in preventing this situation and going to tree stump size headbolts mean diddley if you are suffering from a soft head or poor explosion control .
Tune the engine not the Dyno ......................................
Last edited by A.Wayne; 01-15-2009 at 01:18 PM.